Transition metal selenylation carrier as well as preparation method and application thereof

Abstract

The invention provides a transition metal selenylation carrier as well as a preparation method and application thereof, and relates to the technical field of battery positive electrode carriers. The preparation method provided by the invention comprises the following steps: mixing and coordinating a transition metal solution and an organic ligand, and separating to obtain a composite precursor; and mixing the composite precursor with selenium powder, and selenizing in a nitrogen-containing atmosphere to obtain the transition metal selenylation carrier. The selenylation carrier prepared by the invention can be used for effectively confining and packaging transition metal selenide, inhibiting agglomeration of nanoparticles and improving the surface activity of the carrier, and is beneficial to improving the rate capability and the cycle performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery cathode carriers, and particularly to a transition metal selenide carrier, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of science and technology and the increasingly severe form of energy shortage, high-energy storage fields such as pure electric vehicles, hybrid electric vehicles, and portable electronic devices have an urgent need for high energy density and power density systems. Among many battery systems, lithium-sulfur batteries have a relatively high energy density, and the rich sulfur content in the earth's crust can effectively reduce costs. However, affected by the cathode dissolution-deposition energy storage mechanism, lithium-sulfur batteries still face problems such as severe shuttle effects of polysulfides during the sulfur reduction / oxidation reaction process and slow redox kinetics in practical applications. This results in low utilization rate of active substances in lithium-sulfur batteries, as well as poor rate performance and cycling performance. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0003] The purpose of the present invention is to provide a transition metal selenide carrier, a preparation method thereof, and an application thereof. The prepared selenide carrier can effectively confine and encapsulate transition metal selenides, inhibit nanoparticle aggregation, and improve the surface activity of the carrier, which is beneficial to improving the rate performance and cycling performance of lithium-sulfur batteries.

[0004] In the first aspect, a preparation method of a transition metal selenide carrier provided by the present invention includes: mixing and coordinating a transition metal solution with an organic ligand and then separating to obtain a composite precursor; mixing the composite precursor with selenium powder and then selenizing in a nitrogen-containing atmosphere to obtain a transition metal selenide carrier.

[0005] The preparation method provided by the present invention is based on composite precursor molecular design and in-situ pyrolysis self-assembly, which can synchronously selenize and nitrogen dope, and construct a porous structure and confine the encapsulation of selenized nanoparticles. Therefore, a high-performance porous nitrogen-doped transition metal selenide carrier can be prepared, which can improve the specific capacity and cycling stability after being made into a lithium-sulfur battery.

[0006] Optionally, the molar ratio of the transition metal element in the transition metal solution to the organic ligand is 1:(3 - 5).

[0007] Optionally, the molar ratio of the transition metal element to the organic ligand is 1:4.

[0008] Optionally, the transition metal in the transition metal solution includes at least one of zinc and manganese.

[0009] Optionally, the molar ratio of zinc to manganese in the transition metal solution is (1 - 10):1.

[0010] Optionally, the organic ligand includes one of 2-methylimidazole, 4-methylimidazole, and imidazole.

[0011] Optionally, the organic ligand is 2-methylimidazole.

[0012] Optionally, the transition metal solution and the organic ligand are mixed and coordinated at 20°C - 40°C.

[0013] Optionally, after mixing and coordinating, centrifugal separation is performed at a rotational speed of 2000 rpm - 10000 rpm.

[0014] Optionally, the composite precursor is obtained by drying after separation.

[0015] Optionally, the composite precursor is obtained by grinding after separation.

[0016] Optionally, the particle size of the composite precursor is 0.1 μm - 0.5 μm.

[0017] Optionally, the composite precursor and selenium powder are selenized in a nitrogen-containing atmosphere at 600°C - 800°C.

[0018] Optionally, the nitrogen-containing gas in the nitrogen-containing atmosphere includes nitrogen.

[0019] Optionally, the composite precursor and selenium powder are mixed at a mass ratio of 1:(1 - 4).

[0020] Optionally, one of transition metal nitrate and transition metal chloride is dissolved in the transition metal solution.

[0021] In a second aspect, the present invention provides a transition metal selenized carrier prepared by any one of the above optional preparation methods.

[0022] In a third aspect, the present invention provides an application of a transition metal selenized carrier prepared by any one of the above optional preparation methods in a lithium-sulfur battery. Description of the Drawings

[0023] Figure 1 is a flowchart of a preparation method of a transition metal selenized carrier provided by the present invention;

[0024] Figure 2 is an XRD pattern of the transition metal selenized carrier prepared in Examples 1 to 6 of the present invention;

[0025] Figure 3 is a transmission electron microscope image and an element distribution map of the transition metal selenized carrier prepared in Example 4 of the present invention;

[0026] Figure 4 is a comparison chart of the rate performance of the lithium-sulfur batteries corresponding to Examples 1 to 6 of the present invention;

[0027] Figure 5 It is a comparative diagram of polarization voltages of the lithium-sulfur batteries corresponding to Embodiment 1 to Embodiment 6 of the present invention at different rates;

[0028] Figure 6 It is a charge-discharge curve diagram of the lithium-sulfur battery corresponding to Embodiment 4 of the present invention at different rates;

[0029] Figure 7 It is a cycling performance curve of the lithium-sulfur battery corresponding to Embodiment 4 of the present invention at a rate of 0.2C. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings as understood by those of ordinary skill in the art to which the present invention pertains.

[0031] Refer to Figure 1 , the present invention provides a preparation method of a transition metal selenide carrier, including the following steps:

[0032] S1. Mix and coordinate a transition metal solution with an organic ligand and then separate to obtain a composite precursor;

[0033] S2. Mix the composite precursor with selenium powder and then selenize in a nitrogen-containing atmosphere to obtain a transition metal selenide carrier.

[0034] Actually, the preparation method provided by the present invention obtains a composite precursor by coordinating a transition metal with an organic ligand, and performs one-step selenization and nitrogen doping on the composite precursor. At the same time, a porous carbon skeleton can be formed at high temperature, which can effectively realize the construction of a porous structure and the confined encapsulation of transition metal selenides, and can inhibit the agglomeration of selenized nanoparticles on the surface, thereby improving the surface activity and specific surface area of the selenide carrier, which is beneficial to increasing the loading amount of the active substance on the selenide carrier.

[0035] In some embodiments, the transition metal element in the transition metal solution includes at least one of zinc and manganese, and the molar ratio of the transition metal element to the organic ligand is 1:(3 - 5). Further, the molar ratio of zinc to manganese in the transition metal element is (1 - 10):1, and the molar ratio of the transition metal element to the organic ligand is 1:4.

[0036] Specifically, the organic ligand used in step S1 includes one of 2-methylimidazole, 4-methylimidazole, and imidazole. Preferably, the organic ligand is 2-methylimidazole. In fact, the ZIF material can be obtained by self-assembly after mixing 2-methylimidazole with zinc ions and manganese ions. Further, after mixing and coordinating the transition metal solution with the organic ligand at 20°C - 40°C, centrifugal separation is performed at a rotation speed of 2000 rpm - 10000 rpm.

[0037] In some embodiments, after separation and drying in step S1, the composite precursor with a particle size of 0.1 μm - 0.5 μm is ground.

[0038] In some embodiments, in step S2, the composite precursor and selenium powder are selenized in a nitrogen-containing atmosphere at 600°C - 800°C. The nitrogen-containing gas in the nitrogen-containing atmosphere includes nitrogen, and the composite precursor and selenium powder are mixed at a mass ratio of 1:(1 - 4).

[0039] The present invention also provides a transition metal selenized carrier prepared by the preparation method in any of the above embodiments, and its application in lithium-sulfur batteries.

[0040] Example 1

[0041] This Example 1 provides a preparation method of a transition metal selenized carrier, including the following steps:

[0042] S1. Add 0.02 mol of zinc nitrate to 200 mL of methanol and stir to dissolve to obtain a transition metal solution. Add 0.08 mol of 2-methylimidazole to 200 mL of methanol and stir to obtain an organic ligand solution. Slowly mix the organic ligand solution with the transition metal solution at room temperature, transfer it to a centrifuge tube, centrifuge at a rotation speed of 8000 rpm for 15 min, collect the precipitate, dry it overnight, and then grind it to obtain a composite precursor;

[0043] S2. Mix the composite precursor and selenium powder at a mass ratio of 1:2, place them in a graphite boat, and transfer them to a tube furnace. After purging with nitrogen for gas replacement, the tube furnace is heated to 700°C at a rate of 5°C / min and held for 2 h, and then cooled to room temperature with the furnace to obtain a transition metal selenized carrier (ZnSe@NC).

[0044] Example 2

[0045] This Example 2 provides a preparation method of a transition metal selenized carrier, which is different from Example 1 in that in step S1, 0.018 mol of zinc nitrate and 0.002 mol of manganese nitrate are added to 200 mL of methanol and stirred to dissolve to obtain a transition metal solution, and in step S2, a transition metal selenized carrier (Mn 0.1 Zn 0.9 Se@NC) is obtained.

[0046] Example 3

[0047] Example 3 provides a method for preparing a transition metal selenized carrier. The difference from Example 1 is that in step S1, 0.016 mol of zinc nitrate and 0.004 mol of manganese nitrate are added to 200 mL of methanol and stirred to dissolve to obtain a transition metal solution. In step S2, a transition metal selenized carrier (Mn 0.2 Zn 0.8 Se@NC) is obtained.

[0048] Example 4

[0049] Example 4 provides a method for preparing a transition metal selenized carrier. The difference from Example 1 is that in step S1, 0.014 mol of zinc nitrate and 0.006 mol of manganese nitrate are added to 200 mL of methanol and stirred to dissolve to obtain a transition metal solution. In step S2, a transition metal selenized carrier (Mn 0.3 Zn 0.7 Se@NC) is obtained.

[0050] Example 5

[0051] Example 5 provides a method for preparing a transition metal selenized carrier. The difference from Example 1 is that in step S1, 0.012 mol of zinc nitrate and 0.008 mol of manganese nitrate are added to 200 mL of methanol and stirred to dissolve to obtain a transition metal solution. In step S2, a transition metal selenized carrier (Mn 0.4 Zn 0.6 Se@NC) is obtained.

[0052] Example 6

[0053] Example 6 provides a method for preparing a transition metal selenized carrier. The difference from Example 1 is that in step S1, 0.01 mol of zinc nitrate and 0.01 mol of manganese nitrate are added to 200 mL of methanol and stirred to dissolve to obtain a transition metal solution. In step S2, a transition metal selenized carrier (Mn 0.5 Zn 0.5 Se@NC) is obtained.

[0054] Structural Characterization

[0055] The transition metal selenized carriers prepared in Examples 1 to 6 were characterized by XRD and compared with the standard card PDF#37-1463 as Figure 2 shown. From Figure 2It can be seen that the characteristic peaks at 27.6°, 45.4°, and 53.8° correspond to the (111), (220), and (311) crystal planes of ZnSe, respectively. Therefore, it can be shown that the selenium-containing carrier prepared by the present invention has a high cleanliness and no impurity phase. From Examples 2 to 6, it can be seen that the introduction of Mn does not affect the crystal phase structure of the selenium-containing carrier.

[0056] The transition metal selenium-containing carrier prepared in Example 4 was characterized by transmission electron microscopy and elemental distribution as Figure 3 shown. From Figure 3 it can be seen that the Mn 0.3 Zn 0.7 Se@NC selenium-containing carrier prepared in Example 4 exhibits a regular polyhedral structure, indicating that the ZIF framework structure of the composite precursor can be well retained during the high-temperature treatment process. Moreover, it can be seen from the elemental distribution that the elements Mn, Zn, and Se are evenly distributed.

[0057] Performance testing

[0058] The transition metal selenium-containing carriers in Examples 1 to 6 were respectively mixed evenly with sulfur powder at a mass ratio of 1:3, and then heated to 155°C at a rate of 5°C / min in an argon atmosphere and held for 12 h to obtain the cathode materials. The cathode materials corresponding to Examples 1 to 6 were respectively mixed with carbon black (Super P) and PVDF at a mass ratio of 7:2:1 in NMP to prepare the cathode slurry; the cathode slurry was coated on the surface of the aluminum foil and dried in a drying oven at 60°C for 12 h, and then cut into cathode plates with a diameter of 12 mm. The cathode plates were assembled into coin cells with Celgard 2400 separator and metallic lithium anode in a glove box, and the electrolyte was 1M LiTFSI + 0.2M LiNO3 (the solvent was DME + DOL, with a volume ratio of 1:1). After standing for 4 h, charge-discharge tests were carried out at a current density of 0.1C - 5C within a voltage range of 1.7V - 2.8V. The rate performance is compared as Figure 4 shown, and the polarization voltage values at different rates are as Figure 5 shown. The discharge specific capacities (mAh / g) at different rates are shown in Table 1 below. Among them, the charge-discharge curves of the coin cell corresponding to Example 4 at different rates are as Figure 6 shown.

[0059] Table 1 Discharge specific capacities of the coin cells corresponding to Examples 1 to 6

[0060] 0.1C 0.2C 0.5C 1C 2C 3C 4C 5C Example 1 1376.2 877.6 757.9 645.4 547.1 495.5 455.7 429.5 Example 2 1367.7 976.8 861.4 725.3 643.7 571.7 501.4 432.9 Example 3 1430.4 1046.9 879.2 749.2 609.9 555.3 510.8 499.3 Example 4 1598.3 1114.4 973.9 820.3 741.3 664.0 619.9 566.2 Example 5 1541.1 1045.5 810.6 702.7 625.3 549.9 500.8 463.3 Example 6 1549.3 943.7 752.5 707.3 650.5 602.5 550.5 506.1

[0061] Combined with Figure 4As can be seen from Table 1, the rate performance of lithium-sulfur batteries made of selenium carriers with different Zn / Mn ratios varies significantly. Among them, Example 4 has better rate performance, and the discharge specific capacities of the lithium-sulfur batteries made of selenium carriers in Examples 2 to 6 at high rates are all higher than that in Example 1. From Figure 5 it can be seen that the polarization voltages of the lithium-sulfur batteries made of selenium carriers in different examples vary greatly at different rates; compared with the ZnSe@NC selenium carrier with a single metal site, the lithium-sulfur battery made of the selenium carrier with dual metal sites has a smaller polarization voltage; among them, the lithium-sulfur battery made of the selenium carrier in Example 4 has the smallest polarization voltage. At the same time, from Figure 6 it can be seen that even at high rates, the lithium-sulfur battery made of the selenium carrier in Example 4 still exhibits typical sulfur electrode discharge plateau characteristics. The above results can show that compared with the ZnSe@NC selenium carrier with a single metal site, the selenium carrier with dual metal sites has more advantages in lithium-sulfur batteries; in addition, by regulating the ratio of dual metal sites, the best battery electrochemical performance can be obtained.

[0062] The selenium carrier prepared in Example 4 was combined with sulfur to form a positive electrode material (sulfur loading of 4.2 mg / cm 2 , electrolyte / sulfur concentration ratio of 20 μL / mg) and subjected to a cycle test at a rate of 0.2C as Figure 7 shown. From Figure 7 it can be seen that the initial discharge specific capacity is 916.3 mAh / g, and after 50 cycles it is 798.1 mAh / g, and the capacity retention rate is 87.1%.

[0063] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention described in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A method for preparing a transition metal selenide carrier, characterized in that, Including: Mix and coordinate a transition metal solution with an organic ligand, and then separate to obtain a composite precursor; mix the composite precursor with selenium powder and selenize it in a nitrogen-containing atmosphere at a temperature greater than or equal to the boiling point of selenium to obtain a transition metal selenized carrier.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the transition metal element to the organic ligand in the transition metal solution is 1:(3 - 5). Preferably, the molar ratio of the transition metal element to the organic ligand is 1:

4.

3. The preparation method according to claim 1, characterized in that, The transition metal in the transition metal solution includes at least one of zinc and manganese. Preferably, the molar ratio of zinc to manganese in the transition metal solution is (1 - 10):

1.

4. The preparation method according to claim 1, characterized in that, The organic ligand includes one of 2-methylimidazole, 4-methylimidazole, and imidazole. Preferably, the organic ligand is 2-methylimidazole.

5. The preparation method according to claim 1, characterized in that, Mix and coordinate the transition metal solution with the organic ligand at 20°C - 40°C; and / or, after mixing and coordinating, centrifuge and separate at a rotation speed of 2000 rpm - 10000 rpm.

6. The preparation method according to claim 1, wherein After separation, dry to obtain the composite precursor; and / or, after separation, grind to obtain the composite precursor; and / or, the particle size of the composite precursor is 0.1 μm - 0.5 μm.

7. The preparation method according to claim 1, wherein Selenize the composite precursor and selenium powder in a nitrogen-containing atmosphere at 600°C - 800°C; and / or, the nitrogen-containing gas in the nitrogen-containing atmosphere includes nitrogen; and / or, mix the composite precursor and selenium powder in a mass ratio of 1:(1 - 4).

8. The preparation method according to claim 1, characterized in that, One of transition metal nitrate and transition metal chloride is dissolved in the transition metal solution.

9. A transition metal selenized carrier prepared by the preparation method according to any one of claims 1 to 8.

10. Application of a transition metal selenized carrier prepared by the preparation method according to any one of claims 1 to 8 in a lithium-sulfur battery.

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