Artificial seimembrane for protecting lithium anode of lithium primary battery and preparation method thereof

Abstract

The application relates to an artificial SEI film for protecting a lithium negative electrode of a lithium primary battery and a preparation method based on spin coating. The artificial SEI film is essentially a composite coating film constructed by a polycarbonate organic polymer matrix, an inorganic lithium-containing compound and an organic lithium salt on the surface of a metal lithium negative electrode. The artificial SEI film coated on the surface of the metal lithium negative electrode of the lithium primary battery can effectively isolate the contact between the electrolyte and the metal lithium negative electrode and reduce the occurrence of a side reaction; the artificial SEI film with high ion conductivity and good interface compatibility can accelerate the diffusion of lithium ions and stabilize the lithium negative electrode. Therefore, the lithium negative electrode coated with the artificial SEI film used in the lithium primary battery can not only obviously improve the discharge specific capacity of the lithium primary battery, but also realize excellent rate performance and storage stability of the lithium primary battery; moreover, because the mixed solution configuration and the spin coating process are simple and controllable, the improvement of the electrochemical performance and the safety performance can be realized through simple steps, and large-scale production is easy to realize.

Description

Technical Field

[0001] This invention belongs to the field of lithium primary battery technology. Specifically, it relates to an artificial SEI film for protecting the lithium anode in a lithium primary battery. Background Technology

[0002] A lithium primary battery, also known as a lithium-ion battery, uses metallic lithium or lithium alloys as the negative electrode material and sulfides, oxides, or fluorides as the positive electrode material. Energy is released through the migration of lithium ions formed on the lithium negative electrode in the electrolyte and their reaction with the positive electrode material. It is non-rechargeable. Metallic lithium has an extremely high specific capacity (3860 mAh g⁻¹). -1 With its low reduction potential (-3.04 V vs. standard hydrogen electrode), lithium metal is one of the most attractive anode materials for high-energy-density batteries. Lithium primary batteries using metallic lithium paired with high-capacity cathode materials (such as carbon fluoride, sulfur dioxide, thionyl chloride, and manganese dioxide) achieve nearly twice the energy density (>1000 Wh / kg) of lithium-ion batteries. -1 It has a wide operating temperature range and good safety performance, and has been widely used in the field of energy storage.

[0003] A key problem with lithium primary batteries in application is their low specific capacity and poor storage and safety performance. Current modification methods for lithium primary batteries mainly focus on the cathode material, but the lithium metal anode also significantly impacts the capacity and stability of lithium primary batteries. Lithium metal is chemically reactive and spontaneously reacts with the electrolyte to form a solid electrolyte interphase (SEI) film. Continuous electrolyte consumption and electrochemical corrosion of lithium metal lead to a decrease in operating voltage and capacity decay. Therefore, modifying the lithium metal anode is a crucial issue that urgently needs to be addressed. Modifying the lithium metal anode essentially involves controlling the SEI film. By adjusting the composition and thickness of the artificial SEI film, a stable and robust SEI film can be formed, effectively preventing direct contact between lithium metal and the electrolyte and reducing electrolyte decomposition. Regarding composition control, polycarbonate-based organic polymer matrices containing aliphatic or cyclic carbonates [-O-(C=O)-O-] exhibit high dielectric constants and good interfacial compatibility, effectively stabilizing the electrode / electrolyte interface. Inorganic lithium-containing compounds possess high ionic conductivity, accelerating lithium-ion migration at the interface. In terms of thickness control, spin-coating technology allows for adjustment of film thickness through rotation speed and spin-coating solution concentration, offering advantages such as controllable film thickness, good uniformity, simple process, and low cost. Therefore, spin-coating technology can be used to directly coat a lithium metal anode with an ideal artificial SEI film of optimal composition and thickness. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art, such as the low actual specific capacity and excessively rapid capacity decay of lithium primary batteries.

[0005] This invention includes the following technical solutions:

[0006] This invention provides an artificial SEI film for protecting the lithium anode in lithium primary batteries. The artificial SEI film is a composite material consisting of one or more components selected from polycarbonate organic polymer matrix, inorganic lithium compound, and organic lithium salt, which are directly coated onto the surface of the active material layer of the lithium metal anode using a spin coating method.

[0007] Preferably, the polycarbonate organic polymer matrix is ​​one or a combination of polypropylene carbonate, polyethylene carbonate, polyethylene carbonate, and polytrimethylene carbonate.

[0008] Preferably, the inorganic lithium-containing compound is one or more combinations of lithium nitride, lithium sulfide, lithium fluoride, lithium carbonate, lithium lanthanum zirconium oxide, and lithium lanthanum titanium oxide.

[0009] Preferably, the organolithium salt is one or more combinations of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorooxalateborate, and lithium hexafluorophosphate.

[0010] Preferably, the lithium primary battery is one of lithium-carbon fluoride battery, lithium-aluminum fluoride battery, lithium-manganese dioxide battery, lithium-sulfur dioxide battery, lithium-iron disulfide battery, and lithium-thionyl chloride battery.

[0011] This invention also proposes a method for preparing the artificial SEI film protecting the lithium anode, comprising the following steps: dissolving a polycarbonate-based organic polymer matrix and an organic lithium salt in an organic solvent at a certain ratio, heating and stirring at 60°C for 30 min until the polymer matrix and lithium salt are completely dissolved in the solvent, forming a viscous solution. Adding a certain proportion of an inorganic lithium-containing compound to the solution, and continuing to stir at room temperature for 12 h until the inorganic lithium-containing compound is uniformly dispersed in the solution, forming a slightly viscous mixed solution. Dropping 100 μL of the mixed solution onto a lithium sheet, and after high-speed rotation, the solution can spread on the metallic lithium sheet to form a uniform coating film. Placing the spin-coated lithium sheet on a 60°C heating stage for 24 h until all the organic solvent evaporates, achieving the artificial SEI film coating treatment of the metallic lithium anode.

[0012] Preferably, the organic solvent is one or a combination of anhydrous acetonitrile, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran.

[0013] Preferably, the concentration of the polycarbonate organic polymer matrix in the mixed solution is 0.1-0.5 g / mL, the content of the inorganic lithium compound is 1%-40% of the polymer content, the lithium salt content is 10% of the polymer content, and the spin coating speed is 100-5000 rpm. By adjusting the concentration of the polycarbonate organic polymer matrix, the content of the inorganic lithium compound, and the spin coating speed, the final thickness of the artificial SEI film is 1-20 μm.

[0014] Preferably, the water content of the mixed solution is less than or equal to 10 ppm.

[0015] The advantages and positive effects of this invention are as follows:

[0016] This invention utilizes spin-coating technology to directly coat the surface of the active material layer of a lithium metal anode with an artificial SEI film composed of a polycarbonate-based organic polymer matrix, an inorganic lithium-containing compound, and an organic lithium salt, and applies this film to lithium primary batteries. On one hand, the inorganic lithium-containing compound, possessing high ionic conductivity, is uniformly dispersed within the polycarbonate-based organic polymer matrix, which exhibits good interfacial compatibility and high dielectric properties. The organic and inorganic phases are tightly bonded, forming a robust and stable artificial SEI film. This film effectively isolates the electrolyte from the lithium metal anode, reducing side reactions, and accelerates lithium-ion diffusion at the electrode / electrolyte interface. On the other hand, compared to SEI films and solid electrolyte films generated through in-situ reactions, directly spin-coating the artificial SEI film onto the lithium metal anode provides direct protection, stabilizes the electrode / electrolyte interface, and prevents the loss of lithium active material. Therefore, lithium anodes coated with this artificial SEI film, when used in lithium primary batteries, not only significantly improve the discharge specific capacity of the lithium primary battery but also achieve excellent rate performance and storage stability. Moreover, because the preparation of the mixed solution and the spin coating process are simple and controllable, electrochemical performance and safety performance can be improved through simple steps, making it easy to achieve large-scale production. Attached Figure Description

[0017] Figure 1 Li-CF made from lithium metal sheets coated with an artificial SEI film, as provided in Example 1 of this invention. x Li-CF batteries made from original lithium sheets x A comparison of the specific discharge capacity of batteries at different discharge rates at room temperature;

[0018] Figure 2 Li-CF made from lithium metal sheets coated with an artificial SEI film, as provided in Example 1 of this invention. x Li-CF batteries made from original lithium sheets x The battery operates at room temperature and 55 o C. Comparison of discharge specific capacity at different storage times;

[0019] Figure 3 The original lithium sheet surface SEM image provided as a comparative example of this invention;

[0020] Figure 4 SEM image of the surface of a lithium metal anode coated with an artificial SEI film provided in Example 1 of this invention;

[0021] Figure 5 Li-CF prepared from the original lithium sheet provided as a comparative example of the present invention x SEM image of the lithium anode surface after the battery was discharged at room temperature for 60 days;

[0022] Figure 6 Li-CF made from lithium metal sheets coated with an artificial SEI film, as provided in Example 1 of this invention. x SEM image of the lithium anode surface after the battery was discharged for 60 days at room temperature. Detailed Implementation

[0023] To further disclose the content, features, and effects of this invention, the following examples are provided and detailed in conjunction with the accompanying drawings.

[0024] Example 1:

[0025] In a glove box, 1.5 g (0.3 g / mL) of polypropylene carbonate (PPC) and 0.15 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to 5 mL of anhydrous acetonitrile (ACN), and the mixture was heated to 60 °C. o Stir magnetically at C for 30 min until PPC and LiTFSI are completely dissolved in ACN, forming a viscous solution. Add 0.075 g (5%) of lithium nitride (Li3N) particles to the solution and continue stirring at room temperature for 12 h until Li3N is uniformly dispersed in the solution, forming a slightly viscous mixed solution. Drop 100 μL of the mixed solution onto a 16 mm lithium sheet, and after high-speed rotation at 3000 rpm, the solution spreads on the lithium sheet to form a uniform artificial SEI film. Place the spin-coated lithium sheet on a 60 °C heating stage for 24 h until all organic solvents evaporate, achieving the artificial SEI film coating treatment of the lithium metal anode.

[0026] CF proportionally x Super P and PVDF (in a mass ratio of 80:10:10) were uniformly mixed, and N-methylpyrrolidone was added and stirred (NMP) for 12 h to obtain a uniform slurry, which was then coated onto aluminum foil. oAfter being placed in a constant temperature vacuum oven for 12 hours, the electrode sheet was stamped into a positive electrode with a diameter of 14 mm and then quickly placed in a glove box. It was then assembled with a lithium metal anode coated with an artificial SEI membrane and a separator (permeable polypropylene film Celgard 2325) using an ether-based electrolyte to form a CR2032 type Li-CF electrode. x The coin cells were subjected to constant current discharge testing at room temperature. Battery disassembly was also performed in a glove box, and the resulting lithium anode was repeatedly washed three times with DOL and dried before characterization.

[0027] Comparative example:

[0028] Using the original lithium sheet as the lithium metal anode, and otherwise identical to the example, a CR2032 type Li-CF was assembled. x Button cell battery.

[0029] The CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film in this invention x Button cells and Li-CF made from virgin lithium sheets x The button cells were tested at different rates at room temperature, and the test results are as follows: Figure 1 As shown. The blue one is Li-CF made of lithium metal sheets coated with an artificial SEI film. x The red battery is Li-CF4 made from raw lithium wafers. x Battery. From Figure 1 As can be seen, Li-CF made from lithium metal sheets coated with an artificial SEI film... x The battery shows 940 mAh g at 0.1 C. -1 Its excellent discharge specific capacity is higher than that of Li-CF x Battery (895 mAh g) -1 Li-CF40 ... x The battery still achieves 621 and 492 mAh g⁻¹ at high current densities of 5.0 C and 8.0 C, respectively. -1 Its discharge specific capacity is much higher than that of Li-CF using the original lithium sheet. x The battery has 493 and 440 mAh g -1 (5.0 C and 8.0 C). Li-CF made from lithium metal sheets coated with an artificial SEI film. x The battery's excellent rate performance indicates that coating with an artificial SEI film enhances lithium-ion transport kinetics and improves interfacial compatibility between the electrode and electrolyte, thereby stabilizing the lithium metal electrode and reducing capacity loss at high current densities.

[0030] The CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film in this invention xButton cells and Li-CF made from virgin lithium sheets x Button cells at room temperature and 55 o Tests were conducted after storing data for different durations in C, and the test results are as follows: Figure 2 As shown. Li-CF4 fabricated from lithium metal sheets coated with an artificial SEI film. x The battery operates at room temperature and 55 o After being stored at C for 60 days, the battery can still release 867 and 536 mAh g. -1 High specific capacity. And Li-CF4 made from raw lithium wafers... x The battery operates at room temperature and 55 o After 60 days of storage at temperature C, the capacity decayed significantly, with the discharge specific capacity only reaching 824 and 455 mAh g. -1 Li-CF40 ... x The improved storage performance of the battery can be attributed to the fact that the artificial SEI film can block direct contact between the lithium anode and the electrolyte and suppress the occurrence of side reactions. In addition, the artificial SEI film with high ionic conductivity can improve the transport kinetics of lithium ions in lithium primary batteries, thereby improving their electrochemical performance and storage stability.

[0031] Depend on Figure 3 It can be observed that there is obvious unevenness on the surface of the original lithium sheet, and Figure 4 The surface morphology of the lithium metal sheet coated with an artificial SEI film shows a uniform and dense protective layer, exhibiting a smooth and flat morphology. (Compared to...) Figure 5 The Li-CF shown is made from raw lithium sheets. x Unlike the lithium anode surface of a battery removed after 60 days of storage at room temperature, which was covered with byproducts, Li-CF4 made from lithium metal sheets coated with an artificial SEI film... x The surface morphology of the lithium anode removed after 60 days of discharge at room temperature is as follows: Figure 6 As shown, the surface of the modified lithium anode was relatively smooth after storage and discharge, and no aggregation of byproducts was observed. This indicates that the artificial SEI film coating the surface of the lithium metal anode can effectively protect the lithium metal anode and inhibit the occurrence of side reactions.

[0032] Example 2:

[0033] In a glove box, add 1.0 g (0.2 g / mL) of polypropylene carbonate (PPC) and 0.10 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to 5 mL of anhydrous acetonitrile (ACN) and heat at 60 °C. oStir magnetically at room temperature for 30 min until PPC and LiTFSI are completely dissolved in ACN, forming a viscous solution. Add 0.05 g (5%) of lithium nitride (Li3N) particles to the solution and continue stirring at room temperature for 12 h until Li3N is uniformly dispersed in the solution, forming a slightly viscous mixed solution. Under the same conditions as in Example 1, CR2032 type Li-CF32 was assembled. x Button cell battery.

[0034] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: as shown in Table 1, Li-CF3 with an artificial SEI film coated with a lithium metal anode using a concentration of 0.2 g / mL PPC was used. x The battery's discharge specific capacity is 873 mAh g. -1 This indicates that the artificial SEI film prepared at a lower PPC concentration is unstable and cannot effectively protect the lithium anode, particularly for Li-CF4. x The improvement in the battery's discharge capacity has not had a significant effect.

[0035] Example 3:

[0036] In a glove box, add 2.5 g (0.5 g / mL) of polypropylene carbonate (PPC) and 0.25 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to 5 mL of anhydrous acetonitrile (ACN) and heat at 60 °C. o Stir magnetically at room temperature for 30 min until PPC and LiTFSI are completely dissolved in ACN, forming a viscous solution. Add 0.125 g (5%) of lithium nitride (Li3N) particles to the solution and continue stirring at room temperature for 12 h until Li3N is uniformly dispersed in the solution, forming a slightly viscous mixed solution. Under the same conditions as in Example 1, CR2032 type Li-CF32 was assembled. x Button cell battery.

[0037] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: as shown in Table 1, Li-CF3 with an artificial SEI film coated with a lithium metal anode using a concentration of 0.5 g / mL PPC was used. x The battery's discharge specific capacity is 799 mAh g. -1 This indicates that the artificial SEI film prepared at high PPC concentrations is unstable. It not only fails to effectively protect the lithium anode, but may also hinder lithium-ion migration due to the aggregation of inorganic lithium compounds within the artificial SEI film, thus negatively impacting Li-CF4. x Battery discharge.

[0038] Example 4:

[0039] In a glove box, 1.5 g (0.3 g / mL) of polypropylene carbonate (PPC) and 0.15 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to 5 mL of anhydrous acetonitrile (ACN), and the mixture was heated to 60 °C. o The solution was magnetically stirred at room temperature for 30 min until PPC and LiTFSI were completely dissolved in ACN, forming a viscous solution. 0.045 g (3%) of lithium nitride (Li3N) particles were added to the solution, and stirring was continued at room temperature for 12 h until Li3N was uniformly dispersed in the solution, forming a slightly viscous mixed solution. All other conditions were exactly the same as in Example 1, and a CR2032 type Li-CF32 was assembled. x Button cell battery.

[0040] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: As shown in Table 1, Li-CF3 with an artificial SEI film containing 3% Li3N coated on a lithium metal anode was used. x The battery's discharge specific capacity is 920 mAh g. -1 Compared to Li-CF using original lithium sheets x The battery's discharge specific capacity (895 mAh g) -1 Li-CF4 with an artificial SEI film coating on a lithium metal anode having a slightly higher, but lower, Li3N content than 5%. x Battery (940mAh g) -1 This indicates that the addition of Li3N filler can effectively guide the migration of lithium ions, but the low Li3N content is not ideal for Li-CF4. x The increase in battery capacity is limited.

[0041] Example 5:

[0042] In a glove box, 1.5 g (0.3 g / mL) of polypropylene carbonate (PPC) and 0.15 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to 5 mL of anhydrous acetonitrile (ACN), and the mixture was heated to 60 °C. o The solution was magnetically stirred at room temperature for 30 min until PPC and LiTFSI were completely dissolved in ACN, forming a viscous solution. 0.225 g (15%) of lithium nitride (Li3N) particles were added to the solution, and stirring was continued at room temperature for 12 h until Li3N was uniformly dispersed in the solution, forming a slightly viscous mixed solution. All other conditions were exactly the same as in Example 1, and a CR2032 type Li-CF32 was assembled. x Button cell battery.

[0043] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: As shown in Table 1, Li-CF3 with an artificial SEI film containing 15% Li3N coated on a lithium metal anode was used. x The battery's discharge specific capacity is 766 mAh g. -1 Lower than Li-CF using the original lithium sheet x The battery's discharge specific capacity (895 mAh g) -1 Li-CF3 with an artificial SEI film containing 5% Li3N and a lithium metal anode coated with an artificial SEI film x Battery (940 mAh g) -1 This indicates that adding too much Li3N filler is not only detrimental to capacity improvement, but may also accelerate capacity decay.

[0044] Example 6:

[0045] After high-speed rotation at 1000 rpm, the mixed solution spreads onto the lithium sheet to form a uniform artificial SEI film. All other conditions are exactly the same as in Example 1, and a CR2032 type Li-CF32 film is assembled. x Button cell battery.

[0046] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: as shown in Table 1, Li-CF3 metal lithium anodes were coated with an artificial SEI film at a spin coating speed of 1000 rpm. x The battery's discharge specific capacity is 767 mAh g. -1 Lower than Li-CF using the original lithium sheet x The battery's discharge specific capacity (895 mAh g) -1 Li-CF3 with an artificial SEI film coated on a lithium metal anode at a spin coating speed of 3000 rpm. x Battery (940 mAhg) -1 This indicates that at a low speed of 1000 rpm, the composite film may be too thick and cracked, which not only fails to effectively protect the lithium anode but may also hinder lithium-ion migration, thus being detrimental to Li-CF4. x Battery discharge.

[0047] Example 7:

[0048] After high-speed rotation at 5000 rpm, the mixed solution spreads onto the lithium sheet to form a uniform artificial SEI film. All other conditions are exactly the same as in Example 1, and a CR2032 type Li-CF32 film is assembled. x Button cell battery.

[0049] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: as shown in Table 1, Li-CF3 metal lithium anodes were coated with an artificial SEI film at a spin coating speed of 5000 rpm. x The battery's discharge specific capacity is 820 mAh g. -1 This indicates that when the rotation speed is too high, the artificial SEI film may be too thin, exposing part of the lithium active material layer, which is not conducive to lithium ion migration and results in a lower discharge specific capacity.

[0050] Example 8:

[0051] In a glove box, 1.5 g (0.3 g / mL) of polypropylene carbonate (PPC) and 0.15 g (10%) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were added to 5 mL of N,N-dimethylformamide (DMF) and heated to 60 °C. o Stir magnetically at room temperature for 30 min until PPC and LiTFSI are completely dissolved in DMF, forming a viscous solution. Add 0.075 g (5%) of lithium nitride (Li3N) particles to the solution and continue stirring at room temperature for 12 h until Li3N is uniformly dispersed in the solution, forming a slightly viscous mixed solution. Under the same conditions as in Example 1, CR2032 type Li-CF32 was assembled. x Button cell battery.

[0052] CR2032 type Li-CF32 fabricated using lithium metal sheets coated with an artificial SEI film as described in this invention x Coin cells were tested at room temperature and 0.1 C rate: As shown in Table 1, Li-CF3 metal lithium anodes were coated with an artificial SEI film using the organic solvent N,N-dimethylformamide. x The battery's discharge specific capacity is 910 mAh g. -1 Compared to Li-CF using original lithium sheets x The battery's discharge specific capacity (895 mAh g) -1 Slightly higher, but lower than Li-CF4 using an artificial SEI film coated with anhydrous acetonitrile as an organic solvent for lithium metal anodes. x Battery (940 mAh g) -1 This indicates that using N,N-dimethylformamide as an organic solvent can form a more stable artificial SEI film, reduce the loss of lithium active material, and is beneficial to Li-CF4. x While battery capacity has increased, the discharge specific capacity may not be significantly improved due to the relatively poor stability of polycarbonate organic polymers and inorganic lithium compounds in the organic solvent N,N-dimethylformamide compared to anhydrous acetonitrile.

[0053] Table 1. Application Examples of Li-CF x The specific discharge capacity of the battery at room temperature (0.1 C).

[0054]

[0055] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely adaptive and not restrictive. Those skilled in the art, under the guidance of the present invention, can make many other modifications without departing from the spirit and scope of the claims. These modifications all fall within the scope of protection of the present invention.

Claims

1. A lithium metal anode protected by artificial SEI film for lithium primary batteries, characterized by, The artificial SEI film-protected lithium negative electrode comprises an active material layer and an artificial SEI film protection coating, in particular, an artificial SEI film protection coating formed by a polycarbonate organic polymer matrix, an inorganic lithium-containing compound and an organic lithium salt on the surface of the metal lithium negative electrode active material layer. The polycarbonate organic polymer matrix is polypropylene carbonate, the organic lithium salt is lithium bis-trifluoromethanesulfonimide, and the inorganic lithium-containing compound is lithium nitride. The preparation process of the artificial SEI film protective coating includes: adding 1.5 g of polycarbonate PPC with a concentration of 0.3 g / mL and 0.15 g of lithium bis-trifluoromethanesulfonimide LiTFSI into 5 mL of anhydrous acetonitrile ACN, stirring under magnetic force at 60 o C for 30 min until the PPC and LiTFSI are completely dissolved in the ACN to form a viscous solution, adding 0.075 g of lithium nitride Li3N particles into the solution, and continuing to stir at room temperature for 12 h until the Li3N is uniformly dispersed in the solution to form a viscous mixed solution; spreading the solution on a lithium sheet to form a uniform artificial SEI film.

2. The artificial SEI film-protected lithium anode for lithium primary batteries according to claim 1, characterized by: The lithium primary battery is one of lithium-carbon fluoride batteries, lithium-aluminum fluoride batteries, lithium-manganese dioxide batteries, lithium-sulfur dioxide batteries, lithium-iron disulfide batteries and lithium-thionyl chloride batteries.

3. A method for the preparation of an artificial SEI film-protected lithium negative electrode according to any one of claims 1-2, characterized in that, The method comprises the following steps: dissolving polycarbonate organic polymer matrix and organic lithium salt in organic solvent according to certain proportion, heating and stirring at 60°C for 30 min until the polymer matrix and lithium salt are completely dissolved in the solvent to form a viscous solution; including: adding 1.5 g of polypropylene carbonate PPC with a concentration of 0.3 g / mL and 0.15 g of lithium bis-trifluoromethanesulfonimide LiTFSI into 5 mL of anhydrous acetonitrile ACN, stirring at 60 o C under magnetic stirring for 30 min until the PPC and LiTFSI are completely dissolved in the ACN to form a viscous solution; A certain proportion of inorganic lithium-containing compound is added to the solution, and stirring is continued at room temperature for 12 h until the inorganic lithium-containing compound is uniformly dispersed in the solution to form a mixed solution with viscosity; including: 0.075 g of lithium nitride Li3N particles is added to the solution, and stirring is continued at room temperature for 12 h until Li3N is uniformly dispersed in the solution to form a mixed solution with viscosity; 100 μL of the mixed solution is added dropwise on the lithium sheet, and after high-speed rotation, the solution can spread on the metal lithium sheet to form a uniform coating film; The lithium sheet after spin coating is placed on a 60 ℃ heating table for 24 h until the organic solvent is completely volatilized, and the artificial SEI film coating treatment on the metal lithium negative electrode is achieved.

4. The method of producing an artificial SEI film-protected lithium negative electrode according to claim 3, characterized by: The spin coating speed is 100-5000 rpm, and the thickness of the artificial SEI film is 1-20 μm.

5. The method of producing an artificial SEI film-protected lithium negative electrode according to claim 3, characterized by: The water content of the mixed solution is less than or equal to 10 ppm.

6. A lithium primary battery composed of a negative electrode, an electrolyte and a positive electrode, wherein the positive electrode material is selected from carbon fluoride, aluminum fluoride, manganese dioxide, sulfur dioxide, iron disulfide or thionyl chloride; the negative electrode material is the artificial SEI film-protected lithium negative electrode according to any one of claims 1-2; and the electrolyte is a liquid ether-based electrolyte.

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