Self-healing coating, lithium metal negative electrode and preparation method and application of lithium metal negative electrode
By forming a self-healing coating with multiple hydrogen bonds on the negative electrode surface of the lithium metal battery, the problem of excessive growth and reactivity of lithium dendrites is solved, and the higher stability and safety of lithium metal battery is achieved.
Patent Information
- Application Number
- CN202510229380.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-28
- Publication Date
- 2025-06-03
AI Technical Summary
Lithium metal batteries have safety and cycle stability problems, mainly manifested in the excessive growth and reaction activity of lithium dendrites, resulting in short circuit, thermal runaway and capacity attenuation.
The self-healing monomer with multiple hydrogen bonds is used to copolymerize with fluorine-containing acrylate monomers and dopant with lithium salts to form a self-healing protective coating on the surface of the lithium metal by in-situ polymerization.
This self-healing coating can self-heal when the coating breaks, promotes uniform deposition of lithium ions, improves the stability of lithium metal negative electrodes and battery cycle life, significantly inhibits the growth of lithium dendrites, and improves battery safety.
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Figure CN120082248A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of lithium metal anode materials, and particularly relates to a self-healing coating, a lithium metal anode, and a preparation method and application thereof. Background Art
[0002] In recent years, industries such as new energy vehicles, green energy, and smart power grids have developed rapidly. People's demand for batteries with high energy density and high safety has become increasingly urgent. Traditional liquid lithium-ion batteries use flammable and explosive organic electrolytes, and the safety issue has become increasingly prominent, gradually becoming a key problem restricting the development of lithium-ion batteries.
[0003] Lithium metal batteries are high-energy-density batteries. Their core advantage lies in that lithium metal has the lowest electrode potential (-3.04V vs. standard hydrogen electrode) and extremely high theoretical specific capacity (3860 mAh / g). This makes lithium metal batteries far exceed traditional lithium-ion batteries in terms of energy density and are expected to become the core of the next-generation energy storage technology. However, lithium metal batteries also have significant defects: one is the safety issue. Lithium metal is prone to form lithium dendrites during charge and discharge. The dendrites may pierce the separator, resulting in short circuits, triggering thermal runaway and even explosion; the other is poor cycle stability. Lithium metal reacts with the electrolyte to form an unstable solid electrolyte interface (SEI), resulting in low Coulomb efficiency and rapid capacity decay. Currently, the use of metallic lithium anodes is restricted due to the intense reaction between the lithium metal surface and the electrolyte, uneven deposition of lithium, and lithium dendrite growth.
[0004] Regarding the problem of lithium dendrite growth on lithium metal anodes, the existing solutions include: Method 1: Using solid electrolytes; Method 2: Lithium metal alloying. Alloying can effectively inhibit the formation of lithium dendrites, improve the safety and cycle life of lithium metal batteries by reducing lithium activity, uniform deposition, enhancing mechanical strength, optimizing electrochemical performance, and enhancing interface stability; Method 3: Using electrolyte additives to form a SEI layer on the lithium metal surface that is stable enough for lithium to inhibit lithium dendrites. In addition to the above three common methods, there is also a method of artificially coating a protective layer on the lithium metal surface to inhibit the intense reaction between metallic lithium and the electrolyte, regulate the uniform deposition of lithium ions, reduce lithium dendrite growth, and thus improve the cycle stability of lithium metal batteries. Although this method of artificially coating a protective layer can play a role in inhibiting dendrites, the coating has the problem of cracking during battery cycling. Once the coating cracks, the exposed lithium metal is directly exposed to the electrolyte, and dendrites will grow rapidly at the coating cracks.
[0005] The self-healing lithium metal coating with chitosan as the main chain reported in the literature (Nature Communications, 2023, 14, 4018) can increase the cycle life of lithium-lithium symmetric batteries by more than 50 times and can operate at 10 mA / cm2 It can stably cycle for 3000 hours under a high current density. Another example is the literature (Nano Energy, 2022, 93, 106871), which uses a siloxane-based self-healing coating to significantly reduce the polarization voltage of lithium-lithium symmetric batteries, enabling the battery to stably cycle for more than 1000 hours. However, the above coating preparation process requires the use of DMSO or DME as a solvent, and then the coating is loaded on the lithium metal surface by solvent evaporation method, and the preparation process is complex.
[0006] Therefore, it is necessary to provide an improved self-healing coating to solve the above problems. Summary of the Invention
[0007] The purpose of the present invention is to provide a self-healing coating, a lithium metal negative electrode, and their preparation methods and applications. A self-healing monomer with multiple hydrogen bonds is copolymerized with a fluoroacrylate monomer and doped with a lithium salt, and a self-healing protective coating is formed on the lithium metal surface by in-situ polymerization, so as to improve the stability of the lithium metal negative electrode and the battery cycle life, and solve problems such as dendrites and excessive reaction activity of the lithium metal negative electrode.
[0008] To achieve the above purpose, the first aspect of the present invention provides a self-healing coating, the raw material components of which include monomers, lithium salts, and initiators; the monomers include fluoroacrylate substances and ureidopyrimidinone methacrylate; the raw material components are mixed and cured to obtain the self-healing coating; the molar content of ureidopyrimidinone methacrylate in the monomers is 0.1%-4%.
[0009] Further, the fluoroacrylate substance is 2,2,2-trifluoroethyl acrylate or hexafluorobutyl acrylate.
[0010] Further, the molar content of ureidopyrimidinone methacrylate in the monomers is 0.5%-4%.
[0011] Further, the concentration of the lithium salt in the mixture of the raw material composition is 0.5-2 mol / L, preferably 0.8-1.2 mol / L; and / or, the dosage of the initiator is 0.1 wt%-0.5 wt% of the total mass of the precursor solution.
[0012] Further, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium hexafluorophosphate; and / or, the initiator is a photoinitiator, preferably including one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.
[0013] In a second aspect, the present invention provides a method for preparing a self-healing coating as described in any one of the above, comprising: uniformly mixing a fluorinated acrylate, ureidopyrimidinone methacrylate, a lithium salt, and an initiator to obtain a precursor solution, and then forming a film and curing it to obtain a self-healing coating.
[0014] Further, the film formation is achieved by drop coating, blade coating, spraying, or dipping; the curing is carried out under ultraviolet light irradiation for a time of 0.5 - 2 h.
[0015] In a third aspect, the present invention provides a lithium metal anode, on the surface of which a self-healing coating as described in any one of the above is covered. The precursor solution is drop-coated on the lithium metal surface, and in-situ polymerization is initiated by ultraviolet light to form a self-healing protective coating on the lithium metal surface.
[0016] Further, the thickness of the self-healing coating is 5 - 30 μm.
[0017] In a fourth aspect, the present invention provides a lithium battery, including a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode of the lithium battery is the lithium metal anode as described above.
[0018] The positive electrode of the above lithium battery includes a positive electrode active material, preferably including an intercalation compound positive electrode material (LiFePO 4 ), and the electrolyte includes a liquid electrolyte, preferably a commercial liquid electrolyte LB015.
[0019] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:
[0020] 1. The lithium metal anode with a self-healing coating provided by the present invention uses a self-healing monomer, ureidopyrimidinone methacrylate with multiple hydrogen bonds, to copolymerize with a fluorinated acrylate monomer and adds a lithium salt doping, and forms a self-healing protective coating on the lithium metal surface through in-situ polymerization. The monomer containing multiple hydrogen bonds in the coating is beneficial to self-repair in time when the coating is broken, the fluorinated acrylate monomer can promote the uniform deposition of lithium ions, and the lithium salt helps to improve the ionic conductivity of the polymer. The self-healing coating maintains its structural integrity through rapid and excellent self-healing, realizes long-term protection of lithium metal, solves the problems of the destruction of the SEI film on the surface of the lithium metal anode and the growth of lithium dendrites, thereby improving the stability during the cycling process of the lithium metal battery and avoiding the growth of dendrites.
[0021] 2. 2,2,2-Trifluoroethyl acrylate rich in fluorine atoms has excellent ability to bind with lithium ions. The surface of the lithium metal has a -CF 3 group rich in fluorine atoms, which regulates the uniform deposition of lithium ions on the lithium metal surface, greatly reduces the growth of lithium dendrites, makes the surface of the lithium metal more stable, and enables it to work at a high current density.
[0022] 3. By regulating the dosages of fluorinated acrylate substances and ureidopyrimidinone methacrylate, the self-healing ability and the effect of lithium ion deposition are regulated, so as to obtain a lithium metal negative electrode with a self-healing coating and good comprehensive performance.
[0023] 4. During the preparation process of the present invention, the use of solvents is avoided. There is no need to remove the solvents by evaporation method, which avoids the influence of solvent residues on the coating performance and reduces environmental pollution.
[0024] 5. The in-situ polymerization is adopted in the preparation process, which is beneficial to the close fitting of the coating and the lithium metal, reduces the interfacial impedance between the lithium metal negative electrode and the SEI layer. The preparation process is simple and has certain application value and commercialization potential. Description of the Drawings
[0025] Figure 1 It is the verification of the self-healing performance of the self-healing coating material prepared in Example 1 of the present invention.
[0026] Figure 2 Cross-sectional scanning electron microscope (SEM) image of the self-healing coating material prepared in Example 3 of the present invention.
[0027] Figure 3 Tensile property test of the self-healing coating materials prepared in Example 1, Comparative Specimen 1 and Comparative Specimen 2 of the present invention.
[0028] Figure 4 It is the in-situ lithium deposition experiment of the copper foil with a self-healing coating and the bare copper foil prepared in Example 2 of the present invention.
[0029] Figure 5 It is the voltage-time graph of the lithium-lithium symmetric battery of Example 4 and Comparative Specimen 4 at different current densities.
[0030] Figure 6 It is the cyclic voltage-time graph of the lithium-lithium symmetric batteries of Example 4, Comparative Specimen 4 and Comparative Specimen 5.
[0031] Figure 7 It is for Example 5 and Comparative Specimen 6 with LiFePO 4 as the positive electrode and LiPF 6 / EC:DMC (1:1) as the electrolyte to assemble the cyclic performance graph of the lithium metal battery. Detailed Embodiments
[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0033] The self-healing lithium metal coating can automatically repair the cracks in the SEI layer at the initial stage of the formation of lithium dendrites by coating a layer of polymer or composite material with self-healing function on the surface of lithium metal, and maintain the integrity of its own structure. At the same time, the self-healing coating can also reduce the side reaction between lithium metal and electrolyte, promote the uniform deposition of lithium ions, thereby inhibiting the growth of lithium dendrites and enhancing safety. This technology provides important support for the commercial application of lithium metal batteries. Based on this, the present invention provides a preparation method of a metal lithium negative electrode with a self-healing coating, in which a self-healing monomer, a fluorine-containing monomer, a lithium salt and an initiator are configured into a precursor solution, and then an in-situ polymerization is initiated by ultraviolet light to form a self-healing protective layer for the lithium metal negative electrode.
[0034] The specific preparation steps are as follows:
[0035] (1) According to the molar ratio, 2,2,2-trifluoroethyl acrylate, ureidopyrimidinone methacrylate, and LiTFSI are formulated into a clear solution. 0.5 wt% of the photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone is added to the solution, and it is stirred in a glove box until it is clear and transparent, and the temperature condition is room temperature;
[0036] (2) The precursor solution is drop-coated on the surface of lithium metal by the drop-coating method, and it should be ensured that the surface of lithium metal is completely covered without exposed lithium metal;
[0037] (3) In-situ polymerization is initiated by ultraviolet light on the surface of lithium metal to form a self-healing coating.
[0038] The present invention does not involve solvents in the whole process of coating preparation and does not require solvent removal.
[0039] The main body of the self-healing coating is copolymerized from 2,2,2-trifluoroethyl acrylate (TFA) and ureidopyrimidinone methacrylate (UPyMA).
[0040] The self-healing polymer of the lithium metal battery negative electrode coating with self-healing function can be expressed as TFA-x-UPyMA@Li.
[0041] Among them, in the chemical formula, x represents the molar fraction of the self-healing monomer UPyMA in the total monomers, and the value range of x is 0 < x < 5. For example, when x = 2, TFA-2-UPyMA@Li means that the molar fraction of the UPyMA monomer in the polymer is 2%, and correspondingly the molar fraction of the TFA monomer is 98%.
[0042] Since the C-F single bond is one of the strongest known single bonds with a bond energy of about 485 kJ / mol, its high stability and strength enable its wide application in heat-resistant and chemically corrosion-resistant materials. In addition, the F atom has a strong electronegativity and a small radius, making it easier to combine with lithium ions and capable of regulating the uniform transport and deposition of lithium ions. Therefore, poly(2,2,2-trifluoroethyl acrylate) rich in -CF 3 groups is used for the coating of lithium metal anodes. It can not only be compatible with high-voltage cathode materials, but also contribute to the uniform deposition of lithium ions on the lithium metal surface and inhibit the growth of lithium dendrites. In addition, the quadruple hydrogen bond within the methacryloyl ureidopyrimidinone molecule can endow the polymer with self-healing properties. Compared with ordinary polymer materials, the polymer containing methacryloyl ureidopyrimidinone in the structural unit has the following characteristics: First, the quadruple hydrogen bond of the methacryloyl ureidopyrimidinone molecule can endow the polymer with self-healing performance, and the polymer can actively self-repair after fracture; Second, the multiple hydrogen bonds act as binders to increase the Young's modulus of the polymer, increase the stress on lithium dendrites, and further inhibit lithium dendrites;
[0043] The lithium metal anode coating of the present invention can combine self-healing monomers with monomers rich in -CF 3 to not only maintain the integrity of the coating structure itself, but also be compatible with high-voltage cathodes and inhibit the growth of lithium dendrites.
[0044] The present invention will be described in detail below in conjunction with specific embodiments.
[0045] Example 1
[0046] The liquid of 2,2,2-trifluoroethyl acrylate (TFA) with a raw material purity of 99% and the powder of methacryloyl ureidopyrimidinone (UPyMA) were mixed in a sample bottle in a molar ratio of TFA:UPYMA = 49:1 in a glove box filled with argon. The powder of LiTFSI with a purity of 99.9% was added, and the addition amount was 1 mol of LiTFSI per liter of TFA, that is, the concentration of LiTFSI in TFA was 1 mol / L. And 2-hydroxy-2-methyl-1-phenylpropanone as an initiator accounting for 0.5 wt% of the total mass of the precursor solution was added, and magnetic stirring was carried out in a glove box protected by inert gas. Stirring was continuously carried out at room temperature for 1 hour, and the precursor solution was a colorless transparent liquid. The precursor solution was injected into a rectangular mold with a length of 100 mm and a width of 15 mm, and ultraviolet light polymerization was carried out for 1 hour to obtain a self-healing film.
[0047] Example 2
[0048] The liquid of 2,2,2-trifluoroethyl acrylate with a raw material purity of 99% and the powder of ureidopyrimidinone methacrylate were mixed in a glove box filled with argon according to the molar ratio TFA:UPYMA = 49:1. The powder of LiTFSI with a purity of 99.9% was added to make the lithium salt concentration 1 mol / L, and the initiator 2-hydroxy-2-methyl-1-phenylpropanone with a mass fraction of 0.5 wt% was added. The mixture was magnetically stirred in the glove box protected by inert gas until it became colorless and transparent. After continuously stirring at room temperature for 1 hour, the precursor solution was a clear and transparent liquid. 20 μL of the precursor solution was drop-coated on the surface of a copper foil with a length of 40 mm and a width of 10 mm, and in-situ polymerization was initiated by ultraviolet light for 1 hour to obtain a copper foil with a self-healing coating.
[0049] Example 3
[0050] The liquid of 2,2,2-trifluoroethyl acrylate with a raw material purity of 99% and the powder of ureidopyrimidinone methacrylate were added to a sample bottle in a glove box filled with argon according to the molar ratio TFA:UPYMA = 49:1. The powder of LiTFSI with a purity of 99.9% was added to make the lithium salt concentration of the precursor solution 1 mol / L, and the initiator 2-hydroxy-2-methyl-1-phenylpropanone with a mass fraction of 0.5 wt% was added. The mixture was magnetically stirred in the glove box protected by inert gas. After continuously stirring at room temperature for 1 hour, the precursor solution was a colorless and transparent liquid. 8 μL of the precursor solution was drop-coated on the surface of a circular lithium metal with a diameter of 12 mm, and in-situ polymerization was initiated by ultraviolet light for 1 hour to obtain a lithium metal negative electrode with a self-healing coating. As Figure 2 shown, it can be seen that the thickness of the self-healing coating is about 19.19 μm.
[0051] Example 4
[0052] The lithium metal negative electrode with a self-healing coating prepared in Example 3, the Celgard 2500 separator, and the commercial electrolyte LB015 were assembled into a lithium-lithium symmetric battery in a glove box protected by argon.
[0053] Example 5
[0054] Using LiFePO 4 as the positive electrode, using LiPF 6 / EC:DMC (1:1) as the electrolyte, and a commercial polypropylene separator as the separator, a battery was assembled with the metal lithium protected by the method in Example 3 as the negative electrode.
[0055] Comparative Specimen 1
[0056] The liquid of 2,2,2-trifluoroethyl acrylate with a raw material purity of 99% and the powder of uracil pyrimidinone methacrylate were added into a sample bottle in a glove box filled with argon according to a molar ratio of TFA:UPYMA = 19:1. The powder of LiTFSI with a purity of 99.9% was added to make the lithium salt concentration of the precursor solution 1 mol / L and the initiator 2-hydroxy-2-methyl-1-phenylpropanone with a mass fraction of 0.5 wt%. Magnetic stirring was carried out in the glove box protected by inert gas. Stirring was continuously carried out at room temperature for 1 hour, and the precursor solution was a colorless transparent liquid. The precursor solution was injected into a rectangular mold with a length of 100 mm and a width of 15 mm, and ultraviolet light was irradiated for polymerization for 1 hour to obtain a self-healing film.
[0057] Comparative sample 2
[0058] The liquid of 2,2,2-trifluoroethyl acrylate with a raw material purity of 99% was added into a sample bottle in a glove box filled with argon according to the same mass as described in Example 1. The powder of LiTFSI with a purity of 99.9% was added to make the lithium salt concentration of the precursor solution 1 mol / L and the initiator 2-hydroxy-2-methyl-1-phenylpropanone with a mass fraction of 0.5 wt%. Magnetic stirring was carried out in the glove box protected by inert gas. Stirring was continuously carried out at room temperature for 1 hour, and the precursor solution was a colorless transparent liquid. The precursor solution was injected into a rectangular mold with a length of 100 mm and a width of 15 mm, and ultraviolet light was irradiated for polymerization for 1 hour to obtain a self-healing film.
[0059] Comparative sample 3: Bare copper foil.
[0060] Comparative sample 4: A lithium-lithium symmetric battery was fabricated in the same manner as in Example 4, except that: bare lithium was used instead of lithium metal with a self-healing protective coating to assemble the lithium-lithium symmetric battery.
[0061] Comparative sample 5: A lithium-lithium symmetric battery was fabricated in the same manner as in Example 4, except that: the polymer described in Comparative sample 2 was used as the coating instead of lithium metal with a self-healing protective coating to assemble the lithium-lithium symmetric battery.
[0062] Comparative sample 6: A lithium metal battery was fabricated in the same manner as in Example 5, except that: unprotected bare lithium metal was used as the negative electrode to assemble the battery.
[0063] Experimental test methods and analysis:
[0064] Self-healing performance test: The self-healing polymer film described in Example 1 is prepared in a glove box into a long strip of polymer sample with a width of 100 mm, a length of not less than 15 m, and a thickness of about 1 mm; the sample is cut with a blade from half of the length into two halves. The blade should be kept sharp during the cutting process and a suitable cushioning material should be used to ensure a smooth cut; the cuts of the two halves of the sample are completely aligned and pressed together, and the time is maintained for 10 seconds. A low-power magnifying glass is used to check the joint to ensure that there is no obvious gap at the joint; after 10 seconds, a weight of 30 g is hung at one end of the sample, and the other end is lifted to observe whether the sample is broken; if Figure 1 , the coating material with self-healing function will not break, indicating that it has good self-healing properties.
[0065] Tensile test: The self-healing polymer film described in Example 1 (original intact self-healing film) and the comparative test sample 1 and the comparative sample 2 were subjected to a tensile test at a tensile rate of 5 mm / min and a test temperature of room temperature. The test results are shown in FIG. Figure 3 As shown in Table 1. It can be seen from the test results that with the increase of the content of the multiple hydrogen-bonded molecule UPyMA, the Young's modulus of the polymer is significantly improved. The larger the Young's modulus of the coating, the greater the stress on the lithium dendrites, which is beneficial to inhibit the growth of lithium dendrites. However, Young's modulus and elongation at break are often not achieved at the same time. A coating with too large a Young's modulus may have problems such as cracking, breakage, and low ionic conductivity. Therefore, the polymer material used as a coating should have a moderate Young's modulus. The results of the tensile test show that the addition of multiple hydrogen-bonded molecules is beneficial to improving the Young's modulus of the coating polymer. For this result, the inventor believes that the cross-linking effect between the chain segments of multiple hydrogen bonds improves the Young's modulus of the polymer. Among the three groups of test results, Example 1 has a moderate Young's modulus and exhibits the best performance in subsequent battery tests.
[0066] Table 1 Test results of Young's modulus of different samples
[0067] Mole fraction of self-healing monomer (%) Young's modulus (MPa) Comparative sample 2 0 0.337 Example 1 2 5.929 Comparative sample 1 5 55.727
[0068] In-situ lithium deposition experiment: In a glove box, the copper foil and lithium metal described in Example 2 are respectively attached to the tabs and attached to the opposite sides of a four-way light cuvette. The copper foil is used as the positive electrode and the lithium metal is used as the negative electrode. The commercial electrolyte LB015 is injected into the cuvette and sealed, and the tabs are led out. The cuvette is moved out of the glove box and placed under an optical microscope. Adjust the optical microscope so that the copper foil, coating and electrolyte can be clearly observed. Connect the copper foil as the positive electrode and the lithium metal as the negative electrode to the blue electric test system and apply 4mA / cm 2 The discharge current was 2.5. The lithium deposition morphology on the copper foil surface was observed by optical microscope every 5 minutes. Figure 4As shown, the lithium deposition layer on the surface of the bare copper foil is thicker, and obvious dendritic lithium metal is generated. Below is the lithium deposition on the surface of the copper foil with a self-healing protective layer. The lithium deposition layer is relatively uniform and there are no obvious dendrites, indicating that the self-healing coating has the effect of regulating the uniform deposition of lithium ions.
[0069] Galvanostatic charge-discharge cycling test of lithium-lithium symmetric battery: The lithium-lithium symmetric battery described in Example 4 and Comparative Samples 4 and 5 were subjected to a galvanostatic discharge-galvanostatic charge cycling test using a Blue-Energy system, with a current of 1 mA / cm 2 , and one hour of charging and discharging was taken as one cycle. The test results are as Figure 6 shown. It can be seen from the figure that the lithium-lithium symmetric battery composed of bare lithium in Comparative Sample 4 had a large polarization at 500 h, while both Comparative Sample 5 and Example 4 maintained a small polarization, indicating that the lithium metal protective coating rich in -CF 3 groups can effectively reduce the polarization of the lithium metal negative electrode, and the generation of lithium dendrites is effectively inhibited, obtaining a stable lithium metal negative electrode. From the comparison between Comparative Sample 5 and Example 4, it can be seen that the addition of the self-healing monomer can significantly increase the cycling time of the lithium-lithium symmetric battery, indicating that the self-healing effect can improve the cycling stability of lithium batteries.
[0070] Critical current test of lithium-lithium symmetric battery: The lithium-lithium symmetric batteries described in Example 4 and Comparative Sample 4 were subjected to a galvanostatic discharge-galvanostatic charge cycling test at different current densities using a Blue-Energy system. The current densities were 0.1, 0.2, 0.5, 0.7, 1, 2, 3, 4 mA / cm 2 respectively, and each cycle was carried out 5 times at an areal specific capacity of 0.1, 0.2, 0.5, 0.7, 1, 2, 3, 4 mAh / cm 2 , as Figure 5 shown. As Figure 5 can be seen, the lithium-lithium symmetric battery with a self-healing protective coating can work stably at a larger current density without short-circuiting, indicating that this self-healing coating can effectively inhibit the growth of lithium dendrites and significantly improve the safety of the battery.
[0071] Charge-discharge performance test of lithium iron phosphate on lithium metal battery: The batteries described in Example 5 and Comparative Sample 6 were subjected to a charge-discharge cycling test using a Blue-Energy test system, with a current of 1C (1C = 170 mAh / g). The battery performance is shown in Figure 7 . It can be seen from the figure that the capacity retention rate and Coulomb efficiency of the battery assembled with the lithium metal negative electrode with a self-healing protective layer are significantly higher than those of the battery assembled with bare lithium, indicating that the self-healing lithium metal coating is beneficial to improving the cycling stability and safety of lithium metal batteries, and has application value and commercial potential.
[0072] In summary, the present invention provides a self-healing coating for protecting lithium metal anodes. It uses a self-healing monomer with multiple hydrogen bonds to copolymerize with a fluorinated acrylate monomer and adds lithium salt doping, and forms a self-healing protective coating on the surface of lithium metal through ultraviolet-initiated in-situ polymerization. The monomer containing multiple hydrogen bonds in the coating is beneficial for timely self-repair when the coating is broken, and the fluorinated acrylate monomer can promote the uniform deposition of lithium ions. This method can be simply and efficiently applied to lithium metal batteries, improving the cycle stability and safety of the batteries, and has certain application value and commercial potential.
[0073] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.
Claims
1. A self-healing coating, characterized in that: The raw material components include monomers, lithium salts and initiators; the monomers include fluorine-containing acrylic ester substances and methacrylate ureido pyrimidone; the raw material components are mixed and cured to obtain the self-healing coating.
2. The self-healing coating according to claim 1, characterized in that The fluorine-containing acrylic ester substance is one or both of 2,2,2-trifluoroethyl acrylate and hexafluorobutyl acrylate.
3. The self-healing coating according to claim 1, characterized in that The molar content of ureidopyrimidone methacrylate in the monomer is 0.1%-4%, preferably 0.5%-4%.
4. The self-healing coating according to claim 1, characterized in that The concentration of the lithium salt in the precursor solution of the raw material composition is 0.5-2 mol / L, preferably 0.8-1.2 mol / L; And / or, the amount of the initiator used is 0.1wt%-0.5wt% of the total mass of the precursor solution.
5. The self-healing coating according to claim 1, characterized in that The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium hexafluorophosphate; And / or, the initiator is a photoinitiator, preferably including one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone.
6. A method for preparing the self-healing coating according to any one of claims 1 to 5, characterized in that: include: The fluorine-containing acrylate substance, methacrylate ureido pyrimidone, lithium salt and initiator are uniformly mixed, and then film-formed and cured to obtain a self-healing coating.
7. The preparation method according to claim 6, characterized in that: The film formation is achieved by drip coating, scraping, spraying or dipping; the curing is carried out under ultraviolet light irradiation for 0.5-2 hours.
8. A lithium metal negative electrode, characterized in that The surface of the lithium metal negative electrode is covered with a self-healing coating according to any one of claims 1 to 5.
9. The lithium metal negative electrode according to claim 8, characterized in that The thickness of the self-healing coating is 5-30 μm.
10. A lithium battery, characterized in that: The negative electrode of the lithium battery is the lithium metal negative electrode according to claim 8 or 9.