A negative electrode protective coating suitable for alkali metal batteries, a method for preparing the same and an alkali metal battery

Abstract

This invention discloses a negative electrode protective coating suitable for alkali metal batteries, its preparation method, and the alkali metal battery itself. The negative electrode protective coating comprises a polymer, specifically a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or a poly(terphenyl-piperidine) anionic polymer. The polymer backbone contains terphenyl units and piperidine units, or also contains o-phenanthroline units, and the polymer backbone carries a positive charge and is bound to different anions through electrostatic interactions. When used in alkali metal batteries, this negative electrode protective coating can effectively stabilize the electrode interface and suppress dendrite growth, thereby achieving highly stable electrochemical cycling performance.

Description

Technical Field

[0001] This invention belongs to the technical field of energy storage materials for secondary alkali metal batteries. Specifically, this invention relates to a negative electrode protective coating suitable for alkali metal batteries, its preparation method, and alkali metal batteries. Background Technology

[0002] Group IA metals (currently mainly lithium, sodium, and potassium) possess extremely high theoretical specific capacity and extremely low electrochemical potential, making them ideal anode materials for realizing next-generation high-energy-density batteries. However, alkali metal anodes face severe challenges in practical applications and commercialization. On the one hand, due to the extremely high chemical and electrochemical reactivity of alkali metals, they undergo continuous side reactions with conventional electrolytes, forming a fragile and uneven solid electrolyte interphase (SEI) film on the anode surface. During battery charge-discharge cycles, the SEI film is prone to repeated rupture due to the significant volume changes of the alkali metal anode, inducing uncontrolled alkali metal dendrite growth. The continuous growth of dendrites not only consumes active alkali metal and electrolyte, leading to low coulombic efficiency, but may also puncture the separator, causing internal short circuits and posing serious safety hazards. On the other hand, in systems matching high-voltage cathodes to pursue higher energy densities, bidirectional chemical crosstalk between the positive and negative electrodes is becoming increasingly severe. Under high voltage, various soluble byproducts are easily generated on the positive electrode side (such as dissolved transition metal ions, electrolyte oxidative decomposition fragments, etc.). These byproducts will migrate across the separator to the negative electrode side, causing severe deterioration and corrosion of the negative electrode, further accelerating the deterioration of the negative electrode interface, the increase of impedance, and the decay of battery capacity.

[0003] To address the aforementioned instability issues at the anode interface, constructing artificial protective coatings on the alkali metal anode surface, either in situ or ex-situ, is considered an effective strategy. However, traditional inorganic or conventional polymer coatings often struggle to simultaneously achieve excellent mechanical toughness and efficient ion transport capabilities. More critically, conventional coatings are unable to form a protective SEI layer, thus failing to effectively shield and intercept soluble byproducts migrating from the cathode side. Therefore, developing a novel anode protective coating that combines high mechanical strength, efficient ion transport capabilities, and the ability to form a protective SEI is both urgent and necessary. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a negative electrode protective coating suitable for alkali metal batteries, a method for preparing the same, and an alkali metal battery.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide a negative electrode protective coating suitable for alkali metal batteries. The negative electrode protective coating contains a polymer, which is either a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or a poly(terphenyl-piperidine) anionic polymer. The backbone of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer contains terphenyl units, piperidine units, and o-phenanthroline units, and the backbone carries a positive charge and is bound to different anions A through electrostatic interactions. - The backbone of the poly(terphenyl-piperidine) anionic polymer contains terphenyl units and piperidine units, and the backbone is positively charged and is bound to different anions B through electrostatic interactions. - The repeating unit structure of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer is shown in formula (I); the repeating unit structure of the poly(terphenyl-piperidine) anionic polymer is shown in formula (II).

[0006] Equation (I); In equation (Ⅰ), 0 ≤ x ≤ 10000, 10 ≤ y ≤ 10000, and x and y are both integers; Anion A in formula (Ⅰ) - It is selected from any one of the following: difluorooxalateborate anion, hexafluorophosphate anion, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, tetrafluoroborate anion, and perchlorate anion;

[0007] Formula (II); In equation (II), 10 ≤ z ≤ 10000, and z is an integer; The anion B in formula (II) - It is selected from any one of difluorooxalateborate anion, hexafluorophosphate anion, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, tetrafluoroborate anion, and perchlorate anion.

[0008] The embodiments of the present invention utilize poly(terphenyl-piperidine-o-phenanthroline) anionic polymers or poly(terphenyl-piperidine) anionic polymers to prepare a negative electrode protective coating, and apply it to alkali metal batteries, which can significantly improve the interface stability and overall electrochemical performance of alkali metal batteries.

[0009] In some embodiments, in the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the anion A - Preferably, it contains difluorooxalate-borate anion or hexafluorophosphate anion; And / or, in the poly(terphenyl-piperidine) anionic polymer, the anionic B - The preferred anions are difluorooxalate-borate anions or hexafluorophosphate anions.

[0010] In some embodiments, the thickness of the negative electrode protective coating is 10–50 µm.

[0011] In some embodiments, the alkali metal battery is any one of a lithium metal battery, a sodium metal battery, or a potassium metal battery.

[0012] Secondly, embodiments of the present invention also provide a method for preparing a negative electrode protective coating suitable for alkali metal batteries as described in the first aspect, comprising the following steps: (1) Preparation of polymer: When the polymer is a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the preparation method of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer includes: A-1, at 0°C, dissolving terphenyl, 1-methyl-4-piperidinone and o-phenanthroline in dichloromethane, and adding trifluoroacetic acid and trifluoromethanesulfonic acid, followed by a polycondensation reaction at room temperature. After reacting for 5-12 hours, the reaction product is precipitated in methanol, and then washed with water and filtered to obtain the first precursor; A- 2. Dissolve the first precursor in dimethyl sulfoxide, then add potassium carbonate and iodomethane in sequence. After reacting at room temperature, precipitate the resulting reaction product in ethyl acetate, then wash with water and filter to obtain the second precursor; A-3. Dissolve the second precursor in a mixed solution of dimethyl sulfoxide and water, add lithium salt LiA, react at room temperature, then precipitate the resulting reaction product in water, then wash with water and filter to obtain the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer; When the polymer is a poly(terphenyl-piperidine) anionic polymer, the preparation method of the poly(terphenyl-piperidine) anionic polymer includes: B-1, at 0°C, dissolving terphenyl and 1-methyl-4-piperidinone in dichloromethane, adding trifluoroacetic acid and trifluoromethanesulfonic acid, and then carrying out a polycondensation reaction at room temperature. After reacting for 5-12 hours, the reaction product is placed in methanol for precipitation, and then washed with water and filtered to obtain a first precursor; B-2, dissolving the first precursor in dimethyl sulfoxide, then adding potassium carbonate and iodomethane in sequence, reacting at room temperature, and then placing the resulting reaction product in ethyl acetate for precipitation, and then washing with water and filtering to obtain a second precursor; B-3, dissolving the second precursor in a mixed solution of dimethyl sulfoxide and water, adding lithium salt LiB, reacting at room temperature, and then placing the resulting reaction product in water for precipitation, and then washing with water and filtering to obtain the poly(terphenyl-piperidine) anionic polymer; (2) Preparation of negative electrode protective coating: The poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer is dispersed in an organic solvent and then coated onto the surface of the negative electrode of the alkali metal battery to form the negative electrode protective coating.

[0013] In some embodiments, in step (2), the mass percentage of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer in the organic solvent is 1-10%; Optionally, the organic solvent includes at least one of dimethyl sulfoxide, acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide; And / or, the coating method includes at least one of spin coating and blade coating.

[0014] Thirdly, embodiments of the present invention also provide an alkali metal battery, comprising a positive electrode, a negative electrode, a negative electrode protective coating, and an electrolyte; the negative electrode protective coating is located between the negative electrode and the electrolyte and completely covers the surface of the negative electrode; the negative electrode protective coating is the negative electrode protective coating described in the first aspect or the negative electrode protective coating prepared by the preparation method described in the second aspect.

[0015] In some embodiments, the active material in the positive electrode of the alkali metal battery includes at least one of the following: sulfur-containing positive electrode, selenium-containing positive electrode, sulfur-selenium composite positive electrode, cobalt salt of alkali metal, iron salt of alkali metal, iron manganese salt of alkali metal, manganate of alkali metal, nickel manganate of alkali metal, nickel cobalt manganate of alkali metal, nickel cobalt aluminate of alkali metal, and vanadium salt of alkali metal.

[0016] In some embodiments, the active material in the negative electrode of the alkali metal battery includes at least one of elemental alkali metal, alloy of alkali metal and other metals, graphite, hard carbon, molybdenum disulfide, titanate of alkali metal, graphene, and silicon-carbon composite material.

[0017] In some embodiments, the electrolyte in the alkali metal battery includes at least one of a liquid electrolyte, a polymer electrolyte, and a gel electrolyte.

[0018] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] Figure 1 The image shows a scanning electron microscope (SEM) image of the lithium deposition morphology using the negative electrode protective coating of Example 1 of this invention.

[0020] Figure 2The image shows a scanning electron microscope (SEM) image of the lithium deposition morphology using the negative electrode protective coating of Example 2 of this invention.

[0021] Figure 3 The image shows a scanning electron microscope (SEM) image of the lithium deposition morphology using the negative electrode protective coating of Example 3 of this invention.

[0022] Figure 4 The image shows a scanning electron microscope (SEM) image of the lithium deposition morphology using the negative electrode protective coating of Example 4 of this invention.

[0023] Figure 5 This is a scanning electron microscope image of the lithium deposition morphology without a negative electrode protective coating.

[0024] Figure 6 The graphs show the cycle performance of lithium metal batteries prepared using the negative electrode protective coatings of Examples 1-4 of this invention, and lithium metal batteries prepared without the negative electrode protective coating. Detailed Implementation

[0025] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0027] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0028] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0029] In a first aspect, embodiments of the present invention provide a negative electrode protective coating suitable for alkali metal batteries. The negative electrode protective coating contains a polymer, which is either a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or a poly(terphenyl-piperidine) anionic polymer. The backbone of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer contains terphenyl units, piperidine units, and o-phenanthroline units, and the backbone carries a positive charge and is bound to different anions A through electrostatic interactions. - The backbone of the poly(terphenyl-piperidine) anionic polymer contains terphenyl units and piperidine units, and the backbone is positively charged and is bound to different anions B through electrostatic interactions.- The repeating unit structure of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer is shown in formula (I); the repeating unit structure of the poly(terphenyl-piperidine) anionic polymer is shown in formula (II).

[0030] Equation (I); In equation (Ⅰ), 0 ≤ x ≤ 10000, 10 ≤ y ≤ 10000, and x and y are both integers; Anion A in formula (Ⅰ) - Selected from difluorooxalate-borate anion (DFOB) - ), hexafluorophosphate anion (PF6) - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), difluorosulfonyl imide anion (FSI) - ), tetrafluoroborate anion (BF4) - ), perchlorate anion (ClO4) - Any one of the following;

[0031] Formula (II); In equation (II), 10 ≤ z ≤ 10000, and z is an integer; The anion B in formula (II) - Selected from difluorooxalate-borate anion (DFOB) - ), hexafluorophosphate anion (PF6) - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), difluorosulfonyl imide anion (FSI) - ), tetrafluoroborate anion (BF4) - ), perchlorate anion (ClO4) - Any one of them.

[0032] This invention employs poly(terphenyl-piperidine-o-phenanthroline) anionic polymers or poly(terphenyl-piperidine) anionic polymers to prepare a negative electrode protective coating, which can significantly improve the interfacial stability and overall electrochemical performance of alkali metal batteries. The rigid terphenyl structure in the polymer framework endows the coating with excellent mechanical toughness, effectively buffering the volume expansion of alkali metals during deposition and stripping, and strongly inhibiting dendrite penetration and growth from a physical perspective. More importantly, the nitrogen-rich piperidine or o-phenanthroline units in the polymer framework construct a unique microenvironment, which not only homogenizes the flux of alkali metal ions at the electrode interface, but also effectively intercepts and chelates transition metal ions dissolved and migrating from the positive electrode side through strong coordination and adsorption, thereby significantly suppressing the occurrence of side reactions and bidirectional chemical crosstalk between the positive and negative electrodes. Simultaneously, this invention also introduces different types of anions into the polymer coating, which promotes the formation of a protective SEI. During battery operation, these electrostatically bound anions around the polymer backbone preferentially participate in electrochemical reduction and decomposition at the negative electrode interface, thereby in-situ inducing the formation of an SEI layer rich in inorganic components and with high ionic conductivity between the alkali metal and the polymer coating. This high-quality SEI derived from anions works synergistically with the external polymer backbone to construct a robust organic-inorganic composite interface, completely blocking the continuous side reactions between the electrolyte bulk and the highly active alkali metal negative electrode, and greatly improving interface stability.

[0033] In some embodiments, in the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the anion A - Preferred is difluorooxalate borate anion (DFOB) - ) or hexafluorophosphate anion (PF6) - ); And / or, in the poly(terphenyl-piperidine) anionic polymer, the anionic B - Preferred is difluorooxalate borate anion (DFOB) - ) or hexafluorophosphate anion (PF6) - ).

[0034] In some embodiments, the thickness of the negative electrode protective coating is 10–50 µm.

[0035] In some embodiments, the alkali metal battery is any one of a lithium metal battery, a sodium metal battery, or a potassium metal battery.

[0036] Secondly, embodiments of the present invention also provide a method for preparing a negative electrode protective coating suitable for alkali metal batteries as described in the first aspect, comprising the following steps: (1) Preparation of polymer: When the polymer is a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the preparation method of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer includes: In step A-1, terphenyl, 1-methyl-4-piperidinone, and o-phenanthroline were dissolved in dichloromethane at 0°C, and trifluoroacetic acid and trifluoromethanesulfonic acid were added. A polycondensation reaction was then carried out at room temperature (the reaction equation is shown below; where 0 ≤ x ≤ 10000, 10 ≤ y ≤ 10000, and x and y are integers, and the ratio of x to y is controlled by the molar ratio of o-phenanthroline and terphenyl). After reacting for 5–12 hours, the reaction product was precipitated in methanol, washed with water, and filtered to obtain the first precursor.

[0037] A-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence, and the reaction was carried out at room temperature (the reaction equation is shown below). The resulting reaction product was precipitated in ethyl acetate, and then washed with water and filtered to obtain the second precursor.

[0038] A-3, the second precursor is dissolved in a mixed solution of dimethyl sulfoxide and water, and a lithium salt LiA (e.g., lithium difluorooxalate borate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, or lithium perchlorate) is added. After reacting at room temperature (the reaction equation is shown below), the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer; ; When the polymer is a poly(terphenyl-piperidine) anionic polymer, the preparation method of the poly(terphenyl-piperidine) anionic polymer includes: B-1, at 0°C, terphenyl and 1-methyl-4-piperidinone were dissolved in dichloromethane, and trifluoroacetic acid and trifluoromethanesulfonic acid were added. Then, a polycondensation reaction was carried out at room temperature (the reaction equation is shown below; where 10≤z≤10000 and z is an integer). After reacting for 5-12 hours, the reaction product was placed in methanol for precipitation, and then washed with water and filtered to obtain the first precursor.

[0039] B-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence, and the reaction was carried out at room temperature (the reaction equation is shown below). The resulting reaction product was precipitated in ethyl acetate, and then washed with water and filtered to obtain the second precursor.

[0040] B-3, the second precursor is dissolved in a mixed solution of dimethyl sulfoxide and water, and a lithium salt LiB (e.g., lithium difluorooxalate borate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, or lithium perchlorate) is added. After reacting at room temperature (the reaction equation is shown below), the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain the poly(terphenyl-piperidine) anionic polymer. ; (2) Preparation of negative electrode protective coating: The poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer is dispersed in an organic solvent and then coated onto the surface of the negative electrode of the alkali metal battery to form the negative electrode protective coating.

[0041] In some embodiments, in step (2), the mass percentage of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer in the organic solvent is 1-10%; Optionally, the organic solvent includes at least one of dimethyl sulfoxide, acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide; And / or, the coating method includes at least one of spin coating and blade coating.

[0042] Thirdly, embodiments of the present invention also provide an alkali metal battery, comprising a positive electrode, a negative electrode, a negative electrode protective coating, and an electrolyte; the negative electrode protective coating is located between the negative electrode and the electrolyte and completely covers the surface of the negative electrode; the negative electrode protective coating is the negative electrode protective coating described in the first aspect or the negative electrode protective coating prepared by the preparation method described in the second aspect.

[0043] In some embodiments, the active material in the positive electrode of the alkali metal battery includes at least one selected from the following: sulfur-containing positive electrode, selenium-containing positive electrode, sulfur-selenium composite positive electrode, cobalt salt of alkali metal, iron salt of alkali metal, iron manganese salt of alkali metal, manganate of alkali metal, nickel manganate of alkali metal, nickel cobalt manganate of alkali metal, nickel cobalt aluminum salt of alkali metal, and vanadium phosphate of alkali metal. It should be noted that the aforementioned alkali metals include at least one selected from lithium, sodium, and potassium.

[0044] In some embodiments, the active material in the negative electrode of the alkali metal battery includes at least one of elemental alkali metal, alloy of alkali metal and other metals, graphite, hard carbon, molybdenum disulfide, titanate of alkali metal, graphene, and silicon-carbon composite material; wherein the alkali metal includes at least one of lithium, sodium, and potassium.

[0045] In some embodiments, the electrolyte in the alkali metal battery includes at least one of a liquid electrolyte, a polymer electrolyte, and a gel electrolyte; Optionally, the liquid electrolyte comprises a first metal salt and a first non-aqueous organic solvent; the first metal salt has a mass fraction of 1-60% in the liquid electrolyte, and the first non-aqueous organic solvent has a mass fraction of 5-80% in the liquid electrolyte; the first metal salt is selected from at least one of MPF6, MClO4, MNO3, MTFSI, MFSI, MBOB, MDFOB, and MBF4, wherein M is selected from any one of lithium, sodium, and potassium; the first non-aqueous organic solvent comprises at least one of carbonate solvents, ether solvents, acetonitrile, pyridine, hexahydropyridine, pyrrole, tetrahydropyrrole, and γ-butyrolactone, wherein the carbonate solvent comprises at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethyl propyl carbonate; the ether solvent comprises at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetrahydrofuran, furan, thiophene, 1,3-dioxane, and hexahydropyran; Optionally, the polymer electrolyte comprises a first polymer and a second metal salt; the first polymer has a mass fraction of 5-80% in the polymer electrolyte, and the second metal salt has a mass fraction of 1-60% in the polymer electrolyte; wherein, the type of the first polymer is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the first polymer can be selected from polycarbonate, polyimide, polyamide, polyester, polyether, polyphosphonitrile, polyurethane, polysulfone, polyoxymethylene, polyacrylonitrile, polyvinyl chloride, polysulfide, polyvinylidene fluoride, polyphosphate, polyacrylate, polyether ester, poly(1,3-dioxane), polypropyleneimide, polytetrafluoroethylene, polyhexafluoropropylene, heteroatom-containing polyethylene, heteroatom-containing polypropylene, polysiloxane, or their block copolymers or graft polymers or random copolymers, etc.; the second metal salt is selected from at least one of MPF6, MClO4, MNO3, MTFSI, MFSI, MBOB, MDFOB, MBF4, wherein M is selected from any one of lithium, sodium, and potassium. Optionally, the gel electrolyte comprises a second polymer, a third metal salt, and a second non-aqueous organic solvent; the second polymer has a mass fraction of 5-80% in the gel electrolyte, the third metal salt has a mass fraction of 1-60% in the gel electrolyte, and the second non-aqueous organic solvent has a mass fraction of 5-80% in the gel electrolyte; wherein, the type of the second polymer is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the polymer can be selected from polycarbonate, polyimide, polyamide, polyester, polyether, polyphosphonitrile, polyurethane, polysulfone, polyoxymethylene, polyacrylonitrile, polyvinyl chloride, polysulfide, polyvinylidene fluoride, polyphosphate, polyacrylate, polyether ester, poly(1,3-dioxane), polypropyleneimide, polytetrafluoroethylene, polyhexafluoropropylene, heteroatom-containing polyethylene, heteroatom-containing polyethylene, etc. The third metal salt is selected from at least one of MPF6, MClO4, MNO3, MTFSI, MFSI, MBOB, MDFOB, and MBF4, wherein M is selected from any one of lithium, sodium, and potassium; the second non-aqueous organic solvent comprises at least one of carbonate solvents, ether solvents, acetonitrile, pyridine, hexahydropyridine, pyrrole, tetrahydropyrrole, and γ-butyrolactone, wherein the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethyl propyl carbonate; the ether solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetrahydrofuran, furan, thiophene, 1,3-dioxane, and hexahydropyran.

[0046] Furthermore, the gel electrolyte also includes an inorganic fast ion conductor, the inorganic fast ion conductor having a mass fraction of 5-60% in the gel electrolyte; and the type of the inorganic fast ion conductor is not particularly limited, and those skilled in the art can select it according to actual needs, for example, Li can be selected. 3a La (2 / 3)-a TiO3(0.04 <a<0.14)、Li 3+a X a Y 1-a O4(X=Si, Sc, Ge, Ti; Y=P, As, V, Cr; 0 <a<1)、LiZr2(PO4)3、Li7La3Zr2O 12 Li 1+ a Al a Ti b Ge 2-a-b (PO4)3(0 <a<1;0≤b<2)、Li3OCl、Li3OCl 0.5 Br 0.5 Li10 GeP₂S 12 , Li 14 Zn(GeO₄)₄, Li₅La₃M₂O 12 (M=Ta, Nb), Li 5.5 La₃Nb 1.75 In 0.25 O 12 , Li₃N-LiX (X=Cl, Br, I), Li 9-na M a N₂Cl₃ (M=Na, K, Rb, Cs, Mg, Al; 0<a<0.2; 0<n<10), 3Li₃N-MI (M=Li, Na, K), LiPON, Li₂S-MS a (M=Al, Si, P; 1<a<3), at least one selected from the group consisting of Na₃PS₄, Na₃PSe₄, Na₃SiS₄ and LiBH₄-LiI.

[0047] The following are non-limiting examples and comparative examples of the present invention. It should be noted that the solutions of the comparative examples do not belong to the prior art, and are only set for comparison with the solutions of the examples, and shall not be construed as limiting the present invention. Unless otherwise stated, various raw materials used in the examples and comparative examples are conventional commercially available products, or can be prepared by known methods; and the experimental methods without specific conditions noted in the examples are conventional methods and conventional conditions well known in the art.

[0048] Example 1 This example provides a negative electrode protection coating suitable for alkali metal batteries. The negative electrode protection coating contains poly(terphenyl-piperidine-phenanthroline) hexafluorophosphate anionic polymer, and the repeating unit structure of the poly(terphenyl-piperidine-phenanthroline) hexafluorophosphate anionic polymer is as shown below (wherein 10≤x≤10000, 10≤y≤10000, both x and y are integers, and the ratio of x to y is 1:9): .

[0049] Embodiments of the present invention also provide a preparation method of the above-mentioned negative electrode protection coating suitable for alkali metal batteries, comprising the following steps: (1) Preparing poly(terphenyl-piperidine-phenanthroline) hexafluorophosphate anionic polymer: A-1: at 0°C, dissolve terphenyl, 1-methyl-4-piperidone and phenanthroline in dichloromethane (wherein the molar ratio of phenanthroline to terphenyl is 1:9), add trifluoroacetic acid and trifluoromethanesulfonic acid, then carry out polycondensation reaction at room temperature. After reacting for 5h, precipitate the reaction product in methanol, then wash with water and filter to obtain a first precursor; A-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence. After reacting at room temperature for 5 hours, the resulting reaction product was precipitated in ethyl acetate, washed with water and filtered to obtain the second precursor. A-3, the above second precursor is then dissolved in a mixed solution of dimethyl sulfoxide and water, and lithium hexafluorophosphate is added. After reacting at room temperature for 5 hours, the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain poly(terphenyl-piperidine-o-phenanthroline) hexafluorophosphate anionic polymer. (2) Preparation of negative electrode protective coating: The above-mentioned poly(terphenyl-piperidine-o-phenanthroline) hexafluorophosphate anionic polymer was dispersed in dimethyl sulfoxide at a mass ratio of 5%, and then spin-coated onto the surface of the negative electrode of an alkali metal battery to form a negative electrode protective coating with a thickness of 25µm.

[0050] Example 2 This embodiment provides a negative electrode protective coating suitable for alkali metal batteries. The negative electrode protective coating contains a poly(terphenyl-piperidine)hexafluorophosphate anionic polymer, and the repeating unit structure of the poly(terphenyl-piperidine)hexafluorophosphate anionic polymer is shown below, where 10 ≤ z ≤ 10000, and z is an integer: .

[0051] The above-mentioned method for preparing the negative electrode protective coating suitable for alkali metal batteries includes the following steps: (1) Preparation of poly(terphenyl-piperidine)hexafluorophosphate anionic polymer: B-1, at 0°C, terphenyl and 1-methyl-4-piperidinone were dissolved in dichloromethane, and trifluoroacetic acid and trifluoromethanesulfonic acid were added. Then, a polycondensation reaction was carried out at room temperature. After 5 hours of reaction, the reaction product was placed in methanol for precipitation, and then washed with water and filtered to obtain the first precursor. B-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence, and the reaction was carried out at room temperature for 5 hours. The resulting reaction product was precipitated in ethyl acetate, washed with water and filtered to obtain the second precursor. B-3, then the above second precursor is dissolved in a mixed solution of dimethyl sulfoxide and water, and lithium hexafluorophosphate is added. After reacting at room temperature for 5 hours, the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain poly(terphenyl-piperidine)hexafluorophosphate anionic polymer. (2) Preparation of negative electrode protective coating: The above-mentioned poly(terphenyl-piperidine) hexafluorophosphate anionic polymer was dispersed in dimethyl sulfoxide at a mass ratio of 5%, and then spin-coated onto the surface of the negative electrode of an alkali metal battery to form a negative electrode protective coating with a thickness of 25µm.

[0052] Example 3 This embodiment provides a negative electrode protective coating suitable for alkali metal batteries. The negative electrode protective coating contains a poly(terphenyl-piperidine-o-phenanthroline)difluorooxalate-borate anionic polymer, and the repeating unit structure of the poly(terphenyl-piperidine-o-phenanthroline)difluorooxalate-borate anionic polymer is shown below (where 10 ≤ x ≤ 10000, 10 ≤ y ≤ 10000, x and y are both integers, and the ratio of x to y is 1:9): .

[0053] This invention also provides a method for preparing the above-mentioned negative electrode protective coating suitable for alkali metal batteries, comprising the following steps: (1) Preparation of poly(terphenyl-piperidine-o-phenanthroline) difluorooxalate-borate anionic polymer: A-1, at 0°C, terphenyl, 1-methyl-4-piperidinone and o-phenanthroline were dissolved in dichloromethane (wherein the molar ratio of o-phenanthroline to terphenyl was 1:9), and trifluoroacetic acid and trifluoromethanesulfonic acid were added. Then, a polycondensation reaction was carried out at room temperature. After 5 hours of reaction, the reaction product was placed in methanol for precipitation, and then washed with water and filtered to obtain the first precursor. A-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence. After reacting at room temperature for 5 hours, the resulting reaction product was precipitated in ethyl acetate, washed with water and filtered to obtain the second precursor. A-3, the above second precursor is then dissolved in a mixed solution of dimethyl sulfoxide and water, and lithium difluorooxalate borate is added. After reacting at room temperature for 5 hours, the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain poly(terphenyl-piperidine-o-phenanthroline) difluorooxalate borate anionic polymer. (2) Preparation of negative electrode protective coating: The above-mentioned poly(terphenyl-piperidine-o-phenanthroline) difluorooxalate-borate anionic polymer was dispersed in dimethyl sulfoxide at a mass ratio of 5%, and then spin-coated onto the surface of the negative electrode of an alkali metal battery to form a negative electrode protective coating with a thickness of 25µm.

[0054] Example 4 This embodiment provides a negative electrode protective coating suitable for alkali metal batteries. The negative electrode protective coating contains a poly(terphenyl-piperidine)difluorooxalate-borate anionic polymer, and the repeating unit structure of this poly(terphenyl-piperidine)difluorooxalate-borate anionic polymer is shown below, where 10 ≤ z ≤ 10000, and z is an integer: .

[0055] This invention also provides a method for preparing the above-mentioned negative electrode protective coating suitable for alkali metal batteries, comprising the following steps: (1) Preparation of poly(terphenyl-piperidine)difluorooxalate-borate anionic polymer: B-1, at 0°C, terphenyl and 1-methyl-4-piperidinone were dissolved in dichloromethane, and trifluoroacetic acid and trifluoromethanesulfonic acid were added. Then, a polycondensation reaction was carried out at room temperature. After 5 hours of reaction, the reaction product was placed in methanol for precipitation, and then washed with water and filtered to obtain the first precursor. B-2, after dissolving the first precursor in dimethyl sulfoxide, potassium carbonate and iodomethane were added in sequence, and the reaction was carried out at room temperature for 5 hours. The resulting reaction product was precipitated in ethyl acetate, washed with water and filtered to obtain the second precursor. B-3, then the above second precursor is dissolved in a mixed solution of dimethyl sulfoxide and water, and lithium difluorooxalate borate is added. After reacting at room temperature for 5 hours, the resulting reaction product is placed in water for precipitation, and then washed and filtered to obtain poly(terphenyl-piperidine) difluorooxalate borate anionic polymer. (2) Preparation of negative electrode protective coating: The above-mentioned poly(terphenyl-piperidine) difluorooxalate-borate anionic polymer was dispersed in dimethyl sulfoxide at a mass ratio of 5%, and then spin-coated onto the surface of the negative electrode of an alkali metal battery to form a negative electrode protective coating with a thickness of 25µm.

[0056] The negative electrode protective coatings obtained in Examples 1-4 were used to assemble lithium / copper asymmetric model batteries, and the lithium deposition morphology was tested using scanning electron microscopy at a deposition current density of 0.5 mA cm⁻¹. -2 The deposition capacity is 6 mAh / cm³. -2 The electrolyte is a liquid electrolyte, which is obtained by dissolving 1M lithium bis(trifluoromethanesulfonylimide) in a mixed solvent composed of 1,3-dioxopentane and ethylene glycol dimethyl ether (volume ratio 1 / 1) and stirring magnetically for 2 hours.

[0057] At the same time, LiNi was adopted. 0.8 Co 0.1 Mn 0.1 O2 (NCM811, 10 mg cm) -2A lithium metal full cell was assembled using a positive electrode and a thin lithium negative electrode (50µm thick). Cyclic performance tests were conducted on the batteries assembled with the negative electrode protective coatings prepared in the different embodiments, as well as on a control battery assembled without the negative electrode protective coating. The electrolyte used in the tests was prepared by dissolving 0.6M lithium tetrafluoroborate and 0.6M lithium difluorooxalate borate in a mixed solution of fluoroethylene carbonate and diethyl carbonate (volume ratio 2:1), and stirring magnetically for 2 hours. The voltage range for the cycle tests was 2.8-4.3V, and the charge / discharge rate was 0.5C charge / 1C discharge.

[0058] Figure 1-5 The images show scanning electron microscope (SEM) images of lithium deposition morphology using the negative electrode protective coatings of Examples 1-4 of this invention and without the negative electrode protective coating, respectively. Figure 5 As shown, when lithium metal batteries are assembled without a negative electrode protective coating, there is a significant uneven deposition phenomenon. Current density is concentrated in local areas, easily inducing preferential dendrite growth, resulting in a loose, porous, or even needle-like deposition morphology. Furthermore, a large number of irregular dendrite structures are formed, accompanied by the accumulation of dead lithium, gradually roughening the interface. Simultaneously, the lithium negative electrode surface exhibits obvious dendrite accumulation and a loose structure, lacking integrity in the deposition layer, making it prone to breakage and detachment during cycling. Moreover, at 6 mAh cm⁻¹... -2 Under high areal capacity deposition conditions, it is more prone to forming sharp dendrites and porous structures, resulting in poor interface stability and exacerbated side reactions during cycling. In contrast, when assembling lithium metal batteries using the negative electrode protective coating of Examples 1-4 of this invention, the lithium deposition process is effectively controlled due to the coating modification. Figure 1-4 The coating effectively homogenizes the lithium-ion flux distribution, promotes uniform nucleation at multiple points on the surface, and results in a more continuous and dense deposition morphology. This effectively alleviates local current density fluctuations, significantly suppresses dendrite initiation and propagation, and makes the interface structure more stable. This uniform deposition helps reduce interfacial side reactions and improves coulombic efficiency.

[0059] Figure 6 The figures show the cycle performance of lithium metal batteries fabricated using the negative electrode protective coatings of Examples 1-4 of this invention, and lithium metal batteries fabricated without the negative electrode protective coating. As can be seen from the figures, compared to lithium metal batteries fabricated without the negative electrode protective coating, the embodiments of this invention, by introducing the negative electrode protective coating, significantly improve the cycle stability of the battery, significantly reduce the capacity decay rate, achieve a more stable voltage plateau, suppress interface impedance growth, and exhibit superior cycle life, more stable charge-discharge behavior, and superior interface stability.

[0060] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A negative electrode protective coating suitable for alkali metal batteries, characterized in that, The negative electrode protective coating contains a polymer, which is a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or a poly(terphenyl-piperidine) anionic polymer; the backbone of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer contains terphenyl units, piperidine units, and o-phenanthroline units, and the backbone is positively charged and is bound to different anions A through electrostatic interaction. - The backbone of the poly(terphenyl-piperidine) anionic polymer contains terphenyl units and piperidine units, and the backbone is positively charged and is bound to different anions B through electrostatic interactions. - The repeating unit structure of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer is shown in formula (I); the repeating unit structure of the poly(terphenyl-piperidine) anionic polymer is shown in formula (II). Equation (I); In equation (Ⅰ), 0 ≤ x ≤ 10000, 10 ≤ y ≤ 10000, and x and y are both integers; Anion A in formula (Ⅰ) - It is selected from any one of the following: difluorooxalateborate anion, hexafluorophosphate anion, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, tetrafluoroborate anion, and perchlorate anion; Formula (II); In equation (II), 10 ≤ z ≤ 10000, and z is an integer; The anion B in formula (II) - It is selected from any one of difluorooxalateborate anion, hexafluorophosphate anion, bis(trifluoromethanesulfonyl)imide anion, bis(fluorosulfonyl)imide anion, tetrafluoroborate anion, and perchlorate anion.

2. The negative electrode protective coating for alkali metal batteries according to claim 1, characterized in that, In the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the anion A - Selected from difluorooxalate-borate anion or hexafluorophosphate anion; And / or, in the poly(terphenyl-piperidine) anionic polymer, the anionic B - Selected from difluorooxalate-borate anion or hexafluorophosphate anion.

3. The negative electrode protective coating for alkali metal batteries according to claim 1, characterized in that, The thickness of the negative electrode protective coating is 10–50 µm.

4. The negative electrode protective coating for alkali metal batteries according to any one of claims 1-3, characterized in that, The alkali metal battery is any one of lithium metal battery, sodium metal battery, or potassium metal battery.

5. A method for preparing a negative electrode protective coating suitable for alkali metal batteries as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of polymer: When the polymer is a poly(terphenyl-piperidine-o-phenanthroline) anionic polymer, the preparation method of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer includes: A-1, at 0°C, dissolving terphenyl, 1-methyl-4-piperidinone and o-phenanthroline in dichloromethane, and adding trifluoroacetic acid and trifluoromethanesulfonic acid, followed by a polycondensation reaction at room temperature. After reacting for 5-12 hours, the reaction product is precipitated in methanol, and then washed with water and filtered to obtain the first precursor; A- 2. Dissolve the first precursor in dimethyl sulfoxide, then add potassium carbonate and iodomethane in sequence. After reacting at room temperature, precipitate the resulting reaction product in ethyl acetate, then wash with water and filter to obtain the second precursor; A-3. Dissolve the second precursor in a mixed solution of dimethyl sulfoxide and water, add lithium salt LiA, react at room temperature, then precipitate the resulting reaction product in water, then wash with water and filter to obtain the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer; When the polymer is a poly(terphenyl-piperidine) anionic polymer, the preparation method of the poly(terphenyl-piperidine) anionic polymer includes: B-1, at 0°C, dissolving terphenyl and 1-methyl-4-piperidinone in dichloromethane, adding trifluoroacetic acid and trifluoromethanesulfonic acid, and then carrying out a polycondensation reaction at room temperature. After reacting for 5-12 hours, the reaction product is placed in methanol for precipitation, and then washed with water and filtered to obtain a first precursor; B-2, dissolving the first precursor in dimethyl sulfoxide, then adding potassium carbonate and iodomethane in sequence, reacting at room temperature, and then placing the resulting reaction product in ethyl acetate for precipitation, and then washing with water and filtering to obtain a second precursor; B-3, dissolving the second precursor in a mixed solution of dimethyl sulfoxide and water, adding lithium salt LiB, reacting at room temperature, and then placing the resulting reaction product in water for precipitation, and then washing with water and filtering to obtain the poly(terphenyl-piperidine) anionic polymer; (2) Preparation of negative electrode protective coating: The poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer is dispersed in an organic solvent and then coated onto the surface of the negative electrode of the alkali metal battery to form the negative electrode protective coating.

6. The method for preparing the negative electrode protective coating suitable for alkali metal batteries according to claim 5, characterized in that, In step (2), the mass percentage of the poly(terphenyl-piperidine-o-phenanthroline) anionic polymer or the poly(terphenyl-piperidine) anionic polymer in the organic solvent is 1-10%. Optionally, the organic solvent includes at least one of dimethyl sulfoxide, acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide; And / or, the coating method includes at least one of spin coating and blade coating.

7. An alkali metal battery, characterized in that, It includes a positive electrode, a negative electrode, a negative electrode protective coating, and an electrolyte; the negative electrode protective coating is located between the negative electrode and the electrolyte and completely covers the surface of the negative electrode; the negative electrode protective coating is the negative electrode protective coating according to any one of claims 1-4 or the negative electrode protective coating prepared by the preparation method according to claim 5 or 6.

8. The alkali metal battery according to claim 7, characterized in that, The active material in the positive electrode of the alkali metal battery includes at least one of the following: sulfur-containing positive electrode, selenium-containing positive electrode, sulfur-selenium composite positive electrode, cobalt salt of alkali metal, iron salt of alkali metal, iron manganese salt of alkali metal, manganate of alkali metal, nickel manganate of alkali metal, nickel cobalt manganate of alkali metal, nickel cobalt aluminate of alkali metal, and vanadium phosphate of alkali metal.

9. The alkali metal battery according to claim 7, characterized in that, The active material in the negative electrode of the alkali metal battery includes at least one of the following: alkali metal element, alloy of alkali metal and other metals, graphite, hard carbon, molybdenum disulfide, alkali metal titanate, graphene, and silicon-carbon composite material.

10. The alkali metal battery according to claim 7, characterized in that, The electrolyte in the alkali metal battery includes at least one of liquid electrolyte, polymer electrolyte, and gel electrolyte.

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