A lithium electrode with a Li3N artificial SEI film, its preparation method and application

Abstract

This invention discloses a lithium electrode with a Li3N artificial SEI film, its preparation method, and its application. The invention relates to the field of lithium electrode preparation technology. The method includes the following steps: drying a solid nitrogen source, then decomposing the solid nitrogen source using heating or plasma technology to obtain a reactant gas; and depositing the reactant gas on the surface of a lithium metal foil using plasma chemical vapor deposition (PCVD) to obtain a lithium electrode with a Li3N artificial SEI film. The process involved in this invention is time-efficient, easy to operate, uses very little solid nitrogen source, has low cost, and a high safety factor. Simultaneously, the generated lithium nitride artificial SEI film has controllable thickness, good mechanical properties, and good uniformity. This invention solves the problems of poor mechanical properties, uncontrollable thickness, and poor uniformity of existing lithium nitride layers.

Description

Technical Field

[0001] This invention relates to the field of lithium electrode preparation technology, specifically to a lithium electrode with a Li3N artificial SEI film, its preparation method, and its application. Background Technology

[0002] The surge in demand for electric vehicles and power grids has significantly increased the need for high-energy-density rechargeable batteries. Existing lithium-ion batteries with graphite anodes have reached near-saturation in terms of actual capacity, approaching their theoretical limit (372 mAh g). -1 The limited capacity of lithium metal has severely restricted the development of the energy storage industry, making the search for next-generation anode materials with high specific capacity and high cycle stability an urgent priority. Among many promising candidates, lithium metal stands out due to its lowest electrochemical potential (-3.04V vs. standard hydrogen electrode) and low density (0.59g / cm³). -3 ) and an ultra-high theoretical capacity (3860mAh g) -1 However, lithium metal as an anode presents numerous problems during cycling, such as the accumulation of solid electrolyte interphase (SEI), lithium dendrite growth, and significant volume changes. These issues reduce the coulombic efficiency of lithium metal batteries (LMBs), decrease the actual capacity of the anode, and cause safety accidents such as short circuits or even explosions due to lithium dendrite growth piercing the separator, thus hindering the commercialization of lithium metal batteries (LMBs).

[0003] To address the aforementioned problems, several improvement strategies exist: first, constructing a three-dimensional substrate; second, replacing organic electrolytes with solid electrolytes; and third, constructing an SEI film on the lithium metal surface. Among these, the high mass proportion of the three-dimensional substrate significantly sacrifices the energy density of the lithium metal anode, even falling below that of graphite as the anode. Compared to organic electrolytes, solid electrolytes have a smaller effective contact area with the electrode, resulting in higher interfacial resistance and drastically reduced lithium-ion transport performance. Therefore, designing an SEI film with high ionic conductivity and high interfacial energy becomes the most effective improvement strategy. Lithium nitride (Li3N) is chosen due to its high lithium-ion conductivity (2.3 × 10⁻⁶). -3 S cm -1Its advantages, such as high Young's modulus, stable electrochemical window for lithium metal, and low solubility in electrolytes, have made it a focus of current research. Currently, the preparation methods of Li3N artificial SEI film are mainly divided into the following categories: (1) Electrolyte modification: Nitrates such as (LiNO3) are added to the electrolyte to form Li3N. The generated SEI film is thin and has high ion conductivity. However, organic electrolytes are volatile and highly toxic. Nitrates such as LiNO3 are dangerous chemicals and are relatively dangerous. In addition, the mechanical properties of the formed Li3N film are poor. (2) Rolling method: Commercial Li3N powder is ground and placed on Li foil and rolled. This method will cause uneven thickness of lithium foil and poor integrity and uniformity of the obtained Li3N artificial SEI film. (3) High temperature melting method: Molten Li is exposed in a nitrogen glove box, or g-C3N4 is used to react with molten lithium metal at high temperature to prepare Li3N. The thickness of the Li3N formed by this method is uncontrollable and the uniformity is poor. It is inconvenient to operate in the glove box. High temperature will easily cause damage to rubber gloves, resulting in economic losses. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a lithium electrode with a Li3N artificial SEI film, its preparation method, and its application, thereby solving the problems of poor mechanical properties, uncontrollable thickness, and poor uniformity of existing lithium nitride layers.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a lithium electrode with a Li3N artificial SEI film is provided, comprising the following steps:

[0006] (1) Dry the solid nitrogen source, and then use heating or plasma technology to decompose the solid nitrogen source to obtain the reaction gas;

[0007] (2) The reaction gas obtained in step (1) is deposited on the surface of a lithium metal foil using plasma chemical vapor deposition technology to obtain a lithium electrode with an artificial SEI film of Li3N.

[0008] Based on the above technical solution, the present invention can be further improved as follows:

[0009] Furthermore, in step (1), the solid nitrogen source is urea, thiourea, or ammonium hydrogen fluoride.

[0010] Furthermore, in step (1), drying is carried out at 20-60℃.

[0011] Furthermore, in step (1), heating is performed at 180-220°C.

[0012] Furthermore, in step (1), the mass of the solid nitrogen source is 1-5g.

[0013] Furthermore, in step (2), the diameter of the lithium metal foil is 10-15 mm.

[0014] Furthermore, in step (2), deposition is carried out for 1-10 minutes under a power of 100-500W.

[0015] Furthermore, in step (2), when the solid nitrogen source in step (1) is thiourea, a lithium electrode with an artificial SEI film of Li3N-Li2S is obtained.

[0016] The present invention also provides a lithium electrode with a Li3N artificial SEI film prepared by the above method.

[0017] The present invention also provides the application of the above-mentioned lithium electrode with Li3N artificial SEI film in symmetrical battery assembly.

[0018] The present invention has the following beneficial effects:

[0019] The innovation of this invention lies in using a solid nitrogen source as plasma to prepare lithium nitride on the surface of lithium metal using PECVD technology. The process involved in this invention is time-efficient, easy to operate, uses very little solid nitrogen source, has low cost, and a high safety factor. Simultaneously, the generated lithium nitride artificial SEI film has controllable thickness, good mechanical properties, and good uniformity, overcoming the problems of traditional methods. Furthermore, the use of a solid nitrogen source offers good scalability, allowing for the formation of other artificial SEI films that synergistically protect the lithium metal anode with the lithium nitride SEI film. Attached Figure Description

[0020] Figure 1 XPS image of the lithium electrode prepared in Example 1;

[0021] Figure 2 XPS image of the lithium electrode prepared in Example 1;

[0022] Figure 3 XPS image of the lithium electrode prepared in Example 2;

[0023] Figure 4 XPS image of the lithium electrode prepared in Example 2;

[0024] Figure 5 XPS image of the lithium electrode prepared in Example 3;

[0025] Figure 6 The graphs show the long-cycle performance of the Li3N / Li symmetric cell and the bare Li symmetric cell prepared in Example 1.

[0026] Figure 7 The graph shows the long-cycle performance of the Li3N-Li2S / Li symmetric cell and the bare Li symmetric cell prepared in Example 2. Detailed Implementation

[0027] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0028] Example 1:

[0029] A lithium electrode with a Li3N artificial SEI film is prepared by the following steps:

[0030] (1) In an air atmosphere, place 4g of solid nitrogen source urea in a glass container and dry it at 50°C to remove moisture;

[0031] (2) In the glove box, cut the lithium metal foil into a circle with a diameter of 12 mm, place it in the middle left of the quartz tube, and seal it; take out the glass container containing urea from the oven, connect it to the right side of the quartz tube, put on the heating jacket, heat the glass container to 200℃, and at the same time, place the positive electrode of PECVD on the right side of the quartz tube and the negative electrode on the side of the lithium metal. Under the condition of 300W power, process for 1 min to obtain a lithium electrode with Li3N artificial SEI film.

[0032] Example 2:

[0033] A lithium electrode with a Li3N-Li2S artificial SEI film is prepared by the following steps:

[0034] (1) Weigh 4g of thiourea in air atmosphere, place it in a crucible, and dry it at 50°C to remove the moisture in the thiourea. After the thiourea is dried, cover the surface of the crucible with plastic wrap and quickly transfer it to a glove box.

[0035] (2) In the glove box, cut the lithium metal foil into a circle with a diameter of 12mm and place it in the middle left of the quartz tube. After removing the plastic wrap on the surface of the crucible containing thiourea, place it in the right side of the quartz tube (at a certain distance from the lithium sheet) and seal it. Place the positive electrode of PECVD on the side of the quartz tube containing thiourea and the negative electrode on the other side. Process for 2 minutes under a power of 300W to obtain a lithium electrode with an artificial SEI film of Li3N-Li2S.

[0036] Example 3:

[0037] A lithium electrode with a Li3N artificial SEI film is prepared by the following steps:

[0038] (1) Weigh 2g of ammonium bifluoride in air atmosphere, place it in a crucible, and dry it at 20°C to remove the moisture in the ammonium bifluoride. After the ammonium bifluoride is dried, cover the surface of the crucible with plastic wrap and quickly transfer it to a glove box.

[0039] (2) In the glove box, cut the lithium metal foil into a circle with a diameter of 12 mm and place it in the middle left of the quartz tube. After removing the plastic wrap on the surface of the crucible containing ammonium bifluoride, place it in the right side of the quartz tube (at a certain distance from the lithium sheet) and seal it. Place the positive electrode of PECVD on the side of the quartz tube containing ammonium bifluoride and the negative electrode on the other side. Process for 10 min under a power of 100 W to obtain a lithium electrode with an artificial SEI film of Li3N.

[0040] Test case

[0041] I. The lithium electrodes with artificial SEI films prepared in Examples 1-3 were subjected to XPS detection, and the results are shown in the figure. Figure 1-5 .

[0042] Depend on Figure 1-2 It can be seen that using urea as a plasma source to process lithium metal generates a Li3N SEI film.

[0043] Depend on Figure 3-4 It can be seen that using thiourea as a plasma source to treat lithium metal produces two types of SEI films: Li3N and Li2S.

[0044] Depend on Figure 5 It can be seen that using ammonium bifluoride as a plasma source to process lithium metal generates a Li3N SEI film.

[0045] II. Symmetrical cells were assembled using the lithium electrode with a Li3N artificial SEI film (Li3N / Li) and the lithium electrode without an artificial SEI film (bare Li) prepared in Example 1, respectively. Their long-cycle performance in ester electrolytes was measured, and the results are shown in [Figure 1]. Figure 6 (At the x-axis of 200, the narrow part is Li3N / Li).

[0046] Depend on Figure 6 It can be seen that, in ester electrolytes, the polarization voltage of the Li3N / Li assembled symmetric cell prepared in Example 1 after cycling for more than 200 hours is less than that of the bare Li assembled symmetric cell, indicating that the generated Li3N artificial SEI film can alleviate the growth of lithium dendrites and extend the battery life.

[0047] III. The lithium electrode with Li3N-Li2S artificial SEI film (Li3N-Li2S / Li) and the lithium electrode without artificial SEI film (bare Li) prepared in Example 2 were respectively assembled into symmetrical cells, and their long-cycle performance in ether electrolytes was measured. The results are shown in […]. Figure 7 (At the x-axis of 200, the narrow part is Li3N-Li2S / Li).

[0048] Depend on Figure 7 It can be seen that the polarization voltage of the Li3N-Li2S / Li assembled symmetric cell prepared in Example 2 is lower than that of the bare Li symmetric cell, and the cycle stability is stronger than that of the bare Li assembled cell. This indicates that the generated Li3N-Li2S artificial SEI film can alleviate the growth of lithium dendrites and extend the battery life.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium electrode with a Li3N artificial SEI film, characterized by, The method comprises the following steps: (1) drying a solid nitrogen source, and then decomposing the solid nitrogen source by heating or plasma technology to obtain a reaction gas; (2) depositing the reaction gas obtained in step (1) on a surface of a lithium foil by plasma chemical vapor deposition technology to obtain a lithium electrode with a Li3N artificial SEI film; In step (1), the solid nitrogen source is urea, thiourea or ammonium bifluoride. In step (1), the drying is performed at 20-60℃. In step (2), the deposition is performed at a power of 100-500W for 1-10min.

2. The method for preparing a lithium electrode with a Li3N artificial SEI film according to claim 1, characterized in that, In step (1), the heating is performed at 180-220℃.

3. The method for preparing a lithium electrode with a Li3N artificial SEI film according to claim 1, characterized in that, In step (1), the mass of the solid nitrogen source is 1-5g.

4. The method for preparing a lithium electrode with a Li3N artificial SEI film according to claim 1, characterized in that, In step (2), the diameter of the lithium foil is 10-15mm.

5. The method for preparing a lithium electrode with a Li3N artificial SEI film according to claim 1, characterized in that, In step (2), when the solid nitrogen source in step (1) is thiourea, a lithium electrode with a Li3N-Li2S artificial SEI film is obtained.

6. The lithium electrode with a Li3N artificial SEI film obtained by the method for preparing the lithium electrode with a Li3N artificial SEI film according to any one of claims 1-5.

7. Use of the lithium electrode with a Li3N artificial SEI film according to claim 6 in assembling a symmetric battery.

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