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

Abstract

The present invention discloses a modified current collector and a preparation method thereof, a positive electrode sheet and a negative electrode-free sodium ion battery, and relates to the technical field of sodium ion batteries. The present invention in situ grows aluminum oxide and a solid electrolyte sodium aluminum titanium phosphate on a three-dimensional aluminum metal substrate, which can provide a faster ion conduction rate, reduce the injection amount of the electrolyte, reduce the growth of dendrites, and increase the safety performance of the battery. The solid electrolyte (sodium aluminum titanium phosphate) and the artificial SEI film (sodium carbonate / sodium fluoride) are formed on the surface of the three-dimensional current collector, which is conducive to the deposition of sodium metal inside the three-dimensional substrate, and can prevent sodium dendrites from growing on the surface of the current collector to prevent puncturing the diaphragm. The solid electrolyte, artificial SEI film and negative electrode-free metal battery are used together, so the effect of reducing costs, extending cycle life, and improving battery capacity density and safety is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a modified current collector and a preparation method thereof, a positive electrode sheet, and a negative electrode-free sodium ion battery. Background Art

[0002] Sodium ion batteries are expected to become an alternative to lithium batteries due to their readily available raw materials, low price and excellent performance. The positive electrode of sodium ion batteries mainly includes layered oxide materials, Prussian blue analogue materials, polyanion materials, etc.; the negative electrode of sodium ion batteries mainly includes hard carbon and soft carbon; the electrolyte of sodium ion batteries mainly uses esters and ethers as solvents, and Na is added to the solvent. + Sodium-ion batteries are made from electrolytes containing metal salts (such as sodium fluoride salts, sodium borate salts, and perchlorates) and various additives (such as film-forming, flame-retardant, and overcharge protection). Although sodium-ion batteries offer advantages such as good low-temperature performance, low cost, high safety, and long cycle life, their energy density still lags behind that of lithium-ion batteries. Therefore, improving the energy density of sodium-ion batteries while ensuring safety is a pressing technical challenge.

[0003] Currently, the most studied anode-free sodium metal batteries experience more aggressive sodium dendrite growth at higher energy densities, posing a risk of rapid short circuits and severely hindering their application. The anode current collector, a key component in the battery, is most commonly modified by coating the aluminum foil with a conductive agent. However, this inevitably introduces a binder and increases the current collector thickness, thereby increasing the battery's internal resistance.

[0004] In summary, there is an urgent need to develop a modification process for the negative electrode current collector to improve the energy density and cycle life of sodium-ion batteries while ensuring battery safety performance.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a modified current collector and a preparation method thereof, a positive electrode sheet and a negative electrode-free sodium ion battery, aiming to improve the energy density and cycle life of the sodium ion battery while ensuring the safety performance of the battery.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a modified current collector comprising an aluminum metal three-dimensional substrate, wherein a modified layer comprising aluminum oxide, a solid electrolyte and an artificial SEI film is formed on the surface of the aluminum metal three-dimensional substrate;

[0009] Among them, the solid electrolyte includes sodium aluminum titanium phosphate;

[0010] The artificial SEI film includes sodium carbonate and sodium fluoride.

[0011] In an optional embodiment, the molar ratio of sodium aluminum titanium phosphate, sodium carbonate and sodium fluoride is 1:(0.1-0.2):(0.1-0.2);

[0012] And / or, the modified layer accounts for 5% to 20% by mass in the modified current collector;

[0013] And / or, the aluminum metal three-dimensional substrate is foamed aluminum or aluminum mesh.

[0014] In a second aspect, the present invention provides a method for preparing the modified current collector of the aforementioned embodiment, comprising: forming a modified layer containing aluminum oxide, a solid electrolyte and an artificial SEI film on an aluminum metal three-dimensional substrate.

[0015] In an optional embodiment, the method includes:

[0016] Performing a pre-oxidation treatment on the aluminum metal three-dimensional substrate to form an aluminum oxide layer on the surface;

[0017] mixing sodium hydrogen phosphate, phosphoric acid, sodium carbonate, sodium fluoride, a hydrolysis inhibitor, and water to obtain a reaction solution;

[0018] The reaction solution and the organic titanium source solution are mixed to obtain a modified solution, and the modified solution is hydrothermally reacted with an aluminum metal three-dimensional substrate having an aluminum oxide layer, followed by calcination.

[0019] In an optional embodiment, the process of preparing the reaction solution includes: mixing sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, sodium fluoride and water to obtain a first mixed solution, and mixing the first mixed solution with a hydrolysis inhibitor;

[0020] The molar ratio of sodium hydrogen phosphate, phosphoric acid, complexing agent, sodium carbonate and sodium fluoride is adjusted to (2-4): (7-14): (0.1-0.2): (0.1-0.2): (0.1-0.2); the volume ratio of the first mixed solution and the hydrolysis inhibitor is 1: (2.5-3.5);

[0021] And / or, the sodium hydrogen phosphate salt is selected from at least one of sodium dihydrogen phosphate and sodium monohydrogen phosphate;

[0022] and / or, the hydrolysis inhibitor is selected from at least one of acetic acid, hydrochloric acid, sulfuric acid and nitric acid;

[0023] And / or, the complexing agent is citric acid.

[0024] In an optional embodiment, the organic titanium source solution is obtained by mixing an organic titanium source and an alcohol solvent, the concentration of the organic titanium source solution is 5 mol / L-10 mol / L, the volume ratio of the hydrolysis inhibitor to the organic titanium source is controlled to be 1:(0.8-1.2), and the molar ratio of water to the organic titanium source when preparing the reaction solution is (0.45-0.55):1;

[0025] And / or, the organic titanium source is tetrabutyl titanate.

[0026] In an optional embodiment, the hydrothermal reaction temperature is 120° C.-200° C., and the hydrothermal reaction time is 6 h-12 h;

[0027] And / or, the volume of the modifying liquid per gram of the aluminum metal three-dimensional substrate having the aluminum oxide layer is 50 mL to 150 mL;

[0028] and / or, controlling the calcination temperature to be 500° C.-650° C. and the calcination time to be 4 h-6 h;

[0029] and / or, after calcination, annealing for 3h-6h;

[0030] And / or, calcination is performed under an inert atmosphere.

[0031] In an optional embodiment, the pre-oxidation treatment is a heat treatment in an oxygen-containing atmosphere, the treatment temperature is controlled to be 200° C.-500° C., and the treatment time is 1 hour-2 hours; the mass proportion of aluminum oxide in the pre-oxidized current collector obtained after the pre-oxidation treatment is 5%-20%;

[0032] and / or, before the pre-oxidation treatment, the aluminum metal three-dimensional substrate is subjected to surface treatment to remove a surface oxide layer;

[0033] Preferably, the surface treatment comprises first cleaning with an organic solvent and water, and then cleaning with an inorganic acid solution and water.

[0034] In a third aspect, the present invention provides a positive electrode sheet comprising the modified current collector according to any one of the aforementioned embodiments or the modified current collector prepared by the preparation method according to any one of the aforementioned embodiments;

[0035] Preferably, the modified current collector is coated with a positive electrode active material layer, and the positive electrode active material in the positive electrode active material layer is at least one selected from the group consisting of polyanion materials, layered oxides, and Prussian blue analogs.

[0036] In a fourth aspect, the present invention provides a negative electrode-free sodium ion battery, comprising the sodium ion battery positive electrode of the aforementioned embodiment.

[0037] The present invention has the following beneficial effects: the present invention in situ grows aluminum oxide and solid electrolyte sodium aluminum titanium phosphate on a three-dimensional aluminum metal substrate, which can provide a faster ion conduction rate, reduce the amount of electrolyte injection, reduce the growth of dendrites, and increase the safety performance of the battery. The solid electrolyte (sodium aluminum titanium phosphate) and artificial SEI film (sodium carbonate / sodium fluoride) are formed on the surface of the three-dimensional current collector, which is conducive to the deposition of sodium metal inside the three-dimensional substrate and can prevent sodium dendrites from growing on the surface of the current collector to prevent puncturing the diaphragm. The solid electrolyte, artificial SEI film and negative electrode metal-free battery are used together, so the cost is reduced, the cycle life is extended, and the battery capacity density and safety are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is an element distribution diagram of the modified current collector prepared in Example 1; the figure shows the characterization of P, O, Ti, Na, Al and F elements respectively;

[0040] Figure 2 This is the C element distribution diagram of the modified current collector prepared in Example 1;

[0041] Figure 3 This is a morphology diagram of the modified current collector prepared in Example 1;

[0042] Figure 4 This is the element ratio distribution diagram of the modified current collector prepared in Example 1. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0044] Professional terminology:

[0045] Dendrites: Dendritic crystals are crystals that develop in a typical multi-branched, tree-like pattern. Dendritic crystal growth is very common and can be seen in snowflake formations and frost patterns on windows.

[0046] An embodiment of the present invention provides a method for preparing a modified current collector, comprising: forming a modified layer containing aluminum oxide, a solid electrolyte, and an artificial SEI film on an aluminum metal three-dimensional substrate, the steps being as follows:

[0047] S1. Surface treatment

[0048] Before the pre-oxidation treatment, the aluminum metal three-dimensional substrate is surface treated to remove the surface oxide layer.

[0049] In some embodiments, the aluminum metal three-dimensional substrate may be commercially available foamed aluminum or aluminum mesh, which can better support the solid electrolyte and the artificial SEI film.

[0050] In some embodiments, the surface treatment includes first cleaning with an organic solvent and water to remove surface impurities; then cleaning with an inorganic acid to remove the uneven oxide layer on the surface of the aluminum metal three-dimensional substrate; and then washing with pure water multiple times to remove the surface acid. The organic solvent is not limited to any type and may be acetone, for example; the inorganic acid may be dilute hydrochloric acid, for example.

[0051] S2. Pre-oxidation treatment

[0052] The aluminum metal three-dimensional substrate is pre-oxidized to form a dense and uniform aluminum oxide layer on the surface.

[0053] In some embodiments, the pre-oxidation treatment is performed in an oxygen-containing atmosphere by heat treatment at a temperature of 200°C to 500°C for 1 to 2 hours. The surface of the three-dimensional aluminum metal substrate is uniformly oxidized, forming a dense and uniform oxide layer of Al2O3. The weight percentage of aluminum oxide in the pre-oxidized current collector obtained after the pre-oxidation treatment is 5% to 20%, such as 5%, 10%, 15%, 20%, etc.

[0054] Specifically, the pre-oxidation treatment can be performed in a tube furnace, and the oxygen-containing atmosphere can be pure O2, but is not limited thereto. The pre-oxidation treatment temperature can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, etc., and the treatment time can be 1.0h, 1.3h, 1.5h, 1.8h, 2.0h, etc.

[0055] S3. Hydrothermal reaction

[0056] Sodium hydrogen phosphate, phosphoric acid, sodium carbonate, sodium fluoride, a hydrolysis inhibitor, and water are mixed to form a reaction solution. This reaction solution is then mixed with an organic titanium source solution to form a modified solution, which is then hydrothermally reacted with a three-dimensional aluminum metal substrate with an aluminum oxide layer. During the reaction, the hydrolysis of tetrabutyl titanate allows the in-situ growth of sodium aluminum titanium phosphate on the Al2O3 seed layer. Once the water is consumed, the sodium carbonate and sodium fluoride dissolved in the water precipitate on the surface of the three-dimensional substrate to form an artificial SEI film, which is then further strengthened through calcination.

[0057] In some embodiments, the sodium hydrogen phosphate salt is selected from at least one of sodium dihydrogen phosphate and sodium monohydrogen phosphate, and any one or more of the above can be used. The hydrolysis inhibitor is selected from at least one of acetic acid, hydrochloric acid, sulfuric acid, and nitric acid, and any one or more of the above can be used to slow the strong hydrolysis of tetrabutyl titanate. The complexing agent can be citric acid. The addition of the complexing agent facilitates the regulation of the deposition process and forms a dense and uniform modified layer.

[0058] The molar ratio of each component in the modified layer of the product is further regulated by precisely controlling the amount of each raw material. The process for preparing the reaction solution includes: mixing sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, sodium fluoride, and water to obtain a first mixed solution, and mixing the first mixed solution with a hydrolysis inhibitor; adjusting the molar ratio of sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, and sodium fluoride to be (2-4):(7-14):(0.1-0.2):(0.1-0.2):(0.1-0.2), such as 2:7:0.1:0.1:0.1, 3:10:0.15:0.15:0.15, 4:14:0.2:0.2:0.2, etc.; and the volume ratio of the first mixed solution to the hydrolysis inhibitor is 1:(2.5-3.5). The dosage of each raw material is preferably within the above range, and the concentration and dosage of the organic titanium source solution are coordinated so that each component on the modified layer in the product meets the preset requirements, further improving the cycle performance and energy density of the battery.

[0059] Specifically, the volume ratio of the first mixed liquid to the hydrolysis inhibitor can be 1:2.5, 1:2.8, 1:3.0, 1:3.2, 1:3.5, etc.

[0060] Furthermore, the organic titanium source solution is obtained by mixing an organic titanium source and an alcohol solvent, and the concentration of the organic titanium source solution is 5mol / L-10mol / L (such as 5mol / L, 6mol / L, 7mol / L, 8mol / L, 9mol / L, 10mol / L, etc.), and the volume ratio of the hydrolysis inhibitor and the organic titanium source is controlled to be 1: (0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc. Within this ratio range, the hydrolysis of the organic titanium source can be better regulated. The organic titanium source can be tetrabutyl titanate, but is not limited thereto. When preparing the reaction solution, the molar ratio of water to the organic titanium source is (0.45-0.55):1, such as 0.45:1, 0.48:1, 0.50:1, 0.53:1, 0.55:1, etc.

[0061] Furthermore, the volume of the modification liquid per gram of aluminum metal 3D substrate with an aluminum oxide layer is 50mL-150mL, the hydrothermal reaction temperature is controlled at 120°C-200°C, and the hydrothermal reaction time is controlled at 6h-12h. By adjusting the ratio of the aluminum metal 3D substrate with an aluminum oxide layer to the modification liquid, and adjusting the hydrothermal temperature and time, the proportion of the modified layer in the overall modified current collector can be further adjusted to improve the battery's cycling performance and safety.

[0062] Specifically, the volume of the modification liquid corresponding to each gram of the aluminum metal three-dimensional substrate having an aluminum oxide layer can be 50 mL, 80 mL, 100 mL, 120 mL, 150 mL, etc.; the hydrothermal reaction can be carried out in a hydrothermal reactor, the hydrothermal reaction temperature can be 120°C, 150°C, 180°C, 200°C, etc., and the hydrothermal time can be 6h, 8h, 10h, 12h, etc.

[0063] S4. Calcination

[0064] After the hydrothermal reaction is completed, the aluminum metal three-dimensional precursor is taken out and transferred to a tubular furnace for calcination. During the hydrothermal reaction, sodium carbonate and sodium fluoride will precipitate on the surface of the three-dimensional substrate to form an artificial SEI film. After calcination, the artificial SEI film can be more firmly bonded.

[0065] In some embodiments, calcination is performed under an inert atmosphere at a temperature of 500°C to 650°C for 4 to 6 hours. After calcination, the battery is annealed for 3 to 6 hours. By manipulating the calcination conditions, the modified layer formed on the aluminum metal three-dimensional substrate is more firmly bonded, further reducing dendrite growth and improving battery safety.

[0066] Specifically, the type of inert atmosphere is not limited and may be nitrogen, argon, etc.; the calcination temperature may be 500°C, 530°C, 550°C, 580°C, 600°C, 630°C, 650°C, etc.; the calcination time may be 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, etc. Annealing refers to stepwise cooling after the calcination time meets the requirements, such as a 4-hour cooling stage sequentially undergoing 600°C, 500°C, 400°C, 300°C, 200°C, 100°C, and room temperature. Specifically, the annealing time may be 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0067] In summary, the preparation method of the modified current collector provided by the embodiment of the present invention first evenly distributes Al2O3 seeds on the surface of the aluminum metal three-dimensional substrate, and the subsequent hydrothermal method can in situ grow sodium aluminum titanium phosphate on the basis of the aluminum source Al2O3 seeds; the solid electrolyte sodium aluminum titanium phosphate is in situ grown on the current collector to provide a faster ion conduction rate, thereby reducing the injection volume of the electrolyte, reducing the growth of dendrites, and increasing the safety performance of the battery. Due to the hydrolysis of tetrabutyl titanate, the sodium carbonate and sodium fluoride dissolved in water will precipitate on the surface of the three-dimensional substrate to form an artificial SEI film, which is further strengthened after subsequent calcination. No binder is used in the hydrothermal in situ growth process of sodium aluminum titanium phosphate, which is conducive to the uniform deposition of sodium ions.

[0068] An embodiment of the present invention provides a modified current collector, comprising an aluminum metal three-dimensional substrate, on the surface of which a modified layer containing aluminum oxide, a solid electrolyte, and an artificial SEI film is formed; wherein the solid electrolyte comprises sodium aluminum titanium phosphate; and the artificial SEI film comprises sodium carbonate and sodium fluoride.

[0069] It should be noted that the embodiments of the present invention construct a solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide) @ artificial SEI film (sodium carbonate / sodium fluoride) @ aluminum metal three-dimensional current collector. Since the solid electrolyte sodium aluminum titanium phosphate and aluminum oxide are in situ grown on the current collector, it can provide a faster ion conduction rate, thereby reducing the amount of electrolyte injection, reducing the growth of dendrites, and improving the safety performance of the battery. The formation of the solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide) and artificial SEI film (sodium carbonate / sodium fluoride) on the surface of the three-dimensional current collector is conducive to the deposition of sodium metal inside the three-dimensional substrate, which can prevent sodium dendrites from growing on the surface of the current collector and thus prevent puncturing the diaphragm.

[0070] Furthermore, the molar ratio of sodium aluminum titanium phosphate, sodium carbonate, and sodium fluoride is 1:(0.1-0.2):(0.1-0.2), such as 1:0.10:0.10, 1:0.13:0.13, 1:0.15:0.15, 1:0.18:0.18, 1:0.20:0.20, etc.; the mass proportion of aluminum oxide in the pre-oxidized current collector is 5%-20%, such as 5%, 10%, 15%, 20%, etc.; the mass proportion of the modified layer in the modified current collector is 5%-20%, such as 5%, 10%, 15%, 20%, etc. By adjusting the amount of each component in the modified layer and the mass proportion of the modified layer, the solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide) and the artificial SEI film (sodium carbonate / sodium fluoride) can be better utilized to prevent sodium dendrites from growing on the surface of the current collector, thereby preventing the separator from puncturing and improving the safety performance of the battery.

[0071] An embodiment of the present invention provides a positive electrode sheet, comprising the modified current collector provided by the embodiment of the present invention. The electrochemical performance of the positive electrode can be significantly improved by improving the modified current collector.

[0072] In some embodiments, the modified current collector is coated with a positive electrode active material layer, and the positive electrode active material in the positive electrode active material layer is selected from at least one of a polyanion material, a layered oxide, and a Prussian blue analogue. The positive electrode active material can be any one or more of the above. The method for forming the positive electrode active layer can refer to the existing technology.

[0073] An embodiment of the present invention also provides a negative electrode-free sodium ion battery, comprising the above-mentioned sodium ion battery positive electrode. By using the modified current collector provided by the embodiment of the present invention as the positive electrode current collector, sodium dendrites can be prevented from growing on the surface of the current collector to prevent puncturing the diaphragm, thereby improving the safety performance of the battery.

[0074] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0075] Example 1

[0076] This embodiment provides a method for preparing a modified current collector, and the steps are as follows:

[0077] (1) Surface treatment

[0078] Commercially available foamed aluminum was used as the aluminum metal three-dimensional substrate, with the length, width, and height of the foamed aluminum being 100 mm, 50 mm, and 0.2 mm, respectively, and a porosity of 80%.

[0079] The aluminum metal three-dimensional substrate was cleaned with acetone and pure water in turn to remove surface impurities, and then the original uneven oxide layer on the surface of the aluminum metal three-dimensional substrate was removed by cleaning with dilute hydrochloric acid with a concentration of 0.5 mol / L. Finally, it was washed with pure water several times and dried for use.

[0080] (2) Pre-oxidation treatment

[0081] The aluminum metal three-dimensional substrate treated in step (1) was placed in a tubular furnace, introduced with pure O2, and pre-oxidized at a temperature of 350°C for 1.5 hours. The surface of the aluminum metal three-dimensional substrate was uniformly oxidized in a pure O2 environment, and a dense and uniform oxide layer Al2O3 was generated on the surface.

[0082] (3) Hydrothermal reaction

[0083] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred uniformly to obtain a solution A with a concentration of 5 mol / L.

[0084] A mixed aqueous solution of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was prepared to obtain solution B, wherein the molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was 2:7:0.1:0.1:0.1. The amount of water was adjusted so that the tetrabutyl titanate in the first mixed solution was completely reacted and the water was completely consumed (the molar ratio of water to tetrabutyl titanate was 0.5:1).

[0085] Solution B and acetic acid were mixed in a volume ratio of 1:3 to obtain solution C. In the experiment, the volume ratio of acetic acid and tetrabutyl titanate was maintained at 1:1.

[0086] 3 g of pre-oxidized aluminum metal three-dimensional substrate was placed vertically into the hydrothermal reactor, and solution C and solution A were evenly mixed (the volume of the modified liquid obtained after mixing solution C and solution A was 300 mL), and then immediately poured into the reactor. The hydrothermal reaction temperature was 150°C and the hydrothermal reaction time was 10 h.

[0087] (4) Calcination

[0088] After the hydrothermal reaction, the aluminum metal 3D precursor was removed and transferred to a tube furnace. It was calcined at 600°C under an inert atmosphere (nitrogen) for 5 hours and annealed for 4 hours. After roller pressing, a solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide)@artificial SEI membrane (sodium carbonate / sodium fluoride)@aluminum metal 3D current collector was obtained.

[0089] from Figure 1 and Figure 2 It can be seen that the element distribution of P, O, Ti, Na, Al, F and C, it can be seen that sodium aluminum titanium phosphorus, sodium carbonate and sodium fluoride are present. Figure 4 It can be seen that the total content and approximate proportions show that each element is evenly distributed. Figure 3 It is a morphology picture, and it can be seen that the surface of the modified current collector is flat and evenly distributed.

[0090] Example 2

[0091] This embodiment provides a method for preparing a modified current collector, and the steps are as follows:

[0092] (1) Surface treatment

[0093] Same as Example 1.

[0094] (2) Pre-oxidation treatment

[0095] The aluminum metal three-dimensional substrate treated in step (1) was placed in a tube furnace, pure O2 was introduced, the temperature was 200°C, and pre-oxidation was performed for 2.0 hours. The surface of the aluminum metal three-dimensional substrate was uniformly oxidized in a pure O2 environment, and a dense and uniform oxide layer Al2O3 was generated on the surface.

[0096] (3) Hydrothermal reaction

[0097] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred uniformly to obtain a solution A with a concentration of 10 mol / L.

[0098] A mixed aqueous solution of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was prepared to obtain solution B, wherein the molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was 4:14:0.2:0.2:0.2. The amount of water was adjusted so that the tetrabutyl titanate in the first mixed solution was completely reacted and the water was completely consumed.

[0099] Solution B and acetic acid were mixed in a volume ratio of 1:2.5 to obtain solution C. In the experiment, the volume ratio of acetic acid and tetrabutyl titanate was maintained at 1:0.8.

[0100] 3 g of pre-oxidized aluminum metal three-dimensional substrate was placed vertically into the hydrothermal reactor, and solution C and solution A were evenly mixed (the volume of the modified liquid obtained after mixing solution C and solution A was 300 mL), and then immediately poured into the reactor. The hydrothermal reaction temperature was 120°C and the hydrothermal reaction time was 12 h.

[0101] (4) Calcination

[0102] After the hydrothermal reaction, the aluminum metal 3D precursor was removed and transferred to a tube furnace. It was calcined at 500°C for 6 hours under an inert atmosphere (nitrogen) and annealed for 6 hours. After roller pressing, a solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide)@artificial SEI membrane (sodium carbonate / sodium fluoride)@aluminum metal 3D current collector was obtained.

[0103] Example 3

[0104] This embodiment provides a method for preparing a modified current collector, and the steps are as follows:

[0105] (1) Surface treatment

[0106] Same as Example 1.

[0107] (2) Pre-oxidation treatment

[0108] The aluminum metal three-dimensional substrate treated in step (1) was placed in a tubular furnace, introduced with pure O2, and pre-oxidized at a temperature of 500°C for 1.0 h. The surface of the aluminum metal three-dimensional substrate was uniformly oxidized in a pure O2 environment, and a dense and uniform oxide layer Al2O3 was generated on the surface.

[0109] (3) Hydrothermal reaction

[0110] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred uniformly to obtain a solution A with a concentration of 7.5 mol / L.

[0111] A mixed aqueous solution of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was prepared to obtain solution B, wherein the molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride was 3:10.5:0.15:0.15:0.15. The amount of water was adjusted so that the tetrabutyl titanate in the first mixed solution was completely reacted and the water was completely consumed.

[0112] Solution B and acetic acid were mixed in a volume ratio of 1:3.5 to obtain solution C. In the experiment, the volume ratio of acetic acid and tetrabutyl titanate was maintained at 1:1.2.

[0113] 3 g of pre-oxidized aluminum metal three-dimensional substrate was placed vertically into the hydrothermal reactor, and solution C and solution A were evenly mixed (the volume of the modified liquid obtained after mixing solution C and solution A was 300 mL), and then immediately poured into the reactor. The hydrothermal reaction temperature was 200 ° C and the hydrothermal reaction time was 6 h.

[0114] (4) Calcination

[0115] After the hydrothermal reaction, the aluminum metal 3D precursor was removed and transferred to a tube furnace. It was calcined at 650°C under an inert atmosphere (nitrogen) for 4 hours and annealed for 3 hours. After roller pressing, the resulting solid electrolyte (sodium aluminum titanium phosphate / aluminum oxide)@artificial SEI membrane (sodium carbonate / sodium fluoride)@aluminum metal 3D current collector was obtained.

[0116] Example 4

[0117] The only difference from Example 1 is that the amounts of the raw materials used in the hydrothermal reaction in step (3) are different. The molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride is 2:7:0.5:0.5:0.5. By adjusting the amount of water, the tetrabutyl titanate in the first mixed solution is completely reacted and the water is completely consumed. Solution C is obtained by mixing solution B and acetic acid in a volume ratio of 1:3. The volume ratio of acetic acid and tetrabutyl titanate in the experiment is maintained at 1:1.

[0118] Example 5

[0119] The only difference from Example 1 is that the amounts of the raw materials used in the hydrothermal reaction in step (3) are different. The molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride is 1:3:0.1:0.1:0.1. By adjusting the amount of water, the tetrabutyl titanate in the first mixed solution is completely reacted and the water is completely consumed. Solution C is obtained by mixing solution B and acetic acid in a volume ratio of 1:3. The volume ratio of acetic acid to tetrabutyl titanate in the experiment is maintained at 1:1.

[0120] Example 6

[0121] The only difference from Example 1 is that the amounts of the raw materials used in the hydrothermal reaction in step (3) are different. The molar ratio of sodium dihydrogen phosphate, phosphoric acid, citric acid, sodium carbonate, and sodium fluoride is 2:7:0.1:0.1:0.1. By adjusting the amount of water, the tetrabutyl titanate in the first mixed solution is not completely reacted, and the water is not completely consumed. Solution C is obtained by mixing solution B and acetic acid in a volume ratio of 1:3. The volume ratio of acetic acid to tetrabutyl titanate in the experiment is maintained at 1:1.

[0122] Comparative Example 1

[0123] This comparative example provides unmodified aluminum foil as the current collector.

[0124] Comparative Example 2

[0125] This comparative example provides unmodified foamed aluminum as a current collector.

[0126] Comparative Example 3

[0127] The only difference from Example 1 is that sodium carbonate and sodium fluoride are not added in step (3), and the amounts of other raw materials remain unchanged.

[0128] Test Example 1

[0129] The energy density and cycle performance of the sodium ion batteries prepared in the test examples and comparative examples are shown in Table 1.

[0130] Test method: The modified current collector prepared in the embodiment or comparative example is used as the positive current collector, and a positive active material layer is coated. The positive active material in the positive active material layer is a layered oxide (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) to obtain the positive electrode; aluminum foil is used as the negative electrode; the separator is a commercial dry PP base film, injected with ester electrolyte, and a soft-pack battery cell is made by lamination process. The composition of the ester electrolyte is as follows: the electrolyte is 1M sodium salt (NaPF 6) +Solvent (diethylene glycol dimethyl ether).

[0131] Table 1 Electrochemical properties of sodium ion batteries provided in Examples and Comparative Examples

[0132]

[0133]

[0134] As can be seen from Table 1, the sodium ion battery prepared in the embodiment of the present invention has higher energy density and better cycle performance.

[0135] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A modified current collector, characterized in that: As a cathode current collector for a sodium ion battery without an anode, the present invention comprises an aluminum metal three-dimensional substrate, and a modified layer containing aluminum oxide, a solid electrolyte and an artificial SEI film is formed on the surface of the aluminum metal three-dimensional substrate; Wherein, the solid electrolyte comprises sodium aluminum titanium phosphate; The artificial SEI film includes sodium carbonate and sodium fluoride; The preparation method of the modified current collector comprises: performing a pre-oxidation treatment on an aluminum metal three-dimensional substrate to form an aluminum oxide layer on the surface; mixing sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, sodium fluoride, a hydrolysis inhibitor and water to obtain a reaction solution; Mixing the reaction solution with an organic titanium source solution to obtain a modified solution, hydrothermally reacting the modified solution with an aluminum metal three-dimensional substrate having an aluminum oxide layer, and then calcining; The hydrothermal reaction temperature is 120°C-200°C, and the hydrothermal reaction time is 6h-12h; The calcination temperature is controlled at 500°C-650°C and the calcination time is 4h-6h.

2. The modified current collector according to claim 1, characterized in that The molar ratio of sodium aluminum titanium phosphate, sodium carbonate and sodium fluoride is 1: (0.1-0.2): (0.1-0.2); And / or, the mass proportion of the modified layer in the modified current collector is 5%-20%; And / or, the aluminum metal three-dimensional substrate is foamed aluminum or aluminum mesh.

3. A method for preparing the modified current collector according to claim 1 or 2, characterized in that: include: Performing a pre-oxidation treatment on the aluminum metal three-dimensional substrate to form an aluminum oxide layer on the surface; mixing sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, sodium fluoride, a hydrolysis inhibitor and water to obtain a reaction solution; Mixing the reaction solution with an organic titanium source solution to obtain a modified solution, hydrothermally reacting the modified solution with an aluminum metal three-dimensional substrate having an aluminum oxide layer, and then calcining; The hydrothermal reaction temperature is 120°C-200°C, and the hydrothermal reaction time is 6h-12h; The calcination temperature is controlled at 500°C-650°C and the calcination time is 4h-6h.

4. The preparation method according to claim 3, characterized in that The process of preparing the reaction solution includes: mixing sodium hydrogen phosphate, phosphoric acid, a complexing agent, sodium carbonate, sodium fluoride and water to obtain a first mixed solution, and mixing the first mixed solution with the hydrolysis inhibitor; The molar ratio of sodium hydrogen phosphate, phosphoric acid, complexing agent, sodium carbonate and sodium fluoride is regulated to be (2-4): (7-14): (0.1-0.2): (0.1-0.2): (0.1-0.2); the volume ratio of the first mixed solution to the hydrolysis inhibitor is 1: (2.5-3.5); And / or, the sodium hydrogen phosphate salt is selected from at least one of sodium dihydrogen phosphate and sodium monohydrogen phosphate; and / or, the hydrolysis inhibitor is selected from at least one of acetic acid, hydrochloric acid, sulfuric acid and nitric acid; And / or, the complexing agent is citric acid.

5. The preparation method according to claim 3 or 4, characterized in that: The organic titanium source solution is obtained by mixing an organic titanium source and an alcohol solvent. The concentration of the organic titanium source solution is 5 mol / L-10 mol / L. The volume ratio of the hydrolysis inhibitor to the organic titanium source is controlled to be 1:(0.8-1.2). When preparing the reaction solution, the molar ratio of water to the organic titanium source is (0.45-0.55):

1. And / or, the organic titanium source is tetrabutyl titanate.

6. The preparation method according to claim 3, characterized in that: The volume of the modification liquid corresponding to each gram of the aluminum metal three-dimensional substrate having an aluminum oxide layer is 50 mL to 150 mL; and / or, after calcination, annealing for 3h-6h; And / or, calcination is performed under an inert atmosphere.

7. The preparation method according to claim 3, characterized in that: The pre-oxidation treatment is a heat treatment in an oxygen-containing atmosphere, with the treatment temperature controlled at 200° C. to 500° C. and the treatment time being 1 hour to 2 hours; the mass proportion of aluminum oxide in the pre-oxidized current collector obtained after the pre-oxidation treatment is 5% to 20%; And / or, before the pre-oxidation treatment, the aluminum metal three-dimensional substrate is subjected to surface treatment to remove a surface oxide layer.

8. The preparation method according to claim 7, characterized in that: The surface treatment includes first cleaning with an organic solvent and water, and then cleaning with an inorganic acid solution and water.

9. A positive electrode sheet, characterized in that: The modified current collector comprises the modified current collector according to any one of claims 1 to 2 or the modified current collector prepared by the preparation method according to any one of claims 3 to 8.

10. The positive electrode sheet according to claim 9, characterized in that: The modified current collector is coated with a positive electrode active material layer, wherein the positive electrode active material in the positive electrode active material layer is selected from at least one of a polyanion material, a layered oxide and a Prussian blue analogue.

11. A negative electrode-free sodium ion battery, characterized in that: Including the positive electrode sheet according to claim 9 or 10.

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