Lithium metal negative electrode and preparation method and application thereof

Abstract

The application discloses a lithium metal negative electrode and a preparation method and application thereof. The composition of the lithium metal negative electrode comprises a lithium metal layer and a polymer-ionic liquid composite protective layer, and can further comprise a metal substrate arranged on the side of the lithium metal layer away from the polymer-ionic liquid composite protective layer. The composition of the polymer-ionic liquid composite protective layer comprises a polymer and an ionic liquid. The lithium metal negative electrode can effectively inhibit dendrite formation, and the lithium ion battery assembled therefrom has excellent electrochemical performance and high safety, and is suitable for large-scale popularization and application.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium metal anode, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles, electric motorcycles, and electronic products, commonly used graphite anodes (theoretical specific capacity of only 372 mAh / g) are no longer sufficient to meet the high energy density requirements of lithium-ion batteries. The development of new anode materials has become a research hotspot in recent years. Lithium metal has a theoretical specific capacity as high as 3860 mAh / g and a low density (0.534 g / cm³). 3 Lithium metal has a low redox potential (3.04V vs. standard hydrogen electrode), making it a promising anode material that can significantly increase the energy density of lithium-ion batteries. However, lithium metal is extremely chemically reactive, reacting with almost all electrolytes. The resulting electrolyte interphase (SEI) film can prevent further reaction until the interface stabilizes. During battery cycling, unstable volume changes can cause the SEI film to rupture, exposing fresh lithium metal which then reacts with the electrolyte again. Furthermore, lithium ions preferentially deposit at the rupture sites, forming dendrites. This cyclical process easily leads to capacity decay, low coulombic efficiency, and short circuits in lithium-ion batteries, severely hindering their commercial application.

[0003] Therefore, it is of great significance to develop a lithium metal anode that can effectively suppress dendrites and produce lithium-ion batteries with excellent electrochemical performance. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium metal anode, its preparation method, and its application.

[0005] The technical solution adopted in this invention is:

[0006] A lithium metal anode comprises a lithium metal layer and a polymer-ionic liquid composite protective layer; the polymer-ionic liquid composite protective layer comprises a polymer and an ionic liquid.

[0007] Preferably, the mass ratio of the polymer to the ionic liquid is 1:0.1 to 0.9.

[0008] Preferably, the polymer is at least one of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyurethane (TPU), polyethylene oxide (PEO), and polyvinylpyrrolidone (PVP).

[0009] More preferably, the polymer is poly(vinylidene fluoride-co-hexafluoropropylene).

[0010] Preferably, the number-average molecular weight of the polymer is 50,000 g / mol to 2,000,000 g / mol.

[0011] Preferably, the cation in the ionic liquid is at least one selected from imidazole cations, pyrrole cations, pyridine cations, piperidine cations, morphine cations, and tetraalkylammonium cations, and the anion is Cl. - ,Br - I - [AlCl4] - [SCN] - [BF4] - [PF6] - [CH3SO3] - [CF3SO3] - Alkyl sulfate ([RSO4]) - It includes at least one of dicyandiamide, difluorosulfonylimide, (fluorosulfonyl)(trifluoromethanesulfonyl)imino, bis(trifluoromethanesulfonylimide), and dioxoboronic acid.

[0012] More preferably, the ionic liquid is [CTA][TFSI]. The cation in [CTA][TFSI] is hexadecyltrimethylammonium ([CTA]). + The anion is bis(trifluoromethanesulfonyl)imide ([TFSI]). - ).

[0013] Preferably, the thickness of the polymer-ionic liquid composite protective layer is 0.1 μm to 20 μm.

[0014] Preferably, the lithium metal anode further comprises a metal substrate disposed on the side of the lithium metal layer away from the polymer-ionic liquid composite protective layer.

[0015] Preferably, the metal substrate is composed of at least one of copper (Cu), aluminum (Al), zinc (Zn), tin (Sn), magnesium (Mg), silver (Ag), gold (Au), iron (Fe), sodium (Na), and potassium (K).

[0016] More preferably, the metal substrate is copper foil.

[0017] A method for preparing a lithium metal anode as described above includes the following steps:

[0018] A dispersion made of polymer, ionic liquid and organic solvent is coated on the surface of lithium metal sheet and dried to form a polymer-ionic liquid composite protective layer, thus obtaining lithium metal anode;

[0019] Alternatively, a dispersion made of polymer, ionic liquid and organic solvent is coated on the surface of a metal substrate, dried to form a polymer-ionic liquid composite protective layer, and then immersed in a lithium ion-containing solution for electrodeposition to form a lithium metal layer between the metal substrate and the polymer-ionic liquid composite protective layer, thus obtaining a lithium metal anode.

[0020] Alternatively, the metal substrate can be immersed in a lithium-ion-containing solution for electrodeposition to form a lithium metal layer on the surface of the metal substrate. Then, a dispersion made of polymer, ionic liquid and organic solvent can be coated on the surface of the lithium metal layer and dried to form a polymer-ionic liquid composite protective layer, thus obtaining the lithium metal anode.

[0021] Preferably, the organic solvent is at least one selected from N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), acetonitrile, and acetone.

[0022] Preferably, the electrodeposition is performed at a current density of 0.1 mA / cm². 2 ~1.0mA / cm 2 It is carried out under the following conditions.

[0023] A lithium-ion battery, wherein the negative electrode is the aforementioned lithium metal negative electrode.

[0024] The beneficial effects of this invention are: the lithium metal anode of this invention can effectively suppress dendrite formation, and the lithium-ion battery assembled from it has excellent electrochemical performance and high safety, making it suitable for large-scale promotion and application.

[0025] Specifically, the lithium metal anode of the present invention contains a polymer-ionic liquid composite protective layer. When uneven deposition / stripping occurs on the anode, resulting in a large accumulation of charge at the protrusions, cations anchored on the polymer through ion coupling and hydrogen bonding can reach the protrusions via polymer chain segment movement to achieve electrostatic shielding. By adjusting the metal ion deposition path, uniform deposition / stripping of the anode is achieved, inhibiting dendrite formation. Furthermore, the soft elasticity of the polymer enables the protective layer to adapt to changes in metal volume, while also inhibiting SEI film rupture to reduce side reactions. In addition, the reversible breakage and growth of hydrogen bonds formed between the polymer and the ionic liquid give the protective layer a self-healing function, ensuring the long-term effectiveness of the protective layer. Attached Figure Description

[0026] Figure 1 This is a SEM image of the copper foil in Example 1.

[0027] Figure 2 This is a SEM image of the copper foil containing the polymer-ionic liquid composite protective layer in Example 1.

[0028] Figure 3 This is a SEM image of the lithium metal anode in Example 1.

[0029] Figure 4 The graph shows the electrochemical performance test results of the lithium-ion battery in Example 1.

[0030] Figure 5 The figure shows the electrochemical performance test results of the lithium-ion battery in Comparative Example 1.

[0031] Figure 6 The graph shows the electrochemical performance test results of the lithium-ion battery in Example 2. Detailed Implementation

[0032] The present invention will be further explained and described below with reference to specific embodiments.

[0033] Example 1:

[0034] A lithium metal anode, the preparation method of which includes the following steps:

[0035] 1) Mix PVDF-HFP (number average molecular weight of 455000 g / mol), [CTA][TFSI] and NMP in a mass ratio of 1:0.5:5, then coat the mixture evenly onto a copper foil and vacuum dry it at 80°C for 12 h to form a polymer-ionic liquid composite protective layer on the copper foil. This results in a copper foil containing a polymer-ionic liquid composite protective layer (denoted as IPC-50, with a thickness of 2 μm).

[0036] 2) CR2016 button cells were assembled in an argon-filled glove box. Copper foil with a polymer-ionic liquid composite protective layer was used as the cathode, Celgard 2400 as the separator, a 1 mol / L LiTFSI solution (the solvent consisted of dioxane and ethylene glycol dimethyl ether in a 1:1 volume ratio, with 1% LiNO3 as the additive) was used as the electrolyte, and lithium foil was used as the anode. Electrochemical deposition was then performed on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time was 20 hours, during which a lithium metal layer was formed between the copper foil and the polymer-ionic liquid composite protective layer. The battery with the deposited lithium metal layer was then moved to an argon-filled glove box for removal, yielding the lithium metal anode (denoted as IPC-50-Li, with an areal capacity of 4 mAh / cm²). 2 ).

[0037] A lithium-ion battery, the preparation method of which includes the following steps:

[0038] Using the lithium metal anode (IPC-50-Li) of this embodiment as the positive and negative electrodes to assemble a CR2016 button battery, Celgard2400 as the separator, and a 1 mol / L LiTFSI solution (the solvent is composed of dioxane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and the mass fraction of the additive LiNO3 is 1%) as the electrolyte, a lithium-ion battery is obtained.

[0039] Comparative Example 1:

[0040] A lithium metal anode, the preparation method of which includes the following steps:

[0041] CR2016 button cells were assembled in an argon-filled glove box. Copper foil was used as the cathode, Celgard 2400 as the separator, a 1 mol / L LiTFSI solution (the solvent consisted of dioxane and ethylene glycol dimethyl ether in a 1:1 volume ratio, with 1% LiNO3 as the additive) was used as the electrolyte, and lithium foil was used as the anode. Electrochemical deposition was then performed on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time is 20 hours to form a lithium metal layer on the copper foil. The battery with the deposited lithium metal layer is then moved to a glove box filled with argon gas for removal, thus obtaining the lithium metal anode (denoted as Cu-Li).

[0042] A lithium-ion battery, the preparation method of which includes the following steps:

[0043] The lithium metal anode (Cu-Li) used in this comparative example was used as the positive and negative electrodes to assemble a CR2016 button battery. Celgard 2400 was used as the separator, and a 1 mol / L LiTFSI solution (the solvent consisted of dioxane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and the mass fraction of the additive LiNO3 was 1%) was used as the electrolyte to obtain the lithium-ion battery.

[0044] Performance testing:

[0045] 1) Scanning electron microscope (SEM) image of the copper foil in Example 1 is shown below. Figure 1 As shown, the SEM image of the copper foil containing the polymer-ionic liquid composite protective layer is as follows. Figure 2 As shown, the SEM image of the lithium metal anode is as follows. Figure 3 (a is the surface, b is the cross-section) as shown.

[0046] Depend on Figure 1 It can be seen that the surface of the copper foil is relatively smooth.

[0047] Depend on Figure 2 It can be seen that the polymer-ionic liquid composite protective layer is uniformly covered on the surface of the copper foil, exhibiting a rough and granular surface that is different from the copper foil.

[0048] Depend on Figure 3 It can be seen that the surface of the lithium metal anode has larger particles than that of the copper foil (without lithium metal layer deposited) containing the polymer-ionic liquid composite protective layer, and there is no obvious damage. This indicates that the polymer-ionic liquid composite protective layer can adapt to the volume change of lithium metal, and the surface can maintain a consistent roughness before and after lithium metal deposition. This indicates that lithium metal is completely deposited to the bottom of the polymer-ionic liquid composite protective layer (lithium ions can pass through the polymer-ionic liquid composite protective layer during electrodeposition, and are deposited on the surface of the metal substrate and at the bottom of the polymer-ionic liquid composite protective layer).

[0049] 2) The lithium-ion batteries of Example 1 and Comparative Example 1 were subjected to cycle testing on the LAND battery testing system at a current density of 1 mA / cm². 2 The charge-discharge time was 1 hour, and the electrochemical performance test results are shown in the figure below. Figure 4 and Figure 5 As shown.

[0050] Depend on Figure 4 and Figure 5 It can be seen that the lithium-ion battery in Example 1 can remain stable for 365 hours without any short circuit, while the lithium-ion battery in Comparative Example 1 short circuited after about 160 hours. This indicates that the polymer-ionic liquid composite protective layer enables uniform deposition of lithium ions during the deposition process, resulting in a stable deposition / stripping process.

[0051] Example 2:

[0052] A lithium metal anode, the preparation method of which includes the following steps:

[0053] PVDF-HFP (number-average molecular weight 455000 g / mol), [CTA][TFSI], and NMP were mixed uniformly at a mass ratio of 1:0.5:5, and then uniformly coated onto a lithium metal sheet. The mixture was then vacuum dried at 80°C for 12 h to form a polymer-ionic liquid composite protective layer on the lithium metal sheet, resulting in a lithium metal anode (denoted as IP-50-Li, with a polymer-ionic liquid composite protective layer thickness of 6 μm and an areal capacity of 16 mAh / cm²). 2 ).

[0054] A lithium-ion battery, the preparation method of which includes the following steps:

[0055] The lithium metal anode (IP-50-Li) used in this embodiment is used as the positive and negative electrodes to assemble a CR2016 button battery. Celgard2400 is used as the separator, and a 1 mol / L LiTFSI solution (the solvent is composed of dioxane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and the mass fraction of the additive LiNO3 is 1%) is used as the electrolyte to obtain the lithium-ion battery.

[0056] Performance testing:

[0057] The lithium-ion battery from Example 2 was subjected to cycle testing on the LAND battery testing system at a current density of 1 mA / cm². 2 The charge-discharge time was 1 hour, and the electrochemical performance test results are shown in the figure below. Figure 6 As shown.

[0058] Depend on Figure 6 It can be seen that the lithium-ion battery in Example 2 can remain stable for 750 hours without any short circuit, indicating that the polymer-ionic liquid composite protective layer enables uniform deposition of lithium ions during the deposition process, and ultimately presents a stable deposition / stripping process.

[0059] Example 3:

[0060] A lithium metal anode, the preparation method of which includes the following steps:

[0061] 1) PEO (number average molecular weight of 1,000,000 g / mol), 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ([EMI][FSI]) and NMP are mixed evenly in a mass ratio of 1:0.3:5, and then uniformly coated on copper foil. The mixture is then vacuum dried at 60°C for 12 h to form a polymer-ionic liquid composite protective layer on the copper foil, resulting in a copper foil containing the polymer-ionic liquid composite protective layer (denoted as IEPC-30, with a thickness of 2 μm).

[0062] 2) Assemble CR2016 button cells in an argon-filled glove box. Use copper foil with a polymer-ionic liquid composite protective layer as the cathode, Celgard 2400 as the separator, a 1 mol / L LiFSI solution (ethylene glycol dimethyl ether as the solvent) as the electrolyte, and lithium foil as the anode. Then, perform electrochemical deposition on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time was 20 hours, during which a lithium metal layer was formed between the copper foil and the polymer-ionic liquid composite protective layer. The battery with the deposited lithium metal layer was then moved to an argon-filled glove box for removal, yielding the lithium metal anode (denoted as IEPC-30-Li, with an areal capacity of 4 mAh / cm²). 2 ).

[0063] A lithium-ion battery, the preparation method of which includes the following steps:

[0064] Using the lithium metal anode (IEPC-30-Li) of this embodiment as the positive and negative electrodes to assemble a CR2016 button battery, Celgard2400 as the separator, and a 1 mol / L LiFSI solution (with ethylene glycol dimethyl ether as the solvent) as the electrolyte, a lithium-ion battery is obtained.

[0065] According to the test (the test method is the same as in Example 1), the lithium-ion battery in this example can remain stable for 300 hours without any short circuit.

[0066] Comparative Example 2:

[0067] A lithium metal anode, the preparation method of which includes the following steps:

[0068] CR2016 button cells were assembled in an argon-filled glove box, using copper foil as the cathode, Celgard 2400 as the separator, a 1 mol / L LiFSI solution (ethylene glycol dimethyl ether as the solvent) as the electrolyte, and lithium foil as the anode. Electrochemical deposition was then performed on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time is 20 hours to form a lithium metal layer on the copper foil. The battery with the deposited lithium metal layer is then moved to a glove box filled with argon gas for removal, thus obtaining the lithium metal anode (denoted as Cu-Li-3).

[0069] A lithium-ion battery, the preparation method of which includes the following steps:

[0070] A CR2016 coin cell was assembled using the lithium metal anode (Cu-Li-3) from the comparative example as both the positive and negative electrodes, with Celgard 2400 as the separator and a 1 mol / L LiFSI solution (using ethylene glycol dimethyl ether as the electrolyte) as the electrolyte, thus obtaining a lithium-ion battery.

[0071] According to the test (the test method is the same as in Example 1), the lithium-ion battery in this comparative example experienced a short circuit after only 100 hours.

[0072] Example 4:

[0073] A lithium metal anode, the preparation method of which includes the following steps:

[0074] PEO (number average molecular weight 1,000,000 g / mol), 1-ethyl-3-methylimidazolium difluorosulfonylimide ([EMI][FSI]), and NMP were mixed uniformly at a mass ratio of 1:0.3:5, and then uniformly coated onto a lithium metal sheet. The mixture was then vacuum dried at 60°C for 12 h to form a polymer-ionic liquid composite protective layer on the lithium metal sheet, resulting in a lithium metal anode (denoted as IEP-50-Li, with a polymer-ionic liquid composite protective layer thickness of 6 μm and an areal capacity of 16 mAh / cm²). 2 );

[0075] A lithium-ion battery, the preparation method of which includes the following steps:

[0076] Using the lithium metal anode (IEP-50-Li) of this embodiment as the positive and negative electrodes to assemble a CR2016 button battery, Celgard2400 as the separator, and a 1 mol / L LiFSI solution (with ethylene glycol dimethyl ether as the solvent) as the electrolyte, a lithium-ion battery is obtained.

[0077] According to the test (the test method is the same as in Example 1), the lithium-ion battery in this example can remain stable for 600 hours without any short circuit.

[0078] Example 5:

[0079] A lithium metal anode, the preparation method of which includes the following steps:

[0080] 1) PEO (number average molecular weight of 1,000,000 g / mol), 1-ethyl-3-methylimidazolium difluorosulfonylimide salt ([EMI][FSI]) and NMP are mixed evenly in a mass ratio of 1:0.3:5, and then uniformly coated on silver foil. The mixture is then vacuum dried at 60°C for 12 h to form a polymer-ionic liquid composite protective layer on the silver foil, resulting in a silver foil containing the polymer-ionic liquid composite protective layer (denoted as IEPA-30, with a thickness of 2 μm).

[0081] 2) Assemble CR2016 button cells in an argon-filled glove box. Use silver foil with a polymer-ionic liquid composite protective layer as the cathode, Celgard 2400 as the separator, a 1 mol / L LiFSI solution (ethylene glycol dimethyl ether as the solvent) as the electrolyte, and lithium foil as the anode. Then, perform electrochemical deposition on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time was 20 hours, during which a lithium metal layer was formed between the silver foil and the polymer-ionic liquid composite protective layer. The battery with the deposited lithium metal layer was then moved to an argon-filled glove box for removal, yielding the lithium metal anode (denoted as IEPA-30-Li, with an areal capacity of 4 mAh / cm²). 2).

[0082] A lithium-ion battery, the preparation method of which includes the following steps:

[0083] Using the lithium metal anode (IEPA-30-Li) of this embodiment as the positive and negative electrodes, a CR2016 button battery is assembled. Celgard2400 is used as the separator, and a 1 mol / L LiFSI solution (with ethylene glycol dimethyl ether as the solvent) is used as the electrolyte to obtain a lithium-ion battery.

[0084] According to the test (the test method is the same as in Example 1), the lithium-ion battery in this example can remain stable for 400 hours without any short circuit.

[0085] Comparative Example 3:

[0086] A lithium metal anode, the preparation method of which includes the following steps:

[0087] CR2016 button cells were assembled in an argon-filled glove box, using silver foil as the cathode, Celgard 2400 as the separator, a 1 mol / L LiFSI solution (ethylene glycol dimethyl ether as the solvent) as the electrolyte, and lithium foil as the anode. Electrochemical deposition was then performed on a LAND battery testing system at a current density of 0.2 mA / cm². 2 The deposition time is 20 hours to form a lithium metal layer on the silver foil. The battery with the deposited lithium metal layer is then moved to a glove box filled with argon gas for removal, thus obtaining the lithium metal anode (denoted as Ag-Li).

[0088] A lithium-ion battery, the preparation method of which includes the following steps:

[0089] Using the lithium metal anode (Ag-Li) from this comparative example as both the positive and negative electrodes, a CR2016 coin cell was assembled. Celgard 2400 was used as the separator, and a 1 mol / L LiFSI solution (with ethylene glycol dimethyl ether as the solvent) was used as the electrolyte to obtain a lithium-ion battery.

[0090] According to the test (the test method is the same as in Example 1), the lithium-ion battery in this comparative example experienced a short circuit after only 295 hours.

[0091] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A lithium metal anode, characterized in that, It is composed of a lithium metal layer and a polymer-ionic liquid composite protective layer; the polymer-ionic liquid composite protective layer is composed of a polymer and an ionic liquid; the mass ratio of the polymer to the ionic liquid is 1:0.1 to 0.9; the polymer is polyethylene oxide; the number average molecular weight of the polymer is 50,000 g / mol to 2,000,000 g / mol; the ionic liquid is 1-ethyl-3-methylimidazolium difluorosulfonylimide salt.

2. A lithium metal anode, characterized in that, It is composed of a metal substrate, a lithium metal layer, and a polymer-ionic liquid composite protective layer; the metal substrate is disposed on the side of the lithium metal layer away from the polymer-ionic liquid composite protective layer; the polymer-ionic liquid composite protective layer is composed of a polymer and an ionic liquid; the mass ratio of the polymer to the ionic liquid is 1:0.1 to 0.9; the polymer is polyethylene oxide; the number average molecular weight of the polymer is 50,000 g / mol to 2,000,000 g / mol; the ionic liquid is 1-ethyl-3-methylimidazolium difluorosulfonylimide salt.

3. The lithium metal anode according to claim 2, characterized in that: The metal substrate is composed of at least one of copper, aluminum, zinc, tin, magnesium, silver, gold, iron, sodium, and potassium.

4. The lithium metal anode according to claim 1 or 2, characterized in that: The thickness of the polymer-ionic liquid composite protective layer is 0.1 μm to 20 μm.

5. A method for preparing a lithium metal anode as described in claim 1, characterized in that, The process includes the following steps: coating a dispersion made of polymer, ionic liquid and organic solvent onto the surface of a lithium metal sheet, drying it to form a polymer-ionic liquid composite protective layer, thus obtaining a lithium metal anode.

6. A method for preparing a lithium metal anode as described in claim 2 or 3, characterized in that, Includes the following steps: A dispersion made of polymer, ionic liquid and organic solvent is coated on the surface of a metal substrate, dried to form a polymer-ionic liquid composite protective layer, and then immersed in a lithium ion-containing solution for electrodeposition to form a lithium metal layer between the metal substrate and the polymer-ionic liquid composite protective layer, thus obtaining a lithium metal anode. Alternatively, the metal substrate can be immersed in a lithium-ion-containing solution for electrodeposition to form a lithium metal layer on the surface of the metal substrate. Then, a dispersion made of polymer, ionic liquid and organic solvent can be coated on the surface of the lithium metal layer and dried to form a polymer-ionic liquid composite protective layer, thus obtaining the lithium metal anode.

7. A lithium-ion battery, characterized in that, The negative electrode is the lithium metal negative electrode according to any one of claims 1 to 4.

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