P / sn compound modified solid-state electrolyte, and preparation method and application thereof

Abstract

This invention belongs to the field of solid-state battery technology, and relates to a P / Sn compound modified solid-state electrolyte, its preparation method, and its application. A lithium layer is deposited on the surface of LLZTO, and a modified layer is disposed between the lithium layer and LLZTO. The modified layer is composed of a lithium-tin alloy and lithium phosphostane. The preparation method is as follows: Sn4P3 powder is coated onto the surface of LLZTO to form a Sn4P3 powder layer; a lithium metal layer is attached to the surface of the Sn4P3 powder layer to obtain a composite precursor material; the composite precursor material is heat-treated at 350–450°C under an inert atmosphere to obtain the final product. This invention can effectively reduce the interfacial resistance between the solid-state electrolyte and the negative electrode, improve the inhibition of lithium dendrite growth, and improve cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology, and relates to a P / Sn compound modified solid-state electrolyte, its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In all-solid-state lithium metal batteries, garnet-type solid electrolyte LLZTO (Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Solid electrolytes (SEEs) have attracted much attention due to their stable interface with lithium metal, wide electrochemical window, and high ionic conductivity (up to 1 mS / cm at room temperature). However, they still have two problems: 1) High interfacial resistance with lithium metal leads to accelerated capacity decay and reduced battery life; 2) Lithium dendrites easily grow at electrolyte grain boundary defects, causing battery short-circuit failure. According to the inventors' research, current solutions include applying a coating to the surface of the solid electrolyte or removing lithium-repellent materials and improving the structure of the solid electrolyte. However, these methods still suffer from high interfacial resistance, difficulty in preventing lithium dendrite formation during cycling, and complex and costly operations. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a P / Sn compound modified solid electrolyte, its preparation method, and its application, which can effectively reduce the interfacial resistance between the solid electrolyte and the negative electrode, improve the inhibition of lithium dendrite growth, and modify cycle performance.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] On one hand, a P / Sn compound modified solid electrolyte has a lithium layer disposed on the surface of LLZTO, and a modified layer disposed between the lithium layer and LLZTO. The modified layer is made of lithium-tin alloy and lithium phosphostannate.

[0007] On the other hand, a method for preparing a P / Sn compound modified solid electrolyte involves coating Sn4P3 powder onto the surface of LLZTO to form a Sn4P3 powder layer, attaching a lithium metal layer to the surface of the Sn4P3 powder layer to obtain a composite precursor material, and then heat-treating the composite precursor material at 350–450°C under an inert atmosphere to obtain the final product.

[0008] When heated to 350–450°C under an inert atmosphere, the Sn4P3 powder layer reacts with the inner layer of the lithium metal layer to produce a lithium-tin alloy and lithium phosphostannate. The lithium-tin alloy, as a highly lithium-affinity alloy, ensures close contact between the Li metal anode and LLZTO, while the ionic conductor lithium phosphostannate blocks electron transport, preventing lithium dendrites from depositing within the LLZTO and effectively inhibiting their formation.

[0009] Thirdly, the application of the above-mentioned P / Sn compound modified solid electrolyte in the preparation of all-solid-state lithium metal batteries.

[0010] The beneficial effects of this invention are as follows:

[0011] This invention pre-coats a Sn4P3 powder layer between LLZTO and a lithium metal layer, and then heat-treats it to allow Sn4P3 to react with metallic lithium to produce a lithium-tin alloy and lithium phosphostannate. Studies have shown that this modification method can significantly reduce the interfacial impedance between LLZTO and the lithium metal layer, and significantly improve the ability to suppress lithium dendrite growth and cycle stability. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0013] Figure 1 These are the XRD patterns of the solid electrolyte with Sn4P3 surface coating before and after the reaction in this embodiment of the invention. A is before the reaction, and B is after the reaction.

[0014] Figure 2 The above are XPS spectra of the negative electrode interface before and after lithiation in an embodiment of the present invention. A is the overall spectrum, B is the Sn3d spectrum, C is the P2p spectrum, and D is the Li 1s spectrum.

[0015] Figure 3 This is a diagram showing the impedance detection results in an embodiment of the present invention;

[0016] Figure 4 The graph shows the critical current density detection results in the embodiments of the present invention. A is the symmetrical cell before modification, and B is the symmetrical cell after modification.

[0017] Figure 5 This is a test graph showing the cycle performance of a lithium metal symmetric battery using LLZTO in an embodiment of the present invention.

[0018] Figure 6 The graph shows the cycle performance test results of a lithium metal symmetric battery using modified LLZTO in an embodiment of the present invention. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Given that current methods for modifying the interface between LLZTO and lithium metal are insufficient to address issues such as high interfacial impedance and the persistent formation of lithium dendrites during cycling, this invention proposes a P / Sn compound-modified solid electrolyte, its preparation method, and its applications.

[0022] In a typical embodiment of the present invention, a P / Sn compound modified solid electrolyte is provided, wherein a lithium layer is disposed on the surface of LLZTO, and a modified layer is disposed between the lithium layer and LLZTO, wherein the modified layer is composed of lithium-tin alloy and lithium phosphostannate.

[0023] In some embodiments, LLZTO is in sheet form, with a modified layer and a lithium layer sequentially disposed on one side surface of the sheet LLZTO, and the other side surface of the sheet LLZTO is configured for connecting to the positive electrode.

[0024] Another embodiment of the present invention provides a method for preparing a P / Sn compound modified solid electrolyte, wherein Sn4P3 powder is coated on the surface of LLZTO to form a Sn4P3 powder layer, a lithium metal layer is attached to the surface of the Sn4P3 powder layer to obtain a composite precursor material, and the composite precursor material is heat-treated at 350-450°C under an inert atmosphere to obtain the final product.

[0025] In some embodiments, the particle size of Sn4P3 powder is 1000-2000 mesh.

[0026] In some embodiments, the Sn4P3 powder is prepared by ball milling tin powder and red phosphorus under an inert atmosphere according to a stoichiometric ratio.

[0027] In one or more embodiments, the ball-to-material ratio in the ball mill is 45 to 55:1.

[0028] In one or more embodiments, the ball mill rotation speed is 500–700 r / min. The ball milling time is 10–15 h.

[0029] In some embodiments, Sn4P3 powder is added to an organic solvent and dispersed evenly, and then the evenly dispersed suspension is dropped onto the LLZTO surface and dried to form a Sn4P3 powder layer.

[0030] In one or more embodiments, the organic solvent is isopropanol.

[0031] In some embodiments, the heat treatment time is 4 to 6 minutes.

[0032] A third embodiment of the present invention provides an application of the above-mentioned P / Sn compound modified solid electrolyte in the preparation of all-solid-state lithium metal batteries.

[0033] Specifically, the all-solid-state lithium metal battery includes a positive electrode and the P / Sn compound modified solid electrolyte, wherein the positive electrode is disposed on the opposite side of the lithium layer in the P / Sn compound modified solid electrolyte.

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0035] Example

[0036] 1. Preparation of Sn4P3

[0037] (1) Weigh a certain amount of tin powder and red phosphorus in an argon-filled glove according to the Sn4P3 molar mass ratio and put them into a stainless steel ball mill jar with a ball-to-material ratio of 50:1. Ball mill under an argon atmosphere at a parameter of 600r / min-12h.

[0038] (2) The ball-milled Sn4P3 was sieved through a 1000-mesh sieve to obtain Sn4P3 powder.

[0039] 2. Preparation of Sn4P3-IPA suspension

[0040] Weigh the Sn4P3 powder prepared in step 3 and suspend it in isopropanol at a concentration of 0.1 g / ml. Stir the mixture with a magnetic stirrer at room temperature for 6 h.

[0041] 3. Application of the modified layer

[0042] (1) Place the 9mm diameter electrolyte sheet after surface polishing on clean weighing paper, and use a pipette to take 30μl of suspension and drop it evenly onto the electrolyte surface.

[0043] (2) The isopropanol was accelerated by baking with an infrared lamp for 20 minutes, and Sn4P3 particles were evenly distributed on the electrolyte surface. The same steps were taken on the other side after the reverse side was reversed. Then, the isopropanol was dried in a vacuum oven at 60°C for 4 hours to completely evaporate the isopropanol, resulting in a double-sided modified electrolyte sheet for use in the assembly of lithium symmetric batteries.

[0044] 4. Assembly of lithium-ion symmetric batteries

[0045] (1) Transfer the double-sided modified electrolyte sheet prepared in step 3 to a glove box, attach clean lithium foil with a diameter of 6 mm to both sides, and heat at 400°C for 5 min to allow the lithium foil to fully react with Sn4P3 on the electrolyte surface to generate lithium tin alloy and lithium phosphostannate. The glove box atmosphere should be filled with argon and the water oxygen content should be less than 0.01 ppm.

[0046] Depend on Figure 1 It can be seen that the prepared LLZTO and tin phosphide correspond to standard cards PDF#45-0109 and PDF#45-0109, respectively. After surface-mount lithium bonding and high-temperature lithiation, the signal of tin phosphide disappears, and it reacts with lithium metal to produce Li. 22 Sn5@PDF#18-0753 and Li8SnP4@PDF#27-0296, with a small amount of remaining lithium metal.

[0047] Depend on Figure 2 It can be seen that before lithiation, the Sn spectrum mainly has two characteristic peaks, namely 3d... 3 / 2 and 3D 5 / 2 The peaks at 494.9 eV and 486.5 eV belong to Sn4P3. After lithiation, the Sn 3d peaks shift to 495.5 eV and 487.1 eV, and new characteristic peaks appear at 493.4 eV and 484.9 eV, corresponding to Li8SnP4 and Li 22 The Sn5.P 2p spectrum shows only two peaks at 129.0 eV and 133.5 eV, which are related to the P-Sn bond, while the peak at 138.7 eV is related to the P-Sn bond. 5+ This is likely due to the oxidation of P by oxygen in the air. The P 2p peak shifts to 135.6 eV and 133.5 eV due to the formation of Li8SnP4. In the Li 1s spectrum, the 55.3 eV peak before lithiation originates from Li2CO3 generated on the surface of LLZTO particles exposed to air. After melting, the characteristic peak of Li slightly increases from 55.3 eV to 55.9 eV, which is due to the presence of unreacted Li metal on the LLZTO surface.

[0048] (2) Using a 2032 battery case, the cooled electrolyte sheet is assembled into a lithium symmetric battery according to the following order: positive electrode shell - gasket - modified electrolyte - gasket - spring sheet - negative electrode shell.

[0049] 5. Electrochemical testing

[0050] (1) The assembled lithium symmetric battery was subjected to AC impedance spectroscopy (EIS) using an AUTOLAB electrochemical workstation with a frequency range of 0.1-1000000Hz and an amplitude of 5mV.

[0051] (2) The critical current density CCD of the symmetrical battery was tested using the Xinwei Battery Testing System. The specific method was as follows: a constant current charge-discharge program was set with a step size of 30 minutes and an initial current density of 0.1 mA / cm². -2 The current density increases by 0.1 mA / cm² with the number of cycles. -2 The current density at which the battery polarization voltage drops sharply, resulting in a short circuit, is the critical current density (CCD) of the lithium symmetric battery.

[0052] (3) At 1mA / cm -2 The cycle performance of the symmetrical cell was tested at a certain current density, and the interface impedance and lithium dendrite growth of the symmetrical cell were determined based on the change in polarization voltage.

[0053] Test results:

[0054] The modified lithium symmetric battery was tested using AC impedance spectroscopy, and the results are as follows: Figure 3 As shown, the unmodified lithium metal symmetric battery exhibits a single-sided interfacial impedance as high as 250Ω. After Sn4P3 interfacial modification, the assembled lithium metal symmetric battery has a single-sided interfacial impedance of only 1.25Ω, which is 1 / 200th of the original. This significantly reduces the interfacial resistance between the lithium metal anode and the solid electrolyte, which is beneficial for improving the cycle performance of the lithium metal battery, reducing energy loss during cycling, increasing capacity retention, and enabling rapid charge and discharge at high current densities.

[0055] Critical current density (CCD) is used to evaluate a battery's ability to suppress lithium dendrite growth. A higher CCD value indicates a higher current density the battery can withstand, stronger suppression of lithium dendrite growth, and the ability to operate at higher current densities. The CCD of symmetric batteries before and after modification was tested using the Xinwei Battery Testing System. It was found that the CCD of the unmodified lithium metal symmetric battery was only 0.4 mA / cm². 2 ,like Figure 4 As shown in Figure A, after Sn4P3 interface modification, the critical current density of the assembled lithium metal symmetric battery reached 1.6 mA / cm². 2 Significant improvements have been made, such as Figure 4 As shown in B.

[0056] The modified symmetric battery was further tested using the Newway battery testing system under constant current density, and the cycling performance was found to be at 1 mA / cm². 2 At higher current densities, such as Figure 5 As shown, the modified symmetric cell can maintain stable cycling for 200 cycles, compared to the unmodified lithium symmetric cell at 0.1 mA / cm². 2Significant interfacial polarization appeared after 30 cycles at the current density, such as... Figure 6 As shown, the cycling performance of the symmetric battery was significantly improved. The continuous increase in polarization voltage is due to the increasing interfacial polarization of the symmetric battery with the increase in the number of cycles. During cycling, lithium continuously de-enters and re-enters, and the unevenness of the de-entry and re-entry points leads to the formation of some pores at the interface, resulting in increased interfacial impedance. The modified symmetric battery can also cycle stably for a higher number of cycles at higher current densities, which fully demonstrates the optimizing effect of the modification layer on the lithium symmetric battery. This modification accelerates lithium-ion transport speed, homogenizes electron distribution, promotes uniform lithium metal stripping and deposition, and suppresses the formation of lithium dendrites and pores during cycling.

[0057] 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 method for preparing a P / Sn compound modified solid electrolyte, characterized in that, Sn4P3 powder was coated onto the surface of LLZTO to form a Sn4P3 powder layer. A lithium metal layer was then attached to the surface of the Sn4P3 powder layer to obtain a composite precursor material. The composite precursor material was then heat-treated at 350~450 ℃ under an inert atmosphere to obtain the final product. In the P / Sn compound modified solid electrolyte, a lithium layer is disposed on the surface of LLZTO, and a modification layer is disposed between the lithium layer and LLZTO. The material in the modification layer is lithium-tin alloy and lithium phosphostannate. LLZTO is in sheet form, with a modified layer and a lithium layer sequentially disposed on one side surface, and the other side surface of the sheet LLZTO is configured for connecting the positive electrode.

2. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 1, characterized in that, The particle size of Sn4P3 powder is 1000~2000 mesh.

3. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 1, characterized in that, The preparation process of the Sn4P3 powder is as follows: tin powder and red phosphorus are ball-milled under an inert atmosphere according to the stoichiometric ratio.

4. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 3, characterized in that, The ball-to-material ratio for ball milling is 45~55:

1.

5. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 1, characterized in that, Sn4P3 powder was added to an organic solvent and dispersed evenly. The evenly dispersed suspension was then dropped onto the surface of LLZTO and dried to form a Sn4P3 powder layer.

6. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 5, characterized in that, The organic solvent is isopropanol.

7. The method for preparing the P / Sn compound modified solid electrolyte as described in claim 1, characterized in that, The heat treatment time is 4 to 6 minutes.

8. A P / Sn compound modified solid electrolyte, characterized in that, Obtained by the preparation method described in any one of claims 1 to 7.

9. The application of the P / Sn compound modified solid electrolyte of claim 8 in the preparation of an all-solid-state lithium metal battery.

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