A method of preparing a lithium metal electrode having {110} crystal plane texture

Abstract

This application relates to a method for preparing a lithium metal electrode with a {110} crystal plane texture, characterized in that the method includes the following steps: 1) providing a lithium metal foil, wherein the thickness of the lithium metal foil is 10-100 μm; 2) polishing the surface of the lithium metal foil with sandpaper at a pressure of 0.1-1000 kPa applied to 5000-20000 grit sandpaper to introduce the {110} crystal plane texture into the lithium metal foil, thereby forming the lithium metal electrode. When the lithium metal foil with the {110} crystal plane texture of this invention is used as a negative electrode in a battery, it exhibits significantly improved cycle performance in ether-based and ester-based electrolytes compared to the original commercially available lithium foil lacking crystal plane texture, which can greatly extend the battery's lifespan.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and more specifically to a method for preparing a lithium metal electrode with a {110} crystal plane texture, particularly for lithium with a thickness of 10-100 μm. Background Technology

[0002] Among all available candidate anodes for lithium-ion batteries, lithium metal boasts the highest energy density (3861 mAh / g) and the lowest electrode potential (-3.94 V vs SHE), earning it the reputation of being the ultimate solution for lithium-ion battery anodes. However, two problems with lithium metal electrodes have been hindering the commercialization of lithium-ion batteries. One is the growth of lithium dendrites caused by the uneven electroplating and peeling of lithium metal. On the one hand, lithium dendrites can cause short circuits after piercing the separator, leading to safety issues. On the other hand, the loose structure of the formed dendrites causes them to break off from the substrate, resulting in "dead lithium." Simultaneously, the exposed fresh lithium surface continues to react with the electrolyte, consuming both lithium and electrolyte. These two processes result in low coulombic efficiency and shortened cycle life.

[0003] To suppress lithium dendrite growth, numerous solutions have been proposed, including: using high-shear-modulus separators or solid-state electrolytes to mechanically block dendrite growth; and improving lithium nucleation uniformity by designing the three-dimensional structure of the current collector and the artificial solid-electrolyte interface on the negative electrode surface. While these methods have suppressed lithium dendrite growth to some extent, the root cause of lithium dendrite growth remains unresolved. For lithium metal, the {110} crystal plane has the lowest surface energy and surface diffusion barrier. Therefore, if the {110} crystal plane is made the crystal plane for lithium-ion plating and stripping, the growth of lithium dendrites and side reactions with the electrolyte can be fundamentally suppressed, thereby improving the cycle life of the corresponding battery.

[0004] Several effective methods for preparing {110}-textured lithium have been discovered. For example, the {110} texture of lithium has been prepared by electroplating using the principle of thermodynamic control. However, this method has problems such as the need to consume electrolyte and the low density of lithium foil leading to low energy density. Previously, the applicant also successfully prepared lithium metal foil with {110} texture (denoted as Li{110}) using a simple mechanical method based on the traditional theory of slip system activation. However, due to the soft mechanical properties of lithium metal, this technology can generally only be used to prepare lithium metal anodes with a thickness of more than 200 μm.

[0005] In this context, considering current issues such as commercial cathode loading, battery energy density, and safety, lithium metal foils with a thickness of less than 100 μm, especially less than 50 μm, have greater commercial potential. Therefore, it is still necessary to design special texture introduction technologies for lithium metal foils with poor mechanical properties and low strength below 100 μm, to introduce {110} crystal plane textures into lithium metal foils below 100 μm, thereby successfully improving the electrochemical performance of lithium metal foils from 10 to 100 μm. Summary of the Invention

[0006] Therefore, in order to solve the above-mentioned technical problems, the applicant designed a novel scheme for introducing {110} crystal plane texture into lithium metal foil with a thickness of 10-100μm through a sandpaper polishing process, thereby completing the present invention.

[0007] In a first aspect, this application provides a method for preparing a lithium metal electrode having a {110} crystal plane texture, characterized in that the method includes the following steps:

[0008] 1) Provide a lithium metal foil, wherein the thickness of the lithium metal foil is 10-100 μm; 2) Polish the surface of the lithium metal foil with sandpaper of 5000 to 20000 grit under a pressure of 0.1-1000 kPa to introduce the {110} crystal texture into the lithium metal foil, thereby forming the lithium metal electrode.

[0009] Generally, commercially available lithium metal foils typically do not have a specific crystal plane texture. However, the applicant has surprisingly discovered that by using the method of the present invention, i.e., applying a pressure of 0.1-1000 kPa on sandpaper of 5000 to 20000 grit (e.g., 5000, 8000, 12000, 15000 or 20000 grit, etc.) and polishing the surface of the lithium metal foil with said sandpaper, sufficient shear force can be provided to introduce the {110} crystal plane texture into the lithium metal foil.

[0010] In one embodiment of the present invention, the thickness of the lithium metal foil can be 10-100 μm (e.g., 10 μm, 20 μm, 50 μm, 100 μm or any value between these).

[0011] In one embodiment of the invention, the lithium metal foil may be provided in the form of lithium metal alone, or in a composite form with other metals, such as in the form of a lithium-copper composite foil.

[0012] In one embodiment of the present invention, the pressure may be 1-100 kPa, or more preferably 10-50 kPa.

[0013] In another embodiment of the present invention, before performing step 2), the method may further include: 1.1) performing a first polishing step and a first cleaning step on the provided lithium metal foil to remove the silicone oil or oxide layer on the surface of the lithium metal foil.

[0014] In another embodiment of the invention, before performing step 2), the method may further include: 1.2) performing a first annealing step on the provided lithium metal foil to randomize the crystal orientation in the lithium metal foil.

[0015] In another embodiment of the invention, the first annealing step may be performed for 0.5-12 hours (e.g., 0.5 hours, 2 hours, 5 hours, 12 hours or any value between) at a temperature of 100-175°C (e.g., 100°C, 125°C, 150°C, 175°C or any value between therewith) and / or at a pressure of 0 to -0.2 MPa at atmospheric pressure to negative pressure (e.g., 0 MPa, -0.1 MPa, -0.2 MPa or any value between therewith).

[0016] In another embodiment of the present invention, after performing step 2), the method may further include: 2.1) performing a second annealing step on the lithium metal foil with the {110} crystal texture to further increase the proportion of the {110} crystal texture.

[0017] In another embodiment of the invention, the second annealing step is performed for 0.5 to 12 hours (e.g., 0.5 hours, 2 hours, 5 hours, 12 hours or any value between) at a temperature of 50-175°C (e.g., 50°C, 100°C, 150°C, 175°C or any value between therewith) and / or at a pressure of 0 to -0.2 MPa at atmospheric pressure to negative pressure (e.g., 0 MPa, -0.1 MPa, -0.2 MPa or any value between therewith).

[0018] In another embodiment of the present invention, after step 2), the method may further include: 2.2) performing a second polishing step and a second cleaning step on the lithium metal foil with the {110} crystal texture to modify the surface layer or improve the flatness.

[0019] In another embodiment of the invention, the first polishing step and the second polishing step may be performed using canvas, silk, cotton or sandpaper of 5,000 to 20,000 grit.

[0020] In another embodiment of the present invention, the first cleaning step and the second cleaning step may use a cleaning solution in which naphthalene crystals are dissolved in anhydrous tetrahydrofuran and anhydrous cyclohexane, for example, 0.192g of naphthalene crystals are dissolved in 15mL of anhydrous tetrahydrofuran and anhydrous cyclohexane.

[0021] Therefore, in a preferred embodiment of the present invention, the method may include all or part of the following steps: 1) Provide a lithium metal foil, wherein the thickness of the lithium metal foil is 10-100 μm; 1.1) Perform a first polishing step and a first cleaning step on the provided lithium metal foil to remove the silicone oil or oxide layer on the surface of the lithium metal foil; 1.2) Perform a first annealing step on the provided lithium metal foil to randomize the crystal orientation in the lithium metal foil; 2) Polishing the surface of the lithium metal foil with 5000-20000 grit sandpaper under a pressure of 0.1-1000 kPa to introduce the {110} crystal texture into the lithium metal foil. 2.1) A second annealing step is performed on the lithium metal foil with the {110} crystal texture to further increase the proportion of the {110} crystal texture; 2.2) The lithium metal foil with the {110} crystal texture is subjected to a second polishing step and a second cleaning step to modify the surface layer or improve the flatness; Thus, the lithium metal electrode is formed.

[0022] In a second aspect, the present invention also provides a lithium metal electrode prepared by any of the methods described in the first aspect.

[0023] In one embodiment of the invention, the {110} crystal texture occupies at least 60% of the electrode surface before the first discharge of the battery, for example 60%, 65%, 70%, 75%, 80% or higher.

[0024] In a third aspect, the present invention also provides a battery comprising a lithium metal electrode as described in the second aspect.

[0025] Those skilled in the art will understand that the definitions and preferences described in one aspect of this application also apply to other aspects. Those skilled in the art will appreciate that embodiments of various aspects of this application can be combined in various ways without departing from the subject matter and spirit of this application, and these combinations are also included within the scope of this application.

[0026] Through in-depth research, the inventors unexpectedly discovered that for lithium metal foils with a specific thickness range of 10-100 μm, the {110} crystal plane texture can be effectively introduced through specific mechanical polishing. Generally speaking, thicker lithium foils (such as those above 200 μm) are easier to texture through mechanical processing due to their certain structural strength; while ultrathin lithium foils (such as those less than 50 μm) are prone to breakage or uncontrollable defects during mechanical processing due to their extremely low mechanical strength, making them difficult to use as self-supporting electrodes.

[0027] However, the inventors were surprised to discover that lithium foil with a thickness of 50-100 μm falls precisely within a "critical thickness window": lithium foil within this thickness range is thin enough to undergo effective plastic deformation and grain rotation during mechanical polishing, while simultaneously retaining a certain structural integrity to withstand the mechanical stress during processing without damage. Lithium foil with a thickness below 50 μm, down to 10 μm, is essentially attached to the copper current collector, forming a lithium-copper composite band. Therefore, the copper current collector can provide additional mechanical strength to withstand the mechanical stress during processing without damage. Furthermore, when the sandpaper grit is below 5000 grit, the coarse sandpaper particles lead to uneven processing and easily generate localized stress concentrations, causing lithium foil breakage; when the sandpaper grit is above 20000 grit, the pressure distribution is too uniform, making it difficult to form localized stress concentrations sufficient to activate the slip system. Similarly, when the applied pressure is below 0.1 kPa, the shear force is insufficient to induce plastic deformation; when the pressure is above 1000 kPa, the lithium foil is prone to tearing or excessive thinning.

[0028] Furthermore, research has revealed that when the lithium metal foil with the {110} crystal texture of the present invention is used as the negative electrode in a battery assembly, it exhibits significantly improved cycle performance in ether-based and ester-based electrolytes compared to the original commercial lithium foil lacking crystal texture, which can greatly extend the battery's lifespan. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 A flowchart showing the fabrication process of a lithium metal anode with {110} crystal texture is presented; Figure 2 The XRD pattern of commercially available lithium metal foil (raw lithium foil) is shown; Figure 3 The XRD pattern of the lithium foil after the first annealing is shown; Figure 4 The XRD pattern of the lithium foil after the introduction of the {110} crystal plane texture is shown; Figure 5The XRD pattern of the lithium foil after the second annealing is shown; Figure 6 The results of cycling in an ester electrolyte are shown after assembling 50 μm {110} crystal textured lithium foil and original lithium foil into batteries, respectively. Figure 7 The results of cycling in an ether electrolyte are shown after assembling 50 μm {110} crystal facet textured lithium foil and original lithium foil into batteries, respectively. Figure 8 The XRD pattern of the lithium foil after polishing with 12000-grit sandpaper is shown. Figure 9 The XRD patterns of the treated side and the reverse side of a 50 μm lithium metal foil are shown. Figure 10 The results of cycling in an ester electrolyte are shown, with 50 μm {110} crystal textured lithium foil and original lithium foil assembled into batteries respectively. Figure 11 The XRD patterns of commercially available 100μm lithium foil (raw lithium foil) and lithium foil with texture introduced are shown; Figure 12 The XRD patterns of the treated side and the reverse side of a 100 μm lithium metal foil are shown. Figure 13 The results of cycling in an ester electrolyte are shown after assembling 100 μm {110} crystal textured lithium foil and original lithium foil into batteries.

[0030] Figure 14 The XRD patterns of commercially available 20μm lithium-copper composite strip foil (original lithium-copper composite strip foil) and lithium foil after texture introduction are shown.

[0031] Figure 15 The results of cycling in an ester electrolyte are shown after the 20 μm {110} crystal plane textured lithium-copper composite strip and the original lithium-copper composite strip were assembled into batteries. Detailed Implementation

[0032] The invention is further illustrated below with reference to embodiments; however, these embodiments do not limit the scope of the invention. Unless otherwise stated, all percentages are by weight and all solvent mixture proportions are by volume.

[0033] All embodiments of the present invention relate to the preparation of Li foil having Li{110}, and exemplary flowcharts can be found therein. Figure 1 As shown, and further detailed implementation steps are provided below.

[0034] Example 1 like Figure 2As shown, the XRD pattern indicates that commercially available 50μm lithium foil has no specific texture or is predominantly {100} crystal plane texture. After physical polishing with silk cloth and cleaning with cyclohexane on the metal surface of the commercially available 50μm lithium foil, it was annealed at 130℃ under normal pressure for 6 hours at the first annealing temperature. Figure 3 As shown, the surface has no specific texture orientation. Texture was then introduced by rubbing the surface in one direction under 10 kPa pressure using 5000-grit sandpaper, as shown. Figure 4 As shown, the {110} crystal plane texture has become the dominant crystal plane. A second recrystallization annealing was then performed at 165℃ and ambient pressure for 60 minutes. Figure 5 As shown, the proportion of {110} crystal facet texture is further improved. Finally, physical polishing is performed using silk cloth, followed by chemical cleaning with cyclohexane. Figure 6 and Figure 7 As shown, the cleaned 50μm {110} crystal textured lithium foil, after being cut into electrodes, is assembled into a battery with an NCM811 positive electrode. The cycle performance is significantly improved compared to the original commercial lithium foil in ether electrolytes and ester electrolytes.

[0035] Example 2 After physical polishing the surface of a commercially available 50μm lithium foil without a specific texture using 12000-grit sandpaper under 10 kPa pressure, followed by cleaning with a tetrahydrofuran solution of naphthalene for 1 min, the {110} crystal plane texture was significantly improved compared to the original commercial lithium foil. Figure 8 The material was then subjected to a first recrystallization annealing at 165°C and normal pressure for 30 minutes. A second polishing was then performed using 5000-grit sandpaper at 1 kPa. Figure 9 As shown, X-ray diffraction tests were performed on both sides of the lithium metal foil, revealing a further increase in the proportion of {110} crystal plane texture, with a clear {110} crystal plane orientation on both sides. This indicates that the {110} crystal plane texture has penetrated the entire lithium foil, with a texture thickness of 50 μm. Figure 10 As shown, the polished 50μm {110} crystal textured lithium foil, after being cut into electrodes, is assembled with the NCM811 positive electrode to form a battery. In ester electrolyte, the cycle performance is significantly improved compared with the original commercial lithium foil.

[0036] Example 3 After physical polishing the surface of a commercially available 100μm lithium foil without specific texture using a cotton cloth, it was cleaned with cyclohexane for 1 minute. Figure 11 As shown, commercially available 100μm lithium foil exhibits no obvious orientation. Texture was introduced by rubbing it in a single direction with 5000-grit sandpaper under 50kPa pressure. Figure 11As shown, the {110} crystal plane texture has become the dominant crystal plane. Subsequently, recrystallization annealing was performed at 165°C and ambient pressure for 60 minutes. Then, a second polishing was performed using cotton cloth. Figure 12 As shown, X-ray diffraction tests were performed on both sides of the lithium metal foil, revealing a further increase in the proportion of {110} crystal plane texture, with a clear {110} crystal plane orientation on both sides. This indicates that the {110} crystal plane texture has penetrated the entire lithium foil, with a texture thickness of 100 μm. Figure 13 As shown in the original diagram, the polished 100μm {110} crystal textured lithium foil, after being cut into electrodes, was assembled into a battery with an NCM811 positive electrode. In an ester electrolyte, the cycle performance was significantly improved compared to the original commercial lithium foil.

[0037] Example 4 After physical polishing the surface of a commercially available 20μm non-textured lithium-copper composite strip with cotton cloth, it was cleaned with cyclohexane for 1 minute. Figure 14 As shown, commercially available 20μm textured lithium-copper composite tapes have no obvious orientation. Texture was introduced by rubbing in a single direction with 5000-grit sandpaper under 50 kPa pressure. Figure 14 As shown, the {110} crystal plane texture has become the dominant crystal plane. Subsequently, recrystallization annealing was performed at 150°C and 0.1 MPa for 30 minutes. Then, a second polishing was performed using cotton cloth. Figure 14 The observed proportion of {110} crystal plane texture is further increased. For example... Figure 15 As shown, the polished 20μm {110} crystal textured lithium copper composite tape, after being cut into electrodes, is assembled with NCM811 cathode to form a battery. In ester electrolyte, the cycle performance is significantly improved compared with the original commercial lithium copper composite tape.

[0038] As can be seen from the results of the above embodiments, commercially available lithium metal foils typically lack a specific crystal plane texture. However, by using the method of the present invention, for example, applying a pressure of 0.1-1000 kPa on 5000 to 20000 grit sandpaper and polishing the surface of the lithium metal foil with the sandpaper, sufficient shear force can be provided to introduce the {110} crystal plane texture into the lithium metal foil. This results in a significant improvement in cycle performance of the lithium metal foil with the {110} crystal plane texture of the present invention when it is used as a negative electrode in a battery, compared to the original commercial lithium foil lacking crystal plane texture in ether electrolytes and ester electrolytes. This can greatly extend the battery's lifespan.

[0039] Furthermore, it is worth noting that, as can be seen from Examples 2 and 4, for lithium foils of 10-100 μm, the inventors observed that after single-sided treatment, the other side also exhibited a distinct {110} crystal orientation (e.g., ...). Figure 9 and Figure 12(As shown). This phenomenon can be explained by the shear band propagation mechanism during plastic deformation.

[0040] When a directional shear force is applied to the surface of a lithium foil, plastic deformation is not limited to the surface layer but propagates into the foil through the lithium metal along specific crystallographic directions. Therefore, when the surface layer grains rotate under external force so that their {110} crystal texture is parallel to the shear direction, this orientation information is transmitted downwards layer by layer, ultimately achieving a continuous texture. A thickness of 10-100 μm allows the propagation of the shear bands to cover the entire cross-section without significant attenuation, thus achieving the unique effect of single-sided treatment and double-sided texture.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] References 1. Li, L. et al. , Self-heating–induced healing of lithiumdendrites. Science 2018. 359(6383): p. 1513-1516. 2. Tang, W. et al. , Chemically polished lithium metal anode for highenergy lithium metal batteries. Energy Storage Materials , 2018. 14: pp. 289-296. 3. Coblas, DG et al. , Manufacturing textured surfaces: State of art and recent developments. Proceedings of The Institution of Mechanical Engineers, Part J: Journal Of Engineering Tribology, 2015. 229(1): p. 3-29. 4. Zheng, J. et al. , Textured Electrodes: Manipulating built‐inCrystallographic Heterogeneity of Metal Electrodes via Severe PlasticDeformation. Advanced Materials, 2021.2106867. 5. Gu, Y. et al. , Lithiophilic Faceted Cu (100) Surfaces: HighUtilization of Host Surface and Cavities for Lithium Metal Anodes. Angewandte Chemie International Edition , 2019. 58(10): p. 3092-3096. 6. Li, Y. et al. , Atomic structure of sensitive battery materials andinterfaces revealed by cryo–electron microscopy. Science , 2017. 358(6362): p.506-510. 7. Zhao, Q. et al. , On the crystallography and reversibility oflithium electrodeposits at ultrahigh capacity. Nature Communications , 2021, 12(1), 1-10. 8. Shi, F. et al. , Strong texturing of lithium metal in batteries . Proceedings of the National Academy of Sciences , 2017. 114(46): p. 12138-12143. 9. Hagopian, A. et al., Thermodynamic origin of dendrite growth inmetal anode batteries. Energy Environ. Sci. 2020,13: p. 5186-5197. 10. Hu, X and Q Li, "Preparation of Li and Na Foils with {110} or{100} Surface Texturing" U.S. Patent US-2023-0231105-A1,2022。

Claims

1. A method for preparing a lithium metal electrode with a {110} crystal plane texture, characterized in that, The method includes the following steps: 1) Provide a lithium metal foil, wherein the thickness of the lithium metal foil is 10-100 μm; 2) Polish the surface of the lithium metal foil with sandpaper of 5000 to 20000 grit under a pressure of 0.1-1000 kPa to introduce the {110} crystal texture into the lithium metal foil, thereby forming the lithium metal electrode.

2. The method according to claim 1, wherein the pressure is 10-50 kPa.

3. The method according to claim 1, wherein before performing step 2), the method further comprises: 1.1) Perform a first polishing step and a first cleaning step on the provided lithium metal foil to remove the silicone oil or oxide layer on the surface of the lithium metal foil.

4. The method according to claim 1, wherein before performing step 2), the method further comprises: 1.2) The provided lithium metal foil is subjected to a first annealing step, which is carried out in an atmospheric pressure to negative pressure environment of 0 to -0.2 MPa, so as to randomize the crystal orientation in the lithium metal foil.

5. The method according to claim 4, wherein the first annealing step is performed at a temperature of 100-175°C for 0.5-12 hours.

6. The method of claim 1, wherein after step 2), the method further comprises: 2.1) A second annealing step is performed on the lithium metal foil with the {110} crystal texture. The annealing step is carried out under normal pressure to negative pressure environment of 0 to -0.2 MPa to further increase the proportion of the {110} crystal texture.

7. The method according to claim 6, wherein, The second annealing step is carried out at a temperature of 50-175°C for 0.5-12 hours.

8. The method of claim 1, wherein after step 2), the method further comprises: 2.2) The lithium metal foil with the {110} crystal texture is subjected to a second polishing step and a second cleaning step to modify the surface layer or improve the flatness.

9. The method according to claim 3 or 8, wherein the first polishing step and the second polishing step are performed using canvas, silk, cotton, or sandpaper of 5,000 to 20,000 grit.

10. The method according to claim 3 or 8, wherein the first cleaning step and the second cleaning step use a cleaning solution in which naphthalene crystals are dissolved in anhydrous tetrahydrofuran and anhydrous cyclohexane.

11. A lithium metal electrode, which is prepared by the method according to any one of claims 1-10.

12. The lithium metal electrode according to claim 11, wherein the {110} crystal texture occupies at least 60% of the electrode surface before the first discharge of the battery.

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