Preparation method and application of tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material

Abstract

A method for preparing and applying a tantalum, niobium, magnesium, cerium, lanthanum high-entropy alloy / niobium titanate two-phase heterogeneous material, belonging to the field of secondary batteries, comprises the following steps: preparing a compacted titanium niobate electrode using a conventional high-temperature solid-phase method and a tablet pressing and sintering method; and electrolyzing the tantalum, niobium, magnesium, cerium, lanthanum high-entropy alloy / niobium titanate two-phase heterogeneous material using graphite as the anode, a tabletted niobium titanate material as the cathode, and a chloride molten salt as the electrolyte in a tube furnace. This method is the first to prepare a tantalum, niobium, magnesium, cerium, lanthanum high-entropy alloy / niobium titanate two-phase heterogeneous material. The introduced metal alloy improves the bulk electronic conductivity of the niobium titanate material, and the band structure rearrangement and electron delocalization at the interface between the two phases enhance the adsorption of solvated lithium on the material surface, improves surface / near-surface charge exchange reactions, and reduces the diffusion barrier at the lithium ion interface, significantly improving the initial coulombic efficiency and low-temperature cycling stability of the composite niobium titanate material as a negative electrode material for lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a preparation method and low-temperature application of a tantalum-niobium-magnesium-lanthanum-cerium high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material. Background Art

[0002] In the electronic information age, electric-powered devices can be seen everywhere, and the demand for energy storage is growing. Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, aerospace, energy storage power stations and other fields due to their high energy density, good cycle stability, clean and pollution-free. However, with the expansion of the lithium-ion battery market, its disadvantage of poor low-temperature performance has become more prominent. The traditional graphite negative electrode has a low lithium insertion potential (0.1V vs.Li + / Li) is very prone to "lithium dendrite" growth at low temperatures, resulting in the loss of active lithium, which leads to rapid battery capacity decay and poor fast-charging performance. Therefore, there is an urgent need to explore lithium-ion battery anode materials with good safety, low polarization voltage, high discharge capacity and fast-charging characteristics in low-temperature environments to promote the development of electrochemical energy storage technology in cold regions.

[0003] Since Goodenough’s pioneering work in 2011, niobium titanium oxide (TiNb2O7) has been widely used due to its theoretical capacity close to that of graphite (387 mAh g -1 ), good structural stability and other unique advantages, it has become a research hotspot for high-power negative electrode materials for low-temperature lithium-ion batteries. TiNb2O7 is composed of Nb(Ti)O6 octahedra connected by sharing edges or vertices. Among them, Ti and Nb atoms jointly occupy the 2a and 4i sites in the octahedral gap, forming an open lithium ion transmission channel, and lithium ions are relatively easy to embed / extract, without causing obvious volume expansion, showing excellent fast charging characteristics. At the same time, TiNb2O7 has a high working potential (1.65Vvs.Li + / Li), which can effectively prevent the formation of solid electrolyte interface layer and lithium dendrites, thus having better safety. However, solid-phase synthesized niobium titanium oxide materials have problems such as small specific surface area, poor electronic conductivity, long lithium ion diffusion distance, slow desolvation process at the electrode-electrolyte interface under low temperature conditions, and high energy barrier for bulk lithium ion diffusion, which limit the material's fast charging performance under low temperature conditions. Summary of the Invention

[0004] Based on the above background technology, the present invention provides a preparation method and low-temperature application of a tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material, aiming to improve the electronic / ionic conductivity and desolvation ability of the niobium-titanium oxide material at low temperatures, and improve its electrochemical properties such as the first coulombic efficiency, cycle stability and high-rate performance in low-temperature lithium-ion batteries.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material comprises the following steps:

[0007] Step 1: Prepare a compacted niobium titanium oxide electrode using a conventional high-temperature solid phase method and tablet pressing and sintering method;

[0008] TiO2 and Nb2O5 in a 1:1 molar ratio are weighed and dispersed in anhydrous ethanol and thoroughly mixed. The mixed sample is then transferred to a forced air drying oven for drying and ground to obtain a powder material precursor A. Precursor A is then pressed into a sheet under a certain pressure, referred to as embryo B. Embryo B is then transferred to a tube furnace and calcined at 1100°C-1400°C. After cooling to room temperature, a white, compacted sheet-like niobium titanium oxide electrode is obtained.

[0009] The thorough mixing method is mechanical stirring, magnetic stirring or ball milling, the stirring or ball milling time is 4-10 hours, and the ball milling speed is 300-500 r / min;

[0010] The pressure for preparing the embryo B is 120-180 MPa, and the thickness of the pressed sheet is 2-5 mm; preferably, the embryo B is a Φ9 mm round sheet.

[0011] The calcination time in a tube furnace is 1-30h;

[0012] Step 2: In situ formation of a tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material on the surface of the niobium-titanium oxide material by molten salt electrolysis;

[0013] Using the flake niobium titanium oxide prepared in step 1 as a cathode, graphite as an anode, and a chloride molten salt as a molten salt electrolyte, applying voltage to the two electrodes at a certain temperature to perform molten salt electrolysis, and after the electrolysis is completed, taking out the cathode product obtained after electrolysis, collecting it by centrifugation, drying it at a low temperature, and grinding it to obtain a tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material;

[0014] The chloride molten salt includes NaCl, KCl, TaCl5, NbCl5, MgCl2, CeCl3 and LaCl3. The masses of NaCl and KCl in the chloride molten salt are equal, and the total mass of the two components accounts for 70%-84% of the chloride molten salt. The masses of the five components TaCl5, NbCl5, MgCl2, CeCl3 and LaCl3 are equal, and the total mass of the five components accounts for 16%-30% of the chloride molten salt.

[0015] The temperature of molten salt electrolysis is 700-1000°C; the electrolysis time is 2-8 hours; and the constant voltage applied during the electrolysis process is 0.5-2.4V.

[0016] The protective atmosphere of the molten salt electrolysis furnace is a mixture of hydrogen and argon (the volume ratio of argon to hydrogen is 95%:5%), argon, nitrogen or one of the following;

[0017] The centrifugal speed is 5000-9000r / min, and the centrifugal time is 3-6 minutes each time;

[0018] An application of a tantalum, niobium, magnesium, cerium, lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material prepared by the preparation method, wherein the tantalum, niobium, magnesium, cerium, lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material is used as a negative electrode material in a low-temperature lithium-ion battery.

[0019] The tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material is dispersed in a solvent with a conductive agent and a binder in a certain mass ratio as the negative electrode active material to obtain a lithium-ion battery negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode collector, dried, rolled, and punched to obtain a negative electrode sheet, and then a button battery is assembled.

[0020] The binder is polyvinylidene fluoride (PVDF) or an aqueous dispersion of acrylonitrile multi-polymer (LA133), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP) or ultrapure water.

[0021] The mass ratio of the negative electrode active material: the conductive agent: the binder is 85%: 7.5%: 7.5%.

[0022] The operating temperature range of the low-temperature lithium-ion battery is -40°C to 60°C.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The present invention is the first to use chloride molten salt as an electrolyte to electrolyze in a tubular furnace to produce a tantalum, niobium, magnesium, cerium, and lanthanum high-entropy alloy, resulting in a tantalum, niobium, magnesium, cerium, and lanthanum high-entropy alloy / niobium titanium oxide two-phase heterogeneous material. The introduced metal alloy can improve the bulk electronic conductivity of the niobium titanium oxide material, and the band structure rearrangement and electron delocalization at the interface between the two phases enhance the adsorption performance of the material surface for solvated lithium, improve the surface / near-surface charge exchange reaction, and reduce the diffusion barrier at the lithium ion interface, so that the material still has a high lithium ion diffusion coefficient under low temperature conditions, greatly improving the initial coulombic efficiency and low-temperature cycle stability of the composite niobium titanium oxide material as a negative electrode material for lithium-ion batteries.

[0025] 2) The preparation method of the present invention is simple, has a coherent process, is low in cost, has low requirements on equipment, and is suitable for large-scale production.

[0026] 3) The present invention uses a combination of TaCl5, NbCl5, MgCl2, CeCl3 and LaCl3 as an electrolyte to in situ form a tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy on the surface of niobium-titanium oxide. The composition of the alloy prepared by the present invention has a stable phase diagram, and during the synthesis process, it can be ensured that no other forms of compounds can exist stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the synthesis of the tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium-oxide two-phase heterogeneous material synthesized in Example 1;

[0028] Figure 2 This is a comparison chart of the EIS at -40°C of the tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material and the pure-phase niobium-titanium oxide material synthesized in Example 1;

[0029] Figure 3 This is a comparison chart of the cyclic stability of the tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material and the pure-phase niobium-titanium oxide material at -40°C synthesized in Example 1. DETAILED DESCRIPTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1:

[0032] A method for preparing a tantalum-niobium-magnesium-lanthanum-cerium high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material comprises the following steps:

[0033] Step 1: Prepare a compacted niobium titanium oxide electrode using a traditional high-temperature solid-phase method and tablet pressing and sintering method; disperse 0.16g of TiO2 and 0.53g of Nb2O5 in 30mL of anhydrous ethanol and mechanically stir for 6h. Transfer the mixed sample to a blast drying oven for drying. After drying, grind to obtain a powder material precursor A. Press the precursor A into a 3mm disc with a diameter of 9mm under a pressure of 150MPa, which is called embryo B; transfer the embryo B to a tube furnace and calcine it at 1300℃. After cooling to room temperature, a white compacted sheet-like niobium titanium oxide electrode is obtained.

[0034] Step 2: In situ generate a tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material on the surface of the niobium titanium oxide material by molten salt electrolysis; the flaky niobium titanium oxide electrode prepared in step 1 is used as the cathode, graphite is used as the anode, and NaCl-KCl-TaCl5-NbCl5-MgCl2-CeCl3-LaCl3 is used as the molten salt electrolyte, and the mass ratio of NaCl:KCl:TaCl5:NbCl5:MgCl2:CeCl3:LaCl3 is 35%:35%:6%:6%:6%:6%:6%; a constant voltage of 2.0 V is applied to the two electrodes, and molten salt electrolysis is performed at 800°C for 5 hours. After the electrolysis is completed, the cathode product obtained after the electrolysis is taken out, and the above solution is centrifuged with anhydrous ethanol and distilled water, respectively, three times at a speed of 6500 rpm, each time for 3 minutes, and the product is collected, dried at low temperature and ground to obtain a tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material. Schematic diagram of the preparation of tantalum-niobium-magnesium-cerium-lanthanum high entropy alloy / niobium-titanium oxide two-phase heterogeneous materials Figure 1 As shown, the high entropy alloy is uniformly grown on the niobium titanium oxide material through molten salt electrolysis.

[0035] The tantalum-niobium-magnesium-cerium-lanthanum high-entropy alloy / niobium-titanium oxide two-phase heterogeneous material obtained in this embodiment is applied to the negative electrode of a low-temperature lithium-ion battery to improve the cycle stability and rate performance of the battery at low temperatures.

[0036] The prepared tantalum-niobium-magnesium-cerium-lanthanum high entropy alloy / niobium-titanium oxide two-phase heterogeneous material was dispersed in N-methylpyrrolidone (NMP) solvent with a mass ratio of 85%:7.5%:7.5% with a binder of polyvinylidene fluoride (PVDF) and a conductive agent of acetylene black in an amount of 85%:7.5%:7.5% to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector, dried, rolled, and punched to obtain a negative electrode sheet. Then, a button cell was assembled and the electrochemical performance was tested. The EIS curve at -40°C is shown in FIG. Figure 2 As shown in the figure, compared with pure phase niobium titanium oxide material, the tantalum niobium magnesium cerium lanthanum high entropy alloy / titanium niobate two-phase heterogeneous material electrode also shows lower charge transfer resistance at low temperature, indicating that it has better kinetic properties and is conducive to showing excellent low-temperature fast charging performance. The cycling performance at -40℃ and 0.5C is shown in the figure. Figure 3 As shown, the activation discharge capacity at 0.2C is 129.8 mAh g -1 , the charge capacity is 125.9mAh g -1 The first coulombic efficiency is 96.9%; the first cycle discharge capacity at 0.5C is 82.2mAh g -1 Even at the 100th cycle, the discharge capacity is 112.6 mAh g -1 , charge capacity 111.5mAh g -1 , much higher than pure phase niobium titanium oxide materials (90.6 / 90.2mAhg -1), indicating that the lithium-ion battery assembled using the present invention has good low-temperature cycle performance.

[0037] Example 2

[0038] The differences between the present embodiment and the embodiment 1 in preparing the tantalum-niobium-magnesium-cerium-lanthanum high entropy alloy / niobium-titanium oxide two-phase heterogeneous material are as follows: the pressure for preparing the embryo B is 120 MPa, the thickness of the pressed sheet is 2 mm; the high-temperature calcination time of the embryo B is 1200°C for 15 h; the mass ratio of the molten salt electrolyte is

[0039] NaCl:KCl:TaCl5:NbCl5:MgCl2:CeCl3:LaCl3=40%:40%:4%:4%:4%:4%:4%, and the other parameters are the same as those in Example 1.

[0040] Example 3

[0041] The preparation of tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material in this embodiment is different from that in Example 1 in that: the stirring method of precursor A is ball milling, the ball milling speed is 300 r / min, and the time is 4 hours; the pressure for preparing embryo B is 120 MPa, and the tablet thickness is 4 mm; the high-temperature calcination time of embryo B is 1250°C and the time is 18 hours; the mass ratio of molten salt electrolyte is NaCl:KCl:TaCl5:NbCl5:MgCl2:CeCl3:LaCl3=40%:40%:4%:4%:4%:4%:4%, and the other parameters are the same as in Example 1.

[0042] Example 4

[0043] The preparation of tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material in this embodiment is different from that in Example 1 in that: the stirring method of precursor A is ball milling, the ball milling speed is 300 r / min, and the time is 4 h; the pressure for preparing embryo B is 110 MPa, and the tablet thickness is 3 mm; the high-temperature calcination time of embryo B is 1250°C and the time is 20 h; the mass ratio of molten salt electrolyte is NaCl:KCl:TaCl5:NbCl5:MgCl2:CeCl3:LaCl3=40%:40%:4%:4%:4%:4%:4%, and the other parameters are the same as in Example 1.

[0044] Example 5

[0045] The preparation of tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material in this embodiment is different from that in Example 1 in that: the stirring method of precursor A is ball milling, the ball milling speed is 400 r / min, and the time is 4 h; the pressure for preparing embryo B is 140 MPa, and the tablet thickness is 2 mm; the mass ratio of the molten salt electrolyte is NaCl:KCl:TaCl5:NbCl5:MgCl2:CeCl3:LaCl3=40%:40%:4%:4%:4%:4%:4%; the constant voltage applied during the electrolysis process is 0.8 V, and the other parameters are the same as in Example 1.

[0046] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a tantalum-niobium-magnesium-lanthanum-cerium high entropy alloy / niobium-titanium oxide two-phase heterogeneous material, characterized in that: The following steps are involved: Step 1: Prepare a niobium titanium oxide electrode using a traditional high-temperature solid-phase method and a tablet pressing and sintering method. The specific method for preparing the niobium titanium oxide electrode is as follows: disperse TiO2 and Nb2O5 in anhydrous ethanol at a molar ratio of 1:1 and mix them thoroughly, dry the mixed sample, grind it to obtain a powder material precursor A, press the precursor A into a sheet, transfer it to a tube furnace and calcine it at 1100°C-1400°C to obtain a white compacted sheet-like titanium niobate electrode; Step 2: Using a niobium titanium oxide electrode as a cathode, graphite as an anode, and a chloride molten salt as a molten salt electrolyte, after assembly, applying voltage to the two electrodes for molten salt electrolysis, the temperature of the molten salt electrolysis is 700-1000°C, the time is 2-8 hours, and the constant voltage applied during the molten salt electrolysis process is 0.5-2.4V. The cathode product obtained after electrolysis is taken out and centrifuged, and then dried and ground at low temperature to obtain a tantalum niobium magnesium cerium lanthanum high entropy alloy / niobium titanium oxide two-phase heterogeneous material; The chloride molten salt includes NaCl, KCl, TaCl5, NbCl5, MgCl2, CeCl3 and LaCl3. The masses of NaCl and KCl in the chloride molten salt are equal, and the total mass of the two accounts for 70%-84% of the chloride molten salt. The masses of the five components TaCl5, NbCl5, MgCl2, CeCl3 and LaCl3 are equal, and the total amount of the five components accounts for 16%-30% of the chloride molten salt.

2. The preparation method according to claim 1, wherein: In step 2, the protective atmosphere for the molten salt electrolysis reaction is a mixed gas of argon and hydrogen, argon or nitrogen.

3. The preparation method according to claim 1, wherein: The precursor A is pressed into a sheet at a pressure of 120-180 MPa with a thickness of 2-5 mm.

4. The preparation method according to claim 1, wherein: The calcination time in the tubular furnace is 1-30 hours.

5. An application of a tantalum-niobium-magnesium-lanthanum-cerium high entropy alloy / niobium-titanium oxide two-phase heterogeneous material prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The tantalum-niobium-magnesium-lanthanum-cerium high entropy alloy / niobium-titanium oxide two-phase heterogeneous material is used as a negative electrode active material in the negative electrode of a low-temperature lithium-ion battery.

6. The use according to claim 5, characterized in that: The operating temperature range of the low-temperature lithium-ion battery is -40°C to 60°C.

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