Lithium metal negative electrode, method of making and use thereof

Abstract

This invention provides a lithium metal anode, its preparation method, and its application. The lithium metal anode includes a lithium metal matrix and an activation layer covering at least a portion of its surface; the lithium metal matrix includes lithium and silver; the activation layer includes lithium nitride and a first silver halide, wherein the first silver halide includes silver iodide. This invention provides an activation layer with specific chemical activity on the surface of a silver-containing lithium metal anode. Silver iodide can form lithium transport channels, activating dead lithium and improving the battery's cycle performance. Simultaneously, Li3N is a good SEI component, which can inhibit dendrite growth, isolate the electrolyte from contact with the anode, reduce active lithium loss, and further improve battery cycle performance. Furthermore, halogens existing in the form of silver halides are resistant to high voltage and not easily oxidized; therefore, high-voltage cathode materials with higher energy density can be selected to achieve a significant improvement in the cycle performance of high-energy-density lithium metal batteries.

Description

Technical Field

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

[0002] Batteries for electric vehicles, drones, and aircraft require high energy density to improve range on a single charge, while also needing long cycle life to meet the lifespan of the vehicle or drone. Lithium metal (rechargeable) batteries possess energy density characteristics far exceeding those of commercial lithium-ion (rechargeable) batteries, with energy density >400Wh / kg. This is due to their ultra-high specific capacity, reaching 3860mAh / g, achieved by using metallic lithium, lithium-copper composite strips, or lithium-free copper foil as the negative electrode. However, their short cycle life (<300 cycles) limits the practical application of lithium metal batteries.

[0003] The reason for the short cycle life of lithium metal batteries is that the charging and discharging mechanism of lithium metal in the negative electrode of lithium metal batteries is based on the deposition / stripping principle, which is different from the insertion / extraction mechanism of lithium-ion batteries. The deposition / stripping mechanism is more likely to generate dendrites and cause dead lithium. Dead lithium has no electrochemical activity and is prone to clogging the interface. Certain technical means are needed to reduce the generation of dead lithium in order to improve the cycle life of lithium metal batteries and meet the battery usage requirements. Summary of the Invention

[0004] The main objective of this invention is to provide a lithium metal anode, its preparation method, and its application, in order to solve the problem that lithium metal batteries in the prior art are prone to dendrite and dead lithium formation during cycling due to the lithium metal deposition / stripping mechanism, resulting in short battery cycle life and increased safety risks.

[0005] To achieve the above objectives, according to one aspect of the present invention, a lithium metal anode is provided, comprising a lithium metal substrate and an activation layer, wherein the activation layer covers at least a portion of the surface of the lithium metal substrate; the lithium metal substrate comprises lithium and silver; and the activation layer comprises lithium nitride and a first silver halide, wherein the first silver halide comprises silver iodide.

[0006] Furthermore, the nitrogen atoms in the lithium nitride account for 5-10% of the atomic percentage of the activation layer; and / or, the iodine atoms in the silver iodide account for 5-16% of the atomic percentage of the activation layer; and / or, the activation layer further includes a second silver halide; wherein the second silver halide includes one or more of silver fluoride, silver chloride, and silver bromide; and / or, the halogen atoms in the second silver halide account for 0-5% of the atomic percentage of the activation layer.

[0007] Furthermore, in the lithium metal matrix, the weight ratio of lithium to silver is (80~99):(1~20).

[0008] Furthermore, the thickness of the activation layer is 10~50 nm; and / or, the thickness of the lithium metal substrate is 5~50 μm.

[0009] According to another aspect of the present invention, a method for preparing the lithium metal anode described above is provided, comprising the following steps: Step S1, mixing halopyridine with an organic solvent to obtain a treatment solution; Step S2, immersing a lithium metal matrix raw material in the treatment solution to obtain a lithium metal anode; wherein, the halopyridine has the structure shown in general formula (1):

[0010] (1);

[0011] R1, R2, R3, and R4 are independently selected from H, F, Cl, Br, and I, respectively, and at least one of R1, R2, R3, and R4 is selected from I.

[0012] Further, the lithium metal matrix raw material includes lithium-silver alloy strips and / or silver-coated lithium strips; preferably, the weight percentage of silver in the lithium-silver alloy strip is 1-20%; preferably, the thickness of the silver coating in the silver-coated lithium strip is 1-100 nm; and / or, the halogenated pyridine includes one or more of 3-iodopyridine, 2-bromo-3-iodopyridine, and 5-chloro-3-fluoro-2-iodopyridine; and / or, the mass concentration of the treatment solution is 0.1-5%; and / or, the organic solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0013] Furthermore, the soaking temperature is 15~40℃, and the soaking time is 1s~180s.

[0014] According to another aspect of the present invention, a secondary battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises the lithium metal negative electrode described above.

[0015] Furthermore, the positive electrode includes a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector, wherein the positive electrode material active layer includes a nickel-cobalt-manganese ternary material and / or a lithium-rich manganese-based material.

[0016] Furthermore, the average voltage of the secondary battery is 3.5~4.3V.

[0017] By applying the technical solution of this invention, an activation layer with specific chemical activity is formed on the surface of a silver-containing lithium metal anode. Silver iodide in the activation layer can form lithium transport channels, activating dead lithium during the charging and discharging process of the lithium metal battery, reducing the amount of dead lithium generated throughout the cycle, and improving the battery's cycle performance. Simultaneously, Li3N is a good SEI component, which can inhibit dendrite growth, isolate the electrolyte from the anode, reduce active lithium loss, and further improve battery cycle performance. Furthermore, halogens existing in the form of silver halide are resistant to high voltage and are not easily oxidized; therefore, high-voltage cathode materials with higher energy density can be selected to achieve a significant improvement in the cycle performance of high-energy-density lithium metal batteries. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0019] As described in the background section of this invention, existing technologies suffer from the problem that lithium metal batteries are prone to dendrite and dead lithium formation during cycling due to the lithium metal deposition / stripping mechanism, leading to short battery cycle life and increased safety risks. To address these issues, in a typical embodiment of this invention, a lithium metal anode is provided, comprising a lithium metal substrate and an activation layer, wherein the activation layer coats at least a portion of the surface of the lithium metal substrate; the lithium metal substrate comprises lithium and silver; the activation layer comprises lithium nitride and a first silver halide, wherein the first silver halide comprises silver iodide.

[0020] This invention involves creating an activation layer with specific chemical activity on the surface of silver-containing lithium metal. Silver iodide in the activation layer, as an insoluble silver halide, provides an efficient transport channel for lithium ions during the charge and discharge process of the lithium metal battery, effectively activating dead lithium generated during cycling and significantly reducing its accumulation, thereby greatly improving the cycle performance and lifespan of the lithium metal battery. Simultaneously, lithium nitride in the activation layer, as a component of the solid electrolyte interphase (SEI) film, effectively inhibits the growth of lithium metal dendrites, reducing the opportunity for direct contact between lithium metal and the electrolyte, further reducing the loss of active lithium, and enhancing the stability and safety of the battery. Therefore, this invention, by constructing an activation layer containing silver iodide and lithium nitride on the surface of a lithium metal substrate, can effectively alleviate the generation of dead lithium during cycling and improve the cycle stability of the battery. It is particularly suitable for high-voltage lithium metal batteries because halogens in the form of silver halides are resistant to high voltage and not easily oxidized, thus allowing the selection of high-voltage cathode materials with higher energy density to achieve a significant improvement in the cycle performance of high-energy-density lithium metal batteries.

[0021] In a preferred embodiment, the nitrogen atoms in the lithium nitride account for 5-10% of the atomic percentage of the activation layer; and / or, the iodine atoms in the silver iodide account for 5-16% of the atomic percentage of the activation layer; and / or, the activation layer further includes a second silver halide; wherein the second silver halide includes one or more of silver fluoride, silver chloride, and silver bromide; and / or, the halogen atoms in the second silver halide account for 0-5% of the atomic percentage of the activation layer.

[0022] When the nitrogen atoms in lithium nitride are controlled within the aforementioned range, it enhances the stability of the anode material, passivates the anode, and further isolates the anode from direct contact with the electrolyte to reduce side reactions and improve the cycle stability of lithium metal batteries. Controlling the iodine atoms in silver iodide within the aforementioned range aims to provide a more suitable lithium transport channel length. The aforementioned types of second silver halides can effectively modify the anode surface, aiding in the formation of a more stable SEI film, without elongating the lithium-ion diffusion path and affecting battery performance. Controlling the halogen atoms in the second silver halides within the aforementioned range aims to provide effects similar to silver iodide, while further enriching the composition and widening the lithium transport channels.

[0023] To further balance cost and energy density, in a preferred embodiment, the weight ratio of lithium to silver in the lithium metal matrix is ​​(80~99):(1~20).

[0024] In a preferred embodiment, the thickness of the activation layer is 10-50 nm; and / or, the thickness of the lithium metal substrate is 5-50 μm. The silver in the lithium metal substrate of the lithium metal anode is the residual silver after the preparation reaction. Since the amount of silver reacted is extremely small, it has almost no effect on the silver content in the substrate, and is essentially equivalent to the silver content in the lithium metal substrate raw material. The activation layer of the above thickness can provide more suitable activation and protection effects without significantly increasing the battery's internal resistance and thus affecting the overall energy density.

[0025] In another typical embodiment of the present invention, a method for preparing the lithium metal anode described above is also provided, comprising the following steps: Step S1, mixing halopyridine with an organic solvent to obtain a treatment solution; Step S2, immersing a lithium metal matrix raw material in the treatment solution to obtain a lithium metal anode; wherein, the halopyridine has the structure shown in general formula 1:

[0026] (1);

[0027] R1, R2, R3, and R4 are independently selected from H, F, Cl, Br, and I, respectively, and at least one of R1, R2, R3, and R4 is selected from I.

[0028] First, the lithium metal substrate is immersed in a treatment solution containing halopyridine. In this solution, the silver in the lithium metal substrate reacts directly with the halogen substituents in the halopyridine, forming insoluble silver iodide that adheres to the surface of the lithium metal substrate. Other halogen substituents (if present) react to form insoluble substances such as silver fluoride and silver bromide, which also adhere to the surface of the lithium metal substrate. Silver iodide can activate dead lithium during the charge and discharge process of lithium metal batteries. Its mechanism of action is that the surface silver iodide can form lithium transport channels, thereby activating dead lithium, reducing the amount of dead lithium generated during the entire cycle, and improving the battery's cycle performance.

[0029] Simultaneously, the N in the halopyridine reacts with lithium to form Li3N, which is a good SEI component. This can inhibit dendrite growth, isolate the electrolyte from the negative electrode, reduce the loss of active lithium, and further improve the battery cycle performance. The preparation process of the lithium metal negative electrode of this invention only requires one soaking step, and the organic solvent is easily volatile. The surface of the lithium metal substrate is protected by an activation layer containing silver iodide, and drying can be carried out in a drying chamber. The process is short and the cost is lower. The prepared lithium metal negative electrode can be used in pouch cells, which has great practical significance and is suitable for large-scale industrial production.

[0030] The method described above in this invention can effectively solve the problem of short cycle life caused by the generation of dead lithium during the cycling process of lithium metal batteries, significantly improve the cycle stability and overall performance of the battery, and meet the application requirements of high energy density batteries.

[0031] In a preferred embodiment, the lithium metal matrix raw material includes a lithium-silver alloy strip and / or a silver-coated lithium strip; preferably, the weight percentage of silver in the lithium-silver alloy strip is 1-20%; preferably, the thickness of the silver coating in the silver-coated lithium strip is 1-100 nm; and / or the halogenated pyridine includes one or more of 3-iodopyridine, 2-bromo-3-iodopyridine, and 5-chloro-3-fluoro-2-iodopyridine; and / or the mass concentration of the treatment solution is 0.1-5%; and / or the organic solvent includes one or more of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The aforementioned halogenated pyridines facilitate the formation of a stable lithium nitride and silver iodide activation layer, promote uniform lithium deposition during charging and discharging, significantly inhibit lithium dendrite formation, thereby extending the cycle life of the lithium metal battery. The halopyridine content in the treatment solution is more suitable within the above range, which can fully activate dead lithium while being easy to dry, resulting in lower process costs. Organic solvents can provide a more suitable environment for the dissolution of halopyridine, promote the rapid diffusion and uniform distribution of the treatment solution on the lithium metal substrate surface, accelerate the formation of the activation layer, and further enhance the electrochemical performance of the battery.

[0032] To further promote the effective chemical reaction between pyridine iodopyridine and other halopyridines in the treatment solution and silver elements on the surface of the lithium metal substrate, generating silver iodide and other silver halide compounds, and simultaneously promoting the formation of lithium nitride, in a preferred embodiment, the immersion temperature is 15~40℃ and the time is 1s~180s. These conditions facilitate the more complete and uniform formation and distribution of silver iodide and other silver halide compounds, as well as lithium nitride, on the surface of the lithium metal substrate, forming an activation layer with a moderate degree of passivation. This further effectively activates dead lithium, reduces the formation of dead lithium during battery cycling, enhances the stability of the negative electrode, inhibits the growth of lithium dendrites, and significantly improves the cycle performance and safety of lithium metal batteries.

[0033] The content of the active layer components of the lithium metal anode can be controlled by the addition ratio of lithium metal matrix raw material and halopyridine, or by the mass concentration of the treatment solution, or by the soaking temperature and time, as long as it meets the scope of the present invention.

[0034] In another typical embodiment of the present invention, a secondary battery is also provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises the aforementioned lithium metal negative electrode, wherein the surface of the lithium metal substrate in the negative electrode has an activation layer of lithium nitride and silver halide, which not only promotes the effective transport of lithium ions during battery charging and discharging and prevents the generation of dead lithium, but also, due to its insolubility, can stably adhere to the lithium metal surface, acting as a bridge for lithium ion transport, while effectively inhibiting the growth of lithium dendrites and reducing direct contact between lithium metal and electrolyte. This secondary battery has significantly improved cycle life, can use high-voltage positive electrode materials, and is suitable for high-power applications such as electric vehicles and drones.

[0035] In a preferred embodiment, the positive electrode includes a positive current collector and a positive electrode material active layer disposed on at least one side of the positive current collector. The positive electrode material active layer includes a nickel-cobalt-manganese ternary material and / or a lithium-rich manganese-based material. The aforementioned positive electrode material possesses the characteristics of a high voltage plateau and high specific capacity, which can significantly improve the overall energy density of the battery. In synergy with the lithium metal anode with the activation layer of this application, the silver iodide and lithium nitride components of the activation layer effectively suppress the growth of lithium dendrites and activate dead lithium, thereby achieving a balance between high energy density and long cycle life.

[0036] The electrolyte can be a locally high-concentration electrolyte. In a preferred embodiment, the electrolyte includes a lithium salt and a composite solvent, the composite solvent including an alcohol ether solvent and a fluoroether solvent; preferably, the lithium salt includes LiFSI and / or LiTFSI; preferably, the molar concentration of the lithium salt in the electrolyte is 0.7~2 mol / L; preferably, the alcohol ether solvent includes one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; preferably, the fluoroether solvent includes one or more of 1,1,2,2,-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE458), 1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE347), and bis(2,2,2-trifluoroethyl) ether (BTFE); preferably, the volume ratio of the alcohol ether solvent to the fluoroether solvent is (0.5~1.5):1. The above combination of lithium salt and solvent can significantly enhance the stability and conductivity of the electrolyte, enabling the electrolyte to maintain good performance under high voltage conditions, thus providing a good foundation for the operation of lithium metal batteries under high voltage.

[0037] As described above, the secondary battery of this application can maintain stable performance even at high voltages. In a preferred embodiment, the average voltage of the secondary battery is 3.5~4.3V. In some embodiments, the upper limit voltage for charging the secondary battery is 4.5V, and the lower limit voltage for discharging is 1.5V.

[0038] Typically, but not limitingly, the percentage of nitrogen atoms in the activated layer of lithium nitride is 5%, 6%, 7%, 8%, 9%, 10%, or any two of these values.

[0039] Typical, but not limiting, iodine atoms in silver iodide constitute 5%, 6%, 8%, 10%, 12%, 15%, 16%, or any two of these values ​​within a range.

[0040] Typically, but not limitingly, the percentage of halogen atoms in the second silver halide relative to the atomic content of the active layer is 0%, 1%, 2%, 3%, 4%, 5%, or any two of these values.

[0041] Typical, but not limiting, weight ratios of lithium to silver in a lithium metal matrix are 80:20, 85:15, 90:10, 95:5, 99:1, or any two of these values.

[0042] Typical, but not limited, thicknesses of the activation layer are 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any two of these values.

[0043] Typical, but not limiting, thicknesses of lithium metal substrates are 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any combination of two of these values.

[0044] Typical, but not limiting, lithium-silver alloy strips contain silver by weight of 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any two of these values.

[0045] Typical, but not limiting, silver-coated lithium strips have a silver coating thickness of 1 nm, 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, or any two of these values.

[0046] Typical, but not limiting, concentrations of the treatment solution are 0.1%, 1%, 2%, 3%, 4%, 5%, or any two of these values.

[0047] Typical, but not limiting, immersion temperatures are 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or any two of these values, and immersion times are 1s, 10s, 20s, 50s, 80s, 100s, 120s, 150s, 180s or any two of these values.

[0048] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0049] Example 1

[0050] Step S1: Mix 3-iodopyridine with ethylene glycol dimethyl ether to obtain a treatment solution with a mass concentration of 0.5%;

[0051] Step S2: Immerse a lithium-silver alloy strip with a silver content of 5% in a treatment solution at 25°C for 120s to obtain a lithium metal anode.

[0052] Examples 2 to 10

[0053] The difference from Example 1 is that the lithium metal matrix raw material, halopyridine, mass concentration of the treatment solution, soaking temperature, and soaking time are different, as detailed in Table 1.

[0054] Comparative Example 1

[0055] The difference from Example 1 is that an equal volume of ethylene glycol dimethyl ether was used to replace the treatment solution.

[0056] Comparative Example 2

[0057] The difference from Example 1 is that a lithium strip of equal weight is used instead of a lithium-silver alloy strip.

[0058] Comparative Example 3

[0059] The difference from Example 1 is that 3-iodopyridine is replaced with an equimolar amount of pyridine.

[0060] Comparative Example 4

[0061] The difference from Example 1 is that 3-iodopyridine is replaced with an equimolar amount of 1,3-diiodopropane.

[0062] Comparative Example 5

[0063] Example 1 of Chinese patent application CN120237159A is as follows:

[0064] S1. In a glove box filled with Ar, the lithium metal anode is polished by rolling and cut into a 1.2cm diameter sheet (50μm thick).

[0065] S2. Dissolve ethyl magnesium bromide (C2H5BrMg) in tetrahydrofuran to form a treatment solution (where the concentration of ethyl magnesium bromide is 100mM), and immerse the lithium metal anode in it for 10 seconds before placing it in a clean glass dish for later use.

[0066] S3. The lithium metal treated above is naturally dried in a glove box filled with Ar to obtain lithium metal with a corresponding lithium-magnesium alloy and halide interface layer (thickness of about 1.25 μm) on the surface.

[0067] S4. The treated lithium metal anode, separator (diameter 1.9cm), lithium iron phosphate as positive electrode (thickness 50um), electrolyte composition: solvent is ethylene glycol dimethyl ether (DME) and dioxolane (DOL) in a volume ratio of 1:1, solute is 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and additive is 65μL of lithium nitrate (1M LiTFSI in DME:DOL=1:1:Vol% with 1% LiNO3) at a mass ratio of 1%. Assemble into a coin cell. During cycling, control the charge and discharge voltage range to 2.4V-3.8V.

[0068] Comparative Example 6

[0069] Example 3 of Chinese patent application CN113451580A is as follows:

[0070] S1: Li 6.4 La3Zr 1.4 Nb 0.6 O 12 The solid electrolyte powder is thoroughly dried to remove the influence of trace moisture.

[0071] S2: Li 6.4 La3Zr 1.4 Nb 0.6 O 12 Solid electrolyte powder was cold-pressed into thin sheets at 10 MPa, then sintered at 1200 °C for 4 h, and cooled to room temperature in the furnace.

[0072] S3: Dissolve silver fluoride (AgF) in dimethyl sulfoxide to prepare a precursor solution with a ratio of 5 wt%, and stir thoroughly at 900 rpm for 10 h until a homogeneous solution is obtained.

[0073] S4: Then, the silver fluoride AgF precursor solution from S3 is uniformly coated onto Li. 6.4 La3Zr 1.4 Nb 0.6 O 12 After the solid electrolyte sheet is dip-coated, it is fully vacuum dried at 160°C for 24 hours to form a thin film layer.

[0074] S5: Heat metallic lithium to 220°C until it becomes molten, then uniformly coat it with the Li treated in S4. 6.4 La3Zr 1.4 Nb 0.6 O 12 On the upper surface of the solid electrolyte sheet, at the interface, silver fluoride is converted into lithium fluoride and Ag particles are distributed in the interface layer after an in-situ reaction. The thickness of the interface layer is 480 nm.

[0075] S6: The positive electrode is placed on the lower surface of the solid electrolyte in S5, forming an all-solid-state battery consisting of a lithium metal negative electrode, an interface layer, a solid electrolyte, and a positive electrode in sequence. The positive electrode includes an Al current collector and a positive electrode active material layer coated on the surface of the Al current collector. The areal density of this positive electrode active material layer is 12 mg / cm³. 2 The composition includes 94wt% LiNi 0.5 Co 0.3 Mn 0.2 O2, 2.9 wt% Super-P and 3.1 wt% PVDF-HFP;

[0076] S7: Uniformly impregnate the silver fluoride AgF precursor solution from S3 onto Li 6.4 La3Zr 1.4 Nb 0.6 O 12 After dip-coating, the upper and lower surfaces of the solid electrolyte sheet were thoroughly vacuum-dried at 160°C for 24 hours to form Li. 6.4 La3Zr 1.4 Nb 0.6 O 12Electrolyte film layer; lithium metal is heated to 220°C to molten state, and then uniformly coated onto the above-mentioned Li... 6.4 La3Zr 1.4 Nb 0.6 O 12 On the surface of the solid electrolyte thin film layer, an in-situ reaction occurs at the interface, where silver fluoride is converted into lithium fluoride and Ag particles are distributed in the interface layer, which has a thickness of 480 nm; assemble a Li / interface layer / solid electrolyte / interface layer / Li symmetric cell.

[0077] Comparative Example 7

[0078] Example 1 of Chinese patent application CN116722143A is as follows:

[0079] An anode for an anode-free lithium metal battery was prepared using graphite as the anode active material, PVDF as the binder, conductive carbon black as the conductive agent, and 3% (w / w) of L-aziridinium-2-carboxylic acid lithium as a lithium supplementation additive.

[0080] Step 1: Mix 0.6g of graphite, 0.075g of PVDF and 0.075g of conductive carbon black, and then add 0.0225g of L-aziridine-2-carboxylic acid lithium to obtain an anode mixture;

[0081] Step 2: Add the anode mixture obtained in Step 1 to 2.5 mL of 1-methyl-2-pyrrolidone to prepare a solution, and stir at room temperature for 24 h to obtain the anode slurry;

[0082] Step 3: Apply the anode slurry obtained in Step 2 evenly to the surface of the copper foil, and vacuum dry for 12 hours until 1-methyl-2-pyrrolidone is completely volatilized to obtain the anode electrode.

[0083] Step 4: Cut the copper foil coated with the mixture obtained in Step 3 into circular foils with a diameter of 14 mm to obtain an anode containing 3% L-aziridine-2-carboxylic acid lithium.

[0084] Performance testing:

[0085] The above embodiments and comparative examples were subjected to the following tests, and the results are shown in Tables 2 and 3.

[0086] 1. Lithium metal anode

[0087] The atomic percentage of iodine, halogen, and nitrogen atoms in the active layer: The atomic content of the corresponding elements in the etching depth of 0-50 nm was detected by X-ray photoelectron spectroscopy (XPS).

[0088] Thickness of the activation layer and lithium metal substrate: determined by X-ray photoelectron spectroscopy (XPS) and transmission scanning electron microscopy (TEM).

[0089] The weight percentage of silver in the lithium-silver alloy strip was determined using inductively coupled plasma (ICP).

[0090] Thickness of the silver coating in the silver-coated lithium strip: The thickness of the silver coating was observed using a transmission electron microscope (TEM).

[0091] 2. Lithium metal batteries

[0092] A 2Ah lithium metal pouch cell was assembled using a lithium metal anode, an NCM811 cathode, an electrolyte (1.1mol / L LiFSI, DME:HFE458=1:1(v:v)), and a polyethylene separator.

[0093] Battery energy density: At room temperature, charge to 4.3V using a constant current and constant voltage at 0.1C, cut off current at 0.05C, and let stand for 30 minutes. Discharge to 3V using a constant current at 0.1C, and record the discharge energy. Weigh the battery using an electronic balance, and calculate the energy density according to the formula: Battery energy density = Discharge energy ÷ Battery weight.

[0094] Battery cycle performance: Cyclic charge and discharge tests were conducted at a charge rate of 0.2C and a discharge rate of 0.2C, with a voltage range of 3~4.3V. The number of cycles when the discharge capacity dropped to 80% of the initial discharge capacity was recorded.

[0095] Table 1

[0096]

[0097] Table 2

[0098]

[0099] Table 3

[0100]

[0101] As can be seen, Comparative Examples 1 to 4 failed to form an active layer containing lithium nitride, silver iodide, and other silver halides, thus failing to activate dead lithium generated during the charging and discharging process of lithium metal batteries, resulting in poor cycle performance. In Comparative Example 5, the RAX compound decomposed into free halide ions, which are not resistant to high voltage and are easily oxidized. Therefore, only lithium iron phosphate cathodes could be used, and high-voltage nickel-cobalt-manganese ternary cathodes could not be used. The resulting battery had low energy density and limited practical application. In Comparative Example 6, the absence of silver iodide prevented the formation of a good lithium transport channel, leading to severe dendrite growth and a short battery cycle life. In Comparative Example 7, the failure to form only lithium nitride resulted in a relatively poor lithium transport channel, leading to severe dendrite growth and a short battery cycle life.

[0102] As shown above, lithium metal anodes treated with iodopyridine exhibit excellent lithium transport properties, can activate dead lithium, and improve the cycle life of lithium metal batteries. Compared to the comparative examples, the embodiments of this invention provide an activation layer with specific chemical activity on the surface of the silver-containing lithium metal anode. The silver iodide in the activation layer can form lithium transport channels, activating dead lithium during the charge and discharge process of the lithium metal battery, reducing the amount of dead lithium generated throughout the cycle, and improving the battery's cycle performance. Simultaneously, Li3N is a good SEI component, which can inhibit dendrite growth, isolate the electrolyte from the anode, reduce active lithium loss, and further improve battery cycle performance. Furthermore, halogens existing in the form of silver halide are resistant to high voltage and are not easily oxidized; therefore, high-voltage cathode materials with higher energy density can be selected to achieve a significant improvement in the cycle performance of high-energy-density lithium metal batteries.

[0103] Furthermore, it can be seen that the overall effect is better when all process parameters are within the preferred range of the present invention.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium metal anode, characterized in that, It includes a lithium metal substrate and an activation layer, wherein the activation layer covers at least a portion of the surface of the lithium metal substrate; The lithium metal matrix includes lithium and silver elements; The activation layer comprises lithium nitride and a first silver halide, wherein the first silver halide comprises silver iodide.

2. The lithium metal anode according to claim 1, characterized in that, The nitrogen atoms in the lithium nitride account for 5-10% of the atomic percentage of the activation layer; And / or, the iodine atoms in the silver iodide account for 5-16% of the atomic percentage of the activated layer; And / or, the activation layer further includes a second silver halide; wherein the second silver halide includes one or more of silver fluoride, silver chloride and silver bromide; and / or, the halogen atoms in the second silver halide account for 0 to 5% of the atomic percentage of the activation layer.

3. The lithium metal anode according to claim 1 or 2, characterized in that, In the lithium metal matrix, the weight ratio of lithium to silver is (80~99):(1~20).

4. The lithium metal anode according to any one of claims 1 to 3, characterized in that, The thickness of the activation layer is 10~50 nm; And / or, the thickness of the lithium metal substrate is 5~50μm.

5. The method for preparing the lithium metal anode according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Mix halopyridine with an organic solvent to obtain a treatment solution; Step S2: Immerse the lithium metal matrix raw material in the processing solution to obtain the lithium metal anode; The halopyridine has the structure shown in general formula (1): （1）； R1, R2, R3, and R4 are independently selected from H, F, Cl, Br, and I, respectively, and at least one of R1, R2, R3, and R4 is selected from I.

6. The method for preparing a lithium metal anode according to claim 5, characterized in that, The lithium metal matrix raw material includes lithium-silver alloy strip and / or silver-coated lithium strip; preferably, the weight percentage of silver in the lithium-silver alloy strip is 1~20%; preferably, the thickness of the silver coating in the silver-coated lithium strip is 1~100nm. And / or, the halopyridines include one or more of 3-iodopyridine, 2-bromo-3-iodopyridine, and 5-chloro-3-fluoro-2-iodopyridine; And / or, the mass concentration of the treatment solution is 0.1% to 5%; And / or, the organic solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

7. The method for preparing a lithium metal anode according to claim 5 or 6, characterized in that, The soaking temperature is 15~40℃ and the soaking time is 1s~180s.

8. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode comprises the lithium metal negative electrode according to any one of claims 1 to 4.

9. The secondary battery according to claim 8, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode material active layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode material active layer includes a nickel-cobalt-manganese ternary material and / or a lithium-rich manganese-based material.

10. The secondary battery according to claim 8 or 9, characterized in that, The average voltage of the secondary battery is 3.5~4.3V.

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