Composite current collector and preparation method thereof, and lithium ion battery cell

Abstract

The application discloses a composite current collector and a preparation method thereof, and a lithium ion cell, and belongs to the technical field of lithium ion battery materials. The composite current collector comprises a support body and a metal conductive layer from inside to outside, the support body contains a support film, and the support film comprises an insulating part and a conductive part in the length direction of the support body, wherein the composite current collector comprises a non-tab area and a tab area in the length direction, the insulating part is located in the non-tab area, and the conductive part is located in the tab area. The insulating part and the conductive part are synchronously prepared by adopting an electrostatic spinning technology. The positive electrode and / or the negative electrode of the lithium ion cell comprises the composite current collector. By designing the structure of the current collector, the weight is reduced, the step of tab welding of the composite current collector in the later period is simplified, and the risks of virtual welding and missing welding of tab welding are reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery materials, and particularly relates to a composite current collector, a preparation method thereof and a lithium ion battery cell. BACKGROUND

[0002] Lithium ion batteries have rapidly occupied the global new energy market due to their high energy density, good cycle stability, environmental friendliness and other advantages, and have been applied in various fields from small 3C products to electric vehicles, ships and other large fields. In order to further expand its advantages and reduce the use cost of the battery, optimization design needs to be carried out from various aspects such as battery materials and structure. As an important part of lithium ion batteries, the current metal foil current collector accounts for about 15% of the weight of the battery, not only occupying a large cost, but also restricting the further improvement of the energy density of the battery.

[0003] The current composite current collector can effectively reduce the thickness of the surface metal layer due to the high molecular insulating interlayer, thereby reducing the weight of the battery. However, due to the intermediate support layer between the two metal layers, the welding of multiple composite current collectors in the process of assembling and welding the connecting piece of the battery cell is extremely difficult, and the power performance of the battery is often affected by the fact that part of the metal layer is not connected.

[0004] Through retrieval, for example, the patent application file with the Chinese patent application number 202211393484.1 and the application publication date of February 3, 2023 discloses a composite current collector, a battery cell, a battery and a preparation method of the composite current collector. The composite current collector comprises a support body and a conductive layer. The support body comprises an insulating support film and a conductive foil, the conductive foil is connected to both ends of the insulating support film in the width direction, the conductive foil comprises a lap joint portion and an extension portion, the lap joint portion is lapped with the insulating support film, and in the width direction of the insulating support film, the extension portion is connected to the side of the lap joint portion away from the insulating support film and extends to the outside of the insulating support film, the conductive layer is arranged on both sides of the support body in the thickness direction, and the conductive layers on the same side of the support body are integrally covered on the insulating support film and the conductive foil. However, first of all, the composite current collector uses a conductive foil, and the thickness control is limited by the thickness of the foil, which cannot fully utilize the advantages of the insulating support body, and the weight is not easy to control. Secondly, the composite current collector designs a stepped surface, which requires adjustment of the preparation equipment and cannot adapt to the existing production line. Finally, the rolling process in the preparation method has high cost and complex process, and since the roll gap must be smaller than the thickness of the insulating support film to drag the belt, continuous production cannot be achieved. SUMMARY

[0005] 1. Problem to be solved

[0006] The purpose of the present application is to provide a composite current collector, by designing the current collector structure, to achieve weight reduction while simplifying the later tab welding steps of the composite current collector, and to reduce the risk of virtual welding and missed welding of tab welding.

[0007] Further, the present application proposes a preparation method of a composite current collector and a lithium ion cell.

[0008] 2. Technical solution

[0009] In order to solve the above problems, the technical scheme adopted by the present application is as follows:

[0010] A composite current collector comprises a support body and a metal conductive layer from inside to outside, the surface of the support body contains a support film, and in the length direction of the support body, the support film comprises an insulating part and a conductive part, wherein the composite current collector comprises a non-tab area and a tab area in the length direction, the insulating part is in the non-tab area, and the conductive part is in the tab area.

[0011] Further, according to the length of the tab material area and the length of the tab in the battery design, the length ratio of the insulating part and the conductive part is preferably (100-10):1, for example, the length of the tab material area in the battery design is 100mm, the length of the tab is 5mm, that is, the design length ratio of the tab material area to the tab is 100:5, and then the length of the insulating part and the conductive part of the support body in the current collector can be designed as 90mm and 15mm, because in this way the exposed support layer of the current collector after coating is all the conductive part, so that welding can avoid the participation of the insulating part and thus cannot conduct electricity.

[0012] Further, the composition of the insulating part is an insulating polymer material, and the insulating polymer material comprises at least one of polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, polybutylene terephthalate (PET), poly-p-phenyleneterephthalamide (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, their derivatives, their crosslinked products or their copolymers.

[0013] Further, the conductive part contains a conductive substance, and the conductive substance comprises metal (such as copper / silver nanowire, etc.) and / or non-metal (such as graphite, graphene, carbon nanotube, etc.).

[0014] Further, the conductive part also contains a polymer material, i.e., the conductive part is a polymer system mixed with a conductive material, and the polymer material of the conductive part can be selected from polyethylene oxide, and commercially available composite conductive polymer and structural conductive polymer:

[0015] The composite conductive polymer is a material in which various conductive materials are filled in a polymer matrix by different processing techniques, wherein the filling material provides the conductive property of the material, and the polymer matrix binds the conductive filler together and provides the processing property of the material. For example, the matrix material of the composite conductive polymer is polyethylene, polypropylene, polystyrene, epoxy resin or phenolic resin, and the conductive filler is carbon black, carbon nanotube, graphene, metal and metal oxide.

[0016] The structural conductive polymer, also known as intrinsic conductive polymer, is divided into ionic and electronic types. For example, the ionic conductive polymer is polyethylene oxide, polyethylene glycol succinate, polyethylene glycol imine, etc., and the electronic conductive polymer is polyacetylene, polyphthalocyanine copper, polyaniline, polyphenylene sulfide, polypyrrole, etc.

[0017] Further, the metal conductive layer includes one or more of Cu conductive layer, Al conductive layer, Ni conductive layer, Au conductive layer, Ag conductive layer, Pt conductive layer and alloy conductive layer according to the demand of the battery core, and the thickness is 0.5-1.5 μm.

[0018] Further, the support film is composed of two parts of insulating part and conductive part which are closely connected, and the thickness is 1-20 μm.

[0019] Further, in order to facilitate the adhesion of the metal conductive layer, the surface of the support film is surface treated to form a surface treatment layer, and the material of the surface treatment layer is any one of metal Ni, Ti and non-metal Si, and the thickness is 2-10 nm. The surface treatment layer makes the surface of the support film more flat, and has better bonding ability for the metal conductive layer attached by subsequent methods such as magnetron sputtering and evaporation.

[0020] Further, the thickness of the support film is 1-5 μm, and the thickness of the metal conductive layer is 0.5-2 μm.

[0021] A preparation method of a composite current collector, comprising the following steps:

[0022] S1: preparing a support film by using electrospinning technology:

[0023] The spinning solution for the insulating part consists of at least one of the following: polyamide (PA), polyterephthalate, polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PPE), polyvinyl chloride (PVC), aramid, polybutylene terephthalate (PET), poly(p-phenylene terephthalamide) (PPTA), polypropylene (PPE), polyoxymethylene (POM), epoxy resin, phenolic resin, polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), silicone rubber, polycarbonate (PC), polyvinyl alcohol (PVA), polyethylene glycol (PEG), cellulose, starch, protein, their derivatives, their crosslinks, or their copolymers;

[0024] The spinning solution for the conductive part consists of 0.1% to 5% conductive material (such as carbon black, carbon nanotubes, graphene, metals and metal oxides), 0.1% to 1% surface charge regulator (which can be an organic salt, such as acetate), 1% to 20% polymer material (such as polyethylene oxide, polyethylene, polypropylene, polystyrene, epoxy resin, phenolic resin, etc.), with the remainder being the spinning solution for the insulating part as a solvent.

[0025] The conductive part spinning solution (one example) consists of 0.1-1.0% silver nanowires, 0.1-1.0% surface charge regulator, 1.0-5.0% polyethylene oxide, and the remainder being the insulating part spinning solution, making it 100%.

[0026] Specific process: Add the prepared insulating spinning solution into the syringe of the electrospinning instrument. Place the substrate at a certain distance from the needle of the electrospinning instrument, such as 1 to 10 cm. Add the prepared second-step spinning solution into the syringe of the electrospinning instrument. At the same time, use the electrospinning instrument to prepare the insulating part and the conductive part to obtain the support.

[0027] S2: Deposit a metal and / or non-metallic surface treatment layer on the surface of the support film obtained in step S1 using physical vapor deposition (vacuum sputtering, vacuum ion plating, vacuum evaporation, etc.) and / or chemical vapor deposition to obtain the support precursor.

[0028] S3: The precursor of the support obtained in step S3 is hot-pressed to obtain a precursor of the support with a certain thickness.

[0029] S4: In step S4, a metal coating is deposited on the surface of the surface treatment layer to form a metal conductive layer. The thickness of the metal conductive layer is controlled by electroplating according to the specific design.

[0030] An application of a composite current collector, wherein the composite current collector is used in a lithium-ion battery cell, the application method includes the following steps:

[0031] S11: Prepare the positive and negative composite current collector according to the above method according to the design requirements of the lithium ion cell;

[0032] The present application can achieve the following for both positive and negative current collectors: ①Light weight, thin thickness, and weight and thickness can be accurately designed and controlled according to the design of the cell; ②Compared with the existing technology, the preparation process is simple, and the welding of the additional conductive part is avoided, and the influence of the large contact resistance caused by rolling in the comparative document is also avoided; ③Compared with the traditional copper current collector of the negative electrode, the cost can be reduced and the weight can be effectively controlled by using the design of multiple layers of metal (such as aluminum in the inner layer and copper in the outer layer); ④Compared with the traditional positive aluminum current collector, the conductivity can be improved by using the design of multiple layers of metal (such as copper in the inner layer and aluminum in the outer layer);

[0033] S12: Use the composite current collector in S11 to perform coating, drying, forming, and rolling, etc. to obtain a tab precursor, the coating area covers the entire non-tab area and part of the tab area, and the size of the tab area covered is 1-5mm;

[0034] Specifically:

[0035] Coating: The current collector is fed into the coating machine from the unwinding device, the first and last ends of the substrate are connected into a continuous belt after splicing, the continuous belt is sent into the "tension control" and "automatic deviation correction" devices, and then into the coating device; The tab slurry is coated in sections according to the predetermined coating amount and blank length in the coating device;

[0036] Drying: The wet tab after coating is sent to the drying channel for drying, and the drying temperature is set according to the coating speed and thickness;

[0037] Forming: The dry tab is then formed and wound after "tension control" and "automatic deviation correction";

[0038] Rolling: After the coating of the tab is completed, the tab is fixed on the unwinding mechanism, the tab is correctly threaded through the gap between the two rollers, and the winding system is connected. After turning on the rolling mode, the motor drives the upper and lower rollers to rotate simultaneously, and the winding mechanism pulls the tab to steadily pass through the rolling gap, and finally is pressed to the required compaction density.

[0039] S13: Laser cut the tab area of the tab precursor in S12 according to the design requirements of the lithium ion cell tab;

[0040] S14: The steps of lamination, assembly, and post-process liquid injection, formation, and capacity distribution after S13 are performed according to the normal production process, and a lithium ion cell is obtained.

[0041] A lithium ion cell, the positive and / or negative electrode of the lithium ion cell comprises the above-mentioned composite current collector.

[0042] 3. Beneficial effects

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) The composite current collector connection structure provided by the present invention simplifies the subsequent electrode tab welding steps of the composite current collector by constructing a conductive part on the composite current collector support layer, and reduces the risk of poor welding and missing welding of the electrode tab; the larger conductive contact part of the conductive part can also effectively reduce impedance and improve the power performance and capacity retention rate of the battery. Among them, the insulating part and the conductive part achieve the effect of "integration" by using the simultaneous spraying method. The insulating part and the conductive part are effectively connected by polymer, with higher strength and lower and more stable impedance control. Moreover, both are flat surfaces without steps, which has no impact on the current collector preparation, electrode preparation and stacking processes, and can be directly introduced into existing production lines; the spraying method can accurately control the weight, is technically mature, low in cost and easy to achieve continuous production. Only the size and width of the receiving roller need to be adjusted appropriately to produce products of various specifications, with high overall production efficiency;

[0045] (2) When the current collector of the present invention is applied in the preparation of battery cells, the material area and the conductive part overlap during coating: the larger conductive contact part of the conductive part can also effectively reduce the impedance and improve the power performance and capacity retention of the battery. Attached Figure Description

[0046] Figure 1 A longitudinal cross-sectional view of a composite current collector with tabs provided for this invention;

[0047] Figure 2 A plan view of a composite current collector with tabs provided for this invention;

[0048] Figure 3 This is a simplified diagram illustrating the preparation state of the composite current collector of the present invention;

[0049] In the picture:

[0050] 1. Support body; 11. Insulating part; 12. Conductive part; 2. Surface treatment layer; 3. Metal conductive layer; 4. Non-tab area; 5. Tab area; 6. Receiving roller; 7. Electrospinning instrument cylinder. Detailed Implementation

[0051] The present invention will now be further described with reference to specific embodiments and accompanying drawings.

[0052] Example

[0053] like Figure 1 As shown, in this embodiment, the composite current collector consists of a support 1, a surface treatment layer 2, and two metal conductive layers 3 from the inside out; the support film on the support 1 is divided into an insulating part 11 and a conductive part 12 along its length, as shown in the figure. Figure 2As shown, the composite current collector in this embodiment can be divided into a non-tab region 4 and a tab region 5 along its length.

[0054] like Figure 3 As shown, the receiving roller 6 is made of stainless steel, and its diameter and length are optional. In this embodiment, a stainless steel roller with a diameter of 20cm and a length of 50cm can be selected. The receiving roller needs to be grounded to form a potential difference (10-30kV, 10kV is optional in this embodiment). The receiving roller can be used in conjunction with other stainless steel rollers, hot press rollers, stretching rollers, or rubber rollers to transfer the support and rewind the current collector (e.g., guide it to the metal layer preparation module for magnetron sputtering, vapor deposition, etc.) to achieve continuous production. The preparation method of the composite current collector in this embodiment is as follows:

[0055] Step 1: Add the prepared insulating part spinning solution into the electrospinning apparatus cylinder 7 of No. 1, and place the receiving roller substrate 1-10 cm away from the needle of the electrospinning apparatus; add the prepared conductive part spinning solution into the electrospinning apparatus cylinder 7 of No. 2.

[0056] The insulating part 11 and the conductive part 12 of the support film are prepared simultaneously using two electrospinning machines; that is, the insulating part and the conductive part of the support are simultaneously thickened by two electrostatic spraying heads, and finally integrated preparation is achieved. In this way, the overlap is tightly separated and the surface of the finished support is flat and uniform.

[0057] Step 2: Hot-press the obtained support layer precursor to obtain a support film of a certain thickness;

[0058] Step 3: Deposit a metal and / or non-metallic surface treatment layer 2 on the two surfaces opposite to the support film using physical vapor deposition (vacuum sputtering, vacuum ion plating, vacuum evaporation, etc.) and / or chemical vapor deposition techniques;

[0059] Step 4: Evaporate a metal conductive layer 3 onto the surface of surface treatment layer 2. Continue to control the thickness of the metal conductive layer 3 using electroplating methods according to the specific design.

[0060] Using the current collector of this embodiment, positive and negative current collectors are prepared, and a lithium-ion battery cell is obtained, wherein:

[0061] The negative electrode current collector is composed of: insulating part: 5μm polypropylene (PP); conductive part: 5μm polypropylene loaded with conductive carbon black; surface treatment layer: 2nm thick Ni; and metal conductive layer: 1μm copper.

[0062] The positive electrode current collector is composed of: insulating part: 5μm PET; conductive part: 5μm polypropylene supported conductive carbon black; surface treatment layer: 8nm thick alumina; and metal conductive layer: 1μm aluminum.

[0063] The performance of the fluid and lithium ion cell of the present example is shown in Table 1.

[0064] Table 1 Fluid parameters and lithium battery performance of the example and comparative examples

[0065]

[0066] As shown in Table 1, compared with Example 1, the thickness of the support film of Comparative Example 1 is relatively thick, and the energy density of the battery prepared therefrom is lower than that of Example 1; compared with Example 1, the length ratio of the insulating portion 11 and the conductive portion 12 of Comparative Example 2 is changed: the designed battery material area size is 100 mm, the insulating portion 12 of Comparative Example 2 is 101 mm, and the conductive portion 11 is 4 mm, which will result in that the exposed part of the support 1 contains the insulating portion 12, and the consequence is to cause the impedance to increase, the battery power performance to be poor, and the energy density to be small.

[0067] The examples described in the present application are merely to describe the preferred embodiments of the present application, and do not limit the concept and scope of the present application. Without departing from the design idea of the present application, various modifications and improvements of the technical solutions of the present application made by the engineering and technical personnel in the art shall fall within the protection scope of the present application.

Claims

1. A composite current collector, characterized in that: The structure comprises a support body (1) and a conductive metal layer (3) from the inside out. The support body (1) contains a support film. Along the length of the support body (1), the support film is divided into an insulating part (11) and a conductive part (12). The composite current collector is divided into a non-tab region (4) and a tab region (5) along its length. The insulating part (11) is located in the non-tab region (4), and the conductive part (12) is located in the tab region (5). The length ratio of the insulating part (11) and the conductive part (12) is (100~10):

1. The support film is prepared using electrospinning technology. The method is as follows: the insulating part (11) and the conductive part (12) are prepared simultaneously by preparing the insulating part spinning solution and the conductive part spinning solution to obtain the support film. The spinning solution that forms the insulating part (11) is composed of an insulating polymer. The spinning solution that forms the conductive part (12) consists of 0.1% to 5% conductive material, 0.1% to 1% surface charge regulator, 1% to 20% polymer material, and the remainder is the spinning solution that forms the insulating part (11). The polymer is one or more of polyethylene oxide, polyethylene, polypropylene, polystyrene, epoxy resin, and phenolic resin.

2. The composite current collector according to claim 1, characterized in that: The insulating polymer is at least one of the following: polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, aramid, polybutylene terephthalate, poly(p-phenylene terephthalate), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, polyvinyl alcohol, polyethylene glycol, cellulose, starch, and protein.

3. The composite current collector according to claim 1, characterized in that: The conductive materials include copper nanowires, silver nanowires, graphite, graphene, and / or carbon nanotubes.

4. A composite current collector according to claim 1, characterized in that: The metal conductive layer (3) is one or more of Cu conductive layer, Al conductive layer, Ni conductive layer, Au conductive layer, Ag conductive layer, Pt conductive layer and their alloy conductive layers.

5. A composite current collector according to any one of claims 1 to 4, characterized in that: A surface treatment layer (2) is also attached between the support film and the metal conductive layer (3), and the surface treatment layer (2) is any one of metal Ni, Ti and non-metal Si.

6. A method for preparing the composite current collector according to any one of claims 1 to 5, characterized in that: The steps are as follows: S1: Preparation of a support film using electrospinning technology: The insulating part (11) and the conductive part (12) are prepared simultaneously by preparing the spinning solution of the insulating part and the spinning solution of the conductive part to obtain the support film; S2: Deposit a metal and / or non-metallic surface treatment layer (2) on the surface of the support film prepared in step S1 using physical vapor deposition and / or chemical vapor deposition techniques to obtain the support precursor; S3: The precursor of the support obtained in step S3 is hot-pressed to obtain a precursor of the support with a certain thickness. S4: A metal coating is deposited on the surface of the surface treatment layer (2) to form a metal conductive layer (3).

7. A lithium-ion battery cell, characterized in that: The positive and / or negative electrodes of the lithium-ion battery cell include the composite current collector as described in any one of claims 1 to 5.

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