Modified sulfide electrolyte and preparation method and application thereof

Abstract

The invention provides a modified sulfide electrolyte and a preparation method and application thereof, and belongs to the technical field of lithium metal battery electrolytes. The modified sulfide electrolyte disclosed by the invention innovatively adopts Ca and F element co-doping to improve the stability of the electrolyte to lithium metal, and keeps relatively high ionic conductivity, so that the high-performance requirement of an all-solid-state lithium metal battery to the electrolyte is met. The all-solid-state lithium metal battery prepared based on the modified sulfide electrolyte has excellent cycling stability. The critical current density of the all-solid-state lithium metal battery prepared from the modified sulfide electrolyte 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 electrolytes for lithium metal batteries, and particularly relates to a modified sulfide electrolyte, a preparation method thereof, and an application thereof. 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 (easy to catch fire, explode, etc.), and rapid performance decay in extreme environments (high temperature, low temperature, etc.). As a highly potential 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 with 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, a preparation method thereof, and an application thereof. The modified sulfide electrolyte of the present invention innovatively uses co-doping of Ca and F elements to improve the stability of the electrolyte against 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 preparation method of a modified sulfide electrolyte, comprising the following steps:

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

[0010] Step 2. Make the precursor powder obtained in Step 1 into a sheet-like disc under a preset pressure to prevent the loss of conductivity caused by the volatilization of sulfur at high temperature during sintering;

[0011] Step 3. Sinter the sheet-like sample obtained in Step 2 under a protective atmosphere, and naturally cool it after the sintering reaction ends to obtain the required modified sulfide electrolyte.

[0012] Further, in Step 1, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere, and the inert gas is preferably argon.

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

[0014] Further, in Step 2, the preset pressure is 100 - 200 MPa.

[0015] Further, in Step 3, the protective atmosphere is an inert atmosphere or a nitrogen atmosphere, and the inert gas is preferably argon.

[0016] Further, in Step 3, the sintering temperature is 450 - 600 °C, and the sintering time is 6 - 12 h.

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

[0018] Weigh the obtained modified sulfide electrolyte powder in a glove box filled with argon and place it in a mold, press it into a solid electrolyte sheet under a certain pressure, and place the corresponding positive and negative electrodes at both ends of the electrolyte sheet respectively to prepare an all-solid-state lithium metal battery.

[0019] The mechanism of the present invention is:

[0020] The present invention improves the stability of sulfide electrolyte towards lithium metal by introducing Ca and F elements into the sulfide electrolyte material Li6PS5Cl, while maintaining a relatively high ionic conductivity. Specifically, the introduced Ca and F elements in the Li6PS5Cl electrolyte will respectively form CaS4 and PS3F tetrahedrons. Compared with the original PS4 tetrahedron, the CaS4 and PS3F tetrahedrons have higher chemical stability, which can block the electron exchange between the sulfide electrolyte and lithium metal and inhibit the interfacial side reactions.

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

[0022] The critical current density of the all-solid-state lithium metal battery based on the modified sulfide electrolyte of the present invention can reach 1.6 mA cm -2 , which is more than three times that of the original Li6PS5Cl electrolyte; and the ionic conductivity is maintained at a relatively high level, being 2.68 mS cm -1 . BRIEF DESCRIPTION OF THE DRAWINGS

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

[0024] Figure 2 It is the comparison of the X-ray diffraction (XRD) test patterns of the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

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

[0026] Figure 4 It is the comparison of the alternating current impedance spectroscopy (EIS) test patterns of the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0027] Figure 5 It is the comparison of the cyclic voltammetry test patterns of the sulfide electrolytes prepared in Examples 1-3 and Comparative Example 1 of the present invention.

[0028] Figure 6 It is the comparison of the cyclic stability test results of the lithium symmetric batteries assembled based on the sulfide electrolytes prepared in Examples 1-3 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

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

[0030] A modified sulfide electrolyte, whose chemical formula is 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 shown in Figure 1 shown.

[0031] Example 1

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

[0033] Step 1. In a glove box filled with argon, weigh raw materials of Li2S, P2S5, LiCl, and CaF2 according to a molar ratio of 2.525:0.475:1:0.05. Pour all the raw material mixtures into a planetary ball milling tank. The inner lining and ball milling beads of the planetary ball mill are made of zirconia. The mass ratio of the ball milling beads to the mixed raw materials is 40:1. The diameter of the ball 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 in a 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] Prepare the sulfide electrolyte according to the steps of Example 1, only adjust the raw materials in Step 1 to Li2S, P2S5 and LiCl, and adjust the corresponding ratio to 2.5:0.5:1, and keep the rest of the steps unchanged to obtain the sulfide electrolyte Li6PS5Cl.

[0042] Comparative Example 2

[0043] Prepare the sulfide electrolyte according to the steps of Example 1, only adjust the raw materials in Step 1 to Li2S, P2S5, LiCl and LiF, and adjust the corresponding ratio to 2.4:0.5:1:0.1, and keep the rest of the steps unchanged to obtain the sulfide electrolyte Li 5.9 PS 4.9 F 0.1 Cl.

[0044] Comparative Example 3

[0045] Prepare the sulfide electrolyte according to the steps of Example 1, only adjust the raw materials in Step 1 to Li2S, P2S5, LiCl and CaS, and adjust the corresponding ratio to 2.575:0.475:1:0.05, and keep the rest of the steps unchanged to obtain the sulfide electrolyte Li 6.15 P 0.95 Ca 0.05 S5Cl.

[0046] Performance Test:

[0047] 1. XRD Test

[0048] Perform XRD tests on the sulfide electrolytes prepared in Examples 1-3 and Comparative Examples 1-3. Grind them evenly before testing. The test angle range is 10-90°, and the scanning rate is 2° / min.

[0049] 2. XPS Test

[0050] Perform XPS tests on the sulfide electrolytes prepared in Example 1 and Comparative Example 1. Grind them evenly before testing. The test elements are P, S, Ca and F.

[0051] 3. EIS Test

[0052] The sulfide electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to EIS testing. The testing was carried out using a French Bio-Logic electrochemical workstation. In a glove box filled with argon, 100 mg of electrolyte powder was weighed and placed in a mold with a diameter of 10 mm, 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. The impedance test was carried out under a stacking pressure of 10 MPa, and the test range was 200 KHz to 100 mHz, and the test conditions were at room temperature. The ionic conductivity was calculated based on the measured impedance values. The test results are as Figure 3 shown.

[0053] 4. Cyclic voltammetry testing

[0054] The sulfide electrolytes prepared in Examples 1 to 3 and Comparative Example 1 were subjected to EIS testing. The testing was carried out using a French Bio-Logic electrochemical workstation. In a glove box filled with argon, 100 mg of electrolyte powder was weighed and placed in a mold with a diameter of 10 mm, and pressed into a solid electrolyte sheet under a preset pressure of 480 MPa. An indium sheet with a diameter of 9.5 mm and a lithium sheet with a diameter of 8 mm were placed at both ends of the electrolyte sheet respectively. The cyclic voltammetry testing was carried out under a stacking pressure of 5 MPa, the scanning voltage range was 0 to 5 V, the scanning rate was 0.1 mV / s, and the test conditions were at room temperature.

[0055] 5. Lithium stability testing

[0056] In a glove box filled with argon, 100 mg of electrolyte powder was weighed and placed in a mold with a diameter of 10 mm, and pressed into a solid electrolyte sheet under a preset pressure of 480 MPa. Lithium sheets with a diameter of 8 mm were placed at both ends of the electrolyte sheet to assemble a lithium symmetric battery. The mold battery was taken out of the glove box and placed on a LAND CT2001A tester for cyclic stability testing. The cyclic testing was carried out under a stacking pressure of 5 MPa, the initial cyclic current density was set to 0.1 mA / cm 2 , the single charge-discharge time was set to 0.5 h, and the step current density was set to 0.1 mA / cm 2 , and the test conditions were at room temperature.

[0057] The XRD test results are as Figure 2 shown, and the results show that the added Ca element and F element in the present invention are added to Li6PS5Cl by doping means, and will not bring impurities to the original sulfide electrolyte and do not damage the crystal structure of the original Li6PS5Cl electrolyte.

[0058] The XPS test results are as Figure 3As shown, (a) is Ca element, (b) is F element, (c) is P element, and (d) is S element. The results show that the introduction of F and Ca elements in the sulfide electrolyte Li6PS5Cl forms strong interactions with P and S atoms respectively. Compared with the unstable P-S bond, P-F and Ca-S have higher chemical stability and can resist the attack of highly chemically reactive lithium atoms, thereby improving the lithium stability of the sulfide electrolyte. In addition, from Figure 3 As can be seen from the P 2p and S2p XPS spectra shown in c and 3d, the introduction of Ca and F induces the enrichment and dissipation of S sites and P sites respectively, which confirms the strong interactions between Ca and P, and F and S.

[0059] The EIS test results and the calculated ionic conductivities are shown in Table 1 and Figure 4 as follows. The results show that the introduction of F in 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 reducing the energy barrier for lithium ion diffusion in the electrolyte and accelerating lithium ion conduction. In addition, 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 shown in Figure 5 as follows. The results show that compared with Comparative Example 1, the batteries assembled with the sulfide electrolytes prepared based on Examples 1 to 3 of the present invention show lower current responses in the voltage range of 0 to 1V, indicating lower lithium metal reactivity. This result is because the formation of PS3F and CaS4 tetrahedrons in the F- and Ca-doped sulfide electrolytes makes the sulfide electrolyte have higher chemical stability, which can resist the attack of highly chemically reactive lithium atoms and inhibit interfacial side reactions.

[0063] The test results of the lithium metal stability are shown in Figure 6 as follows. It can be seen that the critical current densities of the lithium symmetric batteries assembled with the sulfide electrolytes prepared based on Examples 1 to 3 of the present invention are all higher than those of the undoped sulfide electrolyte of Comparative Example 1. This result is because the formation of PS3F and CaS4 tetrahedrons in the F- and Ca-doped sulfide electrolytes makes the sulfide electrolyte have higher chemical stability, which can resist the attack of highly chemically reactive lithium atoms and thus improve the lithium stability of the sulfide electrolyte.

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

[0065] As described above, only the specific embodiments of the present invention are provided. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the disclosed features, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

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, It includes the following steps: Step 1. Under a protective atmosphere, ball-mill the raw materials Li2S, P2S5, LiCl, and CaF2 according to a preset molar ratio to obtain a precursor powder; Step 2. Make the precursor powder obtained in Step 1 into a flaky disc under a preset pressure to prevent the loss of conductivity caused by the volatilization of sulfur at high temperature during sintering; Step 3. Sinter the flaky sample obtained in Step 2 under a protective atmosphere, and cool it naturally after the sintering reaction ends to obtain the required modified sulfide electrolyte.

3. The preparation method according to claim 2, wherein In Step 1 and Step 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 the ball-milling beads to the mixed raw materials is 40:1 to 20:1; the diameter of the ball-milling beads is 3 to 10 mm; the ball-milling speed is 400 to 600 rpm, and the ball-milling time is 15 - 20 h.

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

7. The preparation method according to claim 2, characterized in that, In Step 3, the sintering temperature is 450 - 600 °C, and the sintering time is 6 - 12 h.

8. A all-solid-state lithium metal battery, characterized in that, The specific preparation process of the all-solid-state lithium metal battery is as follows: Weigh the modified sulfide electrolyte powder prepared by the preparation method according to any one of claims 2 - 7 in a glove box filled with argon, place it in a mold, press it into a solid electrolyte sheet under a certain pressure, and place the corresponding positive electrode and negative electrode at both ends of the electrolyte sheet respectively to prepare an all-solid-state lithium metal battery.

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