Polyester functional masterbatch for composite current collector and its preparation method

Abstract

The present invention discloses a polyester functional masterbatch for a composite current collector and a preparation method thereof. The composite current collector is composed of a base material layer and conductive layers attached to both sides of the base material layer. The base material layer is made of a polyester film added with the polyester functional masterbatch. Among them, the polyester functional masterbatch is prepared from raw materials including the following parts by weight: 30-50 parts by weight of poly(m-phthaloyldiamine), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silicon dioxide, and 50-100 parts by weight of PET. The polyester film prepared by adding the polyester functional masterbatch of the present application has greatly improved properties such as porosity, water absorption rate, and oxygen transmission rate. Moreover, no obvious crack propagation is observed after forming the metal conductive layer, and the structures on both sides thereof have more excellent consistency.

Description

Technical Field

[0001] The present application relates to a composite current collector in the field of energy storage technology, and particularly to a polyester functional masterbatch for a composite current collector and a preparation method thereof. Background Art

[0002] The current collector is an important component of a lithium battery and is usually composed of a metal foil film. During the charge and discharge process of a lithium-ion battery, lithium ions in the electrolyte move back and forth between the positive and negative electrodes. The current collector, as an inactive component in the battery, does not contribute energy. Its main function is to carry the electrode materials of the positive and negative electrodes, and at the same time collect current and conduct electrons. In order to improve the energy density of the battery, it is necessary to reduce the thickness and weight of the current collector as much as possible, thereby reducing the volume and weight of the battery. The common positive current collector uses aluminum foil, which has been reduced from 16 μm a few years ago to 10 μm. The common negative current collector uses copper foil, which has also been reduced from 12 μm before to 6 μm. However, too thin a metal current collector has great problems in mechanical strength. Since the electrode material is coated on the current collector, the metal foil film requires relatively good ductility and strength, otherwise it is easily broken. In addition, the production of ultra-thin metal current collectors also increases costs. Therefore, there has emerged in the prior art a composite current collector with a non-metallic insulating material as the substrate and conductive layers formed on both sides thereof.

[0003] For example, CN 110165223 A discloses a current collector, a pole piece, a battery and a method for manufacturing a current collector. This prior art points out that after the conductive layer is formed on the insulating layer of the composite current collector, during the subsequent cold pressing process, due to the different cold pressing elongation rates of the insulating layer and the conductive layer, the situation of separation between the conductive layer and the insulating layer is likely to occur, reducing the use stability of the current collector. In addition, the conductive layers on both sides of the insulating layer are usually arranged separately, resulting in a relatively large resistance of the current collector. Therefore, the composite current collector of this prior art has a plurality of through holes formed in the insulating layer; the conductive layer includes a first conductive layer, a second conductive layer and a connecting layer connecting the first conductive layer and the second conductive layer. The first conductive layer and the second conductive layer are arranged on opposite sides of the insulating layer, and the connecting layer is arranged on the inner wall surface of the through hole. Such a design enables the conductive layer to wrap around the insulating layer, which can alleviate the situation where the conductive layer completely detaches from the insulating layer. In addition, since the connecting layer is part of the conductive layer and the connecting layer also has conductivity, by connecting the first conductive layer and the second conductive layer on opposite sides of the insulating layer through the connecting layer, the resistance of the current collector can be reduced.

[0004] The solutions proposed by the above-mentioned prior art only alleviate the situation where the conductive layer completely detaches from the insulating layer. The fundamental reason is that the surface structure of the insulating layer is uneven, resulting in insufficient adhesion of the conductive layer to the insulating layer. Taking the formation of the conductive layer by vacuum sputtering process as an example, since the thickness of the insulating layer made of polymer material is very thin and it is difficult to withstand long-term high-temperature sputtering, it is necessary to sputter while winding and moving. Therefore, the thickness of the conductive layer that can be formed on the surface of the insulating layer in each sputtering chamber is very limited. To reach the required thickness of the conductive layer, it needs to be formed by layer-by-layer stacking through the bombardment of the target material in different chambers, and it may even be necessary to repeatedly sputter the insulating layer coil in the equipment multiple times. At this time, once the surface performance of the insulating layer is poor, the surface differences of the conductive layers sputtered in each chamber will be gradually amplified, and it is very easy to delaminate after multiple stackings, resulting in the phenomenon of peeling and powdering of the stacked layers during subsequent processing.

[0005] In addition, the surface performance of the current collector also has a great impact on the production and performance of the battery. This is because the structural differences on both sides of the current collector lead to asymmetric contact resistances of the coatings on both sides, thereby causing the capacities on both sides to be unable to be released evenly; at the same time, the asymmetry on both sides also leads to inconsistent coating adhesion strengths, resulting in a serious imbalance in the charge-discharge cycle lives of the coatings on both sides, and thus accelerating the attenuation of the battery capacity. This is also closely related to whether the surface structure of the underlying polymer material used as the substrate is uniform. In addition, the structural properties of the substrate are also closely related to the porosity, water absorption rate, oxygen permeability, etc. of the material. During the process of forming the conductive layer by processes such as vacuum sputtering and metal evaporation, it is necessary to cool the film layer at a low temperature before performing high-temperature processing. Excessive pores, high oxygen content, and high moisture content in the substrate will cause the water and gas in the film layer to expand at high temperatures and interfere with the adhesion of the coating, ultimately affecting the film-forming effect of the conductive layer. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a polyester functional masterbatch for composite current collectors and its preparation method to reduce or avoid the problems mentioned above.

[0007] To solve the above technical problems, this application proposes a polyester functional masterbatch for composite current collectors. The composite current collector is composed of a substrate layer and conductive layers attached to both sides of the substrate layer. The substrate layer is made of a polyester film added with the polyester functional masterbatch. Among them, the polyester functional masterbatch is prepared from raw materials including the following weight parts: 30-50 weight parts of poly(m-phenylene isophthalamide), 1-3 weight parts of cobalt neodecanoate, 3-5 weight parts of dibutylhydroxytoluene, 5-10 weight parts of 1,4-diiodobenzene, 20-30 weight parts of silicon dioxide, and 50-100 weight parts of PET.

[0008] In addition, the present application also provides a method for preparing a polyester functional masterbatch for a composite current collector. The composite current collector is composed of a substrate layer and conductive layers attached to both sides of the substrate layer. The substrate layer is made of a polyester film added with the polyester functional masterbatch. Among them, the method for preparing the polyester functional masterbatch includes the following steps: At room temperature, 50-100 parts by weight of powdered PET, 20-30 parts by weight of nano-silica, 30-50 parts by weight of powdered poly(m-phenylene isophthalamide), 1-3 parts by weight of powdered cobalt neodecanoate, 3-5 parts by weight of powdered dibutylhydroxytoluene, and 5-10 parts by weight of powdered 1,4-diiodobenzene are added to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1500-2000 rpm for 30-60 minutes to form a mixed material; then, melt extrusion is carried out through a twin-screw extruder, and then water cooling granulation or slicing is performed to obtain the polyester functional masterbatch.

[0009] The polyester film prepared by adding the polyester functional masterbatch of the present application has significantly improved properties such as porosity, water absorption rate, and oxygen transmission rate, and no obvious crack propagation is observed after forming the metal conductive layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The following drawings are only intended to illustrate and explain the present application schematically and do not limit the scope of the present application.

[0011] Among them, Figure 1 shows a schematic structural diagram of a composite current collector according to a specific embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] For a clearer understanding of the technical features, objectives, and effects of the present application, the specific embodiments of the present application are now described with reference to the drawings. Among them, the same components are denoted by the same reference numerals.

[0013] As Figure 1 shown, it shows a schematic structural diagram of a composite current collector according to a specific embodiment of the present application. Among them, the composite current collector of the present invention is composed of a substrate layer 1 and conductive layers 2 attached to both sides of the substrate layer 1. Among them, the substrate layer 1 is made of a polyester film added with the polyester functional masterbatch. The substrate layer 1 can be a polyester film with a single-layer structure added with the polyester functional masterbatch, or a polyester film with a three-layer structure with the polyester functional masterbatch added to the surface layer (not shown in the figure).

[0014] To improve the performance of the conductive layer 2, a barrier layer (not shown in the figure) of a metal (such as chromium oxide) or a non-metallic material (such as silicon dioxide) can also be sputtered or evaporated between the conductive layer 2 and the substrate layer 1. The conductive layer 2 can be an aluminum conductive layer, a copper conductive layer, or a conductive layer of other metals formed by vacuum sputtering or evaporation. To reduce the resistivity, the conductive layer 2 can also adopt a multi-layer conductive structure formed by different processes. For example, the bottom layer of the conductive layer 2 can be a bottom coating layer with a thickness of 5 - 15 nm formed by vacuum sputtering process, and the surface layer of the conductive layer 2 can be a surface coating layer with a thickness of 100 - 500 nm grown on the bottom coating layer by electroplating process. The surface of the conductive layer 2 can also be passivated by electroplating or chemical etching process to form a dense protective layer (not shown in the figure).

[0015] As described above, in order to reduce the influence of the surface performance of the composite current collector on the production and performance of the battery, the present invention provides a polyester functional masterbatch for a composite current collector, which is prepared from raw materials including the following parts by weight: 30 - 50 parts by weight of poly(m - phenylene isophthalamide), 1 - 3 parts by weight of cobalt neodecanoate, 3 - 5 parts by weight of dibutylhydroxytoluene, 5 - 10 parts by weight of 1,4 - diiodobenzene, 20 - 30 parts by weight of silicon dioxide, and 50 - 100 parts by weight of PET.

[0016] The polyester functional masterbatch of the present invention can be prepared in the form of granules or slices and added to ordinary polyester during the production of polyester films to obtain the substrate layer 1 of the present invention. For example, 80 - 95 wt% of polyester without other components can be melt - blended with 5 - 20 wt% of the polyester functional masterbatch of the present invention, and then the single - layer structure of the substrate layer 1 can be produced through processes such as stretching, or the surface structure of the substrate layer 1 of the present invention can be obtained through a multi - layer co - extrusion process, etc.

[0017] Each raw material component of the polyester functional masterbatch of the present invention can be uniformly mixed in the form of pellet materials and then extruded and granulated by using equipment such as an extruder to obtain the polyester functional masterbatch of the present invention.

[0018] In a specific embodiment, at room temperature, 50 - 100 parts by weight of powdered PET, 20 - 30 parts by weight of nano - silicon dioxide, 30 - 50 parts by weight of powdered poly(m - phenylene isophthalamide), 1 - 3 parts by weight of powdered cobalt neodecanoate, 3 - 5 parts by weight of powdered dibutylhydroxytoluene, and 5 - 10 parts by weight of powdered 1,4 - diiodobenzene are added to a high - speed mixer for pre - dispersion and mixing at a rotation speed of 1500 - 2000 rpm for 30 - 60 minutes to form a mixture. Then, it is melt - extruded through a twin - screw extruder and then water - cooled and granulated or sliced to obtain the polyester functional masterbatch.

[0019] In another specific embodiment, for example, after obtaining the polyester functional masterbatch chips, 5-20 wt% of the polyester functional masterbatch can be taken and added to 80-95 wt% of PET particles for uniform mixing. The two are melt-blended, and finally a single-layer substrate layer 1 is produced through processes such as stretching, or the surface structure of the three-layer substrate layer 1 is obtained through a multi-layer co-extrusion process, etc.

[0020] Taking the single-layer substrate layer as an example, the preparation method of the substrate layer for a composite current collector according to the present invention will be further described below. The preparation method of the substrate layer for a composite current collector according to the present invention includes the following steps:

[0021] Components with the following weight ratios: 80-95 wt% of PET resin and 5-20 wt% of polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin for mixing to form a mixture.

[0022] After that, the mixture enters an exhaust-type twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270°C - 280°C.

[0023] After the materials are melted in the extruder, they are filtered and extruded into thick sheets. The thickness and profile of the thick sheets can be adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the opening of the die head.

[0024] The above-mentioned thick sheets are preheated at a temperature of 50°C - 90°C, enter an infrared heating zone of 300°C - 500°C, and are longitudinally stretched at a linear speed of 40 - 150 m / min. The longitudinal stretching ratio is 4.0 to obtain stretched sheets.

[0025] The stretched sheets are preheated at a temperature of 90°C - 120°C and transversely stretched at a temperature of 100°C - 160°C. The transverse stretching ratio is 3.8. Then, they are shaped at a temperature of 160°C - 240°C and cooled from 160°C to 50°C to obtain the substrate layer for a composite current collector.

[0026] Examples 1 - 5

[0027] According to the raw material weight part ratios in the following table, polyester functional masterbatch chips are respectively prepared, and then ordinary PET resin is put in to prepare a single-layer structure substrate layer for a composite current collector.

[0028]

[0029]

[0030] Comparative Examples 6 - 10

[0031] According to the same method as in the above examples, polyester film substrate layers for comparison are prepared according to the raw material weight part ratios in the following table.

[0032] Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Poly(m-xylylene adipamide) 0 35 40 45 50 Cobalt neodecanoate 1 0 2 2.5 3 Butylated hydroxytoluene 3 3.5 0 4.5 5 1,4-Diiodobenzene 5 7 7.5 0 10 Silicon dioxide 20 22 25 27 0 PET 80 66.5 79 93 130 Slicing amount for preparing single-layer substrate layer 5wt% 10wt% 13wt% 15wt% 20wt% Substrate layer thickness μm 6 7 8 9 10

[0033] The performance parameters of each substrate layer were tested separately. At the same time, a 8-μm-thick film made of pure PET without adding any functional masterbatch was used for comparison. The performance parameters are shown in the following table.

[0034]

[0035]

[0036] Pure copper metal layers were formed on both side surfaces of the substrate layer described in the above table through a vacuum sputtering process. The thickness of the pure copper metal layers on both sides of the vacuum sputtering was controlled to be 5 nm, and the surface crack parameters of the prepared film were tested.

[0037]

[0038] From the performance parameters of the above film layer and the crack situation of the metal coating, it can be seen that for the polyester film prepared by adding the polyester functional masterbatch of the present application, its performance such as porosity, water absorption rate, oxygen permeability rate, etc. has been greatly improved, and there is no obvious crack propagation after forming the metal conductive layer.

[0039] Furthermore, the resistivity differences between the pure copper metal layers on both sides of the polyester film shown in the above table were tested, as shown in the following table.

[0040]

[0041]

[0042] For the polyester film prepared by adding the polyester functional masterbatch of the present application, the resistivity difference of the metal conductive layer formed thereon is significantly smaller than that of the film without adding the functional masterbatch, indicating that the structures on both sides thereof have more excellent consistency.

[0043] Those skilled in the art should understand that although the present application is described in the form of multiple embodiments, not each embodiment only contains an independent technical solution. Such narration in the specification is only for clarity. Those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as ways that can be combined with each other to form different embodiments to understand the protection scope of the present application.

[0044] The above are only the illustrative specific embodiments of the present application and are not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principles of the present application shall fall within the protection scope of the present application.

Claims

1. A preparation method of a polyester functional masterbatch for a composite current collector, the composite current collector being composed of a substrate layer and conductive layers attached to both sides of the substrate layer, the substrate layer being made of a polyester film added with the polyester functional masterbatch, characterized in that, the preparation method of the polyester functional masterbatch comprises the following steps: at room temperature, 50-100 parts by weight of powdered PET, 20-30 parts by weight of nano-silica, 30-50 parts by weight of powdered poly(m-phthaloylene isophthalamide), 1-3 parts by weight of powdered cobalt neodecanoate, 3-5 parts by weight of powdered dibutylhydroxytoluene, and 5-10 parts by weight of powdered 1,4-diiodobenzene are added to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1500-2000 rpm for 30-60 minutes to form a mixed material; then melt extrusion is carried out by a twin-screw extruder, and then water cooling and pelletizing or slicing are carried out to obtain the polyester functional masterbatch.

2. A polyester functional masterbatch prepared by the preparation method according to claim 1, characterized in that, the polyester functional masterbatch is prepared from raw materials including the following parts by weight: 30-50 parts by weight of poly(m-phthaloylene isophthalamide), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silica, and 50-100 parts by weight of PET.

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