Multi-layer structure lithium-free negative electrode, preparation method and solid-state lithium-free negative electrode battery

Abstract

The invention discloses a multi-layer structure lithium-free negative electrode, a preparation method and a solid lithium-free negative electrode battery, the multi-layer structure lithium-free negative electrode comprises a first material layer, a second material layer and a third material layer which are arranged in sequence, the first material layer is a conductive carbon layer, the second material layer is a compact lithium-loving metal or metal oxide layer, and the third material layer is a lithium-loving metal or metal oxide layer. The third material layer is a porous material layer containing Lewis acid sites. The lithium-free negative electrode with the multi-layer structure has a relatively good lithium-loving characteristic, and in the lithium removal process, the copper foil and the coating can keep relatively good structural integrity and maintain a good conductive network, so that the lithium removal reaction can be continuously and stably carried out; the lithium-loving metal layer can be alloyed with lithium to form a relatively low nucleation barrier; the porous material layer containing Lewis acid sites can be compounded with an electrolyte to form an ionic conductor, a stable lithium-loving SEI layer is formed, a large number of Lewis acid sites can effectively improve the lithium deposition morphology and regulate and control uniform deposition of lithium, finally uniform lithium deposition can be achieved, and the cycle performance of a lithium-free negative electrode is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid-state batteries, and particularly relates to a multilayer structure lithium-free negative electrode, a preparation method thereof, and a solid-state lithium-free negative electrode battery comprising the negative electrode. BACKGROUND

[0002] With the continuous progress of science and technology, lithium batteries, as an important energy storage device, have been widely used in the fields of electric vehicles, portable electronic devices, etc. However, the performance of the energy density and cycle life of the traditional lithium battery has gradually been difficult to meet the growing demand. The lithium-free negative electrode lithium battery has no initial active material on the negative electrode side, and all the active lithium in the battery comes from the lithium released from the positive electrode material during the first charging process, which greatly improves the energy density, especially the volume energy density, of the battery system, and has become a research hotspot.

[0003] However, the lithium-free negative electrode battery also faces many challenges. During the cycle process, the battery polarization continuously increases, the specific capacity performance continuously decreases and quickly reaches the minimum value, and finally leads to the failure of the battery. The main reasons are the continuous generation of dead lithium and the damage and reconstruction of the SEI film during the cycle process, among which the negative electrode volume expansion, the poor lithium affinity of the negative electrode, the active lithium detachment from the matrix and other side reactions are the main factors leading to the reduction of the amount of active lithium. Therefore, it is of great practical significance to develop a lithium-free negative electrode preparation method that can effectively improve the cycle performance of the lithium-free negative electrode battery. SUMMARY

[0004] In view of the above problems, the present application provides a multilayer structure lithium-free negative electrode for polymer or sulfide solid-state batteries, a preparation method thereof, and a solid-state lithium-free negative electrode battery comprising the negative electrode, and the technical problems to be solved are the continuous increase of battery polarization during the cycle process of the solid-state lithium-free negative electrode battery, the limited specific capacity performance, and the poor lithium affinity of the negative electrode leading to the detachment of active lithium from the matrix.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions: In a first aspect, the present application provides a multilayer structure lithium-free negative electrode, comprising a first material layer, a second material layer and a third material layer arranged in sequence, the first material layer is a conductive carbon layer, the second material layer is a dense lithium-philic material layer, the lithium-philic material is a lithium-philic metal or a metal oxide; the third material layer is a metal oxide layer with a porous structure and a large number of Lewis acid sites, a molecular sieve material or a metal salt.

[0006] Further, the first material layer is a mixed coating layer of one of Ketjenblack, amorphous carbon, activated carbon, carbon nanotube, graphene and PVDF binder.

[0007] In a second aspect, the present application provides a preparation method of the multi-layer structure lithium-free negative electrode as described above, comprising the following processes: dispersing a certain amount of conductive carbon material, binder and dispersant in a certain amount of NMP, dispersing for a period of time using ultrasonic and stirring, uniformly coating the obtained slurry on the surface of copper foil, and obtaining the first material layer after vacuum drying for standby; using a vacuum evaporation instrument to evaporate the second material layer on the surface of the first material layer, and then loading the third material layer on the second material layer, thereby obtaining the multi-layer structure lithium-free negative electrode. The copper foil serves as the current collector of the lithium-free negative electrode.

[0008] Further, the preparation process further comprises a copper foil pretreatment step, specifically: selecting a copper foil with a purity of ≥99.9%, and sequentially ultrasonically cleaning with acetone, ethanol and deionized water for 15-30 minutes to remove surface oil stains, impurities and the like. Subsequently, the cleaned copper foil is placed in a vacuum drying box and dried at 60-80℃ for 6-8 hours for standby.

[0009] Further, the binder is PVDF; and the dispersant is PVP.

[0010] Further, the lithium-philic layer material in the second material layer is one of Ag, Mg, Al, Zn, Sn and the like lithium-philic metal elements or compounds (such as ZnO, SnO2, etc.) thereof.

[0011] Further, the material containing Lewis acid sites in the third material layer is one of metal oxides (Al2O3, TiO2 or ZrO2), molecular sieve materials (zeolite molecular sieve ZSM-5 or mesoporous molecular sieve MCM-41, SBA-15) or metal salt layers (AlCl3, FeCl3 or BF3), and the preferred material is 200nm zeolite molecular sieve.

[0012] Further, the loading method of the third layer material is one of dipping method, hot-press transfer printing method or coating blade coating method.

[0013] Further, the thickness of the first material layer is 1-5μm, and preferably 2μm; the thickness of the second material layer is 100-400nm, and preferably 100nm; and the thickness of the third material layer is 5-12μm, and preferably 10μm.

[0014] Further, the content of the conductive carbon layer material, binder and dispersant in the first material layer accounts for 87%-96%, 3%-10% and 1%-3% of the total solid mass, respectively; and the content of the material containing Lewis acid sites and the binder in the slurry required for the third layer material accounts for 93.7%-98.8% and 1.2%-6.3% of the total solid mass, respectively.

[0015] Further, the first material layer preparation process will obtain the slurry uniformly coated on the surface of the copper foil, and after drying at 100-120°C for 18-24h under vacuum, it is ready for use; in the third material layer preparation process, the slurry is loaded on the surface of the second material layer, and after drying at 100-120°C for 18-24h under vacuum, it is ready for use.

[0016] In a third aspect, the present application provides a solid-state lithium-free negative electrode battery, comprising a positive electrode, a solid-state electrolyte, and a negative electrode, wherein the positive electrode is a dry positive electrode, the solid-state electrolyte is a polymer solid-state electrolyte or a sulfide solid-state electrolyte, and the negative electrode is a multi-layer structure lithium-free negative electrode as described above.

[0017] Compared with the prior art, the technical scheme of the present application has the following beneficial effects: (taking the first material layer as a conductive carbon layer of Ketjenblack, the second material layer as Ag metal, and the third material layer as zeolite (D50=200nm), and the mass ratio of zeolite to PVDF being 1:0.1, taking the preparation of a multi-layer structure lithium-free negative electrode by way of example, and other conductive carbon materials, metals, or materials containing Lewis acid sites have the same effect).

[0018] 1. The conductive carbon material Ketjenblack coating can alleviate the volume expansion of the composite coating on the surface of the copper foil, enhancing its structural stability. During the delithiation process, the copper foil and the coating can maintain good structural integrity, maintaining a good conductive network, which is conducive to the continuous and stable delithiation reaction.

[0019] 2. The thin Ag layer has good lithium affinity and can alloy with lithium, forming a lower nucleation barrier. It induces uniform deposition of lithium from the zeolite layer downward, and the Li-Ag alloy formed by the reaction of Ag and Li serves as a rapid transport channel for lithium, effectively improving the cycle performance of the lithium-free negative electrode battery.

[0020] 3. The porous zeolite layer containing Lewis acid sites can effectively regulate the uniform deposition of lithium and inhibit the growth and penetration of lithium dendrites. Meanwhile, the pre-solidified polymer electrolyte fully infiltrates the porous zeolite layer, creating a three-dimensional lithium ion transport path.

[0021] 4. The lithium-free negative electrode has the advantages of thin thickness, light weight, and low cost, and has significant advantages in improving battery safety, cycle stability, energy density, and broadening the application range.

[0022] 5. The multi-layer structure preparation process is simple, using the traditional slurry and electrode coating technology of liquid lithium-ion batteries, which is mature and conducive to large-scale production and ensures high production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structural schematic diagram of a full-solid-state lithium-free negative electrode battery multi-layer structure negative electrode of the present application; Figure 2 Structure diagram of a polymer full solid-state lithium-free negative electrode battery prepared according to the present application; Figure 3 Rate performance of a lithium-free negative electrode prepared according to Example 1 assembled into a button cell; Figure 4 Cycle performance comparison of lithium-free negative electrodes of Comparative Example and Example 1 assembled into button cells.

[0024] In the figure: 1, first material layer; 2, second material layer; 3, third material layer; 4, copper foil current collector; 5, positive electrode shell; 6, spring; 7, gasket; 8, positive electrode; 9, polymer electrolyte; 10, negative electrode; 11, negative electrode shell. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0026] Example 1

[0027] Select a copper foil with a purity of ≥99.9%, and sequentially clean it with acetone, ethanol and deionized water for 15-30 minutes each by ultrasonic cleaning to remove surface oil stains, impurities, etc. Then place the cleaned copper foil in a vacuum drying oven and dry it at 60-80°C for 6-8 hours for standby use. Disperse 990 mg of nanocoat black powder, 112.5 mg of PVDF (5 wt% solution) and 22.5 mg of PVP (2 wt% solution) in 1 g of NMP by ultrasonic stirring for 3 h, coat the obtained slurry on the surface of the copper foil, and dry it at 100°C under vacuum for 12 h for standby use.

[0028] Use a vacuum evaporation instrument to evaporate 100 nm of Ag on the surface of the 2 μm KB conductive carbon layer of the copper foil as the second material layer for standby use. Then disperse 1 g of zeolite powder and 2 g of PVDF (5 wt% solution) in 2.5 g of NMP by ultrasonic stirring for 2 h, coat the obtained slurry on the surface of the 100 nm Ag / KB / Cu evaporated with a thickness of 10 μm, and dry it at 100°C under vacuum for 24 h as a multi-layer structure lithium-free negative electrode for standby use.

[0029] Example 2

[0030] A 100 nm Al layer was first evaporated on the surface of a 2 μm KB / Cu foil as a second material layer using a vacuum evaporator. Then, 1 g of zeolite powder and 2 g of PVDF (5 wt% solution) were dispersed in 2.5 g of NMP by ultrasonic agitation for 2 h. The obtained slurry was coated on the surface of the 100 nm Al / KB / Cu foil to a thickness of 10 μm, and dried at 100°C for 24 h in vacuum as a multilayer structure lithium-free negative electrode. The other conditions were the same as in Example 1.

[0031] Example 3

[0032] A 100 nm Sn layer was first evaporated on the surface of a 2 μm KB / Cu foil as a second material layer using a vacuum evaporator. Then, 1 g of zeolite powder and 2 g of PVDF (5 wt% solution) were dispersed in 2.5 g of NMP by ultrasonic agitation for 2 h. The obtained slurry was coated on the surface of the 100 nm Sn / KB / Cu foil to a thickness of 10 μm, and dried at 100°C for 24 h in vacuum as a multilayer structure lithium-free negative electrode. The other conditions were the same as in Example 1.

[0033] Example 4

[0034] A 100 nm Ag layer was first evaporated on the surface of a 2 μm KB / Cu foil as a second material layer using a vacuum evaporator. Then, 1 g of zeolite powder and 2 g of PVDF (5 wt% solution) were dispersed in 2.5 g of NMP by ultrasonic agitation for 2 h. The obtained slurry was coated on the surface of the 100 nm Ag / KB / Cu foil to a thickness of 5 μm, and dried at 100°C for 24 h in vacuum as a multilayer structure lithium-free negative electrode. The other conditions were the same as in Example 1.

[0035] Comparative Example

[0036] 1. A copper foil coated with KB by doctor blade was directly used as a negative electrode; 2. A copper foil coated with a lithium-philic layer / KB by evaporation was directly used as a negative electrode; 3. A copper foil coated with a zeolite layer / KB by doctor blade was used as a negative electrode; The assembly method of the button cell in the above comparative examples was the same as in the examples.

[0037] Battery assembly method:

[0038] Example: A dry cathode, a polymer electrolyte pre-solution, and a lithium-free negative electrode were assembled into a button cell using a sealing machine to apply a pressure of 50 MPa to the button cell. Figure 2 Figure 2 ​The middle piece and the gasket play the same role in assembling the button cell, which is to support the battery. The spring piece is responsible for "conductive path": eliminating the gap by elastic contact to ensure continuous current transmission; the gasket is responsible for "safety protection": sealing to prevent liquid leakage, insulation to prevent short circuit, and buffering to prevent damage, while assisting in optimizing the assembly size.

[0039] The comparative example: only the lithium-philic layer Ag / Ketjen black, only the zeolite layer / Ketjen black and Ketjen black composite copper foil as the negative electrode, the assembly method and the packaging pressure are the same as above.

[0040] Figure 1 To illustrate the structure of the full solid-state lithium-free negative electrode battery multi-layer structure negative electrode prepared by the application, the structure is composed of 3 layers of material layers, the first material layer is loaded on the copper foil, the first material layer can be selected as the Ketjen black conductive carbon layer, the second material layer can be selected as Ag metal, and the third material layer can be selected as zeolite (D50=200nm). The multi-layer structure lithium-free negative electrode is prepared by taking the coating scraping method as an example, and other selected conductive carbon materials, metals (oxides) or materials containing Lewis acid sites have the same effect.

[0041] In terms of rate performance, it can be seen from Figure 3 that the button cell using the zeolite layer / lithium-philic layer / Ketjen black negative electrode can adapt to different size rate charging and discharging (0.1C~1C) in terms of charging and discharging performance. In terms of cycle performance, it can be seen from Figure 4 that its discharge specific capacity is stable at more than 200mAh / g at a charge-discharge rate of 0.2C, and can be stably cycled for more than 20 cycles, and no short circuit occurs (such as Figure 4 ). The lithium-free negative electrode without combining zeolite and lithium-philic layer can be seen from the data in Figure 4 that its discharge specific capacity decays with each cycle at a rate of 0.2C, and it is difficult to stably cycle.

[0042] In summary, the preparation of the multilayer structure lithium-free negative electrode of the embodiment of the present application is to uniformly coat the slurry mixed with the conductive carbon layer and the binder on the copper foil, and dry it for standby; at the same time, the vacuum evaporation technology is used to evaporate the metal layer (such as Ag, Al, Sn plating layer) on the surface of the conductive carbon layer composite copper foil. The metal Ag as the lithiumophilic intermediate layer can improve the interface interaction between lithium and the substrate, regulate the nucleation and growth behavior of lithium, thereby solving the lithium dendrite growth, playing a role in stabilizing the interface and reducing the occurrence of side reactions, reducing the capacity decay rate in the cycle process, improving the cycle life and coulombic efficiency of the battery, and the formation of Ag-Li alloy phase can relieve the substrate rupture or interface peeling caused by the dramatic volume change in the lithium deposition peeling process through the lattice buffer effect. Then the slurry of zeolite and binder is uniformly loaded on the second material layer, and the zeolite layer with porous structure and containing Lewis acid sites can effectively regulate the uniform deposition of lithium, inhibit the growth and penetration of lithium dendrites, and at the same time, the polymer electrolyte pre-solid solution fully infiltrates the porous zeolite layer, constructing a three-dimensional lithium ion transmission channel.

[0043] The above merely describes the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A multi-layered structure lithium-free negative electrode, characterized by, The first material layer is a conductive carbon layer, the second material layer is a compact lithium-philic material layer, the lithium-philic material is a lithium-philic metal or metal oxide, and the third material layer is one of a metal oxide with a porous structure and a large number of Lewis acid sites, a molecular sieve material, or a metal salt layer.

2. The multi-layered structure lithium-free negative electrode of claim 1, wherein, The first material layer is a mixed coating layer of one of ketchen black, amorphous carbon, activated carbon, carbon nanotube, and graphene and a PVDF binder.

3. The multi-layered structure lithium-free negative electrode of claim 1, wherein, The metal in the lithium-philic metal or metal oxide in the second material layer is one of Ag, Mg, Al, Zn, and Sn.

4. The multi-layered structure lithium-free negative electrode of claim 1, wherein, The metal oxide in the third material layer is Al2O3, ZnO, MgO, TiO2, or ZrO2, the molecular sieve material is zeolite molecular sieve ZSM-5, mesoporous molecular sieve MCM-41, or SBA-15, and the metal salt layer is one or more of AlCl3, FeCl3, BF3, MgF, and LiF.

5. The multi-layered structure lithium-free negative electrode of claim 1, wherein, The coating thickness of the first material layer is 1-5 μm, the thickness of the second material layer is 100-400 nm, and the thickness of the third material layer is 5-12 μm.

6. The method of claim 1-5, wherein the multilayer structure lithium-free negative electrode is prepared by the steps of: The process comprises dispersing a conductive carbon layer material, a binder, and a dispersant in NMP, dispersing for a period of time using ultrasonic agitation, uniformly coating the obtained slurry on the surface of a copper foil, and vacuum drying to obtain the first material layer for standby; using a vacuum evaporation instrument to evaporate the second material layer on the surface of the first material layer, then dispersing the third material layer powder and a binder in a certain amount of NMP, ultrasonic stirring and dispersing for a period of time, loading the obtained slurry on the second material layer, and vacuum drying to obtain the multi-layer structure lithium-free negative electrode.

7. The method of claim 6, wherein the multilayer structure lithium-free negative electrode is prepared by the steps of: The binder in the preparation process of the first material layer and the third material layer is PVDF with a concentration of 5 wt%, and the dispersant in the preparation process of the first material layer is PVP; the material loading method of the third material layer is one of immersion method, hot-press transfer printing method, or coating scraping method.

8. The method of claim 6, wherein the multilayer structure lithium-free negative electrode is prepared by the steps of: The content of the conductive carbon layer material, the binder, and the dispersant in the first material layer accounts for 87%-96%, 3%-10%, and 1%-3% of the total solid mass, respectively; and the content of the material with Lewis acid sites and the binder in the slurry required by the third material layer accounts for 93.7%-98.8% and 1.2%-6.3% of the total solid mass, respectively.

9. The method of claim 6, wherein the multilayer structure lithium-free negative electrode is prepared by the steps of: In the preparation process of the first material layer, the obtained slurry is uniformly coated on the surface of a copper foil, and vacuum drying is performed at 100-120°C for 18-24 h for standby; in the preparation process of the third material layer, the obtained slurry is loaded on the surface of the second material layer, and vacuum drying is performed at 100-120°C for 18-24 h for standby.

10. A solid-state lithium-free negative electrode battery, characterized by The solid-state electrolyte is one of a polymer solid-state electrolyte and a sulfide solid-state electrolyte, and the negative electrode is the multi-layer structure lithium-free negative electrode according to any one of claims 1-5.

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