Composite current collector and preparation method thereof

Abstract

The invention discloses a composite current collector and a preparation method thereof. The composite current collector comprises an aluminum foil; the zinc-aluminum alloy layer is located on the surface of the aluminum foil and is composed of ZnxAly, 30 < = x < = 40, and 60 < = y < = 70; and the barrier layer is a PDA-CNT composite barrier layer and is located on the surface of the zinc-aluminum alloy layer, and the thickness of the barrier layer is 2-3 microns. According to the composite current collector provided by the embodiment of the invention, the problems of cycle life and safety of a battery without a negative electrode can be solved through a functional layering strategy. In addition, the PDA-CNT composite barrier layer protects the high-activity ZnxAly layer, so that the ZnxAly layer can stably exert the sodium affinity function for a long time. And the ZnxAly layer induces uniform nucleation from the lower part, and the PDA-CNT composite barrier layer restrains dendritic crystal growth from the upper part and homogenizes an electric field / ion current, so that the deposition uniformity is synergistically improved, and alloy pulverization is inhibited. According to the composite current collector provided by the embodiment of the invention, the capacity retention ratio after circulation is improved compared with that of pure aluminum foil, and the coulombic efficiency in the whole process is always maintained at a relatively high level, which indicates that the circulation stability is improved by reducing sodium consumption and improving deposition uniformity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, and more particularly to a composite current collector and a preparation method thereof. BACKGROUND

[0002] The current sodium-ion battery has a low energy density, usually less than 160 Wh Kg -1 . The anode-free sodium metal battery (AFSMBs) does not contain sodium metal during assembly, thereby maximizing the recoverable energy density and reducing the risk of battery preparation. However, the binding energy of the aluminum foil anode and sodium metal is low, and sodium dendrites can easily penetrate the separator, affecting the safety and electrochemical performance of the battery, thereby limiting the practical application of the anode-free sodium metal battery. Zinc can form various intermetallic compounds with sodium at room temperature, which reduces the nucleation overpotential of sodium, makes the deposition of sodium more uniform and denser, and produces an effect similar to 'induced deposition'. In addition, zinc and aluminum are both abundant and low-cost metals. However, when zinc foil is used to replace aluminum foil to improve the cycle life and safety of the anode-free sodium metal battery, the alloying reaction between sodium and pure zinc is serious, which destroys the structure of the current collector and loses the electronic conduction path, and the battery fails rapidly. SUMMARY

[0003] One object of the present application is to provide a composite current collector, which can solve the technical problems of uneven sodium deposition, dendrite growth caused by low binding energy of the traditional aluminum foil current collector in the anode-free sodium metal battery, and the destruction of the current collector structure caused by the alloying reaction of the pure zinc induced layer.

[0004] Another object of the present application is to provide a preparation method of a composite current collector, which can be used to prepare the above-mentioned composite current collector.

[0005] In order to achieve the above objects, the present application provides the following technical solutions.

[0006] The composite current collector according to the first aspect of the present application comprises: an aluminum foil; a zinc-aluminum alloy layer, which is located on a single side surface of the aluminum foil, and has a composition of Zn x Al y , 30≤x≤40, 60≤y≤70; and a barrier layer, which is a PDA-CNT composite barrier layer and is located on a side surface of the zinc-aluminum alloy layer away from the aluminum foil, and has a thickness of 2 μm-3 μm.

[0007] Optionally, the thickness of the zinc-aluminum alloy layer is 300 nm-500 nm.

[0008] According to the preparation method of the composite current collector according to the second aspect of the present application, the preparation method is used for preparing the composite current collector described above, and the preparation method comprises the following steps: preparing a zinc-aluminum alloy layer on a single side surface of an aluminum foil; and preparing a barrier layer on a side surface of the zinc-aluminum alloy layer away from the aluminum foil.

[0009] Optionally, a composite dispersion liquid composed of CNTs and dopamine is configured, the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer, and the barrier layer is prepared on the surface of the zinc-aluminum alloy layer.

[0010] Optionally, the zinc-aluminum alloy layer is prepared on the surface of the aluminum foil by using a magnetron sputtering process, and after sputtering is completed, the aluminum foil is cooled to room temperature under the protection of an inert gas.

[0011] Optionally, before the zinc-aluminum alloy layer is prepared on the surface of the aluminum foil, the aluminum foil is cleaned to remove surface oil stains and an oxide layer.

[0012] Optionally, the aluminum foil is subjected to plasma activation to increase the content of hydroxyl groups on the surface of the aluminum foil.

[0013] Optionally, before the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer, the surface of the zinc-aluminum alloy layer is wiped with anhydrous ethanol, and after nitrogen blowing and drying, the content of hydroxyl groups on the surface of the aluminum foil is increased.

[0014] Optionally, when the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer, the sample is fixed on a chuck of a spin coater, the composite dispersion liquid is added dropwise, and spin coating is performed.

[0015] Optionally, after spin coating, the sample is placed in an incubator for standing, so that dopamine is polymerized in situ on the surface of CNTs to form a network structure in which CNTs are wrapped by PDA.

[0016] According to the composite current collector according to the embodiments of the present application, the aluminum foil, the zinc-aluminum alloy layer and the barrier layer are combined, the problems of cycle life and safety of a negative electrode-free battery can be solved by a functional layering strategy. Moreover, the PDA-CNT composite barrier layer protects the high-activity Zn x Al y layer, so that the sodium affinity function of the Zn x Al y layer can be stably exerted for a long time instead of being rapidly destroyed by an electrolyte. The Zn x Al y layer induces uniform nucleation from below, the PDA-CNT composite barrier layer restrains dendrite growth and homogenizes an electric field / ion flow from above, and the deposition uniformity is improved in cooperation, and alloy pulverization is inhibited. According to the composite current collector according to the embodiments of the present application, the capacity retention rate after cycling is improved compared with a pure aluminum foil, and the overall coulombic efficiency is always maintained at a high level, which indicates that the cycle stability is improved due to the reduction of sodium consumption and the improvement of deposition uniformity.

[0017] Other features of the present application, its nature and advantages will become apparent from the following detailed description of the exemplary embodiments of the application, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0019] Figure 1 is a structural schematic diagram of a composite current collector according to an embodiment of the present application.

[0020] REFERENCE NUMERALS composite current collector 100; aluminum foil 10; zinc-aluminum alloy layer 20; barrier layer 30. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps set forth in the embodiments, numerical expressions, and numerical values, unless specifically stated otherwise, do not limit the scope of the present application.

[0022] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the scope of the application or its application or uses.

[0023] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered as if the discussion were set forth in detail herein, to the extent that such techniques, methods, and apparatus form part of the prior art and are already known to those of ordinary skill in the art.

[0024] In all of the examples shown and discussed herein, any specific values should be interpreted as illustrative only and not as a limitation. Thus, other examples of exemplary embodiments can have different values.

[0025] It should be noted that like numerals and letters refer to like items throughout the drawings, and as a result, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0026] The composite current collector 100 according to an embodiment of the present application will now be described in detail below with reference to the accompanying drawings.

[0027] As shown in FIG. 1, the composite current collector 100 according to an embodiment of the present application includes an aluminum foil 10, a zinc-aluminum alloy layer 20, and a barrier layer 30. Figure 1

[0028] Specifically, the zinc-aluminum alloy layer 20 is located on a single side surface of the aluminum foil 10, and the composition of the zinc-aluminum alloy layer 20 is Zn x Al y ​, 30≤x≤40, 60≤y≤70; the barrier layer 30 is a PDA-CNT composite barrier layer, and is located on the surface of the zinc-aluminum alloy layer 20 away from the aluminum foil 10, and the thickness d1 of the barrier layer 30 is 2-3 μm.

[0029] The zinc has high affinity for sodium, the Zn atoms on the surface of the zinc-aluminum alloy layer 20 serve as preferential adsorption sites, which can reduce the nucleation energy barrier of sodium, the conductivity of the zinc-aluminum alloy layer 20 is higher than that of pure zinc, and the three-dimensional conductive network formed by the stacking of nano-sized particles can eliminate the local current density concentration, and promote the sodium to form a dense and uniform nucleus on the surface of the zinc-aluminum alloy layer 20. Moreover, the zinc component in the alloy provides a large number of uniformly distributed nucleation sites, avoiding the concentrated deposition of sodium on a few active points, thereby greatly improving the initial uniformity of the deposition. In addition, Al is not alloyed with Na at room temperature, and as an inert skeleton, it helps to stabilize the structure of the alloy layer and buffer the volume change during the Zn-Na alloying process.

[0030] Moreover, the composition of the zinc-aluminum alloy layer 20 is Zn x Al y , 30≤x≤40, 60≤y≤70, the sodium affinity of Zn is better than that of Al, by adopting 30≤x≤40, 60≤y≤70, the proportion of Zn is moderate, the charge and discharge nucleation overpotential is low, and the alloy structure is stable. If the proportion of Zn is too low, the sodium affinity is close to that of pure Al, and the sodium deposition is not uniform. However, too high zinc content leads to the formation of multiple intermetallic compounds of sodium at room temperature, which reduces the first coulomb efficiency and recyclable capacity of the battery. Although the alloying reaction may be reversible, the volume change is large, which leads to the rupture of the PDA-CNT composite barrier layer, thereby losing the protection effect.

[0031] Moreover, the thickness of the barrier layer 30 is 2-3 μm, for example, the thickness d1 of the barrier layer 30 is 2 μm, 2.1 μm, 2.2 μm, 2.5 μm, 2.8 μm or 3 μm, etc. The electronic conductivity of PDA is poor, and if the barrier layer 30 is too thick or dense, it is easy to cause hindering of electron transmission and increase the electrode impedance. If the barrier layer 30 is too thin, it is difficult to cover the underlying metal coating to form a continuous and short-circuit-free barrier, which affects the uniformity of sodium deposition, leading to insufficient isolation effect, serious side reactions and poor cycle life. Therefore, in the embodiment, by controlling the coating thickness or using the barrier layer 30 in combination with other conductive materials, the electronic conductivity is high and the electrode impedance is low.

[0032] In addition, a PDA-CNT composite barrier layer with controllable thickness is constructed on the surface of the prepared zinc-aluminum alloy layer 20. CNTs are combined with PDA through π-π stacking to construct a three-dimensional conductive network, offsetting the insulating property of PDA. The PDA-CNT composite barrier layer can extend the cycle life of the battery by constraining the volume change and side reactions of a small amount of Zn accompanying alloying / deloyling. Among them, the CNT network in the PDA-CNT composite barrier layer constitutes an ultra-high specific surface area conductive network, which can greatly reduce the local current density, which is one of the most critical factors for inhibiting dendrite growth. The PDA layer can effectively isolate the zinc-aluminum alloy layer 20 from direct contact with the liquid electrolyte, significantly reducing side reactions (such as electrolyte decomposition and alloy layer corrosion), thereby reducing sodium consumption due to the formation of unstable SEI. In addition, the tips and defects of CNTs can act as additional nucleation sites, forming a "double induction" with the sodium-philic sites of the underlying zinc-aluminum alloy layer 20, increasing the nucleation density of sodium, which is conducive to uniform sodium deposition.

[0033] Thus, according to the composite current collector 100 of the embodiments of the present application, the combination of the aluminum foil 10, the zinc-aluminum alloy layer 20 and the barrier layer 30 can solve the cycle life and safety problems of the negative electrode-free battery through the functional layering strategy. Moreover, the PDA-CNT composite barrier layer protects the high-activity Zn x Al y layer, so that it can stably play the sodium-philic function for a long time, instead of being rapidly destroyed by the electrolyte. The Zn x Al y layer induces uniform nucleation from below, and the PDA-CNT composite barrier layer restrains dendrite growth and homogenizes the electric field / ion flow from above, which cooperatively improves deposition uniformity and suppresses alloy pulverization. According to the composite current collector 100 of the embodiments of the present application, the capacity retention rate after cycling is improved compared with pure aluminum foil, and the overall coulombic efficiency is always maintained at a high level, indicating that the reduction of sodium consumption and the improvement of deposition uniformity have jointly improved the cycle stability.

[0034] In some embodiments of the present application, the thickness d2 of the zinc-aluminum alloy layer 20 is 300 nm-500 nm, for example, the thickness of the zinc-aluminum alloy layer 20 is 300 nm, 320 nm, 350 nm, 360 nm, 380 nm, 400 nm, 410 nm, 420 nm, 450 nm, 480 nm or 500 nm, etc. It can be understood that, when the zinc-aluminum alloy layer 20 is prepared by spraying, the thermal stress of the zinc-aluminum alloy layer 20 can be alleviated by cooling, but the heat conduction of the zinc-aluminum alloy layer 20 is slow, the internal temperature gradient is large, and the shrinkage difference inside and on the surface of the zinc-aluminum alloy layer 20 is easy to cause, which aggravates the stress. In the present embodiment, the zinc-aluminum alloy layer 20 with a thickness of 300 nm-500 nm can ensure the sodium affinity and uniformity of the zinc-aluminum alloy layer 20, and the accumulated stress is not easy to cause damage to the structure of the zinc-aluminum alloy layer 20, so that the structure of the composite current collector 100 is more stable and the performance is better.

[0035] The present application also discloses a preparation method of a composite current collector, the preparation method is used for preparing the composite current collector of any one of the above embodiments, and the preparation method comprises the following steps: Prepared on one side surface of the aluminum foil 10 is a zinc-aluminum alloy layer 20; Prepared on the side surface of the zinc-aluminum alloy layer 20 away from the aluminum foil 10 is a barrier layer 30.

[0036] By using the above-mentioned preparation process with the steps, the operation is facilitated, and the difficulty of controlling the proportion of Zn in the zinc-aluminum alloy layer 20 and the thickness of the barrier layer 30 is reduced.

[0037] According to one embodiment of the present application, a composite dispersion liquid composed of CNT and dopamine is configured, the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer 20, and the barrier layer 30 is prepared on the surface of the zinc-aluminum alloy layer 20. The preparation method of the composite current collector 100 according to the embodiment of the present application has the advantages of facilitating operation and being easy to prepare.

[0038] In some embodiments of the present application, the zinc-aluminum alloy layer 20 is prepared on the surface of the aluminum foil 10 by using a magnetron sputtering process, and after the sputtering is completed, the sample is cooled to room temperature under the protection of inert gas. In the present embodiment, on the one hand, by using the magnetron sputtering process, it is beneficial to control the thickness of the zinc-aluminum alloy layer 20, for example, the magnetron sputtering process is used to prepare the zinc-aluminum alloy layer 20 with a thickness of 300 nm-500 nm on the surface of the aluminum foil 10, and the deposition thickness is recorded. In addition, after the sputtering is completed, the sample is cooled to room temperature under the protection of inert gas, for example, the sample is cooled to room temperature under the protection of Ar gas after the sputtering is completed, which can avoid oxidation or contamination of the sample. On the other hand, by using the “nanoscale layer-by-layer deposition” mechanism of the magnetron sputtering, it is easy to control the proportion of Zn in the zinc-aluminum alloy layer 20, for example, the proportion of Zn in the zinc-aluminum alloy layer 20 is controlled to be 50% by using the magnetron sputtering process. x Al yThe atomic ratio of Zn and Al is controlled, and the sodium affinity of Zn is used to induce uniform nucleation of sodium, and the dilution effect of Al reduces the consumption of Na-Zn alloying.

[0039] According to an embodiment of the present application, the aluminum foil 10 is cleaned before the zinc-aluminum alloy layer 20 is prepared on the surface of the aluminum foil 10 to remove surface oil and oxide layer. In this embodiment, the adhesion between the aluminum foil 10 and the zinc-aluminum alloy layer 20 can be improved by purifying the aluminum foil 10.

[0040] According to an embodiment of the present application, the aluminum foil 10 is plasma activated to increase the content of hydroxyl groups on the surface of the aluminum foil 10. The cleaned aluminum foil 10 can be dried and then plasma activated to introduce hydroxyl groups on the surface of the aluminum foil 10. For example, the aluminum foil 10 is cut to the required size, and the oxide layer is removed after super-clean pretreatment. In this embodiment, the adhesion between the aluminum foil 10 and the zinc-aluminum alloy layer 20 can be improved by hydroxylating the aluminum foil 10. The adhesion between the aluminum foil 10 and the zinc-aluminum alloy layer 20 can be further improved by purifying the aluminum foil 10 and then hydroxylating the aluminum foil 10.

[0041] In some specific embodiments of the present application, the surface of the zinc-aluminum alloy layer 20 is wiped with anhydrous ethanol before the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer 20, and the zinc-aluminum alloy layer 20 is dried with nitrogen to increase the content of hydroxyl groups on the surface of the aluminum foil 10. After the composite dispersion liquid of CNT and dopamine is prepared, the zinc-aluminum alloy coating sample is gently wiped with anhydrous ethanol, and then dried with nitrogen to increase the content of hydroxyl groups on the surface of the zinc-aluminum alloy and enhance the hydrogen bond adhesion with PDA.

[0042] According to an embodiment of the present application, when the composite dispersion liquid is coated on the surface of the zinc-aluminum alloy layer 20, the sample is fixed on the chuck of the spin coater, the composite dispersion liquid is added dropwise, and spin coating is performed. For example, after the surface of the zinc-aluminum alloy layer 20 is hydroxylated, spin coating is immediately performed, the sample is fixed on the chuck of the spin coater, the composite dispersion liquid of CNT and dopamine is added dropwise, the coating thickness is controlled by the spin coating speed and spin coating time, the balance between electrolyte barrier and conductivity is achieved, and the uniformity of sodium deposition is improved.

[0043] In some specific embodiments of the present application, after spin coating, the sample is placed in an incubator for standing to allow dopamine to polymerize in situ on the surface of CNT to form a network structure of PDA wrapping CNT. For example, after spin coating, the sample is immediately placed in an incubator for standing to allow dopamine to polymerize in situ on the surface of CNT (phenolic hydroxyl oxidation crosslinking) to form a network structure of PDA wrapping CNT. The dense crosslinked structure of PDA (rich in phenolic hydroxyl groups and amine groups) can form a molecular level barrier to prevent electrolyte ions from penetrating.

[0044] The composite current collector 100 of the embodiments of the present application is described in detail below with reference to specific embodiments.

[0045] Example 1 (1) Preparation of negative electrode current collector First, Al / Zn 40 Al 60 . The cut aluminum foil 10 was placed in an ultrasonic cleaning machine and sequentially cleaned with acetone, anhydrous ethanol, and ultrapure water to remove surface oil stains and oxide layers. After being taken out, the surface was dried with a dust-free paper and placed in a vacuum drying oven for 30 min at 60°C. Then, the aluminum foil 10 was plasma-activated, Ar gas was introduced into the vacuum chamber, and the surface hydroxyl content of the aluminum foil 10 was increased by using a radio frequency plasma (100 W) for 5 min to enhance the bonding force between the aluminum foil 10 and the subsequent zinc-aluminum alloy layer 20.

[0046] The magnetron sputtering system was set to a direct current power of 80 W, and the deposition rate was controlled at 0.83±0.1 nm / s. After the sputtering chamber was evacuated, the aluminum foil 10 substrate was heated to 80°C (to reduce internal stress), and the sputtering thickness was controlled at 500 nm. During sputtering, the sample was cooled for 10 s every 60 s of spraying. After sputtering, the sample was cooled to room temperature under Ar protection to avoid oxidation. Nine evenly distributed measurement points (3×3 grid) were selected on the surface of the aluminum foil 10, and an ellipsometer was used to measure the Al / Zn 40 Al 60 layer thickness.

[0047] Second, preparation of Al / Zn 40 Al 60 / PDA-CNT.

[0048] Carbon nanotubes were dispersed in Tris-HCl buffer at a concentration of 0.8 mg / mL. An ultrasonic cell disruptor was used to perform ultrasonic dispersion under ice water bath conditions to obtain a CNT dispersion liquid. In the above CNT mother liquor, PDA was added to a final concentration of 1 mg / mL. PDA was completely dissolved by gentle stirring.

[0049] The Al / Zn 40 Al 60 sample was ultrasonically cleaned with anhydrous ethanol for 10 min to remove surface residual impurities, and after nitrogen blowing, it was immediately immersed in 0.1 mol / L Tris buffer (pH=8.5) for 5 min to hydroxylize the zinc-aluminum alloy surface (-OH) and enhance the hydrogen bond binding force with PDA. The aluminum foil 10 sprayed with Zn 40 Al 60 was cut to the appropriate size and firmly fixed on the vacuum adsorption disc of the spin coater. After spin coating, the sample was placed in a constant temperature and humidity box for 2 h to allow PDA to be adsorbed on the Al / Zn 40 Al 60The PDA-CNT composite layer with a thickness of 3 pm was formed by in-situ polymerization on the surface of the layer. After drying, 9 evenly distributed measuring points (3x3 grid) were selected on the surface of the aluminum foil 10, and an ellipsometer was used to measure the Al / Zn 40 Al 60 / PDA-CNT coating thickness.

[0050] (2) Preparation of positive electrode sheet Na3V2(PO4)3, PVDF, Super-P and CNT conductive agent were added into NMP and stirred uniformly, wherein the mass ratio of each substance was 80%:10%:9%:1%. According to the areal density of 10 mg / cm 2 , coating was carried out, and positive electrode sheets with specific size meeting the requirements were obtained after cutting.

[0051] (3) Assembly of battery The full battery without negative electrode included Na3V2(PO4)3 positive electrode sheet, Al / Zn 40 Al 60 / PDA-CNT negative electrode current collector, glass fiber separator, electrolyte, gasket, spring sheet and button cell shell. It was assembled in the order of negative electrode shell→negative electrode current collector→separator→positive electrode→gasket→spring sheet→positive electrode shell, ensuring that the positive and negative electrodes were aligned, and the edge of the negative electrode sheet exceeded the positive electrode sheet. Na / / Al / Zn 40 Al 60 / PDA-CNT half-cell included Al / Zn 40 Al 60 / PDA-CNT negative electrode current collector, sodium sheet, glass fiber separator, electrolyte, gasket, spring sheet and positive and negative electrode shell. It was assembled in the order of negative electrode shell→sodium sheet→separator→negative electrode current collector→gasket→spring sheet→positive electrode shell. The electrolyte was 1M NaPF6 dissolved in diglycol dimethyl ether solution.

[0052] Example 2 The negative electrode current collector and battery were prepared according to the method described in Example 1, except that Zn 30 Al 70 coating with a thickness of 300 nm; and PDA-CNT composite layer with a thickness of 2 pm.

[0053] Example 3 The negative electrode current collector and battery were prepared according to the method described in Example 1, except that Zn 35 Al 65 coating with a thickness of 400 nm; and PDA-CNT composite layer with a thickness of 2.5 pm.

[0054] Comparative Example 1 The difference from Example 1 is that the thickness of PDA-CNT composite layer is different. In this comparative example, the thickness of PDA-CNT composite layer is 0.5 μm.

[0055] Comparative Example 2 The difference from Example 1 is that the thickness of PDA-CNT composite layer is different. In this comparative example, the thickness of PDA-CNT composite layer is 5 μm.

[0056] Comparative Example 3 The difference from Example 1 is that the proportion of Zn in the alloy layer is different. By increasing the proportion of Zn in the alloy layer, the Al / Zn 35 Al 65 / PDA-CNT negative current collector is replaced by Al / Zn 60 Al 40 / PDA-CNT current collector, and the battery assembly and experimental scheme are the same as in Example 1.

[0057] Comparative Example 4 The difference from Example 1 is that the proportion of Al in the alloy layer is different. By increasing the proportion of Al in the alloy layer, the Al / Zn 35 Al 65 / PDA-CNT negative current collector is replaced by Al / Zn 10 Al 90 / PDA-CNT current collector.

[0058] Comparative Example 5 The difference from Example 1 is that the Al / Zn 35 Al 65 / PDA-CNT negative current collector is replaced by Al current collector, and the battery assembly and experimental scheme are the same as in Example 1.

[0059] The performance test results of the negative current collector and battery of the above comparative examples and examples are shown in Table 1, and the test methods are as follows: (a) Nucleation overpotential test: Na / / Al / Zn x Al y / PDA-CNT half-cell is discharged at a constant current of 0.02 mA / cm², the voltage drop when sodium starts to deposit is observed, and the nucleation overpotential of different current collectors is compared.

[0060] (b) Full cell cycling performance test: at room temperature 25℃, 0.5C constant current and constant voltage charge to 3.8 V, cut-off current 0.05C, then 0.5C constant current discharge to 2.5 V, repeat 3 times, the 3rd discharge capacity as the standard capacity Co. 1C (C=Co) constant current and constant voltage charge to 3.8 V, cut-off current 0.05C, 1C discharge to 2.5 V, cycle 300 times. Finally calculate the discharge capacity retention rate of 1C cycle 150 times, and observe whether the coulombic efficiency is stable during the cycle.

[0061] (c) First coulombic efficiency: the ratio of the first charge (sodium deposition) capacity to the first discharge (sodium dissolution) capacity. At 25℃, 0.5C constant current and constant voltage charge to 3.8 V, cut-off current 0.05C, then 0.5C constant current discharge to 2 V.

[0062] Table 1. Performance comparison of different examples and comparative examples From the test results of examples 1 to 3 and comparative examples 1 and 2, it can be seen that the optimal thickness of the PDA-CNT composite barrier layer of the negative electrode current collector of the application is 2-3 μm. If the thickness of the PDA-CNT composite barrier layer is too thin, it cannot cover the underlying metal coating to form a continuous and short-circuit-free barrier, affecting the uniformity of sodium deposition, resulting in insufficient isolation effect, serious side reactions and poor cycle life. However, a too thick dense layer will increase the difficulty of ion transport, affect the deposition kinetics, and increase the polarization, causing the nucleation overpotential to rise to 19 mV.

[0063] From the test results of examples 1-3 and comparative examples 3-4, it can be seen that the negative electrode current collector Zn x Al y The optimal ratio of the alloy layer is 30≤x≤40, 60≤y≤70. The sodium affinity of Zn is better than that of Al, and when the Zn ratio is moderate, the charge-discharge nucleation overpotential is low and the alloy structure is stable. If the Zn ratio is too low, the sodium affinity is close to that of pure Al, and the nucleation overpotential rises to 25 mV, resulting in uneven sodium deposition. However, too high zinc content leads to the formation of multiple intermetallic compounds at room temperature, which reduces the first coulombic efficiency and the recyclable capacity of the battery. Although the alloying reaction may be reversible, the volume change is large, which causes the PDA-CNT composite barrier layer to break, thereby losing the protection effect.

[0064] From the test results of example 1 and comparative example 5, it can be seen that the affinity between pure aluminum and sodium is poor, and a high energy barrier (high nucleation overpotential) needs to be overcome during sodium deposition, resulting in the tendency of sodium to form dendrites. The capacity retention rate after 150 cycles is only 35.6%, and the coulombic efficiency decreases significantly.

[0065] In summary, the composite current collector and the preparation method thereof according to the embodiments of the present application can induce uniform deposition of sodium, and the composite current collector is a negative electrode current collector which is not prone to side reactions and is stable in circulation. Zinc can form various intermetallic compounds with sodium at room temperature, reduces the nucleation overpotential of sodium, and makes the deposition of sodium more uniform and denser, producing an effect similar to "induced deposition". In addition, zinc and aluminum are both metals with abundant reserves and low prices. Moreover, the zinc-aluminum alloy layer 20 is obtained by spraying on the aluminum foil 10, which takes into account the induced deposition of sodium and the current collector that inhibits the alloying reaction. In addition, the PDA-CNT composite barrier layer is constructed on the surface of the alloy layer, the dense cross-linked structure of PDA reduces the contact area between the electrolyte and Zn, and the three-dimensional network of CNT ensures uninterrupted electron transmission.

[0066] Although some specific embodiments of the present application have been described in detail by examples, those skilled in the art should understand that the above examples are only for illustration, not for limiting the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A composite current collector, characterized in that, include: Aluminum foil; A zinc-aluminum alloy layer is located on one side of the aluminum foil, and the zinc-aluminum alloy layer is composed of Zn. x Al y 30≤x≤40, 60≤y≤70; The barrier layer is a PDA-CNT composite barrier layer and is located on the side of the zinc-aluminum alloy layer away from the aluminum foil. The thickness of the barrier layer is 2μm-3μm.

2. The composite current collector according to claim 1, characterized in that, The thickness of the zinc-aluminum alloy layer is 300 nm-500 nm.

3. A method for preparing a composite current collector, characterized in that, The preparation method is used to prepare the composite current collector according to claim 1 or 2, and the preparation method includes the following steps: A zinc-aluminum alloy layer is prepared on one side of an aluminum foil; A barrier layer is prepared on the surface of the zinc-aluminum alloy layer away from the aluminum foil.

4. The method for preparing the composite current collector according to claim 3, characterized in that, A composite dispersion composed of CNTs and dopamine is prepared, and the composite dispersion is coated on the surface of the zinc-aluminum alloy layer to form the barrier layer.

5. The method for preparing the composite current collector according to claim 3, characterized in that, The zinc-aluminum alloy layer was prepared on the surface of the aluminum foil using a magnetron sputtering process. After sputtering, the aluminum foil was cooled to room temperature under the protection of an inert gas.

6. The method for preparing the composite current collector according to claim 3, characterized in that, Before preparing the zinc-aluminum alloy layer on the surface of the aluminum foil, the aluminum foil is cleaned to remove surface oil and oxide layer.

7. The method for preparing the composite current collector according to claim 3 or 6, characterized in that, The aluminum foil is plasma activated to increase the hydroxyl content on the surface of the aluminum foil.

8. The method for preparing the composite current collector according to claim 3, characterized in that, Before coating the composite dispersion onto the surface of the zinc-aluminum alloy layer, the surface of the zinc-aluminum alloy layer is wiped with anhydrous ethanol and dried with nitrogen to increase the hydroxyl content on the surface of the aluminum foil.

9. The method for preparing the composite current collector according to claim 3, characterized in that, When the composite dispersion is coated onto the surface of the zinc-aluminum alloy layer, the sample is fixed on the suction cup of the spin coater, the composite dispersion is added dropwise, and spin coating is performed.

10. The method for preparing the composite current collector according to claim 9, characterized in that, After spin coating, the sample is placed in a constant temperature oven to allow dopamine to polymerize in situ on the CNT surface, forming a PDA-encapsulated CNT network structure.

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