Stable three-phase alloy negative electrode, preparation method and all-solid-state battery

Abstract

The invention discloses a stable three-phase alloy negative electrode, a preparation method and an all-solid-state battery, and belongs to the technical field of lithium metal battery negative electrodes and solid-state batteries. The three-phase alloy negative electrode material comprises a lithium metal substrate and a two-phase lithium alloy layer located on the single side of the lithium metal substrate, the lithium metal substrate, a metal sheet and an indium foil are compounded and then subjected to cold pressing treatment under a press machine, so that the lithium metal substrate and the metal sheet are in contact to spontaneously form a part of lithium alloy layer; and forming a complete lithium alloy layer and a lithium-indium alloy layer on the cold-pressed unalloyed part of the metal sheet and the covered indium foil in battery circulation, and finally forming the stable three-phase alloy negative electrode cooperatively modified by the lithium alloy layer and the lithium-indium alloy layer on the lithium metal substrate. Wherein the lithium alloy layer formed by the metal sheet provides a stable structure in the charging and discharging process, and the lithium indium alloy layer in contact with the electrolyte enables lithium ions to be uniformly deposited and rapidly diffused on an interface. The high-stability solid-state battery alloy negative electrode is constructed by synthesizing the electrochemical characteristics of the two-phase alloy material and adjusting the metal sheet, the prepared stable three-phase alloy negative electrode material is simple in preparation method and low in cost, and the problems that a traditional lithium metal negative electrode is slow in lithium diffusion, dendritic crystal grows, and the negative electrode structure is fragile are effectively solved; and the rate and the stable cycle of the assembled all-solid-state battery are greatly improved.

Description

Technical Field

[0001] This application belongs to the fields of lithium metal battery anodes and solid-state batteries, and specifically relates to a method and application of a stable three-phase alloy anode prepared by a cold pressing gradient multiphase method for all-solid-state batteries. Background Art

[0002] With the continuous growth of the energy storage demand of intelligent networked electric vehicles, the demand for high energy density and high safety is increasing. The safety problems of traditional organic electrolyte batteries, such as flammability and explosiveness, can no longer meet the requirements. Solid-state batteries directly isolate the positive and negative electrodes through solid electrolytes, reduce the proportion of inactive materials, improve the energy density, and eliminate the disadvantages of liquid electrolytes, fundamentally avoiding the risks of leakage, volatilization, and thermal runaway, which is of great significance for ensuring vehicle safety. However, the solid-solid contact, especially the anode interface problem, of solid-state batteries limits industrialization and practical applications. It involves interface pores and transport, and is prone to piercing, which is a key technical challenge faced. These problems lead to rapid capacity decay of solid-state batteries, poor rate performance, and safety risks of battery short circuits caused by lithium dendrites. In order to enable solid-state batteries to be put into actual production applications, this key technical problem must be solved. For this, researchers at home and abroad have done a lot of modification work. For example, surface modification and lithiophilic design, artificial SEI layer, alloy anode materials, etc. Among them, there are many types of alloy anode materials: lithium indium, lithium aluminum, lithium tin, lithium platinum, lithium gold, lithium silver, lithium magnesium, lithium silicon, lithium zinc, etc. They have different mechanical characteristics and also show different Coulomb efficiencies and voltage drops in full batteries (ACS Energy Lett. 2024, 9, 2554-2563). At the same time, different processing procedures for alloying will have a significant impact on solid-state batteries, including hot pressing, cold pressing, repeated rolling, melt mixing, ball milling mixing, etc. (Adv. Energy Mater. 2024, 2404055). Among the alloy anode materials, the lithium indium anode has fast diffusion kinetics and the lithium aluminum anode has high stability. Among various processing methods, cold pressing of two-phase alloy anodes shows good cycle stability performance, but the shortcoming is obvious. The performance of the lithium indium anode is strongly dependent on the interface phase composition and the mechanical property is weak. The lithium diffusion inside the lithium aluminum anode is slow and "dead lithium" is easily deposited inside. To sum up, the mechanical cracking of the anode, the slow lithium diffusion kinetics at the interface, and the generation of "dead lithium" inside the anode are still problems to be solved for alloy anodes. Summary of the Invention

[0003] The embodiment of this application provides a method for preparing a stable three-phase alloy anode material by cold pressing gradient multiphase, which can obtain a stable three-phase structure, improve the mechanical strength of the anode and the rapid interface lithium diffusion rate, and the assembled all-solid-state battery obtains stable and efficient electrochemical performance.

[0004] In a first aspect, an embodiment of the present application provides a method for preparing an alloy negative electrode material for all-solid-state batteries by a cold pressing three-phase method. The method includes:

[0005] After the lithium metal substrate and the metal sheet are compounded with indium foil, cold pressing treatment is carried out under a press, so that a partial lithium alloy layer is spontaneously formed in contact with the lithium metal substrate and the metal sheet. The unalloyed part of the metal foil and the indium foil covering the metal foil form a complete lithium alloy layer and a lithium-indium alloy layer during battery cycling, and finally a stable three-phase alloy negative electrode co-modified with a lithium alloy layer and a lithium-indium alloy layer is formed on the lithium metal substrate.

[0006] The thickness of the lithium metal substrate is 20-300 μm, and the diameter is greater than 1 mm.

[0007] The metal sheet is any one of metal aluminum, tin, zinc, and magnesium, with a thickness of 10-200 μm and a diameter greater than 1 mm.

[0008] The thickness of the indium foil is 20-200 μm, and the diameter is greater than 1 mm.

[0009] The overall thickness of the three-phase alloy negative electrode is 50 μm-700 μm, and the diameter is greater than 1 mm.

[0010] For the cold pressing, the lithium metal substrate is placed at the bottom, the metal sheet is in the middle, and the indium foil is on the top for stacking.

[0011] For the cold pressing coverage area requirement, indium foil ≥ metal sheet ≥ lithium foil.

[0012] The pressure for the cold pressing treatment is 5-250 MPa.

[0013] The pressing time is 60-600 s.

[0014] In a second aspect, an embodiment of the present application provides a stable three-phase alloy negative electrode material, which is prepared by the method described in the above embodiment, and the assembly application is as follows:

[0015] An application of a stable three-phase alloy negative electrode material and the preparation method thereof, in which a solid-state battery composite negative electrode, a sulfur-carbon composite positive electrode, a ternary nickel-cobalt-manganese positive electrode (LiNixCoMnzO2, where x + y + z = 1), a lithium iron phosphate positive electrode (LiFePO4), a lithium manganate positive electrode (LiMn2O4), and a lithium cobaltate positive electrode (LiCoO2) are used to form a solid-state battery.

[0016] The method for cold pressing to prepare a three-phase alloy negative electrode material for all-solid-state batteries implemented in the present application has simple process, low cost, wide applicability, good repeatability, and can obtain a three-phase alloy negative electrode material with stable structure, and can obtain a negative electrode material for all-solid-state batteries with high Coulomb efficiency, good rate performance, and stable long-cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic diagram of the formation of a stable three-phase alloy negative electrode in the embodiment of the present application.

[0019] Figure 2 It is a photograph of a three-phase alloy negative electrode covered and modified with a lithium metal substrate, a lithium-aluminum alloy layer, and an indium foil in the embodiment of the present application.

[0020] Figure 3 It is a cyclic performance graph of a full cell assembled with the negative electrode material of the embodiment of the present application at room temperature and 0.5C.

[0021] Figure 4 It is a cyclic performance graph of a full cell assembled with the negative electrode material of Comparative Example 1 at room temperature and 0.5C.

[0022] Figure 5 It is a cyclic performance graph of a full cell assembled with the negative electrode material of Comparative Example 2 at room temperature and 0.5C.

[0023] Figure 6 It is a charge-discharge curve graph of a Li|Li symmetric cell assembled with the negative electrode material of the embodiment of the present application.

[0024] Figure 7 It is a room temperature rate performance graph of full cells assembled with the embodiment of the present application and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to enable those skilled in the art to better understand the solution of the present application, the following will clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0026] The terms "first", "second", etc. in the description and claims of this application are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0027] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0028] An embodiment of this application is a solid-state battery three-phase alloy negative electrode material, as Figure 1 shown, including a lithium metal substrate and a lithium aluminum alloy layer) and indium foil coverage. The preparation method includes the following steps: Align a lithium sheet with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm, an aluminum foil with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm, and an indium foil with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm, and place them under a press. Prepare a gradient multi-phase alloy negative electrode at a pressure of 125 - 190 MPa, a pressing time of 300 s, and a pressing temperature of 25°C. Then, a complete lithium alloy layer and a lithium indium alloy layer are formed during battery cycling, and finally, a stable three-phase alloy negative electrode with cooperative modification of the lithium alloy layer and the lithium indium alloy layer is formed on the lithium metal substrate.

[0029] Preparation of sulfur-carbon composite positive electrode: Put the dried single-walled carbon nanotubes and sulfur into a polytetrafluoroethylene inner container, put the polytetrafluoroethylene inner container into a glove box to fill the polytetrafluoroethylene inner container with argon, and then put the polytetrafluoroethylene inner container into a hydrothermal autoclave and seal it in the glove box. Take out the sealed hydrothermal autoclave from the glove box and put it into a muffle furnace for heat preservation for a period of time to obtain a sulfur-carbon composite material. Uniformly mix the sulfur-carbon composite material with LPSC electrolyte and ball mill it under an argon atmosphere to obtain a positive electrode material for an all-solid-state battery.

[0030] Battery assembly and testing: Press LPSC electrolyte and the sulfur-carbon composite positive electrode into a battery mold with a diameter of 10 mm respectively, and assemble them with a gradient multi-alloy negative electrode modified with a lithium aluminum alloy layer and indium foil coverage into a solid-state battery, with a stacking pressure of 125 - 190 MPa and a stacking time of 300 s.

[0031] The negative electrode material obtained in the embodiments of the present application was subjected to electrochemical performance tests. After the electrochemical performance tests, as Figure 7 shown, it showed excellent rate performance at 0.1C; 0.2C; 0.5C; 1C; 2C; 3C, and the specific capacities were 1674 mAh / g; 1501 mAh / g; 1299 mAh / g; 1178 mAh / g; 925 mAh / g; 667 mAh / g respectively. The initial specific capacity at a current density of 0.5C during long cycling was 1262 mAh / g, and the capacity remained at 1010 mAh / g after 500 cycles -1 As Figure 3 shown.

[0032] Comparative Example 1

[0033] A lithium sheet with a diameter of 3 - 8 mm and a thickness of 30 - 80 μm and an indium foil with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm were assembled with the electrolyte and the sulfur-carbon composite positive electrode into a solid-state battery. The battery assembly was the same as above, and charge-discharge tests were carried out at 0.1C; 0.2C; 0.5C; 1C; 2C rates. The corresponding electrochemical performances are also shown in Figure 7 . The initial specific capacity at a current density of 0.5C during long cycling was 1162 mAh / g, and the capacity remained at 697 mAh / g after 100 cycles -1 As Figure 4 shown.

[0034] Comparative Example 2

[0035] A lithium sheet with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm and an aluminum foil with a diameter of 6 - 10 mm and a thickness of 30 - 80 μm were assembled with the electrolyte and the sulfur-carbon composite positive electrode into a solid-state battery. The battery assembly was the same as above, and charge-discharge tests were carried out at 0.1C; 0.2C; 0.5C; 1C; 2C; 3C rates. The corresponding electrochemical performances are also shown in Figure 7 . The initial specific capacity at a current density of 0.5C during long cycling was 693 mAh / g, and the capacity remained at 485 mAh / g after 150 cycles -1 As Figure 5 shown.

[0036] The LPSC electrolyte was placed in a battery mold with a diameter of 10 mm and pressed into an electrolyte sheet under a pressure of 185 MPa. The negative electrode material obtained in the embodiments of the present application was installed on both sides of the electrolyte in the battery mold. Under a pressure of 25 MPa and a pressing time of 300 s, a symmetrical battery was assembled for electrochemical performance tests.

[0037] The electrochemical performances of the solid-state batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0038] When using the lithium-indium alloy negative electrode in Comparative Example 1, the solid-state battery exhibited a short cycle life. This was mainly because a lithium-rich phase appeared at the interface during the charge and discharge process of the lithium-indium alloy negative electrode, resulting in difficult lithium diffusion, local lithium deposition, a decrease in Coulombic efficiency and capacity utilization, and the growth of lithium dendrites during long-term cycling, which deteriorated the electrochemical performance. Therefore, as Figure 4 shown, the initial specific capacity of the solid-state battery assembled with the lithium-indium negative electrode at 0.5C long cycling was 1162 mAh / g, and the specific capacity decreased to less than 60% after 100 cycles.

[0039] When using the lithium-aluminum alloy negative electrode in Comparative Example 2, an alloying reaction also occurred on its surface to form a lithium-aluminum alloy layer, and the Coulombic efficiency and cycle stability were both good in the early stage. However, the lithium diffusion rate of this lithium-aluminum alloy layer was limited, so "dead lithium" was trapped inside the negative electrode, greatly reducing the negative electrode capacity, especially at high rates, where the capacity was basically unable to be released. Therefore, as Figure 5 shown, the initial specific capacity of the solid-state battery assembled with the lithium-aluminum negative electrode at 0.5C long cycling was 693 mAh / g, and the specific capacity decreased to less than 70% after 150 cycles.

[0040] The initial specific capacity of the solid-state battery assembled with the stable three-phase alloy negative electrode at 0.5C long cycling was 1262 mAh / g, and the specific capacity was still above 80% after 500 cycles, as Figure 3 shown, which fully demonstrated that the three-phase alloy negative electrode combined the advantages of the two-phase alloy negative electrode and solved the defects of the two-phase alloy negative electrode.

[0041] The Li|Li symmetric battery assembled with the stable three-phase alloy negative electrode could be cycled stably for more than 1000 h, as Figure 6 shown, indicating that the stable three-phase alloy negative electrode co-modified by the lithium alloy layer and the lithium-indium alloy layer could effectively inhibit the growth of lithium dendrites and exhibited excellent electrochemical stability.

[0042] Based on the above, combining the rate performance of the solid-state batteries prepared in Example 1, Comparative Example 1, and Comparative Example 2, as Figure 7。The results show that the stable three-phase alloy material with a lithium metal substrate, a lithium-aluminum alloy layer in the middle, and an indium foil cold-pressed on the surface has the best electrochemical performance. This is mainly because during the pressing process, the aluminum foil and the lithium sheet form a lithium-aluminum alloy layer on the surface of the lithium sheet through a spontaneous alloying reaction. This lithium-aluminum alloy layer stabilizes the anode during the de-lithiation and lithiation processes as a mechanical framework during the charge and discharge processes. The indium foil on the surface also undergoes the same lithiation and de-lithiation during the charge and discharge processes. The lithium-indium alloy layer completely covers the middle of the lithium-aluminum alloy layer and the solid electrolyte to provide a fast charge transfer surface and a channel for fast lithium diffusion. At the same time, the rapid diffusion of lithium into the lithium-aluminum alloy layer ensures that the phase composition of the lithium-indium alloy layer remains within a reasonable range, preventing the appearance of lithium-rich phases and lithium deposition at the anode-electrolyte interface. Therefore, fast electron transport can be achieved, lithium dendrite growth can be inhibited, a large anode capacity range and a stable anode structure can be provided, and ultimately high Coulombic efficiency, high capacity utilization, and long cycle life can be realized.

[0043] The foregoing are only exemplary embodiments of the present disclosure and should not be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made in accordance with the teachings of the present disclosure still fall within the scope of the present disclosure. After considering the specification and practicing the present disclosure, those skilled in the art will readily think of other embodiments of the present disclosure. This application aims to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common general knowledge or conventional technical means in the technical field not described in the present disclosure. The specification and embodiments are only regarded as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A method for preparing a stable three-phase alloy negative electrode by a cold pressing gradient multiphase method for a solid-state battery, characterized in that, After the lithium metal substrate and the metal sheet are compounded with indium foil, cold pressing treatment is carried out under a press to form a partial lithium alloy layer formed spontaneously by the contact of the lithium metal substrate and the metal sheet. The unalloyed part of the cold-pressed metal foil and the indium foil covering the metal foil form a complete lithium alloy layer and a lithium-indium alloy layer during battery cycling, and finally a stable three-phase alloy negative electrode co-modified by the lithium alloy layer and the lithium-indium alloy layer is formed on the lithium metal substrate.

2. The preparation method of the stable three-phase alloy negative electrode according to claim 1, wherein, The thickness of the lithium metal substrate is 20 - 300 μm, and the diameter is greater than 1 mm.

3. The preparation method of the stable three-phase alloy negative electrode according to claim 1, wherein, The metal sheet is any one of aluminum, tin, zinc, and magnesium, with a thickness of 10 - 200 μm and a diameter greater than 1 mm.

4. The preparation method of the stable three-phase alloy negative electrode according to claim 1, characterized in that, The thickness of the indium foil is 20 - 200 μm, and the diameter is greater than 1 mm.

5. The preparation method of the stable three-phase alloy negative electrode according to claim 1, characterized in that, The overall thickness of the three-phase alloy negative electrode is 50 - 700 μm, and the diameter is greater than 1 mm.

6. The preparation method of the stable three-phase alloy negative electrode according to claim 1, wherein For the cold pressing, the lithium metal substrate is at the bottom, the metal sheet is in the middle, and the indium foil is on the top in sequence for stacking.

7. The method for preparing a stable three-phase alloy negative electrode according to claim 1, wherein, For the cold pressing coverage area requirement, indium foil ≥ metal sheet ≥ lithium foil.

8. The method for preparing a stable three-phase alloy negative electrode according to claim 1, characterized in that, The pressure for the cold pressing treatment is 5 - 250 MPa.

9. The preparation method of the stable three-phase alloy negative electrode according to claim 1, characterized in that, The pressing time is 60 - 600 s.

10. A stable three-phase alloy negative electrode prepared by the method according to any one of claims 1 - 9.

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