Composite current collector, preparation method thereof and negative-electrode-free sodium ion battery comprising composite current collector

Abstract

The invention relates to the technical field of sodium secondary batteries, in particular to a composite current collector, a preparation method of the composite current collector and a negative-electrode-free sodium ion battery comprising the composite current collector. The composite current collector comprises a three-dimensional porous metal framework and artificial SEI layers arranged on at least one outer surface and the hole wall surface of the three-dimensional porous metal framework; and the artificial SEI layer comprises one or more of NaTi2 (PO4) 3, Na3Zr2Si2PO12, NaTaO3 or NaAlF4, and the SEI layer comprises one or more of NaTi2 (PO4) 3, Na3Zr2Si2PO12, NaTaO3 and NaAlF4. According to the present invention, the adjustable ultrathin artificial SEI layer is arranged on the outer surface and the pore wall surface of the three-dimensional metal porous skeleton, such that the problems of non-uniform sodium metal deposition, dendritic crystal growth and the like of the negative-electrode-free sodium ion battery are solved, and the cycle performance and the rate capability of the negative-electrode-free sodium ion battery are effectively improved.

Description

Technical Field

[0001] This disclosure relates to the field of sodium secondary battery technology, and in particular to a composite current collector, its preparation method, and a negative electrode-free sodium-ion battery containing the composite current collector. Background Technology

[0002] The negative electrode-less sodium-ion battery is a novel sodium-ion battery structure that initially contains no negative electrode active material. Instead, during the first charge, sodium ions migrate from the positive electrode to the negative electrode through an electrochemical reduction reaction, depositing sodium metal on the surface of the negative electrode current collector to form the negative electrode active material. This design offers several significant advantages, such as simplified battery structure, reduced cost, and increased energy density, and is expected to promote the widespread application of sodium-ion batteries in the energy storage field.

[0003] However, sodium-ion batteries without a negative electrode also face some pressing technical challenges. On the one hand, the deposition of sodium metal on the surface of the negative electrode current collector is often uneven, easily leading to the formation of sodium dendrites. These sodium dendrites not only reduce the battery's cycle life but may also puncture the battery separator, causing a short circuit and triggering a serious safety accident. On the other hand, the deposition and stripping process of sodium metal on the surface of the negative electrode current collector is accompanied by significant volume changes, which can damage the electrode structure and thus affect the battery's cycle stability and charge / discharge performance.

[0004] Currently, researchers are attempting to alleviate the problem of uneven sodium deposition by constructing three-dimensional current collector structures. In negative electrode-less sodium-ion batteries, sodium is deposited onto the negative electrode current collector during the first charge to form an active sodium layer. Therefore, the geometry of the negative electrode current collector directly determines the density of sodium metal nucleation sites, the buffering capacity of volume changes during deposition / stripping, the probability of dendrite formation, and the ion-electron transport impedance. Compared to traditional two-dimensional planar foils (aluminum foil, copper foil), three-dimensional porous current collectors, through their three-dimensional design, expand the deposition site from a two-dimensional surface to a three-dimensional space, bringing unique advantages. However, existing three-dimensional current collectors still suffer from a lack of synergy in pore structure-interface integration: ① The current density at the pore opening is concentrated, causing sodium metal to preferentially deposit on the surface of the current collector and unable to penetrate deep into the pores, resulting in an areal capacity >2 mAh·cm³. -2 ① The pore opening is immediately blocked by sodium bridges; ② Existing interface layers are mostly formed by wet coating or in-situ electrochemical conversion, resulting in uneven thickness (σ>±20nm), which cannot achieve conformal coverage of three-dimensional pores of 0.1-20μm; ③ The ionic conductivity of the interface layer is generally lower than 1×10⁻⁶. -5 S·cm -1 At high magnification, local polarization >80mV induces dendrites.

[0005] Therefore, there is an urgent need for a synergistic solution that can simultaneously achieve three-dimensional confined deposition and conformal high-conductivity interfaces to break through the energy density-cycle life bottleneck of anode-less sodium-ion batteries. Summary of the Invention

[0006] To address the aforementioned technical problems, this disclosure provides a composite current collector, its preparation method, and a negative electrode-free sodium-ion battery containing the composite current collector.

[0007] In a first aspect, this disclosure provides a composite current collector, the composite current collector comprising a three-dimensional porous metal skeleton and an artificial SEI layer disposed on at least one outer surface and the surface of the pore wall of the three-dimensional porous metal skeleton. The artificial SEI layer comprises one or more of phosphate, tantalate, or fluoride; The phosphate includes NaTi2(PO4)3 and / or Na3Zr2Si2PO4. 12 ; The tantalate includes NaTaO3; The fluoride includes NaAlF4.

[0008] This disclosure solves the problems of uneven sodium metal deposition and dendrite growth in anode-free sodium-ion batteries by setting an adjustable ultrathin artificial solid electrolyte interface (SEI) layer on the outer surface and pore wall surface of a three-dimensional metal current collector, effectively improving the cycle performance and rate performance of anode-free sodium-ion batteries. Specifically: 1. It can induce uniform deposition of sodium metal on the pore walls inside the current collector and fill it along the pore extension direction, eliminating preferential deposition at the top and sodium bridging; 2. It can also improve the interfacial conductivity and reduce local polarization; 3. It can suppress sodium dendrite growth, improving the cycle life and safety of the battery; 4. It supports stable operation under high current density.

[0009] It should be noted that the artificial SEI layer in this disclosure has a coverage rate of ≥99% on all pore wall surfaces of the three-dimensional porous metal skeleton.

[0010] The following are preferred technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.

[0011] As a preferred technical solution of this disclosure, the three-dimensional porous metal skeleton includes a three-dimensional porous aluminum skeleton.

[0012] Preferably, the porosity of the three-dimensional porous metal skeleton is 20-60%, such as 20%, 30%, 40%, 50% or 60%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] Preferably, the three-dimensional porous metal skeleton has micropores and macropores.

[0014] Preferably, the pore size of the micropore is 0.1-2μm, such as 0.1μm, 0.5μm, 1μm, 1.5μm or 2μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the pore size of the macropore is 5-20μm, such as 5μm, 10μm, 15μm or 20μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, in the three-dimensional porous metal skeleton, the micropore volume accounts for 40-60% of the total pore volume, such as 40%, 45%, 50%, 55% or 60%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] Preferably, in the three-dimensional porous metal skeleton, the volume of the macropores accounts for 40-60% of the total pore volume, such as 40%, 45%, 50%, 55% or 60%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In the three-dimensional porous metal framework disclosed herein, micropores provide a high specific surface area, which is beneficial for diluting the apparent current density during cycling (reducing it by 1-2 orders of magnitude compared to two-dimensional current collectors), thus achieving stable cycling at high current densities; macropores ensure ion transport channels. An appropriate distribution ratio of these two components is beneficial for improving the overall performance of the anode-free sodium-ion battery.

[0019] Preferably, in the three-dimensional porous metal skeleton, the pore morphology includes open pores.

[0020] Preferably, the surface roughness of the pore walls of the micropores and the macropores is independently 0.5-2.0 μm, such as 0.5 μm, 1.0 μm, 1.5 μm or 2.0 μm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Suitable surface roughness is beneficial for optimizing the nucleation density of sodium metal.

[0022] As a preferred technical solution of this disclosure, the thickness of the artificial SEI layer is 1-25nm, such as 1nm, 5nm, 10nm, 15nm, 20nm or 25nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 5-12nm.

[0023] Preferably, the thickness deviation of the artificial SEI layer is within ±0.5 nm.

[0024] Within the range of artificial SEI layer thickness selection mentioned above, the required thickness is determined, and the thickness deviation is within ±0.5nm, based on the determined required thickness.

[0025] In this disclosure, an appropriate artificial SEI layer thickness can help further improve the rate performance and cycle performance of the battery. If the artificial SEI layer is too thick, it will lead to: 1. The ion migration path increases linearly with the thickness, thereby increasing the interfacial impedance, especially exacerbating polarization during high-rate charge and discharge; 2. Significantly reducing the effective pore size (or even blocking micropores), weakening the confinement effect of the three-dimensional structure on sodium deposition, reducing the effective specific surface area, causing sodium to preferentially deposit at the pore openings, forming "sodium bridges"; 3. Due to the difference in thermal expansion coefficient and Young's modulus between the SEI layer and the aluminum skeleton, an excessively thick SEI layer is prone to internal stress under the volume change caused by sodium deposition / stripping, which may lead to cracking and peeling of the SEI layer, resulting in loss of protective function; 4. Suppressing electron tunneling, affecting sodium nucleation kinetics, which is not conducive to uniform deposition.

[0026] As a preferred technical solution of this disclosure, the ratio of the thickness (denoted as t) of the artificial SEI layer to the average pore diameter (denoted as d) of the three-dimensional porous metal skeleton is 0.005-0.05.

[0027] It should be noted that the average aperture d is the weighted average aperture, and its calculation formula is as follows:

[0028] Where, d i Let n be the average diameter of the i-th type of pore (e.g., 1.05 μm for micropores and 12.5 μm for macropores). i This represents the percentage of the number of pores (or the percentage of the volume of pores, which is usually represented by the volume fraction of pores because the pores are interconnected).

[0029] In this disclosure, a reasonable t / d ratio is beneficial to improving the rate performance of a negative electrode-free sodium-ion battery. An excessively high t / d ratio will increase the risk of pore blockage, increase the tortuosity of the sodium ion diffusion path, and increase the internal stress of the SEI layer; while an excessively low t / d ratio will lead to incomplete coverage, weak nucleation regulation, and inability to effectively suppress side reactions during cycling.

[0030] Secondly, this disclosure provides a method for preparing a composite current collector as described in the first aspect, the method comprising the following steps: (1) A three-dimensional porous metal skeleton was obtained by constructing a porous structure on a metal substrate using an electrochemical corrosion method; (2) Atomic layer deposition is performed on at least one outer surface and the pore wall surface of the three-dimensional porous metal skeleton to form an artificial SEI layer precursor; (3) After atomic layer deposition is completed, annealing is performed in an inert atmosphere to obtain a composite current collector.

[0031] The preparation method described in this disclosure can achieve nanoscale synchronous control of pore size, pore wall and interface, overcoming the defects of traditional methods such as step-by-step pore formation and interface fabrication and uneven coating; annealing treatment can further enhance the crystallinity and interface stability of the artificial SEI layer.

[0032] As a preferred technical solution of this disclosure, the electrochemical corrosion method in step (1) includes: under alternating current, using the metal substrate as the anode and a platinum sheet as the cathode, performing electrochemical corrosion in an acidic solution containing halide ions to obtain a three-dimensional porous metal skeleton.

[0033] Preferably, the current density of the alternating current is 0.1-1.6 A / cm². 2 For example, 0.1A / cm 2 0.5A / cm 2 0.8A / cm 2 1.0A / cm 2 1.4A / cm 2 Or 1.6A / cm 2 This includes, but is not limited to, the listed values; other unlisted values ​​within this range also apply.

[0034] Preferably, the frequency of the alternating current is 40-60Hz, such as 40Hz, 45Hz, 50Hz, 55Hz or 60Hz, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the components of the acidic solution containing halide ions include hydrochloric acid, sulfuric acid, and chloride salts.

[0036] Preferably, the acidic solution containing halide ions further includes phosphoric acid.

[0037] Preferably, the acidic solution containing halide ions comprises 0.01-0.5 wt% hydrochloric acid, 0.01-0.5 wt% sulfuric acid, and 0.1-0.5 wt% chloride salt.

[0038] Preferably, the temperature of the electrochemical corrosion is 30-80℃, such as 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, the electrochemical corrosion time is 10-60s, such as 10s, 20s, 30s, 40s, 50s or 60s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] As a preferred technical solution of this disclosure, the deposition temperature of the atomic layer deposition in step (2) is 100-300℃, such as 100℃, 150℃, 200℃, 250℃ or 300℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the annealing temperature in step (3) is 300-500℃, such as 300℃, 350℃, 400℃, 450℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the annealing time in step (3) is 1-2 hours, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours or 2 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] As a preferred technical solution of this disclosure, the preparation method further includes: before performing step (1), pre-treating the metal substrate, the pre-treatment including: sequentially cleaning with acetone, ethanol and deionized water to remove oil and impurities from the surface of the metal substrate; optionally, cleaning with NaOH solution to remove the oxide layer from the surface of the metal substrate.

[0044] Thirdly, this disclosure provides a negative electrode-free sodium-ion battery, including a positive electrode, a separator and an electrolyte, and also includes a composite current collector as described in the first aspect or a composite current collector prepared by the preparation method described in the second aspect. The composite current collector is a negative electrode current collector.

[0045] As a preferred technical solution of this disclosure, the positive electrode sheet contains a positive electrode active material, which includes a sodium-containing compound.

[0046] Preferably, the porosity of the diaphragm is 42%-50%, such as 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%; the air permeability is 150-240s / 100mL, such as 150s / 100mL, 180s / 100mL, 220s / 100mL, or 240s / 100mL, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0047] Preferably, the material of the diaphragm includes, but is not limited to, PP or PE diaphragms.

[0048] Preferably, the type of the diaphragm includes, but is not limited to, a base membrane and a ceramic diaphragm.

[0049] The technical solution provided in this disclosure has the following advantages compared with the prior art: (1) Uniform sodium plating: The three-dimensional porous metal framework provided in this disclosure can dilute the apparent current density during cycling, and the artificial SEI layer can provide uniform nucleation sites and 10 -4 -10 -3 S·cm -1 Na + Channels guide sodium preferential deposition and longitudinal filling on the pore walls, eliminating preferential top deposition and sodium bridging, resulting in an areal capacity >4 mAh·cm³. -2 There were still no dendrites at that time; (2) High rate capability and long lifespan: The artificial SEI layer of the composite current collector described in this disclosure has both electronic and ionic conductivity, reducing the interface impedance by more than 60% and supporting ≥2mA·cm -2 High current charge and discharge; three-dimensional sodium storage space + elastic nanolayer effectively buffers volume changes, maintaining more than 80% of capacity after 800 cycles, and improving cycle life by more than 50% compared to planar (two-dimensional) aluminum foil.

[0050] (3) Precise control of pore size-interface in one step: The preparation method described in this disclosure first constructs a three-dimensional network in the metal matrix by electrochemical corrosion, and then forms a high sodium ion conduction SEI layer by atomic deposition, thereby achieving nanoscale synchronous control of pore size-pore wall-interface, overcoming the defects of step-by-step pore formation and interface manufacturing and uneven coating in traditional methods.

[0051] (4) The process conditions are mild and suitable for mass production: the deposition thickness error of the artificial SEI layer obtained by the preparation method described in this disclosure is within ±0.5nm, and it is dense and free of pinholes, which can effectively block the side reactions of the electrolyte. In addition, the roll-to-roll continuous equipment has achieved a single roll processing of 500m, which can be directly embedded into the existing electrode production line, combining consistency and scale-up prospects. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0053] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 The diagram shows the cycle performance of the sodium-ion batteries without negative electrodes obtained in Examples 1-8 and Comparative Examples 1-4 of this disclosure. Detailed Implementation

[0055] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0056] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0057] Example 1 This embodiment provides a composite current collector and its preparation method. The composite current collector includes a three-dimensional porous aluminum skeleton and an artificial SEI layer disposed on all the outer surfaces and all the pore wall surfaces of the three-dimensional porous aluminum skeleton. The three-dimensional porous aluminum skeleton has micropores and macropores, with a porosity of 45% and an open channel morphology. The micropores have a pore size of 0.1-2 μm and account for 50% of the total pore volume; The pore size of the macropores is 5-20 μm; accounting for 50% of the total pore volume; The surface roughness of the pore walls of both the micropores and the macropores is 0.5 μm; The artificial SEI layer is NaTaO3 with a thickness of 5 nm; The ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.01.

[0058] The preparation method includes: (1) Select high-purity aluminum foil (purity ≥ 99.99%) and clean it by ultrasonic cleaning in acetone, ethanol and deionized water in sequence to remove surface oil and impurities; then, immerse the aluminum foil in a 0.8% NaOH solution for 2 minutes to remove the natural oxide layer and rinse it with deionized water. (2) Under 50Hz AC current, using the aluminum foil treated in step (1) as the anode and the platinum sheet as the cathode, in Cl - Electrochemical corrosion was carried out in a H2SO4 solution (containing 0.1 wt% HCl, 0.1 wt% H2SO4, and 0.2 wt% AlCl3) at 40 °C (current density 0.3 A / cm²). 2 (with a time of 30 seconds), a three-dimensional porous metal skeleton was obtained; (3) Using TaCl5, NaOtBu and H2O as precursors, atomic layer deposition is performed on all outer surfaces and all pore wall surfaces of the three-dimensional porous aluminum skeleton obtained in step (2) to form NaTaO3 layer precursor; The pulse time for TaCl5 was controlled to be 0.1 s, the pulse time for NaOtBu was 0.2 s, the pulse time for H2O was 0.2 s, the purging time was 10 s, and the deposition temperature was 200 ℃. (4) After the deposition is completed, the composite current collector is annealed at 400°C in a nitrogen atmosphere to obtain the composite current collector.

[0059] Example 2 This embodiment provides a composite current collector, which is the same as the composite current collector in Embodiment 1, except that: the thickness of the artificial SEI layer is 12nm; and the ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.012.

[0060] Example 3 This embodiment provides a composite current collector, which is the same as the composite current collector in Embodiment 1, except that: the thickness of the artificial SEI layer is 25 nm; and the ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.025.

[0061] Example 4 This embodiment provides a composite current collector and its preparation method. The composite current collector includes a three-dimensional porous aluminum skeleton and an artificial SEI layer disposed on all the outer surfaces and pore wall surfaces of the three-dimensional porous aluminum skeleton. The three-dimensional porous aluminum skeleton has micropores and macropores, with a porosity of 45% and an open channel morphology. The micropores have a pore size of 0.1-2 μm and account for 50% of the total pore volume; The pore size of the macropores is 5-20 μm; accounting for 50% of the total pore volume; The surface roughness of the pore walls of both the micropores and the macropores is 0.5 μm; The artificial SEI layer is Na3Zr2Si2PO4. 12 The thickness is 10nm; The ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.01.

[0062] The preparation method is the same as that in Example 1, except that: (3) Using ZrCl4, SiCl4, POCl3, NaOtBu and H2O as precursors, atomic layer deposition is performed on all outer surfaces and pore wall surfaces of the three-dimensional porous aluminum framework obtained in step (2) to form Na3Zr2Si2PO 12 Layer precursor; The pulse time for ZrCl4 was controlled at 0.15 s, the pulse time for SiCl4 at 0.12 s, the pulse time for POCl3 at 0.1 s, the pulse time for NaOtBu at 0.2 s, the pulse time for H2O at 0.2 s, the purging time at 10 s, and the deposition temperature at 200 ℃.

[0063] Example 5 This embodiment provides a composite current collector and its preparation method. The composite current collector includes a three-dimensional porous aluminum skeleton and an artificial SEI layer disposed on all the outer surfaces and pore wall surfaces of the three-dimensional porous aluminum skeleton. The three-dimensional porous aluminum skeleton has micropores and macropores, with a porosity of 45% and an open channel morphology. The micropores have a pore size of 0.1-2 μm and account for 50% of the total pore volume; The pore size of the macropores is 5-20 μm; accounting for 50% of the total pore volume; The surface roughness of the pore walls of both the micropores and the macropores is 0.5 μm; The artificial SEI layer is NaAlF4 with a thickness of 8 nm.

[0064] The ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.008.

[0065] The preparation method is the same as that in Example 1, except that: (3) Using Al(CH3)3 (TMA), HF / NaOtBu complex and H2O as precursors, atomic layer deposition is performed on all outer surfaces and pore wall surfaces of the three-dimensional porous aluminum skeleton obtained in step (2) to form NaAlF4 layer precursor; The pulse time for controlling TMA was 0.1 s, the pulse time for the HF / NaOtBu complex was 0.2 s, the pulse time for H2O was 0.2 s, the purging time was 10 s, and the deposition temperature was 200 ℃.

[0066] Example 6 This embodiment provides a composite current collector, which is the same as the composite current collector in Embodiment 1, except that: the thickness of the artificial SEI layer is 50 nm; and the ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.05.

[0067] Example 7 This embodiment provides a composite current collector, which is the same as the composite current collector in Embodiment 1, except that the porosity of the three-dimensional porous aluminum skeleton is 60%. The micropores account for 20% of the total pore volume; the macropores account for 80% of the total pore volume.

[0068] Example 8 This embodiment provides a composite current collector, which is the same as the composite current collector in Embodiment 1, except that the porosity of the three-dimensional porous aluminum skeleton is 35%. The micropores account for 80% of the total pore volume; the macropores account for 20% of the total pore volume.

[0069] Comparative Example 1 This comparative example provides a current collector, which is the three-dimensional porous aluminum skeleton in Example 1, without an artificial SEI layer.

[0070] Comparative Example 2 This comparative example provides a current collector, which is the high-purity aluminum foil in Example 1, which is non-electrochemically non-corrosive and does not have an artificial SEI layer.

[0071] Comparative Example 3 This comparative example provides a current collector, which is the high-purity aluminum foil (without electrochemical etching) in Example 1, with an artificial SEI (NaTaO3) layer of 5 nm thickness on both its upper and lower surfaces.

[0072] Comparative Example 4 This comparative example provides a composite current collector, which is the same as the composite current collector in Example 1, except that the artificial SEI layer is sodium carbonate and sodium fluoride, and the molar ratio of sodium carbonate and sodium fluoride is 1:1.

[0073] Test battery This disclosure provides a test-use sodium-ion battery without a negative electrode, the specific composition of which is as follows: Negative electrode: The composite current collector obtained in the embodiments and comparative examples of this disclosure; Positive electrode sheet: A positive electrode active slurry is prepared by mixing and stirring Na4Fe3(PO4)2P2O7, conductive carbon black Super P, CNTs, and PVDF, wherein the mass ratio of Na4Fe3(PO4)2P2O7, conductive carbon black Super P, CNTs, and PVDF is 95:1:1:3; the obtained positive electrode slurry is uniformly coated on the positive electrode current collector, with a double-sided areal density of 350 g / m³. 2 Then, the positive electrode sheet is rolled to a compaction density of 2.0 g / cm³. 3 ; Membrane: Polyolefin membrane, 12μm thick, with a porosity of 40%; Electrolyte: comprising sodium bis(fluorosulfonyl)imide (NaFSI) dissolved in a solvent of ethylene glycol dimethyl ether (DME): triethylene glycol dimethyl ether (G3): bis(2,2,2-trifluoroethyl) ether (BTFE) in a volume ratio of 1:1:1, with a concentration of 3.5 mol / kg; and also comprising a functional additive: cyclopentyl methanesulfonate, accounting for 2 wt% of the electrolyte mass; The positive and negative electrode sheets are separated by a separator, arranged in a regular pattern and stacked multiple times. A positive tab is connected to the positive current collector, and a negative tab is connected to the negative current collector to obtain a semi-finished battery. Then, the semi-finished battery is placed in a vacuum oven at 65°C and baked for 24 hours. After liquid injection, sealing, formation, aging and capacity testing, the negative electrode-free sodium-ion battery is obtained.

[0074] It should be noted that the above-mentioned negative electrode-free sodium-ion battery is only an example listed for testing the performance of the composite current collector. This disclosure is not limited to this type of battery. The raw materials (other than the composite current collector), ratios, parameters and processes can be replaced with other conventional raw materials, ratios, parameters and processes in the art to form a battery different from the negative electrode-free sodium-ion battery used for testing.

[0075] Performance Test 1 The ionic conductivity (σNa) of the current collectors obtained from the test examples and comparative examples + ), electronic conductivity (σ) e - ), lattice mismatch rate (vs Na).

[0076] Among them, ionic conductivity was measured using the blocked electrode AC impedance method at a frequency of 1MHz-0.1Hz; electronic conductivity was measured using the DC polarization method at a bias voltage of 10mV; the lattice mismatch rate was calculated as follows: mismatch rate (%) = [(a film - a sub ) / a sub ]×100%, where a film It is the lattice constant of the epitaxial thin film. This is the lattice constant of the substrate. Before testing, a sodium foil was used to pre-deposit a 1 mAh·cm⁻¹ sodium-ion battery without a negative electrode. -2 Sodium. The test results are shown in Table 1.

[0077] Table 1

[0078] As shown in Table 1, the artificial SEI membrane with composite current collector provided in this disclosure has dual functions of electronic conductivity and ionic conductivity, with an ionic conductivity of up to 10. -4 S·cm -1The above. In addition, the lattice mismatch rate of the artificial SEI film of the composite current collector obtained in this disclosure is all below 5%, which means that it has excellent interfacial compatibility and structural coherence with the three-dimensional porous framework matrix, and can effectively reduce interfacial impedance and suppress dendrites.

[0079] Performance Test 2 The rate performance and cycle performance of the test electrodeless sodium-ion batteries obtained from the test examples and comparative examples are shown.

[0080] Rate performance: The vehicle was fully charged to the upper limit voltage at 0.2C and then discharged at different rates. The rate discharge retention rate was calculated using the following formula: Rate-based discharge retention rate = (Capacity at xC discharge rate / Capacity at 0.2C discharge rate) × 100%. Where x represents the discharge rate.

[0081] Cycling performance: The capacity retention rate is calculated using the following formula: charged at 1C to the upper limit voltage and discharged at 1C to the lower limit voltage. Capacity retention rate = discharge capacity in current cycle / discharge capacity in first cycle × 100%.

[0082] in, Figure 1 The graph shows the cycle performance of the test sodium-ion batteries without negative electrodes obtained from the examples and comparative examples.

[0083] The test results are shown in Table 2.

[0084] Table 2

[0085] As shown in Table 2, the rate performance and cycle performance of the negative electrode-free sodium-ion battery prepared using the composite current collector described in this disclosure are effectively improved. The capacity retention rate at 0.2C / 2C is over 86%, the capacity retention rate at 0.2C / 5C is over 72%, and the capacity retention rate after 800 cycles is still over 80%, with an initial efficiency of over 95%. Furthermore, by further controlling the parameters of the composite current collector, the capacity retention rate at 0.2C / 2C is over 92%, the capacity retention rate at 0.2C / 5C is over 81%, the capacity retention rate after 800 cycles is still over 87%, and the initial efficiency is over 97%.

[0086] Compared with Example 1, the current collectors of Comparative Examples 1-3 did not undergo synergistic improvement through porous construction and artificial deposition of SEI layers, resulting in poor rate performance and cycling performance.

[0087] Compared to Example 1, Comparative Example 4 used other types of artificial SEI membranes, with limited performance improvement.

[0088] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A composite current collector, characterized in that, The composite current collector includes a three-dimensional porous metal skeleton and an artificial SEI layer disposed on at least one outer surface and pore wall surface of the three-dimensional porous metal skeleton. The artificial SEI layer comprises one or more of phosphate, tantalate, or fluoride; The phosphate includes NaTi2(PO4)3 and / or Na3Zr2Si2PO4. 12 ; The tantalate includes NaTaO3; The fluoride includes NaAlF4.

2. The composite current collector according to claim 1, characterized in that, The three-dimensional porous metal skeleton includes a three-dimensional porous aluminum skeleton.

3. The composite current collector according to claim 1 or 2, characterized in that, The porosity of the three-dimensional porous metal framework is 20-60%; Preferably, the three-dimensional porous metal framework has micropores and macropores; Preferably, the pore size of the micropores is 0.1-2 μm; Preferably, the pore size of the macropore is 5-20 μm; Preferably, in the three-dimensional porous metal framework, the micropore volume accounts for 40-60% of the total pore volume; Preferably, in the three-dimensional porous metal framework, the volume of the macropores accounts for 40-60% of the total pore volume; Preferably, in the three-dimensional porous metal skeleton, the pore morphology includes open pores; Preferably, the surface roughness of the pore walls of the micropores and the macropores is independently 0.5-2.0 μm.

4. The composite current collector according to any one of claims 1-3, characterized in that, The thickness of the artificial SEI layer is 1-25 nm, preferably 5-12 nm; Preferably, the thickness deviation of the artificial SEI layer is within ±0.5 nm.

5. The composite current collector according to claim 4, characterized in that, The ratio of the thickness of the artificial SEI layer to the average pore size of the three-dimensional porous metal skeleton is 0.005-0.

05.

6. A method for preparing a composite current collector as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) A three-dimensional porous metal skeleton was obtained by constructing a porous structure on a metal substrate using an electrochemical corrosion method; (2) Atomic layer deposition is performed on at least one outer surface and the pore wall surface of the three-dimensional porous metal skeleton to form an artificial SEI layer precursor; (3) After atomic layer deposition is completed, annealing is performed in an inert atmosphere to obtain a composite current collector.

7. The preparation method according to claim 6, characterized in that, The electrochemical corrosion method in step (1) includes: under alternating current, using the metal substrate as the anode and a platinum sheet as the cathode, electrochemical corrosion is carried out in an acidic solution containing halide ions to obtain a three-dimensional porous metal skeleton. Preferably, the current density of the alternating current is 0.1-1.6 A / cm². 2 ; Preferably, the frequency of the alternating current is 40-60Hz; Preferably, the components of the acidic solution containing halide ions include hydrochloric acid, sulfuric acid, and chloride salts; Preferably, the acidic solution containing halide ions further includes phosphoric acid; Preferably, the acidic solution containing halide ions comprises 0.01-0.5 wt% hydrochloric acid, 0.01-0.5 wt% sulfuric acid, and 0.1-0.5 wt% chloride salt; Preferably, the temperature of the electrochemical corrosion is 30-80℃; Preferably, the electrochemical corrosion time is 10-60 s.

8. The preparation method according to claim 6 or 7, characterized in that, The deposition temperature for atomic layer deposition in step (2) is 100-300℃; Preferably, the annealing temperature in step (3) is 300-500℃; Preferably, the annealing time in step (3) is 1-2 hours.

9. A negative electrode-free sodium-ion battery, comprising a positive electrode, a separator, and an electrolyte, characterized in that, It also includes the composite current collector as described in any one of claims 1-5 or the composite current collector prepared by the preparation method as described in claims 6-8; The composite current collector is a negative electrode current collector.

10. The negative electrode-free sodium-ion battery according to claim 9, characterized in that, The positive electrode sheet contains a positive electrode active material, which includes a sodium-containing compound. Preferably, the diaphragm has a porosity of 42%-50% and an air permeability of 150-240s / 100mL.

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