Composite foil current collector, preparation method and battery

Abstract

The invention relates to the technical field of composite current collectors, and provides a composite foil current collector, a preparation method and a battery, the composite foil current collector comprises a base film layer, and a conductive metal layer and an electrode slice layer which are sequentially laminated on two sides of the thickness direction of the base film layer; wherein step structures are formed on the surfaces of the two sides of the base film layer in the thickness direction, the conductive metal layer comprises a coating section and a welding section, the thickness of the welding section is larger than that of the coating section so as to be matched with the step structures of the base film layer, and a connecting plane is formed on the surface, away from the base film layer, of the conductive metal layer. And an active material is coated in a partial region of the connecting plane to form an electrode slice layer. The protruding step structure is formed on the base film layer, so that the contact area of the conductive metal layer and the base film layer is increased, the adhesion performance of the conductive metal layer and the base film layer is improved, the thickness of the welding section is large, the welding section can serve as a welding area to prepare the tab, the tab can have high overcurrent capacity, the internal resistance of the battery is reduced, and the performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite current collectors, and in particular to a composite foil current collector, a preparation method and a battery. Background Art

[0002] With the rapid development of electric vehicles and renewable energy, lithium-ion batteries, as efficient and reliable energy storage devices, have huge market potential. How to further improve the energy density and safety performance of lithium-ion batteries has become a research hotspot in the field of lithium-ion batteries.

[0003] To improve the safety and energy density of lithium-ion batteries, some industry proposals utilize composite current collectors. While conventional current collectors are single-layer copper or aluminum foil, composite foil current collectors have a three-layer structure, with a polymer insulating layer (base film) in the middle and conductive metal layers on top and bottom. Compared to pure metal current collectors, composite current collectors can reduce weight by 50% to 80%, thereby increasing the battery's energy density. The presence of the polymer base layer in the composite current collector can also reduce the battery's temperature rise, reducing the risk of thermal runaway.

[0004] In related technologies, the surface of the base film layer in the composite current collector is very flat and smooth, and the metal layer deposited on it is easily detached, resulting in a short service life of the current collector. In addition, because the base film isolates the metal layers on both sides of the composite current collector, the current is generally conducted by welding the upper and lower metal foils to the metal layer on the composite current collector. However, the metal layer on the composite current collector is relatively thin and easily melted and welded through, resulting in high welding impedance and poor current capacity. As a result, when using high-rate charging and discharging, the performance of the composite current collector is significantly worse than that of traditional pure metal foil. Summary of the Invention

[0005] The present invention provides a composite foil current collector, a preparation method and a battery, which are used to solve the defects in the prior art that the contact surface between the metal conductive layer and the base film layer is easy to fall off and melt through.

[0006] The first aspect of the present invention provides a composite foil current collector, comprising: a base film layer and a conductive metal layer and an electrode layer stacked in sequence on both sides of the base film layer in the thickness direction; wherein, both side surfaces of the base film layer in the thickness direction form a raised step structure; the conductive metal layer comprises a coating section and a welding section, the thickness of the welding section is greater than the thickness of the coating section, so as to cooperate with the step structure of the base film layer and make the conductive metal layer away from the surface of the base film layer to form a connection plane, and the connection plane is coated with active material to form the electrode layer.

[0007] According to the composite foil current collector provided by the present invention, the electrode layer is provided on the connection plane corresponding to the coating section so that an edge of one side of the electrode layer in the width direction is flush with an edge of the coating section.

[0008] According to the composite foil current collector provided by the present invention, the base film layer includes a first receiving section and a second receiving section, the thickness of the first receiving section is less than the thickness of the second receiving section; and a connecting surface is provided between the first receiving section and the second receiving section to form a first-level step structure on both opposite surfaces of the base film layer; wherein, the first receiving section is connected to the welding section, the second receiving section is connected to the coating section, and the width of the first receiving section is less than the width of the second receiving section.

[0009] According to the composite foil current collector provided by the present invention, a single-side height difference between the first receiving section and the second receiving section in the thickness direction is 0.5-1.2 um.

[0010] According to the composite foil current collector provided by the present invention, the maximum thickness of the base film layer is 3-10.5 μm.

[0011] According to the composite foil current collector provided by the present invention, the step structures on both sides of the base film layer in the thickness direction are symmetrically arranged with respect to the center plane of the base film layer.

[0012] According to the composite foil current collector provided by the present invention, the thickness of the coating section is 0.8-2 μm; and / or the width of the welding section is 1 / 30-1 / 10 of the width of the coating section.

[0013] A second aspect of the present invention provides a method for preparing any of the above-mentioned composite foil current collectors, comprising the following steps: Prepare a base film layer by a casting method or a blown film method, and form a step structure on the surface of both sides of the base film layer in the thickness direction; Using magnetron sputtering technology and controlling the sputtering power to deposit conductive metal layers of different thicknesses on different surfaces of the step structure, and making the conductive metal layers away from the surface of the base film layer to form a connection plane; Active material is coated on the connection plane to form an electrode layer.

[0014] According to the preparation method provided by the present invention, the use of magnetron sputtering technology and controlling the sputtering power to deposit conductive metal layers of different thicknesses on different surfaces of the step structure specifically includes the following steps: In the welding section, the deposition was performed with a power density of 2.5~3.5W / cm² and a sputtering time of 15~20min; During the coating stage, the deposition was performed using a power density of 1-1.8 W / cm² and a sputtering time of 10-15 minutes.

[0015] A third aspect of the present invention provides a battery comprising a plurality of composite foil current collectors as described above, wherein the plurality of composite foil current collectors are stacked.

[0016] The present invention provides a composite foil current collector, which forms a step structure on a base film layer, and a conductive metal layer is located above the step structure and covers the entire step structure. On the one hand, this can increase the contact area between the conductive metal layer and the base film layer, improve the adhesion performance of the two, and effectively prevent them from falling off; on the other hand, a part of the conductive metal layer is thicker and can be used as a welding area for preparing a tab, so that it has a stronger current flow capacity, reduces the internal resistance of the battery, and improves the battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are 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.

[0018] Figure 1 It is a schematic structural diagram of the composite foil current collector provided by the present invention.

[0019] Figure 2 It is a schematic flow chart of the method for preparing the composite foil current collector provided by the present invention.

[0020] Reference numerals: 1. Base film layer; 11. First connecting section; 12. Second connecting section; 2. Conductive metal layer; 21. Welding section; 22. Coating section; 3. Electrode sheet layer. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0022] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of explaining the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as limiting the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0023] In the description of the embodiments of the present invention, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; and direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of the present invention based on specific circumstances.

[0024] In the embodiments of the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0025] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0026] In related technologies, composite foil current collectors typically use a layered structure, with a base film layer in the middle and metal-plated layers on the top and bottom as conductive layers. This structure ensures uniform thickness and overall thinness of the metal layers. This can lead to the conductive metal layer being easily detached and easily penetrated during the roll welding process to form the tabs.

[0027] In view of the problems in the related technology, the following Figure 1 The present invention provides a composite foil current collector, comprising a base film layer 1 and a conductive metal layer 2 and an electrode layer 3 stacked sequentially on both sides of the base film layer 1 in the thickness direction. A raised step structure is formed on both sides of the base film layer 1 in the thickness direction. The conductive metal layer 2 includes a coating section 22 and a welding section 21. The welding section 21 is thicker than the coating section 22 to cooperate with the step structure of the base film layer 1 and to separate the conductive metal layer 2 from the surface of the base film layer 1 to form a connection plane. The connection plane is coated with an active material to form the electrode layer 3. The surface of the base film layer 1 is relatively smooth, which results in insufficient adhesion when depositing the conductive metal layer 2, causing the conductive metal layer 2 to easily fall off. In this embodiment, by providing the step structure on the base film layer 1, on the one hand, the contact area between the conductive metal layer 2 and the base film layer 1 is increased, thereby improving adhesion. On the other hand, because the conductive metal layer 2 fills and covers the entire step structure, the welding section 21 is thicker and can prevent welding through during the formation of the tab, thereby reducing welding impedance and improving current carrying capacity.

[0028] Specifically, if Figure 1 As shown, the overall structure of the composite foil current collector is a plate-like structure, which is obtained by assembling different functional layers. Among them, the cross-section of the base film layer 1 in this embodiment is a stepped structure, and the conductive metal layer 2 covers each step surface of the stepped structure. The side of the conductive metal layer 2 that contacts the electrode layer 3 is a flat structure. This makes the thickness of the welding section 21 greater than the thickness of the coating section 22. This can be achieved through the welding section 21 during the formation of the tab, avoiding the problem of seam welding melting through the conductive metal layer 2. Furthermore, the connection plane is a horizontal plane structure, which allows the conductive metal layer 2 to fill the step height, thereby forming the connection plane.

[0029] It is understandable that the surface of the polymer film (base film layer 1) in the composite current collector is very flat and smooth, and the metal layer deposited on it is easily detached. This is especially true for non-polar materials such as polypropylene, where adhesion is a significant challenge. The metal layer on the polypropylene-based composite current collector easily detaches, resulting in a short lifespan of the current collector. In this embodiment, the step structure can effectively increase the contact area between the base film layer 1 and the conductive metal layer 2, improving their adhesion. The step structure also has a certain limiting effect, further improving the stability of the connection between the two.

[0030] On the other hand, since the base film layer 1 isolates the metal layers on both sides of the composite current collector in the thickness direction, current conduction is generally achieved by transferring the upper and lower metal foils to the metal layers on the composite current collector through welding. However, the metal layer on the composite current collector is relatively thin and easily melted and welded through, resulting in problems such as large welding impedance and poor current capacity. When high-rate charge and discharge are used, the performance of the composite current collector is significantly worse than that of traditional pure metal foil. Therefore, in this embodiment, the step structure is used to make the thickness of the welding section 21 thicker, so that welding through can be prevented during the formation of the tab, effectively reducing impedance and improving current capacity.

[0031] The specific structural form of the step structure is not limited in this embodiment. It can be a single-step structure or a multi-step structure. The step structure can be set on one side or on both sides. For example, a single-step structure can be set on both sides to make the cross-sectional structure of the base film layer 1 have a "J"-shaped structure. This specification describes the method of setting the step structure on one side. Figure 1 In addition, the coverage of the electrode layer 3 is not limited in this embodiment, and it can cover the entire connection plane or a portion of the connection plane.

[0032] In some embodiments, the electrode layer 3 is disposed on a connection plane corresponding to the coating section 22 so that the edge of the electrode layer 3 is flush with the edge of the coating section 22, such as Figure 1 Typically, the tab is formed on the conductive metal layer 2 by ultrasonic roll welding, that is, a layer of metal foil is roll welded onto the surface of the conductive metal layer 2. In this embodiment, the electrode layer 3 only covers the coating section 22, which leaves the welding section 21 exposed, facilitating the formation of the tab in subsequent processes.

[0033] Specifically, the active material is only applied to the connection plane corresponding to the coating section 22, so that the welding section 21 can be naturally exposed, which is beneficial to the formation of the tab in the subsequent process, reduces the overall preparation process, and makes it easier to manufacture.

[0034] In some embodiments, continue as Figure 1 As shown, the base film layer 1 includes a first connecting section 11 and a second connecting section 12. The thickness of the first connecting section 11 is less than that of the second connecting section 12. A connecting surface is formed between the first connecting section 11 and the second connecting section 12, thereby forming a stepped structure on two opposing surfaces of the base film layer 1. The base film layer 1 is used to receive conductive metal. In this embodiment, the two connecting sections can form a stepped structure on both sides of the base film layer 1 in the thickness direction, thereby increasing the contact area with the conductive metal layer 2 on both sides and improving adhesion.

[0035] Specifically, the connecting surface is the surface where the first connecting section 11 and the second connecting section 12 meet, and the connecting surface can be a vertical plane or an inclined plane. When the connecting surface is set as a vertical plane, the step structure of the cross section of the base film layer 1 is a rectangular convex structure, such as Figure 1 When the connection surface is configured as an inclined plane, the stepped structure of the cross-section of the base film layer 1 becomes a trapezoidal raised structure. The choice of connection surface can be adjusted accordingly based on actual needs. For example, if one wishes to further increase the contact area between the base film layer 1 and the conductive metal layer 2, an inclined connection surface can be employed, thereby increasing the contact area and enhancing adhesion performance.

[0036] The first connecting section 11 can be located in the middle of the second connecting section 12, or it can be located on a side of the first connecting section 11 that is offset from the second connecting section 12. Both methods can form steps on the upper and lower opposing surfaces of the base film. The difference is that when the first connecting section 11 is located in the middle of the second connecting section 12, the step heights on the two opposing surfaces are consistent. When the first connecting section 11 is offset from a side of the second connecting section 12, the step heights on the two surfaces will differ. This is not limited in this embodiment, as long as a step structure can be formed on both surfaces of the base film layer 1.

[0037] In a specific embodiment, the width of the first connecting section 11 is smaller than the width of the second connecting section 12. The area occupied by the tab is relatively small, and the overall thickness of the conductive metal layer 2 should not be too large. Therefore, in this embodiment, by limiting the width of the first connecting section 11, the overall thickness of the conductive metal layer 2 is not too large, which does not affect the performance of the entire composite current collector.

[0038] Specifically, excessive thickness of the conductive metal layer 2 can increase the overall current collector weight, thereby impacting the battery's energy density and battery life, particularly in applications requiring lightweighting (such as electric vehicles and portable devices). In this embodiment, the width of the first connecting section 11 is limited to be significantly smaller than the width of the second connecting section 12, thereby minimizing the overall thickness and mass increase and preventing the stepped structure from impacting overall performance.

[0039] In a specific embodiment, the width of the welding section 21 is 1 / 30 to 1 / 10 of the width of the coating section 22. This makes the welding section 21 occupy a smaller proportion of the entire structure, thereby reducing the impact on the overall battery performance.

[0040] Specifically, because the shape of the conductive metal layer 2 matches the stepped structure on the base film, that is, the conductive metal layer 2 completely fills the stepped structure, the width of the first connecting section 11 is 1 / 30 to 1 / 10 of the width of the second connecting section 12, ensuring that the widths of the welding section 21 and the coating section 22 meet the aforementioned proportional relationship after the metal layer is deposited.

[0041] In conjunction with the above embodiment, the welding section 21 is connected to the first receiving section 11, and the coating section 22 is connected to the second receiving section 12. By defining the connection position of the coating section 22 and the welding section 21, the overall structure of the conductive metal layer 2 completely covers the stepped structure, and the position of the electrode layer 3 is more easily determined. For example, when coating the electrode layer 3, the relevant data of the deposition coating section can be called up and used with slight modifications, reducing the overall preparation difficulty.

[0042] Specifically, the welding section 21 is connected to the first receiving section 11, and the corresponding electrode layer 3 is located in the area where the coating section 22 is located, which makes the second receiving section 12 of the base film layer 1 exposed, which is conducive to depositing metal on the first receiving section 11 to form the welding section 21.

[0043] In conjunction with the above embodiment, the second connecting section 12 extends to one side of the width of the base film layer 1. In other words, a stepped structure is formed on one side. This approach reduces the difficulty of preparing the conductive metal layer 2 and effectively reduces the overall weight of the conductive metal layer 2. This approach ensures that the thickness of the welding section 21 equals the thickness of the coating section 22 + the height of the stepped structure, preventing weld penetration during roll welding.

[0044] In a specific embodiment, the height difference between the first connecting section 11 and the second connecting section 12 in the thickness direction is 0.5-1.2 μm. That is, the height of a single step in the step structure is limited to 0.5-1.2 μm. By limiting the step height to between 0.5-1.2 μm, the formed step is neither too high nor too low. Within this range, the contact area of ​​the conductive metal layer 2 can be effectively increased, and a thicker area is provided to achieve the formation of the tab.

[0045] In a preferred example, the single-sided height difference between the first receiving section 11 and the second receiving section 12 in the thickness direction is 1um. By limiting the height of the single-sided step protrusion, the adhesion and overall thickness of the conductive metal layer 2 are balanced at this limited height, and the overall performance is more superior.

[0046] In some embodiments, the maximum thickness of the base film layer 1 is 3-10.5 μm. By limiting the thickness of the base film layer 1, corresponding step structures can be formed on the two surfaces, thereby improving the overall performance.

[0047] In a preferred example, the thickness of the second receiving section 12 of the base film layer 1 is 8um, and the thickness of the first receiving section 11 is 6um. Under this limited size, the adhesion and overall thickness of the conductive metal layer 2 are balanced, and the overall performance is more superior.

[0048] In a specific embodiment, the thickness of the coating section 22 is 0.8-2 μm. By limiting the thickness of the coating section 22, the overall thickness of the conductive metal layer 2 is not too thick, which can avoid affecting the overall weight and improve the overall performance.

[0049] In a preferred example, the coating section 22 has a thickness of 0.5 μm, and the welding section 21 has a thickness of 1.5 μm. By limiting the specifications in this embodiment, the overall thickness of the conductive metal layer 2 is relatively thin, which does not affect the overall weight.

[0050] In combination with the above embodiment, the step structures on both sides of the thickness direction of the base film layer 1 are symmetrically arranged with respect to the center plane of the base film layer 1. By limiting the center plane symmetry, it is possible to facilitate the formation of the step structures on both sides, reduce the difficulty of the overall manufacturing process, and improve the qualified rate of the finished product.

[0051] In conjunction with the aforementioned embodiments, the base film layer 1 is made of one or more of polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, acrylonitrile-butadiene-styrene copolymer, polypropylene, polyoxymethylene, polytetrafluoroethylene, polyvinylidene fluoride, and polycarbonate. It is understood that by providing a stepped structure on the base film layer 1, it can be applied to the surface of various base film layers 1 and can be selected according to different requirements.

[0052] For example, in order to obtain good mechanical properties, polyethylene, polypropylene, polycarbonate and other materials can be used to prepare it, so that it has good impact resistance and wear resistance, is suitable for applications that require strong durability, and can maintain structural stability under extreme conditions. In order to obtain good chemical corrosion resistance, polytetrafluoroethylene, polyvinylidene fluoride, polyoxymethylene and the like can be used to prepare it, so that it has extremely high chemical stability, can resist corrosion from most chemicals, and is suitable for applications in special environments. In order to improve thermal stability, polyethylene terephthalate, polyethylene naphthalate, polycarbonate and the like can be used to prepare it, so that it has good thermal stability and can be used in high temperature environments. Taken together, the enumeration of the above-mentioned various materials enables the base film layer 1 to have excellent physical properties, chemical stability, thermal stability, electrical insulation, processability and other aspects, which can meet different application requirements and improve the overall performance and reliability of the product.

[0053] In some embodiments, the conductive metal layer 2 includes copper or aluminum. In this embodiment, the conductive metal material is limited so that it can be selected according to specific needs, thereby improving the flexibility of its preparation.

[0054] For example, in high-power density batteries or applications requiring efficient current transmission, copper may be preferred as the material for the conductive metal layer 2. In cost-sensitive and weight-sensitive applications, aluminum may be preferred as the material for the conductive metal layer 2.

[0055] like Figure 2 As shown, the second aspect of the present invention provides a method for preparing the composite foil current collector provided by any of the above embodiments, comprising the following steps: Step S10: prepare a base film layer 1 by a casting method or a blown film method, and form a step structure on the surface of both sides of the base film layer 1 in the thickness direction.

[0056] Specifically, when using the cast film method, molten PP (melting temperature 180±5°C) is passed through a casting roll with grooves, with a depth of 0.5-1.2 μm. After cooling, a symmetrical square or trapezoidal step structure is formed. Alternatively, when using the blown film method, the PET extrusion temperature is kept between 200-240°C, and the air pressure is controlled (0.1-0.4 MPa) to form a uniform square step structure on the PET film surface.

[0057] Step S20, using magnetron sputtering technology and controlling the sputtering power to deposit conductive metal layers 2 of different thicknesses on different surfaces of the step structure, and making the conductive metal layer 2 away from the surface of the base film layer 1 to form a connection plane.

[0058] Specifically, a photoelectric sensor (response time 1ms) is used to identify the step structure mark. When the welding section 21 is detected, the power is switched within 0.1 seconds through the IGBT module, and the power output is adjusted in real time through the β-ray thickness gauge (accuracy 0.01μm).

[0059] During the deposition welding section 21, the deposition was performed with a power density of 2.5-3.5 W / cm² and a sputtering time of 15-20 min. During the deposition coating section 22, the deposition was performed with a power density of 1-1.8 W / cm² and a sputtering time of 10-15 min.

[0060] Step S30: coating the connection plane with active material to form an electrode layer 3. Specifically, coating the active material on the corresponding area to form the electrode layer 3, which includes a positive electrode sheet or a negative electrode sheet.

[0061] A third aspect of the present invention provides a battery comprising multiple composite foil current collectors according to any of the aforementioned embodiments, wherein the multiple composite foil current collectors are stacked. Specifically, the conductive layer of the obtained positive electrode sheet or negative electrode sheet welding area (i.e., welding section 21) is roll-welded to form tabs. The positive electrode sheets, negative electrode sheets, and separators obtained in this manner are stacked together, and the multiple layers of cells are welded, assembled, injected, and formed to form a battery.

[0062] The following is an illustrative description of the method for preparing a composite foil current collector through specific embodiments. The following examples can be understood in conjunction with the aforementioned embodiments.

[0063] Example 1 The casting method is used to form molten PP (melting temperature 180±5℃) through a casting roller with grooves. The groove depth is 1.0um. After cooling, a symmetrical 1.0um trapezoidal step structure (the connecting surface is a slope) is formed. The overall thickness of the base film is 4.5um. Then, a 1um thick coating section 22 is obtained by partitioned sputtering. The thickness of the welding section 21 is 2um. The overall thickness of the composite foil current collector is 6.5um.

[0064] Example 2 The preparation of the composite foil current collector is basically the same as that in Example 1, the main difference is that the groove depth is 0.5um, the overall thickness of the base film is 3.5um, the thickness of the coating section 22 is 1um, the thickness of the welding section 21 is 1.5um, and the overall thickness of the composite foil current collector is 5.5um.

[0065] Example 3 The preparation of the composite foil current collector is basically the same as that in Example 1, the main difference is that the groove depth is 0.8um, the overall thickness of the base film is 4.1um, the thickness of the coating section 22 is 1um, the thickness of the welding section 22 is 1.8um, and the overall thickness of the composite foil current collector is 6.1um.

[0066] Example 4 The preparation of the composite foil current collector is basically the same as that in Example 1, the main differences are that the groove depth is 1.2um, the overall thickness of the base film is 4.9um, the thickness of the coating section 22 is 1um, the thickness of the welding section 21 is 2.2um, and the overall thickness of the composite foil current collector is 6.9um.

[0067] Comparative Example The base film in the comparative example is a 4.5 μm thick base film with a flat surface, 1 μm copper plating on both sides, and the overall thickness of the composite foil current collector is 6.5 μm.

[0068] The above embodiment is prepared into a lithium ion battery, which specifically includes the following steps: (1) Preparation of positive electrode sheets: Lithium iron phosphate material, conductive agent (SP) and binder (PVDF) are mixed in a mass ratio of 97:1.2:1.8, and NMP is added and mixed thoroughly to obtain positive electrode slurry. This slurry is evenly coated on 12 μm thick carbon-coated aluminum foil by extrusion coating, and after drying and roller pressing, it is die-cut into positive electrode sheets.

[0069] (2) Preparation of negative electrode sheets: Graphite, conductive agent (SP), dispersant (CMC) and binder (SBR) are fully mixed in a mass ratio of 96:1:1.8:1.2, and deionized water is added thereto to obtain a mixed slurry. The slurry is evenly coated on the current collectors of the above-mentioned embodiments and comparative examples by extrusion coating, rolled and dried, and die-cut into negative electrode sheets. After stacking with the positive electrode sheets, the sheets are welded into a shell, injected with liquid, packaged, formed, and divided into different volumes to obtain a soft-pack lithium-ion battery.

[0070] The lithium-ion batteries obtained in the above embodiments and comparative examples were tested for internal resistance and battery 25°C 3C rate capacity retention rate. The test results are shown in Table 1.

[0071] Table 1 Battery performance test results of various embodiments and comparative examples

[0072] It can be seen from the above data that the composite foil current collector provided in this embodiment can reduce the internal resistance of the battery and improve the battery's current capacity at high rates.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A composite foil current collector, characterized in that: include: A base film layer and a conductive metal layer and an electrode layer sequentially stacked on both sides of the base film layer in a thickness direction; In which, both side surfaces of the base film layer in the thickness direction are formed with a raised step structure; the conductive metal layer includes a coating section and a welding section, and the thickness of the welding section is greater than the thickness of the coating section, so as to cooperate with the step structure of the base film layer and make the conductive metal layer away from the surface of the base film layer to form a connection plane, and the connection plane is coated with active material to form the electrode layer.

2. The composite foil current collector according to claim 1, characterized in that The electrode layer is arranged on the connection plane corresponding to the coating section so that an edge of one side of the electrode layer in the width direction is flush with an edge of the coating section.

3. The composite foil current collector according to claim 1, characterized in that: The base film layer includes a first connecting section and a second connecting section, wherein the thickness of the first connecting section is smaller than the thickness of the second connecting section; and a connecting surface is provided between the first connecting section and the second connecting section to form a step structure on two opposite surfaces of the base film layer; The first connecting section is connected to the welding section, and the second connecting section is connected to the coating section; and the width of the first connecting section is smaller than the width of the second connecting section.

4. The composite foil current collector according to claim 3, characterized in that A single-side height difference between the first connecting section and the second connecting section in the thickness direction is 0.5-1.2 μm.

5. The composite foil current collector according to claim 3, characterized in that: The maximum thickness of the base film layer is 3~10.5um.

6. The composite foil current collector according to claim 1, characterized in that: The step structures on both sides of the base film layer in the thickness direction are symmetrically arranged with respect to the center plane of the base film layer.

7. The composite foil current collector according to claim 1, characterized in that: The thickness of the coating section is 0.8~2um; And / or, the width of the welding section is 1 / 30 to 1 / 10 of the width of the coating section.

8. A method for preparing the composite foil current collector according to any one of claims 1 to 7, characterized in that: The following steps are involved: Prepare a base film layer by a casting method or a blown film method, and form a step structure on the surface of both sides of the base film layer in the thickness direction; Using magnetron sputtering technology and controlling the sputtering power to deposit conductive metal layers of different thicknesses on different surfaces of the step structure, and making the conductive metal layers away from the surface of the base film layer to form a connection plane; Active material is coated on the connection plane to form an electrode layer.

9. The preparation method according to claim 8, characterized in that The method of utilizing magnetron sputtering technology and controlling the sputtering power to deposit conductive metal layers of different thicknesses on different surfaces of the step structure specifically includes the following steps: In the welding section, the deposition was performed with a power density of 2.5~3.5W / cm² and a sputtering time of 15~20min; During the coating stage, the deposition was performed using a power density of 1-1.8 W / cm² and a sputtering time of 10-15 minutes.

10. A battery, characterized in that: The composite foil current collector comprises a plurality of composite foil current collectors according to any one of claims 1 to 7, wherein the plurality of composite foil current collectors are stacked.

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