Composite current collector, method for preparing the same, and lithium ion battery
By setting an elastic modulus gradient transition layer in the composite current collector and performing cold rolling, the problems of coarse grains and high porosity in the metal layer are solved, achieving densification of the metal layer and improvement of battery performance, thus ensuring the stability and safety of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- JIANGSU YINGLIAN COMPOSITE FLUID COLLECTION CO LTD
- Filing Date
- 2026-04-30
- Publication Date
- 2026-07-14
AI Technical Summary
In existing composite current collector processes, the metal layer has large grains and high internal porosity, resulting in high volume resistance and significant heat generation during high-rate charge and discharge, which affects battery power performance and cycle life. Furthermore, the uneven thickness of the metal layer coating leads to uneven current distribution, which exacerbates lithium dendrite growth and localized heating.
The method involves setting metal layers on both sides of the base film layer and then performing cold rolling. An elastic modulus gradient transition layer is set between the base film layer and the metal layer. The plastic deformation during the cold rolling process refines the grains and closes the pores inside the metal layer. At the same time, the elastic modulus gradient transition layer buffers the cold rolling stress and avoids interface delamination.
It significantly improves the density of the metal layer, enhances conductivity and mechanical properties, reduces internal resistance, improves battery power performance and cycle life, and ensures stable bonding between the metal layer and the base film.
Smart Images
Figure CN122393311A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of composite current collector preparation technology, and in particular to a composite current collector, its preparation method, and a lithium-ion battery. Background Technology
[0002] The composite current collector adopts a sandwich structure of "metal layer-polymer base film-metal layer", with a polymer base film such as PET / PP as the core. Composite copper current collectors are usually prepared by magnetron sputtering + water plating, while composite aluminum current collectors are mostly prepared by a one-time vapor deposition process, ultimately forming a sandwich structure of "metal layer-base film layer-metal layer". Compared with traditional copper / aluminum foil current collectors, this structure has the advantages of lightweight, high safety and high energy density, and is a core upgrade material for power batteries.
[0003] However, the existing technology has the following key drawbacks that restrict its large-scale application: Composite current collectors prepared by conventional processes have coarse grains and high internal porosity in the metal layer, resulting in higher resistivity than pure metal current collectors. This leads to significant heat generation during high-rate charge and discharge, affecting battery power performance and cycle life. Furthermore, the uneven thickness of the metal layer coating results in uneven battery current distribution, exacerbating problems such as lithium dendrite growth and localized heating. Summary of the Invention
[0004] One of the objectives of this invention is to provide a composite current collector to at least solve one of the technical problems existing in the prior art.
[0005] The second objective of this invention is to provide a method for preparing a composite current collector.
[0006] A third objective of this invention is to provide a composite current collector or a composite current collector prepared by the aforementioned method for use in the preparation of lithium-ion batteries.
[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a composite current collector, comprising: a base film layer, wherein a metal layer is disposed on at least one side of the base film layer, and the metal layer is subjected to cold rolling treatment.
[0008] Furthermore, the single-pass processing rate of the cold rolling process is 6%-8%.
[0009] Furthermore, a first transition layer and a second transition layer are disposed between the base film layer and the metal layer. The first transition layer and the second transition layer are disposed sequentially in a direction away from the base film layer, and the elastic modulus of the base film layer, the first transition layer, the second transition layer and the metal layer increase sequentially.
[0010] Furthermore, the elastic modulus of the first transition layer is 5-10 GPa, and the elastic modulus of the second transition layer is 30-50 GPa; and / or, the thickness of the first transition layer is 10-40 nm, and the thickness of the second transition layer is 10-40 nm.
[0011] Furthermore, the first transition layer comprises a flexible resin and rigid particles in a mass ratio of (60-70):(20-30); And / or, the second transition layer comprises metal nanoparticles and alumina ceramic particles in a mass ratio of (3-5):(5-7).
[0012] Furthermore, the flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin. And / or, the metal nanoparticles include one or more of the following: copper nanoparticles, aluminum nanoparticles, nickel nanoparticles, and titanium nanoparticles.
[0013] Secondly, the present invention provides a method for preparing a composite current collector, comprising: A coating liquid containing flexible resin and rigid particles is applied to the surface of the base film layer, and after pre-drying, a first transition layer is formed. A second transition layer containing metal nanoparticles and ceramic particles is deposited on the surface of the first transition layer by magnetron sputtering. A metal layer is prepared on the second transition layer by magnetron sputtering and / or vapor deposition. The metal layer is subjected to cold rolling.
[0014] Furthermore, the fabrication of the first transition layer and the fabrication of the second transition layer satisfy one or more of the following conditions: (1) When the first transition layer is prepared, the components of the coating liquid include one or more of flexible resin, rigid particles, dispersant and curing agent; Optionally, the mass ratio of the flexible resin to the rigid particles is (60-70):(20-30). Optionally, the mass ratio of the flexible resin to the dispersant is (60-70):(3-7); Optionally, the mass ratio of the flexible resin to the curing agent is (60-70):(3-7); Optionally, the flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin; Optionally, the dispersant includes one or more of polycarboxylate polymeric dispersants and ammonium polyacrylate dispersants; Optionally, the curing agent includes one or more of low-temperature isocyanate curing agents and modified aliphatic polyisocyanates; Optionally, the coating method includes at least one of slot coating, microgravure coating, and spin coating; (2) When the second transition layer is prepared, the mass ratio of metal nanoparticles to alumina ceramic particles is (3-5):(5-7); Optionally, the metal nanoparticles include one or more of the following: copper nanoparticles, aluminum nanoparticles, nickel nanoparticles, and titanium nanoparticles.
[0015] Furthermore, one or more of the following conditions must be met: (1) After the second transition layer is prepared, it is cured. (2) The rolling force of the cold rolling process is 7-12 kN / cm; the rolling speed of the cold rolling process is 12-18 m / min.
[0016] (3) The elastic modulus of the first transition layer is less than that of the second transition layer.
[0017] Thirdly, the present invention provides a lithium-ion battery, including the composite current collector described above or the composite current collector prepared by the preparation method described above.
[0018] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing the composite current collector provided by the present invention involves applying cold rolling to the metal layer after its formation. The plastic deformation during the cold rolling process causes dislocation slip and grain breakage in the original columnar crystal structure inside the metal layer. At the same time, the rolling pressure causes the micropores distributed inside the metal layer to close, thereby significantly improving the densification of the metal layer and ultimately achieving the technical effects of densification, improved mechanical properties and electrical conductivity of the metal layer. Attached Figure Description
[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0020] Figure 1 A schematic diagram of the composite current collector provided in an embodiment of the present invention.
[0021] Icons: 1-Base film layer; 2-First transition layer; 3-Second transition layer; 4-Metal layer. Detailed Implementation
[0022] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.
[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0024] The first aspect of the present invention provides a composite current collector, comprising: a base film layer 1, wherein a metal layer 4 is disposed on at least one side of the base film layer 1, and the metal layer 4 is subjected to cold rolling treatment.
[0025] In this invention, the composite current collector includes a base film layer 1 and metal layers 4 disposed on both sides of the base film. The metal layers 4 are processed by cold rolling. This invention applies the cold rolling process to the preparation of the metal layer 4 of the composite current collector. By utilizing the plastic deformation effect of cold rolling, the columnar crystal structure inside the metal layer 4 is broken and the pores are closed. At the same time, the grains are guided to grow in a directional manner along the rolling direction, thereby releasing the residual tensile stress in the metal layer 4. Ultimately, this achieves the purpose of densifying the metal layer 4 and improving its mechanical and electrical properties.
[0026] In some preferred embodiments, the single-pass processing rate of the cold rolling process is 6%-8%, for example, it can be 6%, 7%, 8%, etc. The rolling force of the cold rolling process is 7-12 kN / cm, for example, it can be 7 kN / cm, 8 kN / cm, 9 kN / cm, 10 kN / cm, 11 kN / cm, 12 kN / cm, etc.; the rolling speed of the cold rolling process is 12-18 m / min, for example, it can be 12 m / min, 14 m / min, 16 m / min, 18 m / min, etc.
[0027] This invention employs a cold rolling process, controlling the single-pass processing rate at 6%-8%. This ensures that the plastic deformation is primarily borne by the metal layer 4, while the base film undergoes only elastic deformation and minor molecular chain rearrangement, far below its brittle fracture critical value. The formula for calculating the single-pass processing rate is: Single-pass processing rate = (Thickness before rolling h0) / (Thickness before rolling) Thickness after rolling (h1) ÷ Thickness before rolling (h0) × 100%.
[0028] Specifically, the cold rolling processing rate range in this invention is precisely matched with the plastic deformation capacity of the metal layer 4. This ensures that the metal layer 4 undergoes sufficient plastic deformation, achieving residual stress release, grain refinement, and densification. It also avoids excessive processing rate leading to cracking and peeling of the metal layer 4, or insufficient processing rate failing to achieve the strengthening effect. Excessive processing rate exceeds the plastic limit of the metal layer 4, causing network cracks and interface delamination; insufficient processing rate fails to close the pores of the metal layer 4 and release residual stress, thus failing to achieve the strengthening effect of cold rolling. Simultaneously, this range adapts to the stress buffering effect of the subsequent gradient transition layer, further ensuring no damage to the base film and improving mass production yield. It should be noted that the single-pass processing rate is achieved by precisely adjusting the gap size between the upper and lower rolls, combined with a safe rolling force, using the roll gap as the core to control the processing rate, thereby obtaining different single-pass processing rates.
[0029] In alternative implementations, such as Figure 1 As shown, the structure of the composite current collector provided by the present invention specifically includes: A base film layer 1; metal layers 4 disposed on both sides of the base film layer 1; a first transition layer 2 and a second transition layer 3 disposed between the base film layer 1 and the metal layer 4, the first transition layer 2 and the second transition layer 3 being disposed sequentially in a direction away from the base film layer 1, and the elastic modulus of the base film layer 1, the first transition layer 2, the second transition layer 3 and the metal layer 4 increasing sequentially.
[0030] The composite current collector provided by this invention features an elastic modulus gradient transition layer composed of a first transition layer 2 and a second transition layer 3 between the base film layer 1 and each side of the metal layer 4, with the elastic modulus of the base film layer 1, the first transition layer 2, the second transition layer 3, and the metal layer 4 increasing sequentially. The elastic modulus gradient transition layer acts as a stress buffer, dispersing dislocation slip stress step by step when the composite current collector is subjected to external stress (such as cold rolling of the metal layer 4), preventing stress concentration at the interface of the base film layer 1. Simultaneously, the elastic modulus gradient transition layer forms a chemical bond with the base film layer 1 and a mechanical bond with the metal layer 4, synchronously enhancing the interfacial bonding force, allowing the metal layer 4 and the base film to deform synchronously, eliminating base film damage caused by deformation mismatch.
[0031] Regarding the gradient transition of the elastic modulus, specifically: The elastic modulus of the first transition layer is 5-10 GPa, for example, 5 GPa, 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, etc. The elastic modulus of the second transition layer is 30-50 GPa, for example, 30 GPa, 40 GPa, 50 GPa, etc. The elastic modulus of the metal layer is 70-110 GPa, for example, 70 GPa, 80 GPa, 90 GPa, 100 GPa, 110 GPa, etc.
[0032] In this invention, an elastic modulus gradient transition layer is provided between the base film layer and the metal layer, with the elastic modulus of the first and second transition layers gradually increasing along the direction from the base film layer to the metal layer. Due to the significant difference in modulus between the metal layer and the base film layer (20-30 times), the deformation rate and amount of deformation during cold rolling are asynchronous, resulting in severe shear stress at the interface. This leads to room temperature brittle cracking and perforation of the base film (PET / PP), as well as peeling and delamination of the metal layer. The elastic modulus gradient transition layer design eliminates the modulus cliff difference between the metal layer and the base film layer. The gradient structure achieves gradual buffering and uniform transmission of cold rolling stress, avoiding stress concentration. It also avoids the problems caused by the significant difference in modulus between the metal layer and the polymer base film, which leads to asynchronous deformation rate and amount of deformation during cold rolling, severe shear stress at the interface, and consequently, room temperature brittle cracking and perforation of the base film (PET / PP), as well as peeling and delamination of the metal layer. Furthermore, the gradient structure strengthens the interfacial bonding between the base film and the metal layer.
[0033] In some preferred embodiments, the thickness of the first transition layer is 10-40 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, etc. The raw materials of the first transition layer include flexible resin and rigid particles. The flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin; the rigid particles include nano-SiO2 particles. The mass ratio of rigid particles to flexible resin is 20-30:60-70, where "20-30" can be, for example, 20, 25, 30, etc., and "60-70" can be, for example, 60, 65, 70, etc.
[0034] In some preferred embodiments, the thickness of the second transition layer is 10-40 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm, etc. The raw materials of the second transition layer include metal nanoparticles and alumina ceramic particles; wherein the metal nanoparticles include one or more of nano-copper particles, nano-aluminum particles, nano-nickel particles, and nano-titanium particles, the particle size of the metal nanoparticles is 8-15 nm, and the purity is ≥99.99%; wherein the mass ratio of the metal nanoparticles to the alumina ceramic particles is 3-5:5-7, where "3-5" can be, for example, 3, 4, 5, etc., and "5-7" can be, for example, 5, 6, 7, etc.
[0035] In this invention, the first transition layer combines flexible resin with rigid particles. The flexible resin achieves strong bonding with the base film layer, while the rigid particles provide rigid reinforcement, stabilizing the elastic modulus of the first transition layer at 5-10 GPa and smoothly connecting with the modulus of the polymer base film (3.5 GPa). The second transition layer preferably uses nano-Cu particles that are lattice-matched with the subsequently sputtered metal seed layer to form a metallurgical bond, enhancing the bonding force with the metal layer. The alumina ceramic particles are rigid and chemically stable, not reacting chemically with the metal layer or the first transition layer, thus increasing the modulus of the second transition layer and ensuring its elastic modulus remains stable at 30-50 GPa. This connects the first transition layer (5-10 GPa) with the metal layer (70-110 GPa), forming a smooth modulus gradient and ensuring the stability of the gradient structure.
[0036] A second aspect of the present invention provides a method for preparing a composite current collector, which further includes the following steps: A coating liquid containing flexible resin and rigid particles is applied to the surface of the base film layer, and after pre-drying, a first transition layer is formed. A second transition layer containing metal nanoparticles and ceramic particles is deposited on the surface of the first transition layer by magnetron sputtering. A metal layer is prepared on the second transition layer by magnetron sputtering and / or vapor deposition. The metal layer is subjected to cold rolling.
[0037] This invention achieves dual optimization by applying cold rolling after the metal layer is formed, utilizing the plastic deformation capability of the metal layer: on the one hand, cold rolling causes the metal layer to undergo controllable extension and compression, making the thickness fluctuation of the original coating more uniform and reducing the risk of uneven current distribution; on the other hand, the dislocation slip and grain breakage during the cold rolling process refine the coarse columnar crystal structure inside the metal layer, while the pores close under compressive stress, thereby improving the density of the metal layer. However, during cold rolling, the rolls apply constant pressure. The high-modulus Cu / Al metal layer has extremely strong resistance to deformation, and only undergoes controllable micro-plastic deformation (dislocation slip). The deformation amount is small and the deformation rate is slow. On the other hand, the low-modulus polymer base film (such as PET / PP) has extremely weak resistance to deformation. Under the same pressure, it will undergo large elastic compression deformation, and the deformation rate is much faster than that of the metal layer. The deformation rhythms of the two are completely out of sync. There is no buffer space at the interface, and the external force cannot be evenly dissipated. This will generate continuous shear and compressive stress at the interface between the two, and continuously accumulate at local defects, forming stress spurs. This will cause the metal layer to lift and fall off, and the base film to undergo room temperature brittle cracking or perforation. To address this interface mismatch issue, the present invention incorporates an elastic modulus gradient transition layer. By continuously and progressively decreasing the modulus from the metal layer side to the base film side, the cold rolling stress is buffered and uniformly transmitted step by step. Therefore, the cold rolling process and the elastic modulus gradient transition layer work together and complement each other. The transition layer buffers and uniformly transmits the cold rolling stress step by step, avoiding stress concentration that could lead to base film brittleness or interface delamination.
[0038] In some preferred embodiments, when the first transition layer is prepared, the components of the coating liquid include one or more of flexible resin, rigid particles, dispersant and curing agent.
[0039] In some preferred embodiments, the mass ratio of the flexible resin to the rigid particles is 60-70:20-30, where "20-30" can be, for example, 20, 25, 30, etc., and "60-70" can be, for example, 60, 65, 70, etc.
[0040] In some preferred embodiments, the mass ratio of the flexible resin to the dispersant is 60-70:3-7, where "60-70" can be, for example, 60, 65, 70, etc., and "3-7" can be, for example, 3, 4, 5, 6, 7, etc.
[0041] In some preferred embodiments, the mass ratio of the flexible resin to the curing agent is 60-70:3-7, where "60-70" can be, for example, 60, 65, 70, etc., and "3-7" can be, for example, 3, 4, 5, 6, 7, etc.
[0042] In some preferred embodiments, the flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin.
[0043] In some preferred embodiments, the dispersant includes one or more of polycarboxylate polymeric dispersants and polyacrylate ammonium salt dispersants.
[0044] In some preferred embodiments, the curing agent includes one or more of a low-temperature isocyanate curing agent and a modified aliphatic polyisocyanate.
[0045] Preferably, the temperature required to prepare the coating solution is 25-30℃, for example, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, etc., the stirring speed required during the mixing of the components of the coating solution is 800-1000 r / min, for example, 800 r / min, 900 r / min, 1000 r / min, etc., and the stirring time is 30-40 min, for example, 30 min, 35 min, 40 min.
[0046] Preferably, the coating method includes at least one of slit coating, microgravure coating, and spin coating; wherein the slit width of the slit coating device is 50-100μm, for example, 50μm, 75μm, 100μm, etc.; the coating speed is 12-18m / min, for example, 12m / min, 14m / min, 16m / min, 18m / min, etc., and the base film tension is controlled at 10-20N during the coating process, for example, 10N, 15N, 20N, etc.
[0047] Preferably, the temperature of the pre-drying treatment is 50-60℃, for example, 50℃, 55℃, 60℃, etc., the wind speed of the pre-drying treatment is 2-3m / s, and the time of the pre-drying treatment is 15-20s, for example, 15s, 16s, 17s, 18s, 19s, 20s, etc.
[0048] In some preferred embodiments, the preparation process of the second transition layer includes: depositing a composite target containing metal nanoparticles and ceramic particles on the surface of the first transition layer using magnetron sputtering; preferably, the sputtering power is 150-200W, for example, 150W, 175W, 200W, etc., the base film delivery speed is 12-18m / min, for example, 12m / min, 14m / min, 16m / min, 18m / min, etc., and the argon flow rate is 20-30sccm, for example, 20sccm, 25sccm, 30sccm, etc.
[0049] In some preferred embodiments, the preparation method further includes: curing the base film layer on which the second transition layer is prepared.
[0050] Preferably, the curing process includes one or both of UV curing and thermal curing; the curing temperature is 60-80℃, for example, 60℃, 70℃, 80℃, etc.; the UV curing time is 5-10s, for example, 5s, 6s, 7s, 8s, 9s, 10s, etc.; and the thermal curing time is 20-30s, for example, 20s, 25s, 30s, etc.
[0051] The low-temperature curing parameters in this invention can prevent the polymer base film from melting and deforming, while ensuring that the resin in the first transition layer is fully cured. The particles in the second transition layer form a strong interpenetrating network with the first transition layer, which enhances the overall stability and interfacial bonding of the double transition layer.
[0052] A third aspect of the present invention provides a composite current collector or a composite current collector prepared by the aforementioned preparation method, and its application in the preparation of lithium-ion batteries.
[0053] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.
[0054] Example 1 This embodiment provides a composite current collector, which includes a base film layer and metal layers disposed on both sides of the base film. A first transition layer and a second transition layer are stacked between the base film layer and the metal layers. The first transition layer is close to the base film layer, and the second transition layer is far away from the base film layer.
[0055] The preparation process of the composite current collector is as follows: S1. Preparation of the first transition layer: S1.1, Polycaprolactone-type polyurethane resin (purchased from Covestro, brand name Desmopan) in a mass ratio of 65:25:5:5. ® 460), nano-SiO2 particles (particle size 11nm), polycarboxylate polymeric dispersant (brand: BYK-103), and modified aliphatic polyisocyanate (brand: BASF LQ-80) were added to a stirring container and stirred for 35 minutes at 28℃ and 900r / min to prepare the coating solution; S1.2. The coating liquid is applied to the surface of the base film layer (the base film layer material is PET, the base film layer thickness is 4μm, and the elastic modulus is 3.5GPa) by slit coating. The slit width (80μm) and coating speed (15 m / min) of the coating device are adjusted, and the tension of the base film is controlled at 15N during the coating process. S1.3 After coating, the base film is transported to a pre-drying oven and pre-dried for 18 seconds at 55°C and a wind speed of 2-3 m / s to remove moisture from the coating solution, thus obtaining the first transition layer with a thickness of 25 nm and an elastic modulus of 7.5 GPa.
[0056] S2. Preparation of the second transition layer: The base film coated with the first transition layer is sent to the magnetron sputtering chamber. A target material is prepared by mixing nano-aluminum particles and alumina ceramic particles in a mass ratio of 4:6. The sputtering power is adjusted to 180 W, the base film delivery speed is the same as the previous coating speed (15 m / min), and the argon flow rate is 25 sccm. The second transition layer is prepared with a thickness of 25 nm and an elastic modulus of 40 GPa.
[0057] S3. After the second transition layer is prepared, it is cured. The specific steps are as follows: The base film with the second transition layer prepared is transported to a low-temperature curing oven and cured using a combination of UV curing and thermal curing. The curing temperature is 70℃, the UV irradiation time is 8s, and the thermal curing time is 25s.
[0058] S4. Preparation of the metal layer: Place the cured base film into the winding system of the vacuum evaporation equipment, thread the base film through the tape, and then evaporate the evaporation chamber to 9.0 × 10⁻⁶. -1 Pa, a metallic aluminum layer was prepared on the surface of the second transition layer by vacuum evaporation deposition. The thickness of the metallic aluminum layer was 1 μm and the elastic modulus was 90 GPa.
[0059] S5. Simultaneously cold-roll both metal layers: single-pass cold rolling rate 7%, rolling force 10 kN / cm, rolling speed 15 m / min. The final composite current collector is obtained.
[0060] Example 2 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: the thickness of the first transition layer in the composite current collector is 25 nm and the elastic modulus is 10 GPa; the thickness of the second transition layer is 25 nm and the elastic modulus is 30 GPa.
[0061] The preparation process of the composite current collector differs from that in Example 1 in that: In S1, the coating liquid is prepared by adjusting the mass ratio of polycaprolactone-type polyurethane resin (purchased from Covestro, brand name Desmopan® 460) to 60:30:5:5, nano-SiO2 particles (particle size 11nm), polycarboxylate polymeric dispersant (brand name: BYK-103), and modified aliphatic polyisocyanate (brand name: BASF LQ-80) as the curing agent. In S2, the target material is adjusted to be a mixture of nano-aluminum particles and alumina ceramic particles with a mass ratio of 5:5.
[0062] Example 3 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: the thickness of the first transition layer in the composite current collector is 25 nm and the elastic modulus is 5 GPa; the thickness of the second transition layer is 25 nm and the elastic modulus is 50 GPa.
[0063] The preparation process of the composite current collector differs from that in Example 1 in that: In S1, the mass ratio of the coating liquid was adjusted to 70:20:5:5 using polycaprolactone-based polyurethane resin (purchased from Covestro, brand name Desmopan). ® 460), nano-SiO2 particles (particle size 11nm), dispersant is polycarboxylate polymeric dispersant (brand: BYK-103), curing agent is modified aliphatic polyisocyanate (brand: BASF LQ-80); In S2, the target material is adjusted to be a mixture of nano-aluminum particles and alumina ceramic particles with a mass ratio of 3:7.
[0064] Example 4 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: in S5, the single-pass cold rolling processing rate is 6%, the rolling force is 12 kN / cm, and the rolling speed is 12 m / min.
[0065] Example 5 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: in S5, the single-pass cold rolling processing rate is 8%, the rolling force is 7 kN / cm, and the rolling speed is 18 m / min.
[0066] Example 6 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: in S5, the single-pass cold rolling processing rate is 5%.
[0067] Example 7 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: in S5, the single-pass cold rolling processing rate is 9%.
[0068] Example 8 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: the elastic modulus of the first transition layer in the composite current collector is 4 GPa; and the elastic modulus of the second transition layer is 55 GPa.
[0069] The preparation process of the composite current collector differs from that in Example 1 in that: In S1, the mass ratio of the coating solution was adjusted to 72:18:5:5 using polycaprolactone-type polyurethane resin (purchased from Covestro, brand name Desmopan). ® 460), nano-SiO2 particles (particle size 11nm), dispersant is polycarboxylate polymeric dispersant (brand: BYK-103), curing agent is modified aliphatic polyisocyanate (brand: BASF LQ-80); In S2, the target material is adjusted to be a mixture of nano-aluminum particles and alumina ceramic particles with a mass ratio of 2:8.
[0070] Example 9 This embodiment provides a composite current collector, which differs from Embodiment 1 in that: the elastic modulus of the first transition layer in the composite current collector is 15 GPa; and the elastic modulus of the second transition layer is 25 GPa.
[0071] The preparation process of the composite current collector differs from that in Example 1 in that: In S1, the mass ratio of the coating solution is adjusted to 55:35:5:5 using polycaprolactone-type polyurethane resin (purchased from Covestro, brand name Desmopan). ® 460), nano-SiO2 particles (particle size 11nm), dispersant is polycarboxylate polymeric dispersant (brand: BYK-103), curing agent is modified aliphatic polyisocyanate (brand: BASF LQ-80); In S2, the target material is adjusted to be a mixture of nano-aluminum particles and alumina ceramic particles with a mass ratio of 6:4.
[0072] Comparative Example 1 This comparative example provides a composite current collector, which differs from Example 1 in that: no first transition layer and second transition layer are prepared, and the metal layer is not subjected to cold rolling treatment.
[0073] Test case The composite current collectors prepared in the above embodiments and comparative examples were used as samples for testing.
[0074] Test method: The composite current collectors obtained in Examples 1-9 and Comparative Example 1 were subjected to performance tests.
[0075] (1) Sheet resistance test: The sheet resistance of the composite current collector, which is the test object, is tested using a four-probe tester.
[0076] (2) Adhesion test: The adhesion between the composite current collector membrane layers was evaluated by the 180° peel method (refer to ASTM D3330 standard).
[0077] 1. Sample preparation: Cut the prepared composite current collector sample into strips with a width of 15 mm and a length of not less than 150 mm.
[0078] 2. Testing process: a. Use high-strength double-sided tape to fix the sample (test side up) onto a flat steel plate.
[0079] b. Firmly adhere the standard test tape (3M #610) to the surface of the metal layer (aluminum layer) and roll it back and forth 3 times with a standard pressure roller at a constant speed and pressure to ensure no air bubbles.
[0080] c. On a universal testing machine, peel the tape at a peel angle of 180° and a constant speed of 100 mm / min, and continuously record the force values during the peeling process.
[0081] 3. Data processing: Take the average force value (unit: N) during the stable phase of the peeling process, divide it by the sample width (unit: m) to obtain the peel strength, which is N / m.
[0082] (3) Battery stability test The composite current collectors obtained in Examples 1-9 and Comparative Example 1 were used to prepare pouch cells (the positive electrode active material was NCM811, the negative electrode active material was graphite, and the electrolyte was 1M lithium hexafluorophosphate solution, in which the solvent was ethylene carbonate) for electrical performance testing.
[0083] Capacity retention rate: The test steps include: 1) Discharge the battery cell I1 (1-hour discharge current) to the discharge termination voltage at 25℃ and let it stand for 30 minutes; 2) Charge the battery cell at a constant current of I1 to the charging termination voltage, then switch to constant voltage charging until the charging termination current drops to 0.05 times I1, then stop charging and let it stand for 30 minutes; 3) Discharge the battery cell at I1 to the discharge termination voltage; 4) Repeat steps 1)-3) for 500 cycles, record the battery capacity at the first cycle and the 500th cycle, and calculate the battery capacity retention rate, which is the battery capacity at the 500th cycle / the battery capacity at the first cycle × 100%.
[0084] The test data is recorded in Table 1.
[0085] The test results are shown in Table 1.
[0086] Table 1
[0087] As can be seen from the data in Table 1, the elastic modulus of the first transition layer is within 5-10 GPa, and the elastic modulus of the second transition layer is within 30-50 GPa. At this time, the bonding force and conductivity of the composite current collector maintain excellent performance and stability. The data from Examples 1, 4-5 and Comparative Example 1 show that the single-pass processing rate of cold rolling is within 6%-8%. At this time, the bonding force and conductivity of the composite current collector maintain excellent performance and stability, indicating that the metal layer has improved its density and reduced its internal resistance through cold rolling. Data from Examples 1, 6-7, and Comparative Example 1 show that when the single-pass processing rate of cold rolling is less than 6%, the internal resistance of the composite current collector is high and the capacity retention rate decreases. This indicates that a low processing rate can only achieve shallow surface compression of the metal layer, but cannot achieve effective and sufficient plastic deformation. The increase in metal layer density is limited, and the improvement in conductivity and structural stability is poor. When the single-pass processing rate of cold rolling is greater than 8%, the internal resistance of the composite current collector increases and the capacity retention rate decreases. This indicates that the processing rate is too high, the deformation of the metal layer exceeds the plastic limit of the metal layer, and the excessive extension of the metal layer leads to microcracks and grain boundary defects, resulting in increased internal resistance. Data from Examples 1 and 8-9 show that the elastic moduli of the first and second transition layers are outside the range. In this case, the bonding force decreases and the internal resistance increases sharply, indicating that the elastic modulus of the first transition layer is too large, resulting in a large modulus difference with the base film layer. This leads to the inability to buffer stress during cold rolling, causing the interface between the base film and the first transition layer to peel off, resulting in metal layer fracture, increased internal resistance, and decreased bonding force. The elastic modulus of the second transition layer is relatively small, making it unable to connect the first transition layer and the metal layer. During cold rolling, the plastic deformation of the metal layer cannot be effectively transferred, causing the metal layer and the second transition layer to peel off, the metal layer to peel off and crack locally, resulting in increased internal resistance and decreased bonding force.
[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A composite current collector, characterized in that, include: A base film layer, wherein a metal layer is disposed on at least one side of the base film layer, and the metal layer is subjected to cold rolling treatment.
2. The composite current collector according to claim 1, characterized in that, The single-pass processing rate of the cold rolling process is 6%-8%.
3. The composite current collector according to claim 1, characterized in that, A first transition layer and a second transition layer are disposed between the base film layer and the metal layer. The first transition layer and the second transition layer are disposed sequentially in a direction away from the base film layer, and the elastic modulus of the base film layer, the first transition layer, the second transition layer and the metal layer increase sequentially.
4. The composite current collector according to claim 3, characterized in that, The elastic modulus of the first transition layer is 5-10 GPa, and the elastic modulus of the second transition layer is 30-50 GPa; and / or, the thickness of the first transition layer is 10-40 nm, and the thickness of the second transition layer is 10-40 nm.
5. The composite current collector according to claim 3, characterized in that, The first transition layer comprises a flexible resin and rigid particles in a mass ratio of (60-70):(20-30); and / or, The second transition layer comprises metal nanoparticles and alumina ceramic particles in a mass ratio of (3-5):(5-7).
6. The composite current collector according to claim 5, characterized in that, The flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin. And / or, the metal nanoparticles include one or more of the following: copper nanoparticles, aluminum nanoparticles, nickel nanoparticles, and titanium nanoparticles.
7. A method for preparing a composite current collector as described in any one of claims 1 to 6, characterized in that, include: A coating liquid containing flexible resin and rigid particles is applied to the surface of the base film layer, and after pre-drying, a first transition layer is formed. A second transition layer containing metal nanoparticles and ceramic particles is deposited on the surface of the first transition layer by magnetron sputtering. A metal layer is prepared on the second transition layer by magnetron sputtering and / or vapor deposition. The metal layer is subjected to cold rolling.
8. The preparation method according to claim 7, characterized in that, The fabrication of the first transition layer and the fabrication of the second transition layer satisfy one or more of the following conditions: (1) When the first transition layer is prepared, the components of the coating liquid include one or more of flexible resin, rigid particles, dispersant and curing agent; Optionally, the mass ratio of the flexible resin to the rigid particles is (60-70):(20-30). Optionally, the mass ratio of the flexible resin to the dispersant is (60-70):(3-7); Optionally, the mass ratio of the flexible resin to the curing agent is (60-70):(3-7); Optionally, the flexible resin includes one or more of polycaprolactone-type polyurethane resin, polycarbonate-type polyurethane resin, and polyether-type polyurethane resin; Optionally, the dispersant includes one or more of polycarboxylate polymeric dispersants and polyacrylate ammonium salt dispersants; Optionally, the curing agent includes one or more of low-temperature isocyanate curing agents and modified aliphatic polyisocyanates; Optionally, the coating method includes at least one of slot coating, microgravure coating, and spin coating; When the second transition layer is prepared, the mass ratio of metal nanoparticles to alumina ceramic particles is (3-5):(5-7). Optionally, the metal nanoparticles include one or more of the following: copper nanoparticles, aluminum nanoparticles, nickel nanoparticles, and titanium nanoparticles.
9. The preparation method according to claim 7, characterized in that, One or more of the following conditions must be met: (1) After the second transition layer is prepared, it is cured. (2) The rolling force of the cold rolling process is 7-12 kN / cm; the rolling speed of the cold rolling process is 12-18 m / min; (3) The elastic modulus of the first transition layer is less than that of the second transition layer.
10. A lithium-ion battery, characterized in that, The composite current collector includes the composite current collector as described in any one of claims 1 to 6 or the composite current collector prepared by the preparation method described in any one of claims 7 to 9.