A modified sulfide electrolyte and a preparation method and application thereof

Abstract

The application provides a modified sulfide electrolyte as well as a preparation method and application thereof, and belongs to the technical field of lithium metal battery electrolytes. The modified sulfide electrolyte of the application innovatively adopts Ca and F element co-doping to stabilize the lithium metal to the sulfide electrolyte, and maintains a relatively high ionic conductivity, thereby meeting the high performance requirements of the electrolyte of the all-solid-state lithium metal battery. The all-solid-state lithium metal battery prepared based on the modified sulfide electrolyte has excellent cycle stability. The critical current density of the all-solid-state lithium metal battery prepared by the modified sulfide electrolyte of the application can reach 1.6 mA cm ‑2 , which is more than three times that of the original Li6PS5Cl electrolyte, and the ionic conductivity can reach 2.68 mS cm ‑1 .

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal battery electrolytes, and particularly relates to a modified sulfide electrolyte, its preparation method and application. Background Art

[0002] With the continuous growth of energy demand and the increasing performance requirements for energy storage devices such as portable electronic devices and electric vehicles, traditional lithium-ion batteries based on liquid electrolytes have limitations such as leakage risk, poor safety (flammability, explosion, etc.), and rapid performance decay in extreme environments (high temperature, low temperature, etc.). As a highly promising next-generation energy storage technology, all-solid-state lithium metal batteries are expected to overcome many drawbacks of the above-mentioned liquid batteries and have received extensive attention (Nature Reviews Materials 2021, 6, 1003-1019).

[0003] As a key component of all-solid-state lithium metal batteries, the performance of the electrolyte directly affects the overall performance of the battery. Sulfide electrolytes are considered to be one of the ideal electrolyte materials for all-solid-state lithium metal batteries due to their high ionic conductivity and good mechanical ductility (Science 2023, 381, 50). However, existing sulfide electrolytes still have some deficiencies. For example, sulfide electrolytes have poor compatibility with lithium metal, and side reactions occur when they contact lithium metal electrodes, resulting in problems such as decreased battery performance and shortened cycle life.

[0004] Therefore, it is of great practical significance to develop a sulfide electrolyte with high ionic conductivity and good compatibility with lithium metal. Summary of the Invention

[0005] Aiming at the problems existing in the background art, the purpose of the present invention is to provide a modified sulfide electrolyte, its preparation method and application. The modified sulfide electrolyte of the present invention innovatively uses co-doping of Ca and F elements to improve the stability of the electrolyte to lithium metal and maintain a high ionic conductivity, thereby meeting the high-performance requirements of all-solid-state lithium metal batteries for electrolytes. The all-solid-state lithium metal battery prepared based on this modified sulfide electrolyte has excellent cycle stability.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A modified sulfide electrolyte, whose chemical formula is Li 6+x P 1-x Ca x S 5-2x F 2x Cl, where 0 < x ≤ 0.15; the modified sulfide electrolyte is in a cubic phase structure.

[0008] A method for preparing a modified sulfide electrolyte includes the following steps:

[0009] Step 1. Under a protective atmosphere, the raw materials Li2S, P2S5, LiCl and CaF2 are ball-milled according to a preset molar ratio to obtain precursor powder;

[0010] Step 2. The precursor powder obtained in Step 1 is formed into sheet-like discs under a preset pressure to prevent the loss of electrical conductivity caused by the volatilization of sulfur at high temperatures during sintering.

[0011] Step 3. Sinter the sheet sample obtained in Step 2 under a protective atmosphere. After the sintering reaction is completed, allow it to cool naturally to obtain the desired modified sulfide electrolyte.

[0012] Furthermore, in step 1, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere, preferably argon.

[0013] Further, in step 1, during ball milling, the mass ratio of the grinding balls to the mixed raw materials is 40:1 to 20:1; the diameter of the grinding balls is 3 to 10 mm; the ball milling speed is 400 to 600 rpm; and the ball milling time is 15 to 20 hours.

[0014] Furthermore, in step 2, the preset pressure is 100-200 MPa.

[0015] Furthermore, in step 3, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere, preferably argon.

[0016] Furthermore, in step 3, the sintering temperature is 450–600℃, and the sintering time is 6–12 hours.

[0017] This invention also provides the application of the above-mentioned modified sulfide electrolyte in all-solid-state lithium metal batteries, specifically:

[0018] The modified sulfide electrolyte powder, weighed in an argon-filled glove box, is placed in a mold and pressed into a solid electrolyte sheet under a certain pressure. The corresponding positive and negative electrodes are placed at both ends of the electrolyte sheet to prepare an all-solid-state lithium metal battery.

[0019] The mechanism of this invention is as follows:

[0020] This invention improves the stability of the sulfide electrolyte to lithium metal and maintains high ionic conductivity by introducing Ca and F elements into the sulfide electrolyte material Li6PS5Cl. Specifically, the Ca and F elements introduced into the Li6PS5Cl electrolyte form CaS4 and PS3F tetrahedra, respectively. Compared with the original PS4 tetrahedra, CaS4 and PS3F tetrahedra have higher chemical stability, which can block electron exchange between the sulfide electrolyte and lithium metal and suppress interfacial side reactions.

[0021] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0022] The critical current density of the all-solid-state lithium metal battery prepared based on the modified sulfide electrolyte of this invention can reach 1.6 mA cm⁻¹. -2 It is more than three times that of the original Li6PS5Cl electrolyte; and the ionic conductivity remains at a high level, at 2.68 mS cm⁻¹. -1 . Attached Figure Description

[0023] Figure 1 This is a crystal structure diagram of the modified sulfide electrolyte of the present invention.

[0024] Figure 2 The X-ray diffraction (XRD) spectra of the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 of this invention are compared.

[0025] Figure 3 The X-ray photoelectron spectroscopy (XPS) of the sulfide electrolytes prepared in Example 1 and Comparative Example 1 of this invention is compared.

[0026] Figure 4 The electrochemical impedance spectroscopy (EIS) spectra of the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 of this invention are compared.

[0027] Figure 5 Comparison of cyclic voltammetry test spectra of the sulfide electrolytes prepared in Examples 1-3 and Comparative Example 1 of this invention.

[0028] Figure 6 This is a comparison of the cycle stability test results of lithium symmetric batteries assembled based on the sulfide electrolytes prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0030] A modified sulfide electrolyte with the chemical formula Li 6+x P1-x Ca x S 5-2x F 2x Cl, where 0 < x ≤ 0.15; the modified sulfide electrolyte has a cubic phase structure, and the specific crystal system structure diagram is as Figure 1 shown.

[0031] Example 1

[0032] A preparation method of a modified sulfide electrolyte includes the following steps:

[0033] Step 1. Inside a glove box filled with argon, weigh raw materials of Li2S, P2S5, LiCl, and CaF2 in a molar ratio of 2.525:0.475:1:0.05. Pour all the raw material mixtures into a planetary ball milling jar. The lining and milling beads of the planetary ball mill are made of zirconia. The mass ratio of the milling beads to the mixed raw materials is 40:1. The diameter of the milling beads is 3 mm. Set the ball milling rotation speed to 500 rpm and the ball milling time to 18 h to obtain a precursor powder.

[0034] Step 2. Collect the precursor powder obtained in Step 1 inside the glove box filled with argon and perform cold pressing at a preset pressure of 200 MPa to form a disc to prevent sulfur volatilization.

[0035] Step 3. Place the disc obtained in Step 2 in a muffle furnace. Under an argon atmosphere, heat it to 500 °C at a heating rate of 5 °C / min, keep it warm for 10 h, and then naturally cool it to room temperature to obtain the final product, which is the required modified sulfide electrolyte Li 6.05 P 0.95 Ca 0.05 S 4.9 F 0.1 Cl.

[0036] Example 2

[0037] Prepare the modified sulfide electrolyte according to the steps of Example 1, only adjust the ratio of the raw materials in Step 1 to 2.55:0.45:1:0.1, and keep the other steps unchanged. The prepared modified sulfide electrolyte is Li 6.1 P 0.9 Ca 0.1 S 4.8 F 0.2 Cl.

[0038] Example 3

[0039] Prepare the modified sulfide electrolyte according to the steps of Example 1, only adjust the ratio of the raw materials in Step 1 to 2.575:0.425:1:0.15, and keep the other steps unchanged. The prepared modified sulfide electrolyte is Li 6.15 P0.85 Ca 0.15 S 4.7 F 0.3 Cl.

[0040] Comparative Example 1

[0041] The sulfide electrolyte was prepared according to the steps of Example 1, except that the raw materials in step 1 were changed to Li2S, P2S5 and LiCl, and the corresponding ratio was changed to 2.5:0.5:1. The other steps remained unchanged, and the sulfide electrolyte Li6PS5Cl was prepared.

[0042] Comparative Example 2

[0043] The sulfide electrolyte was prepared according to the steps of Example 1, except that the raw materials in step 1 were changed to Li₂S, P₂S₅, LiCl, and LiF, and the corresponding ratio was adjusted to 2.4:0.5:1:0.1. All other steps remained unchanged, and the sulfide electrolyte Li₂S₅ was obtained. 5.9 PS 4.9 F 0.1 Cl.

[0044] Comparative Example 3

[0045] The sulfide electrolyte was prepared according to the steps of Example 1, except that the raw materials in step 1 were changed to Li₂S, P₂S₅, LiCl, and CaS, and the corresponding ratio was adjusted to 2.575:0.475:1:0.05. The other steps remained unchanged, and the sulfide electrolyte Li₂S₅ was obtained. 6.15 P 0.95 Ca 0.05 S5Cl.

[0046] Performance testing:

[0047] 1. XRD test

[0048] The sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to XRD tests. Before the tests, the electrolytes were ground uniformly. The test angle range was 10-90° and the scan rate was 2° / min.

[0049] 2. XPS Test

[0050] The sulfide electrolytes prepared in Example 1 and Comparative Example 1 were subjected to XPS testing. The electrolytes were ground uniformly before testing, and the tested elements were P, S, Ca and F.

[0051] 3. EIS test

[0052] The sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to EIS testing. The tests were performed using a Bio-Logic electrochemical workstation (France). 100 mg of electrolyte powder was weighed into a 10 mm diameter mold in an argon-filled glove box and pressed into a solid electrolyte sheet under a preset pressure of 480 MPa. Indium sheets with a diameter of 9.5 mm were placed at both ends of the electrolyte sheet as blocking electrodes. Impedance testing was conducted at a stacking pressure of 10 MPa, with a test range of 200 kHz to 100 mHz, at room temperature. Ionic conductivity was calculated based on the measured impedance values. The test results are as follows: Figure 3 As shown.

[0053] 4. Cyclic voltammetry test

[0054] The sulfide electrolytes prepared in Examples 1-3 and Comparative Example 1 were subjected to EIS testing. The tests were performed using a Bio-Logic electrochemical workstation (France). 100 mg of electrolyte powder was weighed into a 10 mm diameter mold in an argon-filled glove box and pressed into a solid electrolyte sheet under a preset pressure of 480 MPa. Indium sheets with a diameter of 9.5 mm and lithium sheets with a diameter of 8 mm were placed at both ends of the electrolyte sheet. Cyclic voltammetry was performed at a stacking pressure of 5 MPa, with a scan voltage range of 0–5 V, a scan rate of 0.1 mV / s, and at room temperature.

[0055] 5. Lithium stability test

[0056] 100 mg of electrolyte powder was weighed into a 10 mm diameter mold inside an argon-filled glove box and pressed into a solid electrolyte sheet under a preset pressure of 480 MPa. Lithium sheets with a diameter of 8 mm were then placed at both ends of the electrolyte sheet to assemble a lithium-ion symmetric battery. The molded battery was removed from the glove box and placed on a LAND CT2001A tester for cycle stability testing. The cycle test was conducted under a stacking pressure of 5 MPa, with an initial cycle current density set to 0.1 mA / cm². 2 The single charge / discharge time is set to 0.5 hours, and the step current density is set to 0.1 mA / cm². 2 The test conditions were room temperature.

[0057] XRD test results are as follows Figure 2 As shown, the results indicate that the Ca and F elements added in this invention are added to Li6PS5Cl through doping, which does not introduce impurities into the original sulfide electrolyte and does not damage the original Li6PS5Cl electrolyte crystal structure.

[0058] XPS test results are as follows: Figure 3As shown, (a) represents Ca, (b) represents F, (c) represents P, and (d) represents S. The results indicate that the introduction of F and Ca into the sulfide electrolyte Li6PS5Cl forms strong interactions with P and S atoms, respectively. Compared to the unstable PS bond, PF and Ca-S exhibit higher chemical stability and can resist attacks from highly reactive lithium atoms, thereby improving the lithium stability of the sulfide electrolyte. Furthermore, from... Figure 3 The P 2p and S 2p XPS spectra shown in c and 3d show that the introduction of Ca and F induced the enrichment and dissipation of S and P sites, respectively, which confirms the strong interactions between Ca and F with P and S, respectively.

[0059] The EIS test results and calculated ionic conductivity are shown in Table 1. Figure 4 As shown in the figure. The results indicate that the introduction of F into the sulfide electrolyte Li6PS5Cl leads to a decrease in ionic conductivity, while the introduction of Ca leads to an increase in ionic conductivity. This is because the strong electronegativity of F atoms hinders the migration of lithium ions in the sulfide electrolyte; while the strong interaction between Ca and S weakens the interaction between S sites and lithium ions in the sulfide electrolyte, thereby lowering the energy barrier for lithium ion diffusion in the electrolyte and accelerating lithium ion conduction. Furthermore, as can be seen from Example 1 and Comparative Example 2, the introduction of Ca can compensate for the conductivity loss caused by F doping.

[0060] Table 1

[0061] Sample Name Ionic conductivity (mS / cm) Example 1 <![CDATA[Li 6.05 P 0.95 Ca 0.05 S 4.9 F 0.1 Cl]]> 2.68 Example 2 <![CDATA[Li 6.1 P 0.9 Ca 0.1 S 4.8 F 0.2 Cl]]> 2.42 Example 3 <![CDATA[Li 6.15 P 0.85 Ca 0.15 S 4.7 F 0.3 Cl]]> 1.92 Comparative Example 1 <![CDATA[Li6PS5Cl]]> 3.37 Comparative Example 2 <![CDATA[Li 5.9 PS 4.9 F 0.1 Cl]]> 2.38 Comparative Example 3 <![CDATA[Li 6.15 P 0.95 Ca 0.05 S5Cl]]> 3.58

[0062] The test results of cyclic voltammetry are as follows: Figure 5 As shown. The results indicate that, compared to Comparative Example 1, the batteries assembled based on the sulfide electrolytes prepared in Examples 1-3 exhibit a lower current response in the voltage range of 0-1V, indicating lower lithium metal reactivity. This result is because the formation of PS3F and CaS4 tetrahedra in the F and Ca-doped sulfide electrolytes gives the sulfide electrolytes higher chemical stability, which can resist the attack of highly chemically reactive lithium atoms and suppress interfacial side reactions.

[0063] The test results for the stability of lithium metal are as follows: Figure 6 As shown, the critical current density of the lithium symmetric batteries assembled based on the sulfide electrolytes prepared in Examples 1-3 is higher than that of the undoped sulfide electrolyte in Comparative Example 1. This result is because the formation of PS3F and CaS4 tetrahedra in the F and Ca-doped sulfide electrolytes gives the sulfide electrolytes higher chemical stability, which can resist the attack of highly chemically reactive lithium atoms, thereby improving the lithium stability of the sulfide electrolyte.

[0064] The above embodiments demonstrate that the present invention provides a novel method for preparing sulfide electrolytes and their applications, which provides lithium metal compatibility while maintaining high ionic conductivity by introducing fluorine and calcium elements into the sulfide electrolyte.

[0065] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A modified sulfide electrolyte, characterized in that, Its chemical formula is Li 6+x P 1-x Ca x S 5-2x F 2x Cl, where 0 < x ≤0.15; the modified sulfide electrolyte has a cubic phase structure.

2. A method for preparing the modified sulfide electrolyte as described in claim 1, characterized in that, Includes the following steps: Step 1. Under a protective atmosphere, the raw materials Li2S, P2S5, LiCl and CaF2 are ball-milled according to a preset molar ratio to obtain precursor powder; Step 2. The precursor powder obtained in Step 1 is formed into sheet-like discs under a preset pressure to prevent the loss of electrical conductivity caused by the volatilization of sulfur at high temperatures during sintering. Step 3. Sinter the sheet sample obtained in Step 2 under a protective atmosphere. After the sintering reaction is completed, allow it to cool naturally to obtain the desired modified sulfide electrolyte.

3. The preparation method according to claim 2, characterized in that, In steps 1 and 3, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere.

4. The preparation method according to claim 3, characterized in that, The inert atmosphere is an argon atmosphere.

5. The preparation method according to claim 2, characterized in that, In step 1, during ball milling, the mass ratio of grinding balls to mixed raw materials is 40:1 to 20:1; the diameter of the grinding balls is 3 to 10 mm; the ball milling speed is 400 to 600 rpm; and the ball milling time is 15 to 20 hours.

6. The preparation method according to claim 2, characterized in that, In step 2, the preset pressure is 100~200MPa.

7. The preparation method according to claim 2, characterized in that, In step 3, the sintering temperature is 450~600℃ and the sintering time is 6~12h.

8. An all-solid-state lithium metal battery, characterized in that, The specific fabrication process of the all-solid-state lithium metal battery is as follows: In an argon-filled glove box, the modified sulfide electrolyte powder prepared by the method described in any one of claims 2-7 is weighed and placed in a mold. It is then pressed into a solid electrolyte sheet under a certain pressure. The corresponding positive and negative electrodes are placed at both ends of the electrolyte sheet to prepare an all-solid-state lithium metal battery.

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