Lithium metal negative electrode, preparation method thereof and lithium metal solid-state battery

Abstract

The invention provides a lithium metal negative electrode and a preparation method thereof and a lithium metal solid-state battery, the lithium metal negative electrode comprises lithium metal and a LiFxClyBrz solid-state electrolyte layer formed on the surface of the lithium metal in situ, x is greater than or equal to 0.64 and less than or equal to 0.90, y is greater than or equal to 0.04 and less than or equal to 0.16, z is greater than or equal to 0.06 and less than or equal to 0.20, and x + y + z = 1; and the LiF < x > ClyBr < z > solid electrolyte layer is of a polycrystalline state LiF <->-LiCl <->-LiBr co-continuous structure. The LiFxClyBrz solid electrolyte layer with the polycrystalline LiF-LiCl-LiBr co-continuous structure is formed on the surface of the lithium metal in situ, so that the construction of a compatible interface of the high-stability lithium metal negative electrode and the solid electrolyte is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, specifically to lithium metal solid-state batteries, and particularly to a lithium metal negative electrode, a preparation method thereof, and a lithium metal solid-state battery. Background Art

[0002] In the lithium metal solid-state battery system, there are many problems with the native solid electrolyte interphase (SEI film). Its components are complex and disorderly arranged, the structure is loose, and the thickness is uneven. During the lithium deposition and stripping process, this film is extremely prone to local rupture, which in turn induces the growth of lithium dendrites, causing the battery to face the risk of short circuit and significantly shortening the cycle life. At the same time, the defects in the microstructure of the native solid electrolyte interphase will limit the lithium-ion transport channels, resulting in differences in the local lithium metal deposition rate, further exacerbating the electrode volume expansion and increasing the interfacial side reactions. In addition, when the native solid electrolyte interphase comes into contact with the sulfide solid electrolyte, interfacial side reactions are likely to occur between the two, such as causing the decomposition of sulfide, ultimately resulting in a decrease in the interfacial ion transport efficiency. Therefore, in existing lithium metal solid-state batteries, the native solid electrolyte interphase on the surface of the lithium metal negative electrode usually has key defects such as high interfacial impedance, poor mechanical properties, uneven lithium-ion flux distribution, and insufficient chemical stability.

[0003] CN115084648A discloses a solid electrolyte film, which includes adding a weak acid or other additives that can react gently with lithium metal during the preparation of the polymer composite solid electrolyte, so that the solid electrolyte and lithium metal are tightly combined through chemical reactions at the interface, reducing the interfacial impedance, inhibiting side reactions, consuming lithium dendrites, and promoting ion transport.

[0004] CN117954680A discloses a composite solid electrolyte film based on a high-dielectric ion conductor filler. The solid electrolyte film includes nano-inorganic fillers, and the nano-inorganic fillers include dielectric ion-conducting materials, and the dielectric ion-conducting materials include lithium niobate. By adding lithium niobate ceramic particles as inorganic nano-fillers in the solid electrolyte film, efficient ion transport channels are constructed in the electrolyte, significantly improving the ionic conductivity and improving the room-temperature performance of the solid-state lithium metal battery.

[0005] CN119650579A discloses an artificial SEI film. The artificial SEI film is composed of polytetrafluoroethylene, a dispersant, deionized water, a conductive agent, and a binder. The formed SEI film has the dual effects of promoting uniform deposition of lithium metal and preventing the reaction between lithium metal and the electrolyte, greatly improving the stability of the lithium metal battery without a negative electrode. In addition, due to the addition of a conductive agent in the primer slurry, the rate performance of the battery is greatly improved.

[0006] In the prior art, additives are used to promote the transport of lithium ions in lithium metal batteries and reduce the interfacial impedance, but the improvement effect is not ideal. Therefore, it is of great significance to construct a solid electrolyte membrane interface with good stability and strong compatibility between the lithium metal anode and the solid electrolyte. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a lithium metal anode, its preparation method and a lithium metal solid-state battery. The present invention forms a LiF with a polycrystalline LiF-LiCl-LiBr co-continuous structure in-situ on the surface of the lithium metal. x Cl y Br z The solid electrolyte layer is beneficial to the construction of a compatible interface between the high-stability lithium metal anode and the solid electrolyte. The polycrystalline LiF-LiCl-LiBr co-continuous structure forms a low-barrier Li+ transport path, making the ionic conductivity of the LiF x Cl y Br z solid electrolyte layer on the surface of the lithium metal anode significantly improved; at the same time, during the in-situ generation of the LiF x Cl y Br z solid electrolyte layer on the surface of the lithium metal, it is beneficial to release the internal stress existing in the lithium metal, making the in-situ formed LiF x Cl y Br z solid electrolyte layer structure more stable, reducing the generation of microcracks, which is beneficial to improving the lifespan of the lithium metal solid-state battery.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted by the present invention:

[0009] In the first aspect, the present invention provides a lithium metal anode, which includes lithium metal and a LiF x Cl y Br z solid electrolyte layer formed in-situ on the surface of the lithium metal, where 0.64 ≤ x ≤ 0.90, 0.04 ≤ y ≤ 0.16, 0.06 ≤ z ≤ 0.20, and x + y + z = 1;

[0010] The LiF x Cl y Br z solid electrolyte layer is a polycrystalline LiF-LiCl-LiBr co-continuous structure.

[0011] In the present invention, LiF x Cl y Br zThe solid electrolyte layer is formed in-situ on the surface of the lithium metal and has a polycrystalline LiF-LiCl-LiBr co-continuous structure. The polycrystalline LiF-LiCl-LiBr co-continuous structure forms a low-barrier Li+ transport path, enabling LiF on the surface of the lithium metal anode x Cl y Br z The ionic conductivity of the solid electrolyte layer is significantly improved; meanwhile, LiF is generated in-situ on the surface of the lithium metal x Cl y Br z During the process of forming the solid electrolyte layer, it is beneficial to release the internal stress existing in the lithium metal, making the in-situ formed LiF x Cl y Br z The structure of the solid electrolyte layer is more stable, reducing the generation of microcracks and improving the battery life.

[0012] Preferably, in the LiF x Cl y Br z solid electrolyte layer, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 50nm - 200nm.

[0013] Preferably, the thickness of the LiF x Cl y Br z solid electrolyte layer is 100nm - 500nm.

[0014] In a second aspect, the present invention provides a method for preparing the lithium metal anode as described in the first aspect. The preparation method includes:

[0015] Under an inert atmosphere, a hydrofluoride, a hydrochloride, and a hydrobromide are mixed in an organic solvent to obtain a reaction solution; the lithium metal is immersed in the reaction solution, and a LiF x Cl y Br z ternary composite material layer is formed by in-situ reaction on the surface of the lithium metal, aged, and a LiF x Cl y Br z solid electrolyte layer with a polycrystalline LiF-LiCl-LiBr co-continuous structure is obtained to get the lithium metal anode;

[0016] wherein, 0.64 ≤ x ≤ 0.90, 0.04 ≤ y ≤ 0.16, 0.06 ≤ z ≤ 0.20, and x + y + z = 1.

[0017] Preferably, the hydrofluoride includes a hydrofluoride containing an amino group, and the hydrofluoride containing an amino group includes any one or a combination of at least two of triethylamine trihydrofluoride, tripropylamine trihydrofluoride, or N,N - diisopropylethylamine trihydrofluoride.

[0018] Preferably, the hydrochloride includes a hydrochloride containing an amino group, and the hydrochloride containing an amino group includes any one or a combination of at least two of methylamine hydrochloride, trimethylamine hydrochloride, ethylamine hydrochloride, triethylamine hydrochloride, dipropylamine hydrochloride, isopropylamine hydrochloride, n - butylamine hydrochloride, or isobutylamine hydrochloride.

[0019] Preferably, the hydrobromide includes a hydrobromide containing an amino group, and the hydrobromide containing an amino group includes any one or a combination of at least two of methylamine hydrobromide, ethylamine hydrobromide, propylamine hydrobromide, dipropylamine hydrobromide, or isopropylamine hydrobromide.

[0020] Preferably, the organic solvent includes any one or a combination of at least two of N - methylpyrrolidone, ethylene glycol dimethyl ether, or dimethylformamide.

[0021] Preferably, the temperature of the in - situ reaction is 20°C - 30°C.

[0022] Preferably, the time of the in - situ reaction is 3 min - 10 min.

[0023] Preferably, the temperature of the aging is 60°C - 80°C.

[0024] Preferably, the time of the aging is 3 h - 8 h.

[0025] Preferably, before the lithium metal is immersed in the reaction solution, it further includes performing atomic - level planarization treatment on the surface of the lithium metal under an inert atmosphere.

[0026] Preferably, the atomic - level planarization treatment includes mechanically grinding and rolling the surface of the lithium metal to obtain an atomic - level flat surface.

[0027] Preferably, the mesh number of the sandpaper for mechanical grinding is above 2000 meshes.

[0028] Preferably, the pressure of the rolling is 5 MPa - 10 MPa.

[0029] Preferably, the preparation method further includes cleaning the LiF x Cl y Br z ternary composite material layer after the in - situ reaction and before aging.

[0030] Preferably, the cleaning includes soaking with tetrahydrofuran more than three times, 1 min - 5 min each time.

[0031] In a third aspect, the present invention provides a lithium metal solid-state battery, and the lithium metal solid-state battery includes a lithium metal negative electrode as described in the first aspect.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) By in-situ forming a LiF x Cl y Br z solid electrolyte layer with a polycrystalline LiF-LiCl-LiBr co-continuous structure on the surface of the lithium metal, it is beneficial to construct a compatible interface between the highly stable lithium metal negative electrode and the solid electrolyte. Generating the LiF x Cl y Br z solid electrolyte layer in-situ on the surface of the lithium metal is beneficial to release the internal stress existing in the lithium metal, making the in-situ formed LiF x Cl y Br z solid electrolyte layer structure more stable, reducing the generation of microcracks, and being beneficial to improving the service life of the lithium metal solid-state battery.

[0034] (2) The solid electrolyte layer with a polycrystalline LiF-LiCl-LiBr co-continuous structure on the surface of the lithium metal negative electrode provided by the present invention can form a low-barrier Li+ transport path, significantly improving the ionic conductivity of the lithium metal negative electrode. Among them, LiF can improve the lithium ion transport efficiency and dendrite inhibition ability of the SEI film. The addition of Cl element and Br element can regulate the grain boundaries. At the same time, Br element can enhance the chemical compatibility between the SEI film and the sulfide electrolyte, and improve the interfacial side reaction energy barrier.

[0035] (3) The preparation method of the lithium metal negative electrode provided by the present invention can directly generate a LiF x Cl y Br z solid electrolyte layer with a polycrystalline LiF-LiCl-LiBr co-continuous structure with a specific composition in-situ on the surface of the lithium metal. The preparation method is simple, the preparation time is short, and the prepared lithium metal can be directly assembled into a battery, which can be prepared on a large scale and is suitable for industrial application. Description of the Drawings

[0036] Figure 1 is the EDS test result of the LiF 0.75 Cl 0.11 Br 0.14 solid electrolyte layer on the surface of the lithium metal negative electrode in Example 1. Detailed Embodiments

[0037] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0039] In a specific embodiment, the present invention provides a lithium metal anode, and the lithium metal anode includes lithium metal and LiF formed in situ on the surface of the lithium metal x Cl y Br z a solid electrolyte layer, wherein 0.64 ≤ x ≤ 0.90, 0.04 ≤ y ≤ 0.16, 0.06 ≤ z ≤ 0.20, and x + y + z = 1;

[0040] The LiF x Cl y Br z solid electrolyte layer is a polycrystalline LiF-LiCl-LiBr co-continuous structure.

[0041] In the present invention, the LiF x Cl y Br z solid electrolyte layer is formed in situ on the surface of the lithium metal and has a polycrystalline LiF-LiCl-LiBr co-continuous structure. The polycrystalline LiF-LiCl-LiBr co-continuous structure forms a low-barrier Li+ transport path, enabling the ionic conductivity of the LiF x Cl y Br z solid electrolyte layer on the surface of the lithium metal anode to be significantly improved; at the same time, during the in-situ generation of the LiF x Cl y Br z solid electrolyte layer on the surface of the lithium metal, it is beneficial to release the internal stress existing in the lithium metal, making the in-situ formed LiF x Cl y Br z solid electrolyte layer structure more stable, reducing the generation of microcracks and improving the battery life.

[0042] The present invention regulates the composition of the solid electrolyte layer in the lithium metal anode to be LiF x Cl y Br z, LiF has high ionic conductivity and high modulus, which can improve the lithium-ion transport efficiency and dendrite inhibition ability of the SEI film. The addition of a small amount of Cl element and Br element can regulate grain boundaries, induce lattice distortion, and promote the formation of grain boundaries. At the same time, the appropriate introduction of Br element can enhance the chemical compatibility between the SEI film and the sulfide electrolyte and increase the interfacial side reaction energy barrier.

[0043] If the content of Cl element is too high, it may lead to an increase in the ionic migration barrier of the solid electrolyte layer. If the content of Br element is too high, it may cause excessive corrosion of lithium metal.

[0044] In some embodiments, the LiF x Cl y Br z In the solid electrolyte layer, 0.64 ≤ x ≤ 0.90. For example, x can be 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80, 0.82, 0.84, 0.86, 0.88, or 0.90, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable; 0.04 ≤ y ≤ 0.16. For example, y can be 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or 0.16, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable; 0.06 ≤ z ≤ 0.20. For example, z can be 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, or 0.20, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0045] In the present invention, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is too large, and the grain boundary density is reduced, resulting in a decrease in lithium-ion transport channels and an increase in interfacial impedance. Moreover, large-sized grains are prone to stress concentration during cycling, inducing cracking of the SEI film; while the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is too small, it will lead to an increase in the defect density at grain boundaries, accelerating side reactions. At the same time, the thermodynamic instability of nanograins will reduce the long-term cycling stability of the SEI film.

[0046] In some embodiments, the LiF x Cl y Br zIn the solid electrolyte layer, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 50 nm to 200 nm, and for example, it can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0047] In the present invention, LiF x Cl y Br z If the thickness of the solid electrolyte layer is too large, the lithium ion transmission path is extended, the bulk impedance increases significantly, and the thick solid electrolyte film is prone to peeling due to volume change during lithium deposition, resulting in interface failure. If LiF x Cl y Br z If the thickness of the solid electrolyte layer is too small, the mechanical strength is insufficient, it cannot effectively inhibit the piercing of lithium dendrites, and the coverage of the lithium metal surface is incomplete, exacerbating local side reactions.

[0048] In some embodiments, the LiF x Cl y Br z The thickness of the solid electrolyte layer is 100 nm to 500 nm, and for example, it can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0049] In another specific embodiment, the present invention provides a method for preparing the lithium metal negative electrode described in the foregoing specific embodiment, and the preparation method includes:

[0050] Under an inert atmosphere, a hydrofluoric acid salt, a hydrochloride salt and a hydrobromide salt are mixed in an organic solvent to obtain a reaction solution; the lithium metal is immersed in the reaction solution, and a LiF x Cl y Br z ternary composite material layer is formed by in-situ reaction on the surface of the lithium metal, and aged to form a LiF with a polycrystalline LiF-LiCl-LiBr co-continuous structure x Cl y Br z solid electrolyte layer to obtain the lithium metal negative electrode;

[0051] Among them, 0.64 ≤ x ≤ 0.90, 0.04 ≤ y ≤ 0.16, 0.06 ≤ z ≤ 0.20, and x + y + z = 1.

[0052] The preparation method of the lithium metal anode provided by the present invention selects hydrofluoride, hydrochloride and hydrobromide as raw materials to prepare a reaction solution. Through the decomposition of amine salts, F⁻, Cl⁻, and Br⁻ active ions are provided. Using metallic lithium to undergo a competitive redox reaction with acid root ions: 2Li + 2HB → 2LiB + H₂↑, where B = F, Cl, Br, LiF is in-situ obtained on the surface of the lithium metal. x Cl y Br z A ternary composite material layer, and then through aging, a polycrystalline LiF-LiCl-LiBr co-continuous structure is formed to obtain LiF. x Cl y Br z A solid electrolyte layer, thereby preparing the lithium metal anode.

[0053] The present invention in-situ generates LiF with a polycrystalline LiF-LiCl-LiBr co-continuous structure with a specific composition on the surface of the lithium metal. x Cl y Br z The solid electrolyte layer has a simple preparation method, a short preparation time, and the prepared lithium metal can be directly assembled into a battery, can be prepared on a large scale, and is suitable for industrial application.

[0054] In some embodiments, in the reaction solution, the total molar concentration of hydrofluoride, hydrochloride and hydrobromide is 0.5 mol / L - 2.0 mol / L. For example, it can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L or 2.0 mol / L, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable. A suitable concentration range can ensure the preparation of high-quality LiF. x Cl y Br z The solid electrolyte layer, avoiding the reaction getting out of control due to too high a concentration, resulting in the prepared solid electrolyte layer being too loose, or too low a concentration leading to incomplete film formation.

[0055] In some embodiments, the hydrofluoride includes a hydrofluoride containing an amino group. The hydrofluoride containing an amino group includes any one or at least two combinations of triethylamine trihydrofluoride, tripropylamine trihydrofluoride or N,N-diisopropylethylamine trihydrofluoride. Typical but non-limiting combinations include the combination of triethylamine trihydrofluoride and tripropylamine trihydrofluoride, the combination of tripropylamine trihydrofluoride and N,N-diisopropylethylamine trihydrofluoride, or the combination of triethylamine trihydrofluoride and N,N-diisopropylethylamine trihydrofluoride.

[0056] In some embodiments, the hydrochloride salt includes an amine-containing hydrochloride salt, and the amine-containing hydrochloride salt includes any one or a combination of at least two of methylamine hydrochloride, trimethylamine hydrochloride, ethylamine hydrochloride, triethylamine hydrochloride, dipropylamine hydrochloride, isopropylamine hydrochloride, n-butylamine hydrochloride, or isobutylamine hydrochloride. Exemplary but non-limiting combinations include the combination of methylamine hydrochloride and trimethylamine hydrochloride, the combination of ethylamine hydrochloride and triethylamine hydrochloride, the combination of dipropylamine hydrochloride and isopropylamine hydrochloride, or the combination of n-butylamine hydrochloride and isobutylamine hydrochloride.

[0057] In some embodiments, the hydrobromide salt includes an amine-containing hydrobromide salt, and the amine-containing hydrobromide salt includes any one or a combination of at least two of methylamine hydrobromide, ethylamine hydrobromide, propylamine hydrobromide, dipropylamine hydrobromide, or isopropylamine hydrobromide. Exemplary but non-limiting combinations include the combination of methylamine hydrobromide and ethylamine hydrobromide, the combination of propylamine hydrobromide and dipropylamine hydrobromide, or the combination of isopropylamine hydrobromide and ethylamine hydrobromide.

[0058] In some embodiments, the organic solvent includes any one or a combination of at least two of N-methylpyrrolidone, ethylene glycol dimethyl ether, or dimethylformamide. Exemplary but non-limiting combinations include the combination of N-methylpyrrolidone and ethylene glycol dimethyl ether, the combination of dimethylformamide and N-methylpyrrolidone, or the combination of ethylene glycol dimethyl ether and dimethylformamide.

[0059] In the present invention, a suitable in-situ reaction temperature is beneficial to obtaining high-quality LiF x Cl y Br z For the solid electrolyte layer, if the in-situ reaction temperature is too high, the reaction rate is too fast, the film layer is loose and the crystal grains are coarsened, and the interfacial impedance increases. If the in-situ reaction temperature is too low, the reaction kinetics is limited, the film formation is discontinuous, and local lithium metal exposure causes dendrite growth.

[0060] In some embodiments, the temperature of the in-situ reaction is 20°C - 30°C. For example, it can be 20°C, 22°C, 24°C, 26°C, 28°C, or 30°C, including but not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0061] In the present invention, if the in-situ reaction time is too long, the prepared LiF x Cl y Br z The solid electrolyte layer is too thick, and impurities such as LiOH / Li2CO3 may be generated on the surface, affecting the performance of the lithium metal negative electrode. If the in-situ reaction time is too short, the film formation is incomplete, and a continuous LiF x Cl y Brz The solid electrolyte layer effectively avoids the growth of dendrites caused by local exposure of lithium metal.

[0062] In some embodiments, the time of the in-situ reaction is 3 min - 10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0063] In the present invention, if the aging temperature is too high, it will cause excessive growth of the grains of the polycrystalline LiF-LiCl-LiBr co-continuous structure and a decrease in the grain boundary density; if the aging temperature is too low, it will cause insufficient release of internal stress, LiF x Cl y Br z The solid electrolyte layer is prone to cracking during cycling.

[0064] In some embodiments, the aging temperature is 60°C - 80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0065] In the present invention, if the aging time is too long, it will cause excessive growth of the grains of the polycrystalline LiF-LiCl-LiBr co-continuous structure and excessive grain boundary recombination, and LiF obtained by in-situ growth x Cl y Br z The brittleness of the solid electrolyte layer increases and the bending performance of the battery decreases; if the aging time is too short, the grain growth is not completed, the grain boundary structure is not optimized, and the uniformity of lithium ion transmission is poor.

[0066] In some embodiments, the aging time is 3 h - 8 h, for example, it can be 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0067] In some embodiments, before the lithium metal is immersed in the reaction solution, it further includes performing atomic-level planarization treatment on the surface of the lithium metal under an inert atmosphere.

[0068] In the present invention, the purpose of performing atomic-level planarization treatment on the surface of the lithium metal is to completely remove the native SEI film on the surface of the lithium metal, form an atomic-level flat surface, and eliminate the initial interface defects.

[0069] In some embodiments, the atomic-level planarization treatment includes mechanically polishing and rolling the surface of the lithium metal to obtain an atomic-level flat surface.

[0070] In the present invention, "atomic-level planarization treatment" and "atomically flat surface" refer to a surface roughness ≤ 1 nm.

[0071] The present invention realizes an atomically flat lithium metal surface through the cooperation of mechanical polishing and rolling, ensuring the complete removal of the native SEI film on the lithium metal surface.

[0072] In some embodiments, the grit size of the sandpaper for the mechanical polishing is above 2000 mesh, for example, it can be 2000 mesh, 2500 mesh, 3000 mesh, 3500 mesh, 4000 mesh, 4500 mesh or 5000 mesh, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0073] In some embodiments, the pressure for the rolling is 5 MPa - 10 MPa, for example, it can be 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa or 10 MPa, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0074] In some embodiments, the preparation method further includes, after the in-situ reaction ends and before aging, cleaning the LiF x Cl y Br z ternary composite material layer.

[0075] In the present invention, the purpose of cleaning the LiF x Cl y Br z ternary composite material layer formed by the in-situ reaction is to selectively remove the residual NMP and unreacted organic substances, providing a basis for obtaining a dense polycrystalline LiF-LiCl-LiBr co-continuous structure subsequently.

[0076] In some embodiments, the cleaning includes soaking in tetrahydrofuran three or more times, for example, it can be three times, four times or five times, and each time for 1 min - 5 min, for example, it can be 1 min, 2 min, 3 min, 4 min or 5 min, including but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0077] In yet another specific embodiment, the present invention provides a lithium metal solid-state battery, and the lithium metal solid-state battery includes the lithium metal negative electrode described in the foregoing one specific embodiment.

[0078] Example 1

[0079] This embodiment provides a lithium metal anode, which includes lithium metal and a polycrystalline LiF-LiCl-LiBr co-continuous structure LiF with a grain size of 100 nm formed in-situ on the surface of the lithium metal 0.75 Cl 0.11 Br 0.14 solid electrolyte layer, and the LiF 0.75 Cl 0.11 Br 0.14 The thickness of the solid electrolyte layer is 300 nm.

[0080] The preparation method of the lithium metal anode includes:

[0081] (1) Perform atomic-level planarization on the lithium metal: In an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), mechanically polish the lithium metal with 2000-mesh sandpaper, and then roll it under a pressure of 7.5 MPa to form an atomic-level flat surface.

[0082] (2) Construct the LiF 0.75 Cl 0.11 Br 0.14 solid electrolyte layer in-situ: Using electronic-grade NMP as a solvent, prepare a reaction solution according to the molar ratio of F, Cl, and Br in triethylamine trihydrofluoride: ethylamine hydrochloride: ethylamine hydrobromide of 0.75:0.11:0.14; immerse the atomically planarized lithium metal in the reaction solution and react at 25 °C for 5 min to form a LiF 0.75 Cl 0.14 Br 0.11 ternary composite material layer, then soak it three times with tetrahydrofuran for 2 min each time, and finally age it on a 70 °C heating table for 5 hours to form a polycrystalline LiF-LiCl-LiBr co-continuous structure LiF 0.75 Cl 0.11 Br 0.14 solid electrolyte layer to obtain the lithium metal anode.

[0083] The EDS test results of the LiF 0.75 Cl 0.11 Br 0.14 solid electrolyte layer on the surface of the lithium metal anode provided in this embodiment are as Figure 1 shown.

[0084] Example 2

[0085] This embodiment provides a lithium metal anode, which includes lithium metal and a polycrystalline LiF-LiCl-LiBr co-continuous structure LiF with a grain size of 50 nm formed in-situ on the surface of the lithium metal 0.64 Cl0.16 Br 0.2 Solid electrolyte layer, the LiF 0.64 Cl 0.16 Br 0.2 The thickness of the solid electrolyte layer is 100 nm.

[0086] The preparation method of the lithium metal negative electrode includes:

[0087] (1) Atomically flatten the lithium metal: In an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), mechanically polish the lithium metal with 2200 - mesh sandpaper, and then roll - press it under a pressure of 5 MPa to form an atomically flat surface.

[0088] (2) In - situ reaction to construct LiF 0.64 Cl 0.16 Br 0.2 Solid electrolyte layer: Using electronic - grade NMP as a solvent, prepare a reaction solution according to the molar ratio of F, Cl, and Br in tripropylamine trihydrofluoride: methylamine hydrochloride: dipropylamine hydrobromide of 0.64:0.16:0.2; immerse the atomically flattened lithium metal in the reaction solution, react at 20 °C for 3 min to form LiF on the surface of the lithium metal 0.64 Cl 0.16 Br 0.2 ternary composite layer, then soak it three times with tetrahydrofuran, 1 min each time, and finally age it on a 60 °C heating stage for 3 h to form LiF with a polycrystalline LiF - LiCl - LiBr co - continuous structure 0.64 Cl 0.16 Br 0.24 solid electrolyte to obtain the lithium metal negative electrode.

[0089] Example 3

[0090] This example provides a lithium metal negative electrode, which includes lithium metal and a polycrystalline LiF - LiCl - LiBr co - continuous structure LiF with a grain size of 200 nm formed in - situ on the surface of the lithium metal 0.9 Cl 0.04 Br 0.06 Solid electrolyte layer, the LiF 0.9 Cl 0.04 Br 0.06 The thickness of the solid electrolyte layer is 500 nm.

[0091] The preparation method of the lithium metal negative electrode includes:

[0092] (1) Atomically flatten the lithium metal: In an argon glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), mechanically polish the lithium metal with 2500 - mesh sandpaper, and then roll - press it under a pressure of 10 MPa to form an atomically flat surface.

[0093] (2) In - situ reaction to construct LiF 0.9 Cl 0.04 Br 0.06 Solid - state electrolyte layer: Using electronic - grade NMP as a solvent, prepare a reaction solution according to the molar ratio of F, Cl, and Br in N,N - diisopropylethylamine trihydrofluoride:triethylamine hydrochloride:propylamine hydrobromide of 0.9:0.04:0.06; immerse the atomically flattened lithium metal in the reaction solution and react at 30 °C for 10 min to form LiF on the surface of the lithium metal. 0.9 Cl 0.04 Br 0.06 Ternary composite material layer, then soak it four times with tetrahydrofuran for 5 min each time, and finally age it on an 80 °C heating stage for 8 h to form LiF with a polycrystalline LiF - LiCl - LiBr co - continuous structure. 0.9 Cl 0.04 Br 0.064 Solid - state electrolyte to obtain the lithium - metal negative electrode.

[0094] Example 4

[0095] This example provides a lithium - metal negative electrode. Compared with Example 1, in this example, the composition of the solid - state electrolyte layer is adjusted from LiF 0.75 Cl 0.11 Br 0.14 to LiF 0.14 Cl 0.11 Br 0.75 , and correspondingly adjust the molar ratio of F, Cl, and Br in triethylamine trihydrofluoride:ethylamine hydrochloride:ethylamine hydrobromide in step (2) of the preparation method to 0.14:0.11:0.75, and the rest are the same as in Example 1.

[0096] Example 5

[0097] This example provides a lithium - metal negative electrode. Compared with Example 1, in this example, the grain size of the polycrystalline LiF - LiCl - LiBr co - continuous structure is 25 nm, and the rest are the same as in Example 1.

[0098] The preparation method of the lithium - metal negative electrode is the same as that of Example 1 except that the aging time is 1 h, so that the grain size of the polycrystalline LiF - LiCl - LiBr co - continuous structure grows to 25 nm.

[0099] Example 6

[0100] This embodiment provides a lithium metal anode. Compared with Embodiment 1, in this embodiment, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 250 nm, and the rest are the same as those in Embodiment 1.

[0101] The preparation method of the lithium metal anode is the same as that in Embodiment 1 except that the aging time is adjusted to 12 h, so that the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure grows to 250 nm.

[0102] Embodiment 7

[0103] This embodiment provides a lithium metal anode. Compared with Embodiment 1, in this embodiment, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 45 nm, and the rest are the same as those in Embodiment 1.

[0104] The preparation method of the lithium metal anode is the same as that in Embodiment 1 except that the aging temperature is 40 °C, resulting in the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure growing to 45 nm.

[0105] Embodiment 8

[0106] This embodiment provides a lithium metal anode. Compared with Embodiment 1, in this embodiment, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 280 nm, and the rest are the same as those in Embodiment 1.

[0107] The preparation method of the lithium metal anode is the same as that in Embodiment 1 except that the aging temperature is 100 °C, resulting in the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure growing to 280 nm.

[0108] Embodiment 9

[0109] This embodiment provides a lithium metal anode film. Compared with Embodiment 1, in this embodiment, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 42 nm, and the rest are the same as those in Embodiment 1.

[0110] The preparation method of the lithium metal anode is the same as that in Embodiment 1 except that the in-situ reaction temperature is 15 °C, resulting in the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure growing to 42 nm.

[0111] Embodiment 10

[0112] This embodiment provides a lithium metal anode. Compared with Embodiment 1, in this embodiment, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 250 nm, and the rest are the same as those in Embodiment 1.

[0113] The preparation method of the lithium metal anode is the same as that of Example 1, except that the in-situ reaction temperature is 50°C, which causes the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure to grow to 250 nm.

[0114] Example 11

[0115] This example provides a lithium metal anode. Compared with Example 1, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure in this example is 20 nm, and the rest are the same as those in Example 1.

[0116] The preparation method of the lithium metal anode is the same as that of Example 1, except that the in-situ reaction time is 1 min.

[0117] Example 12

[0118] This example provides a lithium metal anode. Compared with Example 1, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure in this example is 350 nm, and the rest are the same as those in Example 1.

[0119] The preparation method of the lithium metal anode is the same as that of Example 1, except that the in-situ time is 15 min °C.

[0120] Comparative Example 1

[0121] This comparative example provides a lithium metal anode, which includes lithium metal and a LiF 0.75 Cl 0.11 Br 0.14 ternary composite material layer formed in-situ on the surface of the lithium metal.

[0122] Compared with Example 1, the preparation method of the lithium metal anode is the same as that of Example 1, except that step (2) is not aged on a 70°C heating stage for 5 hours.

[0123] Comparative Example 2

[0124] This comparative example provides a lithium metal anode, which only includes lithium metal.

[0125] The preparation method of the lithium metal anode includes: performing the same atomic-level planarization treatment on the lithium metal as in step (1) of Example 1.

[0126] Performance test: The lithium metal anodes provided in all the above examples and comparative examples are respectively assembled into soft-pack batteries with a sulfide electrolyte (Li6PS5Cl, thickness = 50 μm) and a 9-series high-nickel cathode (NCM90, areal capacity = 3.0 mAh / cm 2 )

[0127] Interface impedance test: At 25 °C, EIS test was carried out using an electrochemical workstation, and the test frequency range was 100 kHz - 0.1 Hz.

[0128] Ionic conductivity test: Blocking electrode DC polarization method.

[0129] Cycling performance test: At 25 °C, 3V - 4.3V, charge and discharge at 0.5C for 500 times.

[0130] The test results are shown in Table 1.

[0131] Table 1

[0132]

[0133] According to the test results of all the above-mentioned examples and Comparative Example 2, the lithium metal solid-state battery with the lithium metal negative electrode provided by the present invention has a lower interfacial impedance, a higher ionic conductivity, and a longer cycle life on the surface, attributed to the formation of a low-barrier Li+ transport path by the polycrystalline LiF-LiCl-LiBr co-continuous structure, making LiF on the surface of the lithium metal negative electrode x Cl y Br z The ionic conductivity of the solid electrolyte layer is significantly improved; at the same time, LiF is in-situ generated on the lithium metal surface x Cl y Br z During the process of the solid electrolyte layer, it is beneficial to release the internal stress existing in the lithium metal, making the in-situ formed LiF x Cl y Br z The solid electrolyte layer structure is more stable, reducing the generation of microcracks and improving the battery life.

[0134] According to the data results of Example 1 and Comparative Example 1, if only hydrofluoride, hydrochloride, and hydrobromide react in-situ on the lithium metal surface to form LiF x Cl y Br z ternary composite material layer, without aging reaction to form a polycrystalline LiF-LiCl-LiBr co-continuous structure of LiF x Cl y Br z solid electrolyte layer, then it is impossible to effectively form a low-barrier Li+ transport path and significantly improve the ionic conductivity of LiF x Cl y Br z solid electrolyte layer, and the electrical performance of the lithium metal solid-state battery cannot be improved.

[0135] According to the test results of Example 1 and Example 4, if the solid electrolyte layer is not in-situ grown according to the ratio defined in the present invention, the lithium ion transport efficiency and dendrite inhibition ability of the SEI film cannot be effectively improved, the grain boundaries cannot be regulated, the chemical compatibility between the SEI film and the sulfide electrolyte cannot be enhanced, and the interfacial side reaction energy barrier cannot be increased.

[0136] According to the test results of Example 1 and Examples 5 to 12, if the in-situ growth or aging is not carried out according to the temperature or time defined in the present invention, the grains formed by the reaction cannot grow into a suitable size, resulting in hindrance to the formation of grain boundaries, inability to effectively improve the lithium ion transport efficiency and uniformity, and inability to significantly improve the performance of the lithium metal anode.

[0137] The applicant declares that the above description is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A lithium metal negative electrode, characterized in that The lithium metal negative electrode includes lithium metal and LiF formed in situ on the surface of the lithium metal. x Cl y Br z A solid electrolyte layer, wherein 0.64≤x≤0.90, 0.04≤y≤0.16, 0.06≤z≤0.20, x+y+z=1; The LiF x Cl y Br z The solid electrolyte layer is a polycrystalline LiF-LiCl-LiBr co-continuous structure.

2. The lithium metal negative electrode according to claim 1, characterized in that The LiF x Cl y Br z In the solid electrolyte layer, the grain size of the polycrystalline LiF-LiCl-LiBr co-continuous structure is 50nm-200nm.

3. The lithium metal negative electrode according to claim 1, characterized in that The LiF x Cl y Br z The thickness of the solid electrolyte layer is 100nm-500nm.

4. A method for preparing a lithium metal negative electrode as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises: In an inert atmosphere, hydrofluoride, hydrochloride and hydrobromide are mixed in an organic solvent to obtain a reaction solution; lithium metal is immersed in the reaction solution to react in situ on the surface of the lithium metal to form LiF x Cl y Br z Ternary composite layer, aging, forming a polycrystalline LiF-LiCl-LiBr co-continuous structure of LiF x Cl y Br z A solid electrolyte layer is provided to obtain the lithium metal negative electrode; Among them, 0.64≤x≤0.90, 0.04≤y≤0.16, 0.06≤z≤0.20, x+y+z=1.

5. The preparation method according to claim 4, characterized in that: The hydrofluoride salt includes an amine-containing hydrofluoride salt, and the amine-containing hydrofluoride salt includes any one of triethylamine trihydrofluoride, tripropylamine trihydrofluoride or N,N-diisopropylethylamine trihydrofluoride or a combination of at least two thereof; Preferably, the hydrochloride comprises an amine-containing hydrochloride, and the amine-containing hydrochloride comprises any one of methylamine hydrochloride, trimethylamine hydrochloride, ethylamine hydrochloride, triethylamine hydrochloride, dipropylamine hydrochloride, isopropylamine hydrochloride, n-butylamine hydrochloride or isobutylamine hydrochloride, or a combination of at least two thereof; Preferably, the hydrobromide comprises an amine-containing hydrobromide, and the amine-containing hydrobromide comprises any one of methylamine hydrobromide, ethylamine hydrobromide, propylamine hydrobromide, dipropylamine hydrobromide or isopropylamine hydrobromide, or a combination of at least two thereof; Preferably, the organic solvent includes any one of N-methylpyrrolidone, ethylene glycol dimethyl ether or dimethylformamide, or a combination of at least two thereof.

6. The preparation method according to claim 4, characterized in that: The temperature of the in-situ reaction is 20°C-30°C; Preferably, the in-situ reaction time is 3 min-10 min.

7. The preparation method according to claim 4, characterized in that: The aging temperature is 60°C-80°C; Preferably, the aging time is 3h-8h.

8. The preparation method according to claim 4, characterized in that: Before the lithium metal is immersed in the reaction solution, the surface of the lithium metal is subjected to atomic-level flattening treatment in an inert atmosphere; Preferably, the atomic level flattening treatment comprises mechanically grinding and rolling the surface of the lithium metal to obtain an atomic level flat surface; Preferably, the mesh number of the sandpaper used for mechanical grinding is above 2000 mesh; Preferably, the rolling pressure is 5MPa-10MPa.

9. The preparation method according to claim 4, characterized in that: The preparation method further comprises the steps of: after the in-situ reaction is completed, before aging, treating the LiF formed by the in-situ reaction x Cl y Br z The ternary composite material layer is cleaned; Preferably, the cleaning comprises soaking in tetrahydrofuran for more than three times, each time for 1 min to 5 min.

10. A lithium metal solid-state battery, characterized in that: The lithium metal solid-state battery comprises the lithium metal negative electrode as described in any one of claims 1 to 3.

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