An aqueous sodium-ion battery

Abstract

The present invention belongs to the technical field of sodium-ion batteries, and more specifically, relates to an aqueous sodium-ion battery. Using a polyanion-based titanium material of NaTi2(PO4)3 as the negative electrode active material and a polyanion-based Na2FePO4F as the positive electrode active material, the three-dimensional framework structure of NaTi2(PO4)3 is utilized to achieve the rapid diffusion of sodium ions in the three-dimensional channels, improve the sodium ion conduction rate, and further improve the energy density of the battery; both the positive and negative electrode active materials contain sodium ions, and the advantages of good cycle stability and stability in air of the polyanion-based electrode materials are well utilized. Moreover, when applied to an aqueous solution system, it not only achieves low cost and stable cycling, but also greatly improves the safety performance of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and more specifically, relates to an aqueous sodium-ion battery. Background Art

[0002] Every innovation in energy technology has promoted great progress in human civilization. Although technologies for converting renewable energy such as wind energy, solar energy, and hydropower into electricity, which have developed rapidly in recent years, have been rapidly developed, due to the limitations of natural conditions in the conversion process, the new energy power generation industry still faces serious resource waste. Therefore, it is urgent to develop new and efficient large-scale energy storage technologies to achieve sustainable development of new energy with green, low-carbon, efficient, and economical features.

[0003] Currently, the storage of electrical energy is mainly achieved through technologies such as physical energy storage, chemical energy storage, and electrochemical energy storage. Due to the significant advantages of electrochemical energy storage, such as high energy density, high energy conversion efficiency, and fast response rate, it has a wide range of application prospects in the field of energy storage, and among them, rechargeable batteries that are easily modularized have received more attention. Currently, the rechargeable batteries that have entered the demonstration application of energy storage mainly include lead-acid batteries, high-temperature sodium batteries, vanadium redox flow batteries, and lithium-ion batteries. However, each of these four types of batteries has its own limitations. For example, lead-acid batteries have a low energy density, high-temperature sodium batteries need to operate in a high-temperature environment, vanadium redox flow batteries have a low energy conversion efficiency, and lithium-ion batteries are limited by the shortage of lithium resources. Therefore, new energy storage battery technologies must be developed to support their sustainable development. In recent years, sodium-ion batteries, which have a working principle similar to that of lithium-ion batteries and are technically interoperable, have been favored by many scientific researchers because of their rich resources and low cost. It has been widely used in fields such as energy storage batteries, base station backup power supplies, low-speed four-wheel vehicles, and electric two-wheel vehicles, forming a complementary pattern with lithium batteries.

[0004] Most of the reported sodium-ion batteries are assembled with carbon-based materials as the negative electrode and Prussian blue or layered oxides as the positive electrode. For example, in 2019, Hu et al. designed and proposed a sodium-ion battery with a copper-doped copper-based layered oxide as the positive electrode material and amorphous carbon as the negative electrode material, which initiated a major breakthrough in sodium-ion battery technology in China and promoted the rapid development of global low-speed electric vehicles. However, carbon-based negative electrode materials have problems such as low first-cycle Coulombic efficiency and poor cycle stability. Similarly, as positive electrode materials, layered oxides and Prussian blue, although having a high specific capacity, have prominent problems such as poor cycle performance and easy environmental pollution. Summary of the Invention

[0005] Aiming at the defects of the existing technology, the purpose of the present invention is to provide an aqueous sodium-ion battery to solve the technical problems of the existing sodium-ion batteries, such as low first-cycle Coulombic efficiency, poor cycle stability, and easy environmental pollution.

[0006] To achieve the above object, the present invention provides an aqueous sodium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte. Among them, the positive electrode includes a positive electrode active material, and the positive electrode active material is Na 2 FePO 4 F; the negative electrode includes a negative electrode active material, and the negative electrode active material is NaTi 2 (PO 4 ) 3 ; the electrolyte is an aqueous solution containing sodium salts.

[0007] Preferably, the preparation method of the positive electrode active material Na 2 FePO 4 F comprises the following steps:

[0008] (1) Mix sodium fluoride and FePO 4 ·2H 2 O powders evenly by grinding to obtain a mixed salt containing an iron source, a phosphorus source and a sodium source;

[0009] (2) Mix the mixed aqueous solution of the sodium salt supplement and the carbon source with the mixed salt described in step (1) and carry out a hydrothermal reaction to obtain a Na 2 FePO 4 F precursor;

[0010] (3) Sinter the Na 2 FePO 4 F precursor described in step (2) to obtain the sodium-ion battery positive electrode material Na 2 FePO 4 F.

[0011] Further preferably, the average particle size of the FePO 4 ·2H 2 O powder in step (1) is 0.5 - 10 μm, and more preferably 2 - 6 μm; the molar ratio of the FePO 4 ·2H 2 O powder to sodium fluoride is 1:1 - 2:1.

[0012] Preferably, the preparation method of the negative electrode active material NaTi 2 (PO 4 ) 3 comprises the following steps:

[0013] S1: Add a titanium source to a buffer solution of hydrogen peroxide and ammonia water to obtain a titanium source solution;

[0014] S2: Add an organic acid, (NH 4 ) 2 HPO 4, Mix the sodium salt with the titanium source solution described in step S1 to obtain a mixed solution of titanium source, phosphorus source and sodium source;

[0015] S3: Mix the dispersant with the mixed solution obtained in step S2 and heat it to disperse to obtain a transparent product;

[0016] S4: Perform a hydrothermal reaction on the transparent product obtained in step S3 to obtain NaTi 2 (PO 4 ) 3 precursor;

[0017] S5: Sinter the NaTi 2 (PO 4 ) 3 precursor obtained in step S4 under an inert atmosphere to obtain the sodium ion negative electrode material NaTi 2 (PO 4 ) 3 .

[0018] Further preferably, the titanium source described in step S1 is tetrabutyl titanate and / or isobutyl titanate; the molar ratio of the titanium source, organic acid, (NH 4 ) 2 HPO 4 , sodium salt is 1:(1-10):(1-15):(0.1-1).

[0019] Further preferably, the molar ratio of the titanium source to the dispersant described in step S3 is 1:1 to 1:10, and the dispersant is ethylene glycol or polyethylene glycol.

[0020] Further preferably, the organic acid described in step S2 is citric acid, tartaric acid or gluconic acid; the pH of the mixed solution described in step S2 is 4-8, and more preferably 5-7.

[0021] Preferably, the positive electrode further includes a positive electrode current collector, a conductive agent and a binder. After mixing the positive electrode active material, the conductive agent, the binder and the dispersant, they are adhered to the positive electrode current collector to form the positive electrode;

[0022] The negative electrode further includes a negative electrode current collector, a conductive agent and a binder. After mixing the negative electrode active material, the conductive agent, the binder and the dispersant, they are adhered to the negative electrode current collector to form the negative electrode.

[0023] Preferably, it further includes a separator, and the separator is one of non-woven fabric, glass fiber, porous PP / PE separator, and porous PTEE membrane.

[0024] Preferably, the sodium salt is one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium sulfate, sodium nitrate, sodium phosphate, sodium carbonate, and sodium oxalate.

[0025] Preferably, the conductive agent is selected from one or more of graphite, carbon black, carbon nanotubes, and graphene;

[0026] And / or, the adhesive is selected from one or more of polytetrafluoroethylene, polyacrylic acid, sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, and styrene-butadiene latex;

[0027] And / or, the positive electrode current collector and the negative electrode current collector are each independently selected from one of the foils or meshes of titanium, copper, stainless steel, and nickel.

[0028] Preferably, the mass ratio of the positive electrode active material, the conductive agent and the binder is 1:(0.1-0.8):(0.03-0.15);

[0029] The mass ratio of the negative electrode active material, the conductive agent and the binder is 1:(0.1-1.8):(0.04-0.2).

[0030] According to another aspect of the present invention, there is provided an electronic device comprising the aqueous sodium ion battery.

[0031] In general, the above technical solution conceived by the present invention has the following advantages compared with the prior art:

[0032] Beneficial effects:

[0033] (1) The present invention provides an aqueous sodium ion battery with NaTi 2 (PO 4 ) 3 Polyanion titanium-based materials are negative electrode active materials, with polyanion Na 2 FePO 4 F is the positive electrode active material, using NaTi 2 (PO 4 ) 3 The three-dimensional skeleton structure enables rapid diffusion of sodium ions in three-dimensional channels, improves the sodium ion conduction rate, and thus increases the battery energy density; both the positive and negative active materials contain sodium ions, and make good use of the advantages of polyanion electrode materials such as good cycle stability and stability in air, and are applied to aqueous solution systems, which not only achieves low cost and cycle stability, but also greatly increases the safety performance of the battery.

[0034] (2) The novel aqueous sodium ion battery NaTi proposed by the present invention 2 (PO 4 ) 3 / Na 2 FePO 4The first reversible capacity of F can reach 130 mAh / g, and it has good safety and cycle stability. At the same time, the electrode materials prepared in the present invention are extremely rich in sources, especially the negative electrode material NaTi 2 (PO 4 ) 3 adopts an improved Pechini method, which greatly reduces the cost of phosphorus sources. In the preferred embodiment of the present invention, Na 2 SO 4 solution is used as the electrolyte, making the battery have better safety performance. Therefore, the novel sodium-ion battery prepared in the present invention has wide application value and great market prospects.

[0035] (3) The assembly process of the novel aqueous sodium-ion battery in the present invention is simple and easier to realize industrial production. This sodium-ion battery has the advantages of low cost, high specific capacity, good cycle stability, etc. Therefore, it can be popularized and applied in the field of chemical power source technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of the aqueous sodium-ion battery of the present invention;

[0037] Figure 2 is the X-ray diffraction phase analysis diagram of the sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 prepared in step (1) of Example 1;

[0038] Figure 3 is the X-ray diffraction phase analysis diagram of the sodium-ion positive electrode material Na 2 FePO 4 F prepared in step (2) of Example 1;

[0039] Figure 4 Contents S1 and S2 in it are the scanning electron microscope images of the NaTi 2 (PO 4 ) 3 negative electrode materials prepared in Comparative Example 1 and Example 1 respectively;

[0040] Figure 5 is the first charge-discharge curve diagram of the sodium-ion battery negative electrode material NaTi 2 (PO 4 ) 3 at a 2C rate;

[0041] Figure 6 is the cycle performance curve diagram of the sodium-ion battery negative electrode material NaTi 2 (PO 4 ) 3 in Example 1 and Comparative Example 1;

[0042] Figure 7 is the impedance diagram of NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F of the sodium-ion battery in Example 1 at different temperatures;

[0043] Figure 8 is the first charge-discharge curve diagram of NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F of the sodium-ion battery in Example 1 at different temperatures;

[0044] Figure 9 is the rate performance curve diagram of NaTi 2 (PO4) 3 / Na 2 FePO 4 F of the sodium-ion battery in Example 1 at different temperatures. Detailed implementation manners

[0045] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] Based on the bottleneck of the development of lithium-ion batteries due to resource shortage, the present invention discloses a novel aqueous sodium-ion battery, which can be a beneficial supplement to lithium-ion batteries. An aqueous sodium-ion battery provided by the present invention, as Figure 1 shown, includes a positive electrode, a negative electrode and an electrolyte. Among them, the positive electrode includes a positive electrode active material, and the positive electrode active material is Na 2 FePO 4 F; the negative electrode includes a negative electrode active material, and the negative electrode active material is NaTi 2 (PO 4 ) 3 ; the electrolyte is an aqueous solution containing sodium salts.

[0047] The positive electrode active material Na 2 FePO 4 F and the negative electrode active material used in the aqueous sodium-ion battery of the present invention are NaTi 2 (PO 4 ) 3, it can be prepared by conventional preparation methods of the prior art, as long as the corresponding active material can be obtained. In some preferred embodiments, the positive electrode active material Na 2 FePO 4 F is prepared by the following steps:

[0048] (1) Mix sodium fluoride and FePO 4 ·2H 2 O powder evenly by grinding to obtain a mixed salt containing an iron source, a phosphorus source and a sodium source;

[0049] (2) Mix the mixed aqueous solution of the sodium salt supplement and the carbon source with the mixed salt described in step (1), and then carry out a hydrothermal reaction to obtain a Na 2 FePO 4 F precursor;

[0050] (3) Sinter the Na 2 FePO 4 F precursor described in step (2) to obtain the positive electrode material Na 2 FePO 4 F of the sodium ion battery.

[0051] In some embodiments, the average particle size of the FePO 4 ·2H 2 O powder in step (1) is 0.5 - 10 μm, more preferably 2 - 6 μm. A suitable particle size range of the FePO 4 ·2H 2 O powder is more conducive to preparing the high specific capacity Na 2 FePO 4 F positive electrode material of the present invention. The FePO 4 ·2H 2 O powder within the above particle size range can be obtained by various preparation methods of ultrafine powders. In some embodiments, the FePO 4 ·2H 2 O powder in step (1) is a powder material prepared by using FeSO 4 ·7H 2 O and H 3 PO 4 as raw materials by the turbulent flow circulation method. The turbulent flow circulation method (or turbulent flow circulation reaction method) is to change the flow direction of the material by using a diversion device during the stirring process, so that the material is in a turbulent state. In this state, the movement directions of the substances in the mixture are all random, so the mixing or dispersion of the materials is faster and more uniform, and the reactants can quickly contact each other in a short time to quickly form a uniform microcrystalline particle product. This method is conducive to synthesizing ultrafine and high-purity powder materials. The present invention uses the turbulent flow circulation method to prepare ultrafine FePO 4 ·2H2 O powder, as an iron source and a phosphorus source for preparing the sodium ion cathode material Na 2 FePO 4 F.

[0052] In some embodiments of the present invention, a turbulent flow circulation kettle is used to prepare FePO 4 ·2H 2 O powder through turbulent flow circulation reaction. For its specific structure, please refer to the literature "Hu Yi et al., Synthesis and Characterization of Ultrafine Lithium Phosphate by Turbulent Flow Circulation Method, Journal of Chemical Industry and Engineering, 2014, (000)003, 1099 - 1103". When the turbulent flow circulation kettle operates, the stator and rotor start to rotate, and FeSO 4 ·7H 2 O and H 3 PO 4 are dissolved in a certain mass of deionized water according to a certain ratio, and an excessive amount of H 2 O 2 is added until it is detected by a 1 - 10 phenanthroline ethanol solution that Fe in the freshly prepared oxidation solution is completely changed to Fe 2+ . Then the prepared oxidation solution is pumped into the turbulent flow circulation kettle, sucked into the stator from the bottom for high - speed mixing, and by strictly controlling conditions such as the turbulent flow circulation rate of the reaction system, reaction temperature, concentration of the added NaOH, end - point pH value, aging time, water - washing temperature, drying temperature and time, etc., FePO 3+ ·xH 4 O with good surface morphology and uniform particle size distribution is synthesized. Then it is discharged from the mesh holes on the wall of the stator draft tube and circulated in turn. Finally, the obtained FePO 2 ·xH 4 O dry powder is transferred to a cabinet - type electric furnace and heat - treated at a certain temperature for a certain time to remove the crystal water to obtain micro - nano - scale iron phosphate powder. Its principle is similar to that of an impinging stream reactor (Wu Yuan, Chemical Industry Progress, 2001, 20(11), 8 - 13), forming an impinging zone in the stator, which is beneficial to promoting micro - mixing and preparing nano - or sub - micron - scale FePO 2 ·2H 4 O powder. 2

[0053] During the experimental process of the present invention for preparing the cathode active material, FePO 4 ·2H 2 O powder provides an iron source and a phosphorus source, and sodium fluoride provides a fluorine source and a sodium source. In some embodiments, the FePO 4 ·2H 2 ​The molar ratio of O powder to sodium fluoride is 1:1 to 2:1. The sodium salt supplement described in step (2) is sodium acetate, sodium oxalate or sodium citrate. The concentration of sodium ions in the mixed aqueous solution is 2 to 6 mol / L, the concentration of the carbon source is 0.1 to 0.5 g / mL, and the carbon source is sucrose and / or glucose. The molar ratio of the sodium salt supplement in the mixed aqueous solution in step (2) to sodium fluoride in the mixed salt in step S1 is 0.5 to 1.2:1.

[0054] In some embodiments, in step (2), the mixed aqueous solution of the sodium salt supplement and the carbon source is ultrasonically mixed with the mixed salt in step S1 and then hydrothermally reacted. The time of the ultrasonic mixing is 30 to 45 min. Sufficient ultrasonic mixing helps to prepare a nanoscale cathode material.

[0055] In some embodiments, the temperature of the hydrothermal reaction in step (2) is 40 to 180 °C, and the reaction time is 10 to 40 h. It is found in the experiment that the hydrothermal temperature should not be too high, otherwise it is easy to agglomerate during the sintering process; on the other hand, the hydrothermal temperature should not be too low, otherwise the fluffiness of the prepared precursor material is insufficient, and it will collapse after sintering, resulting in a smaller porosity of the cathode material, thus leading to unstable electrochemical performance. The hydrothermal reaction process of the present invention essentially belongs to the rheological phase synthesis method (the mutual transformation between gas phase and liquid phase). The rheological phase method can be used to synthesize a Na 2 FePO 4 F cathode material structure with ideal porosity and fluffiness.

[0056] In some embodiments, the sintering in step (3) is specifically: pre-sintering at 200 to 400 °C for 1 to 5 h under an inert atmosphere, and then secondary sintering at 500 to 800 °C for 4 to 12 h to obtain Na 2 FePO 4 F sodium ion cathode material. Sintering is preferably carried out in a rotary tube furnace to prevent agglomeration during the sintering process. The inert atmosphere can be N 2 、He、Ar or a mixed gas of N 2 and Ar.

[0057] In some embodiments, the preparation method of the negative electrode active material NaTi 2 (PO 4 ) 3 includes the following steps:

[0058] S1: Add a titanium source to a buffer solution of hydrogen peroxide and ammonia water to obtain a titanium source solution;

[0059] S2: Add an organic acid, (NH 4 ) 2 HPO 4, Mix the sodium salt with the titanium source solution described in step S1 to obtain a mixed solution of titanium source, phosphorus source and sodium source;

[0060] S3: Mix the dispersant with the mixed solution obtained in step S2, and heat it to disperse to obtain a transparent product;

[0061] S4: Perform a hydrothermal reaction on the transparent product obtained in step S3 to obtain NaTi 2 (PO 4 ) 3 precursor;

[0062] S5: Sinter the NaTi 2 (PO 4 ) 3 precursor obtained in step S4 in an inert atmosphere to obtain a sodium ion negative electrode material NaTi 2 (PO 4 ) 3 .

[0063] In some embodiments, the titanium source is tetrabutyl titanate and / or isobutyl titanate. The molar ratio of the titanium source, organic acid, (NH 4 ) 2 HPO 4 , and sodium salt is 1:(1-10):(1-15):(0.1-1); the molar ratio of the titanium source to the dispersant in step S3 is 1:1-1:10, and the dispersant is ethylene glycol or polyethylene glycol, more preferably ethylene glycol. In a preferred embodiment, the molar ratio of the titanium source, organic acid, (NH 4 ) 2 HPO 4 , and sodium salt is 1:(1-5):(1-5):(0.1-1).

[0064] In some embodiments, the organic acid in step S2 is citric acid, tartaric acid or gluconic acid; the pH of the mixed solution in step S2 is 4-8, more preferably 5-7. In some embodiments, 30% H 2 O 2 and 28% NH 3 ·H 2 O are fully stirred and mixed to obtain a buffer solution. The organic acid serves as a chelating agent for titanium ions in the titanium source. The chelate of titanium ions is further mixed with the dispersant and then heated in a water bath to make it uniformly dispersed, and then a hydrothermal reaction and a sintering reaction are carried out to obtain the negative electrode material NaTi 2 (PO 4 ) 3 . It is found in the experiment that the pH of the mixed solution of titanium source, phosphorus source and sodium source obtained in step S2 has an impact on the final obtained NaTi 2 (PO 4 ) 3has a great influence on the electrochemical performance. In some embodiments, (NH 4 ) 2 HPO 4 is used as the phosphorus source, and the pH of the obtained mixed solution is 6, and the obtained mixed solution is a stable colloid; in the experiment, if NH 4 H 2 PO 4 is used as the phosphorus source, the pH of the mixed solution is about 3, and a stable colloid cannot be obtained; it is confirmed by characterization that using (NH 4 )

[0065] 2 HPO 4 as the phosphorus source has a significant improvement in its corresponding electrochemical performance compared to using NH 4 H 2 PO 4 as the phosphorus source; it is also found in the experiment that when using (NH 4 ) 2 HPO 4 as the phosphorus source, if organic acids and sodium salts are mixed in, the pH of the mixed solution is too small. Even if the pH is adjusted to 6 by adding ammonia water, a stable colloidal mixed solution cannot be obtained, and ultimately the electrochemical performance of the prepared material will also be affected.

[0066] In some embodiments, the sodium salt is sodium nitrate or sodium carbonate. In order to reduce costs, in some embodiments, sodium carbonate is dissolved in dilute nitric acid solution to obtain sodium nitrate as the sodium source.

[0067] In some embodiments, in step S3, the dispersant is mixed with the mixed solution obtained in step S2, and the reaction is carried out at 60-100 °C for 1-8 h, preferably 2-5 h, to obtain a transparent product. In step S4, the transparent product obtained in step S3 is subjected to a hydrothermal reaction at 80-180 °C for 1-8 h, preferably, a hydrothermal reaction is carried out at 120-160 °C for 2-6 h to obtain a NaTi 2 (PO 4 ) 3 precursor.

[0068] In some embodiments, the inert atmosphere in step S5 is N 2 , He, Ar or a mixed gas of N 2 and Ar; the sintering is specifically: first pre-sinter at 200-400 °C for 1-5 h, and then secondarily sinter at 500-800 °C for 4-12 h.

[0069] In some embodiments, the positive electrode of the aqueous sodium-ion battery of the present invention further includes a positive electrode current collector, a conductive agent, and a binder. The positive electrode active material, the conductive agent, the binder, and the dispersant are mixed and then adhered to the positive electrode current collector to form the positive electrode; the negative electrode further includes a negative electrode current collector, a conductive agent, and a binder. The negative electrode active material, the conductive agent, the binder, and the dispersant are mixed and then adhered to the negative electrode current collector to form the negative electrode.

[0070] In some embodiments, the aqueous sodium-ion battery of the present invention further includes a separator, and the separator is one of non-woven fabric, glass fiber, porous PP / PE separator, and porous PTFE membrane.

[0071] In some embodiments, the sodium salt used in the electrolyte of the aqueous sodium-ion battery of the present invention is one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium sulfate, sodium nitrate, sodium phosphate, sodium carbonate, and sodium oxalate.

[0072] In some embodiments, the conductive agent is selected from one or more of graphite, carbon black, carbon nanotubes, and graphene; and / or, the binder is selected from one or more of polytetrafluoroethylene, polyacrylic acid, sodium alginate, polyvinyl alcohol, sodium carboxymethyl cellulose, and styrene-butadiene latex; and / or, the positive electrode current collector and the negative electrode current collector are each independently selected from one of titanium, copper, stainless steel, and nickel foils or meshes; the dispersant is a conventional dispersant such as ethanol, which is used to increase the fluidity during the grinding and mixing process.

[0073] In some embodiments, the preparation method of the aqueous sodium-ion battery of the present invention specifically comprises the following steps:

[0074] (1) Mix the prepared sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 (active material), the conductive agent, and the binder in a certain proportion in an agate mortar, grind evenly, add the dispersant ethanol, grind and adjust to a shiny thick paste, and then press and form a film with a tablet press to obtain the negative electrode film;

[0075] (2) Mix the prepared sodium-ion positive electrode material Na 2 FePO 4 F (active material), the conductive agent, and the binder in a certain proportion in an agate mortar, grind evenly, add the dispersant ethanol, grind and adjust to a shiny thick paste, and then press and form a film with a tablet press to obtain the positive electrode film;

[0076] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven to dry, and make it into a 1 cm 2 square electrode sheet to obtain the negative electrode sheet;

[0077] (4) Place the positive electrode film prepared in step (2) in a vacuum drying oven for drying, and make it into a square electrode sheet with a size of 1 cm 2 , thus obtaining the positive electrode sheet;

[0078] (5) Use the negative electrode sheet and the positive electrode sheet prepared in steps (3) and (4) as the negative electrode and the positive electrode for assembling the full cell respectively. Use a glass fiber separator as the separator and 1 M Na 2 SO 4 solution as the electrolyte to assemble a full cell, and place it in an oven for static placement, thus obtaining an aqueous sodium-ion battery. The assembled full cell is placed in an oven with a temperature ranging from 20 to 80 °C for static placement for 2 to 20 h.

[0079] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 1:(0.1 - 0.8):(0.03 - 0.15); the mass ratio of the negative electrode active material, the conductive agent, and the binder is 1:(0.1 - 1.8):(0.04 - 0.2).

[0080] The present invention also provides an electronic device, including the aqueous sodium-ion battery as described above.

[0081] The present invention designs and proposes to use a polyanion-based titanium-based material as the negative electrode active material and a polyanion-based Na 2 (PO 4 ) 3 as the positive electrode active material for the sodium-ion battery. Utilize the three-dimensional framework structure of NaTi 2 FePO 4 F to achieve the rapid diffusion of sodium ions in the three-dimensional channels, improve the sodium ion conduction rate, and further improve the battery energy density. The significant advantage of the present invention is that it uses a polyanion-based NaTi 2 (PO 4 ) 3 negative electrode material as the negative electrode, a polyanion-based Na 2 (PO 4 ) 3 as the positive electrode, and Na 2 FePO 4 F as the positive electrode, and Na 2 SO 4 as the electrolyte. It makes good use of the advantages of polyanion-based electrode materials such as good cycle stability and stability in air, and is applied to an aqueous solution system. It not only achieves low cost and stable cycling, but also greatly increases the safety performance of the battery.

[0082] The following are examples:

[0083] Example 1

[0084] A new type of aqueous sodium-ion battery and its preparation method are as follows:

[0085] (1) Weigh 0.2 g of the prepared sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 (active material), 0.03 g of conductive agent (acetylene black), and 0.01 g of binder (polytetrafluoroethylene) into an agate mortar. Add the dispersant ethanol, grind and mix to form a shiny thick paste, and then press and form a film with a tablet press to obtain the negative electrode film. Among them, the negative electrode active material NaTi 2 (PO 4 ) 3 The preparation method is as follows: Measure 40 ml of 30% H 2 O 2 and 15 ml of 28% NH 3 ·H 2 O, stir and mix well to obtain a buffer solution; Weigh 3.0 g of tetrabutyl titanate and slowly add it to the prepared buffer solution, stir well to obtain a titanium source; Weigh 4.0 g of citric acid, 2 g of (NH 4 ) 2 HPO 4 (dissolved in 10 ml of deionized water) and 0.5 g of NaNO 3 (dissolved in 10 ml of deionized water), and add them to the obtained solution in sequence, stir well to obtain a mixed solution of phosphorus source, sodium source and titanium source; Measure the pH of the mixed solution to be 6; Weigh 1.0 g of ethylene glycol and add it to the obtained solution, react in a constant temperature water bath at 90 °C for 1 h to obtain a transparent liquid; Transfer the obtained transparent solution to a hydrothermal autoclave, and place the hydrothermal autoclave in an oven at 160 °C for heating and insulation for 1 h to obtain NaTi 2 (PO 4 ) 3 precursor; Place the prepared NaTi 2 (PO 4 ) 3 precursor in a tubular furnace, pre-sinter at 400 °C for 3 h and secondary sinter at 500 °C for 8 h under an argon atmosphere to obtain the sodium-ion negative electrode active material NaTi 2 (PO 4 ) 3 .

[0086] (2) Weigh 0.6 g of the prepared sodium-ion positive electrode material Na 2 FePO 4 F (active material), 0.1 g of conductive agent (acetylene black), and 0.04 g of binder (polytetrafluoroethylene) into an agate mortar. Add the dispersant ethanol, grind and mix to form a shiny thick paste, and then press and form a film with a tablet press to obtain the positive electrode film. Among them, the positive electrode active material Na 2 FePO 4Method for preparing F, the specific steps are as follows: Put 3.6 g of ferrous phosphate powder with an average particle size of 4 μm and 1.0 g of NaF into an agate mortar and grind for 30 min to obtain a mixed salt; Weigh 1.8 g of CH 3 COONa and dissolve it in 4 ml of deionized water, add 1.0 g of sucrose, and stir until a transparent solution is obtained, that is, a transparent solution; Put the prepared mixed salt into a hydrothermal reaction kettle, and slowly drop the obtained transparent solution into the hydrothermal reaction kettle, and ultrasonically stir for 40 min until uniform. Place the reaction kettle containing the mixed solution in an oven at 80 °C and heat and keep warm for 20 h to obtain Na 2 FePO 4 F precursor; Put the prepared Na 2 FePO 4 F precursor into a rotary tube furnace, and pre-sinter at 300 °C for 3 h and secondarily sinter at 600 °C for 8 h under an argon atmosphere to obtain Na 2 FePO 4 F sodium ion positive electrode active material.

[0087] Among them, the ferrous phosphate powder with an average particle size of 4 μm is synthesized by the turbulent circulation method to obtain FePO 4 ·2H 2 O. The preparation method is as follows: Dissolve FeSO 4 ·7H 2 O and H 3 PO 4 in deionized water at a ratio of 3:1, add an excessive amount of H 2 O 2 (the addition amount is 1.5 times that of phosphoric acid) until it is detected with a 1-10 phenanthroline ethanol solution that the Fe 2+ in the freshly prepared oxidation solution is completely changed to Fe 3+ . Then pump the prepared oxidation solution into a turbulent circulation kettle, strictly control the turbulent circulation rate of the reaction system at 3000 r / min, the reaction temperature at 85 °C, the dropping 10% NaOH concentration, the end point pH value at 2.08, the aging time at 1 h, wash at 60 °C for 4 times, and dry at 140 °C for 8 h to synthesize FePO with good surface morphology and uniform particle size distribution 4 ·xH 2 O. Finally, transfer the obtained FePO 4 ·xH 2 O dry powder to a cabinet-type electric furnace, and heat-treat at 80 °C for 12 h to remove crystal water to obtain ferrous phosphate powder with an average particle size of 4 μm.

[0088] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven at 60 °C for 10 h, and make it into a square electrode sheet with a size of 1 cm 2 , that is, the negative electrode sheet is obtained;

[0089] (4) The cathode film prepared in step (2) was placed in a vacuum drying oven at 60°C for 10 h and made into a 1 cm 2 The square electrode sheet is the positive electrode sheet;

[0090] (5) The negative electrode sheet and the positive electrode sheet prepared in steps (3) and (4) are used as the negative electrode and positive electrode of the assembled full battery, respectively, with a glass fiber diaphragm as the diaphragm, 1M Na 2 SO 4 The solution is an electrolyte, which is assembled into a full battery and placed in an oven to stand, thereby obtaining an aqueous sodium ion battery.

[0091] Example 2

[0092] A novel aqueous sodium ion battery and a preparation method thereof, the specific steps are as follows:

[0093] (1) Weigh 0.1 g of the prepared sodium ion negative electrode material NaTi 2 (PO 4 ) 3 (active material), 0.02g conductive agent (acetylene black), 0.008g binder (polyvinylidene fluoride) in an agate mortar, add dispersant propanol, grind into a shiny thick slurry, and then use a tablet press to form a film to obtain a negative electrode film; negative electrode material active material NaTi 2 (PO 4 ) 3 The specific preparation method is as follows: 40 ml of 30% H 2 O 2 and 28% 15ml NH 3 ·H 2 O was stirred thoroughly to obtain a buffer solution; 3.0 g of tetrabutyl titanate was weighed and slowly added to the prepared buffer solution, and stirred thoroughly to obtain a titanium source; 4.0 g of citric acid, 1.75 g of (NH 4 ) 2 HPO 4 (dissolved in 10 ml of deionized water) and 0.3 g of Na 2 CO 3 (dissolved in 10 ml 60% HNO 3 ), and added them to the obtained solution in sequence, and stirred them thoroughly to obtain a mixed solution of phosphorus source, sodium source and titanium source; the pH of the mixed solution was measured to be 6; 1.0g of ethylene glycol was weighed and added to the obtained mixed solution, and reacted in a constant temperature water bath at 80℃ for 3h to obtain a transparent solution; the obtained transparent solution was transferred to a hydrothermal kettle, and the hydrothermal kettle was placed in an oven at 140℃ and heated for 3h to obtain the sodium ion negative electrode material NaTi 2 (PO 4 ) 3 Precursor: Prepared sodium ion negative electrode material NaTi 2(PO 4 ) 3 The precursor is placed in a tubular furnace and pre-sintered at 300 °C for 3 h and then secondarily sintered at 700 °C for 7 h under an argon atmosphere to obtain the sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 .

[0094] (2) Weigh 0.5 g of the prepared sodium-ion positive electrode material Na 2 FePO 4 F (active material), 0.08 g of conductive agent (acetylene black), and 0.02 g of binder (polyvinylidene fluoride) into an agate mortar, add the dispersant propanol, grind and mix to form a shiny thick paste, and then press and mold it with a tablet press to obtain the positive electrode film; the preparation method of the active material Na 2 FePO 4 F of the positive electrode material is specifically as follows: Grind 3.6 g of ferrous phosphate powder with an average particle size of 4 μm (the preparation method is the same as in Example 1) and 1.0 g of NaF in an agate mortar for 30 min to obtain a mixed salt; Weigh 6.0 g of sodium citrate and dissolve it in 6 ml of deionized water, add 1.0 g of sucrose, and stir until a transparent solution is obtained, that is, a transparent solution; Place the mixed salt prepared in step (2) in a hydrothermal reaction kettle, and slowly add the transparent solution obtained in step (3) to the hydrothermal reaction kettle, and ultrasonically stir until uniform. Place the reaction kettle containing the mixed solution in an oven at 100 °C and heat and keep warm for 18 h to obtain the Na 2 FePO 4 F precursor; Place the prepared Na 2 FePO 4 F precursor in a tubular furnace, and pre-sinter at 400 °C for 3 h and then secondarily sinter at 700 °C for 8 h under an argon atmosphere to obtain the Na 2 FePO 4 F sodium-ion positive electrode material;

[0095] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven at 40 °C for 12 h, and make it into a 1 cm 2 square electrode sheet to obtain the negative electrode sheet;

[0096] (4) Place the positive electrode film prepared in step (2) in a vacuum drying oven at 40 °C for 12 h, and make it into a 1 cm 2 square electrode sheet to obtain the positive electrode sheet;

[0097] (5) Use the negative electrode sheet and positive electrode sheet prepared in steps (3) and (4) as the negative electrode and positive electrode for assembling a full cell respectively, use a glass fiber separator as the separator, and 1 M of Na 2 SO 4The solution is an electrolyte, which is assembled into a full cell and placed in an oven for static setting to obtain an aqueous sodium-ion battery.

[0098] Example 3

[0099] A novel aqueous sodium-ion battery and its preparation method are as follows:

[0100] (1) Weigh 0.5 g of the prepared sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 (active material), 0.09 g of conductive agent (acetylene black), and 0.08 g of binder (styrene-butadiene rubber) in an agate mortar. Add dispersant isopropanol, grind and modulate into a shiny thick paste, and then press and form a film with a tablet press to obtain the negative electrode film; the preparation method of the negative electrode material active material NaTi 2 (PO 4 ) 3 is the same as that in Example 1;

[0101] (2) Weigh 1.2 g of the prepared sodium-ion positive electrode material Na 2 FePO 4 F (active material), 0.8 g of conductive agent (acetylene black), and 0.1 g of binder (styrene-butadiene rubber) in an agate mortar. Add dispersant isopropanol, grind and modulate into a shiny thick paste, and then press and form a film with a tablet press to obtain the positive electrode film;

[0102] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven at 70 °C for 8 h, and make it into a square electrode sheet with a size of 1 cm 2 to obtain the negative electrode sheet;

[0103] (4) Place the positive electrode film prepared in step (2) in a vacuum drying oven at 70 °C for 8 h, and make it into a square electrode sheet with a size of 1 cm 2 to obtain the positive electrode sheet;

[0104] (5) Use the negative electrode sheet and positive electrode sheet prepared in steps (3) and (4) as the negative electrode and positive electrode for assembling the full cell respectively. Use a glass fiber separator as the separator, and 1 M Na 2 SO 4 solution as the electrolyte, assemble it into a full cell, and place it in an oven for static setting to obtain an aqueous sodium-ion battery.

[0105] Example 4

[0106] A novel aqueous sodium-ion battery and its preparation method are as follows:

[0107] (1) Weigh 0.8 g of the prepared sodium-ion negative electrode material NaTi 2 (PO4 ) 3 (Active material), 0.12 g of conductive agent (acetylene black), 0.08 g of binder (styrene-butadiene rubber) in an agate mortar, add dispersant isopropanol, grind and modulate into a shiny thick paste, and then press and form with a tablet press to obtain the negative electrode film; the active material of the negative electrode material is NaTi 2 (PO 4 ) 3 The preparation method is as follows: Measure 40 ml of 30% H 2 O 2 and 15 ml of 28% NH 3 ·H 2 O and stir well to obtain a buffer solution; Weigh 3.0 g of tetrabutyl titanate and slowly add it to the buffer solution prepared above, stir well to obtain a titanium source; Weigh 4.0 g of citric acid, 2.0 g of (NH 4 ) 2 HPO 4 (dissolved in 10 ml of deionized water) and 0.5 g of Na 2 CO 3 (dissolved in 10 ml of 60% HNO 3 ), and add them to the obtained solution in sequence, stir well to obtain a mixed solution of phosphorus source, sodium source and titanium source; Measure the pH of the mixed solution to be 6; Weigh 1.0 g of polyethylene glycol (molecular weight 380 - 420) and add it to the obtained mixed solution, keep it in a constant temperature water bath at 60 °C for 4 h to obtain a transparent liquid; Transfer the obtained transparent solution to a hydrothermal reactor, and place the hydrothermal reactor in an oven at 120 °C for heating and insulation for 5 h to obtain the sodium ion negative electrode material NaTi 2 (PO 4 ) 3 precursor; Place the prepared sodium ion negative electrode material NaTi 2 (PO 4 ) 3 precursor in a tubular furnace, pre-sinter at 400 °C for 4 h and secondary sinter at 800 °C for 6 h under an argon atmosphere to obtain the sodium ion negative electrode material NaTi 2 (PO 4 ) 3 ;

[0108] (2) Weigh 2.0 g of the prepared sodium ion positive electrode material Na 2 FePO 4 F (active material), 0.5 g of conductive agent (acetylene black), 0.2 g of binder (styrene-butadiene rubber) in an agate mortar, add dispersant isopropanol, grind and modulate into a shiny thick paste, and then press and form with a tablet press to obtain the positive electrode film; the active material of the positive electrode material is Na 2 FePO 4The preparation method of F is as follows: 3.6 g of ferrous phosphate powder with an average particle size of 4 μm (prepared in the same way as in Example 1) and 1.0 g of NaF are placed in an agate mortar and ground for 30 min to obtain a mixed salt; 3.0 g of sodium oxalate is dissolved in 5 ml of deionized water, 2.0 g of glucose is added, and stirred until a transparent solution is obtained, that is, a transparent solution; the prepared mixed salt is placed in a hydrothermal reaction kettle, and the obtained transparent solution is slowly added to the hydrothermal reaction kettle, and ultrasonically stirred until uniform. The reaction kettle containing the mixed solution is placed in an oven at 180 °C and heated and kept warm for 10 h to obtain Na 2 FePO 4 F precursor; the prepared Na 2 FePO 4 F precursor is placed in a tube furnace, pre-sintered at 400 °C for 4 h and then secondarily sintered at 800 °C for 10 h under an argon atmosphere to obtain Na 2 FePO 4 F sodium ion cathode material;

[0109] (3) The negative electrode film prepared in step (1) is placed in a vacuum drying oven at 50 °C for 10 h and made into a square electrode sheet with a size of 1 cm 2 , that is, the negative electrode sheet is obtained;

[0110] (4) The positive electrode film prepared in step (2) is placed in a vacuum drying oven at 50 °C for 10 h and made into a square electrode sheet with a size of 1 cm 2 , that is, the positive electrode sheet is obtained;

[0111] (5) The negative electrode sheet and the positive electrode sheet prepared in steps (3) and (4) are used as the negative electrode and the positive electrode for assembling a full cell respectively, a glass fiber separator is used as the separator, and a 1 M Na 2 SO 4 solution is used as the electrolyte, assembled into a full cell, and placed in an oven for static settlement to obtain an aqueous sodium ion battery.

[0112] Example 5

[0113] A novel aqueous sodium ion battery and its preparation method are as follows:

[0114] (1) Weigh 0.5 g of the prepared sodium ion negative electrode material NaTi 2 (PO 4 ) 3 (active material), 0.09 g of conductive agent (acetylene black), 0.04 g of binder (polytetrafluoroethylene) in an agate mortar, add dispersant propanol, grind and modulate into a shiny thick paste, and then press and form a film with a tablet press to obtain a negative electrode film; the preparation method of the negative electrode material active substance NaTi 2 (PO 4 ) 3 is the same as that in Example 1;

[0115] (2) Weigh 1.5 g of the prepared sodium-ion cathode material Na 2 FePO 4 F (active material), 0.6 g of conductive agent (acetylene black), and 0.1 g of binder (polytetrafluoroethylene) into an agate mortar. Add the dispersant propanol, grind and mix to form a shiny thick paste, and then press and mold it with a tablet press to obtain the positive electrode film; the preparation method of the active material Na 2 FePO 4 F is the same as that in Example 1;

[0116] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven at 60 °C for 8 h, and make it into a 1 cm 2 square electrode sheet, that is, obtain the negative electrode sheet;

[0117] (4) Place the positive electrode film prepared in step (2) in a vacuum drying oven at 60 °C for 8 h, and make it into a 1 cm 2 square electrode sheet, that is, obtain the positive electrode sheet;

[0118] (5) Use the negative electrode sheet and positive electrode sheet prepared in steps (3) and (4) as the negative electrode and positive electrode for assembling the full cell respectively. Use a glass fiber separator as the separator and 1 M Na 2 SO 4 solution as the electrolyte, assemble it into a full cell, and place it in an oven for static settlement, that is, obtain an aqueous sodium-ion battery.

[0119] Example 6

[0120] A new type of aqueous sodium-ion battery and its preparation method are as follows:

[0121] (1) Weigh 0.8 g of the prepared sodium-ion anode material NaTi 2 (PO 4 ) 3 (active material), 0.1 g of conductive agent (acetylene black), and 0.05 g of binder (polyvinylidene fluoride) into an agate mortar. Add the dispersant ethanol, grind and mix to form a shiny thick paste, and then press and mold it with a tablet press to obtain the negative electrode film; the preparation method of the active material NaTi 2 (PO 4 ) 3 is the same as that in Example 1;

[0122] (2) Weigh 2.4 g of the prepared sodium-ion cathode material Na 2 FePO 4F (active material), 0.6 g of conductive agent (acetylene black), 0.1 g of binder (polyvinylidene fluoride) are placed in an agate mortar, and dispersant ethanol is added. After grinding and modulating into a shiny thick paste, it is pressed into a film by a tablet press to obtain the positive electrode film; the active material of the positive electrode material is Na 2 FePO 4 The preparation method of F is the same as that in Example 1;

[0123] (3) Place the negative electrode film prepared in step (1) in a vacuum drying oven at 70 °C for 7 h, and make it into a 1 cm 2 square electrode sheet, that is, the negative electrode sheet is obtained;

[0124] (4) Place the positive electrode film prepared in step (2) in a vacuum drying oven at 70 °C for 7 h, and make it into a 1 cm 2 square electrode sheet, that is, the positive electrode sheet is obtained;

[0125] (5) Use the negative electrode sheet and positive electrode sheet prepared in steps (3) and (4) as the negative electrode and positive electrode for assembling the full cell respectively. Using a glass fiber separator as the separator and 1 M Na 2 SO 4 solution as the electrolyte, assemble it into a full cell, and place it in an oven for static settlement to obtain an aqueous sodium-ion battery.

[0126] Comparative Example 1

[0127] In Comparative Example 1, other steps are the same as those in Example 1, except that (NH 4 ) 2 HPO 4 in Example 1 is replaced with NH 4 H 2 PO 4 to obtain a mixed solution of phosphorus source, sodium source and titanium source, and the pH of the mixed solution is measured to be 3.

[0128] Place the sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 prepared in step (1) of Example 1 on an X-ray diffractometer to obtain the X-ray diffraction phase analysis of the sodium-ion negative electrode material NaTi 2 (PO 4 ) 3 . The result is consistent with the standard card ICDD#97-020-3038, proving that the prepared product is NaTi Figure 2 . Substance. Place the sodium-ion positive electrode material Na 2 (PO 4 ) 3 prepared in step (2) of Example 1 on an X-ray diffractometer to obtain the sodium-ion positive electrode material Na 2 FePO 4 F on the X-ray diffractometer, that is,2 FePO 4 The X-ray diffraction phase analysis of F is shown in Figure 3 . It can be seen that a significantly split triple peak appears at 2θ = 34.2°, 20 == 34.5° and 20 = 34.8°, which is consistent with the 2 FePO 4 F characteristic peak, indicating that the Na 2 FePO 4 F cathode material is prepared by this method.

[0129] The prepared sodium-ion anode material was observed and processed using a scanning electron microscope, and the SEM image shown in Figure 4 was obtained. Among them, Figure 4 the contents S1 and S2 in are the scanning electron microscope images of the NaTi 2 (PO 4 ) 3 anode material prepared in Comparative Example 1 and Example 1, respectively. It can be clearly seen from the figure that the NaTi 2 (PO 4 ) 3 anode material prepared in Comparative Example 1 has no obvious micro-nano secondary structure, and the particles are relatively dispersed. The primary particle size is between 200 and 300 nm, and the particle surface is rough and the shape regularity is not high. While the NaTi 2 (PO 4 ) 3 anode material prepared in Example 1 shows a relatively obvious but irregular micro-nano secondary structure. The primary particle size is 200 - 300 nm, and most of them are spherical or elliptical particles with a smooth surface.

[0130] Using the NaTi 2 (PO 4 ) 3 prepared in Example 1 as the anode material, the electrochemical performance was tested using a silver chloride reference electrode, and the results are shown in Figure 5 and Figure 6 . Figure 5 and Figure 6 The S1 and S2 in are the charge-discharge curves of the NaTi 2 (PO 4 ) 3 anode material prepared in Comparative Example 1 and Example 1 at a 2C rate. Among them, Figure 5 is the first-cycle charge-discharge curve, Figure 6 is the cycle performance curve of the first 40 cycles. It can be clearly seen from Figure 5 that the first-cycle discharge specific capacity of the material prepared in Comparative Example 1 is 108 mAh / g, while the first-cycle discharge specific capacity of the material prepared in Example 1 is 120 mAh / g. At the same time, it can be seen from Figure 6It can be seen that the discharge specific capacity of the material prepared in Comparative Example 1 is 74.5 mAh / g after 40 cycles, and the capacity retention rate is 68%. The discharge specific capacity of the material prepared in Example 1 is 102 mAh / g after 40 cycles, and the capacity retention rate is 85.3%. Moreover, the initial discharge specific capacity of the sodium ion negative electrode material NaTi 2 (PO 4 ) 3 prepared in Example 1 can reach 120 mAh / g, which is relatively close to the theoretical specific capacity. The other conditions of Comparative Example 1 and Example 1 are the same, except that ammonium dihydrogen phosphate in Comparative Example 1 is replaced by diammonium hydrogen phosphate in Example 1. There are such great differences in the morphology and electrochemical performance of the prepared sodium titanate phosphate negative electrode material, which may be due to the stronger alkalinity of diammonium hydrogen phosphate compared with ammonium dihydrogen phosphate, which is beneficial to maintaining the neutrality of the reaction system and inhibiting the occurrence of hydrogen evolution reaction on the electrode, thus significantly improving the specific capacity and cycle stability of the sodium ion battery; or different pH environments have a certain influence on the crystal structure of the prepared NaTi 2 (PO 4 ) 3 , resulting in significant differences in the corresponding electrochemical performance.

[0131] Figure 7 are the impedance diagrams of the sodium ion battery NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F at different temperatures (S1, S2, S3, S4, and S5 correspond to 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C respectively). It can be seen that the resistance of this aqueous sodium ion battery is small and the current generated under the same voltage is large. The sodium ion battery NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F prepared in Example 1 was tested for electrochemical performance at different temperatures. Figure 8 and Figure 9 are respectively the first charge-discharge curve diagram and the rate performance curve diagram of the sodium ion battery NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F at different temperatures (S1 corresponds to 25 °C and S2 corresponds to 35 °C). The test results show that the battery has a higher initial reversible discharge specific capacity at 25 °C and 35 °C, up to 130 mAh / g. The increase in temperature may be more conducive to the insertion and extraction of sodium ions between the positive and negative electrodes, thereby improving the conduction rate of sodium ions.

[0132] In summary, the aqueous sodium-ion battery NaTi 2 (PO 4 ) 3 / Na 2 FePO 4 F prepared by the present invention has the advantages of low cost, high specific capacity, high temperature resistance, good cycle stability, etc. Therefore, the preparation method in the present invention is suitable for popularization and application in the field of chemical power sources.

[0133] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An aqueous sodium-ion battery, characterized in that It includes a positive electrode, a negative electrode and an electrolyte. Among them, the positive electrode includes a positive electrode active material, and the positive electrode active material is Na 2 FePO 4 F; the negative electrode includes a negative electrode active material, and the negative electrode active material is NaTi 2 (PO 4 ) 3 ; the electrolyte is an aqueous solution containing sodium salt; Among them, the preparation method of the negative electrode active material NaTi 2 (PO 4 ) 3 comprises the following steps: S1: Add a titanium source to a buffer solution of hydrogen peroxide and ammonia water to obtain a titanium source solution; the titanium source is tetrabutyl titanate and / or isobutyl titanate; S2: Mix an organic acid, (NH 4 ), 2 HPO 4 , a sodium salt with the titanium source solution described in step S1 to obtain a mixed solution of a titanium source, a phosphorus source and a sodium source; the molar ratio of the titanium source, the organic acid, (NH 4 ), 2 HPO 4 , the sodium salt is 1:(1-10):(1-15):(0.1-1); the organic acid is citric acid, tartaric acid or gluconic acid; the pH of the mixed solution is 5-7; S3: Mix a dispersant with the mixed solution obtained in step S2, and heat it to disperse to obtain a transparent product; the molar ratio of the titanium source to the dispersant is 1:1 to 1:10, and the dispersant is ethylene glycol or polyethylene glycol; S4: Hydrothermally react the transparent product obtained in step S3 to obtain NaTi 2 (PO 4 ) 3 precursor; the temperature of the hydrothermal reaction is 80-180 °C, and the reaction time is 1-8 h; S5: Subject the NaTi 2 (PO 4 ) 3 precursor obtained in step S4 to sintering under an inert atmosphere to obtain a sodium ion negative electrode material NaTi 2 (PO 4 ) 3 .

2. The aqueous sodium-ion battery according to claim 1, characterized in that The positive electrode active material Na 2 FePO 4 The preparation method of F comprises the following steps: (1) Mix sodium fluoride and FePO 4 ·2H 2 O powders evenly by grinding to obtain a mixed salt containing an iron source, a phosphorus source and a sodium source; (2) Mix the mixed aqueous solution of the sodium salt supplement and the carbon source with the mixed salt described in step (1), and then carry out a hydrothermal reaction to obtain a Na 2 FePO 4 F precursor; (3) Sinter the Na 2 FePO 4 F precursor to obtain the positive electrode material Na 2 FePO 4 F for sodium-ion batteries.

3. The aqueous sodium-ion battery according to claim 2, characterized in that The average particle size of the FePO 4 ·2H 2 O powder is 0.5 - 10 μm; the molar ratio of the FePO 4 ·2H 2 O powder to sodium fluoride is 1:1 - 2:

1.

4. The aqueous sodium-ion battery according to claim 1, characterized in that The positive electrode further includes a positive electrode current collector, a conductive agent, and a binder. The positive electrode active material, the conductive agent, the binder, and the dispersant are mixed and adhered to the positive electrode current collector to form the positive electrode; The negative electrode further includes a negative electrode current collector, a conductive agent, and a binder. The negative electrode active material, the conductive agent, the binder, and the dispersant are mixed and adhered to the negative electrode current collector to form the negative electrode.

5. The aqueous sodium-ion battery according to claim 1, characterized in that The sodium salt is one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium sulfate, sodium nitrate, sodium phosphate, sodium carbonate, and sodium oxalate.

6. An electronic device, characterized in that it includes the aqueous sodium-ion battery according to any one of claims 1 to 5.

Images