Composite solid electrolyte membrane for all-solid-state lithium metal batteries and its preparation method

Abstract

This invention relates to the field of lithium battery technology, and more particularly to a composite solid electrolyte membrane for all-solid-state lithium metal batteries and its preparation method. This invention utilizes a composite solid electrolyte membrane consisting of a halide, a sulfide, and a polymer. The halide, being resistant to high voltage, is placed on top of the sulfide layer in contact with the positive electrode material, thereby increasing the upper limit of the voltage window of the composite electrolyte membrane. The polymer, stable for lithium, is placed below the sulfide layer in contact with lithium metal, reducing side reactions between the composite electrolyte membrane and lithium metal, and lowering interfacial impedance. Simultaneously, by controlling the thickness of the three membranes, the side reaction problem at the positive and negative electrode contact surfaces is effectively solved while maintaining high ionic conductivity, reducing impedance, improving battery cycle life, and enhancing safety. This invention achieves an initial efficiency of 89% for all-solid-state lithium metal batteries and a capacity retention rate of over 70% after 50 cycles.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a composite solid electrolyte membrane for all-solid-state lithium metal batteries and its preparation method. Background Technology

[0002] With the increasing demands for energy density and safety from electric vehicles, portable electronic devices, and large-scale energy storage systems, traditional lithium-ion batteries, which use intercalated negative electrodes (such as graphite) and organic liquid electrolytes, are approaching their theoretical energy density limits and pose safety hazards such as leakage and combustion. Therefore, developing next-generation lithium battery systems that combine high energy density and high safety has become a research hotspot. Among these, all-solid-state lithium batteries, due to their use of non-flammable solid electrolytes instead of organic liquid electrolytes, are considered one of the most promising development directions.

[0003] To achieve the ultra-high energy density of all-solid-state batteries, fundamental innovations are needed in the positive and negative electrode material systems. On the positive electrode side, traditional lithium iron phosphate (LiFePO4) Although it has good thermal stability, its specific capacity (approximately 170 mAh / g) and operating voltage plateau (approximately 3.45 V vs.) are limited. The relatively low specific capacity limits further improvements in energy density. On the anode side, traditional graphite anodes (theoretical specific capacity 372 mAh / g) also cannot meet the demands for ultra-high energy density, while lithium metal anodes (theoretical specific capacity 3860 mAh / g, minimum potential -3.04 V vs. SHE) are key to achieving breakthroughs in energy density due to their extremely high specific capacity and extremely low operating potential. However, lithium metal has extremely high surface reactivity, easily undergoing side reactions with various electrolytes and inducing lithium dendrite growth.

[0004] Among various solid electrolyte systems, sulfide solid electrolytes (such as...) (etc.) have extremely high room temperature ionic conductivity (up to With their large volume (approaching or even exceeding that of liquid electrolytes), good machinability, and grain boundary ion transport capabilities, sulfide electrolytes have been extensively studied in all-solid-state batteries. However, sulfide electrolytes face two major challenges in practical applications: firstly, their electrochemical stability window is relatively narrow (typically below 2.5 V vs. 100 V). Firstly, sulfide electrolytes (with an oxidation decomposition potential below 2.5 V) undergo severe oxidation decomposition reactions at the interface when in contact with high-voltage cathode materials (such as ternary or lithium-rich manganese, with a charging potential > 4.3 V), generating high-resistivity interface layers (such as thiophosphates, sulfates, and phosphates). This leads to a sharp increase in interface impedance, a decrease in first-cycle coulombic efficiency, and rapid capacity decay. Secondly, sulfide electrolytes exhibit poor chemical / electrochemical stability to lithium metal anodes and are easily reduced by lithium metal to form... , These are interfacial products that are electronically insulating but have poor ionic conductivity. They also cannot effectively suppress the penetration of lithium dendrites. Lithium dendrites grow along the electrolyte grain boundaries or pores, and may eventually pierce the electrolyte membrane, causing internal short circuits and thermal runaway, which poses a serious safety risk.

[0005] To address the challenge of simultaneously integrating high-voltage cathodes and lithium metal anodes with sulfide electrolytes, researchers have proposed constructing gradient or bilayer composite electrolyte systems by combining different types of solid electrolyte membranes. For example, patent CN112599846A, while combining sulfide and polymer solid electrolytes and exhibiting good compatibility with lithium metal anodes, still suffers from a low voltage window due to the sulfide's low voltage window and significant side reactions at the cathode material interface, leading to increased impedance and low cycle life. Patent CN115458801A, while combining sulfide and halide solid electrolytes and showing good compatibility with high-voltage cathode materials, fails to resolve the issue of sulfide reduction at the lithium metal anode, resulting in high impedance, low cycle life, and poor safety. Summary of the Invention

[0006] To address the issues that existing composite solid electrolyte membranes cannot simultaneously accommodate high-voltage cathode materials and lithium metal anodes, resulting in high impedance, low cycle life, and poor safety, this application provides a composite solid electrolyte membrane for all-solid-state lithium metal batteries and its preparation method.

[0007] In a first aspect, this application provides a composite solid electrolyte membrane for all-solid-state lithium metal batteries, which has a three-layer composite structure, consisting of a halide electrolyte layer, a sulfide electrolyte layer, and a polymer electrolyte layer from top to bottom; the halide electrolyte layer includes a halide solid electrolyte and a binder; the sulfide electrolyte layer includes a sulfide solid electrolyte and a binder; and the polymer electrolyte layer includes a polymer solid electrolyte, a lithium salt, and an inorganic filler.

[0008] This invention utilizes a composite electrolyte membrane consisting of three solid electrolytes: a halide, a sulfide, and a polymer. The halide, being resistant to high voltage, is placed on top of the sulfide layer in contact with the positive electrode material, thereby increasing the upper limit of the voltage window of the composite electrolyte membrane. The polymer, being stable for lithium, is placed on the bottom layer of the sulfide layer in contact with lithium metal, reducing side reactions between the composite electrolyte membrane and lithium metal and lowering interfacial impedance. Furthermore, by controlling the thickness of the three membranes, the invention effectively solves the problem of side reactions at the positive and negative electrode contact surfaces while ensuring high ionic conductivity, thus reducing impedance, improving battery cycle life, and enhancing safety.

[0009] Furthermore, the structural formula of the halide solid electrolyte is as follows: Where M = Sc, Y, La Lu, Al, Ga, In, X = at least one of F, Cl, Br, I;

[0010] The adhesive is at least one of PTFE, cellulose mesh, nylon mesh or Kevlar mesh.

[0011] Furthermore, the mass ratio of the halide solid electrolyte to the binder is 90. 100:1 6.

[0012] Furthermore, the structural formula of the sulfide solid electrolyte is as follows: At least one of the following, wherein X = at least one of F, Cl, Br, and I;

[0013] The adhesive is at least one of PTFE, cellulose mesh, nylon mesh or Kevlar mesh.

[0014] Furthermore, the mass ratio of the sulfide solid electrolyte to the binder is 90. 100:1 6.

[0015] Furthermore, the polymer solid electrolyte is at least one of PEO, PMMA, PAN, PS, and PVDF;

[0016] The lithium salt is At least one of them;

[0017] The inorganic filler is at least one of LLZTO, LATP, LLZO, LLTP, LiPON and LZG.

[0018] Furthermore, the mass ratio of the polymer solid electrolyte, lithium salt, and inorganic filler is 40. 60:30-50:5 15.

[0019] Furthermore, the thickness of the halide electrolyte layer is 10. 40 μm; the thickness of the sulfide electrolyte layer is 40 μm. 140 μm; the thickness of the polymer electrolyte layer is 10 μm. 40μm.

[0020] Preferably, the thickness of the composite solid electrolyte membrane is 80 mm. 200μm.

[0021] Furthermore, the thickness of the halide electrolyte layer is 10. 20 μm; the thickness of the sulfide electrolyte layer is 60 μm. 100 μm; the thickness of the polymer electrolyte layer is 10 μm. 20 μm.

[0022] Secondly, this application provides an all-solid-state lithium metal battery, including a positive electrode, a negative electrode, and the composite solid electrolyte membrane described in this application.

[0023] Furthermore, the preparation method of the all-solid-state lithium metal battery is as follows: First, a sulfide solid electrolyte is mixed with a binder and compacted to obtain a sulfide electrolyte layer; then, a halide solid electrolyte is mixed with a binder and compacted on top of the sulfide electrolyte layer to obtain a halide-sulfide composite electrolyte layer; then, a positive electrode is placed in the mixture and pressurized; next, a polymer solid electrolyte layer is compacted and composited with the sulfide electrolyte layer; finally, a negative electrode is added and pressurized to fix the mixture, thus completing the all-solid-state lithium metal battery.

[0024] Beneficial effects: 1. This invention utilizes three solid-state electrolyte membranes: a composite halide membrane, a sulfide membrane, and a polymer membrane. The halide membrane is resistant to high voltage; placing it on top of the sulfide membrane in contact with the positive electrode material increases the upper limit of the composite electrolyte membrane's voltage window. The polymer membrane is stable for lithium; placing it below the sulfide membrane in contact with lithium metal reduces side reactions between the composite electrolyte membrane and lithium metal, lowering interfacial impedance. Furthermore, by controlling the thickness of the three membranes, the invention effectively solves the side reaction problem at the positive and negative electrode contact surfaces while ensuring high ionic conductivity, reducing impedance, improving battery cycle life, and enhancing safety. It achieves an initial efficiency of 89% for the all-solid-state lithium metal battery and a capacity retention rate of over 70% after 50 cycles.

[0025] 2. In the three-layer composite solid electrolyte membrane of this invention, the synergistic optimization of the thicknesses of the halide layer, sulfide layer, and polymer layer achieves functional complementarity: the halide layer adopts a thickness sufficient to completely isolate the high-pressure oxidation environment of the positive electrode but as thin as possible, sacrificing ionic conductivity to achieve high-pressure protection for the sulfide matrix; the sulfide layer, as the thickest core conductive layer, fully utilizes its highest ionic conductivity, serving as the main body for rapid long-distance lithium ion transport; the polymer layer, with its thinnest thickness, ensures effective isolation of the sulfide from the lithium metal negative electrode side reaction and suppresses initial lithium dendrite penetration, while minimizing the impact of its low ionic conductivity on the overall impedance; controlling the thickness of the halide and polymer layers to prevent them from being too thick also... The thickness cannot be too thin. The entire composite solid electrolyte membrane is mainly composed of the middle sulfide layer (to ensure high conductivity; too thick a layer will reduce energy density). If the halide / polymer layer is too thick, it will reduce ionic conductivity and increase impedance. If the halide layer is too thin, it will reduce the protection of the positive and negative electrodes, increase the risk of contact between the positive and negative electrode interfaces and the sulfide layer, increase interfacial side reactions, increase impedance, reduce lifetime, and reduce safety. The synergistic optimization of the thickness of the three layers constructs a gradient ion channel of "high voltage tolerance - high speed transport - lithium metal compatibility", thereby systematically solving the problems of rapid interfacial impedance growth, cycle capacity decay, and poor safety, and achieving both high ionic conductivity and high interfacial stability. Detailed Implementation

[0026] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0027] Example 1: An all-solid-state lithium metal battery, comprising a positive electrode, a negative electrode, and a composite solid electrolyte membrane.

[0028] The composite solid electrolyte membrane has a three-layer composite structure, consisting of a halide electrolyte layer, a sulfide electrolyte layer, and a polymer electrolyte layer from top to bottom.

[0029] Halide layer: The mass ratio of the halide solid electrolyte Li3YCl6 to the binder PTFE is 97:3, and the thickness is 20μm.

[0030] Sulfide layer: The mass ratio of sulfide solid electrolyte Li6PS5Cl to binder PTFE is 97:3, and the thickness is 60μm.

[0031] Polymer layer: The polymer solid electrolyte PEO, lithium salt LiFSI and inorganic filler LATP are in a mass ratio of 50:40:10, and the thickness is 20μm.

[0032] All-solid-state lithium metal batteries consist of a positive electrode, a negative electrode, and an electrolyte.

[0033] Positive electrode: The positive electrode active material is a ternary positive electrode material. The positive electrode active material, conductive agent, and binder polyvinylidene fluoride (PVDF) are dispersed in a mass ratio of 97:1.5:1.5 to 20% of the total solid mass of N. The positive electrode slurry is mixed with methylpyrrolidone and then thoroughly stirred according to the homogenization process. The uniformly dispersed positive electrode slurry is then evenly coated onto aluminum foil, and after baking, rolling, slitting, and stamping, a positive electrode sheet is obtained.

[0034] Negative electrode: The negative electrode is a lithium metal foil.

[0035] In the composite solid electrolyte membrane, the upper halide electrolyte layer is in contact with the positive electrode in the battery, and the lower polymer electrolyte layer is in contact with the negative electrode in the battery.

[0036] Mold battery assembly: First, the sulfide solid electrolyte is mixed with a binder and compacted in a mold to obtain a sulfide electrolyte layer; then, the halide solid electrolyte is mixed with a binder, added to the mold, and compacted on top of the sulfide electrolyte layer to obtain a halide-sulfide composite electrolyte layer; finally, the cut positive electrode sheet is placed in the mold and pressure is applied and maintained for 3 seconds. 5 minutes; then open the negative electrode side, add the polymer solid electrolyte layer into the mold, and compact and composite it with the sulfide electrolyte layer; finally add the lithium metal foil, pressurize and fix the mold battery to complete the assembly of the all-solid-state lithium metal battery.

[0037] Example 2, an all-solid-state lithium metal battery, differs from Example 1 in that: the halide layer thickness in the composite solid electrolyte membrane is 10 μm, the sulfide layer thickness is 80 μm, and the polymer layer thickness is 10 μm.

[0038] Example 3, an all-solid-state lithium metal battery, differs from Example 1 in that: the thickness of the halide layer in the composite solid electrolyte membrane is 30 μm, the thickness of the sulfide layer is 40 μm, and the thickness of the polymer layer is 30 μm.

[0039] Comparative Example 1 is an all-solid-state lithium metal battery, which differs from Example 1 in that the composite solid electrolyte membrane contains only a sulfide layer with a thickness of 100 μm.

[0040] Comparative Example 2, an all-solid-state lithium metal battery, differs from Example 1 in that: the composite solid electrolyte membrane contains only a sulfide layer and a polymer layer, with the sulfide layer having a thickness of 80 μm and the polymer layer having a thickness of 20 μm.

[0041] Comparative Example 3 is an all-solid-state lithium metal battery, which differs from Example 1 in that the composite solid electrolyte membrane contains only a halide layer and a sulfide layer, with the halide layer having a thickness of 20 μm and the sulfide layer having a thickness of 80 μm.

[0042] Comparative Example 4, an all-solid-state lithium metal battery, differs from Example 1 in that: the halide layer thickness in the composite solid electrolyte membrane is 5 μm, the sulfide layer thickness is 150 μm, and the polymer layer thickness is 50 μm.

[0043] Performance testing

[0044] The examples and comparative examples were tested and their performance differences were compared using the following methods:

[0045] Room temperature cycle test: The batteries in the examples and comparative examples were subjected to room temperature cycle tests according to the following steps: At room temperature, the batteries were charged at a constant current of 0.2C with a cutoff voltage of 4.25V, and then discharged at a constant current of 0.2C to 2.8V. The batteries were cycled according to the above steps, and the initial charge-discharge capacity, initial coulombic efficiency, and discharge capacity retention rate after 50 cycles were recorded. Specific test data are shown in Table 1.

[0046] Table 1. List of Performance Tests for Examples and Comparative Examples

[0047]

[0048] In Comparative Example 1, the solid electrolyte membrane only contained a sulfide layer. The positive electrode side of the electrolyte membrane was not resistant to high voltage, and the negative electrode side was unstable to lithium metal. Side reactions at both contact surfaces were severe, resulting in high interfacial impedance. This led to a high initial charge capacity but low discharge capacity and low coulombic efficiency, failing to complete 50 cycles. In Comparative Example 2, the electrolyte membrane incorporated both a sulfide layer and a polymer layer, improving the stability of the negative electrode side to lithium metal. In Comparative Example 3, the electrolyte membrane incorporated both a sulfide layer and a halide layer, improving the high voltage resistance of the positive electrode side. In both examples, the initial coulombic efficiency and cycle capacity retention were improved, but the performance improvement was limited due to the lack of effective protection on the other side. In Example 1, the electrolyte membrane incorporated a halide layer, a sulfide layer, and a polymer layer, forming a three-layer composite structure. This effectively protected the interfaces on both the positive and negative electrodes, reduced interfacial side reactions, and lowered interfacial impedance, thereby significantly improving the initial efficiency and cycle capacity retention. In Example 2, compared to Example 1, the thickness of the halide layer and polymer layer in the composite solid electrolyte membrane was reduced, resulting in minimal impact during the initial cycling stage and near-perfect first-efficiency. However, due to the thinner halide and polymer layers, the risk of contact between the sulfide layer and the positive and negative electrodes increased. During cycling, localized direct contact between the sulfide layer and the positive and negative electrodes could occur, leading to increased impedance and decreased cycle capacity retention. In Example 3, compared to Example 1, the thickness of the halide and polymer layers in the composite solid electrolyte membrane was increased, resulting in decreased overall ionic conductivity and reduced capacity utilization, with both first-efficiency and cycle capacity retention decreasing.

[0049] Comparative Example 4 shows that due to the large thickness of the sulfide layer and polymer layer, the conductivity is low, resulting in low initial charge and discharge capacity. Furthermore, the halide layer is too thin, providing poor protection for the positive electrode, leading to severe interfacial side reactions and poor cycle performance.

[0050] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A composite solid electrolyte membrane for all-solid-state lithium metal batteries, characterized in that, It has a three-layer composite structure, consisting of a halide electrolyte layer, a sulfide electrolyte layer, and a polymer electrolyte layer from top to bottom; the halide electrolyte layer includes a halide solid electrolyte and a binder; the sulfide electrolyte layer includes a sulfide solid electrolyte and a binder; and the polymer electrolyte layer includes a polymer solid electrolyte, a lithium salt, and an inorganic filler.

2. The composite solid electrolyte membrane for all-solid-state lithium metal batteries according to claim 1, characterized in that, The structural formula of the halide solid electrolyte is as follows: Where M = Sc, Y, Al, Ga, In, X = at least one of F, Cl, Br, I; The adhesive is at least one of PTFE, cellulose mesh, nylon mesh or Kevlar mesh.

3. The composite solid electrolyte membrane for all-solid-state lithium metal batteries according to claim 2, characterized in that, The mass ratio of the halide solid electrolyte to the binder is: .

4. According to claim 1 3. A composite solid electrolyte membrane for all-solid-state lithium metal batteries as described in any one of the claims, characterized in that, The structural formula of the sulfide solid electrolyte is: At least one of the following, wherein X = at least one of F, Cl, Br, and I; The adhesive is at least one of PTFE, cellulose mesh, nylon mesh or Kevlar mesh.

5. According to the claims A composite solid electrolyte membrane for all-solid-state lithium metal batteries according to any one of the claims, characterized in that, The polymer solid electrolyte is at least one of PEO, PMMA, PAN, PS, and PVDF; The lithium salt is At least one of them; The inorganic filler is at least one of LLZTO, LATP, LLZO, LLTP, LiPON and LZG.

6. A composite solid electrolyte membrane for all-solid-state lithium metal batteries according to claim 5, characterized in that, The mass ratio of the polymer solid electrolyte, lithium salt, and inorganic filler is 40. 60:30-50:5 15.

7. According to claim 1 A composite solid electrolyte membrane for all-solid-state lithium metal batteries as described in any one of claims 3 and 6, characterized in that, The thickness of the halide electrolyte layer is 10. 40 μm; the thickness of the sulfide electrolyte layer is 40 μm. 140 μm; the thickness of the polymer electrolyte layer is 10 μm. 40μm.

8. A composite solid electrolyte membrane for all-solid-state lithium metal batteries according to claim 7, characterized in that, The thickness of the halide electrolyte layer is 10. 20 μm; the thickness of the sulfide electrolyte layer is 60 μm. 100 μm; the thickness of the polymer electrolyte layer is 10 μm. 20 μm.

9. An all-solid-state lithium metal battery, characterized in that, Including a positive electrode, a negative electrode, and as claimed in claim 1 The composite solid electrolyte membrane described in any one of the 8 claims.

10. A solid-state lithium metal battery according to claim 9, characterized in that, The preparation method of all-solid-state lithium metal battery is as follows: First, sulfide solid electrolyte is mixed with binder and compacted to obtain sulfide electrolyte layer; then, halide solid electrolyte is mixed with binder and compacted on top of sulfide electrolyte layer to obtain halide-sulfide composite electrolyte layer, then positive electrode sheet is placed in and pressure is applied and maintained; next, polymer solid electrolyte layer is compacted and composited with sulfide electrolyte layer; finally, negative electrode sheet is added and pressure is applied to fix it, thus completing the all-solid-state lithium metal battery.

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