A high-stability sulfide solid-state electrolyte and a preparation method thereof

Abstract

This invention discloses a highly stable sulfide solid electrolyte and its preparation method, belonging to the field of solid electrolyte materials technology. The chemical formula of the electrolyte is Li. 11＋4z P 2－2z M 2z S 9－ 2x O 2x Cl 3－2y N 2y Where M is at least one of B, Al, Ga, In, Mn, and Cr, and N is at least one of F, Br, and I, with 2.25 ≤ x ≤ 4.5, 0.75 ≤ y ≤ 1.5, and 0.01 ≤ z ≤ 1. This invention reduces the PS4 content, which is easily attacked by polar groups, by doping the P-site with metal element M, the S-site with element O, and the Cl-site with halogen element N. 3‑ The proportion of sulfide solid electrolytes is adjusted, and lattice changes caused by dual doping are compensated by halogen atoms, thereby significantly improving the air and thermal stability of the sulfide solid electrolyte. The sulfide solid electrolyte provided by this invention exhibits excellent ionic conductivity and stability, making it suitable for the field of all-solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte materials technology, and more specifically, to a highly stable sulfide solid electrolyte and its preparation method. Background Technology

[0002] Sulfide solid electrolytes are considered one of the most promising solid electrolyte materials due to their extremely high ionic conductivity and good machinability. However, actual research has found that when sulfide solid electrolytes are exposed to air, they readily react with moisture in the air, leading to electrolyte decomposition and the release of harmful H2S gas. The reason for this lies in the poor stability of sulfide electrolytes, particularly the presence of PS4 in their structure. 3- The unit cells are easily attacked by polar groups such as water molecules, leading to structural decomposition and a significant decrease in ionic conductivity. This defect greatly limits the practical application and large-scale preparation of sulfide solid electrolytes.

[0003] Therefore, developing a sulfide solid electrolyte that combines high ionic conductivity and high stability is of great significance for promoting the development of all-solid-state battery technology. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a highly stable sulfide solid electrolyte and its preparation method. This invention reduces unstable PS4 in the structure by performing multi-element synergistic doping in the sulfide solid electrolyte, specifically by doping metal elements at P sites, O elements at S sites, and halogen elements at Cl sites. 3- The proportion of functional groups is adjusted, and lattice changes caused by metal element doping are compensated by halogen atoms and O atoms, thereby significantly improving the air stability and thermal stability of the electrolyte while maintaining high ionic conductivity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a sulfide solid electrolyte with the chemical formula Li. 11＋4z P 2－2z M 2z S 9－2x O 2x Cl 3－2y N 2y Wherein, M is at least one of B, Al, Ga, In, Mn and Cr, N is at least one of F, Br and I, and 2.25≤x≤4.5, 0.75≤y≤1.5, 0.01≤z≤1.

[0006] In the electrolyte chemical formula of this invention, the doping amount of metal element M at the P-site is controlled by the z-value, the doping amount of element O at the S-site is controlled by the x-value, and the doping amount of halogen element N at the Cl-site is controlled by the y-value. The introduction of metal elements M and O can effectively replace part of P and S, reducing PS4 in the structure. 3- The proportion of functional groups is adjusted to reduce the electrolyte's sensitivity to moisture in the air and improve its chemical stability. However, the dual doping of metal and oxygen elements may lead to changes in lattice parameters, affecting ion conduction pathways. Therefore, this invention further dops the Cl site with halogen element N, compensating for lattice distortion through the size and electronegativity effects of halogen atoms, stabilizing the crystal structure, and ensuring that stability is improved without sacrificing ionic conductivity. By controlling x, y, and z within the aforementioned ranges, a sulfide solid electrolyte exhibiting both high ionic conductivity and high stability can be obtained.

[0007] In a preferred embodiment of the present invention, M is Al or Cr. Al and Cr are effective doping elements that can significantly improve the stability of the material while having little impact on the ionic conductivity.

[0008] In another preferred embodiment of the present invention, N is F. F has high electronegativity and a moderate ionic radius, which can effectively compensate for lattice changes and further stabilize the electrolyte structure.

[0009] The present invention also provides a method for preparing the above-mentioned sulfide solid electrolyte, comprising the following steps: The precursor materials of each element are weighed and mixed according to the stoichiometric ratio of the chemical formula. The precursor materials include lithium source, phosphorus source, sulfur source, oxygen source, halogen source and metal M source. The mixed precursor materials were placed in a ball milling jar, and ball milling media and organic solvent were added for ball milling to obtain a ball-milled mixture. The ball-milled mixture is dried to remove the organic solvent, resulting in a dry powder. The dried powder was sintered in a protective atmosphere and then naturally cooled to obtain the sulfide solid electrolyte.

[0010] This preparation method employs a wet ball milling process combined with high-temperature sintering, which enables uniform mixing of elements at the molecular level, facilitating the formation of electrolyte materials with the target chemical composition and crystal structure.

[0011] In a preferred embodiment of the method of the present invention, in step 2, the ball milling speed is 400-600 rpm, the ball milling time is 16-32 h, the ball-to-material ratio is 10-40:1, and the mass ratio of solvent to the mixed precursor material is 0.5-1.5:1. By controlling the ball milling parameters, the precursor can be fully mixed and refined, creating favorable conditions for subsequent sintering, thereby obtaining an electrolyte product with pure phase and high crystallinity.

[0012] In another preferred embodiment of the method of the present invention, in step 4, the sintering temperature is 450~550℃, the heating rate is 1~5℃ / min, and the holding time is 24~48h. This sintering regime is beneficial to the formation of the target crystal structure, while avoiding excessively high temperatures that could lead to material decomposition or volatilization.

[0013] In another preferred embodiment of the method of the present invention, both the drying treatment and the sintering treatment are carried out in an argon protective atmosphere. The inert atmosphere protection can effectively prevent the material from reacting with moisture and oxygen in the air during the preparation process, ensuring the purity and stability of the final product.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) High stability: By doping metal elements at the P site and O elements at the S site, the PS4 in the structure that is easily attacked by polar groups is reduced. 3- The ratio significantly improved the electrolyte's tolerance to air, inhibited the generation of H2S, and reduced the decay of ionic conductivity.

[0015] (2) Lattice compensation effect: By doping the halogen element N at the Cl site, the lattice distortion that may be caused by the dual doping of metal elements and O elements is effectively compensated, the ion conduction network is stabilized, and high ionic conductivity is maintained while improving stability.

[0016] (3) Excellent thermal stability: The electrolyte modified by multi-element synergistic doping exhibits good thermal stability and is not easily ignited in air, which improves the safety of the material.

[0017] (4) Controllable preparation process: The preparation method provided is simple and the parameters are controllable, which is suitable for large-scale production and has good industrial application prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 A flowchart illustrating the preparation method of the highly stable sulfide solid electrolyte provided by this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0020] This invention provides a highly stable sulfide solid electrolyte with the chemical formula Li. 11＋4z P 2－2z M 2z S 9－ 2x O 2x Cl 3－2y N 2y Wherein, M is at least one of B, Al, Ga, In, Mn and Cr, N is at least one of F, Br and I, and 2.25≤x≤4.5, 0.75≤y≤1.5, 0.01≤z≤1.

[0021] In one specific embodiment, M is Al or Cr; and N is F.

[0022] See also Figure 1 As shown, the present invention also provides a method for preparing the highly stable sulfide solid electrolyte, comprising the following steps: Step S1: Weigh and mix the precursor materials of each element according to the stoichiometric ratio of the chemical formula. The precursor materials include lithium source, phosphorus source, sulfur source, oxygen source, halogen source and metal M source. Step S2: Place the mixed precursor material in a ball mill jar, add ball milling media and organic solvent for ball milling treatment to obtain a ball milling mixture; Step S3: The ball-milled mixture is dried to remove the organic solvent, resulting in a dried powder; Step S4: The dried powder is sintered in a protective atmosphere and then naturally cooled to obtain a highly stable sulfide solid electrolyte.

[0023] In step S1, the ball milling speed is 400~600 rpm, the ball milling time is 16~32 h, the ball-to-material ratio is 10~40:1, and the mass ratio of solvent to the mixed precursor material is 0.5~1.5:1.

[0024] In step S4, the sintering temperature is 450~550℃, the heating rate is 1~5℃ / min, and the holding time is 24~48h.

[0025] Furthermore, both the drying process and the sintering process are carried out in an argon protective atmosphere.

[0026] The present invention will now be described in detail with reference to specific embodiments and comparative examples.

[0027] In the following examples, all raw materials used were commercially available analytical grade or chemically pure reagents. All air-sensitive material handling, ball milling, drying, and sintering operations, unless otherwise specified, were performed in an argon-protected glove box or atmosphere furnace.

[0028] Precursor materials involved in the embodiments: Li source: Li2S; P source: one or more of P2S5 and P2O5; S source: originates from Li2S, P2S5 and metal sulfides (such as B2S3, Al2S3, Ga2S3, In2S3, MnS, Cr2S3, etc.). O source: one or more of Li2O and Al2O3; Halogen source: one or more of LiF, LiCl, LiBr, and LiI; Metal M source: metal chlorides (such as AlCl3, GaCl3, InCl3, MnCl2, CrCl3, etc.) or metal sulfides (such as B2S3, Al2S3, Ga2S3, In2S3, MnS, Cr2S3, etc.) Example 1 This embodiment 1 provides a sulfide solid electrolyte with the chemical formula Li. 5.7 P 0.9 Cr 0.1 S4O 0.5 Cl 1.5 This chemical formula corresponds to the general formula Li. 11＋4z P 2－2z M 2z S 9－2x O 2x Cl 3－2y N 2y In this case, M = Cr, and N is undoped (i.e., the Cl sites are not replaced by N, corresponding to y = 0.75, N). 2y The case where x = 2.25 and z = 0.05 (where z is 0).

[0029] The preparation method is as follows: Based on the molar ratio of the elements in the chemical formula, Li₂S, LiCl, CrCl₃, LiF, Li₂O, and P₂S₅ are weighed as precursor materials. The weighed raw materials are placed in a zirconia ball mill jar, and zirconia grinding beads are added at a ball-to-material ratio of 40:1. Xylene solvent is then added at a solvent-to-raw material mass ratio of 1.5:1. The mixture is ball-milled at 400 rpm for 16 hours using a planetary ball mill to obtain a ball-milled mixture. The ball-milled mixture is removed and dried in a vacuum drying oven at 80℃ for 16 hours to remove residual solvent, obtaining a dry powder. The dry powder is placed in an alumina crucible and heated to 550℃ at a heating rate of 1℃ / min, held at that temperature for 12 hours for sintering, and then naturally cooled to obtain the sulfide solid electrolyte.

[0030] Example 2 This embodiment 2 provides a sulfide solid electrolyte with the chemical formula Li. 5.7 P 0.9 Cr 0.1 S4O 0.5 ClF 0.5 This chemical formula corresponds to the general formula Li. 11＋4z P 2－2z M 2z S 9－2x O 2x Cl 3－2y N 2y In this example, M=Cr, N=F, and x=2.25, y=1.0, z=0.05. Compared to Example 1, Example 2 introduces F element to partially substitute the Cl site, aiming to further stabilize the lattice through the compensation effect of halogen atoms, and is expected to obtain better air stability while maintaining high electrical conductivity.

[0031] The preparation method is the same as in Example 1, except that the raw material ratio is modified according to the chemical formula of Example 2.

[0032] Example 3 This embodiment 3 provides a sulfide solid electrolyte with the chemical formula Li. 5.7 P 0.9 Cr 0.1 S4O 0.5 Cl 0.5 F. This chemical formula corresponds to the case where x=2.25, y=1.25, z=0.05, M=Cr, and N=F in the general formula. In Example 3, the doping amount of F was further increased to investigate the effect of different halogen doping ratios on performance.

[0033] The preparation method is the same as in Example 1, except that the raw material ratio is modified according to the chemical formula of Example 3.

[0034] Example 4 This embodiment 4 provides a sulfide solid electrolyte with the chemical formula Li. 5.7 P 0.9 Cr 0.1 S4O 0.5 Cl 0.3 F 1.2 This chemical formula corresponds to the case where x=2.25, y=1.35, z=0.05, M=Cr, and N=F in the general formula. In Example 4, the doping amount of F is further increased to investigate the effect of the upper limit of halogen doping amount on performance.

[0035] The preparation method is the same as in Example 1, except that the raw material ratio is modified according to the chemical formula of Example 4.

[0036] Example 5 This embodiment 5 provides a sulfide solid electrolyte with the chemical formula Li. 5.6 P 0.95 Al 0.05 S4O 0.5 ClF 0.5 This chemical formula corresponds to the general formula Li. 11＋4z P 2－2z M 2z S 9－2x O 2x Cl 3－2y N 2y In this example, M=Al, N=F, and x=2.25, y=1.0, z=0.025. In Example 5, the doping metal element is replaced by Al instead of Cr, aiming to investigate the effect of different metal element doping on material properties.

[0037] The preparation method is as follows: Based on the molar ratio of the elements in the chemical formula, Li₂S, LiCl, AlCl₃, LiF, Li₂O, and P₂S₅ are weighed as precursor materials. The weighed raw materials are placed in a zirconia ball mill jar, and zirconia grinding beads are added at a ball-to-material ratio of 10:1. Xylene solvent is then added at a solvent-to-raw material mass ratio of 1:1. The mixture is ball-milled at 600 rpm for 24 hours using a planetary ball mill to obtain a ball-milled mixture. The ball-milled mixture is removed and dried in a vacuum drying oven at 80℃ for 16 hours to remove residual solvent, obtaining a dry powder. The dry powder is placed in an alumina crucible and heated to 450℃ at a heating rate of 1℃ / min, held at that temperature for 24 hours for sintering, and then naturally cooled to obtain the sulfide solid electrolyte.

[0038] Example 6 This embodiment 6 provides a sulfide solid electrolyte with the chemical formula Li. 5.7 P 0.9 Al 0.1 S4O 0.5 ClF 0.5This chemical formula corresponds to the case where x=2.25, y=1.0, z=0.05, M=Al, and N=F in the general formula. Compared with Example 5, Example 6 increases the doping amount of Al to investigate the effect of the metal doping ratio on performance.

[0039] The preparation method is the same as in Example 5, except that the raw material ratio is modified according to the chemical formula of Example 6.

[0040] Example 7 This embodiment 7 provides a sulfide solid electrolyte with the chemical formula Li. 5.8 P 0.85 Al 0.15 S4O 0.5 ClF 0.5 This chemical formula corresponds to the case where x=2.25, y=1.0, z=0.075, M=Al, and N=F in the general formula. Example 7 further increases the Al doping amount.

[0041] The preparation method is the same as in Example 5, except that the raw material ratio is modified according to the chemical formula of Example 7.

[0042] Example 8 This embodiment 8 provides a sulfide solid electrolyte with the chemical formula Li. 5.9 P 0.8 Al 0.2 S4O 0.5 ClF 0.5 This chemical formula corresponds to the case where x=2.25, y=1.0, z=0.1, M=Al, and N=F in the general formula. Example 8 further increases the Al doping amount to investigate the effect of the upper limit of metal doping amount on performance.

[0043] The preparation method is the same as in Example 5, except that the raw material ratio is modified according to the chemical formula of Example 8.

[0044] Comparison Example This comparative example provides a sulfide solid electrolyte that has not undergone the multi-element synergistic doping modification of this invention, and its chemical formula is Li. 5.5 PS 4.5 Cl 1.5 , serving as a benchmark for performance comparison.

[0045] The preparation method is as follows: Based on the molar ratio of the elements in the chemical formula, Li₂S, LiCl, and P₂S₅ were weighed as precursor materials. The weighed raw materials were placed in a zirconia ball mill jar, and zirconia grinding beads were added at a ball-to-material ratio of 10:1. Xylene solvent was then added at a solvent-to-raw material mass ratio of 1:1. The mixture was ball-milled at 600 rpm for 24 hours using a planetary ball mill to obtain a ball-milled mixture. The ball-milled mixture was removed and dried in a vacuum drying oven at 80℃ for 16 hours to remove residual solvent, yielding a dry powder. The dry powder was placed in an alumina crucible and heated to 450℃ at a heating rate of 1℃ / min, held at that temperature for 24 hours for sintering, and then naturally cooled to obtain the sulfide solid electrolyte.

[0046] Performance testing The performance of the sulfide solid electrolytes prepared in the above examples and comparative examples was tested using the following methods: Ionic conductivity test: The prepared sulfide solid electrolyte was ground into powder, 150mg of powder was weighed, and a mold was used to assemble it into a mold battery. After being kept at 25℃ for 1h, its room temperature ionic conductivity was tested by electrochemical impedance spectroscopy (EIS).

[0047] Air stability test: Take a certain amount of sulfide solid electrolyte powder and place it in a closed air environment with 30% humidity. After exposure for 3 hours, test its room temperature ionic conductivity again using the electrochemical impedance spectroscopy (EIS) method and calculate the conductivity retention rate (conductivity after exposure / initial conductivity × 100%).

[0048] Thermal stability test (combustion test): Under an argon protective atmosphere, 200 mg of electrolyte powder from Example 6 (optimal performance) and the control example were weighed and cold-pressed into discs with a diameter of 10 mm under a pressure of 350 MPa. The discs were then removed and placed in air, heated with an alcohol lamp, and observed to see if they ignited.

[0049] Test Results Table 1 summarizes the ionic conductivity and air stability test results of each embodiment and control example.

[0050] Table 1. Room temperature ionic conductivity and air stability data for the examples and control examples. As can be seen from the data in Table 1: Comparing Examples 1-4, the conductivity retention rate was significantly improved with the introduction of F element (Example 2) compared to Example 1 without F doping, demonstrating the contribution of halogen doping to stability. However, excessive F doping (Examples 3 and 4) may lead to a slight decrease in conductivity.

[0051] Compared to Examples 5-8, the Al-doped series of samples exhibited higher initial ionic conductivity and conductivity retention than the Cr-doped series. Among them, Example 6 (Li 5.7 P 0.9 Al 0.1 S4O 0.5 ClF 0.5 The sample exhibited optimal overall performance, with an initial ionic conductivity as high as 5.76 mS / cm. After exposure to air with 30% humidity for 3 hours, the conductivity retention rate still reached 69.79%, far superior to the control example without multi-element synergistic doping. This indicates that appropriate amounts of Al and F doping have a synergistic effect, which can optimize the ion transport path while stabilizing the structure.

[0052] Thermal stability test results: For the best performing example 6 (Li 5.7 P 0.9 Al 0.1 S4O 0.5 ClF 0.5 ) and control case (Li 5.5 PS 4.5 Cl 1.5 An air combustion test was conducted. The results showed that the electrolyte disc in the control example was quickly ignited and completely burned by the alcohol lamp, while the electrolyte disc in Example 6 did not ignite, exhibiting excellent thermal stability and flame retardancy. This is attributed to the fact that the present invention reduces easily decomposable PS4 through multi-element doping. 3- The group forms a more stable crystal structure, thereby significantly improving the thermal safety of the material.

[0053] In summary, the high-stability sulfide solid electrolyte and its preparation method provided by this invention successfully solve the technical problem of poor stability of existing sulfide electrolytes through multi-element synergistic doping at P-sites, S-sites and Cl-sites, and obtain a novel electrolyte material with high ionic conductivity, high air stability and high thermal stability, which has broad application prospects in the field of all-solid-state batteries.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly stable sulfide solid electrolyte, characterized in that, Its chemical formula is Li 11＋4z P 2－2z M 2z S 9－ 2x O 2x Cl 3－2y N 2y Wherein, M is at least one of B, Al, Ga, In, Mn and Cr, N is at least one of F, Br and I, and 2.25≤x≤4.5, 0.75≤y≤1.5, 0.01≤z≤1.

2. The highly stable sulfide solid electrolyte according to claim 1, characterized in that, M is either Al or Cr.

3. The highly stable sulfide solid electrolyte according to claim 1 or 2, characterized in that, N is F.

4. A method for preparing a highly stable sulfide solid electrolyte as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Weigh and mix the precursor materials of each element according to the stoichiometric ratio of the chemical formula. The precursor materials include lithium source, phosphorus source, sulfur source, oxygen source, halogen source and metal M source. Step S2: Place the mixed precursor material in a ball mill jar, add ball milling media and organic solvent for ball milling treatment to obtain a ball milling mixture; Step S3: The ball-milled mixture is dried to remove the organic solvent, resulting in a dried powder; Step S4: The dried powder is sintered in a protective atmosphere and then naturally cooled to obtain a highly stable sulfide solid electrolyte.

5. The method according to claim 4, characterized in that, In step S1, the ball milling speed is 400~600 rpm, the ball milling time is 16~32 h, the ball-to-material ratio is 10~40:1, and the mass ratio of solvent to the mixed precursor material is 0.5~1.5:

1.

6. The method according to claim 4, characterized in that, In step S4, the sintering temperature is 450~550℃, the heating rate is 1~5℃ / min, and the holding time is 24~48h.

7. The method according to claim 4, characterized in that, Both the drying and sintering processes are carried out in an argon protective atmosphere.

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