A dry method for recycling waste self-supporting membrane sheets / scraps

Abstract

The present invention belongs to the field of dry-process self-supporting membrane recycling and regeneration technology, and in particular discloses a dry-process self-supporting membrane waste / scraps recycling and regeneration method, the recycling and regeneration method comprising: collecting and classifying the waste or scraps cut off during the production process; splicing the waste membranes together, covering the splicing gaps or holes with waste membranes to form a splicing long strip, and then performing a first hot-pressing regeneration molding; folding the membrane formed by the first hot-pressing in half, performing a second regeneration hot-pressing; and finally performing step-by-step thinning molding. The present invention recycles waste membranes / scraps to form a self-supporting membrane, which to a certain extent reduces waste, improves the utilization rate of raw materials, and achieves a 100% utilization rate of the dry process self-supporting membrane. In addition, the regenerated membrane provided by the present invention has better processing performance and higher toughness. This method is simple in steps, efficient, green, and environmentally friendly, has strong industrial practicality, and can generate significant economic and environmental benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of battery preparation, and in particular to a dry process self-supporting film waste sheet / scraps recycling and regeneration method. Background Art

[0002] Wet and dry processes are the two mainstream technology paths for lithium battery front-end equipment. Compared to traditional wet processes, dry processes offer greater scalable application prospects in the manufacture of electrode membranes and electrolytes for semi-solid and all-solid-state batteries with high specific energy content. Dry film deposition technology has fewer steps in the manufacturing process and offers significant advantages over wet processes in terms of eliminating toxic solvents, reducing electrode delamination, shortening production lines, reducing equipment investment, lowering energy consumption, and lowering production costs. Furthermore, dry film deposition can achieve higher energy density and superior electrical and mechanical properties. For example, dry electrode technology can achieve higher compaction density: the compaction density of lithium iron phosphate can be increased from the current mainstream 2.30 g / cm³ to 3.05 g / cm³, an increase of over 30%. Ternary materials can also be increased from 3.34 g / cm³ to 3.62 g / cm³, an increase of over 8%. This means that the material contains more active material per unit volume, thereby increasing the energy density of the battery cell. It is reported that Tesla's dry electrode process can reduce production costs by 18%, shorten production line processes by 70%, and reduce equipment investment by 41%.

[0003] Currently, during the dry process for preparing membranes, the cut scraps are treated as waste. This not only reduces raw material utilization, but more importantly, wastes resources and increases the difficulty of recycling. This is also detrimental to environmental protection. In light of this, the present invention provides a simple, efficient, and economical dry process for recycling and reusing waste membranes, which has significant economic and environmental significance. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a dry process for recycling waste sheets / scraps of self-supporting films, which is used to improve the utilization rate of raw materials.

[0005] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A dry process for recycling waste self-supporting membrane sheets / scraps comprises the following steps:

[0007] (1) Collect the waste / scraps cut off during the dry film forming process;

[0008] (2) Splicing waste / scrap film into complete spliced long strips;

[0009] (3) hot pressing the long strips spliced in step (2) to form a regenerated film;

[0010] (4) The regenerated film in step (3) is thinned step by step, hot pressed, and trimmed to form a regenerated self-supporting film.

[0011] In the step (1), the waste / scraps of film are classified according to thickness. The purpose of this step is to avoid excessive local compaction of the film in the subsequent hot pressing step, which may cause local cracking, curling, and unevenness of the film. This step lays the foundation for the regeneration of good film in the subsequent steps.

[0012] In the step (1), the waste / scrap film sheets are collected in batches, and the consistency of the film sheets is good.

[0013] The step (2) of splicing into a complete spliced long strip includes the following steps: first, the waste / scraps of film with a larger area and similar thickness are preliminarily spliced into a primary strip, which is beneficial to reducing the gap area and gap rate between the film sheets and is more conducive to the formation of the film sheets.

[0014] The gaps, holes, and leaks in the primary strip are covered with small pieces of waste film of similar or smaller thickness, forming a complete overlap area, called a spliced long strip. This step is done to connect the film sheets together during the subsequent hot pressing process to form a complete overlap area, reducing the voids in the film during the hot pressing process and improving the film forming rate.

[0015] The step (3) of hot pressing and forming includes hot pressing once to form a primary regenerated film, and folding the film in half along the length direction and then hot pressing and forming again to form a secondary regenerated film.

[0016] The temperatures of the first hot pressing and the second hot pressing are both 100-180°C.

[0017] In the steps (2) and (3), the spliced long strips are conveyed by steel strips. Lithium-ion battery foils are not used. Lithium-ion battery foils such as copper foil and aluminum foil have a thickness of 6-15 μm and are generally ductile. They are prone to cracking and breaking during transmission and hot pressing.

[0018] The first hot pressing is performed at 50% to 90% of the maximum thickness to prevent the diaphragm from being over-pressed, thereby preventing cracks at the edges, center, and gaps of the diaphragm.

[0019] The second hot pressing is performed at 50%-90% of the total thickness. After folding in half, the second pressing is performed with virtually no gaps, greatly increasing the proportion of intact membranes. The thickness does not include the transport medium.

[0020] The secondary regenerated film is then subjected to step-by-step hot pressing and thinning to form a regenerated self-supporting film of target thickness.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention provides a method for recycling and regenerating dry waste membranes using physical methods. This method uses a simple physical method for recycling with a high recovery rate, avoids the use of chemical substances that pollute the environment, and does not produce secondary pollution.

[0023] 2. The present invention can also realize the recycling and reuse value of scrapped films, reduce costs to a certain extent, improve the utilization rate of raw materials, achieve 100% utilization of raw materials into diaphragms, and also generate certain economic benefits.

[0024] 3. The waste film sheets of the present invention are slit, rolled, and overlapped to form strips, and then rotated to form a transverse and longitudinal structure after one and two regeneration hot rolling, thereby forming an isotropic arrangement of polytetrafluoroethylene fibers. In this process, the strength of the film material is greatly improved, which is more conducive to automatic winding.

[0025] 4. In the primary and secondary regeneration processes of the present invention, the final original hot rolling direction is perpendicular to the hot rolling direction, which is more beneficial to the stability of the PTFE entanglement network structure and has an excellent three-dimensional conductive network.

[0026] 5. The entire process of the present invention is simple and efficient, has great potential for industrial promotion, and can generate greater economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 It is a flow chart of the steps of the present invention.

[0029] Figure 2 This is a photo of the once-regenerated membrane in Example 1.

[0030] Figure 3 This is a photo of the secondary regeneration membrane of Example 2.

[0031] Figure 4 This is a photo of the secondary regeneration membrane of Example 3.

[0032] Figure 5 This is a photo of the membrane after step-by-step thinning and cutting.

[0033] Figure 6This is a photo of the membrane regenerated by secondary hot pressing in comparative example 1.

[0034] Figure 7 This is a photo of the membrane regenerated by secondary hot pressing in comparative example 2.

[0035] Figure 8 This is a photo of the membrane regenerated by one-time hot pressing in comparative example 3.

[0036] Figure 9 Comparison of tensile strength between the regenerated diaphragm and the original diaphragm in Example. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a dry process for recycling waste self-supporting film sheets / scraps, comprising the following steps:

[0040] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0041] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0042] The spliced long strip is subjected to the first hot pressing molding at 90% of the maximum thickness at a hot pressing temperature of 150°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is subjected to the second hot pressing molding at 50% of the total thickness at a hot pressing temperature of 150°C to form a secondary regenerated film;

[0043] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0044] Example 2

[0045] This embodiment provides a dry-process self-supporting film waste sheet / scraps recycling and regeneration method. The difference from Example 1 is that the first hot pressing is performed at 50% of the maximum thickness to form a primary regenerated film; after being folded in half, the film is hot pressed again for a second time at 50% of the total thickness to form a secondary regenerated film; the remaining steps are the same.

[0046] The specific steps are as follows:

[0047] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0048] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0049] The spliced long strip is subjected to the first hot pressing molding at 50% of the maximum thickness at a hot pressing temperature of 150°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is subjected to the second hot pressing molding at 50% of the total thickness at a hot pressing temperature of 150°C to form a secondary regenerated film;

[0050] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0051] Example 3

[0052] This embodiment provides a dry-process self-supporting film waste sheet / scraps recycling and regeneration method. The difference from Example 1 is that the first hot pressing is performed at 50% of the maximum thickness to form a primary regenerated film; after being folded in half, the film is hot pressed again for a second time at 90% of the total thickness to form a secondary regenerated film, and the remaining steps are the same.

[0053] The specific steps are as follows:

[0054] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0055] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0056] The spliced long strip is first hot-pressed at 50% of the maximum thickness at a temperature of 150°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is again hot-pressed at 90% of the total thickness at a temperature of 150°C to form a secondary regenerated film;

[0057] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0058] Example 4

[0059] This embodiment provides a dry process for recycling waste self-supporting film sheets / scraps, and the specific steps are as follows:

[0060] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0061] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0062] The spliced long strip is subjected to the first hot pressing molding at 80% of the maximum thickness at a hot pressing temperature of 180°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is subjected to the second hot pressing molding at 50% of the total thickness at a hot pressing temperature of 100°C to form a secondary regenerated film;

[0063] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0064] Example 5

[0065] This embodiment provides a dry process for recycling waste self-supporting film sheets / scraps, and the specific steps are as follows:

[0066] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0067] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0068] The spliced long strip is first hot-pressed at 60% of the maximum thickness at a temperature of 100°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is again hot-pressed at 80% of the total thickness at a temperature of 170°C to form a secondary regenerated film;

[0069] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0070] Example 6

[0071] This embodiment provides a dry process for recycling waste self-supporting film sheets / scraps, and the specific steps are as follows:

[0072] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0073] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0074] The spliced long strip is first hot-pressed at 80% of the maximum thickness at a temperature of 180°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is again hot-pressed at 60% of the total thickness at a temperature of 150°C to form a secondary regenerated film;

[0075] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0076] Comparative Example 1

[0077] This comparative example provides a dry-process self-supporting film waste sheet / scraps recycling and regeneration method. The difference from Example 1 is that the first hot pressing is performed at 90% of the maximum thickness to form a primary regenerated film; after being folded in half, the film is hot pressed again for a second time at 45% of the total thickness to form a secondary regenerated film, and the remaining steps are the same.

[0078] The specific steps are as follows:

[0079] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0080] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0081] The spliced long strip is subjected to the first hot pressing molding at 90% of the maximum thickness at a hot pressing temperature of 150°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is subjected to the second hot pressing molding at 45% of the total thickness at a hot pressing temperature of 150°C to form a secondary regenerated film;

[0082] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0083] Comparative Example 2

[0084] This comparative example provides a dry-process self-supporting film waste sheet / scraps recycling and regeneration method. The difference from Example 2 is that the first hot pressing is performed at 50% of the maximum thickness to form a primary regenerated film; after being folded in half, the film is hot pressed again for a second time at 45% of the total thickness to form a secondary regenerated film, and the remaining steps are the same.

[0085] The specific steps are as follows:

[0086] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0087] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0088] The spliced long strip is first hot-pressed at 50% of the maximum thickness at a temperature of 150°C to form a primary regenerated film; the primary regenerated film is folded in half along the length direction, and after the folding, the film is again hot-pressed at 45% of the total thickness at a temperature of 150°C to form a secondary regenerated film;

[0089] Finally, the secondary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0090] Comparative Example 3

[0091] This comparative example provides a dry process for recycling waste self-supporting film sheets / scraps. The difference from Example 3 is that the first hot pressing is performed at 45% of the maximum thickness and the hot pressing temperature is 150°C to form a regenerated film.

[0092] The specific steps are as follows:

[0093] Taking the scraps of ternary material NCM811 dry process waste membrane as an example, the scraps are collected and preliminarily classified according to thickness;

[0094] The membrane sheets with larger area and similar thickness are preliminarily spliced together to form a splicing strip. The gaps, holes and leaks in the splicing strip are covered with small-area waste membrane sheets of similar or smaller thickness to form a complete overlapping area, which is called a splicing long strip.

[0095] The spliced long strip is hot-pressed for the first time at 45% of the maximum thickness at a temperature of 150°C to form a regenerated film;

[0096] Finally, the primary regenerated membrane is thinned step by step and hot-pressed to form a regenerated self-supporting membrane.

[0097] The membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively as follows Figures 2 to 7 As shown, Figure 2 In Example 1, after one regeneration hot pressing, the diaphragms did not move, and there were no gaps between the diaphragms. The diaphragms were slightly hot pressed. Figure 3 The morphology of the membrane after the second regeneration hot pressing in Example 2 is complete, the appearance of the membrane is uniform and the surface is flat; Figure 4 The morphology of the membrane after secondary regeneration and hot pressing in Example 3 is shown in Figure 3. Figure 3 similar; Figure 5 The membrane formed by step-by-step thinning in Example 3 has a smooth and uniform surface without any defects such as depressions. Figure 6 In Comparative Example 1, the diaphragm was partially over-compacted, the surface of the diaphragm was shiny, the morphology was distorted, uneven, and could not be wound into shape; Figure 7 For the diaphragm in comparative example 2, Figure 6 Similar appearance; Figure 8 In Comparative Example 3, the diaphragms are partially separated due to uneven stress, and separation occurs between the diaphragms;

[0098] Figure 9 To compare the tensile strength of the regenerated membranes in the examples with that of the original membranes, the tensile test was conducted according to the test standard GB / T 36363-2018 for polyolefin separators for lithium-ion batteries. The specimen length was 60 mm, the gauge length was 50 mm, the width was 15 mm, and the thickness was 155 ± 3 μm. The maximum tensile strength and productivity of the regenerated membranes prepared in Examples 1-3 were both greater than those of the unregenerated membranes. This is because the waste membranes were slit, rolled, and spliced into strips, and then subjected to primary and secondary hot rolling to form a partially rotated longitudinal structure, resulting in an isotropic arrangement of the polytetrafluoroethylene fibers. This process significantly improved the strength and toughness of the membranes.

[0099] The above embodiments of the present invention are intended to serve as a guide. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical spirit of the present invention. The technical scope of the present invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A dry process for recycling waste self-supporting membrane sheets / scraps, characterized in that: The steps include: (1) Collect and classify the waste / scraps cut off during the dry film forming process; (2) Splicing the waste / scraps into a complete spliced long strip; specifically, the following steps are involved: first, the waste / scraps with a larger area and similar thickness are preliminarily spliced into a primary strip; the gaps, holes, and holes in the primary strip are covered with small-area waste films with similar or smaller thickness to form a complete overlap area, which is called a spliced long strip; (3) hot pressing the long strips spliced in step (2) to form a regenerated film; The hot pressing forming includes a first hot pressing forming a primary regenerated film, and a second hot pressing forming forming after folding in half along the length direction to form a secondary regenerated film; The temperature of the first hot pressing and the second hot pressing is 100-180°C; The first hot pressing is performed at 50%-90% of the maximum thickness; the second hot pressing is performed at 50%-90% of the total thickness; (4) thinning the regenerated film in step (3) step by step, hot pressing, trimming and forming, and finally forming a regenerated self-supporting film; The membrane in step (1) is a dry-process self-supporting membrane for the positive electrode of a lithium battery or a dry-process self-supporting membrane for the negative electrode of a lithium battery; In the step (1), the waste / scrap film sheets are classified according to thickness.

2. The dry process for recycling waste self-supporting membrane sheets / scraps according to claim 1, characterized in that: In the step (1), the waste / scrap film sheets are collected and classified according to batches.

3. The dry process for recycling waste self-supporting membrane sheets / scraps according to claim 1, characterized in that: In the steps (2) and (3), the spliced long strips are transported by steel strips; the thickness does not include the transport medium.

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