An aluminum-plastic composite film, its preparation method and application

Abstract

This invention provides an aluminum-plastic composite film, its preparation method, and its application. The aluminum-plastic composite film includes a nylon layer, an aluminum foil layer, an absorbent layer, and a polypropylene layer. The raw materials for preparing the absorbent layer, by weight, include: 50-60 parts of polyethylene wax emulsion, 5-10 parts of waterborne epoxy resin, 0.5-2 parts of amine curing agent, 0.5-2 parts of silane coupling agent, and 20-30 parts of water. The absorbent layer is positioned between the aluminum foil layer and the polypropylene layer. Using polyethylene wax emulsion as the main material, the absorbent layer exhibits relatively flexible and soft properties. Simultaneously, the waterborne epoxy resin and amine curing agent, after thermosetting, form a network structure. During the stamping process, the absorbent layer effectively absorbs the impact force on the polypropylene layer, thereby improving the toughness of the aluminum-plastic composite film and mitigating the whitening problem of the polypropylene layer after deep stamping. Furthermore, the softness and low-temperature properties of the absorbent layer reduce the encapsulation temperature, and the epoxy resin network structure further enhances the electrolyte resistance.

Description

Technical Field

[0001] This invention relates to the field of flexible packaging technology for batteries, and more particularly to an aluminum-plastic composite film, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, as a crucial component of new energy systems, are widely used in digital products, transportation, military applications, and energy storage, especially in the new energy vehicle industry. Their packaging film, as the flexible packaging material, plays a vital role in the battery's performance and safety. Currently, aluminum-plastic composite film is the primary flexible packaging film for lithium-ion batteries, and its structure includes a nylon layer, an aluminum foil layer, and a polypropylene film. However, this type of aluminum-plastic composite film is subjected to high-intensity impacts during the stamping process. Due to its high crystallinity, the polypropylene film is prone to whitening under stress. Simultaneously, both the polypropylene film and the aluminum foil layer are susceptible to localized micro-cracks, thus affecting the lifespan and performance of the aluminum-plastic composite film.

[0003] Therefore, developing an aluminum-plastic composite film with excellent impact resistance to improve the whitening caused by deep drawing is of great significance for improving the safety and stability of lithium-ion batteries. Summary of the Invention

[0004] In view of the above problems, the purpose of this invention is to provide an aluminum-plastic composite film that can improve the whitening caused by deep drawing and achieve excellent impact resistance.

[0005] To achieve the above objectives, the present invention provides an aluminum-plastic composite film, comprising:

[0006] An aluminum foil layer having a matte and a glossy finish;

[0007] A nylon layer disposed on the matte surface;

[0008] The absorbent layer and the polypropylene layer are sequentially disposed on the glossy surface. The raw materials for preparing the absorbent layer, by weight, include:

[0009] The composition consists of 50-60 parts polyethylene wax emulsion, 5-10 parts water-based epoxy resin, 0.5-2 parts amine curing agent, 0.5-2 parts silane coupling agent, and 20-30 parts water. The polyethylene wax emulsion is made of low-density polyethylene.

[0010] Compared with existing technologies, the aluminum-plastic composite film of the present invention comprises a nylon layer, an aluminum foil layer, an absorbent layer, and a polypropylene layer. An absorbent layer is added between the aluminum foil layer and the polypropylene layer. The absorbent layer is prepared from materials comprising 50-60 parts of polyethylene wax emulsion, 5-10 parts of waterborne epoxy resin, 0.5-2 parts of amine curing agent, 0.5-2 parts of silane coupling agent, and 20-30 parts of water. Using polyethylene wax emulsion as the main material, the absorbent layer exhibits relatively flexible and soft properties. Simultaneously, the waterborne epoxy resin and amine curing agent are thermally cured during drying to form a network structure in the absorbent layer. Through hot pressing, the aluminum foil layer, absorbent layer, and polypropylene layer are effectively bonded together. During the die-cutting process, the absorbent layer can effectively absorb the impact force on the polypropylene layer, improving the toughness of the aluminum-plastic composite film and mitigating the whitening problem of the polypropylene layer after deep die-cutting. Furthermore, the softness and low-temperature properties of the absorbent layer can reduce the encapsulation temperature, and the epoxy resin network structure further contributes to improved electrolyte resistance.

[0011] In some preferred embodiments, the content of polyethylene wax emulsion may be, but is not limited to, 50 parts, 52 parts, 54 parts, 56 parts, 58 parts, or 60 parts; the content of waterborne epoxy resin may be, but is not limited to, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts; the content of amine curing agent may be, but is not limited to, 0.5 parts, 1 part, 1.5 parts, or 2 parts; the content of silane coupling agent may be, but is not limited to, 0.5 parts, 1 part, 1.5 parts, or 2 parts; and the content of water may be, but is not limited to, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, or 30 parts.

[0012] In some preferred embodiments, the polyethylene wax emulsion is made of low-density polyethylene with a density ranging from 0.910 to 0.925 g / cm³. 3 Preferably, the polyethylene wax emulsion is low-density polyethylene with a solid content of 30-50%.

[0013] In some preferred embodiments, the melting point of the polyethylene wax emulsion is between 110 and 135°C.

[0014] In some preferred embodiments, the pH value of the polyethylene wax emulsion is 7 to 9.

[0015] In some preferred embodiments, the amine curing agent is selected from at least one of triethanolamine and N,N-dimethylethanolamine.

[0016] In some preferred embodiments, the epoxy equivalent of the waterborne epoxy resin is 400-800 g / eq.

[0017] In some preferred embodiments, the silane coupling agent is selected from at least one of γ-glycidoxypropyltrimethoxysilane (KH560) and γ-aminopropyltriethoxysilane (KH550).

[0018] In some preferred embodiments, the preparation steps of the absorber layer are as follows:

[0019] The polyethylene wax emulsion, the water-based epoxy resin, and a portion of water are added to a mixing tank and stirred.

[0020] The silane coupling agent and the remaining water are added to the mixing tank and stirred.

[0021] The amine curing agent is added while stirring, and the mixture is stirred evenly to obtain the coating liquid;

[0022] The coating liquid is applied to the glossy side of the aluminum foil layer and dried to form the absorbent layer.

[0023] In some preferred embodiments, the drying temperature is 90–130°C. Optionally, the drying temperature is 100–130°C, 110–130°C, or 90–120°C. As an example, the drying temperature may be, but is not limited to, 90°C, 100°C, 110°C, 120°C, or 130°C. Below this temperature, the reaction between the epoxy resin and the amine curing agent fails to be effectively cured, and the whitening problem during extrusion cannot be improved; above this temperature, energy consumption is too high, resulting in higher costs.

[0024] In some preferred embodiments, the coating amount of the coating liquid is 10-15 g / m². 2 Optionally, approximately 12–15 g / m 2 10~13g / m 2 As an example, the coating amount of the coating liquid can be, but is not limited to, 10 g / m². 2 11g / m 2 12g / m 2 13g / m 2 14g / m 2 15g / m 2 When the coating amount of the coating liquid is too low, the improvement is not obvious.

[0025] Accordingly, the present invention also provides a method for preparing an aluminum-plastic composite film, comprising the following steps:

[0026] (1) Provide aluminum foil;

[0027] (2) The raw material for preparing the absorbent layer is coated on the bright side of the aluminum foil, dried and shaped to obtain the absorbent layer;

[0028] (3) A polypropylene layer is laminated onto the surface of the absorbent layer;

[0029] (4) Lay a nylon layer onto the matte surface of the aluminum foil;

[0030] (5) Baking and molding to obtain aluminum-plastic composite film.

[0031] Furthermore, the present invention also provides an application of this aluminum-plastic composite film in lithium-ion batteries, which can effectively improve the safety performance of lithium-ion batteries. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the aluminum-plastic composite film of the present invention.

[0033] Figure 2 The aluminum-plastic composite film of Example 1 is shown after the shell-punching process.

[0034] Figure 3 This shows the aluminum-plastic composite film of Comparative Example 1 after the shell-punching process.

[0035] Figure 4 This shows the aluminum-plastic composite film of Comparative Example 2 after the shell-punching process. Detailed Implementation

[0036] The following are preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the protection scope of the present invention.

[0037] Please refer to Figure 1 This invention provides an aluminum-plastic composite film, comprising a nylon layer 10, an aluminum foil layer 20, an absorbent layer 30, and a polypropylene layer 40. The aluminum foil layer 20 has a matte surface and a glossy surface. The nylon layer 10 is disposed on the matte surface of the aluminum foil layer 20, and the absorbent layer 30 and the polypropylene layer 40 are sequentially disposed on the glossy surface of the aluminum foil layer 20. The absorbent layer 30 is formed by coating the raw material for preparing the absorbent layer 30 onto the glossy surface of the aluminum foil layer 20 and drying it.

[0038] The following description uses several specific embodiments, but these are not intended to limit the scope of protection of the present invention.

[0039] Example 1

[0040] A method for preparing an aluminum-plastic composite film includes the following steps:

[0041] I. Preparation of the coating solution, using the raw materials for the absorbent layer, includes the following steps:

[0042] Add 50 parts of polyethylene wax emulsion (model DM-3130N, low-density polyethylene, melting point 110℃), 5 parts of waterborne epoxy resin (model E0430, epoxy equivalent of 500g / eq) and 15 parts of water to a mixing tank and stir.

[0043] Add 0.5 parts of silane coupling agent (KH560) and 15 parts of water to a mixing tank, and stir at a speed of 150-400 rpm and a temperature of 30-40℃ until the mixture is homogeneous.

[0044] While stirring, add 0.5 parts of N,N-dimethylethanolamine and stir until homogeneous to obtain the coating solution;

[0045] II. Preparation of Aluminum-Plastic Composite Film

[0046] (1) Provide aluminum foil;

[0047] (2) A coating liquid is applied to the bright surface of the aluminum foil, with a coating amount of 10 g / m². 2 The absorbent layer is obtained by drying at 90°C.

[0048] (3) The polypropylene layer is hot-pressed with the absorbent layer at 160°C.

[0049] (4) Apply polyurethane adhesive to the matte surface of the aluminum foil, and then laminate it with a nylon layer;

[0050] (5) The aluminum-plastic composite film was obtained by baking at 60℃ for 3 days.

[0051] Example 2

[0052] Example 2 is basically the same as Example 1, except that the coating amount of the coating liquid in Example 2 is 15 g / m³. 2 In Example 1, the coating amount of the coating liquid was 10 g / m². 2 The rest is the same as in Example 1, and will not be described again here.

[0053] Example 3

[0054] A method for preparing an aluminum-plastic composite film includes the following steps:

[0055] I. Preparation of the coating solution, using the raw materials for the absorbent layer, includes the following steps:

[0056] Add 60 parts of polyethylene wax emulsion (model DM-3130N, low-density polyethylene, melting point 110℃), 7 parts of waterborne epoxy resin (model E0430, epoxy equivalent of 500g / eq) and 10 parts of water to a mixing tank and stir.

[0057] Add 1 part of silane coupling agent (KH560) and 10 parts of water to a mixing tank, and stir at a speed of 150-400 rpm and a temperature of 30-40℃ until the mixture is homogeneous.

[0058] While stirring, add 1 part of N,N-dimethylethanolamine and stir until homogeneous to obtain the coating solution;

[0059] II. Preparation of Aluminum-Plastic Composite Film

[0060] (1) Provide aluminum foil;

[0061] (2) A coating liquid is applied to the bright surface of the aluminum foil, with a coating amount of 12 g / m². 2 The absorbent layer is obtained by drying at 100°C.

[0062] (3) The polypropylene layer is hot-pressed with the absorbent layer at 160°C.

[0063] (4) Apply polyurethane adhesive to the matte surface of the aluminum foil, and then laminate it with a nylon layer;

[0064] (5) The aluminum-plastic composite film was obtained by baking at 60℃ for 3 days.

[0065] Example 4

[0066] A method for preparing an aluminum-plastic composite film includes the following steps:

[0067] I. Preparation of the coating solution, using the raw materials for the absorbent layer, includes the following steps:

[0068] Add 55 parts of polyethylene wax emulsion (model DM-3130N, low-density polyethylene, melting point 110℃), 10 parts of waterborne epoxy resin (model E0430, epoxy equivalent of 500g / eq) and 13 parts of water to a mixing tank and stir.

[0069] Add 2 parts of silane coupling agent (KH560) and 12 parts of water to a mixing tank, and stir at a speed of 150-400 rpm and a temperature of 30-40℃ until the mixture is homogeneous.

[0070] While stirring, add 2 parts of N,N-dimethylethanolamine and stir until homogeneous to obtain the coating solution;

[0071] II. Preparation of Aluminum-Plastic Composite Film

[0072] (1) Provide aluminum foil;

[0073] (2) A coating liquid is applied to the bright surface of the aluminum foil, with a coating amount of 14 g / m². 2 The absorbent layer is obtained by drying at 120°C.

[0074] (3) The polypropylene layer is hot-pressed with the absorbent layer at 160°C.

[0075] (4) Apply polyurethane adhesive to the matte surface of the aluminum foil, and then laminate it with a nylon layer;

[0076] (5) The aluminum-plastic composite film was obtained by baking at 60℃ for 3 days.

[0077] Example 5

[0078] A method for preparing an aluminum-plastic composite film includes the following steps:

[0079] I. Preparation of the coating solution, using the raw materials for the absorbent layer, includes the following steps:

[0080] Add 50 parts of polyethylene wax emulsion (model DM-X20, low-density polyethylene, melting point 112℃), 5 parts of waterborne epoxy resin (model E0430, epoxy equivalent of 500g / eq) and 15 parts of water to a mixing tank and stir.

[0081] Add 0.5 parts of silane coupling agent (KH550) and 15 parts of water to a mixing tank, and stir at a speed of 150-400 rpm and a temperature of 30-40℃ until the mixture is homogeneous.

[0082] While stirring, add 0.5 parts of N,N-dimethylethanolamine and stir until homogeneous to obtain the coating solution;

[0083] II. Preparation of Aluminum-Plastic Composite Film

[0084] (1) Provide aluminum foil;

[0085] (2) A coating liquid is applied to the bright surface of the aluminum foil, with a coating amount of 12 g / m². 2 The absorbent layer is obtained by drying at 90°C.

[0086] (3) The polypropylene layer is hot-pressed with the absorbent layer at 160°C.

[0087] (4) Apply polyurethane adhesive to the matte surface of the aluminum foil, and then laminate it with a nylon layer;

[0088] (5) The aluminum-plastic composite film was obtained by baking at 60℃ for 3 days.

[0089] Comparative Example 1

[0090] This comparative example does not use an absorption layer, but is otherwise the same as Example 1, as follows:

[0091] A method for preparing an aluminum-plastic composite film includes the following steps:

[0092] (1) Provide aluminum foil;

[0093] (2) The polypropylene layer is hot-pressed with the bright side of the aluminum foil at 160°C.

[0094] (3) Apply polyurethane adhesive to the matte surface of the aluminum foil, and then laminate it with a nylon layer;

[0095] (4) The aluminum-plastic composite film was obtained by baking at 60℃ for 3 days.

[0096] Comparative Example 2

[0097] Comparative Example 2 is basically the same as Example 1, except that the coating amount of the coating liquid in Comparative Example 2 is 8 g / m². 2 In Example 1, the coating amount of the coating liquid was 15 g / m². 2 The rest is the same as in Example 1, and will not be described again here.

[0098] Comparative Example 3

[0099] The method of Comparative Example 3 is basically the same as that of Example 1, except that the content of waterborne epoxy resin (model E0430) in Comparative Example 3 is 2 parts, while the content of waterborne epoxy resin (model E0430) in Example 1 is 5 parts. The rest is the same as that of Example 1, and will not be described here.

[0100] Comparative Example 4

[0101] The method of Comparative Example 4 is basically the same as that of Example 1, except that the drying temperature in Comparative Example 4 is 80°C, while the drying temperature in Example 1 is 90°C. The rest is the same as that of Example 1 and will not be described here.

[0102] Comparative Example 5

[0103] The comparative example is basically the same as the method in Example 1. The difference is that the polyethylene wax emulsion in Comparative Example 5 is DM-9240 (high-density polyethylene, melting point 138°C), while the polyethylene wax emulsion in Example 1 is DM-3130N (low-density polyethylene, melting point 110°C). The rest is the same as in Example 1 and will not be described here.

[0104] The performance of the aluminum-plastic composite films prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

[0105] The test items and methods are as follows:

[0106] Deep Drawing Whitening Test Method

[0107] The aluminum-plastic composite film was cut into samples with a length and width of 70*120mm. The punching mold core had a diameter of 18mm, a length of 35mm, and a punching depth of 8.0mm. After punching, the whitening degree of the sample surface was observed. + indicates slight whitening degree, ++ indicates moderate whitening degree, and +++ indicates severe whitening degree. As + increases, the whitening degree gradually becomes more severe.

[0108] Please refer to Figure 2 This demonstrates the condition of the aluminum-plastic composite film of Example 1 after the shell-punching process. Figure 2 It can be seen that the aluminum-plastic composite film of Example 1 has a slight whitening degree after punching (+).

[0109] Please refer to Figure 3 This demonstrates the condition of the aluminum-plastic composite film in Comparative Example 1 after the stamping process. Figure 3 It can be seen that the aluminum-plastic composite film of Comparative Example 1 is severely whitened after being punched (+++).

[0110] Please refer to Figure 4 This demonstrates the condition of the aluminum-plastic composite film in Comparative Example 2 after the stamping process. Figure 4 It can be seen that the aluminum-plastic composite film of Comparative Example 2 has the second-highest degree of whitening after being punched (++).

[0111] Heat seal strength

[0112] The heat-sealing strength of the aluminum-plastic composite film after it has been made is tested according to QB-T 2358-1998 Test Method for Heat Sealing Strength of Plastic Film Packaging Bags. The greater the strength, the better the heat-sealing effect of the product.

[0113] Electrolyte resistance

[0114] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate are mixed in a molar ratio of 1:1:1. Lithium hexafluorophosphate is then added to the mixture to prepare a solution with a lithium hexafluorophosphate concentration of 1.0 mol / L. The electrolyte is prepared with a free acid content of no more than 50 parts per million.

[0115] Cut the aluminum-plastic composite film into samples with a length and width of 15mm*200mm. Place the aluminum-plastic composite film samples into a container, add a known weight of electrolyte and 1% water, seal and shake well. Place it in an 85℃ oven to bake for 1 day, then take it out and let it cool naturally to room temperature. Take out each sample, wipe it clean, and immediately test the peel strength between CPP and aluminum foil, which is the electrolyte resistance performance.

[0116] Drawing depth

[0117] The aluminum-plastic composite film was cut into samples measuring 70*120mm. A punching machine was used to punch the samples, with a punching core diameter of 18mm and a length of 35mm. The punching depth was set to Xmm. Forty samples were punched consecutively. In a darkroom, a strong flashlight was used to observe the holes for light transmission to determine if there was any damage. If no damage was found, the depth was increased by 0.2mm from Xmm. If damage occurred probabilistically at Xmm, the depth was decreased by 0.2mm from Xmm. This process of punching depth and observing damage was continued. The final punching depth H was determined by a point where no damage occurred, and a probabilistic damage occurred at a 0.2mm increase. This point of no damage was taken as the final punching depth.

[0118] Table 1 Results of each performance test

[0119]

[0120] As shown in Table 1, compared to Comparative Example 1, the aluminum-plastic composite films in Examples 1-4 exhibit more severe whitening after punching, while the samples in Examples 1-4 show only slight whitening. This is likely because the absorbent layer improves the toughness of the aluminum-plastic composite film, thus mitigating the whitening problem of the polypropylene layer after deep punching. Furthermore, the aluminum-plastic composite films in Examples 1-4 also demonstrate superior electrolyte resistance, heat-sealing strength, and punching depth. This is likely because the absorbent layer forms an epoxy resin network structure, contributing to improved electrolyte resistance. In particular, the aluminum-plastic composite films in Examples 1-4 exhibit high heat-sealing strength even at a relatively low encapsulation temperature of 160°C. This indicates that the absorbent layer can lower the encapsulation temperature, achieving low-temperature encapsulation and reducing energy consumption and cost.

[0121] The data from Comparative Example 2 show that when the coating amount of the coating liquid is relatively small, the degree of whitening during deep drawing is improved compared to Comparative Example 1, but it is still worse than that of Example 1, and the electrolyte resistance is significantly reduced.

[0122] The data from Comparative Example 3 show that when the content of waterborne epoxy resin is insufficient, a dense network structure cannot be formed during the film-forming curing and hot-pressing process, and it does not play a significant role. Compared with Comparative Example 1, the degree of whitening during deep drawing is slightly improved, but it is still worse than Example 1. Furthermore, the low-temperature heat-sealing strength and electrolyte resistance are significantly reduced.

[0123] The data from Comparative Example 4 shows that the baking and drying temperature of the absorbent layer was too low, which prevented the reaction between the water-based epoxy resin and the amine curing agent from being effectively cured. This resulted in an additional loose structure between the aluminum foil layer and the polypropylene layer (CPP film), affecting the heat sealability and electrolyte resistance, and also failing to improve the whitening problem during the molding process.

[0124] As can be seen from the data of Comparative Example 5, because the main material of the absorbent layer is high-density polyethylene with a high melting point, it failed to achieve a good fusion effect with the aluminum foil and polypropylene film. At the same time, its flexibility was also slightly poor, which was equivalent to adding a loose structure between the aluminum foil layer and the polypropylene layer (CPP film), affecting the heat sealability and electrolyte resistance, and also failing to improve the whitening problem of the casing.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An aluminum-plastic composite film, characterized in that, include: An aluminum foil layer having a matte and a glossy finish; A nylon layer disposed on the matte surface; An absorbent layer and a polypropylene layer are sequentially disposed on the glossy surface. The absorbent layer comprises an epoxy resin network structure. The raw materials for preparing the absorbent layer, by weight, include: The composition comprises 50-60 parts polyethylene wax emulsion, 5-10 parts waterborne epoxy resin, 0.5-2 parts amine curing agent, 0.5-2 parts silane coupling agent, and 20-30 parts water, wherein the polyethylene wax emulsion is a low-density polyethylene wax emulsion. The preparation steps of the absorption layer are as follows: The polyethylene wax emulsion, the water-based epoxy resin, and a portion of water are added to a mixing tank and stirred. The silane coupling agent and the remaining water are added to the mixing tank and stirred. The amine curing agent is added while stirring, and the mixture is stirred evenly to obtain the coating liquid; The coating liquid is applied to the glossy side of the aluminum foil layer, and then dried to form the absorbent layer. The drying temperature is 90~130℃, and the coating amount of the coating liquid is 10~15g / m². 2 .

2. The aluminum-plastic composite film according to claim 1, characterized in that, The polyethylene wax emulsion is a low-density polyethylene wax emulsion with a solid content of 30-50%, and the melting point of the low-density polyethylene wax is 110-135℃.

3. The aluminum-plastic composite film according to claim 1, characterized in that, The pH value of the polyethylene wax emulsion is 7-9.

4. The aluminum-plastic composite film according to claim 1, characterized in that, The epoxy equivalent of the waterborne epoxy resin is 400-800 g / eq.

5. The aluminum-plastic composite film according to claim 1, characterized in that, The amine curing agent is selected from at least one of triethanolamine and N,N-dimethylethanolamine.

6. A method for preparing an aluminum-plastic composite film as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Provide aluminum foil; (2) The raw material for preparing the absorbent layer is coated on the bright side of the aluminum foil, dried and shaped to obtain the absorbent layer; (3) A polypropylene layer is laminated onto the surface of the absorbent layer; (4) Lay a nylon layer onto the matte surface of the aluminum foil; (5) Baking and molding to obtain aluminum-plastic composite film.

7. The application of an aluminum-plastic composite film prepared by any one of claims 1-5 or by the method of preparing an aluminum-plastic composite film as described in claim 6 in a lithium-ion battery.

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