Lithium metal anode and its preparation method, lithium metal battery and electrical device

Abstract

This application provides a lithium metal anode, a method for preparing the same, a lithium metal battery, and an electrical device thereof. The lithium metal anode includes a lithium metal substrate and a modification layer disposed on the surface of the lithium metal substrate. The modification layer comprises an inner layer and an outer layer, with the inner layer disposed between the outer layer and the lithium metal substrate. The inner layer contains zirconium hydrogen phosphate nanosheets, and the outer layer contains a cationic polymer. This application improves the cycle performance of the lithium metal battery by providing a modification layer on the surface of the lithium metal substrate with an inner layer of zirconium hydrogen phosphate nanosheets and an outer layer protected by a cationic polymer.

Description

Technical Field

[0001] This application relates to the field of liquid lithium metal battery technology, and in particular to a lithium metal anode and its preparation method, a lithium metal battery, and an electrical device. Background Technology

[0002] In recent years, lithium metal has become a candidate anode material for achieving 500Wh / kg batteries due to its extremely high theoretical specific capacity (3860mAh / g), low potential, and low density. However, in practical applications, lithium metal anodes suffer from excessive lithium dendrite growth that punctures the separator, leading to poor battery cycle performance. While constructing a modification layer on the lithium metal surface can suppress lithium dendrite growth to some extent, most modification layers eventually fail during lithium metal battery cycling. Summary of the Invention

[0003] The purpose of this application is to overcome the problem of lithium dendrite growth in lithium metal anodes piercing the separator, resulting in poor cycle performance.

[0004] To achieve the above objectives, a first aspect of this application provides a lithium metal anode, comprising a lithium metal body and a modification layer disposed on the surface of the lithium metal body, the modification layer comprising an inner layer and an outer layer, the inner layer being disposed between the outer layer and the lithium metal body, the inner layer comprising zirconium hydrogen phosphate nanosheets, and the outer layer comprising a cationic polymer.

[0005] As an embodiment of this application, the Young's modulus of the modified layer is E GPa, and the thickness of the modified layer is D nm, satisfying: 0.1 <E / D<0.6。

[0006] As an embodiment of this application, the thickness of the modified layer is D nm, which satisfies: 14≤D≤30.

[0007] As an embodiment of this application, the Young's modulus of the modified layer is E GPa, which satisfies: 2≤E≤10.

[0008] As an embodiment of this application, the cationic polymer includes at least one of polyethyleneimine, polyacrylamide, and polyaniline.

[0009] As an embodiment of this application, the zirconium hydrogen phosphate nanosheets are single-layer or few-layer nanosheets.

[0010] As an embodiment of this application, the zirconium hydrogen phosphate nanosheets are parallel to the lithium metal body.

[0011] A second aspect of this application provides a method for preparing the lithium metal anode, comprising the following steps:

[0012] The lithium metal body is successively immersed in a dispersion liquid containing zirconium hydrogen phosphate nanosheets and a solution containing a cationic polymer, and after drying, the lithium metal negative electrode is obtained.

[0013] In the third aspect of the present application, a lithium metal battery is provided, and the lithium metal battery includes the lithium metal negative electrode described in the first aspect of the present application.

[0014] In the fourth aspect of the present application, an electrical device is provided, and the electrical device includes the lithium metal battery described in the third aspect of the present application.

[0015] Compared with the prior art, the beneficial effects of the present application are:

[0016] The lithium metal negative electrode described in the present application includes a lithium metal body and a modification layer. The modification layer includes an inner layer and an outer layer. The inner layer is disposed between the outer layer and the lithium metal body. The inner layer contains zirconium hydrogen phosphate nanosheets, and the outer layer contains a cationic polymer. By providing a modification layer with an inner layer of zirconium hydrogen phosphate nanosheet layer and an outer layer protected by a cationic polymer on the surface of the lithium metal body, the cycle performance of the lithium metal battery is improved. Specific Embodiments

[0017] To better illustrate the purpose, technical solution and advantages of the present application, the present application will be further described below in conjunction with specific embodiments, but the embodiments do not impose any form of limitation on the present application. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0018] In the first aspect of the present application, a lithium metal negative electrode is provided. The lithium metal negative electrode includes a lithium metal body and a modification layer disposed on the surface of the lithium metal body. The modification layer includes an inner layer and an outer layer. The inner layer is disposed between the outer layer and the lithium metal body. The inner layer contains zirconium hydrogen phosphate nanosheets, and the outer layer contains a cationic polymer. By providing a modification layer with an inner layer of zirconium hydrogen phosphate nanosheet layer and an outer layer protected by a cationic polymer on the surface of the lithium metal body, the cycle performance of the lithium metal battery is improved.

[0019] In some embodiments, the Young's modulus of the modification layer is E GPa, and the thickness of the modification layer is D nm, satisfying: 0.1 < E / D < 0.6. In some embodiments, 0.13 ≤ E / D ≤ 0.35. In some embodiments, E / D is 0.11, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.56 or the range composed of any two of the above values. When E / D is within the above range, it helps to further improve the cycle performance of the lithium metal battery.

[0020] In some embodiments, the thickness of the modification layer is D nm, satisfying: 14 ≤ D ≤ 30. In some embodiments, 16 ≤ D ≤ 26. In some embodiments, D is 14, 16, 18, 20, 22, 24, 26, 28, 30, or any two of the above values. When D is within the above range, the modification layer does not significantly impede the ion-electron conduction on the negative electrode side during battery operation, and can achieve the effect of suppressing lithium dendrite growth without affecting the performance of the lithium metal negative electrode itself.

[0021] In some embodiments, the Young's modulus of the modified layer is E GPa, satisfying: 2≤E≤10. In some embodiments, 4≤E≤8. In some embodiments, E is 2, 3, 4, 5, 6, 7, 8, 9, 10, or any two of the above values. When the Young's modulus of the modified layer is within the above range, the toughness and brittleness of the modified layer can be balanced, making it difficult to break when faced with lithium dendrite formation, effectively suppressing lithium dendrite penetration into the separator, thereby improving the cycle life of the battery.

[0022] In some embodiments, the cationic polymer includes at least one of polyethyleneimine, polyacrylamide, and polyaniline. A cationic polymer refers to a positively charged polymer. Using a positively charged polymer as the outer layer, the electrostatic interaction between the polymer and the zirconium hydrogen phosphate nanosheets allows the polymer to form a thin polymer layer on top of the zirconium hydrogen phosphate nanosheet layer. The outer polymer layer helps ensure compatibility with the electrolyte and interface, and more importantly, it protects the inner zirconium hydrogen phosphate nanosheets from easily detaching from the lithium metal substrate.

[0023] In some embodiments, the zirconium hydrogen phosphate nanosheets are single-layer or few-layer (less than 10 layers) nanosheets. Using single-layer or few-layer zirconium hydrogen phosphate nanosheets as the inner layer can reduce the total thickness of the modification layer and give the modification layer a high modulus. At the same time, the zirconium hydrogen phosphate nanosheets themselves are acidic and have a strong interaction with lithium metal, which can ensure that the zirconium hydrogen phosphate nanosheets will not detach from the surface of the lithium metal substrate.

[0024] In some embodiments, the zirconium hydrogen phosphate nanosheets are parallel to the lithium metal body. The inner zirconium hydrogen phosphate nanosheets are arranged parallel to the plane of the lithium metal body, which can induce lithium dendrites to grow parallel to the zirconium hydrogen phosphate nanosheets, thereby better preventing lithium dendrites from penetrating the separator and causing a short circuit.

[0025] It should be noted that the parallelism described in this application is not absolute; that is, the angle between the zirconium hydrogen phosphate nanosheets and the lithium metal body can be 0 to 5°.

[0026] A second aspect of this application provides a method for preparing the lithium metal anode, comprising the following steps:

[0027] The lithium metal bulk was sequentially immersed in a dispersion containing zirconium hydrogen phosphate nanosheets and a solution containing a cationic polymer, and then dried to obtain the lithium metal anode.

[0028] This application employs a dip-coating method to coat a dispersion of zirconium hydrogen phosphate nanosheets onto a lithium metal substrate, followed by a second dip-coating with a cationic polymer solution, and finally drying to obtain a lithium metal anode protected by a modified layer. During the dip-coating of the zirconium hydrogen phosphate nanosheet dispersion, due to the nanosheet layer structure of zirconium hydrogen phosphate itself, the nanosheets tend to adsorb parallel to the lithium metal plane. Furthermore, zirconium hydrogen phosphate itself is acidic and interacts strongly with the lithium metal, ensuring that the zirconium hydrogen phosphate nanosheets do not detach from the lithium metal surface. The second dip-coating with the cationic polymer solution utilizes the electrostatic interaction between the cationic polymer and the zirconium hydrogen phosphate nanosheets, allowing the polymer to form a thin polymer layer on top of the zirconium hydrogen phosphate nanosheet layer. The final product is a modified layer with an outer layer containing cationic polymer and an inner layer containing zirconium hydrogen phosphate nanosheets. The outer polymer layer helps ensure compatibility between the electrolyte and the interface and also protects the inner zirconium hydrogen phosphate nanosheets from detaching from the lithium metal. The inner zirconium hydrogen phosphate nanosheet layer primarily serves to suppress lithium dendrite formation.

[0029] A third aspect of this application provides a lithium metal battery, the lithium metal battery including the lithium metal negative electrode described in the first aspect of this application.

[0030] In some embodiments, the lithium metal battery further includes a positive electrode, a separator, and an electrolyte.

[0031] In some embodiments, the positive electrode sheet includes a current collector and a positive active material layer, wherein the positive active material layer includes a positive active material, a positive conductive agent, and a positive binder.

[0032] In some embodiments, the positive current collector includes at least one of aluminum foil and carbon-coated aluminum foil.

[0033] In some embodiments, the positive electrode active material includes at least one of ternary positive electrode materials, lithium phosphates with an olivine structure, lithium cobalt oxide, and lithium manganese oxide.

[0034] In some embodiments, the ternary cathode material includes nickel cobalt manganese oxide and / or nickel cobalt aluminum oxide.

[0035] In some embodiments, the lithium phosphate having an olivine structure includes lithium iron phosphate and / or lithium manganese iron phosphate.

[0036] In some embodiments, the positive electrode conductive agent includes at least one of acetylene black, graphene, and carbon nanotubes.

[0037] In some embodiments, the positive electrode binder comprises polyvinylidene fluoride.

[0038] In some embodiments, the diaphragm includes at least one of a polyethylene diaphragm and a polypropylene diaphragm.

[0039] In some embodiments, the electrolyte comprises a lithium salt, an organic solvent, and additives. The lithium salt comprises at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0040] In some embodiments, the organic solvent includes at least one of linear carbonates, cyclic carbonates, and carboxylic acid esters. The linear carbonate includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate. The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate. The carboxylic acid ester includes at least one of ethyl acetate and ethyl propionate.

[0041] In some embodiments, the additive includes at least one selected from vinyl sulfate, vinylene carbonate, fluorovinyl carbonate, and 1,3-propanesulfonate lactone.

[0042] A fourth aspect of this application provides an electrical device, which includes the lithium metal battery described in the third aspect of this application. The electrical device includes a backup power supply, a motor, an electric vehicle, an electric motorcycle, a power-assisted bicycle, a bicycle, power tools, a large household storage battery, etc.

[0043] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0044] Example 1

[0045] Example 1 provides a lithium metal battery, the preparation method of which includes the following steps:

[0046] S1. Disperse zirconium hydrogen phosphate nanosheets in N-methylpyrrolidone (NMP) to obtain a dispersion A with a mass fraction of 0.5%; dissolve polyethyleneimine (PEI) in NMP to obtain a solution B with a mass fraction of 0.5%; immerse a lithium strip in dispersion A for 30 seconds, then remove the lithium strip and soak it in pure NMP for 10 seconds to wash away excess zirconium hydrogen phosphate on the surface of the lithium strip; after the lithium strip dries at room temperature, immerse the lithium strip again in solution B for 30 seconds, then wash away excess PEI with NMP again, and finally dry it to obtain a lithium metal anode with a modified layer protection;

[0047] S2. NCM811(LiNi) 0.8 Co 0.1 Mn0.1 O2):SP (acetylene black):PVDF (polyvinylidene fluoride) are mixed in a mass ratio of 8:1:1, NMP is added to form a slurry, and the mixture is coated onto aluminum foil and dried to obtain an NCM positive electrode with an areal capacity of 4mAh / cm². 2 ;

[0048] S3. Assemble a lithium metal anode with an NCM cathode, a Celgard 2320 separator, and an electrolyte to form a lithium metal battery; wherein the concentration of LiPF6 in the electrolyte is 1M, the organic solvent is a mixture of EC, DMC and EMC, the volume ratio of EC, DMC and EMC is 1:1:1, and the additive is 10% FEC.

[0049] Example 2

[0050] Example 2 provides a lithium metal battery, which differs from Example 1 in that solution B is 0.5% polyacrylamide by mass.

[0051] Example 3

[0052] Example 3 provides a lithium metal battery, which differs from Example 1 in that solution B is 0.5% polyaniline by mass.

[0053] Example 4

[0054] Example 4 provides a lithium metal battery, which differs from Example 1 in that the mass fraction of dispersion A is 0.3% and the mass fraction of solution B is 0.3%.

[0055] Example 5

[0056] Example 5 provides a lithium metal battery, which differs from Example 2 in that the mass fraction of dispersion A is 0.3% and the mass fraction of solution B is 0.3%.

[0057] Example 6

[0058] Example 6 provides a lithium metal battery, which differs from Example 3 in that the mass fraction of dispersion A is 0.3% and the mass fraction of solution B is 0.3%.

[0059] Example 7

[0060] Example 7 provides a lithium metal battery, which differs from Example 1 in that the mass fraction of dispersion A is 0.1% and the mass fraction of solution B is 0.1%.

[0061] Example 8

[0062] Example 8 provides a lithium metal battery, which differs from Example 2 in that the mass fraction of dispersion A is 0.1% and the mass fraction of solution B is 0.1%.

[0063] Example 9

[0064] Example 9 provides a lithium metal battery, which differs from Example 3 in that the mass fraction of dispersion A is 0.1% and the mass fraction of solution B is 0.1%.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides a lithium metal battery, which differs from Example 1 in that it uses a lithium strip without a modification layer as the negative electrode.

[0067] The performance of the lithium metal batteries obtained in the above embodiments and comparative examples was characterized and tested. The specific characterization, testing items, methods, and results are as follows:

[0068] Cycling performance: The lithium metal battery was first charged to 4.25V at a constant current and constant voltage of 0.1C, then discharged to 2.8V at a rate of 0.1C, for 2 cycles; then it was charged to 4.25V at a constant current and constant voltage of 0.5C, and discharged to 2.8V at 0.5C for a long-term cycle test. The number of cycles when the capacity retention was 80% was recorded in Table 1.

[0069] 0.5C specific capacity: Select the first cycle of discharge at 0.5C to 2.8V and read the specific capacity data.

[0070] Young's modulus: Lithium sheets and modified lithium sheets were tested using a nanoindenter. The Young's modulus test results were calculated from the curve of force versus indentation depth.

[0071] Table 1. Parameters and performance test results of the lithium metal anodes described in the examples and comparative examples.

[0072]

[0073]

[0074] Note: *Data refers to the Young's modulus of lithium-ion batteries.

[0075] The results above show that by setting a modification layer with an inner layer of zirconium hydrogen phosphate nanosheets and an outer layer of cationic polymer protection on the surface of lithium metal, the cycle performance of lithium metal batteries can be significantly improved.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A lithium metal anode, characterized by, The lithium metal negative electrode comprises a lithium metal body and a modification layer arranged on the surface of the lithium metal body, the modification layer comprises an inner layer and an outer layer, the inner layer is arranged between the outer layer and the lithium metal body, the inner layer comprises zirconium hydrogen phosphate nanosheets, and the outer layer comprises a cationic polymer. The thickness of the modification layer is D nm, and the following condition is met: 14≤D≤30. The Young's modulus of the modification layer is E GPa, and the following condition is met: 2≤E≤10.

2. The lithium metal anode of claim 1, wherein, The Young's modulus of the modification layer is E GPa, and the thickness of the modification layer is D nm, and the following condition is met: 0.1<E / D<0.

6.

3. The lithium metal anode of claim 1, wherein, The cationic polymer comprises at least one of polyethyleneimine, polyacrylamide and polyaniline.

4. The lithium metal anode of claim 1, wherein, The zirconium hydrogen phosphate nanosheets are single-layer or few-layer nanosheets.

5. The lithium metal anode of claim 1, wherein, The zirconium hydrogen phosphate nanosheets are parallel to the lithium metal body.

6. The method of producing a lithium metal negative electrode according to any one of claims 1 to 5, characterized by, The method comprises the following steps: The lithium metal body is sequentially immersed in a dispersion liquid containing zirconium hydrogen phosphate nanosheets and a solution containing a cationic polymer, and then dried to obtain the lithium metal negative electrode.

7. A lithium metal battery, characterized in that, The lithium metal negative electrode comprises any one of claims 1-5.

8. An electrical device, characterized by The lithium metal battery comprises the lithium metal negative electrode of claim 7.

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