Release film for lithium transfer and method for producing same

Abstract

The present invention relates to a release film for lithium transfer and a method for manufacturing the same, and more particularly, to a release film for transferring lithium (Li) to a battery current collector after depositing the lithium (Li) on the release film. The present invention relates to a release film for lithium transfer and a method for manufacturing the same, and more particularly, to a release film for lithium transfer and a method for manufacturing the same, which not only have excellent deposition efficiency, but also have excellent efficiency of transferring lithium deposited on a release film to a current collector by minimizing the generation of pin holes when depositing lithium (Li) on the release film.

Description

Technical Field

[0001] This invention relates to a release film for lithium transfer and a method for manufacturing the same. More specifically, this invention relates to a release film for depositing lithium (Li) on a release film and transferring it to a battery current collector, wherein the release film minimizes the generation of pinholes during lithium (Li) deposition, thereby exhibiting excellent deposition efficiency, and also exhibits excellent efficiency in transferring lithium deposited on the release film to the current collector. Background Technology

[0002] In batteries, especially rechargeable batteries, some of the lithium ions released from the positive electrode during the first charge are absorbed into the negative electrode, resulting in a battery capacity lower than the theoretical capacity of the negative electrode material. To avoid this irreversible capacity loss, a technique has been disclosed in which lithium equivalent to the irreversible capacity loss is pre-absorbed into the negative electrode before assembling the rechargeable battery and initiating charge and discharge. By utilizing this technique, lithium ions released from the positive electrode during the first charge can be recovered to the negative electrode in a higher proportion, thereby increasing the battery capacity.

[0003] On the other hand, a common method for pre-capturing lithium in the negative electrode is to deposit lithium onto the negative electrode. To increase the amount of lithium deposited, equivalent to the irreversible capacity, previous studies have explored pre-treating graphite or silicon-graphite materials on the current collector to increase the amount of lithium deposited.

[0004] However, graphite materials have limited capacity during lithium-ion movement, while silicon-graphite materials cause a sharp volume expansion during lithium-ion movement, which may affect battery durability.

[0005] For the reasons mentioned above, there is a need to develop a method for pre-charging the negative electrode with sufficient lithium and / or a new method to prevent volume expansion due to the increase in lithium content. One such method is to first deposit lithium metal on a release film and then transfer it to a current collector, preferably a negative electrode current collector.

[0006] In summary, regarding the method of transferring lithium deposited on a release film to a current collector, a solution is needed to ensure uniform lithium deposition and achieve high transfer efficiency. Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] The present invention is proposed to solve the above-mentioned problems, and its purpose is to provide a lithium transfer release film and its manufacturing method that can ensure uniform deposition performance and transfer efficiency.

[0009] Furthermore, for ease of use, the objective is to provide a lithium transfer release film and a method for manufacturing the same, which, even when multiple lithium transfer release films of the present invention are stacked and separated again, still exhibit excellent unwinding properties and can prevent lithium (Li) from transferring to portions other than the portion where lithium (Li) is deposited.

[0010] means for solving problems

[0011] To address the aforementioned issues, the lithium transfer release film of the present invention may have a structure in which a first release layer, a base film, and a second release layer are stacked sequentially.

[0012] In a preferred embodiment of the present invention, a lithium transfer release film of the present invention can satisfy the following condition (1):

[0013] (1) A

[0014] In condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0015] In a preferred embodiment of the present invention, a lithium transfer release film of the present invention can further satisfy the following condition (2):

[0016] (2) A:B = 1:1.1~5.0

[0017] In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0018] In a preferred embodiment of the present invention, the base film and the first release layer may have a thickness ratio of 1:0.0014 to 0.0026.

[0019] In a preferred embodiment of the present invention, the base film and the first release layer may have a thickness ratio of 2:0.001 to 0.0018.

[0020] In a preferred embodiment of the present invention, after lithium is deposited on one side of the second release layer with a thickness of 2 to 25 μm, when the first release layer is irradiated with white light, the number of pinholes generated per unit area of ​​10 cm × 10 cm in the deposited lithium can be less than 100.

[0021] In a preferred embodiment of the present invention, after lithium is deposited on one side of the second release layer of the lithium transfer release film of the present invention with a thickness of 2 to 8 μm, when the first release layer is irradiated with white light, the number of pinholes generated per unit area of ​​10 cm × 10 cm in the deposited lithium can be less than 100. ​

[0022] In a preferred embodiment of the present invention, the second release layer may include a resin composition.

[0023] In a preferred embodiment of the present invention, the resin composition comprises 10 to 70% by weight of a silicone resin.

[0024] In a preferred embodiment of the present invention, the second release layer may include 0.1 to 5 parts by weight of catalyst and 0.1 to 5 parts by weight of adhesion enhancer relative to 100 parts by weight of resin composition.

[0025] In a preferred embodiment of the present invention, the first release layer may include 2.2 to 25% by weight of silicon (Si) based on the total weight percentage.

[0026] In a preferred embodiment of the present invention, the second release layer may include 2 to 5% by weight of silicon (Si) based on the total weight percentage.

[0027] In a preferred embodiment of the present invention, the base film may include one or more selected from polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), and polyethylene (PE).

[0028] In a preferred embodiment of the present invention, the resin composition may include silicone resins and non-silicone resins.

[0029] In a preferred embodiment of the present invention, the silicone resin may include one or more selected from addition-reactive silicone resins, condensation-reactive silicone resins, and UV-reactive silicone resins.

[0030] In a preferred embodiment of the present invention, the non-silicone resin may include one or more selected from cellulose resin, acrylate resin, melamine resin and alkyd resin.

[0031] On the other hand, the method for manufacturing the lithium transfer release film of the present invention includes the following steps: a first step of preparing a base film; and a second step of coating a first release layer forming composition on one side of the base film and coating a second release layer forming composition on the other side of the base film and then curing it, thereby forming a first release layer on one side of the base film and a second release layer on the other side of the base film; and can satisfy the following condition (1):

[0032] (1) A

[0033] In condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0034] In a preferred embodiment of the present invention, the method for manufacturing the lithium transfer release film of the present invention can further satisfy the following condition (2):

[0035] (2) A:B = 1:1.1~5.0

[0036] In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0037] In a preferred embodiment of the present invention, after lithium is deposited on one side of the second release layer with a thickness of 2 to 25 μm, when the first release layer is irradiated with white light, the number of pinholes generated per unit area of ​​10 cm × 10 cm in the deposited lithium can be less than 100.

[0038] In a preferred embodiment of the present invention, the composition for forming the second release layer may be a mixture of a resin composition, a catalyst, an adhesion enhancer, and a solvent.

[0039] In a preferred embodiment of the present invention, the resin composition may be a mixture of 10 to 70% by weight of silicone resin.

[0040] In a preferred embodiment of the present invention, the second release layer forming composition, relative to 100 parts by weight of the resin composition, may be a mixture of 0.1 to 5 parts by weight of catalyst, 0.1 to 5 parts by weight of adhesion enhancer, and 800 to 1000 parts by weight of solvent.

[0041] In a preferred embodiment of the present invention, the curing can be carried out at a temperature of 100-140°C for 10-40 seconds.

[0042] The effects of the invention

[0043] The lithium transfer release film and its manufacturing method of the present invention are release films used to transfer lithium (Li) to a battery current collector after deposition on the release film. The release film can pre-absorb lithium equivalent to the amount of lithium ions irreversibly lost during the first charge and discharge of the secondary battery in the negative electrode current collector, thereby increasing the capacity of the secondary battery.

[0044] Furthermore, the lithium transfer release film and its manufacturing method of the present invention can minimize the generation of pinholes when depositing lithium (Li) on the release film, thereby achieving excellent deposition efficiency.

[0045] ​Furthermore, the lithium transfer release film and its manufacturing method of the present invention have excellent efficiency in transferring lithium deposited on the release film to the current collector.

[0046] Furthermore, for ease of use, the lithium transfer release film and its manufacturing method of the present invention exhibit excellent unwinding properties even when multiple lithium transfer release films of the present invention are stacked and separated again.

[0047] Furthermore, for ease of use, the lithium transfer release film and its manufacturing method of the present invention can prevent lithium (Li) from transferring to parts other than the deposited lithium (Li) portion, even when multiple lithium transfer release films of the present invention are stacked and separated again. Attached Figure Description

[0048] Figure 1 A cross-sectional view of a lithium transfer release film formed on one side is shown to illustrate a preferred embodiment of the invention.

[0049] Figure 2 To illustrate a preferred embodiment of the present invention, after lithium is deposited on one side of the second release layer, white light is irradiated onto the first release layer to observe the pinholes generated in the deposited lithium. Detailed Implementation

[0050] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement the present invention. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. For clarity, parts unrelated to the description have been omitted from the drawings, and the same reference numerals are used for the same or similar constituent elements throughout the specification.

[0051] Reference Figure 1 As can be explained, the lithium transfer release film of the present invention may have a structure in which a first release layer 10, a base film 20 and a second release layer 30 are stacked in sequence.

[0052] The first release layer 10 is a film that not only improves unwinding properties but also prevents lithium deposited on the second release layer 30 from transferring to the opposite side. This film may comprise a silicone resin, preferably at least one selected from addition-reactive silicone resins, condensation-reactive silicone resins, and UV-reactive silicone resins, and more preferably includes an addition-reactive silicone resin.

[0053] In addition, the first release layer 10 may have a thickness of 0.05 to 5 μm, preferably 0.1 to 1 μm, more preferably 0.1 to 0.3 μm. If the thickness is less than 0.05 μm, there may be a problem of excessive release force. If it exceeds 5 μm, adhesion may occur.

[0054] Furthermore, the first release layer 10 may include 2.2 to 25% silicon (Si) by weight, preferably 3 to 20% by weight, more preferably 5 to 15% by weight, and even more preferably 10 to 15% by weight. If the silicon content is less than 2.2% by weight, the lithium transfer suppression effect may be reduced due to the increase in release force. If it exceeds 25% by weight, the silicon (Si) component in the first release layer 10 may transfer to the lithium that can be deposited on the second release layer 30.

[0055] In addition, the first release layer 10 may include 0.1 to 5 parts by weight of catalyst, preferably 0.5 to 3.0 parts by weight, and more preferably 1.0 to 2.0 parts by weight, relative to 100 parts by weight of silicone resin. If the catalyst content is less than 0.1 parts by weight, there may be a problem of incomplete curing. If it exceeds 5 parts by weight, it may cause the release force to rise to an excessively high level.

[0056] Furthermore, the catalyst can be any catalyst commonly used in the art, but preferably can include platinum.

[0057] Furthermore, the first release layer 10 may include 0.1 to 5 parts by weight of an adhesion enhancer relative to 100 parts by weight of the silicone resin, preferably 0.5 to 3.0 parts by weight, more preferably 0.5 to 1.5 parts by weight. If the content of the adhesion enhancer is less than 0.1 parts by weight, there may be a problem of poor adhesion between the first release layer 10 and the base film 20. If it exceeds 5 parts by weight, there may be a problem of silicon (Si) contained in the first release layer 10 transferring to the back side of the base film 20 (the side forming the second release layer).

[0058] The adhesion enhancer is a material used to improve the adhesion between the first release layer 10 and the base film 20. It can be any adhesion enhancer commonly used in the art, and preferably can include dimethyl,methylvinyl siloxane with epoxide.

[0059] The base film 20 serves not only as a substrate for forming the first release layer 10 and the second release layer 30, but also as a substrate capable of uniformly depositing lithium on the second release layer 30 and / or as a support for transferring lithium deposited on the second release layer 30 to the current collector. It can be any base film material commonly used in the art, preferably including one or more selected from polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), and polyethylene (PE).

[0060] Furthermore, the base film 20 of the present invention can have a thickness of 10 to 250 μm, preferably 25 to 100 μm. If the thickness is less than 10 μm, the base film 20 may undergo thermal deformation during the lithium (Li) deposition process carried out at high temperature. If the thickness exceeds 250 μm, there may be economic problems.

[0061] The second release layer 30 is a layer that allows lithium (Li) to be uniformly deposited or smoothly transferred to the current collector, and is a layer in which lithium is deposited on one side for lithium transfer.

[0062] The second release layer 30 can have a thickness of 0.01 to 1 μm, preferably 0.05 to 0.5 μm, more preferably 0.05 to 0.3 μm. If the thickness is less than 0.01 μm, there may be problems with poor transfer. If the thickness exceeds 1 μm, there may be problems with adhesion during winding.

[0063] On the other hand, the base film 20 and the first release layer 10 may have a thickness ratio of 1:0.0014 to 0.0026, preferably 1:0.0016 to 0.0024.

[0064] Furthermore, the base film 20 and the second release layer 30 may have a thickness ratio of 1:0.001 to 0.0018, preferably 1:0.0011 to 0.0016.

[0065] The second release layer 30 may include a resin composition, which may include 10 to 70% by weight of a silicone resin, preferably 30 to 70% by weight, more preferably 45 to 70% by weight, and even more preferably 55 to 65% by weight, based on the total weight percentage. If the content of the silicone resin is less than 10% by weight, there may be a problem of significantly reduced lithium transfer efficiency. If it exceeds 70% by weight, there may be a problem of increased pinhole rate in the deposited lithium when lithium is deposited on one side of the second release layer.

[0066] On the other hand, the silicone resin may include one or more selected from addition-reactive silicone resins, condensation-reactive silicone resins and UV-reactive silicone resins, and preferably may include addition-reactive silicone resins.

[0067] In addition, the non-silicone resin may include 30 to 90% by weight, preferably 30 to 70% by weight, more preferably 30 to 55% by weight, and even more preferably 35 to 45% by weight, based on the total weight percentage of the resin composition.

[0068] In addition, non-silicone resins are resins that do not contain silicon (Si) as components, and may include one or more selected from cellulose resins, acrylate resins, melamine resins and alkyd resins, preferably including cellulose resins.

[0069] Furthermore, the second release layer 30 may include 2 to 5% silicon (Si) by weight, preferably 3 to 5% by weight, more preferably 3.3 to 5% by weight, and even more preferably 3.8 to 4.9% by weight. If the silicon content is less than 2% by weight, there may be a problem of significantly reduced lithium transfer efficiency. If it exceeds 5% by weight, there may be a problem of increased pinhole rate in the deposited lithium when lithium is deposited on one side of the second release layer 30.

[0070] Furthermore, the second release layer 30 may include 0.1 to 5 parts by weight of catalyst relative to 100 parts by weight of the resin composition, preferably 0.5 to 3.0 parts by weight, more preferably 1.0 to 2.0 parts by weight; if the catalyst content is less than 0.1 parts by weight, there may be a problem of incomplete curing, while if it exceeds 5 parts by weight, there may be a problem of the peel force rising to a certain level.

[0071] Furthermore, the catalyst can be any catalyst commonly used in the art, but preferably can include platinum.

[0072] Furthermore, the second release layer 30 may include 0.1 to 5 parts by weight of an adhesion enhancer relative to 100 parts by weight of the resin composition, preferably 0.5 to 3.0 parts by weight, more preferably 0.5 to 1.5 parts by weight. If the content of the adhesion enhancer is less than 0.1 parts by weight, there may be a problem of poor adhesion between the second release layer 30 and the base film 20. If it exceeds 5 parts by weight, there may be a problem of silicon (Si) contained in the second release layer 30 transferring to the back side of the base film 20 (the side that forms the first release layer).

[0073] The adhesion enhancer is a material used to improve the adhesion between the second release layer 30 and the base film 20. It can be any adhesion enhancer commonly used in the art, and preferably can include dimethyl,methylvinyl siloxane with epoxide.

[0074] On the other hand, the lithium transfer release film of the present invention can satisfy the following condition (1):

[0075] (1) A

[0076] In condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0077] If condition (1) is not met, there may be a problem of lithium deposited in the second release layer transferring to the first release layer.

[0078] Furthermore, the lithium transfer release film of the present invention can further satisfy the following condition (2):

[0079] (2) A:B = 1:1.1 to 5.0, preferably A:B = 1:1.5 to 5.0, more preferably A:B = 1:2.5 to 5.0, and even more preferably A:B = 1:3.5 to 4.5

[0080] In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0081] If A and B are less than 1:1.1, there may be a problem of lithium that can be deposited on the second release layer transferring to the first release layer. If they exceed 1:5.0, the silicon (Si) content of the first release layer may increase, and the increased silicon (Si) content may lead to the problem of silicon (Si) transferring to the lithium surface that can be deposited on the second release layer.

[0082] Furthermore, referring to Figure 2 To illustrate, the lithium transfer release film of the present invention deposits lithium 40 with a thickness of 2 to 25 μm, preferably 2 to 20 μm, more preferably 2 to 15 μm, more preferably 2 to 8 μm, more preferably 3 to 7 μm, and more preferably 4 to 6 μm, on one side of the second release layer 30. Subsequently, when the first release layer 10 is irradiated with white light, the number of pinholes generated per 10 cm × 10 cm unit area in the deposited lithium 40 can be less than 100. Pinholes refer to pores generated during the lithium 40 deposition process. If more than 100 pinholes are generated per 10 cm × 10 cm unit area of ​​lithium 40, it may lead to uneven lithium 40 deposition. Furthermore, white light refers to light with a wavelength of 400 to 700 nm. ​

[0083] On the other hand, the method for manufacturing the lithium transfer release film of the present invention includes a first step and a second step.

[0084] First, the first step of the method for manufacturing the lithium transfer release film of the present invention can prepare a base film. At this time, the base film is as described above.

[0085] Next, the second step of the method for manufacturing the lithium transfer release film of the present invention is as follows: a first release layer forming composition is coated on one side of the base film prepared in the first step, and a second release layer forming composition is coated on the other side of the base film and then cured, thereby forming a first release layer on one side of the base film and a second release layer on the other side of the base film.

[0086] The first release layer forming composition may be a mixture of a silicone resin, a catalyst, an adhesion enhancer, and a solvent. Specifically, the first release layer forming composition may comprise, relative to 100 parts by weight of the silicone resin, 0.1 to 5 parts by weight of the catalyst, preferably 0.5 to 3.0 parts by weight, more preferably 1.0 to 2.0 parts by weight; 0.1 to 5 parts by weight of the adhesion enhancer, preferably 0.5 to 3.0 parts by weight, more preferably 0.5 to 1.5 parts by weight; and 500 to 5000 parts by weight of the solvent, preferably 550 to 4000 parts by weight. In this case, the catalyst and adhesion enhancer are as described above. Furthermore, the solvent may be any solvent commonly used in the art, preferably containing one or more of toluene, methyl ethyl ketone (MEK), n-hexane, and methyl isobutyl ketone (MIBK).

[0087] Furthermore, the first release layer formed by curing the first release layer forming composition may include 2.2 to 25% silicon (Si) by weight, preferably 3 to 20% by weight, more preferably 5 to 15% by weight, and even more preferably 10 to 15% by weight, based on the total weight percentage. The first release layer is as described above.

[0088] The composition for forming the second release layer can be a mixture of a resin composition, a catalyst, an adhesion enhancer, and a solvent. Specifically, relative to 100 parts by weight of the resin composition, the composition for forming the second release layer may include 0.1 to 5 parts by weight of the catalyst, preferably 0.5 to 3.0 parts by weight, more preferably 1.0 to 2.0 parts by weight; 0.1 to 5 parts by weight of the adhesion enhancer, preferably 0.5 to 3.0 parts by weight, more preferably 0.5 to 1.5 parts by weight; and 800 to 1000 parts by weight of the solvent, preferably 850 to 950 parts by weight. In this case, the catalyst and adhesion enhancer are as described above. Furthermore, the solvent can be any solvent commonly used in the art, preferably containing one or more of toluene, methyl ethyl ketone (MEK), n-hexane, and methyl isobutyl ketone (MIBK).

[0089] Furthermore, the resin composition can be a mixture of silicone resin and non-silicone resin. The silicone resin, based on the total weight percentage of the resin composition, can be 10-70% by weight, preferably 30-70% by weight, more preferably 45-70% by weight, and even more preferably 55-65% by weight. The non-silicone resin, based on the total weight percentage of the resin composition, can be 30-90% by weight, preferably 30-70% by weight, more preferably 30-55% by weight, and even more preferably 35-45% by weight. In this case, the silicone resin and non-silicone resin are as described above.

[0090] Furthermore, the second release layer formed by curing the composition for forming the second release layer may include 2 to 5% by weight of silicon (Si), preferably 3 to 5% by weight, more preferably 3.3 to 5% by weight, and even more preferably 3.8 to 4.9% by weight, based on the total weight percentage. Additionally, the second release layer is as described above.

[0091] In addition, the second curing step can be carried out at a temperature of 100-140°C, preferably 110-130°C, for 10-40 seconds, preferably 15-25 seconds. If the curing temperature is below 100°C, there may be a problem of incomplete curing. If it exceeds 140°C, there may be a problem of thermal deformation of the base film.

[0092] Furthermore, the lithium transfer release film prepared by the manufacturing method of the lithium transfer release film of the present invention, after depositing lithium on one side of the second release layer with a thickness of 2 to 25 μm, preferably 2 to 20 μm, more preferably 2 to 15 μm, even more preferably 2 to 8 μm, more preferably 3 to 7 μm, and even more preferably 4 to 6 μm, can produce fewer than 100 pinholes per unit area of ​​10 cm × 10 cm in the deposited lithium when white light is irradiated on the first release layer.

[0093] Furthermore, the lithium transfer release film prepared by the manufacturing method of the lithium transfer release film of the present invention can meet the following condition (1).

[0094] (1) A

[0095] In condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0096] Furthermore, the lithium transfer release film prepared by the manufacturing method of the lithium transfer release film of the present invention can further satisfy the following condition (2).

[0097] (2) A:B = 1:1.1 to 5.0, preferably A:B = 1:1.5 to 5.0, more preferably A:B = 1:2.5 to 5.0, and even more preferably A:B = 1:3.5 to 4.5

[0098] In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

[0099] The present invention has been described above with reference to embodiments, but these embodiments are merely examples and do not limit the invention. Those skilled in the art will understand that various modifications and applications not shown above can be made without departing from the essential characteristics of the invention. For example, the constituent elements specifically shown in the embodiments of the present invention can be modified. Differences related to these modifications and applications should be interpreted as being included within the scope of the invention as defined in the appended claims.

[0100] Preparation Example 1-1: Preparation of the composition for forming the first release layer

[0101] A first release layer forming composition is prepared by mixing 100 parts by weight of a silicone resin, 1.5 parts by weight of a catalyst, 1 part by weight of an adhesion enhancer, and 600 parts by weight of a solvent. The silicone resin used is an addition-reaction silicone resin (dimethyl, 5-hexenylmethyl siloxane), the catalyst is platinum, the adhesion enhancer is methylvinyl siloxane with epoxide, and the solvent is toluene.

[0102] Preparation Example 1-2: Preparation of Composition for First Release Layer Formation

[0103] ​A first release layer forming composition is prepared by mixing 100 parts by weight of a silicone resin, 1.5 parts by weight of a catalyst, 1 part by weight of an adhesion enhancer, and 1100 parts by weight of a solvent. The silicone resin used is an addition-reaction silicone resin (dimethyl, 5-hexenylmethyl siloxane), the catalyst is platinum, the adhesion enhancer is methylvinyl siloxane with epoxide, and the solvent is toluene.

[0104] Preparation Examples 1-3: Preparation of Compositions for Forming the First Release Layer

[0105] A first release layer forming composition is prepared by mixing 100 parts by weight of a silicone resin, 1.5 parts by weight of a catalyst, 1 part by weight of an adhesion enhancer, and 3500 parts by weight of a solvent. The silicone resin used is an addition-reaction silicone resin (dimethyl, 5-hexenylmethyl siloxane), the catalyst is platinum, the adhesion enhancer is methylvinyl siloxane with epoxide, and the solvent is toluene.

[0106] Preparation Examples 1-4: Preparation of Compositions for Forming the First Release Layer

[0107] To prepare a first release layer forming composition, 1.5 parts by weight of catalyst, 1 part by weight of adhesion enhancer, and 900 parts by weight of solvent were added to 100 parts by weight of the mixed composition. In this case, the mixed composition, by weight percentage, contained 80% by weight of a silicone resin and 20% by weight of dimethylvinylated and trimethylated silica (CAS Reg. No. 68988-89-6), the catalyst was platinum, the adhesion enhancer was methylvinyl siloxane with epoxide, and the solvent was toluene. Furthermore, the silicone resin used was an addition-reaction type silicone resin (dimethyl, 5-hexenylmethyl siloxane).

[0108] Preparation Examples 1-5: Preparation of Compositions for Forming the First Release Layer

[0109] To prepare a first release layer forming composition, 1.5 parts by weight of catalyst, 1 part by weight of adhesion enhancer, and 900 parts by weight of solvent are added to 100 parts by weight of the mixed composition. In this case, the mixed composition contains, by weight, 78% silicone resin and 20% by weight of dimethylvinylated and trimethylated silica (CAS Reg. No. 68988-89-6), the catalyst is platinum, the adhesion enhancer is methylvinyl siloxane with epoxide, and the solvent is toluene. Furthermore, the silicone resin used is an addition-reaction type silicone resin (dimethyl, 5-hexenylmethyl siloxane).

[0110] Preparation Examples 1-6: Preparation of Compositions for Forming the First Release Layer

[0111] To prepare a first release layer forming composition, 1.5 parts by weight of catalyst, 1 part by weight of adhesion enhancer, and 900 parts by weight of solvent are added to 100 parts by weight of the mixed composition. In this case, the mixed composition contains, by weight, 70% of a silicone resin and 20% by weight of dimethylvinylated and trimethylated silica (CAS Reg. No. 68988-89-6), with platinum as the catalyst, Methylvinyl Siloxane with Epoxide as the adhesion enhancer, and toluene as the solvent. Furthermore, the silicone resin used is an addition-reaction type silicone resin (Dimethyl, 5-hexenylmethyl siloxane).

[0112] Preparation Example 2-1: Preparation of Composition for Forming the Second Release Layer

[0113] A second release layer forming composition is prepared by mixing 100 parts by weight of a resin composition, 1.5 parts by weight of a catalyst, 1 part by weight of an adhesion enhancer, and 900 parts by weight of a solvent. In this composition, the resin composition contains 60% by weight of a silicone resin and 40% by weight of a non-silicone resin, with platinum used as the catalyst, dimethyl siloxane (containing an epoxy group) as the adhesion enhancer, and toluene as the solvent. Furthermore, an addition-reaction silicone resin (dimethyl, 5-hexenylmethyl siloxane) is used as the silicone resin, and a cellulose resin is used as the non-silicone resin.

[0114] Preparation Example 2-2: Preparation of Composition for Forming the Second Release Layer

[0115] The second release layer forming composition was prepared using the same method as in Preparation Example 2-1. However, unlike Preparation Example 2-1, the resin composition contained 50% by weight of a silicone resin and 50% by weight of a non-silicone resin.

[0116] Preparation Example 2-3: Preparation of Composition for Forming the Second Release Layer

[0117] The second release layer forming composition was prepared using the same method as in Preparation Example 2-1. However, unlike Preparation Example 2-1, the resin composition contained 40% by weight of a silicone resin and 60% by weight of a non-silicone resin.

[0118] Preparation Example 2-4: Preparation of Composition for Forming the Second Release Layer

[0119] The second release layer forming composition was prepared using the same method as in Preparation Example 2-1. However, unlike Preparation Example 2-1, the resin composition contained 20% by weight of a silicone resin and 80% by weight of a non-silicone resin.

[0120] Preparation Example 2-5: Preparation of Composition for Forming the Second Release Layer

[0121] The second release layer forming composition was prepared using the same method as in Preparation Example 2-1. However, unlike Preparation Example 2-1, the resin composition contained 80% by weight of a silicone resin and 20% by weight of a non-silicone resin.

[0122] Preparation Example 2-6: Preparation of Composition for Forming the Second Release Layer

[0123] The second release layer forming composition was prepared using the same method as in Preparation Example 2-1. However, unlike Preparation Example 2-1, only a silicone resin was used as the resin composition.

[0124] Example 1: Preparation of release film for lithium transfer

[0125] (1) Prepare a polyethylene terephthalate (PET) film (XD510P, TAK) with a thickness of 75μm as the base film.

[0126] (2) Using a bar coater, the first release layer forming composition prepared in Preparation Example 1-1 is coated on one side of the prepared base film, and the second release layer forming composition prepared in Preparation Example 2-1 is coated on the other side of the base film. The film is then cured at 120°C for 20 seconds and aged at 40°C for 2 days to form a first release layer with a thickness of 0.15 μm on one side of the base film and a second release layer with a thickness of 0.1 μm on the other side of the base film, thereby preparing a lithium transfer release film.

[0127] Example 2: Preparation of release film for lithium transfer

[0128] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the first release layer forming composition prepared in Preparation Examples 1-2 was used instead of the first release layer forming composition prepared in Preparation Example 1-1, thereby forming a first release layer with a thickness of 0.08 μm, and finally preparing a release film for lithium transfer.

[0129] Example 3: Preparation of release film for lithium transfer

[0130] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the first release layer forming composition prepared in Preparation Examples 1-3 was used instead of the first release layer forming composition prepared in Preparation Example 1-1, thereby forming a first release layer with a thickness of 0.025 μm, and finally preparing a release film for lithium transfer.

[0131] Example 4: Preparation of release film for lithium transfer

[0132] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the first release layer forming composition prepared in Preparation Examples 1-4 was used instead of the first release layer forming composition prepared in Preparation Example 1-1, thereby forming a first release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0133] Comparative Example 1: Preparation of Release Film for Lithium Transfer

[0134] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the first release layer forming composition prepared in Preparation Examples 1-5 was used instead of the first release layer forming composition prepared in Preparation Example 1-1, thereby forming a first release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0135] Comparative Example 2: Preparation of Release Film for Lithium Transfer

[0136] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the first release layer forming composition prepared in Preparation Examples 1-6 was used instead of the first release layer forming composition prepared in Preparation Example 1-1, thereby forming a first release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0137] Example 5: Preparation of release film for lithium transfer

[0138] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the second release layer forming composition prepared in Preparation Example 2-2 was used instead of the second release layer forming composition prepared in Preparation Example 2-1, thereby forming a second release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0139] Example 6: Preparation of release film for lithium transfer

[0140] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the second release layer forming composition prepared in Preparation Examples 2-3 was used instead of the second release layer forming composition prepared in Preparation Example 2-1, thereby forming a second release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0141] Example 7: Preparation of release film for lithium transfer

[0142] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the second release layer forming composition prepared in Preparation Examples 2-4 was used instead of the second release layer forming composition prepared in Preparation Example 2-1, thereby forming a second release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0143] Example 8: Preparation of release film for lithium transfer

[0144] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the second release layer forming composition prepared in Preparation Examples 2-5 was used instead of the second release layer forming composition prepared in Preparation Example 2-1, thereby forming a second release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0145] Example 9: Preparation of release film for lithium transfer

[0146] A release film for lithium transfer was prepared using the same method as in Example 1. However, unlike Example 1, the second release layer forming composition prepared in Preparation Examples 2-6 was used instead of the second release layer forming composition prepared in Preparation Example 2-1, thereby forming a second release layer with a thickness of 0.1 μm, and finally preparing a release film for lithium transfer.

[0147] Experimental Example 1: Evaluation of unwinding properties and lithium transfer to the first release layer

[0148] Lithium was deposited on one side of the release layer of the lithium transfer release films prepared in Examples 1-9 and Comparative Examples 1-2 using physical vapor deposition (PVD) to a thickness of 5 μm. Two lithium transfer release films with deposited lithium were stacked, and a load of 2 kg / cm² was applied to the lithium layer formed on the surface of the lithium transfer release films. The films were then left to stand at 40°C for 2 days. Subsequently, when separating the two stacked lithium transfer release films with deposited lithium, the following evaluations were made: ◎ if no sticky sound was produced; ○ if only a very slight sticky sound was produced; and X if a large sticky sound was produced. The unwinding properties were evaluated, and the results are shown in Table 1 below. Subsequently, after evaluating the unwindability, it was confirmed whether lithium transfer occurred on the first release layer of the separated lithium transfer release film. If no lithium transfer occurred, it was evaluated as ○, and if lithium transfer occurred, it was evaluated as X. The evaluation of whether lithium transfer occurred in the first release layer is shown in Table 1 below.

[0149] Experiment Example 2: Determination of the number of pinholes

[0150] Lithium was deposited on one side of the second release layer of each of the lithium transfer release films prepared in Examples 1-9 and Comparative Examples 1-2 using physical vapor deposition (PVD) to a thickness of 5 μm. Subsequently, the first release layer of each of the lithium transfer release films prepared in Examples 1-9 and Comparative Examples 1-2 was irradiated with white light, and the deposited lithium was observed with the naked eye. The number of pinholes generated per 10 cm × 10 cm unit area is shown in Table 1.

[0151] Experimental Example 3-1: Determination of Release Force of the First Release Layer

[0152] Acrylic tape (TESA7475) with a width of 25 mm and a length of 175 mm was attached to the first release layer of the lithium transfer release film prepared in Examples 1 to 9 and Comparative Examples 1 to 2, respectively. Then, the release force of the first release layer of the lithium transfer release film prepared in each example and comparative example was measured according to the Finat-10 evaluation method. The results are shown in Table 1 below.

[0153] Experimental Example 3-2: Determination of Release Force of the Second Release Layer

[0154] Acrylic adhesive tape (TESA7475) with a width of 25 mm × a length of 175 mm was pasted onto the second release layer of the lithium transfer release film prepared in Examples 1-9 and Comparative Examples 1-2, respectively. Then, the release force of the second release layer of the lithium transfer release film prepared in Examples 1-9 and Comparative Examples 1-2 was measured according to the Finat-10 evaluation method, and the results are shown in Table 1 below.

[0155] Experimental Example 4: Determination of Silicon (Si) Content

[0156] The silicon (Si) content in the first and second release layers of the lithium transfer release films prepared in Examples 1-9 and Comparative Examples 1-2 was measured using a scanning electron microscope (SEM) equipped with an EDS (Energy Dispersive X-ray Spectroscopy) device. The results are shown in Table 1 below.

[0157] Experimental Example 5: Lithium Transfer Efficiency Measurement

[0158] Lithium was deposited on one side of the second release layer of each of the lithium transfer release films prepared in Examples 1-9 and Comparative Examples 1-2 using physical vapor deposition (PVD) to a thickness of 5 μm. Subsequently, the lithium deposited on the lithium transfer release film was rolled-laminating onto a copper foil (Cu foil) used as a negative electrode current collector, and the lithium was transferred to the copper foil by removing the lithium transfer release film. After transfer, the area of ​​residual lithium on the lithium transfer release film was visually assessed, and the lithium transfer efficiency was calculated using Equation 1 below. The results are shown in Table 1 below.

[0159] [Calculation Formula 1]

[0160] Lithium transfer efficiency (%) = (Area of ​​lithium deposited on the lithium transfer release film - Area of ​​lithium remaining on the lithium transfer release film after transferring lithium deposited on the lithium transfer release film to copper foil) / Area of ​​lithium deposited on the lithium transfer release film

[0161]

[0162]

[0163] As shown in Tables 1 and 2, the lithium transfer release films prepared in Examples 1 to 6 not only exhibit excellent unwinding performance, but also show that lithium is not transferred to the first release layer, the number of pinholes is less than 100, and the lithium transfer efficiency is excellent.

[0164] Experiment Example 6: Determination of the Number of Pinholes

[0165] Lithium was deposited on the second release layer side of the lithium transfer release film prepared in Example 1 using physical vapor deposition (PVD) with thicknesses of 5 μm, 10 μm, 15 μm, 20 μm, and 30 μm, respectively. Subsequently, the first release layer of each lithium transfer release film prepared in Example 1 (each layer having a different lithium deposition thickness) was irradiated with white light, and the deposited lithium was observed visually. Table 3 shows the number of pinholes generated per 10 cm × 10 cm unit area.

[0166]

[0167] As shown in Table 3, even when lithium is deposited on the second release layer side of the lithium transfer release film prepared in Example 1 with thicknesses of 5 μm, 10 μm, 15 μm, and 20 μm, the number of pinholes per 10 cm × 10 cm unit area is still less than 100. However, when lithium is deposited on the second release layer side of the lithium transfer release film prepared in Example 1 with a thickness of 30 μm, thermal deformation during the deposition process can be confirmed.

[0168] Simple variations or modifications of the present invention can be easily implemented by those skilled in the art, and all such variations or modifications should be considered to be included within the scope of the present invention.

[0169] [National research and development projects supporting this invention]

[0170] [Project Unique Number] 1415185120

[0171] [Project Number] 20011254

[0172] [Department Name] Trade, Industry and Resources Department

[0173] [Name of the project management (professional) organization] Korea Institute for Industrial Technology Evaluation

[0174] [Research Project Name] Material Component Technology Development (Investigation and Analysis Project Name: Material Component Technology Development)

[0175] [Research Project Title] Development of Ultra-Easy-to-Peel Functional Release Adhesive Thin Film Technology with Minimal Time-Related Changes

[0176] [Contribution Rate] 1 / 1

[0177] [Name of the organization undertaking the project] Kurimura Chemical Co., Ltd.

[0178] [Research Period] 2023.01.01~2023.12.31.

Claims

1. A release film for lithium transfer, comprising a first release layer, a base film, and a second release layer sequentially stacked, characterized in that, The following condition (1) must be met: (1) In the condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

2. The release film for lithium transfer according to claim 1, characterized in that, Further satisfy the following condition (2): (2) A:B = 1:1.1~5.0 In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

3. The release film for lithium transfer according to claim 1, characterized in that, After lithium is deposited on one side of the second release layer with a thickness of 2 to 25 μm, when the first release layer is irradiated with white light, fewer than 100 pinholes are generated per unit area of ​​10 cm × 10 cm in the deposited lithium.

4. The release film for lithium transfer according to claim 3, characterized in that, After lithium is deposited on one side of the second release layer with a thickness of 2 to 8 μm, when the first release layer is irradiated with white light, fewer than 100 pinholes are generated per unit area of ​​10 cm × 10 cm in the deposited lithium.

5. The release film for lithium transfer according to claim 1, characterized in that, The second release layer comprises a resin composition. The resin composition comprises 10 to 70% by weight of silicone resin, based on the total weight percentage.

6. The release film for lithium transfer according to claim 5, characterized in that, The second release layer comprises, relative to 100 parts by weight of the resin composition, 0.1 to 5 parts by weight of a catalyst and 0.1 to 5 parts by weight of an adhesion enhancer.

7. The release film for lithium transfer according to claim 1, characterized in that, The first release layer comprises 2.2 to 25% silicon (Si) by weight. The second release layer comprises 2 to 5% by weight of silicon (Si) in total weight percentage.

8. The release film for lithium transfer according to claim 1, characterized in that, The base film includes one or more selected from polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyimide (PI), and polyethylene (PE).

9. The release film for lithium transfer according to claim 5, characterized in that, The resin composition includes silicone resins and non-silicone resins. The silicone resin includes one or more selected from addition-reaction silicone resins, condensation-reaction silicone resins, and UV-reaction silicone resins. The non-silicone resin includes one or more selected from cellulose resin, acrylate resin, melamine resin and alkyd resin. Includes the following steps:

10. A method for manufacturing a release film for lithium transfer, characterized in that, The first step is to prepare the base film; and The second step involves coating one side of the base film with a first release layer forming composition and coating the other side of the base film with a second release layer forming composition, followed by curing, thereby forming a first release layer on one side of the base film and a second release layer on the other side of the base film. The following condition (1) must be met: (1) A <B ​ In condition (1), A represents the release force of the first release layer and B represents the release force of the second release layer.

11. The method for manufacturing a release film for lithium transfer according to claim 10, characterized in that, Further satisfy the following condition (2): (1) A:B = 1:1.1~5.0 In condition (2), A represents the release force of the first release layer and B represents the release force of the second release layer.

12. The method for manufacturing a release film for lithium transfer according to claim 10, characterized in that, After lithium is deposited on one side of the second release layer with a thickness of 2 to 25 μm, when the first release layer is irradiated with white light, fewer than 100 pinholes are generated per unit area of ​​10 cm × 10 cm in the deposited lithium.

13. The method for manufacturing a release film for lithium transfer according to claim 10, characterized in that, The second release layer forming composition is a mixture of a resin composition, a catalyst, an adhesion enhancer, and a solvent. The resin composition comprises 10 to 70% by weight of silicone resin, based on the total weight percentage.

14. The method for manufacturing a release film for lithium transfer according to claim 13, characterized in that, The second release layer forming composition is composed of 0.1 to 5 parts by weight of catalyst, 0.1 to 5 parts by weight of adhesion enhancer and 800 to 1000 parts by weight of solvent, relative to 100 parts by weight of resin composition.

15. The method for manufacturing a release film for lithium transfer according to claim 10, characterized in that, The curing process is carried out at a temperature of 100–140°C for 10–40 seconds.

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