Lithium metal negative electrode and preparation method thereof, precursor solution, lithium ion battery and electric equipment

Abstract

The invention provides a lithium metal negative electrode and a preparation method thereof, a precursor solution, a lithium ion battery and electric equipment, and relates to the technical field of new energy. The first protective layer of the lithium metal negative electrode provided by the invention comprises a ZrF6 < 2-> and LiF compact protective film, so that the interface stability is effectively improved, and the electrochemical performance is improved. The ZrF6 < 2-> coordination anions can reduce the ion pair acting force in the lithium salt, increase the number of free lithium ions and increase the transference number of the lithium ions. By introducing ZrF6 < 2->, the conductivity of lithium ions is improved, and the overall ionic conductivity is remarkably improved, so that the first efficiency and the capacity retention rate are improved. The Zr element in ZrF6 < 2-> can be used as a lithium-loving induction point of lithium ions, so that uniform lithium deposition can be guided, and dendritic crystal growth can be inhibited.

Description

Technical Field

[0001] The present application relates to the field of new energy technologies, and particularly to a lithium metal negative electrode, a preparation method thereof, a precursor solution, a lithium ion battery, and an electricity-related device. Background Art

[0002] A lithium battery is a battery that uses a lithium metal or a lithium alloy as a negative electrode material and a non-aqueous electrolyte solution. Due to the extremely high chemical activity of lithium element, the lithium battery has a very high energy density. However, the chemical activity of lithium element also causes some problems during the use of lithium batteries, such as the growth of lithium dendrites and the decomposition of electrolytes. These problems may lead to a decline in battery performance and even cause safety problems. To solve these problems, the existing solutions mainly form a protective layer on the surface of the lithium negative electrode to inhibit the growth of lithium dendrites and the decomposition of electrolytes. This protective layer is usually formed by the reaction of solvents and additives in the electrolyte on the surface of the lithium negative electrode. For example, a stable solid electrolyte interface membrane (SEI membrane) can be formed by dropping a mixed solution containing ethylene carbonate (EC) and dimethyl ether (DME) on the surface of the lithium negative electrode, thereby protecting the lithium negative electrode.

[0003] However, these existing solutions still have some problems. First, the formation process of these protective layers often requires complex operations, such as precise control of the ratio of solvents and additives, as well as reaction conditions. Second, it is difficult to ensure the stability and uniformity of these protective layers, which may affect the performance and safety of the battery. In addition, the protective ability of these protective layers against lithium puncture is limited. Once lithium puncture occurs, the battery performance may decline rapidly. Summary of the Invention

[0004] The purpose of the present application is to provide a lithium metal negative electrode, a preparation method thereof, a precursor solution, a lithium ion battery, and an electricity-related device, aiming to solve the problem of poor stability and uniformity of the protective layer of the existing lithium metal negative electrode.

[0005] To achieve the above purpose, the present application provides a lithium metal negative electrode, including: a lithium metal and a protective layer formed on the surface of the lithium metal, the protective layer includes a first protective layer, and the first protective layer includes t-ZrF6 2- and LiF.

[0006] In some embodiments, the first protective layer further includes: a MOF material.

[0007] In some embodiments, the MOF material is selected from at least one of ZIF-8, UiO-66, MIL-101, and MOF-74.

[0008] In some embodiments, the protective layer further includes a second protective layer formed on the surface of the first protective layer, and the second protective layer includes a flexible polymer and a lithium salt;

[0009] and / or, the sum of the thicknesses of the first protective layer and the second protective layer is 300 - 800 nm.

[0010] In some embodiments, the mass ratio of the flexible polymer to the lithium salt is (75 - 85):(10 - 20).

[0011] and / or, the flexible polymer is selected from any one of PEO, PVDF, and P(VDF - HFP);

[0012] and / or, the lithium salt is selected from any one of LiTFSI, LiFSi, and LiPF6.

[0013] In some embodiments, the lithium metal negative electrode further includes a third protective layer formed on the surface of the second protective layer, and the third protective layer includes PEO or a ceramic composite coating.

[0014] The present application also provides a precursor solution for coating on a lithium metal to form a protective layer on the surface of the lithium metal, and the precursor solution includes Li2ZrF6;

[0015] Or, the precursor solution includes Li2ZrF6 and a MOF material;

[0016] Or, the precursor solution includes Li2ZrF6, a flexible polymer, and a lithium salt;

[0017] Or, the precursor solution includes Li2ZrF6, a flexible polymer, a lithium salt, and a MOF material. In some embodiments, the precursor solution includes a solute and a solvent, and the mass ratio of the solute to the solvent is 1:(5 - 10);

[0018] The solute is only Li2ZrF6;

[0019] Or, the solute includes Li2ZrF6 and a MOF material; the mass ratio of Li2ZrF6 to the MOF material is (80 - 100):(0 - 20);

[0020] Or, the solute includes Li2ZrF6, a flexible polymer, and a lithium salt, and the mass ratio of Li2ZrF6, the flexible polymer, and the lithium salt is (5 - 15):(75 - 85):(10 - 20);

[0021] Alternatively, the solute includes Li2ZrF6, a flexible polymer, a lithium salt, and a MOF material, and the mass ratio of Li2ZrF6, the flexible polymer, the lithium salt, and the MOF material is (4-14):(75-85):(10-20):(1-3).

[0022] The present application also provides a method for preparing a lithium metal negative electrode as described above, including: coating the above-mentioned precursor solution on the surface of the lithium metal to form a protective layer, thereby obtaining the lithium metal negative electrode.

[0023] In some embodiments, a third protective layer is further coated on the protective layer, and the third protective layer includes PEO or a ceramic composite coating.

[0024] The present application also provides a lithium-ion battery including the above-mentioned lithium metal negative electrode.

[0025] The present application also provides an electric device including the above-mentioned lithium-ion battery.

[0026] Compared with the prior art, the beneficial effects of the present application include:

[0027] The first protective layer of the lithium metal negative electrode provided by the present application includes t-ZrF6 2- and LiF, and ZrF6 2- and LiF can in-situ form a dense protective film at the interface, thereby effectively suppressing the side reaction between the electrolyte and the electrode, effectively improving the interface stability, and enhancing the electrochemical performance. The ZrF6 2- coordination anion can reduce the ion pair force in the lithium salt, increase the number of free lithium ions, and improve the lithium ion transference number. By introducing ZrF6 2- the conduction performance of lithium ions is improved, the overall ionic conductivity is significantly increased, thereby improving the initial efficiency and capacity retention rate. The Zr in ZrF6 2- can serve as a "lithium-philic" induction point for lithium ions, which helps to guide uniform lithium deposition and inhibit dendrite growth.

[0028] Furthermore, the first protective layer further includes a MOF material. The MOF material has a highly adjustable pore structure and surface functional groups. The porous structure of the MOF material is used to uniformly disperse ZrF6 2- and LiF, so that a dense protective layer is formed on the surface of the lithium metal negative electrode. Precise interface regulation can be achieved in the protective layer, optimizing the ion distribution and transmission path, and playing a mechanical support and chemical isolation role, thereby further enhancing the battery performance and cycle stability.

[0029] Further, the lithium metal anode protective layer further includes a second protective layer, and the second protective layer includes a flexible polymer and a lithium salt. The introduction of the flexible polymer endows the coating with a certain deformation ability, which can effectively relieve the volume change stress during charge and discharge, prevent cracks or peeling, and thus extend the cycle life. The lithium salt provides a Li + source, reduces the impedance, and improves the capacity and cycle performance.

[0030] Further, the lithium metal anode further includes a third protective layer, and the third protective layer includes a PEO or ceramic composite coating, which provides air stability and inhibits electrolyte degradation. Through the layered design, the synergistic effect of the functions of each layer is realized to ensure the long-term cycle performance of the lithium metal anode. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0032] Figure 1 is a schematic structural diagram of the lithium metal anode of the present application;

[0033] Figure 2 is an SEM image of the pure lithium metal layer and the composite protective layer of the lithium metal anode in Example 1;

[0034] Figure 3 is a data graph of the sulfide battery cell before and after cycling in Example 1.

[0035] Reference Numerals:

[0036] 10 - lithium metal; 20 - first protective layer; 30 - second protective layer; 40 - third protective layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] As used herein, the terms:

[0038] "prepared from" is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus containing the recited elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0039] The connective "consisting of" excludes any unrecited element, step, or component. If used in a claim, this phrase renders the claim closed-ended, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause within the body of a claim rather than immediately following the subject, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0040] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, whether or not that range is separately disclosed. For example, when the range "1 - 5" is disclosed, the described range should be interpreted to include ranges "1 - 4", "1 - 3", "1 - 2", "1 - 2 and 4 - 5", "1 - 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its endpoint values and all integers and fractions within that range.

[0041] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0042] "Parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. Suppose we say that the mass of component A is a parts by mass and the mass of component B is b parts by mass, then it represents the mass ratio of component A to component B as a:b. Or, it represents that the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0043] "And / or" is used to indicate that either or both of the stated circumstances may occur. For example, A and / or B includes (A and B) and (A or B).

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of those features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0045] This application provides a lithium metal anode. Please refer to Figure 1, including: lithium metal 10 and a protective layer formed on the surface of the lithium metal 10, the protective layer includes a first protective layer 20, and the first protective layer 20 includes t-ZrF6 2- and LiF.

[0046] ZrF6 in the first protective layer 20 of the lithium metal negative electrode provided by this application 2- and LiF can in-situ form a dense protective film at the interface, thereby effectively suppressing the side reaction between the electrolyte and the electrode, effectively improving the interface stability, and enhancing the electrochemical performance. ZrF6 2- coordination anions can reduce the ion pair force in the lithium salt, increase the number of free lithium ions, and improve the lithium ion transference number. By introducing ZrF6 2- the conduction performance of lithium ions is improved, the overall ionic conductivity is significantly increased, thereby improving the initial efficiency and capacity retention rate. ZrF6 2- The Zr element in can serve as a "lithium-philic" induction point for lithium ions, which helps to guide uniform lithium deposition and inhibit dendrite growth.

[0047] In some embodiments, the first protective layer 20 further includes: MOF material. The MOF material has a highly adjustable pore structure and surface functional groups. Utilize the porous structure of the MOF material to uniformly disperse ZrF6 2- and LiF, so that a dense protective layer is formed on the surface of the lithium metal negative electrode. Precise interface regulation can be achieved in the protective layer, optimizing the ion distribution and transmission path, playing a mechanical support and chemical isolation role, thereby further enhancing the battery performance and cycle stability.

[0048] Among them, Metal-Organic Frameworks (abbreviated as MOFs) are a class of porous crystal materials formed by the self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. They usually have a highly ordered network structure, combining the rigidity of inorganic materials and the flexibility of organic materials. MOFs have a high specific surface area and adjustable pore size, and the pore size and shape can be customized by selecting different metal centers and organic ligands.

[0049] Common MOF materials include the following:

[0050] 1. ZIF-8 (Zeolitic Imidazolate Framework-8)

[0051] Metal center: zinc ion (Zn 2+ )

[0052] Organic ligand: imidazole

[0053] Features: ZIF-8 is a highly stable MOF with excellent chemical and thermal stability. Its regular nanopores can promote the conduction of lithium ions. In addition, the stable structure of ZIF-8 helps to improve the mechanical properties at the interface and prevent interface rupture.

[0054] Potential role: ZIF-8 can enhance the compatibility between the polymer and the electrolyte, improve the ionic conductivity, and enhance the overall chemical and mechanical stability.

[0055] 2. UiO-66 (Universitetet i Oslo MOF-66)

[0056] Metal center: zirconium ion (Zr 4+ )

[0057] Organic ligand: terephthalic acid

[0058] Features: UiO-66 is known for its high chemical and thermal stability and can perform excellently in a variety of electrochemical environments. Due to the high stability of zirconium, UiO-66 can provide a strong interfacial layer, reducing the decomposition of the electrolyte and the formation of lithium dendrites.

[0059] Potential role: UiO-66 can be used as a stable framework material to combine with the polymer matrix, protecting the lithium anode while improving the overall cycle performance and interfacial stability of the battery.

[0060] 3. MIL-101(Cr)

[0061] Metal center: chromium ion (Cr 3 )

[0062] Organic ligand: terephthalic acid

[0063] Features: MIL-101(Cr) has a very large porosity and surface area, which helps to promote the diffusion and conduction of ions. Its structure has high stability, which can effectively reduce the interfacial impedance. In addition, the pore structure of MIL-101 can be optimized by adjusting solvents or additives, thereby enhancing the lithium ion transport efficiency.

[0064] Potential role: MIL-101 can effectively improve the ionic conduction between the electrolyte and the lithium anode interface, thereby improving the rate performance of all-solid-state batteries.

[0065] 4. MOF-74 (CPO-27)

[0066] Metal center: various metal ions such as magnesium, zinc, cobalt, nickel

[0067] Organic ligand: 2,5-dihydroxyterephthalic acid

[0068] Features: The metal centers of MOF-74 are diverse and can be selected according to different battery requirements. Its open metal sites can enhance the interaction with the electrolyte, thereby improving ionic conductivity. This material also has a large porosity, which is conducive to the diffusion of lithium ions.

[0069] Potential effect: Through its open metal sites, MOF-74 can bind to the polymer matrix, providing additional ion channels, thereby enhancing the interfacial performance and lithium ion conductivity.

[0070] In some embodiments, the MOF material is selected from at least one of ZIF-8, UiO-66, MIL-101, and MOF-74.

[0071] In some embodiments, please continue to refer to Figure 1 , the protective layer further includes a second protective layer 30, the second protective layer 30 is formed on the surface of the first protective layer 20, and the second protective layer 30 includes a flexible polymer and a lithium salt.

[0072] The introduction of the flexible polymer endows the coating with certain deformation ability, which can effectively relieve the volume change stress during charge and discharge, prevent cracks or peeling, and thus extend the cycle life. The lithium salt provides a Li + source, reduces the impedance, and improves the capacity and cycle performance.

[0073] In some embodiments, the sum of the thicknesses of the first protective layer 20 and the second protective layer 30 is 300 - 800 nm, for example, it can be 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, or any value between 300 - 800 nm.

[0074] In some embodiments, the mass ratio of the flexible polymer to the lithium salt is (75 - 85):(10 - 20), for example, it can be 75:10, 75:15, 75:17, 75:20, 80:10, 80:13, 80:15, 80:20, 85:10, 85:15, 85:18, 85:20, or any ratio between (75 - 85):(10 - 20).

[0075] In some embodiments, the flexible polymer is selected from any one of PEO, PVDF, and P(VDF-HFP); optionally, the flexible polymer is selected from PEO.

[0076] Among them, Polyethylene Oxide (PEO), also known as Polyethylene Oxide, is a linear polyether formed by the ring-opening polymerization of ethylene oxide. PEO is a water-soluble polymer that can dissolve in water and some organic solvents. PEO is a thermoplastic resin with good ductility and plasticity. PEO has good chemical stability and is resistant to bacterial erosion. Even at low concentrations, PEO solutions have a very high viscosity.

[0077] PVDF (Polyvinylidene Fluoride) is a high-performance thermoplastic fluoropolymer formed by the polymerization of vinylidene fluoride monomers, with high chemical stability and good mechanical properties.

[0078] P(VDF-HFP) is a fluororesin material copolymerized from vinylidene fluoride (VDF) and hexafluoropropylene (HFP), with excellent comprehensive properties. Compared with pure polyvinylidene fluoride (PVDF), P(VDF-HFP) changes the aggregation state structure of PVDF by introducing HFP chain segments, reducing its crystallinity and fracture strength and making it more flexible.

[0079] In some embodiments, the lithium salt is selected from any one of LiTFSI, LiFSi, and LiPF6.

[0080] Among them, LiTFSI is the English abbreviation of "Lithium bis(trifluoromethanesulfonyl)imide", which is an important lithium salt compound. As an important component of the electrolyte of lithium-ion batteries, LiTFSI can provide a stable ion transport environment for the battery to ensure the normal charging and discharging of the battery. LiTFSI helps the rapid transfer of charges inside the battery and improves the charging and discharging rate of the battery.

[0081] LiFSI (Lithium bis(fluorosulfonyl)imide) is a new type of electrolyte lithium salt. Due to its excellent performance and broad application prospects, it is gradually becoming an important research direction in the field of lithium battery electrolytes. The fluoride ions in LiFSI have strong electron-withdrawing properties, weakening the coordination effect between anions and cations in the lithium salt, making the lithium ions more active, thereby improving the conductivity of the electrolyte. LiFSI shows excellent performance in electrochemical stability, supporting the battery to operate within a wider working temperature range, especially showing better performance in low-temperature environments.

[0082] In some embodiments, please continue to refer to Figure 1 , the lithium metal negative electrode further includes a third protective layer 40, the third protective layer 40 is formed on the surface of the second protective layer 30, and the third protective layer 40 includes a PEO or ceramic composite coating.

[0083] The third protective layer 40 is disposed on the outermost layer, providing air stability and inhibiting electrolyte degradation. Through a layered design, the synergistic effect of each layer's function is achieved, ensuring the long-term cycling performance of the lithium metal anode.

[0084] Among them, the ceramic composite coating is an advanced coating material that combines the high hardness, wear resistance, and corrosion resistance of ceramic materials with the ductility and thermal conductivity of metal materials. The ceramic composite coating is usually composed of ceramic particles (such as Al2O3, ZrO2, etc.) and a metal matrix (such as stainless steel, nickel-based alloys, etc.). By adjusting the type, particle size, and content of the ceramic particles, the optimization of the coating performance can be achieved.

[0085] This application also provides a precursor solution for coating on the lithium metal to form a protective layer on the surface of the lithium metal. The precursor solution includes Li2ZrF6.

[0086] Among them, Li2ZrF6 is a lithium hexafluorozirconate compound with two crystal structures: monoclinic phase (m-Li2ZrF6) and trigonal phase (t-Li2ZrF6). However, the monoclinic phase (m-Li2ZrF6) is unstable and easily transforms into the trigonal phase (t-Li2ZrF6). Inside the t-Li2ZrF6 crystal and at the grain boundaries are Li + provides fast migration channels, significantly improving the lithium ion transport efficiency. The lithiumophilic sites on the surface of the t-Li2ZrF6 crystal can induce uniform deposition of the lithium metal, effectively inhibiting the formation of lithium dendrites, thereby improving the safety and cycling stability of the battery. t-Li2ZrF6 releases ZrF6 2- ions in the solution, which can timely repair the damaged SEI layer and provide long-term protection for the lithium metal anode.

[0087] By coating the Li2ZrF6 solution on the surface of the lithium metal, Li2ZrF6 will undergo an in-situ chemical reaction with the lithium metal to generate LiF, thereby forming a first protective layer including LiF and ZrF6 2- ions on the surface of the lithium metal.

[0088] In some embodiments, the precursor solution includes Li2ZrF6 and a MOF material.

[0089] By coating a mixed solution of Li2ZrF6 and a MOF material on the surface of the lithium metal, Li2ZrF6 will undergo an in-situ chemical reaction with the lithium metal to generate LiF, thereby forming a first protective layer including LiF, ZrF6 2- ions and the MOF material on the surface of the lithium metal, and LiF, ZrF6 2- ions are dispersed in the porous structure of the MOF material.

[0090] In some embodiments, the precursor solution comprises Li2ZrF6, a flexible polymer, and a lithium salt.

[0091] By coating a mixed solution of Li2ZrF6, a flexible polymer, and a lithium salt on the surface of lithium metal, Li2ZrF6 will undergo an in-situ chemical reaction with lithium metal prior to the lithium salt to form LiF, thereby forming a first protective layer including LiF and ZrF6 2- ions on the surface of the lithium metal, and a second protective layer including a flexible polymer and a lithium salt is formed on the first protective layer.

[0092] In some embodiments, the precursor solution comprises Li2ZrF6, a flexible polymer, a lithium salt, and a MOF material.

[0093] By coating a mixed solution of Li2ZrF6, a flexible polymer, a lithium salt, and a MOF material on the surface of lithium metal, Li2ZrF6 will undergo an in-situ chemical reaction with lithium metal prior to the lithium salt to form LiF, and the MOF material will settle on the surface of the lithium metal, thereby forming a first protective layer including LiF, ZrF6 2- ions and the MOF material on the surface of the lithium metal, and a second protective layer including a flexible polymer and a lithium salt is formed on the first protective layer.

[0094] In some embodiments, the precursor solution comprises a solute and a solvent, and the mass ratio of the solute to the solvent is 1:(5 - 10), for example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any ratio between 1:(5 - 10).

[0095] In some embodiments, the solute in the precursor solution is only Li2ZrF6.

[0096] In some embodiments, the solute in the precursor solution comprises Li2ZrF6 and a MOF material; the mass ratio of Li2ZrF6 to the MOF material is (80 - 100):(0 - 20), for example, it can be 80:20, 85:15, 90:10, 95:5, or 100:0, or any ratio between (80 - 100):(0 - 20).

[0097] In some embodiments, the solute in the precursor solution comprises Li2ZrF6, a flexible polymer, and a lithium salt, and the mass ratio of Li2ZrF6, the flexible polymer, and the lithium salt is (5 - 15):(75 - 85):(10 - 20), for example, it can be 5:75:10, 10:80:15, 10:75:10, 15:85:20, 15:80:10, or any ratio between (5 - 15):(75 - 85):(10 - 20).

[0098] In some embodiments, the solute in the precursor solution includes Li2ZrF6, a flexible polymer, a lithium salt, and a MOF material. The mass ratio of Li2ZrF6, the flexible polymer, the lithium salt, and the MOF material is (4 - 14):(75 - 85):(10 - 20):(1 - 3). For example, it can be 4:75:10:1, 5:80:12:2, 10:80:15:3, 14:85:20:3, 8:82:15:2, 12:85:20:1, or any ratio between (4 - 14):(75 - 85):(10 - 20):(1 - 3).

[0099] This application also provides a method for preparing a lithium metal negative electrode as described above, including: coating the above-mentioned precursor solution on the surface of the lithium metal to form a protective layer, thereby obtaining the lithium metal negative electrode.

[0100] In some embodiments, a third protective layer is further coated on the protective layer. The third protective layer includes PEO or a ceramic composite coating.

[0101] This application also provides a lithium-ion battery including the above-mentioned lithium metal negative electrode.

[0102] This application also provides an electric device including the above-mentioned lithium-ion battery.

[0103] The following will describe the implementation scheme of this application in detail with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those without specific conditions noted in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0104] Example 1

[0105] Example 1 provides a lithium metal negative electrode, and its preparation method includes the following steps:

[0106] Step 1: Prepare raw materials, including polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Li2ZrF6, and ZIF-8. The masses of the four substances are 0.8 g, 0.15 g, 0.1 g, and 0.025 g respectively.

[0107] Step 2: Dissolve PEO in 10 g of tetrahydrofuran solution and stir at 400 rpm / min until completely dissolved; then add LiTFSI and mix, stirring for 30 minutes at 400 rpm / min and a mixing temperature of 25 °C; then add Li2ZrF6 and ZIF-8 particles and mix at a speed of 500 rpm to form a uniform sol state.

[0108] Step 3: Spin-coat the mixed sol on the Li metal surface. The dropping conditions are as follows: temperature is 25°C, time is 30 minutes, and the spin-coating speed is 4000 rpm / min. In this step, Li2ZrF6 will undergo a chemical reaction on the Li negative electrode surface to form a corresponding first protective layer including ZrF6 2- / ZIF-8 and LiF, and a second protective layer including PEO / LiTFSI, obtaining the lithium metal negative electrode of Example 1. The SEM images of the lithium metal and the composite protective layer are as Figure 2 shown, and the thickness of the protective layer is 700 nm.

[0109] Step 4: Apply the optimized Li negative electrode to a sulfide solid electrolyte battery cell. In this step, due to the formation of a stable protective layer on the Li negative electrode surface, the battery cell exhibits good cycle stability.

[0110] Example 2

[0111] Example 2 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that the amounts of PEO and LiTFSI are 0.75 g and 0.1 g respectively, and the remaining steps are the same as those of Example 1.

[0112] Example 3

[0113] Example 3 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that the amounts of PEO and LiTFSI are 0.85 g and 0.2 g respectively.

[0114] Example 4

[0115] Example 4 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that the amounts of Li2ZrF6 and ZIF-8 are 0.14 g and 0.030 g respectively.

[0116] Example 5

[0117] Example 5 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that the amounts of Li2ZrF6 and ZIF-8 are 0.05 g and 0.0125 g respectively.

[0118] Example 6

[0119] Example 6 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that PEO and LiTFSI are not added to the raw materials.

[0120] Example 7

[0121] Example 7 provides a lithium metal negative electrode, and the difference in its preparation method from that of Example 1 is that PEO, LiTFSI, and MOF materials are not added to the raw materials.

[0122] Example 8

[0123] Example 8 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the raw materials do not contain MOF materials.

[0124] Example 9

[0125] Example 9 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: ZiF-8 in the raw materials is changed to UiO-66.

[0126] Example 10

[0127] Example 10 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: LiTFSI in the raw materials is changed to LiFSI.

[0128] Comparative Example 1

[0129] Comparative Example 1 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: Li2ZrF6 and ZiF-8 are not added to the raw materials.

[0130] Comparative Example 2

[0131] Comparative Example 2 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the amounts of PEO and LiTFSI are 0.9 g and 0.15 g respectively, and the thickness of the protective layer then becomes 1000 nm.

[0132] Comparative Example 3

[0133] Comparative Example 3 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the amounts of PEO and LiTFSI are 0.85 g and 0.21 g respectively.

[0134] Comparative Example 4

[0135] Comparative Example 4 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the amounts of PEO and LiTFSI are 0.85 g and 0.09 g respectively.

[0136] Comparative Example 5

[0137] Comparative Example 5 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the amounts of Li2ZrF6 and ZIF-8 are 0.15 g and 0.025 g respectively.

[0138] Comparative Example 6

[0139] Comparative Example 6 provides a lithium metal anode, and the difference in its preparation method from that of Example 1 is that: the amounts of Li2ZrF6 and ZIF-8 are 0.03 g and 0.025 g respectively.

[0140] Comparative Example 7

[0141] Comparative Example 7 provides a lithium metal anode. The difference in its preparation method from that of Example 1 is that the amounts of Li2ZrF6 and ZIF-8 are 0.05 g and 0.009 g, respectively.

[0142] Comparative Example 8

[0143] Comparative Example 8 provides a lithium metal anode. The difference in its preparation method from that of Example 1 is that the amounts of Li2ZrF6 and ZIF-8 are 0.05 g and 0.031 g, respectively.

[0144] Comparative Example 9

[0145] Comparative Example 9 provides a lithium metal anode. The difference in its preparation method from that of Example 1 is that Li2ZrF6 is not added to the raw materials.

[0146] Electrochemical performance tests were carried out on the batteries obtained in each example and comparative example. The assembly and testing process is as follows:

[0147] Prepare 100 mg of LiPSCl or Li 5.5 PS 4.5 Cl 1.5 and prepare a sulfide solid electrolyte sheet under a pressure of 2 t; then add a composite cathode. The mass of the composite cathode material is taken as 8.2 mg, where NCM811:(LiPSCl or Li 5.5 PS 4.5 Cl 1.5 ) = 7:3, and press the composite cathode under a pressure of 4 t; finally, place the optimized lithium anode and prepare a sulfide all-solid-state battery under a pressure of 1 t. Cycle at 0.2C and a test voltage of 2.6 - 4.3 V vs Li / Li + and calculate the efficiency (initial efficiency) and the corresponding capacity of the first cycle, and calculate the capacity retention rate. The data graph of the sulfide battery cell of Example 1 before and after cycling is as Figure 3 shown.

[0148] The test results of the batteries in each example and comparative example are shown in Table 1.

[0149] Table 1 Electrochemical performance results of the batteries in each example and comparative example

[0150]

[0151]

[0152] As can be seen from Table 1, the initial efficiency and capacity retention rate of the battery in the embodiment scheme are both higher than those in the comparative example scheme. This is mainly because the lithium metal anode in the embodiment is coated with a solution including Li2ZrF6 on the lithium metal surface. Li2ZrF6 can react with the lithium metal to generate LiF, and Li2ZrF6 can release ZrF6 2- , ZrF6 2- and LiF can in-situ form a dense protective film at the interface, thereby effectively inhibiting the side reaction between the electrolyte and the electrode, effectively improving the interface stability, and enhancing the electrochemical performance.

[0153] In Example 9, UiO-66 uses Zr as the metal node and has high chemical stability. However, in the lithium battery environment, especially when in contact with the sulfide solid electrolyte, its stability may be affected. The carboxylic acid ligand (such as terephthalic acid) of UiO-66 reacts with the sulfide, resulting in a decrease in the interface stability. Therefore, under the same dosage, the capacity retention rate of Example 9 is lower than that of Example 1. ZIF-8 uses Zn as the metal center, and the imidazole ligand provides a more hydrophobic surface environment, which may play a better role in inhibiting the oxidative degradation of the sulfide solid electrolyte and has a better capacity retention rate.

[0154] LiTFSI has a lower decomposition tendency at high-voltage positive electrodes (such as NCM, LCO). The lithium salt in Example 10 uses LiFSI, and LiFSI is prone to degradation at high voltages and generates unstable F- by-products on the interface. These by-products may react with the sulfide solid electrolyte, reducing the electrochemical stability. Therefore, under the same dosage, the initial efficiency and capacity retention rate of Example 10 are lower than those of Example 1.

[0155] In the comparative example 2 scheme, too much flexible polymer PEO will increase the impedance, thereby reducing the initial efficiency and capacity retention rate.

[0156] The lithium salt content in Comparative Example 3 exceeds the scope of this application, affecting the viscosity, evaporation rate, and gelation degree of the solution, which may lead to phase separation, affecting the uniformity and stability of the membrane, and even forming defects, having a greater impact on the overall performance of the battery. In Comparative Example 4, too low a lithium salt will result in insufficient lithium ion concentration, thereby reducing the mobility of lithium ions (Li + is overly bound and ion transport is restricted), thereby affecting the cycle performance of the battery.

[0157] In Comparative Examples 5 and 6, excessive Li2ZrF6 may lead to uneven dispersion, agglomeration, or local precipitation, forming an uneven interface, increasing the interface impedance, and affecting the overall electrochemical performance; too low a content of Li2ZrF6 may lead to discontinuous ion migration paths, and the protective layer may become soft or not dense enough, affecting the long-cycle stability.

[0158] In Comparative Example 7 and Comparative Example 8, excessive MOF causes uneven interfaces, hindering ion transport; insufficient MOF may result in discontinuous or partially blocked ion channels, leading to a decrease in ionic conductivity and thus affecting battery performance.

[0159] In the solution of the present application, the dosage windows of PEO, LiTFSI, Li2ZrF6 and MOF in this system are extremely strict. Even a minor change may lead to significant changes in the material structure, ion transport and interface stability.

[0160] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0161] In addition, those skilled in the art can understand that although some embodiments herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the claims above, any one of the claimed embodiments can be used in any combination. The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present application, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art.

Claims

1. A lithium metal negative electrode, characterized in that include: Lithium metal and a protective layer formed on the surface of the lithium metal, the protective layer comprising a first protective layer, the first protective layer comprising t-ZrF6 2- and LiF.

2. The lithium metal negative electrode according to claim 1, characterized in that The first protective layer also includes: MOF material.

3. The lithium metal negative electrode according to claim 2, characterized in that The MOF material is selected from at least one of ZIF-8, UiO-66, MIL-101 and MOF-74.

4. The lithium metal negative electrode according to any one of claims 1 to 3, characterized in that The protective layer further includes a second protective layer, which is formed on the surface of the first protective layer, and the second protective layer includes a flexible polymer and a lithium salt; And / or, the sum of the thickness of the first protective layer and the second protective layer is 300-800 nm.

5. The lithium metal negative electrode according to claim 4, characterized in that The mass ratio of the flexible polymer to the lithium salt is (75-85):(10-20). And / or, the flexible polymer is selected from any one of PEO, PVDF, and P(VDF-HFP); And / or, the lithium salt is selected from any one of LiTFSI, LiFSi, and LiPF6.

6. The lithium metal negative electrode according to claim 4, characterized in that The lithium metal negative electrode further includes a third protective layer, which is formed on the surface of the second protective layer and includes PEO or a ceramic composite coating.

7. A precursor solution for coating on lithium metal to form a protective layer on the surface of lithium metal, characterized in that: The precursor solution includes Li2ZrF6; Alternatively, the precursor solution includes Li2ZrF6 and MOF material; Alternatively, the precursor solution includes Li2ZrF6, a flexible polymer and a lithium salt; Alternatively, the precursor solution includes Li2ZrF6, a flexible polymer, a lithium salt and a MOF material.

8. The precursor solution according to claim 7, characterized in that The precursor solution includes a solute and a solvent, and the mass ratio of the solute to the solvent is 1:(5-10); The solute is only Li2ZrF6; Alternatively, the solute includes Li2ZrF6 and MOF material; the mass ratio of Li2ZrF6 to the MOF material is (80-100): (0-20); Alternatively, the solute includes Li2ZrF6, a flexible polymer and a lithium salt, and the mass ratio of the Li2ZrF6, the flexible polymer and the lithium salt is (5-15): (75-85): (10-20); Alternatively, the solute includes Li2ZrF6, a flexible polymer, a lithium salt and a MOF material, and the mass ratio of the Li2ZrF6, the flexible polymer, the lithium salt and the MOF material is (4-14): (75-85): (10-20): (1-3).

9. A method for preparing a lithium metal negative electrode according to any one of claims 1 to 5, characterized in that: include: The precursor solution according to claim 7 or 8 is coated on the surface of lithium metal to form a protective layer to obtain the lithium metal negative electrode.

10. The method for preparing a lithium metal negative electrode according to claim 9, characterized in that: A third protective layer is also coated on the protective layer, wherein the third protective layer comprises a PEO or ceramic composite coating.

11. A lithium ion battery, characterized in that: A lithium metal negative electrode comprising the lithium metal negative electrode according to any one of claims 1 to 6.

12. An electrical equipment, characterized in that: Includes the lithium ion battery as claimed in claim 11.

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