Modified current collector, preparation method thereof and negative electrode-free sodium battery

Abstract

The application provides a modified current collector, a preparation method thereof and a negative electrode-free sodium battery. The modified current collector comprises a current collector substrate and a modified coating arranged on at least one side surface of the current collector substrate; and the modified coating is obtained by compounding PEDOT:PSS and oxygen vacancy modified metal oxide. The modified coating obtained by compounding PEDOT:PSS and oxygen vacancy modified metal oxide is arranged on the current collector substrate, can effectively bind sodium ions migrated to the negative electrode, improve the diffusion rate of sodium ions, and induce uniform deposition of sodium ions on the current collector; through the synergistic effect of PEDOT:PSS and oxygen vacancy modified metal oxide, the deposition dynamics of sodium ions can be effectively regulated to adapt to the volume change, the non-uniform deposition of sodium ions is inhibited, the consumption of sodium ions in the positive electrode material by the SEI film is reduced, and the specific capacity performance and cycle performance of the negative electrode-free sodium battery are improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a modified current collector and its preparation method, and a sodium-free negative electrode battery. Background Technology

[0002] In recent years, the volatile price of lithium carbonate in the market has raised concerns within the industry about cost control in lithium-ion batteries. This has spurred the rapid development of sodium-ion battery technology; currently, almost all lithium-ion battery manufacturers have invested in the research and development of sodium-ion batteries. Even so, the energy density of current sodium-ion batteries is still below 160Wh / kg, lower than that of commercially available lithium-ion batteries. Using sodium metal anodes with high theoretical specific capacity (1166mAh / g) holds promise for further improving the energy density of sodium-ion batteries. However, metallic sodium is soft, easily oxidized by air, and has a certain degree of viscosity, posing significant difficulties in processing and molding, which is highly detrimental to the large-scale production of sodium metal batteries.

[0003] The design of sodium-based electrodeless batteries can solve the above problems. In electrodeless batteries, the negative electrode is formed in situ through an electrochemical process during the first charge and discharge of the battery. Since the active sodium ions in electrodeless batteries come entirely from the positive electrode material, there is no excess sodium as in sodium metal negative electrode batteries. This not only reduces the difficulty of the manufacturing process but also significantly improves the energy density of sodium-ion batteries.

[0004] Currently, sodium-based anode-free batteries mainly face two problems: 1. Due to the limited amount of active sodium, the volume change of deposited metallic sodium causes the SEI to continuously consume sodium ions for breakage and reconstruction, resulting in extremely rapid capacity decay; 2. During the repeated insertion and extraction of sodium ions, without the constraint of anode material, sodium ions tend to exhibit uneven deposition patterns on the current collector, resulting in "dead sodium," which affects the capacity utilization and coulombic efficiency of the anode-free battery.

[0005] Therefore, how to effectively regulate the dynamic adaptation of sodium ion deposition to volume changes and suppress the uneven deposition of sodium ions on the current collector, thereby improving the electrochemical performance of anode-free sodium batteries, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a modified current collector, its preparation method, and a negative electrode-free sodium battery. The present invention involves depositing a modified coating, obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides, onto a current collector substrate. PEDOT:PSS exhibits high flexibility, effectively trapping sodium ions migrating to the negative electrode and suppressing uneven sodium ion deposition. The oxygen vacancy-modified metal oxide possesses good conductivity and can capture sodium ions migrating from the positive electrode using oxygen vacancies, increasing the sodium ion diffusion rate and further inducing uniform sodium ion deposition on the current collector. Through the synergistic effect of PEDOT:PSS and oxygen vacancy-modified metal oxides, the dynamic adaptation of sodium ion deposition to volume changes can be effectively controlled, suppressing uneven sodium ion deposition on the current collector, reducing the consumption of sodium ions in the positive electrode material by the SEI film, and improving the specific capacity and cycle performance of the negative electrode-free sodium battery.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a modified current collector, the modified current collector comprising a current collector substrate and a modified coating disposed on at least one side surface of the current collector substrate;

[0009] The modified coating is obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides.

[0010] This invention involves depositing a modified coating, obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides, onto a current collector substrate. PEDOT:PSS exhibits high flexibility, effectively trapping sodium ions migrating to the negative electrode and suppressing uneven sodium ion deposition. The oxygen vacancy-modified metal oxides, through oxygen vacancies, capture sodium ions migrating from the positive electrode, increasing the sodium ion diffusion rate and further inducing uniform sodium ion deposition on the current collector. Through the synergistic effect of PEDOT:PSS and oxygen vacancy-modified metal oxides, the dynamics of sodium ion deposition can be effectively controlled to adapt to volume changes, suppressing uneven sodium ion deposition on the current collector, reducing the consumption of sodium ions in the positive electrode material by the SEI film, and improving the specific capacity and cycle performance of the negative electrode-free sodium battery.

[0011] In this invention, the metal oxide rich in oxygen vacancies has good electrical conductivity, which can further improve the rate performance of the negative electrode-free sodium battery and alleviate polarization.

[0012] As a preferred technical solution of the present invention, the mass ratio of PEDOT:PSS to oxygen vacancy modified metal oxide is 1:(0.05-0.1), for example, it can be 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09 or 1:0.1, etc.

[0013] In this invention, if the mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is too small, it is difficult to completely bind the induced sodium ions, resulting in a large volume change; if the mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is too large, it is difficult to induce sodium ion deposition through oxygen vacancies, resulting in uneven deposition of sodium ions.

[0014] As a preferred technical solution of the present invention, the thickness of the modified coating is 10-25μm, for example, it can be 10μm, 15μm, 20μm or 25μm.

[0015] In this invention, if the thickness of the modified coating is too low, it will not be able to completely bind the sodium ions migrating from the positive electrode, which will lead to the growth of sodium dendrites; if the thickness of the modified coating is too high, it will increase the difficulty of sodium ion deposition in the current collector and also affect the energy density of the battery.

[0016] In a preferred embodiment of the present invention, the chemical formula of the metal oxide is D₂O. r Where D is a metallic element, Q D -2r = 0, Q D Let represent the valence of the metallic element D.

[0017] Preferably, D is any one or a combination of at least two of Ti, Al, Cu, Zn, Mg, Mn, Ca, Zr, Ce, Co, Fe, Ni, V, Mo, Sr, Ta, La, Sn, or Cr.

[0018] Preferably, the particle size D50 of the metal oxide is 20-50 nm, for example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm.

[0019] As a preferred technical solution of the present invention, the current collector substrate includes any one or a combination of at least two of aluminum foil, carbon-coated aluminum foil, porous aluminum foil, foamed aluminum foil or electroplated aluminum foil, preferably electroplated aluminum foil or carbon-coated aluminum foil.

[0020] Preferably, the porous aluminum foil is a carbon-containing porous aluminum foil.

[0021] Preferably, the electroplated aluminum foil includes nickel-plated aluminum foil.

[0022] In a second aspect, the present invention provides a method for preparing a modified current collector as described in the first aspect, the method comprising the following steps:

[0023] A PEDOT:PSS solution and an oxygen vacancy-modified metal oxide are mixed to obtain a mixed solution. The mixed solution is then coated onto at least one side of the current collector substrate and dried to obtain the modified current collector.

[0024] The preparation method provided by this invention is simple, low-cost, and easy to scale up.

[0025] As a preferred technical solution of the present invention, the coating method includes spin coating, and the spin coating speed is 1500-3500 rpm, for example, it can be 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm or 3500 rpm.

[0026] Preferably, the spin coating time is 25-50 seconds, for example, it can be 30 seconds, 35 seconds, 40 seconds, 45 seconds or 50 seconds.

[0027] Preferably, the drying method includes blower drying and / or vacuum drying.

[0028] Preferably, the temperature of the blower drying is 60-80℃, for example, 60℃, 65℃, 70℃, 75℃ or 80℃, and the time is 5-8h, for example, 5h, 6h, 7h or 8h.

[0029] Preferably, the vacuum drying temperature is 100-120℃, for example, 100℃, 105℃, 110℃, 115℃ or 120℃, and the time is 10-15h, for example, 10h, 11h, 12h, 13h or 14h.

[0030] As a preferred embodiment of the present invention, the method for preparing the oxygen vacancy-modified metal oxide includes:

[0031] Metal oxides are sintered under a protective atmosphere to obtain oxygen vacancy-modified metal oxides.

[0032] Preferably, the protective atmosphere includes hydrogen and an inert gas.

[0033] Preferably, the inert gas includes argon.

[0034] Preferably, the volume ratio of hydrogen to inert gas is (5-20):(80-95), wherein the range of hydrogen selection "5-20" can be, for example, 5, 10, 15 or 20, and the range of inert gas selection "80-95" can be, for example, 80, 85, 90 or 95.

[0035] Preferably, the sintering temperature is 250-550℃, for example, 250℃, 350℃, 450℃ or 550℃, and the time is 1.5-6h, for example, 1.5h, 2h, 3h, 4h, 5h or 6h.

[0036] Preferably, the heating rate of the sintering process is 1-10℃ / min, for example, it can be 1℃ / min, 3℃ / min, 5℃ / min, 7℃ / min or 9℃ / min, etc.

[0037] Preferably, the method for preparing the PEDOT:PSS solution includes:

[0038] (a) Mix PSS and water, then add monomeric EDOT and pH adjuster to obtain an acidic solution;

[0039] (b) The acidic solution and the oxidant are mixed and reacted to obtain the PEDOT:PSS solution.

[0040] In this invention, the purpose of adding the pH adjuster is to promote the polymerization reaction of PSS and EDOT.

[0041] Preferably, the PSS is polystyrene sulfonic acid and / or sodium polystyrene sulfonate.

[0042] Preferably, the mass ratio of PSS to water is (0.01-0.06):1, for example, it can be 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1 or 0.06:1, etc.

[0043] Preferably, the mass ratio of the monomer EDOT to PSS is (0.3-0.65):1, for example, it can be 0.3:1, 0.32:1, 0.35:1, 0.45:1, 0.55:1 or 0.65:1, etc.

[0044] Preferably, the pH adjuster comprises hydrochloric acid.

[0045] Preferably, the oxidant is sodium persulfate.

[0046] In this invention, sodium persulfate is used as an oxidant; its functions are as follows: 1. To prevent the introduction of other impurity cations; 2. The sulfate ions in sodium persulfate that have participated in the reaction can be adsorbed and removed by the anion exchange resin column, while sodium ions can participate in the film formation in the subsequent electrochemical process, reducing the consumption of sodium ions in the positive electrode active material.

[0047] Preferably, the mass ratio of the oxidant to the monomer EDOT is (1.05-1.5):1, for example, it can be 1.05:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, etc.

[0048] Preferably, the reaction time is 15-20 hours, for example, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours.

[0049] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0050] (1) Mix PSS and deionized water at a mass ratio of (0.01-0.06):1, add monomer EDOT dropwise while stirring, and add hydrochloric acid after the addition is complete to make the pH of the mixed solution 2-5 to obtain an acidic solution.

[0051] The mass ratio of monomer EDOT to PSS is (0.3-0.65):1;

[0052] (2) Sodium persulfate was added dropwise to the acidic solution and the reaction was carried out for 15-20 hours. After the reaction was completed, impurity anions were adsorbed by an anion exchange resin column for purification to obtain PEDOT:PSS solution.

[0053] The mass ratio of sodium persulfate to monomer EDOT is (1.05-1.5):1.

[0054] (3) Under a protective atmosphere composed of hydrogen and inert gas, the metal oxide is sintered at a temperature of 250-550℃ for 1.5-6h to obtain oxygen vacancy modified metal oxide.

[0055] The volume ratio of hydrogen to inert gas is (5-20):(80-95), and the heating rate of the sintering process is 1-10℃ / min.

[0056] (4) The PEDOT:PSS solution and the oxygen vacancy modified metal oxide are stirred and mixed evenly to obtain a mixed solution. Then, the mixed solution is spin-coated onto at least one side surface of the current collector substrate at a spin-coating rate of 1500-3500 rpm for 25-50 s. The spin-coated current collector substrate is then placed in a forced-air drying oven at 60-80℃ for 5-8 h and transferred to a vacuum drying oven at 100-120℃ for 10-15 h to obtain the modified current collector.

[0057] Thirdly, the present invention provides a negative electrode-free sodium battery, wherein the negative electrode-free sodium battery includes the modified current collector as described in the first aspect.

[0058] Preferably, the negative electrode sheet of the anodeless sodium battery is the modified current collector.

[0059] Preferably, the positive electrode sheet of the anodeless sodium battery comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0060] It should be noted that the present invention does not specifically limit the positive active material in the positive active material layer. By way of example, it can be any one or a combination of at least two of three-dimensional porous sodium vanadium phosphate, sodium vanadium phosphate, sodium iron phosphate, sodium pyrophosphate, Prussian blue, Prussian white or layered metal oxide.

[0061] It should be noted that the layered metal oxide can be Na x Ni i Fe j Mn k M m O2, Na x Ni i Fe j Mn k M m O2 satisfies: 0<i≤0.4, 0<j≤0.5, 0<k≤0.6, 0<m≤0.2, i+j+k+m=1. When 0.6<x≤0.8, the material is a P2-phase layered oxide; when 0.8<x≤1, the material is an O3-phase layered oxide.

[0062] It should be noted that the present invention does not specifically limit the material of the positive electrode current collector. By way of example, it can be carbon-coated aluminum foil, porous aluminum foil, foamed aluminum foil or electroplated aluminum foil.

[0063] It should be noted that the present invention does not limit the preparation method of the positive electrode sheet. By way of example, the following steps may be adopted:

[0064] Mix the positive active material, conductive agent and binder at a mass ratio of (80-99):(0.5-10):(0.5-10) to prepare a positive electrode slurry, then coat the slurry on the positive electrode current collector, and after drying, rolling and cutting, the positive electrode sheet of the sodium battery is obtained.

[0065] It should be noted that the present invention does not limit the type of the conductive agent. By way of example, it can be few-walled carbon nanotubes, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, conductive graphite or graphene.

[0066] It should be noted that the present invention does not limit the type of adhesive. For example, it may be a monomer, polymer or copolymer of polyvinylidene fluoride, acrylonitrile, vinylidene fluoride, vinyl alcohol, methacrylamide, acrylic acid, lithium acrylate, acrylamide, amide, imide, acrylate, sodium alginate, chitosan, ethylene glycol, guar gum, etc.

[0067] Preferably, the sodium-free battery further includes a separator.

[0068] The present invention does not limit the type of the diaphragm. For example, it can be a polymer diaphragm such as glass fiber, polyethylene, polypropylene, polysulfonyl, polyacrylonitrile, polyvinyl alcohol, polyarylethersulfone, polyvinylidene fluoride, or polymalonic acid.

[0069] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] (1) In this invention, a modified coating obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxide is placed on the current collector substrate. PEDOT:PSS has extremely high flexibility and can effectively bind sodium ions migrating to the negative electrode, suppressing the uneven deposition of sodium ions. The oxygen vacancy-modified metal oxide has good conductivity and can capture sodium ions migrating from the positive electrode with the help of oxygen vacancies, thereby increasing the diffusion rate of sodium ions and further inducing the uniform deposition of sodium ions on the current collector. Through the synergistic effect of PEDOT:PSS and oxygen vacancy-modified metal oxide, the dynamic adaptation of sodium ion deposition to volume change can be effectively controlled, the uneven deposition of sodium ions on the current collector can be suppressed, the consumption of sodium ions in the positive electrode material by the SEI film can be reduced, and the specific capacity and cycle performance of the negative electrode-free sodium battery can be improved.

[0072] (2) The preparation method provided by the present invention is simple, low in cost, and easy to implement on a large scale. Attached Figure Description

[0073] Figure 1 This is a schematic diagram of the structure of a sodium-free battery made using the modified current collector prepared in Example 1 as the negative electrode sheet in this invention.

[0074] Figure 2 This is a scanning electron microscope image of the modified current collector prepared in Example 1 of this invention.

[0075] Figure 3This is a schematic cross-sectional view of the modified current collector prepared in Example 1 of this invention, and a schematic cross-sectional view after it is fully filled.

[0076] Figure 4 This is a schematic diagram of the cross-section of the current collector prepared in Comparative Example 1 of this invention, and a schematic diagram of the cross-section after it is fully filled. Detailed Implementation

[0077] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0078] Example 1

[0079] This embodiment provides a modified current collector, which includes a current collector substrate and a modified coating disposed on at least one side surface of the current collector substrate;

[0080] The modified coating is obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides;

[0081] The mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is 1:0.05, the thickness of the modified coating is 15 μm, the chemical formula of the metal oxide is ZrO2, the particle size D50 of the metal oxide is 25 nm, and the current collector substrate is carbon-coated aluminum foil.

[0082] This embodiment also provides a method for preparing the above-mentioned modified current collector, the preparation method comprising the following steps:

[0083] (1) Place PSS and deionized water in a beaker with a mass ratio of 0.03:1 and stir until homogeneous with the aid of a magnetic stirrer; under stirring conditions, add monomer EDOT dropwise to the beaker, and after the addition is complete, add a certain amount of hydrochloric acid to make the pH of the mixed solution 4, thus obtaining an acidic solution;

[0084] The mass ratio of monomer EDOT to PSS is 0.4:1.

[0085] (2) Sodium persulfate was added dropwise to the acidic solution and the reaction was carried out for 18 hours. After the reaction was completed, impurity anions were adsorbed by an anion exchange resin column for purification to obtain a purified PEDOT:PSS solution.

[0086] The mass ratio of sodium persulfate to monomer EDOT is 1.1:1.

[0087] (3) ZrO2 nanoparticles were placed in a tube furnace with a heating rate of 5℃ / min and sintered under a protective atmosphere of hydrogen and argon. The sintering temperature was 450℃ and the time was 6h. After sintering, the furnace was cooled to room temperature of 25℃ to obtain oxygen vacancy modified ZrO2 material, which was denoted as ZrO2-OVs material.

[0088] The volume ratio of hydrogen to argon is 5:90.

[0089] (4) The oxygen vacancy modified ZrO2 material was added to the PEDOT:PSS solution and stirred at high speed to obtain a mixed solution. Then, the mixed solution was spin-coated onto one side of the carbon-coated aluminum foil using a spin coater at a spin coating speed of 1500 rpm for 25 s. The spin-coated current collector substrate was then placed in an 80°C forced-air drying oven for 8 h and then transferred to a 110°C vacuum drying oven for 12 h to obtain the modified current collector.

[0090] The mass ratio of oxygen vacancy-modified ZrO2 material to PEDOT:PSS solution was 0.05:1.

[0091] Figure 1 A schematic diagram of a sodium-free battery made using the modified current collector prepared in this embodiment as the negative electrode sheet is shown.

[0092] Figure 2 The image shows a scanning electron microscope (SEM) image of the modified current collector prepared in this embodiment. As can be seen from the image, PEDOT:PSS and oxygen vacancy-modified oxides are uniformly attached to the negative electrode current collector.

[0093] Figure 3 The diagram shows a cross-sectional schematic of the modified current collector prepared in this embodiment and a cross-sectional schematic of it after full charge. Figure (a) is a cross-sectional schematic of the uncharged state, and Figure (b) is a cross-sectional schematic of the fully charged state. As can be seen from the figures, the current collector of the negative electrode sodium-free battery coated with PEDOT:PSS / ZrO2-OVs has a very uniform negative electrode sodium deposition after the battery is fully charged.

[0094] Example 2

[0095] This embodiment provides a modified current collector, which includes a current collector substrate and a modified coating disposed on at least one side surface of the current collector substrate;

[0096] The modified coating is obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides;

[0097] The mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is 1:0.07, the thickness of the modified coating is 10 μm, the chemical formula of the metal oxide is ZnO2, the particle size D50 of the metal oxide is 20 nm, and the current collector substrate is carbon-coated aluminum foil.

[0098] This embodiment also provides a method for preparing the above-mentioned modified current collector, the preparation method comprising the following steps:

[0099] (1) Place PSS and deionized water in a beaker with a mass ratio of 0.02:1 and stir until homogeneous with the aid of a magnetic stirrer; under stirring conditions, add monomer EDOT dropwise to the beaker, and after the addition is complete, add a certain amount of hydrochloric acid to make the pH of the mixed solution 4, thus obtaining an acidic solution;

[0100] The mass ratio of monomer EDOT to PSS is 0.35:1.

[0101] (2) Sodium persulfate was added dropwise to the acidic solution and the reaction was carried out for 15 hours. After the reaction was completed, impurity anions were adsorbed by an anion exchange resin column for purification to obtain a purified PEDOT:PSS solution.

[0102] The mass ratio of sodium persulfate to monomer EDOT is 1.3:1.

[0103] (3) ZnO2 nanoparticles were placed in a tube furnace with a heating rate of 1℃ / min and sintered under a protective atmosphere of hydrogen and argon. The sintering temperature was 250℃ and the time was 6h. After sintering, the furnace was cooled to room temperature of 25℃ to obtain oxygen vacancy modified ZnO2 material, which was denoted as ZnO2-OVs material.

[0104] The volume ratio of hydrogen to argon is 10:85.

[0105] (4) The oxygen vacancy modified ZnO2 material was added to the PEDOT:PSS solution and stirred at high speed to obtain a mixed solution. Then, the mixed solution was spin-coated onto one side of the carbon-coated aluminum foil using a spin coater at a spin coating speed of 2500 rpm for 35 s. The spin-coated current collector substrate was then placed in a 70°C forced-air drying oven for 6 h and then transferred to a 100°C vacuum drying oven for 15 h to obtain the modified current collector.

[0106] The mass ratio of oxygen vacancy-modified ZnO2 material to PEDOT:PSS solution was 0.07:1.

[0107] Example 3

[0108] This embodiment provides a modified current collector, which includes a current collector substrate and a modified coating disposed on at least one side surface of the current collector substrate;

[0109] The modified coating is obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxides;

[0110] The mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is 1:0.1, the thickness of the modified coating is 25 μm, the chemical formula of the metal oxide is TiO2, the particle size D50 of the metal oxide is 50 nm, and the current collector substrate is carbon-coated aluminum foil.

[0111] This embodiment also provides a method for preparing the above-mentioned modified current collector, the preparation method comprising the following steps:

[0112] (1) Place PSS and deionized water in a beaker with a mass ratio of 0.05:1 and stir until homogeneous with the aid of a magnetic stirrer; under stirring conditions, add monomer EDOT dropwise to the beaker, and after the addition is complete, add a certain amount of hydrochloric acid to make the pH of the mixed solution 4, thus obtaining an acidic solution;

[0113] The mass ratio of monomer EDOT to PSS is 0.6:1.

[0114] (2) Sodium persulfate was added dropwise to the acidic solution and the reaction was carried out for 20 hours. After the reaction was completed, impurity anions were adsorbed by an anion exchange resin column for purification to obtain a purified PEDOT:PSS solution.

[0115] The mass ratio of sodium persulfate to monomer EDOT is 1.5:1.

[0116] (3) TiO2 nanoparticles were placed in a tube furnace with a heating rate of 10℃ / min and sintered under a protective atmosphere of hydrogen and argon. The sintering temperature was 550℃ and the time was 1.5h. After sintering, the particles were cooled to room temperature of 25℃ with the furnace to obtain oxygen vacancy modified TiO2 material, which is denoted as TiO2-OVs material.

[0117] The volume ratio of hydrogen to argon is 20:80.

[0118] (4) The oxygen vacancy modified TiO2 material was added to the PEDOT:PSS solution and stirred at high speed to obtain a mixed solution. Then, the mixed solution was spin-coated onto one side of the carbon-coated aluminum foil using a spin coater at a spin coating speed of 3500 rpm for 40 s. The spin-coated current collector substrate was then placed in a 60°C forced-air drying oven for 8 h and then transferred to a 120°C vacuum drying oven for 10 h to obtain the modified current collector.

[0119] The mass ratio of oxygen vacancy-modified TiO2 material to PEDOT:PSS solution was 0.1:1.

[0120] Example 4

[0121] The difference between this embodiment and embodiment 1 is that in step (1), the mass ratio of PSS to deionized water is 0.01:1, and ZrO2 is replaced with Al2O3.

[0122] The remaining preparation methods and parameters are consistent with those in Example 1.

[0123] Example 5

[0124] The difference between this embodiment and embodiment 1 is that the mass ratio of PSS to deionized water in step (1) is 0.06:1, and ZrO2 is replaced by Al2O3.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Example 6

[0127] The difference between this embodiment and embodiment 1 is that the mass ratio of monomer EDOT to PSS in step (1) is 0.3:1, the mass ratio of sodium persulfate to monomer EDOT in step (2) is 1.05:1, and the mass ratio of oxygen vacancy modified ZrO2 material to PEDOT:PSS solution in step (4) is 0.08:1.

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Example 7

[0130] The difference between this embodiment and embodiment 1 is that the mass ratio of monomer EDOT to PSS in step (1) is 0.5:1, and the mass ratio of oxygen vacancy modified ZrO2 material to PEDOT:PSS solution in step (4) is 0.1:1.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Example 8

[0133] The difference between this embodiment and embodiment 1 is that the mass ratio of PSS to deionized water in step (1) is 0.005:1.

[0134] The remaining preparation methods and parameters are consistent with those in Example 1.

[0135] Example 9

[0136] The difference between this embodiment and embodiment 1 is that the mass ratio of PSS to deionized water in step (1) is 0.1:1.

[0137] The remaining preparation methods and parameters are consistent with those in Example 1.

[0138] Example 10

[0139] The difference between this embodiment and embodiment 1 is that the mass ratio of the oxygen vacancy modified ZrO2 material and the PEDOT:PSS solution in step (4) is 0.3:1.

[0140] The remaining preparation methods and parameters are consistent with those in Example 1.

[0141] Example 11

[0142] The difference between this embodiment and embodiment 1 is that the mass ratio of the oxygen vacancy modified ZrO2 material and the PEDOT:PSS solution in step (4) is 0.02:1.

[0143] The remaining preparation methods and parameters are consistent with those in Example 1.

[0144] Example 12

[0145] The difference between this embodiment and embodiment 1 is that the thickness of the modified coating is 5 μm by adjusting the spin coating process parameters in step (4).

[0146] The remaining preparation methods and parameters are consistent with those in Example 1.

[0147] Example 13

[0148] The difference between this embodiment and embodiment 1 is that the thickness of the modified coating is 30 μm by adjusting the spin coating process parameters in step (4).

[0149] The remaining preparation methods and parameters are consistent with those in Example 1.

[0150] Example 14

[0151] The difference between this embodiment and embodiment 1 is that sodium persulfate is replaced with ammonium persulfate in step (2).

[0152] The remaining preparation methods and parameters are consistent with those in Example 1.

[0153] Comparative Example 1

[0154] This comparative example provides a current collector, which is the carbon-coated aluminum foil described in Example 1, wherein the carbon-coated aluminum foil is not provided with a modified coating.

[0155] Figure 4 The cross-sectional schematic diagrams of the current collector prepared in this comparative example and the cross-sectional schematic diagram after full charge are shown. In Figure (a), the cross-sectional schematic diagram is uncharged, and in Figure (b), the cross-sectional schematic diagram is fully charged. It can be clearly seen from the figures that there is a problem of sodium dendrite growth. This indicates that the current collector of the non-negative electrode sodium battery without modified coating will lead to severe non-uniform sodium ion deposition behavior.

[0156] Comparative Example 2

[0157] The difference between this comparative example and Example 1 is that the modified coating of the carbon-coated aluminum foil is a PEDOT:PSS layer, that is, step (3) is not performed, but the obtained PEDOT:PSS solution is directly spin-coated onto the carbon-coated aluminum foil.

[0158] The remaining preparation methods and parameters are consistent with those in Example 1.

[0159] Performance testing

[0160] The current collectors prepared in the above examples and comparative examples were cut into 14mm circular pieces as negative electrode sheets, and assembled with positive electrode sheets, separators and electrolytes in a glove box under a high-purity argon atmosphere to obtain CR2032 button-type sodium battery without negative electrode.

[0161] The preparation method of the positive electrode includes: NaNi 0.33 Fe 0.33 Mn 0.34 O2 material, conductive agent Super P, and binder PVDF are ground evenly at a mass ratio of 8:1:1. Then, an appropriate amount of NMP is added to make a slurry, which is then evenly coated on the pretreated aluminum foil. The slurry is dried at 80°C for 1 hour in a forced-air drying oven, and then dried at 120°C for 12 hours in a vacuum drying oven. Finally, it is cut into 13mm circular positive electrode sheets using a cutting machine.

[0162] Separator: Whatman GF / F glass fiber with a diameter of 16mm.

[0163] Electrolyte: 0.1 mol / L sodium hexafluorophosphate / ethylene carbonate / dimethyl carbonate solution.

[0164] The sodium-ion battery without negative electrode assembled above was subjected to constant current charge-discharge mode and charge-discharge test at a current density of 0.1C. The discharge cutoff voltage was 2.0V and the charge cutoff voltage was 4.0V. The first discharge capacity and first efficiency of the sodium-ion battery without negative electrode were tested. The discharge capacity and capacity retention rate after 200 charge-discharge cycles of the sodium-ion battery without negative electrode were tested at 1C.

[0165] In addition, the deposition of sodium on the current collector was tested. The test method was as follows: using the CR2032 battery case as the base, a 10mm diameter observation port was punched in the middle of the negative electrode shell of the battery case, and gold was sprayed on the negative electrode side as the current collector for sodium deposition. The sodium deposition on the current collector was observed during the charging process.

[0166] The test results are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] analyze:

[0171] As can be seen from Examples 1-7, the sodium-free battery prepared by the modified current collector provided by the present invention exhibits good capacity performance and capacity retention. After the first charge, the sodium deposition of the negative electrode current collector was found to be uniform under an optical microscope.

[0172] As can be seen from Examples 1 and 8-9, when the mass ratio of PSS to deionized water is too low or too high, it will affect the stability of PEDOT:PSS film formation and hinder sodium deposition on the current collector, thus leading to poor cycle performance.

[0173] As can be seen from Examples 1 and 10-11, if the mass ratio of oxygen vacancy-modified ZrO2 material to PEDOT:PSS solution is too large, it is difficult to bind the induced sodium ions, affecting the deposition of sodium ions on the current collector and causing a large volume change, resulting in the battery's cycle performance being lower than expected. If the mass ratio of oxygen vacancy-modified ZrO2 material to PEDOT:PSS solution is too small, it is difficult to induce sodium ion deposition through oxygen vacancies, which will lead to poor battery cycle performance.

[0174] As can be seen from Examples 1 and 12-13, if the thickness of the modified coating is too low, it cannot completely bind the sodium ions migrating from the positive electrode, which will lead to the growth of sodium dendrites, which will affect the deposition of sodium ions to a certain extent and thus reduce the cycle performance of the battery; if the thickness of the modified coating is too high, it will increase the difficulty of sodium ion deposition in the current collector, which will lead to low energy density of the battery.

[0175] As can be seen from Examples 1 and 14, if the oxidant used is ammonium persulfate, the battery will exhibit poor capacity performance because ammonium persulfate cannot provide sodium ions to assist in film formation.

[0176] As can be seen from Example 1 and Comparative Example 1, if conventional carbon-coated aluminum foil is used without a modified coating, the battery exhibits poor electrochemical performance, and the sodium on the current collector is unevenly deposited under an optical microscope.

[0177] As can be seen from Example 1 and Comparative Example 2, if the current collector is a carbon-coated aluminum foil coated with PEDOT:PSS, the prepared battery exhibits poor capacity performance at 1C, indicating poor rate performance.

[0178] In summary, the modified current collector provided by this invention effectively suppresses the problem of uneven sodium deposition on the negative electrode current collector in a negative electrode-free sodium battery. At the same time, by using sodium persulfate as an oxidant for the PEDOT:PSS self-polymerization reaction, it can provide some sodium ions, reduce the excessive consumption of active sodium ions in the positive electrode material during the formation of the SEI film, and improve the capacity utilization of the negative electrode-free sodium metal battery.

[0179] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A modified current collector, characterized in that, The modified current collector includes a current collector substrate and a modified coating disposed on at least one side surface of the current collector substrate; The modified coating is obtained by combining PEDOT:PSS and oxygen vacancy-modified metal oxide, wherein the mass ratio of PEDOT:PSS to oxygen vacancy-modified metal oxide is 1:(0.05-0.1). The method for preparing the modified current collector includes the following steps: mixing a PEDOT:PSS solution and an oxygen vacancy-modified metal oxide to obtain a mixed solution, then coating the mixed solution onto at least one side surface of the current collector substrate, and drying it to obtain the modified current collector; the method for preparing the oxygen vacancy-modified metal oxide includes: sintering the metal oxide under a protective atmosphere composed of hydrogen and an inert gas at a temperature of 250-550℃ for 1.5-6 hours to obtain the oxygen vacancy-modified metal oxide; wherein the PSS is polystyrene sulfonic acid and / or sodium polystyrene sulfonate.

2. The modified current collector according to claim 1, characterized in that, The thickness of the modified coating is 10-25 μm.

3. The modified current collector according to claim 1, characterized in that, The chemical formula of the metal oxide is D2O r Where D is a metallic element, Q D -2r=0, Q D The valence of the metallic element D is given. The D is any one or a combination of at least two of Ti, Al, Cu, Zn, Mg, Mn, Ca, Zr, Ce, Co, Fe, Ni, V, Mo, Sr, Ta, La, Sn, or Cr.

4. The modified current collector according to claim 1, characterized in that, The particle size D50 of the metal oxide is 20-50 nm.

5. The modified current collector according to claim 1, characterized in that, The current collector substrate includes any one or a combination of at least two of the following: aluminum foil, carbon-coated aluminum foil, porous aluminum foil, foamed aluminum foil, or electroplated aluminum foil.

6. The modified current collector according to claim 5, characterized in that, The current collector substrate is electroplated aluminum foil or carbon-coated aluminum foil.

7. A method for preparing a modified current collector as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: A PEDOT:PSS solution and an oxygen vacancy-modified metal oxide are mixed to obtain a mixed solution. The mixed solution is then coated onto at least one side surface of a current collector substrate and dried to obtain the modified current collector. The preparation method of the oxygen vacancy-modified metal oxide includes: sintering the metal oxide under a protective atmosphere composed of hydrogen and an inert gas at a temperature of 250-550°C for 1.5-6 hours to obtain the oxygen vacancy-modified metal oxide. The PSS is polystyrene sulfonic acid and / or sodium polystyrene sulfonate.

8. The preparation method according to claim 7, characterized in that, The coating method includes spin coating, and the spin coating speed is 1500-3500 rpm; The spin coating time is 25-50 seconds.

9. The preparation method according to claim 7, characterized in that, The drying methods include forced-air drying and / or vacuum drying.

10. The preparation method according to claim 9, characterized in that, The temperature for blower drying is 60-80℃, and the time is 5-8 hours.

11. The preparation method according to claim 9, characterized in that, The vacuum drying temperature is 100-120℃, and the time is 10-15h.

12. The preparation method according to claim 7, characterized in that, The volume ratio of hydrogen to inert gas is (5-20):(80-95).

13. The preparation method according to claim 7, characterized in that, The heating rate of the sintering process is 1-10℃ / min.

14. The preparation method according to claim 7, characterized in that, The method for preparing the PEDOT:PSS solution includes: (a) Mix PSS and water, then add monomer EDOT and pH adjuster to obtain an acidic solution; (b) The acidic solution and the oxidant are mixed and reacted to obtain the PEDOT:PSS solution.

15. The preparation method according to claim 14, characterized in that, The mass ratio of PSS to water is (0.01-0.06):

1.

16. The preparation method according to claim 14, characterized in that, The mass ratio of the monomer EDOT to PSS is (0.3-0.65):

1.

17. The preparation method according to claim 14, characterized in that, The pH adjuster includes hydrochloric acid.

18. The preparation method according to claim 14, characterized in that, The oxidant is sodium persulfate.

19. The preparation method according to claim 14, characterized in that, The mass ratio of the oxidant to the monomer EDOT is (1.05-1.5):

1.

20. The preparation method according to claim 14, characterized in that, The reaction time is 15-20 hours.

21. The preparation method according to claim 7, characterized in that, The preparation method includes the following steps: (1) Mix PSS and deionized water at a mass ratio of (0.01-0.06):1, add monomer EDOT dropwise while stirring, and add hydrochloric acid after the addition is complete to make the pH of the mixed solution 2-5 to obtain an acidic solution; The mass ratio of monomer EDOT to PSS is (0.3-0.65):1; (2) Sodium persulfate was added dropwise to the acidic solution and the reaction was carried out for 15-20 hours. After the reaction was completed, impurity anions were adsorbed by an anion exchange resin column for purification to obtain PEDOT:PSS solution. The mass ratio of sodium persulfate to monomer EDOT is (1.05-1.5):

1. (3) Under a protective atmosphere composed of hydrogen and inert gas, the metal oxide is sintered at a temperature of 250-550℃ for 1.5-6h to obtain oxygen vacancy modified metal oxide. The volume ratio of hydrogen to inert gas is (5-20):(80-95), and the heating rate of the sintering process is 1-10℃ / min. (4) The PEDOT:PSS solution and the oxygen vacancy modified metal oxide are stirred and mixed evenly to obtain a mixed solution. Then, the mixed solution is spin-coated onto at least one side surface of the current collector substrate at a spin-coating rate of 1500-3500 rpm for 25-50 s. The spin-coated current collector substrate is then placed in a forced-air drying oven at 60-80℃ for 5-8 h and transferred to a vacuum drying oven at 100-120℃ for 10-15 h to obtain the modified current collector.

22. A sodium battery without a negative electrode, characterized in that, The negative electrode-free sodium battery includes the modified current collector as described in any one of claims 1-6.

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