Separator for lithium secondary battery, method for manufacturing the same, and lithium secondary battery comprising the same

Abstract

A separator for a lithium secondary battery comprising a thermally conductive material and a lithium-affinity material, a method for manufacturing the separator, and a lithium secondary battery comprising the separator.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0188522, filed with the Korean Intellectual Property Office on December 17, 2024, entitled “Separator for Lithium Secondary Battery, Method for Manufacturing Thereof and Lithium Secondary Battery Including Thereof”, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to a separator for a lithium secondary battery, comprising a thermally conductive material and a lithium affinity material, a method for manufacturing the separator, and a lithium secondary battery comprising the separator. background

[0004] Due to their high energy density and excellent lifespan, lithium batteries are widely used in various fields, from small electronic devices to large-scale energy storage systems. In particular, with the increasing popularity of high-performance applications such as electric vehicles and energy storage systems (ESS), the demand for lithium batteries, especially lithium rechargeable batteries with high output power, high energy density, and safety, is growing.

[0005] Due to the low redox potential of lithium metal (-3.045V vs Li / Li+) and a capacity of 3,860 mAh g / L, lithium metal has a low redox potential of -3.045V (vs Li / Li+) and a capacity of 3,860 mAh g / L. -1 Due to its extremely high theoretical capacity, lithium metal has attracted much attention as a next-generation anode material. However, during the charging and discharging process of lithium metal anodes, lithium dendrites form and grow, which increases the risk of internal short circuits in the battery. Furthermore, the charging and discharging efficiency also decreases due to the repeated formation and decomposition of the solid electrolyte interphase (SEI) layer.

[0006] Therefore, to address this issue, a technical solution has been proposed in recent years: coating the negative electrode with a protective coating to suppress dendrite growth, or coating the separator. In addition, many methods have been explored to effectively control heat generation by introducing an additional thermally conductive layer inside the battery. While these methods have achieved some success, the introduction of additional components has led to reduced energy density and decreased battery efficiency and performance. Furthermore, limitations remain, such as the vulnerability of components (e.g., coatings) to repeated charging and discharging, or the inability to adequately guarantee thermal conductivity.

[0007] Therefore, there is a need to develop new technologies that can effectively manage internal battery heat generation, suppress lithium dendrite growth, and simultaneously improve battery performance. Summary of the Invention

[0008] One aspect of this disclosure is to provide a separator for a lithium secondary battery with excellent safety and electrochemical properties, comprising a thermally conductive material and a lithium-affinity material, a method for manufacturing the separator, and a lithium secondary battery comprising the separator.

[0009] In embodiments thereof, this disclosure provides a separator for a lithium secondary battery, comprising: a porous substrate; a first coating coating at least a portion of the porous substrate; and a second coating coating at least a portion of the first coating.

[0010] According to an exemplary embodiment of this disclosure, the first coating may comprise a thermally conductive material, and the second coating may comprise a lithium-affinity material.

[0011] Another aspect of this disclosure is to provide a lithium secondary battery comprising a separator for a lithium secondary battery according to various aspects and embodiments of this disclosure.

[0012] Another aspect of this disclosure is to provide a method for manufacturing a separator for a lithium secondary battery, comprising: forming a first coating on a porous substrate; and forming a second coating on the first coating.

[0013] In an exemplary embodiment, the first coating may contain a thermally conductive material, and the second coating may contain a lithium-affinity material.

[0014] It has been found that the separator for lithium secondary batteries according to this disclosure can reduce local temperature rise by incorporating a thermally conductive material. Furthermore, this can suppress any internal short circuits that may be associated with thermal shrinkage by improving heat resistance.

[0015] It has also been discovered that the separator for lithium secondary batteries according to this disclosure can promote the formation of a lithium coating on a lithium-compatible material by incorporating a lithium-affinity material. Therefore, resistance can be reduced by providing nucleation sites. Furthermore, dendrite growth and any internal short circuits that may be associated with dendrite growth can be prevented.

[0016] Therefore, in some embodiments, the separator for lithium secondary batteries according to this disclosure can effectively release the heat generated inside the battery during overcharging or high-speed charging / discharging by forming a thin coating on a porous substrate, thereby suppressing battery ignition and degradation. Attached Figure Description

[0017] The above and other aspects, features and advantages of this disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0018] Figure 1 This is a schematic diagram illustrating the steps involved in forming the first coating.

[0019] Figure 2 This is a schematic diagram illustrating the steps involved in forming the second coating.

[0020] Figure 3 It is based on the SEM image of Experiment Example 1;

[0021] Figure 4 This is a diagram illustrating the thickness measurement results based on Experiment Example 2;

[0022] Figure 5 This is an explanation of the electrochemical characteristics diagram based on Experiment Example 2;

[0023] Figure 6 This is to explain the thermal conductivity characteristic diagram based on Experiment Example 3;

[0024] Figure 7 This is an explanation of the electrochemical characteristics diagram based on Experiment Example 4. Detailed Implementation

[0025] Unless otherwise stated, it should be understood that all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that, unless expressly defined herein, terms used throughout this disclosure generally have their common meanings as used in dictionaries, as well as any specific meanings in the relevant field context.

[0026] In this application, terms such as “first” and “second” may be used to describe various components, but these components should not be construed as limited to these terms. These terms are only used to distinguish one component from another. For example, without departing from the scope of this disclosure (i.e., identifying individual components in a certain way), a first component may be named a second component, and a second component may similarly be named a first component.

[0027] The terminology used in this specification is for describing specific exemplary embodiments only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, the singular form includes the plural form. It should be understood that the terms "comprising," "having," or "including" as used in this specification specify the presence of a feature, number, step, operation, component, part, or combination thereof mentioned in this specification, but do not exclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. These terms should also be understood to include transitional terms such as "consisting of" and "essentially composed of," which may be used to specify the presence of the stated feature and a small number of other components or features that have no substantial impact on the operability of the embodiment, and / or may be used to specify the presence of only the stated feature, excluding any other features.

[0028] In one aspect, the separator for lithium secondary batteries disclosed herein may include a porous substrate 10, a first coating 20 coated with at least a portion of the porous substrate 10, and a second coating 30 coated with at least a portion of the first coating 20.

[0029] In one embodiment, the porous substrate 10 may comprise a polyolefin material. The polyolefin material may be polypropylene (PP) or polyethylene (PE).

[0030] In an embodiment, the porous substrate 10 of this disclosure may contain pores of a certain size, which can be used as channels for lithium ions while preventing electrical short circuits between the positive and negative electrodes.

[0031] In one exemplary embodiment, the porosity of the porous substrate 10 of this disclosure can be from 30% to 80%. In some preferred embodiments, the porosity can be from 40% to 70%. Furthermore, the aforementioned porosity can be determined using any method known in the art.

[0032] In some embodiments, the thickness of the porous substrate 10 disclosed herein can be from 3 μm to 30 μm. In some preferred embodiments, the thickness of the porous substrate can be from 5 μm to 10 μm.

[0033] In one embodiment, the first coating 20 may coat at least a portion of the porous substrate 10. The first coating 20 of this disclosure may comprise a thermally conductive material.

[0034] In embodiments of this disclosure, any thermally conductive material can be used as a thermally conductive material. In some further embodiments, the thermally conductive material may include any one selected from aluminum nitride (AlN), boron nitride (BN), silicon nitride (Si3N4), magnesium nitride (Mg3N4), silicon carbide (SiC), beryllium oxide (BeO), aluminum oxide (Al2O3), aluminum (Al), silver (Ag), gold (Au), copper (Cu), and / or nickel (Ni), or a composition thereof.

[0035] In some embodiments, the thermal conductivity of the thermally conductive material can be 20 W / m·K or higher. In some exemplary embodiments, the thermally conductive material can be aluminum nitride (AlN). In these embodiments, the particle size of aluminum nitride can be from 1 μm to 4 μm, and in some preferred embodiments, the particle size can be from 1.2 μm to 2 μm.

[0036] In embodiments of this disclosure, sufficient thermal conductivity can be obtained and localized temperature rise of the diaphragm can be prevented. Therefore, in some embodiments of this disclosure, the thickness of the first coating 20 can be from 1 μm to 10 μm, and in some preferred embodiments, its thickness can be from 2 μm to 5 μm.

[0037] In embodiments of this disclosure, the second coating 30 may coat at least a portion of the first coating 20. In some embodiments, the second coating 30 of this disclosure may contain a lithium-affinity material.

[0038] In some further embodiments, the lithium-affinity material can be a material that is highly reactive with lithium, and can be a material that forms and induces uniform lithium metal layering by minimizing nucleation resistance during the reduction of lithium ions to lithium metal.

[0039] According to one embodiment of this disclosure, the lithium affinity material may include any one or more of the following, or may be selected from gold (Au), silver (Ag), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO) and / or manganese oxide (MnO).

[0040] According to one embodiment of this disclosure, the thickness of the second coating 30 can be from 10 nm to 100 nm. In such an embodiment, the second coating 30 of this disclosure can be formed within the above range, and unlike the prior art, it can remain unaffected by the energy density of the battery. Furthermore, it can effectively dissipate heat generated during overcharging or high-speed charging / discharging. In this way, battery ignition and degradation can be suppressed. Additionally, resistance can be reduced by providing nucleation sites.

[0041] According to these embodiments, the separator for lithium secondary batteries disclosed herein includes a porous substrate 10, a first coating 20, and a second coating 30, and can have a thickness of 8 μm to 15 μm and a thickness of 0.550 mS cm. -1 Up to 0.710 mS cm -1 ionic conductivity.

[0042] In some aspects, this disclosure provides a lithium secondary battery comprising a separator for lithium secondary batteries according to the various embodiments described above. The lithium secondary battery of this disclosure exhibits excellent battery life and rate performance by effectively controlling internal heat generation.

[0043] In one aspect, this disclosure provides a method for manufacturing a separator for lithium secondary batteries as described herein, comprising forming a first coating on a porous substrate (S100); and forming a second coating on the first coating (S200).

[0044] In the embodiments, the method for manufacturing a separator for lithium secondary batteries, the porous substrate, the first coating and the second coating of the present disclosure are the same as those described above.

[0045] The formation of the first coating 20 (S100) on the porous substrate of this disclosure can be carried out by applying a mixture comprising an adhesive, a solvent and a thermally conductive material onto the porous substrate.

[0046] In the embodiments, the adhesive may include any one or more of the following, or may be selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

[0047] In the embodiments, the solvent may include any one or more of the following, or may be selected from N-methylpyrrolidone (NMP), isopropanol (IPA) and water.

[0048] In one exemplary embodiment, the adhesive may be polyvinylidene fluoride (PVDF) and the solvent may be N-methylpyrrolidone (NMP).

[0049] In some embodiments of this disclosure, the mixture may comprise a thermally conductive material and a binder in a mass ratio of 8:1 to 10:1.

[0050] The mixture described above forms the first coating. Figure 1 The explanation is in the text. Figure 1 In this context, thermally conductive materials, adhesives, and solvents are arbitrarily illustrated, represented, and identified, and the thickness and length of the diaphragm and the first coating are arbitrarily illustrated, represented, and identified, and are not limited to any particular form shown.

[0051] In this disclosure, the formation of the second coating on the first coating (S200) can be performed by a sputtering process. Sputtering can be a physical vapor deposition (PVD) process, and in one embodiment, it can be a radio frequency (RF) sputtering process. For clarity, RF sputtering refers to a method that uses high-frequency power to generate plasma on a target surface, separates the target material at the atomic level when ions in the plasma collide with the target, and then deposits the separated material onto a substrate.

[0052] In this disclosure, the sputtering process can use lithium-affinity materials as targets and can be performed at an output power of 10W to 20W.

[0053] In one embodiment, a second coating may be formed on the first coating of this disclosure (S200) to achieve a thickness in the range of 10 nm to 100 nm.

[0054] According to the above embodiment, a second coating is formed on the first coating (S200). Figure 2 As shown. In Figure 2 In this context, lithium-affinity materials, electrons, and cations are arbitrarily illustrated, represented, and identified, and the thickness and length of the separator, the first coating, and the second coating are also arbitrarily illustrated, represented, and identified, and are not limited to any particular form shown.

[0055] The present disclosure will be described in more detail below through the following embodiments and experimental descriptions. These embodiments and experimental descriptions are only used to illustrate aspects and implementations of the present disclosure in more detail. It should be understood that the scope of the present disclosure is not limited to the following embodiments and experimental descriptions.

[0056] Example 1

[0057] To prepare a first coating that coats at least a portion of a porous substrate, aluminum nitride (AlN), polyvinylidene fluoride (PVDF) binder, and N-methylpyrrolidone (NMP) solvent are mixed. In this embodiment, aluminum nitride with a particle size of 1.4 μm and a thermal conductivity of 100–200 W / m·K is used, and the aluminum nitride and PVDF binder are mixed at a mass ratio of 9:1.

[0058] The prepared mixture was coated onto a porous substrate using a bar coating method. In this embodiment, the porous substrate has a porosity of approximately 50% and comprises a polyethylene material with a thickness of 8.6 μm.

[0059] Next, in order to form the second coating, the porous substrate with the first coating (which has a thickness of 2.4 μm) is fixed onto the substrate of the RF sputtering equipment equipped with a silver target.

[0060] During the sputtering process, when the internal pressure of the RF sputtering equipment reaches 2×10⁻⁶... -5 When the pressure is 7 × 10⁻⁶ or lower, argon (Ar) is introduced to maintain the working pressure at 7 × 10⁻⁶. -3 Entrust.

[0061] Subsequently, silver is deposited on the upper surface of the first coating for 1 minute at an output power of 10W to form a second coating and to provide a separator for lithium secondary batteries, wherein the thickness of the second coating formed is 15nm.

[0062] Comparative Example 1

[0063] After preparing the same porous substrate as in Example 1, a separator for lithium secondary batteries without the first or second coating was prepared.

[0064] Comparative Example 2

[0065] A separator for lithium secondary batteries comprising a porous substrate and a first coating was prepared in the same manner as in Example 1, except that a second coating was not applied.

[0066] Comparative Example 3

[0067] After preparing a porous substrate identical to that in Example 1, a second coating was formed without forming the first coating. In this example, the second coating was formed in the same manner as in Example 1, except that silver was deposited on the upper surface of the porous substrate for 1 minute at an output power of 20W. A separator for a lithium secondary battery comprising a porous substrate and a second coating was prepared.

[0068] Comparative Example 4

[0069] A separator for a lithium secondary battery was prepared in the same manner as in Comparative Example 3, except that silver was deposited on the upper surface of the porous substrate for 1 minute at an output power of 15W when forming the second coating.

[0070] Comparative Example 5

[0071] A separator for a lithium secondary battery was prepared in the same manner as in Comparative Example 3, except that silver was deposited on the upper surface of the porous substrate for 1 minute at an output power of 10W when forming the second coating.

[0072] Experimental Example 1

[0073] In this experiment, the performance of the diaphragms according to the examples and comparative examples was analyzed.

[0074] The membrane thickness was measured according to the examples and comparative examples, and the air permeability, resistance and ionic conductivity were also measured.

[0075] The air permeability of the diaphragms according to the examples and comparative examples was measured using a densometer to measure the time required for 100 ml of air to pass through. The densometer is an air permeability measuring device.

[0076] The resistance and ionic conductivity of the separator according to the examples and comparative examples were calculated by measuring the bulk resistance of the button cell (SUS / separator / SUS) made of stainless steel (SUS).

[0077] The results of the performance measurement are shown in Table 1 below.

[0078] [Table 1]

[0079]

[0080] Referring to Table 1, Example 1 (which includes a first coating and a second coating) has the lowest resistivity of 0.836 Ohm and excellent ionic conductivity of 0.655 mS / cm. -1 .

[0081] In Comparative Example 2, its thickness was approximately 11 μm, similar to Example 1 which included the first coating, and its ionic conductivity was also higher than that of Comparative Examples 1, 3 to 5. However, compared to Example 1 which also included the second coating, it exhibited lower ionic conductivity and higher resistance. Therefore, the data suggest that the second coating may affect the electrical properties of the diaphragm.

[0082] A review of Comparative Examples 1, 3 to 5 shows that their air permeability and ionic conductivity are much lower than those of Example 1, and their resistance is also higher.

[0083] Therefore, the data shows that the separator for lithium secondary batteries according to an exemplary embodiment of the present disclosure, having a first coating containing a thermally conductive material, exhibits excellent ionic conductivity.

[0084] Next, SEM images of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 5 were obtained, as follows: Figure 3 As shown.

[0085] See Figure 3 Unlike Comparative Examples 1 and 5, Examples 1 and 2 appear to have significantly larger particles, which is due to the inclusion of a thermally conductive material in the first coating. Furthermore, when comparing Examples 1 and 2, it can be seen that smaller nanoscale particles are densely coated due to the inclusion of a lithium-affinity material in the second coating of Example 1.

[0086] Experiment Example 2

[0087] In this experiment, the effect of the second coating containing lithium-affinity materials was analyzed.

[0088] Therefore, the coating thickness of the diaphragms in Comparative Examples 3 to 5 was first measured. The thickness was measured using an Alpha-step height measuring instrument.

[0089] The results are shown in Table 2 and Figure 4 As shown.

[0090] [Table 2]

[0091]

[0092]

[0093] See Table 2 and Figure 4 It can be seen that during the sputtering process to form the second coating, the coating thickness increases with the increase of output power.

[0094] Next, the electrochemical characteristics of the membranes of Comparative Examples 1 and 3 to 5 were analyzed.

[0095] To this end, a symmetric cell using lithium metal was fabricated to prepare a lithium secondary battery, and the electrochemical performance was compared based on the thickness of the second coating by measuring the change in voltage over time.

[0096] The results are as follows Figure 5 As shown.

[0097] See Figure 5 As can be seen, Comparative Example 3 exhibits a larger resistance compared to Comparative Example 1. It can also be observed that Comparative Examples 4 and 5 exhibit excellent lifetime characteristics because the total overvoltage formed is lower than that of Comparative Example 1.

[0098] Combination Figure 4and Figure 5 The data shows that the thickness of the second coating is preferably between 10 nm and 40 nm, which can minimize the increase in resistance caused by the coating. Furthermore, in Example 1, the output power of the sputtering process was 10 W, the same as in Comparative Example 5, thus confirming that the coating thickness formation is similar to that of Comparative Example 5, thereby obtaining excellent electrochemical properties.

[0099] Experimental Example 3

[0100] In this experiment, the thermal conductivity properties of the diaphragms of Example 1, Comparative Example 1, and Comparative Example 2 were measured. The thermal behavior was examined in real time by irradiating the diaphragm surface with a laser and then analyzed using an infrared thermal imager.

[0101] The results are shown in Table 3 and Figure 6 As shown.

[0102] [Table 3]

[0103] Example 1 Comparative Example 1 Comparative Example 2 Maximum temperature (°C) 71.5 111.8 76.1 Average temperature (°C) 25.1 24.4 25.1

[0104] See Table 3 and Figure 6 As can be seen, the highest temperature of the diaphragm in Example 1 and Comparative Example 2 is lower than that in Comparative Example 1. This indicates that the thermal conductivity can be excellent when a first coating containing a thermally conductive material is included. Furthermore, since the highest temperature value of Example 1 is lower than that of Comparative Example 2, this data suggests that the second coating may cause additional effects.

[0105] Experiment Example 4

[0106] In this experiment, the electrochemical characteristics of the separators from Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 5 were measured. For this purpose, lithium-ion secondary batteries were fabricated using NMC622 as the positive electrode and lithium metal as the negative electrode. Subsequently, the capacity retention rate according to the rate of change was measured.

[0107] The results are as follows Figure 7 As shown.

[0108] See Figure 7 As can be seen, compared to Comparative Examples 1, 2 and 5, Example 1 exhibits superior capacity retention, and its high-speed characteristics are particularly outstanding. This is likely due to the characteristics of the first and second coatings (i.e., compared to Comparative Example 5, Example 1 includes a first coating; compared to Comparative Example 2, Example 1 includes a second coating).

[0109] This disclosure has been described with reference to several non-limiting exemplary embodiments. Those skilled in the art to which this disclosure pertains will understand that this disclosure can be implemented in modified forms without departing from its essential characteristics. Therefore, the embodiments disclosed herein should be considered illustrative rather than restrictive. The scope of the claims is defined by the claims and their equivalents, and is interpreted based on the exemplary aspects and embodiments of this disclosure.

Claims

1. A separator for lithium secondary batteries, comprising: Porous substrate; A first coating is applied to at least a portion of the porous substrate; and A second coating is applied to at least a portion of the first coating. The first coating comprises a thermally conductive material, and The second coating contains a lithium-affinity material.

2. The diaphragm according to claim 1, wherein, The porous substrate comprises a polyolefin material.

3. The diaphragm according to claim 1, wherein, The porous substrate has a thickness of 3 μm to 30 μm and a porosity of 30% to 80%.

4. The diaphragm according to claim 1, wherein, The thermally conductive material includes aluminum nitride (AlN), boron nitride (BN), silicon nitride (Si3N4), magnesium nitride (Mg3N4), silicon carbide (SiC), beryllium oxide (BeO), aluminum oxide (Al2O3), aluminum (Al), silver (Ag), gold (Au), copper (Cu) and / or nickel (Ni), or any combination thereof.

5. The diaphragm according to claim 4, wherein, The thermal conductivity of the thermally conductive material is 20 W / m·K or higher.

6. The diaphragm according to claim 1, wherein, The thickness of the first coating is 1 μm to 10 μm.

7. The diaphragm according to claim 1, wherein, The lithium-affinity material includes gold (Au), silver (Ag), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO) and / or manganese oxide (MnO), or any combination thereof.

8. The diaphragm according to claim 1, wherein, The thickness of the second coating is 10 nm to 100 nm.

9. The diaphragm according to claim 1, wherein, The thickness of the separator used in the lithium secondary battery is 8 μm to 15 μm, and the ionic conductivity is 0.550 mS / cm. -1 Up to 0.710 mS cm -1 .

10. The diaphragm according to claim 1, wherein the thermally conductive material comprises aluminum nitride (AlN), and the lithium affinity material comprises silver (Ag).

11. A lithium secondary battery comprising a separator for a lithium secondary battery according to any one of claims 1-10.

12. A method for manufacturing a separator for lithium secondary batteries, comprising: A first coating comprising a thermally conductive material is formed on at least a portion of a porous substrate; and A second coating comprising a lithium affinity material is formed on at least a portion of the first coating.

13. The method according to claim 12, wherein, The porous substrate comprises a polyolefin material.

14. The method according to claim 12, wherein, The thermally conductive material includes aluminum nitride (AlN), boron nitride (BN), silicon nitride (Si3N4), magnesium nitride (Mg3N4), silicon carbide (SiC), beryllium oxide (BeO), aluminum oxide (Al2O3), aluminum (Al), silver (Ag), gold (Au), copper (Cu) and / or nickel (Ni), or any combination thereof.

15. The method according to claim 12, wherein, The lithium-affinity material includes gold (Au), silver (Ag), platinum (Pt), zinc (Zn), silicon (Si), magnesium (Mg), copper oxide (CuO), zinc oxide (ZnO), cobalt oxide (CoO) and / or manganese oxide (MnO), or any combination thereof.

16. The method according to claim 12, wherein, The step of forming the first coating includes: applying a mixture comprising an adhesive, a solvent, and the thermally conductive material onto the porous substrate, and The mixture comprises the thermally conductive material and the adhesive in a mass ratio of 8:1 to 10:

1.

17. The method according to claim 16, wherein, The adhesive is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP).

18. The method according to claim 12, wherein, The step of forming the second coating on the first coating includes: a sputtering process using the lithium affinity material as a target, and performed at an output power of 10W to 20W.

19. The method according to claim 12, wherein, The second coating formation step provides a second coating with a thickness of 10 nm to 100 nm.

20. The method of claim 12, wherein the thermally conductive material comprises aluminum nitride (AlN) and the lithium-affinity material comprises silver (Ag).

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