Preparation method of artificial SEI on lithium surface and protective film

Abstract

The invention provides a preparation method of a lithium surface artificial SEI and a protective film. The core of the method is to synthesize an artificial SEI, and the artificial SEI comprises an organic polymer and a porous material. Wherein the organic polymer is poly (2, 2, 6, 6-tetramethyl-1-piperidine epoxy-4 alkyl acrylate) (PTPA), not only can be ionized in situ to generate cation free radicals and inhibit anion movement, but also can be used as an electron transfer mediator to optimize the selective transport of Li < + > and accelerate the migration of lithium ions; the high specific surface area and rich pore structure of the porous material not only have an ion screening function, but also can provide more transmission channels for lithium ions, so that the diffusion efficiency of the lithium ions is improved, volume change can be buffered, mechanical support can be provided to inhibit the growth of lithium dendrites, the flexibility and mechanical stability of the SEI membrane are enhanced, and the service life of the SEI membrane is prolonged. The method can adapt to the volume change of the lithium metal electrode in the charging and discharging process, and the electrochemical performance of the metal lithium battery is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of chemical power sources, and in particular relates to a preparation method and a protective film of artificial SEI on a lithium surface. Technical Background

[0002] With the rapid development of new energy and energy storage technologies in my country, the demand for safe, high-energy-density lithium batteries is increasing. Lithium-ion batteries, the dominant secondary battery type in the energy storage market, have become ubiquitous in nearly every aspect of life over the past few decades, from handheld electronic devices to all-electric vehicles and even micro-smart grids. However, due to their limited density (400Wh / kg), lithium-ion batteries cannot meet the high demand for future energy storage. Lithium metal anodes have an extremely low electrochemical potential (-3.040V vs. standard hydrogen electrode) and a very high theoretical specific capacity (3860mAh / g). Lithium-sulfur batteries, using sulfur as the positive electrode material, have high theoretical specific capacity and battery specific energy, reaching 1675mAh / g and 2600Wh / kg, respectively. These lithium-sulfur (Li-S) batteries offer numerous advantages, including high energy density (2600Wh / kg), low cost, and environmental friendliness. They are a promising candidate for next-generation energy storage systems and have become a research hotspot in recent years.

[0003] However, when the lithium metal anode contacts the organic electrolyte, a side reaction will spontaneously occur, thereby forming a solid electrolyte interface film (SEI) on the surface of the lithium metal. The SEI formed in situ during the cycle is mostly uneven, and the internal mechanical structure is unstable and has limited flexibility. + ) will be unevenly deposited on the surface of the lithium negative electrode during migration, resulting in the formation of dead lithium and lithium dendrites. Sharp lithium dendrites can pierce the separator, causing a short circuit between the positive and negative electrodes, thereby causing serious safety issues. At the same time, this uneven deposition will lead to continuous electrolyte loss, which in turn leads to a decrease in Coulombic efficiency and a sharp decrease in battery capacity. These problems are particularly prominent under conditions of high positive electrode surface loading, seriously restricting the development and application of lithium-sulfur batteries.

[0004] In this regard, this patent proposes a composition of artificial SEI for lithium-sulfur batteries. The organic polymer poly (2, 2, 6, 6-tetramethyl-1-piperidinyl epoxy-4-alkyl acrylate) PTPA can in situ ionize to generate cationic free radicals, inhibiting the movement of anions and optimizing the Li +It can also regulate the local chemical microenvironment, promote the effective dissociation of lithium salts, accelerate the migration of lithium ions, promote the formation of LiF-rich SEI layer, and slow down the growth of dendrites. The high specific surface area and rich pore structure of porous materials provide more transmission channels for lithium ions, reduce the ion transmission resistance, and thus improve the diffusion efficiency of lithium ions. It can also inhibit the growth of lithium dendrites by buffering volume changes and providing mechanical support. It can also accommodate the volume expansion of lithium metal during the charge and discharge process, reduce the pulverization and structural damage of the electrode material, and enhance the flexibility and mechanical stability of the SEI film, so that it can adapt to the volume changes of the lithium metal electrode during the charge and discharge process. Summary of the Invention

[0005] In order to solve the technical problems existing in the background technology, the present invention provides a preparation method of artificial SEI on lithium surface and a protective film.

[0006] The present invention adopts the following technical solution: a method for preparing an artificial SEI on a lithium surface comprises the following steps:

[0007] S1: dispersing an appropriate amount of organic polymer poly (2, 2, 6, 6-tetramethyl-1-piperidinyl epoxy-4-alkyl acrylate) and porous materials in an organic solvent and mixing them evenly to prepare an artificial SEI on the lithium surface;

[0008] S2: Equip the battery with the artificial SEI on the treated lithium surface.

[0009] In a further embodiment, the porous material (0-50 nm) in step S1 is at least one of a molecular sieve, a MOF, a COF, and a metal oxide;

[0010] The organic solvent is one of acetone, NMP, DMF, chloroform, acetonitrile and ether.

[0011] In a further embodiment, the mass ratio of the organic polymer to the porous material in step S1 is (1:1-20).

[0012] In a further embodiment, the metal oxide is one of aluminum oxide, aluminum oxide, indium oxide, zinc oxide, magnesium oxide, copper oxide, and cobalt oxide.

[0013] In a further embodiment, the mixed organic solution prepared in step S1 is independently formed into a film.

[0014] In a further embodiment, the mixed organic solution prepared in step S1 is evenly coated on the surface of the lithium metal.

[0015] In a further embodiment, the material prepared in step S1 is coated on the surface of the battery separator used.

[0016] The protective film prepared by the above-mentioned method for preparing artificial SEI on lithium surface is characterized in that it is applied to metal lithium negative electrode batteries.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The organic polymer in this patent is poly (2, 2, 6, 6-tetramethyl-1-piperidinyl-4-epoxy-4-alkyl acrylate) (PTPA), which can not only generate cationic free radicals by in-situ ionization and inhibit the movement of anions, but also serve as an electron transfer medium to optimize Li + Selective transport accelerates the migration of lithium ions

[0019] (2) The high specific surface area and rich pore structure of porous materials provide more transmission channels for lithium ions, reducing resistance, thereby improving the diffusion efficiency of lithium ions; they also buffer volume changes and provide mechanical support to inhibit the growth of lithium dendrites, which can enhance the flexibility and mechanical stability of the SEI film, enabling it to adapt to the volume changes of the lithium metal electrode during the charging and discharging process. This technology greatly improves the electrochemical properties of lithium metal.

[0020] (3) The artificial SEI membrane in this patent has the advantages of being simple and easy to operate, convenient for large-scale use, and conducive to the commercialization of lithium metal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the rate curve of Example 1. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner in conjunction with preferred experimental examples below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0024] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0025] Example 1

[0026] In this embodiment, the composition of the artificial SEI includes the following steps: dissolving 2g PTPA and 10g COF-5 in an acetonitrile mixture, stirring at 60°C and 800rpm / min with magnetic stirring for 24h to obtain a uniform slurry. The slurry is then evenly coated on the metal lithium negative electrode. Afterwards, the metal lithium with artificial SEI is used as the negative electrode, the carbon-sulfur composite is used as the positive electrode, and polypropylene (PP) is used as the separator for assembly testing. The rate results are shown in Figure 2. Figure 1 As shown, at a 3C rate, the discharge capacity of the material is 591mAh / g, and when it returns to the initial condition at a 0.1C rate, the discharge capacity is 1150.6mAh / g. + PTPA can generate cation radicals by in-situ ionization in subsequent cycles, inhibiting the movement of anions and optimizing the Li + It can also regulate the local chemical microenvironment, promote the effective dissociation of lithium salts, accelerate the migration of lithium ions, promote the formation of LiF-rich SEI layer, and slow down the growth of dendrites.

[0027] Example 2

[0028] In this implementation case, the composition of the artificial SEI includes the following steps: dissolving 1.5g PTPA and 9g UiO-66 in an acetonitrile mixture, stirring at 60°C and 600rpm / min with magnetic stirring for 12h to obtain a uniform slurry. The slurry is then formed into a separate film to obtain an artificial electrolyte membrane. The artificial electrolyte membrane, metallic lithium, ternary, and polypropylene (PP) are then assembled and tested. The added porous material UiO-66 has a high specific surface area and rich pore structure, providing more transmission channels for lithium ions and reducing resistance, thereby improving the diffusion efficiency of lithium ions. It can also intercept polysulfides and provide mechanical support to inhibit the growth of lithium dendrites by buffering volume changes, enhancing the flexibility and mechanical stability of the SEI film, enabling it to adapt to the volume changes of the lithium metal electrode during charge and discharge. This technology greatly improves the cycle performance of lithium-sulfur batteries. At a current density of 0.5C, the initial discharge capacity reached 197.7mAh / g, and after 600 cycles, it still had a specific capacity of 181.5mAh / g.

Claims

1. A method for preparing an artificial SEI on a lithium surface, characterized in that: The following steps are involved: S1: dispersing an appropriate amount of organic polymer poly (2, 2, 6, 6-tetramethyl-1-piperidinyl epoxy-4-alkyl acrylate) and porous materials in an organic solvent and mixing them evenly to prepare an artificial SEI on the lithium surface; S2: Equip the battery with the artificial SEI on the treated lithium surface.

2. The method for preparing artificial SEI on lithium surface according to claim 1, wherein: The porous material (0-50 nm) in step S1 is at least one of molecular sieve, MOF, COF, and metal oxide; The organic solvent is one of acetone, NMP, DMF, chloroform, acetonitrile and ether.

3. The method for preparing artificial SEI on lithium surface according to claim 1, characterized in that: In step S1, the mass ratio of the organic polymer to the porous material is (1:1-20).

4. The method for preparing artificial SEI on lithium surface according to claim 2, characterized in that: The metal oxide is one of aluminum oxide, aluminum oxide, indium oxide, zinc oxide, magnesium oxide, copper oxide and cobalt oxide.

5. The method for preparing artificial SEI on lithium surface according to claim 1, characterized in that: The mixed organic solution prepared in step S1 forms a separate film.

6. The method for preparing artificial SEI on lithium surface according to claim 1, characterized in that: The mixed organic solution prepared in step S1 is evenly coated on the surface of the lithium metal.

7. The method for preparing artificial SEI on lithium surface according to claim 1, characterized in that: The material prepared in step S1 is coated on the surface of the battery separator used.

8. A protective film prepared using the method for preparing an artificial SEI on a lithium surface according to any one of claims 1 to 7, characterized in that: Used in metal lithium negative electrode batteries.

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