Composite metal lithium negative electrode, preparation method thereof and battery

Abstract

The invention belongs to the technical field of batteries, and provides a composite metal lithium negative electrode, a preparation method thereof and a battery, the composite metal lithium negative electrode comprises a metal lithium base layer, and a first passivation layer, an intermediate polymer layer and a surface barrier layer are sequentially arranged in the thickness direction of the metal lithium base layer; the first passivation layer comprises lithium sulfide and an organic sulfur derivative; the middle polymer layer comprises a first polymer matrix, a lithium salt and a functional additive; the surface barrier layer comprises a second polymer matrix and an inorganic solid electrolyte. By arranging the first passivation layer, the middle polymer layer and the surface barrier layer on the metal lithium base layer, a gradient functionalized multi-layer synergistic protection structure is formed, a closed loop mechanism of chemical passivation-ion regulation-physical barrier is realized, and the problems of SEI film stability, lithium ion uniform transmission and dendritic crystal growth are solved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite lithium metal anode, its preparation method, and a battery. Background Technology

[0002] Lithium metal is a high-capacity anode material (3860 mAh·g). -1 Lithium metal has great application potential in secondary lithium batteries and lithium-air batteries. However, due to its chemical reactivity, metallic lithium also poses significant safety risks. When lithium deposits are affected by concentration polarization and electric fields, dendrites can easily grow, leading to membrane puncture and a series of safety problems. Summary of the Invention

[0003] In view of the problems existing in the prior art, the purpose of this invention is to provide a composite lithium metal anode and its preparation method and battery. By designing a gradient functionalized multilayer synergistic protection structure, a closed-loop mechanism of "chemical passivation-ion regulation-physical barrier" is realized, which is beneficial to solving the problems of SEI film stability, uniform lithium ion transport and dendrite growth.

[0004] To achieve this objective, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a composite lithium metal anode, comprising a lithium metal substrate, wherein a first passivation layer, an intermediate polymer layer and a surface barrier layer are sequentially disposed in the thickness direction of the lithium metal substrate.

[0006] The first passivation layer comprises lithium sulfide and an organic sulfur derivative;

[0007] The intermediate polymer layer comprises a first polymer matrix, a lithium salt, and functional additives;

[0008] The surface barrier layer comprises a second polymer matrix and an inorganic solid electrolyte.

[0009] In some embodiments, the thickness of the first passivation layer is 5 nm to 200 nm; the lithium-ion conductivity of the first passivation layer is ≥1×10⁻⁶. -3 S / cm.

[0010] In some embodiments, the lithium sulfide in the first passivation layer is formed by an in-situ reaction of a sulfur-containing compound with the lithium metal in the lithium metal substrate.

[0011] In some embodiments, the thickness of the intermediate polymer layer is 1 μm to 10 μm.

[0012] In some embodiments, based on the total mass of the intermediate polymer layer as 100%, the first polymer matrix accounts for 80% to 96%, the lithium salt accounts for 3% to 15%, and the functional additives account for 1% to 5%.

[0013] In some embodiments, the thickness of the surface barrier layer is 5 μm to 50 μm; the lithium-ion conductivity of the surface barrier layer is 1 × 10⁻⁶. -4 ~1×10 -3 S / cm.

[0014] In some embodiments, the inorganic solid electrolyte accounts for 50% to 80% of the total mass of the surface barrier layer, and the second polymer matrix accounts for 20% to 50%.

[0015] In a second aspect, the present invention provides a method for preparing a composite lithium metal anode as described in the first aspect, comprising the following steps:

[0016] S1. A treatment solution containing sulfur compounds is provided, and a lithium metal substrate is immersed in the treatment solution to generate a first passivation layer on its surface through an in-situ reaction.

[0017] S2. Provide a slurry comprising a first polymer matrix, a lithium salt, and functional additives, coat the slurry onto the first passivation layer, and dry it to form an intermediate polymer layer;

[0018] S3. Provide a dispersion comprising a second polymer matrix and an inorganic solid electrolyte, coat the dispersion onto the intermediate polymer layer and dry and hot-press it to form a surface barrier layer;

[0019] S4. The composite lithium metal anode is obtained.

[0020] In some embodiments, in step S1, the concentration of sulfur-containing compounds in the treatment solution is 0.01M to 0.5M; the temperature of the in-situ reaction is 25℃ to 50℃, and the time is 1h to 5h.

[0021] Thirdly, the present invention provides a battery comprising the composite lithium metal anode disclosed in the first aspect, or a composite lithium metal anode prepared by the method for preparing the composite lithium metal anode disclosed in the second aspect.

[0022] The advantages of this invention are as follows:

[0023] (1) The composite lithium metal anode provided by the present invention realizes a gradient functional synergy mechanism, and realizes the functional progression of “chemically stable substrate → uniform ion transport → rigid physical barrier” from the lithium metal base layer outward. It can adapt to the dynamic process of lithium ion deposition / dissolution, and the inner layer flexibility is conducive to coping with volume changes, while the outer layer rigidity is conducive to blocking dendrites; the first passivation layer and the middle polymer layer have chemical compatibility (both contain Li). + The conductive channels, intermediate polymer layer, and surface barrier layer have polarity matching (all containing polar groups), which can effectively reduce interlayer charge accumulation, lower impedance, and enhance interlayer bonding.

[0024] (2) A protective structure is formed by sequentially setting a first passivation layer, an intermediate polymer layer, and a surface barrier layer on a lithium metal substrate. The first passivation layer combines high ion conductivity with flexibility, which helps reduce electrolyte decomposition and gas generation, reducing gas generation by more than 50% compared to traditional lithium metal electrodes. The intermediate polymer layer lowers the lithium-ion migration barrier through complexation, improving the uniformity of ion distribution. The surface barrier layer utilizes the high mechanical strength of the inorganic solid electrolyte to suppress dendrite penetration, and its high ion conductivity, combined with the bonding effect of the polymer, helps reduce interfacial porosity. By setting a multi-layered protective structure on the lithium metal substrate, the stability of the lithium metal surface can be improved, avoiding the possibility of side reactions between lithium metal and the electrolyte or other components. The multi-layered protection has a stronger affinity for lithium ions, and the multi-level interfacial bonding design allows the interfacial impedance to be controlled at 100 Ω·cm. 2 This, in turn, improves battery cycle life. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used in the detailed description is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this invention are intended to cover non-exclusive inclusion.

[0027] In the description of specific embodiments of the present invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, "multiple" means two or more, unless otherwise explicitly defined.

[0028] In this invention, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0029] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this invention, the character " / " generally indicates that the preceding and following associated objects have an "or" relationship.

[0030] Throughout this invention, numerical values ​​represent approximate measures or limits of a range to cover minute deviations from a given value, as well as embodiments with approximately the mentioned value and embodiments with the exact mentioned value. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this specification (including the appended claims) should be understood to be modified in all cases by the term “about,” regardless of whether “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows for some minor inaccuracy (approaching the exact value in some way; approximately or reasonably approaching the value; almost). If the inaccuracy provided by “about” is not otherwise understood in this general sense in the art, then “about” as used in this invention at least indicates a variation that can be produced by common methods of measuring and using such a parameter. For example, “about” may include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some respects, optionally less than or equal to 0.1%.

[0031] Additionally, the disclosure of the range includes the disclosure of all values ​​across the entire range and the disclosure of further subdivided ranges, including the endpoints and subranges given for these ranges.

[0032] Lithium metal is a high-capacity anode material (3860 mAh·g). -1Lithium metal has great application potential in secondary lithium batteries and lithium-air batteries. However, due to its chemical reactivity, metallic lithium also poses significant safety risks. When lithium deposits are affected by concentration polarization and electric fields, dendrites can easily grow, leading to membrane puncture and a series of safety problems.

[0033] Current technical solutions mostly focus on single-function interface modification (such as a pure Li3PO4 passivation layer or a MoS2 barrier layer) or simply stack different materials, failing to construct an integrated protective structure with progressive functional gradients between layers, compatible chemical and physical properties, and synergistic operation. Moreover, while a single SEI film formed on the surface of the lithium metal anode or a single passivation layer such as a LiF layer can suppress side reactions, it cannot solve the problem of dendrite growth caused by uneven lithium-ion transport. Placing a lithiophilic layer such as a MoS2 layer between the solid electrolyte layer and the metal anode can physically block dendrites, but its poor compatibility with the lithium metal interface leads to excessively high impedance. Furthermore, when setting up a physically stacked multilayer structure, problems such as peeling caused by volume changes during charging and discharging will be encountered, further exacerbating performance degradation.

[0034] To address the aforementioned issues, this invention provides a composite lithium metal anode, its preparation method, and a battery. By designing a gradient functionalized multilayer synergistic protection structure, a closed-loop mechanism of "chemical passivation-ion regulation-physical barrier" is achieved, which helps to solve problems related to SEI film stability, uniform lithium ion transport, and dendrite growth.

[0035] The technical solution of this invention is implemented as follows:

[0036] In one aspect, this application provides a composite lithium metal anode, comprising a lithium metal substrate, wherein a first passivation layer, an intermediate polymer layer and a surface barrier layer are sequentially disposed in the thickness direction of the lithium metal substrate.

[0037] The first passivation layer comprises lithium sulfide and an organic sulfur derivative;

[0038] The intermediate polymer layer comprises a first polymer matrix, a lithium salt, and functional additives;

[0039] The surface barrier layer comprises a second polymer matrix and an inorganic solid electrolyte.

[0040] The composite lithium metal anode provided by this invention achieves a gradient functional synergy mechanism, sequentially realizing the functional progression of "chemically stable substrate → uniform ion transport → rigid physical barrier" from the lithium metal substrate outwards. This allows it to adapt to the dynamic process of lithium-ion deposition / dissolution, with the inner layer's flexibility facilitating volume changes and the outer layer's rigidity helping to prevent dendrite formation. The first passivation layer and the intermediate polymer layer are chemically compatible (both contain Li). +The conductive channels, intermediate polymer layer, and surface barrier layer have polarity matching (all containing polar groups), which can effectively reduce interlayer charge accumulation, lower impedance, and enhance interlayer bonding.

[0041] In some embodiments, the first passivation layer is disposed on and in contact with the surface of the lithium metal substrate, the intermediate polymer layer is disposed on the side of the first passivation layer away from the lithium metal substrate, and the surface barrier layer is disposed on the side of the intermediate polymer layer away from the first passivation layer.

[0042] In some embodiments, the thickness of the lithium metal substrate is 5 μm to 500 μm, for example, 5 μm, 10 μm, 30 μm, 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc. This invention does not impose any limitations on this.

[0043] In some embodiments, the lithium metal substrate comprises elemental lithium or a lithium alloy.

[0044] Preferably, the lithium alloy comprises a Li-Sn alloy and / or a Li-Al alloy. This invention is not limited thereto.

[0045] In some embodiments, the thickness of the first passivation layer is 5 nm to 200 nm; the lithium-ion conductivity of the first passivation layer is ≥1×10⁻⁶. -3 S / cm.

[0046] For example, the thickness of the first passivation layer can be selected as 5nm, 8nm, 10nm, 30nm, 50nm, 80nm, 100nm, 130nm, 150nm, 180nm, 200nm, etc.; the lithium-ion conductivity of the first passivation layer is 1×10⁻⁶. -3 S / cm, 2×10 -3 S / cm, 3×10 -3 S / cm, 4×10 -3 S / cm, 5×10 -3 S / cm, 6×10 -3 S / cm, 7×10 -3 S / cm, 8×10 -3 S / cm, 9×10 - 3 S / cm, etc. This invention does not impose any limitations on this.

[0047] In some embodiments, the lithium sulfide in the first passivation layer is formed by an in-situ reaction of a sulfur-containing compound with the lithium metal in the lithium metal substrate.

[0048] It is understood that the first passivation layer formed by the in-situ reaction mainly comprises lithium sulfide (Li2S) and also includes organic sulfur derivatives. Therefore, the first passivation layer comprises a mixture of Li2S and organic sulfur derivatives. In this invention, the "organic sulfur derivatives" refer to organic compounds or intermediates containing sulfur elements generated after the sulfur-containing compounds (such as thiourea, carbon disulfide, etc.) undergo an in-situ reaction with metallic lithium, except for the formation of Li2S, which are not completely converted or partially reduced / reacted. These compounds intertwine with Li2S to jointly constitute the interpenetrating network structure, where Li2S provides a fast ion conduction channel, while the organic sulfur derivatives contribute to the flexibility of the structure and interfacial compatibility with the upper polymer layer.

[0049] In some embodiments, the sulfur-containing compound includes at least one of thiourea (CS(NH2)2), carbon disulfide (CS2), methyl mercaptan (CH3SH), or ethanethiol (C2H5SH).

[0050] In some embodiments, the thickness of the intermediate polymer layer is 1 μm to 10 μm.

[0051] For example, the thickness of the intermediate polymer layer can be selected as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc. This invention does not impose any limitations on this.

[0052] In some embodiments, based on the total mass of the intermediate polymer layer as 100%, the first polymer matrix accounts for 80% to 96%, the lithium salt accounts for 3% to 15%, and the functional additives account for 1% to 5%.

[0053] For example, taking the total mass of the intermediate polymer layer as 100%, the proportion of the first polymer matrix can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, etc.; the proportion of the lithium salt can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.; and the proportion of the functional additives can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. This invention does not impose any limitations in this regard.

[0054] In some embodiments, the first polymer matrix includes at least one of polyethylene oxide (PEO), polymethyl methacrylate (PMMA), or polypropylene carbonate (PPC).

[0055] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB).

[0056] In some embodiments, the functional additive includes at least one of 12-crown ether-4, 15-crown ether-5, or ethylene glycol diethyl ether (EGDE).

[0057] In some embodiments, the thickness of the surface barrier layer is 5 μm to 50 μm; the lithium-ion conductivity of the surface barrier layer is 1 × 10⁻⁶. -4 ~1×10 -3 S / cm.

[0058] For example, the thickness of the surface barrier layer can be selected as 5μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc.;

[0059] The lithium-ion conductivity of the surface barrier layer can be 1×10⁻⁶. -4 S / cm, 2×10 -4 S / cm, 3×10 -4 S / cm, 4×10 -4 S / cm, 5×10 -4 S / cm, 6×10 -4 S / cm, 7×10 -4 S / cm, 8×10 -4 S / cm, 9×10 -4 S / cm, 1×10 -3 S / cm, etc. This invention does not impose any limitations on this.

[0060] In some embodiments, the inorganic solid electrolyte accounts for 50% to 80% of the total mass of the surface barrier layer, and the second polymer matrix accounts for 20% to 50%.

[0061] For example, the inorganic solid electrolyte may comprise 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 71%, 73%, 75%, 78%, 80%, etc.; and the second polymer matrix may comprise 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, etc. This invention does not impose any limitations on this.

[0062] In some embodiments, the second polymer matrix includes at least one of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyimide (PI), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).

[0063] In this invention, the surface barrier layer containing the second polymer matrix and the inorganic solid electrolyte is an inorganic-organic composite solid electrolyte layer.

[0064] In some embodiments, the inorganic solid electrolyte includes at least one of a sulfide solid electrolyte, a halide solid electrolyte, or an oxide solid electrolyte.

[0065] In some embodiments, the sulfide solid electrolyte comprises xLi₂S·(100-x)P₂S₅, 60≤x≤80, or Li₇P₃S. 11 , Li6PS5Cl, Li6PS5Br, Li6PS5Cl x Br 1-x x=0~1.0, Li 6+x P 1-x Ge x S5I, Li5PS4X2, where X is at least one of Cl, Br, or I, or Li 10 MP2S 12 M is at least one of Si, Ge, or Sn (e.g., it could be Li). 10 GeP2S 12 (LGPS)), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of them;

[0066] In some embodiments, the halide solid electrolyte includes Li3InBr 6-x Cl xx≤4 (e.g., including Li3InBr3Cl3, Li3InBr6), LiInBr4, Li3InCl6, Li3YX6, where X is at least one of Cl, Br, or I, Li3ErX6, where X is at least one of Cl, Br, or I, Li3ScX6, where X is at least one of Cl, Br, or I, Li3LaI6, Li3LuCl6, Li 3-x Er 1- x Zr x Cl6, x≤0.6, Li 3-x Y 1-x Zr x Cl6, x≤0.6, Li3Y 1-x In x Cl6, 0≤x<1, CsSnCl3 or Li x ScCl 3+x A mixture of one or more of them;

[0067] In some embodiments, the oxide solid electrolyte includes Li7La3Zr2O 12 (LLZO), Li 0.33 La 0.56 TiO3 (LLTO), Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO), Li3PO4, LiAlO2, β-Al2O3, LiTaO3, LiNbO3, Li4Ti5O 12 At least one of Li2SiO3, Li3BO3 or Li2ZrO3;

[0068] Preferably, the inorganic solid electrolyte includes Li 10 GeP2S 12 (LGPS), Li7La3Zr2O 12 At least one of (LLZO) or Li3InBr6.

[0069] In some embodiments, the mechanical strength of the inorganic solid electrolyte is ≥2 GPa, such as 2 GPa, 2.2 GPa, 2.5 GPa, 2.8 GPa, 3 GPa, 3.3 GPa, 3.5 GPa, 4 GPa, 4.2 GPa, or 4.5 GPa. This invention does not impose any limitations on this.

[0070] Secondly, the present invention provides a method for preparing the composite lithium metal anode disclosed in the first aspect, comprising the following steps:

[0071] S1. A treatment solution containing sulfur compounds is provided, and a lithium metal substrate is immersed in the treatment solution to generate a first passivation layer on its surface through an in-situ reaction.

[0072] S2. Provide a slurry comprising a first polymer matrix, a lithium salt, and functional additives, coat the slurry onto the first passivation layer, and dry it to form an intermediate polymer layer;

[0073] S3. Provide a dispersion comprising a second polymer matrix and an inorganic solid electrolyte, coat the dispersion onto the intermediate polymer layer and dry and hot-press it to form a surface barrier layer;

[0074] S4. The composite lithium metal anode is obtained.

[0075] In the preparation method described in this invention, the first passivation layer and the lithium metal base layer are combined through in-situ reaction, the intermediate polymer layer and the first passivation layer are combined through intermolecular forces, and then the surface barrier layer and the intermediate polymer layer are fused by hot pressing. This multi-level combination method forms a protective structure, which is conducive to further improving the bonding and matching degree between the layers, effectively reducing the accumulation of interlayer charge, reducing impedance, and better exerting synergistic and optimization effects.

[0076] In some embodiments, the treatment solution includes an anhydrous solvent in which the sulfur-containing compound is dissolved.

[0077] In some embodiments, the anhydrous solvent includes at least one of ethylene glycol dimethyl ether (DME), tetrahydrofuran (THF), or 1,3-dioxane (DOL).

[0078] In some embodiments, in step S1, the concentration of sulfur-containing compounds in the treatment solution is 0.01M to 0.5M; the temperature of the in-situ reaction is 25℃ to 50℃, and the time is 1h to 5h. In this invention, if the temperature of the in-situ reaction exceeds 50℃, it will easily lead to the decomposition of sulfur-containing compounds, while if it is below 25℃, the reaction rate will be too slow; the temperature range of 25℃ to 50℃ is beneficial to balance high ionic conductivity and flexibility.

[0079] For example, the concentration of sulfur-containing compounds in the treatment solution can be 0.01M, 0.03M, 0.05M, 0.08M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.35M, 0.4M, 0.45M, 0.5M, etc.; the temperature of the in-situ reaction can be 25℃, 28℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc.; the time of the in-situ reaction can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc. This invention does not impose any limitations on these aspects.

[0080] In some embodiments, the method of mixing the lithium metal substrate with the treatment liquid may include coating, spraying, roller coating, or drop coating, in addition to impregnation. However, it is not limited to these methods.

[0081] In some embodiments, the slurry in step S2 further includes a solvent, which includes at least one of acetonitrile (AN), dimethyl carbonate (DMC), propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, N,N dimethylacetamide, or N-methyl-2-pyrrolidone.

[0082] In this invention, the slurry is coated and dried to form an intermediate polymer layer, which can reduce the lithium ion migration barrier through complexation and improve the uniformity of ion distribution.

[0083] In some specific embodiments, the drying process in step S2 is carried out in a vacuum environment.

[0084] In some embodiments, the drying temperature in step S2 is 60°C to 80°C and the drying time is 2h to 4h. If the drying time is too short, it may lead to increased resistance due to solvent residue, while if it is too long, it may lead to excessive shrinkage of polymer chain segments.

[0085] For example, the drying temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, etc.; the time can be 2h, 2.5h, 3h, 3.5h, 4h, etc. The present invention does not impose any limitations on this.

[0086] In some specific implementations, the drying process described in step S3 is also carried out under vacuum.

[0087] In some embodiments, the drying temperature is 70°C to 90°C, and the drying time is 10 hours to 20 hours.

[0088] For example, the drying temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, etc.; the time can be 10h, 12h, 14h, 16h, 18h, 20h, etc. The present invention does not impose any limitations on this.

[0089] In some embodiments, the hot-pressing temperature in step S3 is 60°C to 150°C, and the pressure is 0.5 MPa to 2 MPa. In this invention, a hot-pressing pressure below 0.5 MPa can easily lead to loose interlayer bonding, while a pressure above 2 MPa may crush the inorganic solid electrolyte particles.

[0090] For example, the temperature of the hot pressing in step S3 can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc.; the pressure can be 0.5MPa, 0.8MPa, 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa, 2MPa, etc., preferably 1MPa~1.5MPa.

[0091] In some embodiments, in addition to coating, preparation methods S2 and S3 can also be roller coating, blade coating, casting, spraying, dip coating, or vapor deposition.

[0092] Thirdly, the present invention provides a battery comprising the composite lithium metal anode disclosed in the first aspect, or a composite lithium metal anode prepared by the preparation method of the composite lithium metal anode disclosed in the second aspect.

[0093] It should be noted that, due to space limitations and to avoid redundancy, this invention does not exhaustively list all point values ​​within the above numerical range, but it is not limited to the listed values ​​either; other unlisted values ​​within the above numerical range are also applicable.

[0094] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0095] Those skilled in the art will understand that the embodiments described are merely illustrative of the invention and should not be construed as limiting the invention.

[0096] Example 1

[0097] This embodiment provides a composite lithium metal anode, including a lithium metal substrate, and a first passivation layer, an intermediate polymer layer, and a surface barrier layer stacked on one side of the lithium metal substrate. The first passivation layer is disposed on and in contact with the surface of the lithium metal substrate, the intermediate polymer layer is disposed on the surface of the first passivation layer away from the lithium metal substrate, and the surface barrier layer is disposed on the surface of the intermediate polymer layer away from the first passivation layer.

[0098] The thickness of the lithium metal substrate is 250 μm, and the lithium metal substrate is a Li-Sn alloy foil;

[0099] The first passivation layer comprises lithium sulfide and an organic sulfur derivative; the thickness of the first passivation layer is 100 nm, and the lithium-ion conductivity of the first passivation layer is ≥10. -3 S / cm; The first passivation layer is formed by in-situ reaction of a sulfur-containing compound with lithium metal in the lithium metal substrate; The sulfur-containing compound is CS(NH2)2 and CS2 in a mass ratio of 1:2;

[0100] The intermediate polymer layer comprises a first polymer matrix, a lithium salt, and a functional additive; the thickness of the intermediate polymer layer is 5 μm; the first polymer matrix is ​​a mixture of PEO and PMMA in a mass ratio of 3:1, the lithium salt is LiTFSI, and the functional additive is 12-crown ether-4; based on the total mass of the intermediate polymer layer as 100%, the first polymer matrix accounts for 92%, the lithium salt accounts for 5%, and the functional additive accounts for 3%.

[0101] The surface barrier layer comprises a second polymer matrix and an inorganic solid electrolyte; the thickness of the surface barrier layer is 40 μm, and the lithium-ion conductivity of the surface barrier layer is 1 × 10⁻⁶. -4 ~1×10 -3 S / cm; the second polymer matrix is ​​PVDF-HFP (wherein the mass ratio of PVDF to HFP is 1:0.5), and the inorganic solid electrolyte is LLZO and LGPS in a mass ratio of 1:1; based on the total mass of the surface barrier layer as 100%, the inorganic solid electrolyte accounts for 80%, and the second polymer matrix accounts for 20%.

[0102] This embodiment also provides a method for preparing the aforementioned lithium metal anode, comprising:

[0103] (1) Preparation of the first passivation layer: A sulfur-containing compound is dissolved in anhydrous solvent DME to form a treatment solution with a concentration of 0.1M. A lithium metal substrate is immersed in the treatment solution and reacted in situ at 25°C for 3 hours to generate an interpenetrating network structure of Li2S with thiourea derivatives and carbon disulfide derivatives. This organic-inorganic interpenetrating network structure maintains the high ionic conductivity of Li2S, and its organic phase also endows the layer with good flexibility to buffer volume changes. The first passivation layer formed is beneficial to balance high ionic conductivity and flexibility.

[0104] (2) Preparation of intermediate polymer layer: A slurry is formed by dissolving 92% by mass of the first polymer matrix, 5% by mass of lithium salt and 3% by mass of functional additives in a mixed solvent (AN and DMC in a volume ratio of 1:1). The slurry is coated on the surface of the first passivation layer and dried in a vacuum environment at 60°C for 3 hours to form an intermediate polymer layer. The functional additives (such as crown ethers) in this layer can not only improve ionic conductivity through reversible complexation, but more importantly, they can homogenize the lithium ion flow distribution, guide uniform lithium deposition, and thus inhibit dendrite nucleation.

[0105] (3) Preparation of surface barrier layer: 80% by mass of inorganic solid electrolyte and 20% by mass of second polymer matrix are mixed in solution to form a dispersion. This dispersion is then cast onto the surface of the intermediate polymer layer and dried under vacuum at 85°C for 12 hours. Finally, it is hot-pressed at 120°C and 1.5 MPa to form a surface barrier layer. This process leverages the high mechanical strength (Young's modulus 25 GPa) of LLZO and the high ionic conductivity (1×10⁻⁶ GPa) of LGPS. -3 The bonding effect of PVDF-HFP effectively reduces interfacial porosity, resulting in a lithium metal anode.

[0106] Example 2

[0107] The difference between Example 2 and Example 1 is that Li-Al alloy foil is used as the lithium metal base layer, the sulfur-containing compound used to form the first passivation layer is CS(NH2)2, the intermediate polymer layer includes a first polymer matrix PEO with a mass percentage of 92%, 5% lithium salt LiTFSI and 3% functional additive 15-crown ether-5, and the inorganic solid electrolyte in the surface barrier layer is LLZO. Except for the above, the other conditions are exactly the same as in Example 1.

[0108] Example 3

[0109] The difference between Example 3 and Example 1 is that the sulfur-containing compound used to form the first passivation layer is CS2; the intermediate polymer layer includes a first polymer matrix PMMA with a mass percentage of 92%, a lithium salt LiFSI of 5%, and a functional additive of ethylene glycol diethyl ether of 3%; and the inorganic solid electrolyte in the surface barrier layer is LGPS. Apart from the above, the other conditions are exactly the same as in Example 1.

[0110] Comparative Example 1

[0111] The difference between Comparative Example 1 and Example 1 is that only a lithium metal base layer is used, and the first passivation layer, intermediate polymer layer and surface barrier layer are not provided. Apart from the above, the other conditions are exactly the same as those in Example 1.

[0112] Comparative Example 2

[0113] The difference between Comparative Example 2 and Example 1 is that only a lithium metal substrate is used, and the lithium metal substrate is a Li-Al alloy foil. At the same time, the first passivation layer, the intermediate polymer layer and the surface barrier layer are not provided. Apart from the above, the other conditions are exactly the same as those in Example 1.

[0114] Characterization and testing:

[0115] I. Battery fabrication: Providing commercially available positive electrodes, the active layer of which contains 96% by weight of high-nickel ternary material (LiNi). 0.8 Co0.1 Mn 0.1 The mixture consists of 2% O2, 2% PVDF, 1.5% conductive carbon black (SP), and 0.5% carbon nanotubes (CNTs). The positive electrode slurry is prepared by stirring it evenly in a solvent, then uniformly coated onto a 12μm aluminum foil, and cut into regular sizes after rolling.

[0116] The above-mentioned positive electrode and the negative electrode obtained in the examples and comparative examples are assembled into a pouch battery by a stacking process. A small amount (less than 5% of the battery weight) of electrolyte (1M LiPF6, EC / DMC / EMC volume ratio 1:1:1) is added to assemble a semi-solid pouch battery. The pouch battery air bag and the electrode group are slightly conductive. The battery is tested with a clamp (silicone plate).

[0117] II. Cyclic Performance Testing:

[0118] ① At room temperature, charge at 1C or the specified current to the termination voltage of 4.5V, cut off current of 0.05C, and let stand for 30 minutes; ② Then discharge at 1C to the final discharge voltage (2.75V), record the discharge capacity, and let stand for 30 minutes.

[0119] Repeat steps ① to ② until the discharge capacity is lower than the initial capacity, then end the experiment and record the number of cycles.

[0120] III. Gas Production Test:

[0121] The aforementioned pouch battery was charged and discharged at 1C current in an environment of 45°C. The cycle was stopped after 200 cycles. The gas in the gas bag was collected and sealed. The volume of water discharged in the measuring cylinder was observed.

[0122] IV. Interface Impedance Test:

[0123] The aforementioned pouch cells were subjected to electrochemical impedance spectroscopy (EIS) testing using an electrochemical workstation before cycling and after 200 cycles. The EIS results were then used to fit an equivalent circuit using ZView software to extract the interfacial impedance values.

[0124] The test results are recorded in Table 1:

[0125] Table 1

[0126]

[0127] As can be seen from Table 1:

[0128] Test results verified the synergistic advantages of the gradient multilayer structure. The cycle life of the batteries in Examples 1-3 (650-860 cycles) was significantly extended compared to Comparative Examples 1-2 (290-410 cycles). This was attributed to the combined effect of the homogenization of ion flow by the intermediate polymer layer and the physical suppression by the outer surface barrier layer, effectively delaying battery failure. Furthermore, in Examples 1-3, the first passivation layer effectively suppressed the side reactions between metallic lithium and the electrolyte, keeping the gas production below 2.5 mL over 200 cycles, a reduction of over 52% compared to Comparative Examples 1-2 (3.8 mL~4.5 mL), significantly improving battery safety (reducing the risk of casing rupture due to gas expansion). In the initial state (before cycling), the interfacial impedance of Examples 1-3 was 85.2 Ω·cm. 2 ~98.4Ω·cm 2 The value was significantly lower than that of the control group (159.3 Ω·cm). 2 ~175.2Ω·cm 2 Thanks to the multi-level interface design of "in-situ reaction bonding - intermolecular forces - thermo-pressing fusion" in this invention, interlayer porosity and charge accumulation can be effectively reduced; after 200 cycles, the interfacial impedance of Example 1 only increased to 132.8 Ω·cm. 2 This represents a 55.9% increase over the initial value, while the impedance of Comparative Example 1 increased to 328.9 Ω·cm. 2 The improvement of 106.5% demonstrates that the multilayer structure of this invention has better interface stability, can suppress impedance growth in the long term, and avoids the problem of battery capacity decay caused by excessive impedance.

[0129] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0130] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0131] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A composite lithium metal anode, comprising a lithium metal substrate, characterized in that, A first passivation layer, an intermediate polymer layer, and a surface barrier layer are sequentially disposed in the thickness direction of the lithium metal substrate. The first passivation layer comprises lithium sulfide and an organic sulfur derivative; The intermediate polymer layer comprises a first polymer matrix, a lithium salt, and functional additives; The surface barrier layer comprises a second polymer matrix and an inorganic solid electrolyte.

2. The composite lithium metal anode according to claim 1, characterized in that, The thickness of the first passivation layer is 5nm~200nm; the lithium-ion conductivity of the first passivation layer is ≥1×10⁻⁶. -3 S / cm.

3. The composite lithium metal anode according to claim 1, characterized in that, The lithium sulfide in the first passivation layer is formed by an in-situ reaction between a sulfur-containing compound and the lithium metal in the lithium metal substrate.

4. The composite lithium metal anode according to claim 1, characterized in that, The thickness of the intermediate polymer layer is 1 μm to 10 μm.

5. The composite lithium metal anode according to claim 1, characterized in that, Based on the total mass of the intermediate polymer layer as 100%, the first polymer matrix accounts for 80% to 96%, the lithium salt accounts for 3% to 15%, and the functional additives account for 1% to 5%.

6. The composite lithium metal anode according to claim 1, characterized in that, The thickness of the surface barrier layer is 5μm~50μm; the lithium-ion conductivity of the surface barrier layer is 1×10⁻⁶. -4 ~1×10 -3 S / cm.

7. The composite lithium metal anode according to claim 1, characterized in that, Based on the total mass of the surface barrier layer being 100%, the inorganic solid electrolyte accounts for 50% to 80%, and the second polymer matrix accounts for 20% to 50%.

8. A method for preparing a composite lithium metal anode as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. A treatment solution containing sulfur compounds is provided, and a lithium metal substrate is immersed in the treatment solution to generate a first passivation layer on its surface through an in-situ reaction. S2. Provide a slurry comprising a first polymer matrix, a lithium salt, and functional additives, coat the slurry onto the first passivation layer, and dry it to form an intermediate polymer layer; S3. Provide a dispersion comprising a second polymer matrix and an inorganic solid electrolyte, coat the dispersion onto the intermediate polymer layer and dry and hot-press it to form a surface barrier layer; S4. The composite lithium metal anode is obtained.

9. The preparation method according to claim 8, characterized in that, In step S1, the concentration of sulfur-containing compounds in the treatment solution is 0.01M~0.5M; the temperature of the in-situ reaction is 25℃~50℃, and the time is 1h~5h.

10. A battery, characterized in that, It includes the composite lithium metal anode as described in any one of claims 1-7, or the composite lithium metal anode prepared by the preparation method described in any one of claims 8-9.

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