Current collector with self-healing SEI film, preparation method of current collector, pole piece and battery

Abstract

The present invention discloses a current collector with a self-healing SEI film and a preparation method thereof, a pole piece and a battery, the current collector comprises a polymer substrate layer, metal layers and a self-healing SEI film layer, the polymer substrate layer is a center layer, the metal layers are located on the front and back surfaces of the polymer substrate layer, and the self-healing SEI film layer is located on the center layer. The self-healing SEI film layer is a self-repairing material layer formed by compounding a shape memory alloy, a carbon nano tube and a lithium-containing compound. The shape memory alloy SMA / CNT / Li three-dimensional composite SEI coating with thermoelastic response capability is constructed on the current collector, so that the adaptability of the SEI film to a microcrack / stress concentration area is improved, interface self-repairing is realized, the conductivity and mechanical toughness of the SEI film are improved, and the structural stability and the service life of the composite current collector in the circulating process are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a current collector with a self-healing SEI film, its preparation method, an electrode, and a battery. Background Technology

[0002] With the increasing demands on lithium battery performance from new energy vehicles and energy storage devices, composite current collectors are widely used due to their lightweight and high conductivity. However, composite current collectors still face problems such as interface instability, metal layer peeling, and poor adaptability to volume expansion, especially under high loads on the negative electrode material or during high-rate charge-discharge cycles. These problems accelerate the degradation of the SEI film, leading to a decline in cycle performance. Therefore, there is an urgent need to develop a novel surface functional film that can improve interface stability, adapt to stress, and be compatible with composite current collector structures. Summary of the Invention

[0003] The purpose of this invention is to provide a current collector with a self-healing SEI film, its preparation method, electrode, and battery, thereby improving structural stability and service life during cycling.

[0004] To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of this application provides a current collector with a self-healing SEI membrane, comprising: A polymer substrate layer, wherein the polymer substrate layer is the central layer; A metal layer, wherein the metal layer is located on both sides of the polymer substrate layer; The metal layer also has a self-healing SEI film layer, which is a self-healing material layer composed of shape memory alloy, carbon nanotubes and lithium-containing compounds.

[0005] The second aspect of this application provides a method for preparing a current collector with a self-healing SEI membrane, comprising the following steps: S1: A metal layer is set or prepared on both sides of the polymer substrate layer; S2: Prepare a self-healing SEI film on the surface of the metal layer; The self-healing SEI film is sprayed onto the surface of the metal layer using electrospinning technology. The sprayed material is a mixture containing shape memory alloy, carbon nanotubes, and lithium compounds. The temperature of the sprayed material is 45~60°C.

[0006] To optimize the above technical solution, the specific measures also include: The preparation method of the sprayed material is as follows: Dissolve 5-15 wt% PAN or PVDF-HFP in a solvent, add 3-10 wt% shape memory alloy SMA particles, 2-5 wt% carbon nanotube material and 3-10 wt% lithium-containing compound, and mix thoroughly.

[0007] Preferably, the shape memory alloy SMA is selected from NiTi and NiTiCu; the particle size of the shape memory alloy SMA is 50~200nm.

[0008] The carbon nanotube material is selected from at least one of CNT, MWCNT, or SWCNT; the lithium-containing compound is selected from at least one of LiF or Li2CO3; and the solvent is DMF or acetone.

[0009] Furthermore, the self-healing SEI film is sprayed onto the surface of the metal layer using electrospinning technology, with the following process parameters: Voltage 15~20 kV, jet flow rate 0.5~1 mL / h, distance 12~18 cm, spinning thickness 5~20 μm.

[0010] Furthermore, after electrospinning, the current collector undergoes drying and hot pressing treatment, as follows: Vacuum drying temperature 50~70°C, time 1.5~2.5 h; Then the current collector is subjected to hot pressing treatment at a temperature of 110~130°C, 0.8~1.2 MPa, for 4~8 min.

[0011] The thorough mixing steps are as follows: first, stir magnetically for 5-7 hours, then disperse ultrasonically for 0.5-2 hours.

[0012] A third aspect of this application provides an electrode comprising the aforementioned current collector with a self-healing SEI film.

[0013] A fourth aspect of this application provides a battery comprising the aforementioned electrode.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the problems of interfacial stress concentration, SEI film fragility, and dendrite-induced interlayer delamination in current collectors, especially composite copper current collectors, under high-rate / high-load operation. It proposes a three-dimensional composite SEI coating scheme of shape memory alloy SMA / carbon nanotube CNT / Li with thermoelastic response capability to improve the SEI film's adaptability to microcracks / stress concentration areas, achieve interface self-healing, enhance the conductivity and mechanical toughness of the SEI film, and improve the structural stability and lifespan of the composite current collector during cycling. Detailed Implementation The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the subject matter of the present invention to the following embodiments. All technologies implemented based on the above content of the present invention fall within the scope of the present invention.

[0015] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0016] This invention provides a current collector with a self-healing SEI membrane, comprising: The polymer substrate layer is the central layer. Metal layer, which is located on both sides of the polymer substrate layer; In addition to the self-healing SEI film, the metal layer also has a self-healing SEI film layer, which is a self-healing material layer composed of shape memory alloy, carbon nanotubes and lithium-containing compounds.

[0017] This invention also provides a method for preparing a current collector with a self-healing SEI membrane, comprising the following steps: S1: A metal layer is set or prepared on both sides of the polymer substrate layer; S2: Prepare a self-healing SEI film on the surface of the metal layer; Among them, the self-healing SEI film layer is sprayed onto the surface of the metal layer by electrospinning technology. The sprayed material is a mixture containing shape memory alloy, carbon nanotubes and lithium compounds. The temperature of the sprayed material is 45~60°C. This invention utilizes electrospinning to construct a three-dimensional fibrous interfacial coating on a composite current collector, consisting of shape memory alloy SMA nanoparticles, carbon nanotubes, and lithium-containing compounds. The coating leverages the austenitic structure of the shape memory alloy SMA within a specific temperature range. The reversible phase transformation property of martensite allows it to be added as a functional particle to the electrospinning solution, where it forms a three-dimensional fiber network coating together with carbon nanotubes and lithium-containing compounds.

[0018] In some embodiments, the polymer substrate layer of the present invention may be made of PET film, PP film or other polymer substrate, and the metal layer is copper with a thickness ranging from 400 to 2000 nm.

[0019] In some embodiments, the metal layer of the present invention can be prepared by one or more of the following methods: vapor deposition, magnetron sputtering, electroless plating, electroplating, CVD, etc.

[0020] In some embodiments, the method for preparing the sprayed material is as follows: Dissolve 5-15 wt% PAN or PVDF-HFP in a solvent, add 3-10 wt% shape memory alloy SMA particles, 2-5 wt% carbon nanotube material and 3-10 wt% lithium-containing compound, and mix thoroughly; wherein PAN or PVDF-HFP serves as the matrix, connecting all added materials to form a gel-like network.

[0021] The shape memory alloy SMA is selected from NiTi and NiTiCu; the particle size of the shape memory alloy SMA is 50~200nm.

[0022] The carbon nanotube material is selected from at least one of CNT, MWCNT, or SWCNT; the lithium-containing compound is selected from at least one of LiF or Li2CO3; and the solvent is DMF or acetone.

[0023] In some embodiments, the self-healing SEI film is sprayed onto the surface of the metal layer using electrospinning technology, with the following process parameters: Voltage 15~20 kV, jet flow rate 0.5~1 mL / h, distance 12~18 cm, spinning thickness 5~20 μm.

[0024] In some embodiments, the current collector is dried and hot-pressed after electrospinning, as follows: Vacuum drying temperature 50~70°C, time 1.5~2.5 h; Then the current collector is subjected to hot pressing treatment at a temperature of 110~130°C, 0.8~1.2 MPa, for 4~8 min.

[0025] In some implementations, the thorough mixing steps are as follows: first, magnetic stirring for 5-7 hours, followed by ultrasonic dispersion for 0.5-2 hours.

[0026] A third aspect of this application provides an electrode comprising the aforementioned current collector with a self-healing SEI film.

[0027] A fourth aspect of this application provides a battery comprising the aforementioned electrode.

[0028] The principle of this invention is as follows: When the battery is working, during the deposition of lithium-containing compounds on the surface of the current collector, local stress concentration or microcrack propagation is induced by electrochemical reactions. The shape memory alloy SMA nanoparticles undergo a martensitic phase transformation, accompanied by volume expansion to release stress and fill the microcrack region, thereby actively repairing the SEI film structure. Subsequently, after the stress is relieved, it can return to the austenitic state, realizing reversible self-healing behavior.

[0029] Meanwhile, carbon nanotubes construct a through-electronic conduction network in the self-healing SEI film fiber structure, effectively reducing electron migration impedance and improving interface electronic uniformity; while LiF, as a typical electrolyte decomposition product, has high stability and strong lithium compound transport capability, which can synergistically improve the ion selectivity, thermal stability and corrosion resistance of the SEI film, further extending battery life.

[0030] The technical solution of the present invention will be further described in detail below with reference to specific embodiments: Example 1 A composite copper current collector with a self-healing SEI film is prepared by the following steps: 1. Material preparation: A PET film with a thickness of 4.5 μm was selected. A 200 nm copper layer was first deposited on both sides of the film by magnetron sputtering, and then the film was thickened by electroplating: 800 μm copper layers were electroplated on both sides, forming a 1 μm copper layer on each side of the PET film, resulting in a PET composite copper current collector with a total thickness of about 6.5 μm. 2. Preparation of fiber coating: 10 wt% PVDF-HFP was dissolved in DMF, and 5 wt% 100 nm SMA particles NiTi, 3 wt% MWCNT and 5 wt% LiF were added. The mixture was magnetically stirred for 6 h and ultrasonically dispersed for 1 h. 3. Preparation of self-healing SEI film by electrospinning: voltage 18 kV, flow rate 0.8 mL / h, jetting distance 15 cm, spinning to a thickness of 10 μm; 4. Drying: Vacuum drying at 60°C for 2 h; hot pressing at 120°C and 1 MPa for 5 min; 5. Battery assembly: The positive electrode current collector uses a composite aluminum current collector / traditional aluminum foil, and the positive electrode material uses NCM622. For the negative electrode: the negative electrode current collector uses the above-mentioned composite copper current collector, and the negative electrode material uses artificial graphite; For the diaphragm, an alumina ceramic-coated polyethylene diaphragm (25 μm thick) is used. For the electrolyte, use 1 mol·L -1 The carbonate solution of LiPF6 is a mixture of propylene carbonate, ethylene carbonate and ethyl methyl carbonate in a mass ratio of 1:1:1. Stacking assembly: The negative electrode, separator, and positive electrode are stacked in sequence, injected with electrolyte (standard electrolyte), and packaged into a soft-pack battery (capacity approximately 200mAh).

[0031] Example 2 The scheme in this embodiment is basically the same as that in embodiment 1, except that the SMA particles are replaced by NiTiCu instead of NiTi.

[0032] Example 3 The scheme in this embodiment is basically the same as that in embodiment 1, except that when configuring the fiber coating, the amount of SMA particles NiTi added is replaced with 3 wt%.

[0033] Example 4 The scheme in this embodiment is basically the same as that in embodiment 1, except that when configuring the fiber coating, the amount of SMA particles NiTi added is replaced with 10 wt%.

[0034] Example 5 The scheme in this embodiment is basically the same as that in embodiment 1, except that when preparing the self-healing SEI film by electrospinning, the thickness is 5 μm.

[0035] Example 6 The scheme in this embodiment is basically the same as that in embodiment 1, except that: when preparing the self-healing SEI film layer by electrospinning, the thickness is 20 μm.

[0036] Example 7 The scheme in this embodiment is basically the same as that in embodiment 1, except that the particle size of the SMA NiTi particles is replaced with 50nm.

[0037] Example 8 The scheme in this embodiment is basically the same as that in embodiment 1, except that the particle size of the SMA NiTi particles is replaced with 200nm.

[0038] Comparative Example 1 Compared to Example 1, this comparative example did not add SMA particles when configuring the fiber coating.

[0039] Comparative Example 2 Compared to Example 1, this comparative example does not include the addition of MWCNTs when configuring the fiber coating.

[0040] Comparative Example 3 Compared to Example 1, this comparative example did not add LiF when configuring the fiber coating.

[0041] Comparative Example 4 Compared with Example 1, the scheme of this comparative example does not include steps 2-4, i.e., there is no preparation of the self-healing SEI film.

[0042] Comparative Example 5 The scheme of this comparative example is basically the same as that of Example 1, except that the particle size of the SMA NiTi particles is replaced with 400nm.

[0043] Comparative Example 6 The scheme of this comparative example is basically the same as that of Example 1, except that when configuring the fiber coating, the amount of SMA particles NiTi added is replaced with 15 wt%.

[0044] Comparative Example 7 The scheme of this comparative example is basically the same as that of Example 1, except that when preparing the self-healing SEI film by electrospinning, the thickness is 25 μm.

[0045] Test Evaluation: 1. SEI surface crack density increase rate: First, a representative area (100µm × 100µm) was selected on the normalized electrode surface, and the reference state crack density and size were obtained by field emission SEM at 3000× magnification; after 100 cycles, the aged state crack density was detected in the same area, and the number of cracks was determined according to the crack length (≥0.5µm) and crack width (≥100nm) standards. The crack increase rate was calculated to determine the mechanical structural stability of the SEI film. 2. Cycle life: under 1C rate (based on nominal capacity) conditions, continuous charge and discharge, the cutoff standard is when the discharge capacity decays to 80% of the initial capacity, and the cycle life is the number of cycles at the cutoff point; 3. EIS Testing: Using GB / T39482.3-2020 as the reference standard, an electrochemical workstation was used to conduct the test at a frequency of 100kHz~10mHz and an amplitude of 5mV. The Rct (charge transfer resistance) value was extracted. The results of the experiments conducted on each embodiment and comparative example are shown in Table 1: Table 1 Comparison of test results between each embodiment and the comparative example

[0046] Analysis of experimental conclusions: The surface crack density increase rate in Examples 1-8 was significantly lower than that in the comparative example, indicating that the self-healing SEI film can effectively suppress crack propagation. In Example 1, the crack density was reduced by approximately half compared to Comparative Example 1, demonstrating that the phase change filling effect of SMA particles significantly improves the toughness of the SEI film. The cycle life of Examples 1-8 far exceeded that of the comparative example, indicating that the self-healing mechanism can effectively delay SEI film failure, proving the crucial role of the SEI film in the long-term stability of the battery. The Rct values ​​of each example were significantly lower than those of the comparative example, indicating that the self-healing SEI film can effectively reduce interfacial impedance, and the synergistic effect of the CNT network and LiF significantly improves electron conduction efficiency.

[0047] The crack density of Example 3 (3wt% SMA) was higher than that of Example 1 (5wt% SMA), indicating that the SMA content needs to reach a certain threshold to fully release stress at 3-10wt%. However, excessive SMA, such as in Example 4 (10wt% SMA), may lead to agglomeration, which is detrimental to uniform repair. Example 1 (5wt% SMA) also had the longest cycle life. In addition, Example 4 (10wt% SMA) had a higher Rct, possibly due to excessive SMA causing fiber densification and hindering ion transport. After multiple experiments, the optimal SMA content for this scheme is 4-7wt%.

[0048] The crack density and cycle life of Example 7 (particle size 50 nm) and Example 8 (particle size 200 nm) are similar. The phase transformation efficiency of SMA particles in the 50~200 nm particle size range is not significantly different. However, the cycle life of Comparative Example 5 (particle size 400 nm) is significantly reduced. Excessive particle size may hinder the phase transformation efficiency.

[0049] The crack density difference between Example 5 (5μm) and Example 6 (20μm) is small. Although the thickness of Example 6 is increased, the cycle life is also slightly shorter and the Rct is increased. The self-healing SEI film should not be less than 5μm. If it is too thin, the repair ability will be insufficient. However, if the self-healing SEI film is too thick, it may lead to ion transport obstruction.

[0050] The crack density of Comparative Example 2 (without MWCNT) and Comparative Example 3 (without LiF) was significantly higher than that of the other examples, indicating that CNT and LiF improve the integrity of the SEI film by enhancing electron conduction and ion selectivity. The higher Rct of Comparative Example 2 (without MWCNT) and Comparative Example 3 (without LiF) indicates that CNT is the key to constructing the electron conduction network, while LiF indirectly reduces impedance by improving ion selectivity.

[0051] The addition of excessive SMA content (15 wt%) in Comparative Example 6 led to a significant increase in the SEI film cracking rate, a decrease in cycle life, and a significant increase in Rct. Excessive SMA caused excessive volume expansion, damaged the fiber structure, and accelerated crack propagation. At the same time, it hindered the carbon nanotube conductive network and increased the interfacial impedance. The SMA content needs to be controlled within a reasonable range. Excessive addition will impair the self-healing effect and battery life.

[0052] The coating of Comparative Example 7 was too thick (25 μm), resulting in a significant increase in the crack increase rate, a large decrease in cycle life, and a significant increase in Rct. The thick coating led to an increase in stress accumulation inside the fiber network, weakening the stress self-adaptive ability of the SMA and reducing the microcrack repair efficiency. At the same time, the excessively thick coating would hinder the transport path of lithium ions in the SEI film, increase the interface impedance, and thus affect the rate performance and cycle stability of the battery.

[0053] The self-healing SEI film of the present invention can effectively suppress SEI surface cracks, extend battery cycle life and reduce impedance through phase change repair of SMA particles, conductive network of CNT and stability enhancement of LiF.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent substitutions, and improvements made by those skilled in the art to the above embodiments without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A current collector with a self-healing SEI membrane, characterized in that, include: A polymer substrate layer, wherein the polymer substrate layer is the central layer; A metal layer, wherein the metal layer is located on both sides of the polymer substrate layer; The metal layer also has a self-healing SEI film layer, which is a self-healing material layer composed of shape memory alloy, carbon nanotubes and lithium-containing compounds.

2. The method for preparing the current collector with a self-healing SEI film according to claim 1, characterized in that, Includes the following steps: S1: A metal layer is set or prepared on both sides of the polymer substrate layer; S2: Prepare a self-healing SEI film on the surface of the metal layer; The self-healing SEI film is sprayed onto the surface of the metal layer using electrospinning technology. The sprayed material is a mixture containing shape memory alloy, carbon nanotubes, and lithium compounds. The temperature of the sprayed material is 45~60°C.

3. The method for preparing a current collector with a self-healing SEI membrane according to claim 2, characterized in that: The preparation method of the sprayed material is as follows: Dissolve 5-15 wt% PAN or PVDF-HFP in a solvent, add 3-10 wt% shape memory alloy SMA particles, 2-5 wt% carbon nanotube material and 3-10 wt% lithium-containing compound, and mix thoroughly.

4. The method for preparing a current collector with a self-healing SEI membrane according to claim 2, characterized in that: The shape memory alloy SMA is selected from NiTi and NiTiCu; the particle size of the shape memory alloy SMA is 50~200nm.

5. The method for preparing a current collector with a self-healing SEI membrane according to claim 2, characterized in that: The carbon nanotube material is selected from at least one of CNT, MWCNT, or SWCNT; the lithium-containing compound is selected from at least one of LiF or Li2CO3; and the solvent is DMF or acetone.

6. The method for preparing a current collector with a self-healing SEI film according to claim 2, characterized in that: The self-healing SEI film is applied to the surface of the metal layer via electrospinning technology, with the following process parameters: Voltage 15~20 kV, jet flow rate 0.5~1 mL / h, distance 12~18 cm, spinning thickness 5~20 μm.

7. The method for preparing a current collector with a self-healing SEI film according to claim 2, characterized in that: After electrospinning, the current collector is dried and hot-pressed, as follows: Vacuum drying temperature 50~70°C, time 1.5~2.5 h; Then the current collector is subjected to hot pressing treatment at a temperature of 110~130°C, 0.8~1.2 MPa, for 4~8 min.

8. The method for preparing a current collector with a self-healing SEI membrane according to claim 3, characterized in that: The thorough mixing steps are as follows: first, stir magnetically for 5-7 hours, then disperse ultrasonically for 0.5-2 hours.

9. An electrode sheet, characterized in that: A current collector containing a self-healing SEI membrane prepared by the method described in claim 1 or any one of claims 2 to 8.

10. A battery, characterized in that: It includes the electrode sheet as described in claim 9.

Images