Composite metal lithium negative electrode and preparation method thereof

Abstract

The invention discloses a composite metal lithium negative electrode and a preparation method thereof, and the composite metal lithium negative electrode with an artificial SEI layer is obtained by coating a lithium metal negative electrode base material with para-aramid nanofibers and forming an ultrathin aramid nanofiber (ANF) membrane with a net structure on the lithium metal negative electrode base material. The artificial SEI layer with excellent ion transmission rate and high electrolyte affinity is arranged on the surface of the composite metal lithium negative electrode, so that the problems of safety and interface stability of the metal lithium negative electrode can be solved, the resistance of an interface between the metal lithium negative electrode and an electrolyte can be reduced, the electrochemical performance of a battery is improved, and the service life of the battery is prolonged. The industrialization of the lithium metal battery is favorably promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage, and in particular, to a composite metal lithium anode and a preparation method thereof. Background Art

[0002] In terms of energy density, traditional lithium-ion batteries have approached the theoretical limit and cannot meet the growing social demand for advanced power sources. Against this background, researchers have turned their attention to high-energy-density lithium metal batteries (LMBs). Due to the lowest electrochemical potential of lithium metal (-3.04 V relative to the standard hydrogen electrode) and an ultra-high theoretical specific capacity of 3860 mAh·g -1 , the lithium metal anode (LMA) has become one of the most ideal candidate materials for manufacturing high-energy rechargeable batteries. However, due to large volume changes during the repeated lithium plating / stripping process, instability of the solid electrolyte interface (SEI), and growth of lithium dendrites, etc., the stability of LMBs has not been solved yet. The growth of lithium dendrites may pierce the separator to cause a circuit, posing a great safety hazard. Lithium dendrites not only may cause safety problems but also detach from the electrode to form electrochemically inactive "dead lithium". Therefore, with the increase of overpotential, the capacity of LMA decays rapidly and cannot be used in actual batteries. Therefore, suppressing the growth of Li dendrites and inducing uniform Li deposition are crucial for constructing an efficient LMA suitable for LMBs. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a composite metal lithium anode and a preparation method thereof.

[0004] The present invention proposes a preparation method of a composite metal lithium anode, comprising the following steps:

[0005] S1. Mix chopped para-aramid fibers, dimethyl sulfoxide, a strong base, and a proton donor solvent, and then fully crack them under stirring to obtain a para-aramid nanofiber dispersion;

[0006] S2. Add a proton donor solvent to the para-aramid nanofiber dispersion under stirring until a gel-like substance precipitates;

[0007] S3. Add the gel-like substance to a proton donor solvent, first perform ultrasonic treatment, and then stir and disperse it to obtain a para-aramid nanofiber coating solution;

[0008] S4. Coat the para-aramid nanofiber coating solution on a metal lithium anode substrate, and dry it to form an aramid nanofiber membrane, thereby obtaining a metal lithium anode with an artificial SEI layer.

[0009] In the present invention, para-aramid nanofibers are coated on the lithium metal negative electrode substrate to form an ultra-thin aramid nanofiber (ANF) film with a network structure on the lithium metal negative electrode substrate, which inhibits the growth of Li dendrites and induces uniform Li deposition. The above ANF film covers the surface of the lithium metal to form an artificial SEI layer, which has the characteristics of fast electrolyte diffusion rate and high lithium ion conductivity, and can inhibit the generation of lithium dendrites, effectively improving the electrochemical performance and safety of the battery, thereby obtaining an efficient lithium metal anode suitable for LMBs.

[0010] Preferably, in S1, the diameter of the para-aramid nanofibers is 5-20 nm and the length is 6-8 μm. By controlling the diameter of the para-aramid nanofibers obtained by pyrolysis, the formed aramid nanofiber (ANF) film has a suitable pore diameter, which can promote the ion transport in the electrolyte, thereby reducing the formation of Li dendrites.

[0011] Preferably, in S1, the mass ratio of the para-aramid short fibers to the strong base is 1:(1.5-3), the ratio of the para-aramid short fibers to dimethyl sulfoxide is (0.1-1) g:100 mL, and the volume ratio of the proton donor solvent to dimethyl sulfoxide is 0.2-1.5:3.5-5.5. By controlling the solvent environment used for the pyrolysis of the para-aramid short fibers, the pyrolysis can be more complete, and the obtained para-aramid nanofibers have a more uniform morphology, so that the pores of the ANF film formed on the lithium metal negative electrode substrate are more uniform, which is beneficial to further reducing the formation of Li dendrites.

[0012] Preferably, the strong base is NaOH, KOH or a combination thereof.

[0013] Preferably, in S1, the stirring speed is 1000-2000 rpm.

[0014] Preferably, in S2, the volume ratio of the para-aramid nanofiber dispersion to the proton donor solvent is 0.4-1:1.5-2. By controlling the appropriate volume ratio of the para-aramid nanofiber dispersion to the proton donor solvent, the para-aramid nanofibers in the solution can settle sufficiently, improving the yield.

[0015] Preferably, in S2, the stirring speed is 1000-2000 rpm.

[0016] Preferably, in S3, the power of the ultrasonic treatment is 50-150 W, and the time is 30-60 min; in S3, the temperature of the stirring and dispersion is 30-80 °C, the rotation speed is 1000-2000 rpm, and the time is 10-20 h. By controlling the appropriate process parameters of the ultrasonic treatment and the stirring and dispersion, the uniformity of the coating liquid can be effectively improved, so that the ANF film formed by coating on the lithium metal negative electrode substrate is more uniform, which is beneficial to further improve the uniform distribution of Li ions and reduce the formation of Li dendrites.

[0017] Preferably, in S3, the solid content of the para-aramid nanofiber coating liquid is 85%-97%. By controlling the appropriate solid content of the para-aramid nanofiber coating liquid, the formed ANF film can be made more uniform, which is beneficial to further improve the uniform distribution of Li ions and reduce the formation of Li dendrites.

[0018] Preferably, the proton donor solvent is at least one of deionized water, isopropanol, absolute ethanol, and tert-butanol.

[0019] Preferably, in S4, the thickness of the aramid nanofiber membrane is 40-60 μm.

[0020] Preferably, in S4, the drying temperature is 105-250 °C.

[0021] Preferably, the lithium metal negative electrode substrate is a lithium sheet or a lithium strip.

[0022] Preferably, in S4, the coating method is drop coating, spraying or blade coating.

[0023] The present invention also provides a composite lithium metal negative electrode prepared by the above preparation method.

[0024] The beneficial effects of the present invention are as follows:

[0025] The present invention provides a composite lithium metal negative electrode with an artificial SEI layer and a preparation method thereof. The artificial SEI layer is an aramid nanofiber (ANF) film. On the one hand, there are a large number of polar functional groups (C=O, N-H) on the surface and structure of the ANF film. These functional groups provide high-concentration functional sites for the efficient adhesion and uniform distribution of Li ions at the molecular level. On the other hand, the nanoscale porosity of the ANF film provides a fast path for the diffusion of the electrolyte, while reducing the risk of being pierced by micron-scale lithium dendrites. Moreover, the ANF film also has ultra-high stability and a high safety factor. In summary, the composite lithium metal negative electrode of the present invention has an artificial SEI layer with excellent ion transport rate and high electrolyte affinity on its surface, which can solve the safety and interfacial stability problems of the lithium metal negative electrode, and can reduce the resistance at the interface between the lithium metal electrode and the electrolyte, improve the electrochemical performance of the battery, and is beneficial to promoting the industrialization of lithium metal batteries. Description of the Drawings

[0026] Figure 1 This is a performance test chart of the full charge cycle capacity retention rate when the composite metal lithium anode (ANF-Li) of the present invention and the ordinary metal lithium anode (Li) without an artificial SEI layer on the surface are respectively assembled with the LFP cathode into a battery at 1C.

[0027] Figure 2 This is a performance test chart of the full charge cycle capacity when the ANF-Li anode of the present invention and the ordinary metal lithium anode (Li) without an artificial SEI layer on the surface are respectively assembled with the LFP cathode into a battery at 1C. Detailed Description of the Invention

[0028] Next, the technical solution of the present invention will be described in detail through specific embodiments.

[0029] Example 1

[0030] A preparation method of a composite metal lithium anode includes the following steps:

[0031] S1. After mixing 0.1 g of para-aramid short cut fibers, 100 mL of dimethyl sulfoxide, 0.15 g of KOH, and 4 mL of deionized water, they are fully cracked under stirring at room temperature. The stirring speed is 1500 rpm, and the stirring time is 4 h to obtain a para-aramid nanofiber dispersion liquid, where the diameter of the para-aramid nanofibers is 15 nm and the length is 8 μm;

[0032] S2. Under stirring, 200 mL of isopropanol is added to 100 mL of the para-aramid nanofiber dispersion liquid until a gel-like substance precipitates, where the stirring speed is 1500 rpm;

[0033] S3. The gel-like substance is added to isopropanol, first ultrasonicated at a power of 90 W for 30 min, and then stirred and dispersed at 50°C and 1500 rpm for 12 h to obtain a para-aramid nanofiber coating liquid with a solid content of 87%;

[0034] S4. The para-aramid nanofiber coating liquid is double-sided coated on a metal lithium anode substrate and dried at 150°C to form an ANF film with a thickness of 48 μm, obtaining a composite metal lithium anode.

[0035] The above-prepared composite metal lithium anode (ANF-Li) and the ordinary metal lithium anode (Li) without an artificial SEI layer on the surface and the lithium iron phosphate (LFP) cathode are respectively assembled into a battery for a full charge cycle performance test at 0.5C. Figure 1 And Figure 2The full charge cycle capacity retention rate and capacity performance test diagrams at 1C of the batteries assembled with the above-prepared composite metal lithium anode (ANF-Li) and the ordinary metal lithium anode (Li) without an artificial SEI layer on the surface, respectively, and the lithium iron phosphate cathode. From Figure 2 it can be seen that the initial specific capacities of the batteries assembled with the two anodes are similar, being 125.4 mAh·g -1 and 123.8 mAh·g -1 . After 2000 cycles, the reversible discharge capacity of the fully charged ANF-Li / LFP battery reaches 122.2 mAh·g -1 , while the reversible discharge capacity of the Li / LFP battery is 108.5 mAh·g -1 . . From Figure 1 it can be seen that after 3500 cycles, the ANF-Li / LFP fully charged battery has a stable Coulomb efficiency of nearly 95%. While at 3000 cycles, the Coulomb efficiency of the Li / LFP battery is lower than 85%. This shows that the electrochemical cycle stability of the composite metal lithium anode with an artificial SEI layer of the present invention is much higher than that of the ordinary metal lithium anode without an artificial SEI layer on the surface.

[0036] Example 2

[0037] A preparation method of a composite metal lithium anode, comprising the following steps:

[0038] S1. After mixing 0.2 g of para-aramid short-cut fibers, 100 mL of dimethyl sulfoxide, 0.3 g of KOH, and 4 mL of deionized water, fully crack them under stirring at room temperature. The stirring speed is 1500 rpm, and the stirring time is 4 h to obtain a para-aramid nanofiber dispersion liquid, wherein the diameter of the para-aramid nanofibers is 17 nm and the length is 6 μm;

[0039] S2. Under stirring, add 200 mL of isopropanol to 100 mL of the para-aramid nanofiber dispersion liquid until a gel-like substance precipitates, wherein the stirring speed is 1500 rpm;

[0040] S3. Add the gel-like substance to isopropanol, first perform ultrasonic treatment at a power of 90 W for 30 min, and then stir and disperse it at 70 °C and 1500 rpm for 12 h to obtain a para-aramid nanofiber coating liquid with a solid content of 88%;

[0041] S4. Double-side coat the para-aramid nanofiber coating liquid on the metal lithium anode substrate, and dry it at 150 °C to form an ANF film with a thickness of 44 μm to obtain the composite metal lithium anode.

[0042] Example 3

[0043] A preparation method of a composite metal lithium anode, comprising the following steps:

[0044] S1. Mix 0.3 g of para-aramid short-cut fibers, 100 mL of dimethyl sulfoxide, 0.45 g of KOH, and 4 mL of deionized water, and then fully lyse them under stirring at room temperature. The stirring speed is 1500 rpm, and the stirring time is 4 h to obtain a para-aramid nanofiber dispersion. The diameter of the para-aramid nanofibers is 11 nm and the length is 6 μm.

[0045] S2. While stirring, add 200 mL of isopropanol to 100 mL of the para-aramid nanofiber dispersion until a gel-like substance precipitates. The stirring speed is 1500 rpm.

[0046] S3. Add the gel-like substance to isopropanol, first perform ultrasonic treatment at a power of 90 W for 30 min, and then stir and disperse it at 30 °C and 1500 rpm for 12 h to obtain a para-aramid nanofiber coating solution with a solid content of 95%.

[0047] S4. Double-side coat the para-aramid nanofiber coating solution on a metallic lithium negative electrode substrate, and dry it at 150 °C to form an ANF film with a thickness of 47 μm to obtain a composite metallic lithium negative electrode.

[0048] Example 4

[0049] A method for preparing a composite metallic lithium negative electrode, comprising the following steps:

[0050] S1. Mix 0.2 g of para-aramid short-cut fibers, 100 mL of dimethyl sulfoxide, 0.3 g of KOH, and 4 mL of deionized water, and then fully lyse them under stirring at room temperature. The stirring speed is 2000 rpm, and the stirring time is 4 h to obtain a para-aramid nanofiber dispersion. The diameter of the para-aramid nanofibers is 12 nm and the length is 7.5 μm.

[0051] S2. While stirring, add 200 mL of isopropanol to 100 mL of the para-aramid nanofiber dispersion until a gel-like substance precipitates. The stirring speed is 2000 rpm.

[0052] S3. Add the gel-like substance to isopropanol, first perform ultrasonic treatment at a power of 50 W for 60 min, and then stir and disperse it at 60 °C and 2000 rpm for 10 h to obtain a para-aramid nanofiber coating solution with a solid content of 92%.

[0053] S4. Double-side coat the para-aramid nanofiber coating solution on a metallic lithium negative electrode substrate, and dry it at 200 °C to form an ANF film with a thickness of 43 μm to obtain a composite metallic lithium negative electrode.

[0054] Example 5

[0055] A preparation method of a composite metal lithium anode, comprising the following steps:

[0056] S1. After mixing 0.1 g of para-aramid short-cut fibers, 100 mL of dimethyl sulfoxide, 0.15 g of KOH, and 4 mL of deionized water, fully crack them under stirring at room temperature. The stirring speed is 1500 rpm, and the stirring time is 4 h to obtain a para-aramid nanofiber dispersion liquid, wherein the diameter of the para-aramid nanofibers is 12 nm and the length is 6 μm;

[0057] S2. Under stirring, add 200 mL of absolute ethanol to 100 mL of the para-aramid nanofiber dispersion liquid until a jelly-like substance precipitates, wherein the stirring speed is 1500 rpm;

[0058] S3. Add the jelly-like substance to absolute ethanol, first perform ultrasonic treatment at a power of 90 W for 30 min, and then stir and disperse at 70 °C and 1500 rpm for 12 h to obtain a para-aramid nanofiber coating liquid with a solid content of 95%;

[0059] S4. Double-side coat the para-aramid nanofiber coating liquid on a metal lithium anode substrate, and dry it at 250 °C to form an ANF film with a thickness of 43 μm to obtain a composite metal lithium anode.

[0060] As mentioned above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a composite metal lithium negative electrode, characterized in that: The following steps are involved: S1, after mixing para-aramid chopped fibers, dimethyl sulfoxide, a strong base and a proton donor solvent, the mixture is fully cracked under stirring to obtain a para-aramid nanofiber dispersion; S2. adding a proton donor solvent to the para-aramid nanofiber dispersion under stirring until a colloid is precipitated; S3, adding the colloid into a proton donor solvent, firstly performing an ultrasonic treatment, and then stirring and dispersing the colloid to obtain a para-aramid nanofiber coating liquid; S4, coating the para-aramid nanofiber coating liquid on both sides of the metal lithium negative electrode substrate, drying to form an aramid nanofiber film, and obtaining a composite metal lithium negative electrode.

2. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S1, the diameter of the para-aramid nanofiber is 5 to 20 nm and the length is 6 to 8 μm.

3. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S1, the mass ratio of the para-aramid chopped fibers to the strong base is 1:(1.5-3), the ratio of the para-aramid chopped fibers to dimethyl sulfoxide is (0.1-1) g:100 mL, the volume ratio of the proton donor solvent to dimethyl sulfoxide is 0.2-1.5:3.5-5.5; and the strong base is NaOH, KOH or a combination thereof.

4. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S2, the volume ratio of the para-aramid nanofiber dispersion to the proton donor solvent is 0.4-1:1.5-2.

5. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S3, the power of ultrasonic treatment is 50-150W, and the time is 30-60min; in S3, the temperature of stirring and dispersing is 30-80°C, the rotation speed is 1000-2000rpm, and the time is 10-20h.

6. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S3, the solid content of the para-aramid nanofiber coating liquid is 85% to 97%.

7. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: The proton donor solvent is at least one of deionized water, isopropanol, anhydrous ethanol and tert-butanol.

8. The method for preparing a composite metal lithium negative electrode according to claim 1, characterized in that: In S4, the thickness of the aramid nanofiber membrane is 40 to 60 μm.

9. A composite metal lithium negative electrode, characterized in that: The method is prepared according to any one of claims 1 to 8.

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