Preparation method of lithium foil anode for all-solid-state lithium batteries

Abstract

A method for preparing a lithium foil anode for an all-solid-state lithium battery includes the following steps: (a) dispersing a nano-carbon material in water to obtain a dispersion; (b) mixing dopamine with the dispersion and allowing the dopamine to undergo a polymerization reaction in the dispersion to obtain a polydopamine-modified nano-carbon material; (c) forming a regular uneven texture structure on a lithium foil; and (d) mixing the polydopamine-modified nano-carbon material with a lithium-ion-containing polymer and coating it onto the lithium foil with the regular uneven texture structure. The all-solid-state lithium battery with a lithium foil anode prepared by the method of this invention exhibits a smaller polarization potential difference, lower bulk impedance after charge / discharge cycles, lower interfacial charge transfer impedance after cycles, and higher discharge capacity retention, demonstrating superior long-term charge / discharge cycle stability.

Description

[Technical Field]

[0001] This invention relates to a method for preparing an anode, and more particularly to a method for preparing a lithium foil anode for an all-solid-state lithium battery. [Previous Technology]

[0002] Existing all-solid-state lithium batteries (ASSLBs) that use lithium metal as the anode have a very high theoretical energy density, making them suitable as an energy source for portable electronic devices and electric vehicles.

[0003] However, during the charge / discharge cycle of the battery, the formation of needle-shaped lithium dendrites is a major factor leading to problems such as short circuits and thermal runaway, which limits the large-scale commercialization of all-solid-state lithium batteries. In addition, the thick solid electrolyte interphase (SEI) layer formed by the grown lithium dendrites and dead lithium makes the solid electrolyte membrane and electrodes prone to high interfacial resistance due to insufficient contact, which leads to severe battery capacity decay and affects the battery's cycle life. [Summary of the Invention]

[0004] Therefore, the object of the present invention is to provide a method for preparing a lithium foil anode for an all-solid-state lithium battery, which can overcome the disadvantages of the prior art.

[0005] Therefore, the method for preparing the lithium foil anode of the all-solid-state lithium battery of the present invention includes the following steps: (a) dispersing a nano-carbon material in water to obtain a dispersion; (b) mixing dopamine with the dispersion and allowing the dopamine to undergo a polymerization reaction in the dispersion to obtain a nano-carbon material modified with polydopamine; (c) forming a regular textured structure on a lithium foil, the regular textured structure being at the submillimeter scale; and (d) mixing the polydopamine-modified nano-carbon material with a lithium-ion-containing polymer and coating it onto the lithium foil with the regular textured structure to obtain the lithium foil anode of the all-solid-state lithium battery.

[0006] The advantages of this invention are: the all-solid-state lithium battery with lithium foil anode prepared by the method of this invention has a small polarization potential difference, a low bulk impedance value after cycling, a low interfacial charge transfer impedance value after cycling, and a high discharge capacity retention rate, and has excellent long-term charge / discharge cycle stability.

[0007] The following will describe the content of the present invention in detail:

[0008] Preferably, step (c) involves cold pressing a metal mesh template with a regular structure onto the lithium foil to form the textured structure. More preferably, in step (c), the metal mesh template is selected from copper mesh, nickel mesh, titanium mesh, platinum mesh, or stainless steel mesh. In a specific embodiment of the present invention, the metal mesh template is a copper mesh.

[0009] More preferably, the textured structure includes a plurality of longitudinal grooves spaced apart and regularly arranged, and a plurality of transverse grooves spaced apart and regularly arranged. The longitudinal grooves extend along a first direction, and the transverse grooves extend along a second direction different from the first direction. The longitudinal and transverse grooves are at the same horizontal level. Each longitudinal groove has a plurality of discontinuous longitudinal groove segments, and each transverse groove has a plurality of discontinuous transverse groove segments. In a specific embodiment of the invention, the first direction is perpendicular to the second direction. Even more preferably, each longitudinal groove segment and each transverse groove segment are spindle-shaped structures with a length in the range of 450~650 μm.

[0010] More preferably, the cold pressing process is performed at a pressure of 25 to 150 psi. In a specific embodiment of the invention, the cold pressing process is performed at a pressure of 50 to 100 psi.

[0011] Preferably, in step (a), the carbon nanomaterial is selected from carbon fiber, carbon nanotubes, graphene, graphene oxide, carbon black, or a combination thereof. In a specific embodiment of the present invention, the carbon nanomaterial is vapor-grown carbon fiber.

[0012] Preferably, step (b) includes adding a tris(hydroxymethyl)aminomethane buffer to the dispersion to allow dopamine to polymerize in the dispersion. More preferably, in step (b), the dopamine polymerizes in the dispersion at a pH range of 8.0 to 9.0. In a specific embodiment of the invention, in step (b), the dopamine polymerizes in the dispersion at a pH range of about 8.5.

[0013] Preferably, in step (d), the weight ratio of the polydopamine-modified carbon nanomaterial to the lithium-ion-containing polymer is in the range of 1:2 to 1:20. In a specific embodiment of the present invention, the weight ratio of the polydopamine-modified carbon nanomaterial to the lithium-ion-containing polymer is 1:10.

[0014] Preferably, in step (d), the lithium-ion-containing polymer is lithium-ion-containing Nafion (Li-Nafion). Alternatively, the source of the lithium ions may be selected from lithium hydroxide, lithium nitrate, lithium acetate, lithium chloride, lithium hydrogen phosphate, lithium phosphate, lithium carbonate, or combinations thereof. In a specific embodiment of the invention, the source of the lithium ions is lithium hydroxide monohydrate.

Implementation Method

[0015] The present invention will be further described with reference to the following embodiments, but it should be understood that the embodiments are only for illustrative purposes and should not be construed as limiting the implementation of the present invention.

[0016] <Example> Method for preparing lithium foil electrode E of all-solid-state lithium battery

[0017] One embodiment of the method for preparing the lithium foil anode of the all-solid-state lithium battery of the present invention includes the following steps:

[0018] (a) 100 mg of one-dimensional vapor-grown carbon fiber (VGCF, purchased from Xin Yongyu Applied Technology Materials Co., Ltd., model GS013010) nano carbon material powder was dispersed in 100 mL of deionized water and subjected to vibration dispersion treatment for 75 min using a probe-type sonicator (purchased from QSONICA, model Q700) (operating power 2~3 W, amplitude 10 mV, frequency 20 kHz, pulse ON for 20 min, pulse OFF for 5 min) to avoid aggregation, and a uniform dispersion was obtained.

[0019] (b) Subsequently, 100 mg of dopamine was added to the dispersion obtained in step (a) above under stirring, and the pH value was adjusted to about 8.5 by adding tris(hydroxymethyl)aminomethane-hydrochloric acid buffer (Tris-HCl, 99%, purchased from Polyhe International Co., Ltd.). The mixture was stirred at 25°C for 24 h to allow the dopamine to undergo polymerization in the dispersion. The mixture was then centrifuged at 6000 rpm for 30 min and the solid was collected. The solid was washed with deionized water and dried in an oven at 80°C for 12 h to obtain a vapor-grown carbon fiber with a one-dimensional structure modified with polydopamine.

[0020] (c) A copper mesh with a regular structure (as a metal mesh template with a thickness of 100~300 μm) is cold-pressed onto a smooth circular lithium foil (radius of 0.75 cm and thickness of 200 μm) with a pressure of 50~100 psi to form a regular textured structure, which is sub-millimeter scale.

[0021] (d) 25.2 mg of lithium hydroxide monohydrate (LiOH·H2O, purchased from Sigma-Aldrich) was mixed with 10 mL of Nafion solution (5 wt%, solvent being aliphatic alcohol and water, purchased from Sigma-Aldrich), stirred at 60 °C for 2 h, and then vacuum dried at 80 °C for 12 h to obtain lithium-ion-containing Nafion (Li-Nafion). The Li-Nafion was then dispersed in N-methylpyrrolidone (NMP) to obtain an NMP dispersion of Li-Nafion, and stirred continuously at 80 °C for 6 h. The polydopamine-modified vapor-grown carbon fiber obtained in step (b) above was mixed with Li-Nafion at a weight ratio of 1:10. The mixture was then coated onto the lithium foil with a regular textured structure formed in step (c) above using a polyethylene terephthalate (PET) film. Finally, the mixture was dried in an argon atmosphere at 25°C and then vacuum dried at 80°C for 2 hours to obtain the lithium foil electrode E of the all-solid-state lithium battery of this embodiment.

[0022] In addition, by measuring the thickness of the lithium foil before and after the above step (d) using a digital thickness gauge, the thickness of the polydopamine-modified vapor-grown carbon fiber and Li-Nafion coated on the lithium foil can be found to be 5~7 μm.

[0023] <Comparative Example 1> Lithium foil electrode CE1 of an all-solid-state lithium battery

[0024] The lithium foil electrode CE1 of the all-solid-state lithium battery in Comparative Example 1 is a smooth circular lithium foil (radius 0.75 cm, thickness 200 μm).

[0025] <Comparative Example 2> Method for preparing lithium foil electrode CE2 of all-solid-state lithium battery

[0026] The preparation method of the lithium foil electrode CE2 of the all-solid-state lithium battery in Comparative Example 2 is similar to that of the above-described embodiments. The difference is that step (d) is not performed in the preparation method of Comparative Example 2. That is, the lithium foil electrode CE2 of the all-solid-state lithium battery in Comparative Example 2 is a lithium foil with a regular concave-convex texture structure formed in step (c) above.

[0027] <Comparative Example 3> Method for preparing lithium foil electrode CE3 of all-solid-state lithium battery

[0028] The preparation method of the lithium foil electrode CE3 of the all-solid-state lithium battery in Comparative Example 3 is similar to that of the above-described embodiments. The difference is that in the preparation method of Comparative Example 3, step (c) is not performed, and step (d) is to mix the polydopamine-modified vapor-grown carbon fiber obtained in step (b) with Li-Nafion and then coat it onto a smooth circular lithium foil (radius of 0.75 cm and thickness of 200 μm) to obtain the lithium foil electrode CE3 of the all-solid-state lithium battery in Comparative Example 3.

[0029] [Optical Microscope Observation]

[0030] The lithium foil electrodes E, CE1 to CE3 of the all-solid-state lithium batteries of the above-mentioned examples and comparative examples 1 to 3 were observed using an optical microscope. The results are shown in Figures 1(A) to 1(D).

[0031] As can be seen from Figures 1(A) and 1(C), the lithium foil electrodes E and CE2 obtained after the cold pressing process in step (c) above have a regular sub-millimeter scale textured structure on their surfaces. This textured structure includes multiple longitudinal grooves spaced apart and regularly arranged, and multiple transverse grooves spaced apart and regularly arranged. The longitudinal grooves extend along the longitudinal direction, and the transverse grooves extend in the transverse direction perpendicular to the longitudinal direction. The longitudinal grooves and the transverse grooves are at the same level. Each longitudinal groove has multiple discontinuous longitudinal groove segments, and each transverse groove has multiple discontinuous transverse groove segments. Each longitudinal groove segment and each transverse groove segment are spindle-shaped structures with a length of approximately 590 μm, a width of approximately 135 μm, and a depth of 30~60 μm, respectively. As can be seen from Figures 1(B) and 1(D), the lithium foil electrodes CE1 and CE3 obtained without the above step (c) above are flat and do not have a regular textured structure.

[0032] 〈Application Example 1〉All-solid-state symmetric battery SCE

[0033] Two identical lithium foil electrodes E from the all-solid-state lithium batteries described in the above embodiments were used as the positive electrode (cathode) and negative electrode (anode) of the all-solid-state symmetric battery, respectively. A sandwich structure consisting of aluminum-doped lithium lanthanum zirconium oxide (Li6.25Al0.25La3Zr2O12, Al-LLZO) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) was used as the composite polymer electrolyte membrane (CPE membrane with a thickness of 240 μm) of the all-solid-state symmetric battery to form the all-solid-state (lithium foil-lithium foil) symmetric battery SCE of Application Example 1.

[0034] 〈Comparative Application Examples 1~3〉All-solid-state symmetric batteries SCCE1~SCCE3

[0035] The all-solid-state symmetric batteries SCCE1 to SCCE3 of Comparative Application Examples 1 to 3 are similar to those of Application Example 1, except that Comparative Application Examples 1 to 3 use the lithium foil electrodes CE1 to CE3 of two identical all-solid-state lithium batteries of Comparative Examples 1 to 3 as the positive and negative electrodes of the all-solid-state symmetric batteries, respectively, to form the all-solid-state (lithium foil-lithium foil) symmetric batteries SCCE1 to SCCE3 of Comparative Application Examples 1 to 3.

[0036] [Measurement of the electrical properties of all-solid-state symmetric batteries]

[0037] Using a battery testing device (purchased from Chia-Yu Technology Co., Ltd., model BAT-750B), deposition / stripping polarization cycle tests (current density of 0.1 mA·cm⁻², areal capacity of 0.1 mAh·cm⁻²) were conducted on the all-solid-state (lithium foil-to-lithium foil) symmetric batteries SCE and SCCE1~SCCE3 of Application Example 1 and Comparative Application Examples 1~3 to measure the polarization potential difference. The bulk impedance Rb (after 100 h of charge / discharge cycles at 0.1 mA·cm⁻²) and interface charge transfer impedance Rct (after 100 h of charge / discharge cycles at 0.1 mA·cm⁻²) of the all-solid-state (lithium foil-to-lithium foil) symmetric batteries SCE and SCCE1~SCCE3 of Application Example 1 and Comparative Application Examples 1~3 were measured using AC impedance spectroscopy. The results are shown in Figures 2~3 and Table 1 below. [Table 1] Polarization potential difference (mV) Body impedance value R b (Ω) Interfacial charge transfer impedance R ct (Ω) SC E 241 47.69 591.16 SC CE1 257 59.86 990.36 SC CE2 262 57.66 876.73 SC CE3 278 65.03 593.03

[0038] As can be seen from Table 1, the polarization potential difference, bulk impedance value Rb after charge / discharge cycle, and interface charge transfer impedance value Rct after cycle of the all-solid-state (lithium foil-lithium foil) symmetric battery SCE of Application Example 1 are all significantly smaller than those of the all-solid-state (lithium foil-lithium foil) symmetric batteries SCCE1-SCCE3 of Comparative Application Examples 1-3. The results show that the all-solid-state (lithium foil-lithium foil) symmetric battery SCE of Application Example 1 has superior long-term charge / discharge cycle stability.

[0039] 〈Application Example 2〉All-Solid-State Lithium Battery LBE

[0040] One lithium foil electrode E of the all-solid-state lithium battery of the above embodiment is used as the negative electrode (anode) of the all-solid-state lithium battery, one piece of LiNi0.8Co0.1Mn0.1O2 (NCM811, with a thickness of 40 μm) is used as the positive electrode (cathode) of the all-solid-state lithium battery, and one piece of the above-mentioned PVDF-HFP / PVDF-HFP@Al-LLZO / PVDF-HFP sandwich structure is used as the composite polymer electrolyte membrane of the all-solid-state lithium battery to form the all-solid-state lithium battery LBE of Application Example 2.

[0041] <Comparative Application Examples 4-6> All Solid-State Lithium Batteries LBCE1-LBCE3

[0042] The all-solid-state lithium batteries LBCE1 to LBCE3 of Comparative Application Examples 4 to 6 are similar to those of Application Example 2, except that in Comparative Application Examples 4 to 6, one lithium foil electrode CE1 to CE3 of the all-solid-state lithium battery of Comparative Examples 1 to 3 is used as the negative electrode of the all-solid-state lithium battery to form the all-solid-state lithium batteries LBCE1 to LBCE3 of Comparative Application Examples 4 to 6 respectively.

[0043] [Measurement of the electrical properties of all-solid-state lithium batteries]

[0044] The initial specific capacity (at room temperature, activated by 3 charge / discharge cycles at 0.1C) and capacity retention (CR) of the all-solid-state lithium batteries LBE and LBCE1~LBCE3 of Application Example 2 and Comparative Application Examples 4~6 were measured using battery testing equipment (purchased from Chia-Yu Technology Co., Ltd., model BAT-750B). (At room temperature, 100 charge / discharge cycles at 0.2C) The bulk impedance Rb (after 3 activation cycles at 0.1C; and after 100 charge / discharge cycles at 0.2C) and interface charge transfer impedance Rct (after 3 activation cycles at 0.1C; and after 100 charge / discharge cycles at 0.2C) of the all-solid-state lithium batteries LBE and LBCE1~LBCE3 in Application Example 2 and Comparative Application Examples 4~6 were measured using AC impedance spectroscopy. The results are shown in Figures 4~5, Table 2 (after 3 activation cycles at 0.1C) and Figures 6~7, Table 3 (after 100 charge / discharge cycles at 0.2C). [Table 2] Initial discharge capacity (mAh·g) -1 ) Body impedance value R b (Ω) Interfacial charge transfer impedance R ct (Ω) LB E 177.03 13.07 78.24 LB CE1 173.64 27.61 118.73 LB CE2 178.29 45.76 98.78 LB CE3 174.89 14.97 106.42 Table 3 Capacity maintenance Body impedance value R b (Ω) Interfacial charge transfer impedance R ct (Ω) LB E 83.16% 15.21 53.45 LB CE1 7.30% 63.76 411.29 LB CE2 78.05% 53.03 224.14 LB CE3 80.00% 18.22 71.75

[0045] As can be seen from Tables 2 and 3, the initial discharge specific capacity of the all-solid-state lithium battery LBE in Application Example 2 is similar to that of the all-solid-state lithium batteries LBCE1 to LBCE3 in Comparative Application Examples 4 to 6. However, the specific capacity retention rate of the all-solid-state lithium battery LBE in Application Example 2 after cycling is higher than that of the all-solid-state lithium batteries LBCE1 to LBCE3 in Comparative Application Examples 4 to 6. In particular, the specific capacity retention rate of the all-solid-state lithium battery LBCE1 in Comparative Application Example 4 drops significantly to 7.30%. The bulk impedance value Rb after activation and after cycling and the interface charge transfer impedance value Rct after activation and after cycling of the all-solid-state lithium battery LBE in Application Example 2 are significantly smaller than those of the all-solid-state lithium batteries LBCE1 to LBCE3 in Comparative Application Examples 4 to 6, indicating that the all-solid-state lithium battery LBE in Application Example 2 has superior long-term charge / discharge cycle stability.

[0046] In summary, the lithium foil anode prepared by the method of the present invention helps to enable the all-solid-state lithium battery to have a smaller polarization potential difference, a smaller bulk impedance value after charge / discharge cycle, a smaller interfacial charge transfer impedance value after cycle, and a higher discharge capacity retention rate, thus exhibiting excellent long-term charge / discharge cycle stability. Therefore, it can indeed achieve the purpose of the present invention.

[0047] However, the above description is only an embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the contents of the patent specification shall still fall within the scope of the patent of the present invention. [Simplified Explanation of the Diagram]

[0048] Other features and effects of the present invention will be clearly presented in the embodiments with reference to the figures, wherein: [Figure 1] is an optical microscope photograph of the lithium foil anode of the all-solid-state lithium battery of (A) embodiment of the present invention and (B) comparative example 1, (C) comparative example 2, and (D) comparative example 3; [Figure 2] is a time-battery potential relationship diagram of the all-solid-state symmetric batteries SCE and SCCE1~SCCE3 of application example 1 and comparative application examples 1~3 of the present invention after deposition / stripping polarization cycle test; [Figure 3] is an AC impedance spectrum diagram of the all-solid-state symmetric batteries SCE and SCCE1~SCCE3 of application example 1 and comparative application examples 1~3 after charge / discharge cycle for 100 h at 0.1 mA·cm-2; [Figure 4] is a specific capacity-battery potential relationship diagram of the all-solid-state lithium batteries LBE and LBCE1~LBCE3 of application example 2 and comparative application examples 4~6 of the present invention after activation (charge / discharge cycle 3 times at 0.1C rate); [Figure 5] is an AC impedance spectrum diagram of the all-solid-state lithium batteries LBE and LBCE1-LBCE3 of Application Example 2 and Comparative Application Examples 4-6 after activation (3 charge / discharge cycles at 0.1C rate); [Figure 6] is a graph showing the relationship between the number of cycles and the discharge capacity of the all-solid-state lithium batteries LBE and LBCE1-LBCE3 of Application Example 2 and Comparative Application Examples 4-6 after 100 charge / discharge cycles at 0.2C rate; and [Figure 7] is an AC impedance spectrum diagram of the all-solid-state lithium batteries LBE and LBCE1-LBCE3 of Application Example 2 and Comparative Application Examples 4-6 after 100 charge / discharge cycles at 0.2C rate.

Claims

1. A method for preparing a lithium foil anode for an all-solid-state lithium battery, comprising the following steps: (a) dispersing a nano-carbon material in water to obtain a dispersion; (b) mixing dopamine with the dispersion and allowing the dopamine to undergo a polymerization reaction in the dispersion to obtain a polydopamine-modified nano-carbon material; (c) cold-pressing a metal mesh template with a regular structure onto a lithium foil to form a regular textured structure, the regular textured structure being sub-millimeter scale; and (d) mixing the polydopamine-modified nano-carbon material with a lithium-ion-containing polymer and coating it onto the lithium foil with the regular textured structure to obtain the lithium foil anode for the all-solid-state lithium battery.

2. The preparation method as described in claim 1, wherein, The textured structure includes multiple longitudinal grooves spaced apart and regularly arranged and multiple transverse grooves spaced apart and regularly arranged. The longitudinal grooves extend along a first direction, and the transverse grooves extend along a second direction different from the first direction. The longitudinal grooves and the transverse grooves are at the same level. Each longitudinal groove has multiple discontinuous longitudinal groove segments, and each transverse groove has multiple discontinuous transverse groove segments.

3. The preparation method as described in claim 1, wherein, The cold pressing process is carried out at a pressure of 25 to 150 psi.

4. The preparation method as described in claim 1, wherein, In step (a), the nano-carbon material is selected from carbon fiber, carbon nanotube, graphene, graphene oxide, carbon black, or a combination thereof.

5. The preparation method as described in claim 1, wherein, Step (b) involves adding a tris(hydroxymethyl)aminomethane buffer to the dispersion to allow dopamine to polymerize in the dispersion.

6. The preparation method as described in claim 5, wherein, In step (b), dopamine is polymerized in the dispersion at a pH range of 8.0 to 9.

0.

7. The preparation method as described in claim 1, wherein, In step (d), the weight ratio of the polydopamine-modified nanocarbon material to the lithium-ion-containing polymer is in the range of 1:2 to 1:

20.

8. The preparation method as described in claim 1, wherein, In step (c), the metal mesh template is selected from copper mesh, nickel mesh, titanium mesh, platinum mesh or stainless steel mesh.

9. The preparation method as described in claim 2, wherein, Each longitudinal groove segment and each transverse groove segment have a spindle-shaped structure with a length ranging from 450 to 650 μm.

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