Fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material and preparation method thereof

Abstract

The invention relates to the technical field of solid-state electrolyte materials, in particular to a fluorine-doped lithium-yttrium-chlorine-sulfur system solid-state electrolyte material and a preparation method thereof, the fluorine-doped lithium-yttrium-chlorine-sulfur system solid-state electrolyte material has a chemical formula as shown in a formula (I): LiaYbClcFqSd, wherein 0.5 < = (a + b) / (c + d + q) < = 1; gt; 0, bgt; 0, cgt; 0, dgt; 0; 0 lt; q < = 0.5; stable phases such as LiF generated by F doping form a compact protective layer on the surface of the lithium negative electrode, so that direct reduction erosion of lithium metal to active components in the electrolyte can be effectively blocked. Experiments show that when the fluorine-doped electrolyte is in contact with lithium metal, the interface impedance is obviously lower than that of an undoped contrast, and the fluorine-doped electrolyte is kept stable (the interface impedance change is very small) under long-time circulation, and no obviously thickened impedance layer is generated, which means that the lithium negative electrode interface side reaction is inhibited, and lithium dendrites are not easy to form at the interface; therefore, the long-life cycle of the battery is ensured.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte materials technology, and in particular to a fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material and its preparation method. Background Technology

[0002] All-solid-state batteries significantly improve battery safety by using solid electrolytes instead of traditional flammable liquid electrolytes, making them a research hotspot for next-generation high-energy-density batteries. Existing solid electrolytes mainly fall into three categories: oxide-based, sulfide-based, and halide-based. However, different types of solid electrolytes have their own problems: oxide electrolytes have low ionic conductivity and high interfacial impedance; sulfide electrolytes have poor electrochemical stability (easily reduced by lithium) and usually contain toxic P2S5 components; while halide electrolytes have a wide electrochemical window, their room-temperature ionic conductivity is generally low (most only 10). -4 -10 - 3 (S / cm). Therefore, how to obtain a solid electrolyte that combines high ionic conductivity and good stability is a technical problem that urgently needs to be solved.

[0003] Recent studies have shown that combining halide and sulfide components to form "halosulfide" solid electrolytes is an effective way to improve ionic conductivity. For example, patent literature has reported solid electrolyte materials in the Li–Zr–Cl–S system, which have a room-temperature ionic conductivity as high as 4.34 × 10⁻⁶. -2 S / cm; another study disclosed a Li–Y–Cl–S solid electrolyte system, achieving an ionic conductivity greater than 4 × 10⁻⁶ by adjusting the ratio of Li, Y, Cl, and S. -3 S / cm, and can even exceed 1.5×10 -2 S / cm. It is evident that halosulfide electrolytes have a significant advantage in ionic conductivity. However, these halosulfides still suffer from insufficient interfacial stability when in direct contact with metallic lithium: on the one hand, the reduction decomposition potential of the halide component is approximately 0.6V (relative to Li / Li). +When in contact with a 0V lithium anode, the lithium chloride will still be reduced by metallic lithium; on the other hand, sulfide components are also easily reduced to products such as Li2S at low potentials. As a result, a mixture containing ionic or electronic insulating phases such as LiCl and Li2S is formed at the lithium / electrolyte interface, leading to increased interfacial impedance and inducing lithium dendrite growth. This interfacial side reaction continues with battery cycling, severely affecting the cycle life and safety of all-solid-state batteries. To address the aforementioned interfacial stability issues, some studies have begun to explore the introduction of highly electronegative halogen elements into solid-state electrolytes to construct stable interfacial passivation layers. Among these, fluorine (F) has attracted considerable attention due to its higher electronegativity and chemical stability. It has been reported that doping F into halide electrolytes improves compatibility with lithium anodes: for example, after introducing F doping into Li3YBr6 halide, a Li|Li symmetric battery was assembled at 0.75 mA / cm². 2 Under cyclic discharge at current density, lithium deposition / stripping remained stable for over 1000 hours without short circuit. XPS analysis showed that fluorine doping induced the in-situ formation of a stable LiF-rich passivation layer at the interface during cycling, effectively preventing further reduction reactions between the electrolyte and metallic lithium. This phenomenon demonstrates that the LiF formed at the interface by fluorine acts as a protective barrier, significantly improving the reduction resistance of the solid electrolyte to the lithium anode. Although fluorine doping shows potential for improving interfaces in halide systems, there is currently a lack of relevant doping modification research and mature technical solutions for sulfur-containing halosulfide solid electrolytes.

[0004] Therefore, we propose a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material and its preparation method.

[0006] A fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material, wherein the chemical formula of the solid electrolyte is shown in formula (I): LiaYbClcFqSd; wherein: 0.5≤(a+b) / (c+d+q)≤1; a>0, b>0, c>0, d>0; 0 <q≤0.5。

[0007] Preferably, in the solid electrolyte, Y is used as the metal central cation, and the chloride matrix composed of Y and Li is obtained through F. - Cl in the substituted chloride matrix - Examples of high electrochemical stability windows and ion transference numbers include Li3YCl6.

[0008] Preferably, the solid electrolyte has an ionic conductivity ≥1.0×10⁻⁶ at room temperature. -3 S / cm.

[0009] Preferably, a method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material is characterized by comprising the following steps: under an inert atmosphere, lithium source, yttrium source, chlorine source, fluorine source and sulfur source are weighed according to stoichiometry, mixed, and ball-milled to obtain a solid electrolyte with a uniform crystal structure.

[0010] Preferably, the lithium source is selected from LiCl, LiF and Li2S; the yttrium source is selected from YCl3 and YF3; the chlorine source is selected from LiCl and YCl3; the fluorine source is selected from LiF and YF3; and the sulfur source is selected from Li2S.

[0011] Preferably, the inert gas used in the inert atmosphere is at least one of argon, helium, neon, krypton, xenon, and nitrogen, and the dew point of the inert gas is less than or equal to -60°C.

[0012] Preferably, the ball milling time is 20–60 hours and the rotation speed is 300–500 rpm.

[0013] Preferably, after ball milling, heat treatment is performed at a temperature of 200–300℃ for 2–10 hours.

[0014] The beneficial effects of this invention are: 1. The stable phases such as LiF generated by fluorine doping form a dense protective layer on the surface of the lithium anode, which can effectively prevent the direct reduction and erosion of the active components in the electrolyte by lithium metal. Experiments show that the interfacial impedance of the fluorine-doped electrolyte when in contact with lithium metal is significantly lower than that of the undoped control, and remains stable under long-term cycling (with very small changes in interfacial impedance), without the formation of a significantly thickened impedance layer. This means that the side reactions at the lithium anode interface are suppressed, and lithium dendrites are not easy to form at the interface, thus ensuring the long cycle life of the battery.

[0015] 2. The material system of this invention optimizes the crystal structure through a halogen-sulfur combination, resulting in excellent lithium-ion conductivity, with room temperature ionic conductivity consistently above 10. -3 S / cm or higher, approaching 10 -2 On the order of S / cm, trace amounts of fluorine doping have little impact on the main lattice and do not significantly reduce the number and activity of lithium-ion migration channels. Compared with external protection methods such as adding coatings, fluorine doping modification achieves interface stability without sacrificing the intrinsic ionic conductivity of the material.

[0016] 3. Due to its more stable interface and better ion conductivity, the all-solid-state lithium metal battery using the electrolyte of this invention exhibits lower polarization voltage and longer cycle life during charge-discharge cycles (approximately 400 hours in the experiment, significantly better than the control group). This demonstrates that the long-term stable cycling of the lithium anode can be effectively ensured by controlling the internal composition of the electrolyte, without the need for additional interface engineering measures, simplifying the battery manufacturing process and improving battery reliability. The material of this invention holds promise for use in high-energy-density all-solid-state batteries, enabling the stable utilization of lithium metal anodes.

[0017] 4. In summary, this invention innovatively improves the stability of halosulfide solid electrolytes in the lithium metal anode environment by means of fluorine doping, taking into account both ionic conductivity and interfacial compatibility, and achieving a balance and breakthrough in performance. Detailed Implementation

[0018] The present invention will be further explained below with reference to specific embodiments.

[0019] Example 1, Material Preparation: In this example, a Li–Y–Cl–S solid electrolyte material with a fluorine-doped molar ratio q=0.1 was prepared, and its chemical formula is Li6YCl. 4.9 F 0.1 S2. In an argon atmosphere glove box with extremely low water and oxygen content, anhydrous LiCl, YCl3, Li2S, and LiF powders (purity ≥99%) were weighed as raw materials in a molar ratio of 1:1.9:2:0.1. The raw materials were pre-ground and mixed evenly in an agate mortar, and then quickly transferred to a 45mL stainless steel ball mill jar (the jar was pre-dried in the glove box). Stainless steel balls were added as the grinding medium, controlling the ball-to-material mass ratio to be approximately 10:1. The jar was then sealed tightly and removed from the glove box. High-energy planetary ball milling was performed at 500 rpm for 50 hours, with periodic stops to release gas and prevent overheating. After milling, the ball mill jar was returned to the glove box, and the sample was removed, yielding homogeneous Li6YCl. 4.9 F 0.1 X-ray diffraction (XRD) analysis of the S2 solid electrolyte material powder showed that the powder mainly exhibited the characteristic diffraction peaks of halosulfide solid electrolytes, indicating that the target product has been synthesized.

[0020] Example 2, Material Preparation: In this example, a solid electrolyte material with a fluorine-doped molar ratio q=0.3 and the chemical formula Li6YCl was prepared. 4.7 F 0.3S2. The same raw materials and process steps as in Example 1 were used, except that the raw material ratio was adjusted to 1:1.7:2:0.3 (i.e., LiCl:YCl3:Li2S:LiF=1:1.7:2:0.3). Raw material weighing and mixing were completed under the same argon glove box protection, and high-energy ball milling was maintained at 300 rpm for 60 hours. The ball-milled product was characterized by XRD, and its main phase corresponded to the target composition Li6YCl. 4.7 F 0.3 S2, no impurity peaks appear.

[0021] Example 3, Material Preparation: In this example, a solid electrolyte material with a fluorine doping molar ratio of q=0.5 (upper limit of doping) and the chemical formula Li6YCl was prepared. 4.5 F 0.5 S2. The raw materials used were the same as those described above: LiCl, YCl3, Li2S, and LiF. They were weighed and mixed in a glove box at a molar ratio of 1:1.5:2:0.5. After ball milling at 500 rpm for 20 hours, a light gray fine powder product was obtained. XRD analysis showed that the main crystalline phase of the material was consistent with that of Examples 1 and 2, but the diffraction peaks were slightly broadened, possibly due to the introduction of lattice micro-strain by the higher F content. This indicates that at the q=0.5 doping level, F has been maximally dissolved into the lattice but still maintains the overall structure of the material.

[0022] Example 4, Material Preparation: In this example, a solid electrolyte material with a fluorine-doped molar ratio q=0.3 and the chemical formula Li4YCl was prepared. 5.7 F 0.3 S 0.5 The same raw materials and process steps as in Example 1 were used, except that the raw material ratio was adjusted to 2.7:1:0.5:0.3 (i.e., LiCl:YCl3:Li2S:LiF = 2.7:1:0.5:0.3). Raw material weighing and mixing were completed under the same argon glove box protection, and high-energy ball milling was maintained at 500 rpm for 50 hours. The ball-milled product was characterized by XRD, and its main phase corresponded to the target composition Li4YCl. 5.7 F 0.3 S 0.5 No impurity peaks appeared.

[0023] Example 5, Material Preparation: In this example, a solid electrolyte material with a fluorine-doped molar ratio q=0.3 and the chemical formula Li3YCl was prepared. 4.7 F 0.3 S 0.5The same raw materials and process steps as in Example 1 were used, except that the raw material ratio was adjusted to 1.7:1:0.5:0.3 (i.e., LiCl:YCl3:Li2S:LiF = 1.7:1:0.5:0.3). Raw material weighing and mixing were completed under the same argon glove box protection, and high-energy ball milling was maintained at 500 rpm for 50 hours. The ball-milled product was characterized by XRD, and its main phase corresponded to the target composition Li3YCl. 4.7 F 0.3 S 0.5 No impurity peaks appeared.

[0024] Example 6, Material Preparation: In this example, a solid electrolyte material with a fluorine-doped molar ratio q=0.3 and the chemical formula Li₂Y₃Cl was prepared. 8.7 F 0.3 S. The same process steps as in Example 1 were adopted, except that YF3 was used instead of LiF in the raw materials, and the ratio was adjusted to 0:2.9:1:0.1 (i.e., LiCl:YCl3:Li2S:YF3=0:2.9:1:0.1). The raw materials were weighed and mixed under the same argon glove box protection, and high-energy ball milling was maintained at 500 rpm for 50 hours. The ball-milled product was characterized by XRD, and its main phase corresponded to the target composition Li2Y3Cl. 8.7 F 0.3 S, no impurity peaks appear.

[0025] Example 7: Compared to Example 2, after ball milling, heat treatment was performed at 300°C for 2 hours. The product was characterized by XRD, and its main phase corresponded to the target composition Li6YCl. 4.7 F 0.3 S2, no impurity peaks appear.

[0026] Example 8, compared to Example 2, involved heat treatment after ball milling at 200°C for 10 hours. The product was characterized by XRD, and its main phase corresponded to the target composition Li6YCl. 4.7 F 0.3 S2, no impurity peaks appear.

[0027] Comparative Example 1, Material Preparation: Undoped Li–Y–Cl–S solid electrolyte material was prepared in this comparative example. A sample with the chemical formula Li6YCl5S2 (i.e., q=0, corresponding to Li6YCl5F0S2) was synthesized using the same method as in Example 2 above. The raw materials used were LiCl, YCl3, and Li2S, without the addition of LiF, in a molar ratio of 2:1:2 (this ratio is the same as the Cl:S ratio before fluorine doping in Example 2). The ball milling process conditions were the same as in Example 2. XRD characterization of the obtained powder showed it to be a single-phase halosulfide, with a crystal structure consistent with the corresponding undoped matrix material in Example 2.

[0028] Comparative Example 2, Material Preparation: In this comparative example, an undoped Li–Y–Cl–S solid electrolyte material was prepared by synthesizing the chemical formula Li4YCl6S using the same method as in Example 4 above. 0.5 The sample (i.e., q=0, corresponding to Li6YCl5F0S) 0.5 The raw materials used were LiCl, YCl3, and Li2S, without the addition of LiF, in a molar ratio of 3:1:0.5 (this ratio is the same as the Cl:S ratio before fluorine doping in Example 4). The ball milling process conditions were the same as in Example 4. XRD characterization of the obtained powder showed it to be a single-phase halosulfide, with a crystal structure consistent with the corresponding unfluorinated matrix material in Example 4.

[0029] Comparative Example 3, Material Preparation: In this comparative example, an undoped Li–Y–Cl–S solid electrolyte material was prepared. A sample with the chemical formula Li₂Y₃Cl₉S (i.e., q=0, corresponding to Li₂Y₃Cl₉F₀S) was synthesized using the same method as in Example 6. The raw materials used were LiCl, YCl₃, and Li₂S, without the addition of LiF, in a molar ratio of 0:3:1 (this ratio is the same as the Cl:S ratio before fluorine doping in Example 6). The ball milling process conditions were the same as in Example 6. XRD analysis of the obtained powder revealed it to be a single-phase halosulfide, with a crystal structure consistent with the undoped matrix material of Example 6.

[0030] Performance Testing: The powders prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance testing. The powders were placed in a steel mold and cold-pressed under vacuum at 300 MPa to prepare circular electrolyte samples with a diameter of 10 mm and a thickness of approximately 2 mm. The ionic conductivity was measured using AC impedance spectroscopy: metal blocking electrodes (e.g., electroplated Au or coated stainless steel sheets) were coated on both sides of the sample. Impedance spectra were obtained by scanning the frequency range of 0.1 Hz–1 MHz at room temperature, where S / cm (calculated based on electrolyte resistance, thickness, and cross-sectional area) was measured. Subsequently, two lithium metal discs were attached to both sides of the electrolyte sample in a glove box to assemble a symmetrical cell (Li|Li symmetrical cell), maintaining good contact with a constant pressure (80 MPa light pressure). After standing for 6 hours, the initial interfacial impedance was measured (estimated from the diameter of the low-frequency semicircle of the impedance spectrum). An AC impedance of 0.1 mA / cm was applied to this symmetrical cell. 2The current density was repeatedly charged and discharged (i.e., constant current reciprocating electroplating / stripping of metallic lithium, with a single polarization time of 1 hour per cycle) for continuous cyclic testing, and the number of cycles in which the interfacial impedance showed no significant increase was recorded. Electrochemical impedance spectroscopy (EIS) was performed using a Bio-Logic VSP-300 potentiostat, with a test frequency range of 1MHz–0.1Hz and an AC perturbation voltage of 10mV. In the measured Nyquist plot, the transverse difference between the high-frequency intercept and the low-frequency intercept corresponds to the interfacial impedance (ASR), which is converted to Ω·cm based on the electrode area. 2 The test results are shown in Table 1.

[0031] Table 1

[0032] As shown in the table above, the ionic conductivity of the material remains essentially constant at 10 as the F doping content increases (0→0.1→0.3→0.5). -3 -10 -2 The high S / cm level indicates that F doping did not adversely affect lithium-ion transport capability. However, the interface impedance and polarization voltage were significantly improved by F doping: the undoped control showed a sharp increase in interface impedance and polarization voltage after short-term cycling, leading to battery failure, while the F-doped material maintained a low and stable interface impedance (approximately 60 Ω / cm) even after long-term cycling. 2 The cycle life section further reveals the differences: the comparative battery experienced a short circuit in a short time due to interface instability (approximately 40 hours of cycle time), while the symmetric battery with fluorine-doped material showed a significantly longer cycle time (averaging over 500 hours) and no signs of failure. These results fully demonstrate the significant improvement of the interface stability between the Li–Y–Cl–S solid electrolyte and lithium metal by trace fluorine doping, thus verifying the effectiveness and superiority of the present invention.

[0033] This invention successfully solves the problem of instability in direct contact between halide sulfide electrolytes and metallic lithium by introducing fluorine (F) doping into a Li–Y–Cl–S halide sulfide solid electrolyte, thereby constructing a stable LiF interfacial buffer layer in situ within the material. While maintaining high ionic conductivity, it significantly reduces interfacial impedance and polarization effects, extending battery cycle life. The preparation method of this fluorine-doped solid electrolyte material is simple and feasible, and it has significant implications for the practical application of all-solid-state lithium metal batteries.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material, characterized in that, The chemical formula of the solid electrolyte is shown in formula (I): Li a Y b Cl c F q S d ; in: 0.5≤(a+b) / (c+d+q)≤1; a>0, b>0, c>0, d>0; 0<q≤0.5。 2. The fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material according to claim 1, characterized in that, In the solid electrolyte, Y is used as the metal central cation, and the chloride matrix composed of Y and Li is obtained through F. - Cl in the substituted chloride matrix - .

3. The fluorine-doped lithium-yttrium-chlorine-sulfur system solid electrolyte material according to claim 1, characterized in that, The solid electrolyte has an ionic conductivity ≥1.0×10⁻⁶ at room temperature. -3 S / cm.

4. A method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material according to any one of claims 1-3, characterized in that, The process includes the following steps: Under an inert atmosphere, lithium source, yttrium source, chlorine source, fluorine source and sulfur source are weighed according to stoichiometry, mixed and ball-milled to obtain a solid electrolyte with a uniform crystal structure.

5. The method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material according to claim 4, characterized in that, The lithium source is selected from LiCl, LiF and Li2S; the yttrium source is selected from YCl3 and YF3; the chlorine source is selected from LiCl and YCl3; the fluorine source is selected from LiF and YF3; and the sulfur source is selected from Li2S.

6. The method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material according to claim 4, characterized in that, Under the inert atmosphere, the selected inert gas is at least one of argon, helium, neon, krypton, xenon, and nitrogen, and the dew point of the inert gas is less than or equal to -60°C.

7. The method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material according to claim 4, characterized in that, The ball milling time is 20–60 hours, and the rotation speed is 300–500 rpm.

8. The method for preparing a fluorine-doped lithium-yttrium-chlorine-sulfur solid electrolyte material according to claim 4, characterized in that, After ball milling, heat treatment is performed at a temperature of 200–300℃ for 2–10 hours.

Images