Three-dimensional vertical porous lithium metal negative electrode, preparation method and battery

Abstract

The embodiment of the invention provides a three-dimensional vertical porous lithium metal negative electrode, a preparation method and a battery, a periodic three-dimensional vertical hole array is arranged on the surface of one side of lithium metal with the thickness of 30-50 [mu] m, and the depth of the three-dimensional vertical holes is 10-30 [mu] m; the content and distribution of carbon nanotubes in an electroplated metal layer are adjusted through three-section composite electrodeposition, so that on one hand, rich ion / electron transmission channels are provided, the local current density is remarkably reduced, and the electrochemical reaction kinetics is accelerated; an electric field and an ion concentration field formed on the inner wall of the hole can guide lithium ions to preferentially deposit at the bottom and in the hole, so that disordered growth of lithium dendrites on the surface is effectively inhibited, and finally, a volume expansion buffer space is provided; and moreover, a space is reserved for deposition of lithium in the circulation process, and stress can be dispersed and absorbed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery materials, and particularly relates to a three-dimensional vertical porous lithium metal negative electrode, a preparation method and a battery. BACKGROUND

[0002] Lithium metal is considered as the ultimate negative electrode material for the next generation of high-energy-density batteries (such as lithium-sulfur batteries, lithium-air batteries and solid-state batteries) due to its extremely high theoretical specific capacity and the most negative electrochemical potential.

[0003] However, the practical application of lithium metal negative electrodes has long been restricted by two fundamental problems: firstly, lithium dendrite growth caused by the non-uniform deposition / stripping of lithium ions during the cycle process, which may pierce the separator and cause short circuits, bringing serious safety hazards; and secondly, the huge infinite volume change of lithium metal (the "host-free" characteristic), which leads to the repeated rupture and regeneration of the solid electrolyte interface film, continuously consumes electrolyte and active lithium, resulting in low coulombic efficiency, rapid capacity decay and short cycle life of the battery. SUMMARY

[0004] Therefore, the application provides a three-dimensional vertical porous lithium metal negative electrode, a preparation method and a battery to solve the technical problems that it is difficult to process microstructures on ultra-thin lithium metal with high fidelity and the interface protection of the structure negative electrode is insufficient in the prior art, thereby significantly improving the cycle stability, rate performance and safety of the lithium metal battery.

[0005] In order to achieve the above-mentioned purpose, the application provides the following technical solutions: In a first aspect, the application provides a three-dimensional vertical porous lithium metal negative electrode on one side surface of lithium metal with a thickness of 30-50 μm, which is provided with a periodic three-dimensional vertical pore array, and the three-dimensional vertical pore has a depth of 10-30 μm.

[0006] Preferably, the cross-sectional shape of the three-dimensional vertical pore is a square, and the pore shape is a vertical rectangular cuboid.

[0007] Preferably, the side length of the three-dimensional vertical pore is 40-60 μm, and the interval between adjacent pores is 80-120 μm.

[0008] Preferably, the side length of the three-dimensional vertical pore is 50 μm, the interval is 100 μm, and the depth is 20 μm.

[0009] In a second aspect, the application provides a preparation method of the above-mentioned three-dimensional vertical porous lithium metal negative electrode. The core of the method is to use a customized mold for pressure imprinting, which mainly includes the following steps: S1: providing a customized mold with a convex array on the surface; S2: aligning the protrusion array side of the mold with the flat lithium metal foil surface; S3: applying vertical pressure to the mold, causing the mold protrusions to press into the lithium metal foil, forming the three-dimensional vertical pores; S4: separating the shaped lithium metal anode from the mold, obtaining a three-dimensional vertical porous lithium metal anode.

[0010] Preferably, the material of the mold is hard resin.

[0011] Preferably, in step S3, the applied pressure is 70-100 N, and the holding time is 20-40 seconds.

[0012] Preferably, the applied pressure is 80 N, and the holding time is 30 seconds.

[0013] In a third aspect, the present application provides a lithium metal battery comprising the above-mentioned three-dimensional vertical porous lithium metal anode. The battery also includes a positive electrode, a separator, and an electrolyte.

[0014] Compared with the prior art, the present application has the following beneficial effects: 1) Structural advantage and performance improvement: The present application successfully constructs a regular three-dimensional vertical pore array on an ultra-thin lithium metal. This structure has the following functions: a. Provide abundant ion / electron transport channels: significantly reduce local current density, regulate uniform distribution of ion concentration, and accelerate electrochemical reaction kinetics. Experiments show that the average specific capacity of a 50-micron hole Li anode (50μm hole Li) at 7C high rate is 152.7 mAh / g, with excellent rate performance.

[0015] b. Guide the directional and uniform deposition of lithium: The electric field and ion concentration field formed by the inner wall of the pore can guide the preferential deposition of lithium ions at the bottom and inside of the pore, effectively inhibiting the disorderly growth of lithium dendrites on the surface. In-situ observation confirms that lithium deposition occurs inside the pore, and the stripping also starts preferentially from the inside of the pore, with a highly reversible process.

[0016] c. Provide volume expansion buffer space: The pore structure has a certain mechanical strength and reserves space for lithium deposition during the cycling process, which can disperse and absorb stress. Tests with a 40 mg / cm² high-nickel positive electrode show that the volume expansion rate after cycling can be reduced by 182.25%, with extremely significant swelling relief effect.

[0017] 2) Advantages of the preparation method: The mold imprinting method used in this invention is simple, efficient, and low-cost, and is particularly suitable for the microstructure processing of ultrathin lithium metal. By precisely controlling the mold material, pressure, and holding time, the demolding problem in the microforming of soft lithium metal is successfully solved, resulting in a microporous structure with high integrity and repeatability, providing a feasible path for industrial production.

[0018] 3) Overall Electrochemical Performance: Benefiting from the aforementioned structural advantages, the anode of this invention exhibits excellent cycle stability and capacity retention. Under test conditions of 0.5 mA / cm² and 1 mA / cm², its cycle life far exceeds that of a flat lithium anode. Simultaneously, the lower overpotential and the thinner, more stable SEI film indicate fewer side reactions and less interfacial polarization. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a three-dimensional vertical porous lithium metal anode in one embodiment of the present invention.

[0020] Figure 2 This is a schematic flowchart of the preparation method of the present invention: (a) providing a mold and lithium foil; (b) aligning and overlapping; (c) applying pressure to imprint; (d) separating to obtain a porous negative electrode.

[0021] Figure 3 This is a comparison chart of the current density distribution of Example 1 (50μm hole Li) with Bare Li, 15μm hole Li, and 150μm hole Li.

[0022] Figure 4 This is a comparison of the ion concentration distribution of Example 1 (50 μm hole Li) with Bare Li, 15 μm hole Li, and 150 μm hole Li after deposition at 1C for 10 minutes.

[0023] Figure 5 The curves show the current density versus time for Example 1 (50μm hole Li) and Bare Li, 15μm hole Li, and 150μm hole Li with 1μm seed crystals set at the bottom, sidewall, and platform, respectively.

[0024] Figure 6 This is a comparison chart of the 1C performance of Example 1 (50μm hole Li) with Bare Li, 15μm hole Li, and 150μm hole Li.

[0025] Figure 7 This is a comparison chart of the rate performance of Example 1 (50μm hole Li) with Bare Li, 15μm hole Li, and 150μm hole Li.

[0026] Figure 8 This is a comparison of the cycling stability of Example 1 (50μm hole Li) with Bare Li, 15μm hole Li, and 150μm hole Li at different current densities.

[0027] Figure 9 This is a comparison of the cycling stability of Example 1 (50μm hole Li) with Bare Li, 15μm hole Li, and 150μm hole Li at different current densities.

[0028] Figure 10 This is a schematic diagram of in-situ optical microscopy observation of lithium deposition behavior in Example 1 (50μm hole Li).

[0029] Figure 11 These are comparative photos of volume expansion after Bare Li is paired with a high areal loading cathode and cycled for 1, 5, and 20 cycles respectively.

[0030] Figure 12 These are comparative photos of the volume expansion of Example 1 (50μm hole Li) after cycling for 1, 5, and 20 cycles with a high areal loading cathode. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0032] Before providing a further detailed description of the present invention, the nouns and terms used in the embodiments of the present invention will be explained, and the nouns and terms used in the embodiments of the present invention shall be interpreted as follows.

[0033] Please see Figure 1 This invention provides a three-dimensional vertical porous lithium metal anode, its preparation method, and a battery. The key to this method lies in: 1) selecting a high-strength, rigid resin (such as polymethyl methacrylate (PMMA) or polycarbonate (PC)) as the mold material to ensure the mold does not deform during the imprinting process; and 2) precisely controlling the imprinting process parameters. Preferably, a pressure of 70-90N is applied and held for 20-40 seconds, more preferably 80N pressure for 30 seconds. This parameter combination ensures the complete formation of a 20-micron-deep porous structure on a 40-micron-thick soft lithium foil, while preventing damage to the structure edges during demolding, achieving high-fidelity molding.

[0034] Example 1 Please see Figure 2 Three-dimensional vertical porous lithium metal anode with 50 μm pores was prepared. Mold preparation: A raised array is machined on a rigid polycarbonate sheet using precision machining technology. Each raised piece is a regular square prism with a base side length of 50 micrometers and a height of 20 micrometers, and the center-to-center distance between adjacent raised pieces is 150 micrometers (i.e., 100 micrometers apart).

[0035] Imprinting: In an argon-protected glove box, a 40-micron-thick, clean sheet of commercially available lithium metal foil is laid flat on a smooth base. The raised side of the mold is aligned with the surface of the lithium foil. Using an imprinting device equipped with a pressure sensor, a pressure of 80 N is applied vertically downwards and held for 30 seconds.

[0036] Demolding: After the pressure holding is completed, the mold is slowly and vertically lifted, and precision tweezers are used to assist in separation to obtain a lithium metal anode with a three-dimensional vertical cubic hole array with a side length of 50 micrometers, a depth of 20 micrometers, and a spacing of 100 micrometers (denoted as 50μm hole Li).

[0037] Example 2 Fabrication of a three-dimensional vertical porous lithium metal anode with 15 μm pores The steps are the same as in Example 1, except that the side length of the bottom surface of the mold protrusion is changed to 15 micrometers, the center spacing is changed to 115 micrometers (100 micrometer interval), and the imprinting pressure is adjusted to 75N to obtain a 15μm hole Li anode.

[0038] Example 3 Fabrication of a three-dimensional vertical porous lithium metal anode with 150 μm pores The steps are the same as in Example 1, except that the side length of the bottom surface of the mold protrusion is changed to 150 micrometers, the center spacing is changed to 250 micrometers (100 micrometer intervals), and the imprinting pressure is adjusted to 85N to obtain a 150μm hole Li anode.

[0039] Comparative Example 1 Flat lithium metal anode A 40-micron-thick commercial lithium foil without any treatment was used directly as the negative electrode (denoted as Bare Li).

[0040] Simulation test Current density distribution simulation: The current density distribution of 15μm hole Li, 50μm hole Li, and 150μm hole Li during the initial deposition was simulated, respectively. Figure 3 Simulation results show that the current density distribution of 50μm hole Li is the most uniform, which can better achieve the bottom deposition mode from bottom to top, thereby delaying lithium dendrite growth, optimizing battery performance and suppressing volume expansion.

[0041] Ion concentration distribution simulation: The ion concentration distribution of 15μm hole Li, 50μm hole Li, and 150μm hole Li deposited at 1C rate for 10 minutes was simulated, respectively. Figure 4 The results showed that the ion concentration distribution of 50 μm hole Li was the most uniform, demonstrating excellent ion transport capability.

[0042] Polycrystalline nucleus simulation: 1μm crystal nuclei were placed at the bottom, sidewalls, and plateau of 15μm hole Li, 50μm hole Li, and 150μm hole Li. The change in current density over time was dynamically detected. Figure 5 The 50μm hole Li maintained the most stable current density distribution in all regions, avoiding local concentration, thus achieving a uniform and dense deposition process.

[0043] Performance testing and characterization The negative electrode prepared above is assembled with lithium foil to form a battery.

[0044] 1C performance: such as Figure 6 As shown, at a 1C rate, Example 1 (50 μm hole Li) maintained a specific capacity of 152 mAh / g and a capacity retention of 81.7% after 100 cycles, while the capacity retention of the comparative examples (Bare Li), 15 μm hole Li, and 150 μm hole Li was 69.7%, 72.4%, and 77.8%, respectively. This demonstrates its excellent cycling stability and capacity retention.

[0045] Ratio performance: such as Figure 7 As shown, the discharge capacity of the full battery was tested at different rates (0.1C, 0.5C, 1C, 2C, 5C, 7C). Example 1 (50μm hole Li) exhibited the highest capacity at all rates, especially at 7C, with the highest capacity retention and an average specific capacity of 152.7 mAh / g, significantly better than Comparative Example 1 and other examples, demonstrating its excellent fast charge and discharge capability.

[0046] Cycle stability: Symmetric cells were tested under conditions of 0.5 mA / cm², 0.5 mAh / cm², and 1 mA / cm², 1 mAh / cm². Figures 8-9 As shown, Example 1 exhibits the lowest and most stable overpotential, with a cycle life exceeding 1000 hours, far surpassing Comparative Example 1 (which failed after approximately 600 hours). This indicates that its interface is more stable and has fewer side reactions.

[0047] Observation of sediment morphology: The deposition process of Example 1 was observed using in-situ optical microscopy, such as... Figure 10It can be clearly observed that lithium metal preferentially deposits inside the pores and fills upwards, with no dendritic deposits in the planar region above the pore opening. During stripping, lithium within the pores preferentially dissolves, indicating that the deposition / stripping process is highly reversible and the structure is stable.

[0048] Volume expansion test: Half-cells of Example 1 and Comparative Example 1 were assembled with high-load NCM811 cathodes, respectively, and the thickness change was measured after 20 cycles. The results showed that the thickness of the Comparative Example 1 cell increased significantly, while the volume expansion rate of the Example 1 cell decreased by 182.25%. Figures 11-12 As shown, this intuitively demonstrates the remarkable effect of three-dimensional porous structures in mitigating volume expansion.

[0049] In summary, Example 1 (50 μm hole Li) performed best among all examples. Its structural parameters of 50 μm side length, 100 μm spacing, and 20 μm depth achieved the best balance between increased specific surface area (reduced polarization), optimized ion transport channels (improved rate performance), and framework structural stability (improved cycle stability). The 15 μm hole showed a more significant increase in specific surface area and high framework mechanical strength, but suffered from uneven current density distribution, relatively narrow ion transport channels, and less reserved expansion space. The 150 μm hole provided greater expansion space, but its deposition behavior was worse than the 50 μm hole, and its framework mechanical strength was lower. Therefore, the 50 μm parameter became the preferred option of this invention.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and scope of the present invention are included within the scope of protection of the present invention.

Claims

1. A three-dimensional vertical porous lithium metal anode, characterized in that, A periodic three-dimensional vertical hole array is provided on one side surface of lithium metal with a thickness of 30-50 μm, and the depth of the three-dimensional vertical holes is 10-30 μm.

2. The three-dimensional vertical porous lithium metal anode according to claim 1, characterized in that, The cross-sectional shape of the three-dimensional vertical hole is square, and the hole shape is a vertical cuboid.

3. The three-dimensional vertical porous lithium metal anode according to claim 2, characterized in that, The side length of the three-dimensional vertical hole is 40-60μm, and the interval between adjacent holes is 80-120μm.

4. The three-dimensional vertical porous lithium metal anode according to claim 3, characterized in that, The three-dimensional vertical holes have a side length of 50μm, a spacing of 100μm, and a depth of 20μm.

5. A method for preparing a three-dimensional vertical porous lithium metal anode as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Provides customized molds with a surface array of protrusions; S2: Align one side of the protrusion array of the mold with the flat surface of the lithium metal foil; S3: Apply vertical pressure to the mold to press the mold protrusion into the lithium metal foil, forming the three-dimensional vertical hole; S4: Separate the formed lithium metal anode from the mold to obtain a three-dimensional vertical porous lithium metal anode.

6. The preparation method according to claim 5, characterized in that, The mold is made of hard resin.

7. The preparation method according to claim 5 or 6, characterized in that, In step S3, the applied pressure is 70-90N, and the pressure holding time is 20-40 seconds.

8. The preparation method according to claim 7, characterized in that, In step S3, the applied pressure is 80N and the pressure holding time is 30 seconds.

9. A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is a three-dimensional vertical porous lithium metal negative electrode as described in any one of claims 1 to 4.

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