Preparation method of artificial modified CEI material layer and application thereof

Abstract

The application relates to a preparation method of an artificially modified CEI material, and the preparation steps comprise the following steps: mixing polymer monomers, a crosslinking agent, an organic plasticizer, a lithium salt, a photoinitiator and a diluent to obtain a precursor solution; performing spin coating on the surface of a high-nickel ternary positive electrode, standing to make the precursor solution fully wet, using a purple light lamp to initiate polymerization, and performing vacuum drying to obtain a high-nickel ternary positive electrode with an artificially modified CEI layer. The artificially modified CEI material is prepared by in-situ polymerization reaction of polyethylene glycol diacrylate and a fluorine-substituted product of ethylene carbonate, is used for a lithium metal battery positive electrode, can effectively stabilize the electrode / electrolyte interface, inhibit electrolyte decomposition and transition metal dissolution, reduce the occurrence of side reactions, and improves the cycle stability of the lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal batteries, specifically relating to a method for preparing an artificially modified CEI material layer and its application. Background Technology

[0002] Based on the low reduction potential of lithium metal (-3.045 V compared to the standard hydrogen electrode) and 3860 mAhg -1 With their high specific capacity, lithium metal batteries (LMBs) offer tremendous promise for next-generation energy storage. Among the various cathode materials for LMBs, LiNi... 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is known for its significantly high specific capacity (over 200 mAh g / L). -1 High-nickel ternary lithium cathodes are widely used due to their relatively low cost. However, during charging and discharging, the repeated insertion and extraction of lithium ions causes the cathode material particles to break down and pulverize, leading to battery capacity decay and reduced safety. Simultaneously, under high voltage, the side reactions between the electrolyte and the cathode material intensify, generating a large number of harmful byproducts that further degrade battery performance. Therefore, maintaining the structural stability of the cathode material and reducing side reactions under high voltage conditions are urgent problems that need to be solved in high-nickel ternary lithium batteries.

[0003] Existing high-nickel ternary lithium cathode materials (such as LiNi) 0.8 Co 0.1 Mn 0.1 O2 (Lithium Oxide) has become a key material for next-generation lithium batteries due to its high energy density and low cost. However, it suffers from the following problems under high voltage conditions (≥4.3 V): Poor structural stability: During charge-discharge cycles, repeated insertion / extraction of lithium ions causes expansion / contraction of the cathode material lattice, leading to particle breakage and pulverization, resulting in rapid capacity decay; Electrolyte side reactions: Under high voltage, the electrolyte decomposes to form an unstable CEI (solid electrolyte interface film), which exacerbates metal ion dissolution and oxygen evolution reactions, affecting battery cycle life and safety; Insufficient thermal stability: High-temperature environments can easily trigger thermal runaway, posing safety hazards. Existing technologies mainly improve the performance of high-nickel ternary lithium cathodes through the following methods: Ion doping: Doping with elements such as aluminum and magnesium stabilizes the lattice, but the improvement effect is limited and the process is complex; Surface inorganic layer coating: Coating with inorganic materials such as Al2O3 and TiO2, but there are problems such as uneven coating and difficulty in controlling the thickness; Conductive polymer coating: Such as polypyrrole (PPy), but it is easy to decompose under high voltage and cannot be stable for a long time. Existing modification technologies have the following drawbacks: the coating layer has weak bonding with the cathode substrate and is prone to detachment during cycling; the coating layer has poor conductivity, which affects the lithium-ion transport rate; and the preparation process is complex and costly, making it difficult to industrialize.

[0004] The goal of this study is to develop a novel "protective layer" that can be effectively polymerized on the surface of a high-nickel ternary lithium cathode to improve its battery performance under high-voltage conditions. Specific objectives include improving battery cycle stability and thermal stability, enhancing battery safety, and increasing capacity retention. The artificial CEI layer, by artificially constructing a stable solid electrolyte film on the electrode material surface, effectively suppresses side reactions between the electrolyte and electrode materials, reduces lithium metal deposition and dissolution, and improves battery cycle life and safety. Summary of the Invention

[0005] The purpose of this invention is to address the problem of battery capacity decay and safety degradation caused by the repeated insertion and extraction of lithium ions during the charging and discharging process of high-nickel ternary cathodes, which leads to particle breakage and pulverization of the cathode material. This invention provides a method for preparing an artificially modified CEI material layer and its application. Specifically, this invention uses polymer monomers to construct a framework network, adds organic plasticizers, lithium salts, and photoinitiators to form a precursor solution, and then uses in-situ polymerization technology to synthesize the CEI material layer. The artificially modified CEI material layer prepared by this method can significantly improve the cycle performance of the battery, possessing good compatibility with high-nickel cathodes and lithium metal anodes, excellent mechanical strength, and superior cycle capability.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing an artificially modified CEI material layer, comprising the following steps:

[0008] S1. Mix the polymer monomer, crosslinking agent, organic plasticizer, lithium salt, photoinitiator, and diluent to obtain a precursor solution;

[0009] S2. Spin-coat the precursor solution onto the surface of the high-nickel ternary cathode, let it stand to fully wet it, then use a UV lamp to irradiate and initiate polymerization. After vacuum drying, a high-nickel ternary cathode with an artificially modified CEI layer is obtained (artificially modified CEI layer is obtained).

[0010] As one embodiment of the present invention, in step S1, the polymer monomer includes one or more of polyethylene glycol diacrylate monomer (PEGDA), polyethylene glycol dimethacrylate monomer (PEGDMA), methyl methacrylate monomer (MMA), and polyether acrylate monomers.

[0011] In one embodiment of the present invention, in step S1, the crosslinking agent includes one or more of pentaerythritol tetraacrylate (PETRA), pentaerythritol triacrylate (PETA), ethoxylated trimethylolpropane triacrylate (ETPTA), and trimethylolpropane trimethacrylate (TMPTMA). Monomer polymerization alone results in a linear polymer, which is easily dissolved by electrolytes. Adding a crosslinking agent increases the degree of crosslinking, forming a three-dimensional polymer with a higher degree of polymerization.

[0012] In some embodiments, the crosslinking agent is preferably pentaerythritol tetraacrylate (PETRA). Compared to other crosslinking agents (such as PETA), PETRA has better compatibility with fluorinated solvents (FEC, FEMC) and a higher degree of crosslinking. Other crosslinking agents (such as PETA) show an increasing trend in cycling capacity in the early stages, but their performance declines rapidly in the later stages.

[0013] In one embodiment of the present invention, in step S1, the organic plasticizer is at least one or more of the following: carbonates (dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate), ethers (1,2-dimethoxyethane, diethylene glycol dimethyl ether), carboxylic acid esters (γ-butyrolactone), nitriles (butyronitrile), aromatic hydrocarbons (1,3,5-trifluorobenzene), fluorinated solvents (fluorinated ethylene carbonate, methyl trifluoroethyl carbonate), phosphate esters (trimethyl phosphate, triethyl phosphate), sulfate esters (ethylene sulfate), cyclic sulfone additives (sulfolane, 3-methyl-sulfolane), and alkyl carbonates (diethyl dicarbonate (DEC2O)).

[0014] In some embodiments, the organic plasticizer is a fluorinated solvent; the fluorinated solvent includes one or more of fluoroethylene carbonate (FEC) and methyl trifluoroethyl carbonate (FEMC).

[0015] In one embodiment of the present invention, in step S1, the lithium salt is at least one selected from lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium perchlorate. Preferably, it is one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide. The C=N bond in the sulfonic acid group has a strong attraction for Li+.

[0016] In one embodiment of the present invention, in step S1, the photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone (HMPP), benzoin dimethyl ether (651), benzophenone (BP), Irgacure 2959, Irgacure 819, and PyBN.

[0017] In one embodiment of the present invention, in step S1, the diluent is at least one of DME (ethylene glycol dimethyl ether), DMC (dimethyl carbonate), DEC (diethyl carbonate), MB (methyl butyrate), and tetrahydrofuran (THF).

[0018] The ratio of polymer monomer to organic plasticizer is 0.1-1 mol: 0.1-1 L, preferably 0.1-0.3 mol: 0.5 L.

[0019] The volume ratio of organic plasticizer to diluent is 1:0.2-2, preferably 1:0.4-1.2.

[0020] The molar ratio of polymer monomer to crosslinking agent is 1:0.01-0.3, preferably 1:0.15-0.25.

[0021] The molar ratio of polymer monomer to lithium salt is 1:2-10, preferably 1:2-6.

[0022] The molar ratio of polymer monomer to photoinitiator is 1:0.01-0.2, preferably 1:0.08-0.12.

[0023] As one embodiment of the present invention, in step S2, the high-nickel ternary cathode includes NCM622 (LiNi) 0.6 Co 0.2 Mn 0.2 O2), NCM811 (LiNi) 0.8 Co 0.1 Mn 0.1 O2), Ni90 (LiNi) 0.9 Co 0.05 Mn 0.05 One of the types of O2.

[0024] In one embodiment of the present invention, in step S2, the spin coating speed is 3000-8000 r / s, and the spin coating time is 3-10 s. Magnetic spin coating is used. The droplet volume for spin coating is 10-50 μL / cm. 2 .

[0025] In one embodiment of the present invention, in step S2, the standing time is 5-30 min, and the standing temperature is 20-40 ℃. The surface of the ternary cathode is rough and porous, and the purpose of wetting is to allow the precursor solution to fully enter the pores and enhance its integrity.

[0026] In one embodiment of the present invention, in step S2, the irradiation wavelength of the ultraviolet lamp is 345-365 nm, and the power of the ultraviolet lamp is 30-160 W. The irradiation time of the ultraviolet lamp is 1-3 min.

[0027] In one embodiment of the present invention, in step S2, the vacuum drying time is 30-60 min and the vacuum drying temperature is 60-120 ℃, preferably 60-180 ℃.

[0028] In one embodiment of the present invention, in step S2, the thickness of the obtained artificially modified CEI layer is 10-30 μm, preferably 20-30 μm.

[0029] A second aspect of this application provides the application of the high-nickel ternary cathode with an artificially modified CEI layer prepared by the above preparation method in lithium metal batteries.

[0030] A third aspect of this application provides a lithium metal battery comprising a lithium anode, a separator, an electrolyte, and the aforementioned high-nickel ternary cathode having an artificially modified CEI layer.

[0031] As one embodiment of the present invention, the lithium anode comprises lithium metal or a lithium metal composite;

[0032] As one embodiment of the present invention, the diaphragm includes any one of polyolefin diaphragm, ceramic coated diaphragm, PVDF coated diaphragm, aramid coated diaphragm, nonwoven fabric diaphragm, cellulose diaphragm, polyimide (PI) diaphragm, polyester (PET) diaphragm or composite material diaphragm.

[0033] As one embodiment of the present invention, the electrolyte includes: lipid liquid electrolytes (4.0M LiPF6 in EMC=100 Vol% with 2.0% VC, 1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol% with 5.0% FEC, 1.0M LiPF6 in EC:EMC=3:7 Vol% with 2.0% VC, etc.), ether liquid electrolytes (0.5M LITFSI, 0.4M LiNO3 in DME:DOL=1:1 Vol%, 2.0M LiTFSI in DOL=100 Vol%, 1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.5 w% LiNO3, etc.), lipid gel electrolytes (in situ polymerization by adding polymer monomer molecules to lipid liquid electrolytes), and ether gel electrolytes (in situ polymerization by adding polymer monomer molecules to ether liquid electrolytes).

[0034] This invention prepares an artificial CEI material through in-situ polymerization of polymer monomers (such as polyethylene glycol diacrylate) and plasticizers (such as fluoroethylene carbonate). When used as the cathode in lithium metal batteries, it effectively stabilizes the electrode / electrolyte interface, inhibits electrolyte decomposition and transition metal dissolution, reduces side reactions, and improves the cycle stability of lithium metal batteries. In the artificial CEI material of this invention, the F and C=N bonds are coupled to the Li... + It possesses strong attraction capabilities, increases the lithiophilic sites in the framework material, and can significantly improve the ionic conductivity and lithium-ion transference number of the material, providing Li... + High-speed transmission channels, thus ensuring uniform Li + The deposition and stripping processes reduce the occurrence of side reactions at the lithium metal interface and the formation of lithium dendrites, thereby achieving lithium metal batteries with improved electrochemical performance.

[0035] If the polymer monomer is polyethylene glycol diacrylate, the chemical formula for the photoinitiated polymerization reaction is shown below. The area within the dashed box represents the photoinitiator (HMPP). Photogenerated electrons generated by light irradiation play a role in chain initiation, and n ranges from 8000 to 12000. PEGDA monomers serve as reactive monomers to construct the network framework, while plasticizers such as FEC and lithium salts act as fillers for the ion-conducting network.

[0036]

[0037] Compared with the prior art, the beneficial effects of this application are as follows:

[0038] (1) The artificial CEI material of this invention has excellent electrochemical stability. First, it can improve the cycle stability of the battery: the artificial CEI layer can effectively suppress the structural changes and interfacial side reactions of the NCM811 cathode material during charging and discharging, reduce the loss of active materials, and thus significantly improve the cycle life of the battery. Experimental data show that the NCM811 cathode battery coated with the artificial CEI layer can still maintain a high capacity retention rate after multiple cycles. Second, it enhances battery safety: it can prevent direct contact between the electrolyte and the cathode material, reducing the safety risks of the battery under extreme conditions such as high voltage. For example, in high-temperature environments, the artificial CEI layer can reduce the probability of thermal runaway and ensure the safe operation of the battery. Third, it improves the rate performance of the battery: it optimizes the charge transport process at the electrode / electrolyte interface, reduces the interfacial impedance, and enables the battery to perform better under high-rate charging and discharging conditions, meeting the needs of fast charging and discharging.

[0039] (2) The performance indicators of the artificial CEI layer coating technology are as follows: protective layer thickness: 10-30 μm (precisely controllable); high voltage resistance test: after 200 cycles at 2.8-4.5 V high voltage, the capacity retention rate is ≥85% (conventional materials ≤70%); its ionic conductivity at different temperatures is ≥1×10-5 S / cm (meets fast charging requirements).

[0040] (3) The equipment requirements only require conventional coating equipment and low-temperature post-treatment (such as UV lamp irradiation); and the process flow is short: precursor solution preparation → coating → in-situ polymerization → post-treatment; the industrialization prospects are applicable to new energy vehicles, energy storage power stations, high-end consumer electronics and other fields. It is expected to replace existing surface modification technologies, reduce battery costs by 15%-20%, and promote the commercialization of high-nickel ternary lithium batteries. In summary, the technical solution of coating an artificial CEI layer on the surface of the NCM811 cathode of lithium metal batteries has important practical value. It can effectively improve battery performance, improve cycle stability, safety and rate performance, but it still faces some challenges in practical applications. Through continuous research and innovation, optimizing the preparation process, improving the stability and durability of the CEI layer, and strengthening compatibility with other battery components, this technical solution is expected to be widely used in the future lithium metal battery field and make important contributions to promoting the development of energy storage technology. Attached Figure Description

[0041] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0042] Figure 1 The thickness of the artificially modified CEI layer prepared in Example 1 of this invention;

[0043] Figure 2 The bar chart shows the ionic conductivity of the artificially modified CEI layer prepared in Example 1 of this invention at different temperatures.

[0044] Figure 3 This is a schematic diagram of the coating of the artificially modified CEI material onto the positive electrode structure of the present invention, wherein 1-artificially modified CEI layer, 2-active material layer, and 3-current collector;

[0045] Figure 4 This is a puncture test diagram of a soft-pack battery assembled after the artificially modified CEI material prepared in Example 1 of the present invention was coated onto an NCM811 cathode.

[0046] Figure 5 The graph shows the cycle performance of the lithium metal full cells assembled in Examples 1-4 and Comparative Examples 1-6. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0048] This invention provides a method for preparing an artificially modified CEI material layer, comprising the following steps:

[0049] S1. Mix the polymer monomer, crosslinking agent, organic plasticizer, lithium salt, photoinitiator, and diluent to obtain a precursor solution;

[0050] S2. Spin-coat the precursor solution onto the surface of the high-nickel ternary cathode, let it stand for 1-3 hours to fully wet it, then use a UV lamp to irradiate and initiate polymerization. After vacuum drying, the artificially modified CEI layer is obtained.

[0051] The positive electrode structure of the present invention is as follows: Figure 3 As shown, the electrode includes an artificially modified CEI layer 1, an active material layer 2 (high-nickel ternary cathode), and a current collector 3. The artificially modified CEI layer 1 is obtained by spin-coating the precursor solution onto the surface of the active material layer 2 (high-nickel ternary cathode).

[0052] To address the problem of poor conductivity in existing cathode materials, which affects lithium-ion transport rates, this invention employs a composite coating of "fluoropolymer + fluorinated lithium salt," which combines chemical stability, mechanical strength, and ionic conductivity. The fluoropolymer provides excellent resistance to electrolyte corrosion and electrochemical stability, preventing coating cracking. The CEI layer on the surface of the high-nickel ternary cathode material of this invention improves cycle life: at a high voltage of 2.8-4.5 V, the capacity retention after 200 cycles is ≥85% (compared to ≤70% for traditional materials).

[0053] To address the issue of fragile cathode substrates being prone to interfacial reactions and detachment during cycling, this invention utilizes an "in-situ polymerization + UV curing" technology to achieve a strong chemical bond between the protective layer and the cathode surface. This invention reacts the precursor solution with the cathode surface to form a uniform and dense protective layer, avoiding the "physical accumulation" defects of traditional coatings; for example... Figure 4 As shown, the safety of the lithium metal battery of the present invention is improved, with no risk of fire or explosion during the nail penetration test; the high-voltage cycle stability, thermal stability and safety of the battery are significantly improved.

[0054] Unless otherwise specified, the reagents, methods and equipment used in this invention are conventional reagents, methods and equipment in this technical field.

[0055] The Celgard 2500 was purchased from Celgard Diaphragm Company in the United States.

[0056] Example 1

[0057] In an argon-filled glove box (H2O ≤ 0.01 ppm, O2 ≤ 0.01 ppm), 0.2 mol of PEGDA (polymer monomer) was dissolved in 1 L of a 1:1 volume ratio mixture of fluoroethylene carbonate (FEC, organic plasticizer) and diluent ethylene glycol dimethyl ether (DME). After thorough stirring, 0.04 mol of pentaerythritol tetraacrylate (PETRA, crosslinking agent) was added, with a polymer monomer to crosslinking agent molar ratio of 1:0.2, to obtain a monomer solution. 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, lithium salt) was dissolved in the monomer solution and mixed thoroughly to obtain a lithium salt solution, wherein the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to polymer monomer was 5:1. 20 mmol of 2-hydroxy-2-methylphenylacetone (HMPP, photoinitiator) was dissolved in the lithium salt solution and mixed thoroughly to obtain a precursor solution.

[0058] The precursor solution was spin-coated onto the surface of the NCM811 cathode under an argon atmosphere, with a spin-coating drop volume of 30 μl / cm. 2 The spin coating speed was 5000 r / s, and the spin coating time was 5 s. After spin coating, the surface was left to stand at 25℃ for 20 min to fully wet the positive electrode surface. Polymerization was initiated by irradiation with a UV lamp (365 nm, 70 W power) for 2 min. After vacuum drying at 70℃ for 30 min, an NCM811 positive electrode with an artificially modified CEI layer (27 μm thick) was obtained. Thickness measurement and optical microscopy revealed the formation of dense layered structures, such as... Figure 1 As shown, the thickness of the artificially modified CEI layer is 27 μm.

[0059] In-situ polymerization assembly of Li||NCM811 cells.

[0060] The preparation method of the Li||NCM811 battery is as follows:

[0061] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR 2032 stainless steel button cell was assembled using Li as the negative electrode, NCM811 with an artificially modified CEI layer as the positive electrode, and Celgard-2500 as the separator. 80 μL of a commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0 w% LiNO3) was added, and the cell was assembled under a pressure of 9 MPa. After assembly, the cell was subjected to in-situ polymerization in a 60℃ oven for 5 h to obtain the Li||NCM811 cell.

[0062] In-situ polymerization assembly of Li||NCM811 pouch cells with a capacity of 0.2Ah.

[0063] Electrode and component preparation: Cut the pre-prepared NCM811 positive electrode with artificially modified CEI layer and the lithium metal negative electrode to the designed dimensions (45x62mm). Prepare the corresponding aluminum-plastic film shell, positive and negative electrode inner conductors, and Celgard-2500 separator.

[0064] Stacking and Packaging: Z-shaped stacking is performed in the order of "negative electrode shell / lithium negative electrode / separator / NCM811 positive electrode / positive electrode shell". The stacked cells are placed into the aluminum-plastic film recess, and the top sealing machine is used to vacuum heat seal the three sides except for the liquid injection port.

[0065] Electrolyte and prepolymer solution injection: A precise amount of commercial electrolyte (1.0 MLiTFSI in DME:DOL = 1:1 vol%, with 1.0 wt% LiNO3), 400 μL, is injected into the cell through the injection port.

[0066] Injection port sealing and pressurization: After injection, the injection port is immediately vacuum heat-sealed. Then, the sealed pouch battery is placed in a special fixture and a uniform pressure (1 MPa) is applied to ensure tight contact between the interfaces of each cell layer.

[0067] In-situ polymerization: The battery under pressure was transferred to a constant temperature oven at 60°C and left to stand for 6 hours.

[0068] Example 2

[0069] In an argon-filled glove box (H₂O ≤ 0.01 ppm, O₂ ≤ 0.01 ppm), 0.2 mol of PEGDA was dissolved in 1 L of a 1:1 volume ratio mixture of fluoroethylene carbonate (FEC) and dimethyl ethylene glycol (DME). After thorough stirring, 0.04 mol of pentaerythritol triacrylate (PETA) was added, with a polymer monomer to crosslinking agent molar ratio of 1:0.2, to obtain a monomer solution. 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in the monomer solution and mixed thoroughly to obtain a lithium salt solution, wherein the ratio of lithium bis(trifluoromethanesulfonyl)imide to polymer monomer was 2:1. 20 mmol of 2-hydroxy-2-methylphenylacetone (HMPP) was dissolved in the lithium salt solution and mixed thoroughly to obtain a precursor solution.

[0070] The precursor solution was spin-coated onto the surface of the NCM811 cathode under an argon atmosphere, with a spin-coating drop volume of 30 μl / cm. 2 The spin coating speed was 5000 r / s and the spin coating time was 5 s. After spin coating, the cathode surface was left to stand at 25°C for 20 min to fully wet it. Polymerization was initiated by irradiating with a UV lamp (365 nm, 70 W power) for 2 min. After vacuum drying at 70°C for 30 min, NCM811 cathode with artificially modified CEI layer was obtained.

[0071] In-situ polymerization assembly of Li||NCM811 cells.

[0072] The preparation method of the Li||NCM811 battery is as follows:

[0073] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR2032 stainless steel button cell was assembled using Li as the negative electrode, NCM811 with an artificially modified CEI layer as the positive electrode, and Celgard-2500 as the separator. 80 μL of a commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0 w% LiNO3) was added, and the cell was assembled under a pressure of 9 MPa. After assembly, the cell was subjected to in-situ polymerization in a 60℃ oven for 5 h to obtain the Li||NCM811 cell.

[0074] Example 3

[0075] In an argon-filled glove box (H₂O ≤ 0.01 ppm, O₂ ≤ 0.01 ppm), 0.2 mol of PEGDA was dissolved in 1 L of a 2:1 volume ratio mixture of methyltrifluoroethyl carbonate (FEMC) and dimethyl glycol ether (DME). After thorough stirring, 0.04 mol of pentaerythritol tetraacrylate (PETRA) was added, wherein the molar ratio of polymer monomer to crosslinking agent was 1:0.2, to obtain a monomer solution. 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in the monomer solution and mixed thoroughly to obtain a lithium salt solution, wherein the ratio of lithium bis(trifluoromethanesulfonyl)imide to polymer monomer was 5:1. 20 mmol of 2-hydroxy-2-methylphenylacetone (HMPP) was dissolved in the lithium salt solution and mixed thoroughly to obtain a precursor solution.

[0076] The precursor solution was spin-coated onto the surface of the NCM811 cathode under an argon atmosphere, with a spin-coating drop volume of 30 μl / cm. 2 The spin coating speed was 5000 r / s and the spin coating time was 5 s. After spin coating, the cathode surface was left to stand at 25°C for 20 min to fully wet it. Polymerization was initiated by irradiating with a UV lamp (365 nm, 70 W power) for 2 min. After vacuum drying at 70°C for 30 min, NCM811 cathode with artificially modified CEI layer was obtained.

[0077] In-situ polymerization assembly of Li||NCM811 cells.

[0078] The preparation method of the Li||NCM811 battery is as follows:

[0079] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR2032 stainless steel button cell was used. Li was used as the negative electrode, NCM811 with an artificially modified CEI layer was used as the positive electrode, and Celgard-2500 was used as the separator. 80 μL of commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0 w% LiNO3) was added, and the cell was assembled under a pressure of 9 MPa. After assembly, the cell was subjected to in-situ polymerization in an oven at 60℃ for 5 h to obtain the Li||NCM811 cell.

[0080] Example 4

[0081] In an argon-filled glove box (H₂O ≤ 0.01 ppm, O₂ ≤ 0.01 ppm), 0.2 mol of PEGDA was dissolved in 1 L of a 2:1 volume ratio mixture of methyltrifluoroethyl carbonate (FEMC) and dimethyl glycol ether (DME). After thorough stirring, 0.04 mol of pentaerythritol triacrylate (PETA) was added, with a polymer monomer to crosslinking agent molar ratio of 1:0.2, to obtain a monomer solution. 1.0 mol of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in the monomer solution and mixed thoroughly to obtain a lithium salt solution, wherein the ratio of lithium bis(trifluoromethanesulfonyl)imide to polymer monomer was 5:1. 20 mmol of 2-hydroxy-2-methylphenylacetone (HMPP) was dissolved in the lithium salt solution and mixed thoroughly to obtain a precursor solution.

[0082] The precursor solution was spin-coated onto the surface of the NCM811 cathode under an argon atmosphere, with a spin-coating drop volume of 30 μl / cm. 2 The spin coating speed was 5000 r / s and the spin coating time was 5 s. After spin coating, the cathode surface was left to stand at 25°C for 20 min to fully wet it. Polymerization was initiated by irradiating with a UV lamp (365 nm, 70 W power) for 2 min. After vacuum drying at 70°C for 30 min, NCM811 cathode with artificially modified CEI layer was obtained.

[0083] In-situ polymerization assembly of Li||NCM811 cells.

[0084] The preparation method of the Li||NCM811 battery is as follows:

[0085] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR2032 stainless steel button cell was assembled using Li as the negative electrode, NCM811 with an artificially modified CEI layer as the positive electrode, and Celgard-2500 as the separator. 80 μL of a commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0w% LiNO3) was added, and the cell was assembled under a pressure of 9MPa. After assembly, the cell was subjected to in-situ polymerization in a 60℃ oven for 5h to obtain the Li||NCM811 cell.

[0086] Comparative Example 1

[0087] Comparative Example 1 provides a CR2032 coin cell with an NCM811 positive electrode without a CEI layer on the surface, and its negative electrode is a lithium sheet.

[0088] Its preparation methods include:

[0089] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR2032 stainless steel button cell was used. Li was used as the negative electrode, NCM811 without an artificial CEI layer was used as the positive electrode, and Celgard-2500 was used as the separator. 80 μL of commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0w%LiNO3) was added, and the cell was assembled under a pressure of 9MPa. After assembly, the cell was subjected to in-situ polymerization in an oven at 60℃ for 5h to obtain the Li||NCM811 cell.

[0090] Comparative Example 2

[0091] Comparative Example 2 provides a CR2032 coin cell with a conventional polyurethane (PU) artificial CEI layer and its positive electrode carrier is also NCM811 lithium sheet.

[0092] Its preparation methods include:

[0093] In an argon-filled glove box (H₂O ≤ 0.01 ppm, O₂ ≤ 0.01 ppm), 0.2 mol of PU was dissolved in 1 L of a 2:1 volume ratio mixture of methyltrifluoroethyl carbonate (FEEC) and dimethyl glycol ether (DME) to obtain a monomer solution. 1.0 M of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was dissolved in the monomer solution and mixed thoroughly to obtain a lithium salt solution, wherein the ratio of lithium bis(trifluoromethanesulfonyl)imide to the polymer monomer was 5:1. 20 mmol of 2-hydroxy-2-methylphenylacetone (HMPP) was dissolved in the lithium salt solution and mixed thoroughly to obtain a precursor solution.

[0094] The precursor solution was spin-coated onto the surface of the NCM811 cathode under an argon atmosphere, with a spin-coating drop volume of 30 μl / cm. 2 The spin coating speed was 5000 r / s and the spin coating time was 5 s. After spin coating, the cathode surface was left to stand at 25°C for 20 min to fully wet it. Polymerization was initiated by irradiating with a UV lamp (365 nm, 70 W power) for 2 min. After vacuum drying at 70°C for 30 min, NCM811 cathode with artificially modified CEI layer was obtained.

[0095] In-situ polymerization assembly of Li||NCM811 batteries

[0096] The preparation method of the Li||NCM811 battery is as follows:

[0097] In a glove box under an argon atmosphere (H2O≤0.01ppm, O2≤0.01ppm), a CR2032 stainless steel button cell was assembled using Li as the negative electrode, NCM811 with an artificially modified CEI layer as the positive electrode, and Celgard-2500 as the separator. 80 μL of a commercial electrolyte solution (1.0M LiTFSI in DME:DOL=1:1 Vol% with 1.0w% LiNO3) was added, and the cell was assembled under a pressure of 9MPa. After assembly, the cell was subjected to in-situ polymerization in a 60℃ oven for 5h to obtain the Li||NCM811 cell.

[0098] The compositions of the precursor solutions in each embodiment and comparative example are as follows:

[0099] Table 1

[0100]

[0101] Comparative Example 3 (excluding F)

[0102] This comparative example is basically the same as Example 1, except that fluoroethylene carbonate (FEC, organic plasticizer) is replaced with an equal amount of ethylene carbonate (EC).

[0103] Comparative Example 4 (FEC as filler only)

[0104] This comparative example is basically the same as Example 1, except that lithium is replaced with an equal amount of FEC.

[0105] Comparative Example 5 (Lithium salt as filler only)

[0106] This comparative example is basically the same as Example 1, except that FEC is replaced with an equal amount of lithium salt.

[0107] Comparative Example 6 (without cross-linking agent)

[0108] This comparative example is basically the same as Example 1, except that no crosslinking agent is added.

[0109] Performance testing:

[0110] To investigate the coulombic efficiency and lithium deposition / stripping behavior of different battery examples, the active material loading at the positive electrode was 10 mg·cm³ in the full-cell test. -2 After assembly, the CR2032 coin cell battery was left to stand for 24 hours. Then, it underwent two cycles at a 0.1C rate under a charge / discharge voltage of 2.8-4.5V, followed by a long-cycle test at a 0.5C rate. The results are shown in Table 2 below. The charge / discharge tests were conducted using a Newway Battery Testing System (Newway Electronics Co., Ltd., China).

[0111] Table 2 Long-cycle test data of lithium metal batteries

[0112]

[0113] As shown in Table 2, the lithium metal batteries assembled with the artificially modified CEI material of the present invention have higher initial coulombic efficiency, and their capacity retention rate can reach 82-93% after 200 cycles. In contrast, the lithium metal batteries assembled with the unprotected NCM811 cathode and the PU-protected NCM811 cathode in the comparative examples have lower initial coulombic efficiency than those of the coated examples, and their capacity retention rate after multiple cycles is much lower than that of the lithium metal batteries assembled with the electrolyte of this application.

[0114] The lithium metal batteries assembled in Examples 1-4 and Comparative Examples 1-6 were subjected to two cycles at a 0.1C rate under charge / discharge voltages of 2.8-4.5V, followed by a long-term cycle test at a 0.5C rate. The results are as follows: Figure 5 As shown.

[0115] Depend on Figure 5 It can be seen that the lithium metal battery with a CEI layer prepared in Example 1 has an initial coulombic efficiency of 93.5%, and after 200 cycles, the capacity retention rate is 92.77%. In contrast, the lithium metal battery without a CEI layer prepared in Comparative Example 1 has an initial coulombic efficiency of only 85.3% under the same conditions, and after 70 cycles, the capacity decays to 40.5%. Adding a CEI layer made from the artificial CEI material of this application to the positive electrode of the lithium metal battery significantly improves the initial coulombic efficiency and greatly enhances the cycle stability. The artificial CEI material of this application, used as an artificial CEI layer for positive electrode protection, can effectively reduce side reactions between lithium metal and the electrolyte, achieve more uniform lithium deposition, and suppress the formation of lithium dendrites, thereby greatly improving the initial coulombic efficiency of the lithium metal battery and enhancing its stability during cycling.

[0116] The ionic conductivity testing method was as follows: In a glove box, an artificially modified CEI layer was prepared using the same method as in Example 1, the difference being that the precursor solution was spin-coated onto release paper. After peeling off the prepared artificially modified CEI layer, it was sandwiched between two polished and clean stainless steel (SS) sheets to prepare a 316 coin cell symmetric cell. After standing for 24 hours, it was transferred to a constant temperature oven and its resistance was tested using a Bio-Logic electrochemical workstation at 0.1 Hz-2 MHz under conditions of 20°C, 30°C, 40°C, 50°C, 60°C, and 70°C. (Results:)

[0117]

[0118] σ: Ionic conductivity (unit: S / cm)

[0119] L: Electrolyte thickness (unit: cm)

[0120] R b Body resistance obtained from EIS (unit: Ω)

[0121] A: Effective contact area between stainless steel electrode and electrolyte (unit: cm²) 2 )

[0122] Calculate its ionic conductivity at different temperatures. The bar chart of ionic conductivity at different temperatures is shown below. Figure 2 As shown.

[0123] The acupuncture test method is as follows:

[0124] A needle penetration tester was used to puncture the battery with a conical steel needle (8mm in diameter, 35° tip angle) made of tungsten carbide at a precisely controllable speed (25mm / s), and the puncture force was recorded. The test was conducted in an explosion-proof chamber at room temperature (e.g., 25°C). The pouch battery, prepared with an artificially modified CEI material layer, was at 80% SOC and underwent standardized pretreatment to achieve thermal equilibrium. During the test, the battery was fixed flat, and the steel needle was inserted into the center area between the tabs in a standard direction, such as perpendicular to the large surface. After puncture, the needle was held for a period of time before being withdrawn. Throughout the process, the voltage, temperature, and phenomena were continuously monitored, and the battery was observed for at least 1 hour until it cooled down and showed no abnormalities.

[0125] The puncture test of the assembled pouch battery in Example 1 is as follows: Figure 4 As shown.

[0126] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. A method for preparing an artificially modified CEI material layer, characterized in that, Includes the following steps: S1. Mix the polymer monomer, crosslinking agent, organic plasticizer, lithium salt, photoinitiator, and diluent to obtain a precursor solution; S2. Spin-coat the precursor solution onto the surface of the high-nickel ternary cathode, let it stand to fully wet it, then use a UV lamp to irradiate and initiate polymerization. After vacuum drying, a high-nickel ternary cathode with an artificially modified CEI layer is obtained. The polymer monomers include one or more of polyethylene glycol diacrylate monomers, polyethylene glycol dimethacrylate monomers, methyl methacrylate monomers, and polyether acrylate monomers; The crosslinking agent is pentaerythritol tetraacrylate; The organic plasticizer is a fluorinated solvent, which is one or more of fluoroethylene carbonate and methyl trifluoroethyl carbonate. The ratio of polymer monomer to organic plasticizer is 0.1-1 mol: 0.1-1 L; The thickness of the artificially modified CEI layer is 10-30 μm.

2. The method for preparing the artificially modified CEI material layer according to claim 1, characterized in that, In step S1, the lithium salt is at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalateborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, and lithium perchlorate. And / or, in step S1, the photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone, benzoin dimethyl ether, benzophenone, Irgacure 2959, Irgacure 819, and PyBN; And / or, in step S1, the diluent is at least one of DME, DMC, DEC, MB, and THF.

3. The method for preparing the artificially modified CEI material layer according to claim 1, characterized in that, In step S1, the volume ratio of organic plasticizer to diluent is 1:0.2-2; And / or, the molar ratio of polymer monomer to crosslinking agent is 1:0.01-0.3; And / or, the molar ratio of polymer monomer to lithium salt is 1:2-10; And / or, the molar ratio of polymer monomer to photoinitiator is 1:0.01-0.

2.

4. The method for preparing the artificially modified CEI material layer according to claim 1, characterized in that, In step S2, the high-nickel ternary cathode includes one of NCM622, NCM811, and Ni90.

5. The method for preparing the artificially modified CEI material layer according to claim 1, characterized in that, In step S2, the spin coating speed is 3000-8000 r / s, and the spin coating time is 3-10 s; And / or, in step S2, the amount of material added during spin coating is 10-50 μL / cm. 2 ; And / or, in step S2, the settling time is 5-30 min and the settling temperature is 20-40 ℃; And / or, in step S2, the irradiation wavelength of the ultraviolet lamp is 345-365 nm, and the power of the ultraviolet lamp is 30-160W. And / or, in step S2, the irradiation time of the ultraviolet lamp is 1-3 minutes; And / or, in step S2, the vacuum drying time is 30-60 min and the vacuum drying temperature is 60-120 ℃.

6. The application of a high-nickel ternary cathode with an artificially modified CEI layer obtained by the preparation method as described in claim 1 in lithium metal batteries.

7. A lithium metal battery, characterized in that, The invention comprises a lithium anode, a separator, an electrolyte, and a high-nickel ternary cathode with an artificially modified CEI layer obtained by the preparation method described in claim 1.

8. The lithium metal battery according to claim 7, characterized in that, The lithium anode comprises lithium metal or a lithium metal composite. And / or, the membrane includes any one of polyolefin membrane, ceramic-coated membrane, PVDF-coated membrane, aramid-coated membrane, cellulose membrane, polyimide membrane, and polyester membrane; And / or, the electrolyte includes one or more of the following: lipid liquid electrolyte, ether liquid electrolyte, lipid gel electrolyte, and ether gel electrolyte.

Images