Lithium-sulfur battery composite positive electrode material based on high-entropy rare-earth metal oxide carrier and preparation method of lithium-sulfur battery composite positive electrode material

Abstract

The invention provides a lithium-sulfur battery composite positive electrode material based on a high-entropy rare-earth metal oxide carrier and a preparation method of the lithium-sulfur battery composite positive electrode material, and relates to the technical field of lithium-sulfur batteries. The lithium-sulfur battery composite positive electrode material based on the high-entropy rare-earth metal oxide carrier is prepared by mixing, grinding and roasting the high-entropy rare-earth metal oxide carrier and elemental sulfur, the mass ratio of the HE-REO2 to the elemental sulfur is 1: (1-4); rE is La, Ce, Pr, Nd or Sm. The four rare earth elements La, Pr, Nd and Sm are introduced into CeO2 crystal lattices to form a nanofiber carrier of a single cubic fluorite structure, the chemical adsorption and catalytic capacity to lithium polysulfide is remarkably enhanced by means of the high oxygen vacancy concentration characteristic of the nanofiber carrier, the shuttle effect is effectively inhibited, and the finally constructed sulfur-based composite material shows excellent comprehensive electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and particularly to a composite cathode material for a lithium-sulfur battery based on a high-entropy rare-earth metal oxide support and a preparation method thereof. Background Art

[0002] Lithium-ion batteries dominate the portable energy storage market due to their good reliability and mature assembly technology. However, limited by the lithium-ion insertion / extraction chemical mechanism of electrode materials (transition metal oxide cathodes and graphite anodes), traditional lithium-ion battery systems can only provide an energy density of 250-300 Wh kg -1 and cannot meet the growing energy demand.

[0003] Lithium-sulfur batteries use sulfur as the cathode and metallic lithium as the anode, with a theoretical energy density as high as 2600 Wh kg -1 . However, their practical applications still face many problems, such as: (1) The electronic conductivity of sulfur and the final reaction product lithium sulfide is extremely low, seriously hindering the electron transfer of the electrode and resulting in incomplete electrode conversion reactions; (2) The electrode reaction intermediate polysulfide is easily soluble in ether-based electrolytes, forming a "shuttle effect", which leads to the loss of active substances and rapid decay of the electrode discharge capacity; (3) The redox of sulfur involves a solid-liquid-solid multiphase conversion process, and the reaction kinetics is slow. Therefore, how to effectively inhibit the shuttle effect and improve the electrode reaction kinetics performance has become the key to improving the specific capacity of lithium-sulfur batteries and improving their cycling performance.

[0004] Developing a sulfur cathode support material to effectively anchor polysulfides has been proven to be an effective method to inhibit the shuttle effect in the system. Transition metal and its compound materials have been widely reported for inhibiting the shuttle effect and improving electrode kinetics performance. Compared with transition metals, rare-earth metals have a unique 4f valence shell energy level and can induce rich orbital coupling effects, gradually attracting extensive research interest in the fields of catalysis and energy. Among many rare-earth metal oxides, cerium dioxide has a dynamic and reversible Ce 3+ / Ce 4+ redox couple and oxygen vacancy defects, and has a strong adsorption effect on polysulfides.

[0005] In addition, considering the diversity of polysulfide intermediates and the complexity of sulfur species conversion paths, metal compound catalysts with a single active site are difficult to meet the catalytic requirements for all conversion steps. Therefore, designing and synthesizing catalysts with multiple catalytic sites and adjustable electronic structures has more application prospects. Summary of the Invention

[0006] In view of this, the present invention provides a composite cathode material for lithium-sulfur batteries based on a high-entropy rare-earth metal oxide support (HE-REO2) and a preparation method thereof. The present invention utilizes the strong chemisorption of HE-REO2 on polar polysulfide lithium, greatly inhibiting the dissolution of polysulfide lithium in ether electrolytes, thereby slowing down the shuttle effect, and then enabling the composite material to exhibit the characteristics of high sulfur content, high specific capacity, and high cycle stability.

[0007] In the first aspect of the present invention, there is provided a composite cathode material for lithium-sulfur batteries based on HE-REO2, which is prepared by mixing, grinding, and roasting HE-REO2 and elemental sulfur; The mass ratio of the HE-REO2 to the elemental sulfur is 1:(1 - 4); The rare-earth element RE is La, Ce, Pr, Nd, or Sm.

[0008] Preferably, the HE-REO2 is (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )O2.

[0009] In the second aspect of the present invention, there is provided a preparation method for a composite cathode material for lithium-sulfur batteries based on HE-REO2, comprising the following steps: S1. Preparation of HE-REO2: Dissolve a rare-earth element precursor and a polymer in DMF, stir evenly to obtain a precursor solution, then perform electrospinning, dry after electrospinning, and calcine to obtain HE-REO2; S2. Preparation of the composite cathode material for lithium-sulfur batteries: Mix HE-REO2 and elemental sulfur, grind, and perform heat treatment to obtain the composite cathode material for lithium-sulfur batteries; Preferably, the RE is La, Ce, Pr, Nd, or Sm; the rare-earth element precursor is a soluble salt of rare earth, more preferably rare-earth nitrate; the polymer is polyacrylonitrile (molecular weight ≤ 150,000); the molar ratio of La, Ce, Pr, Nd, and Sm in the precursor solution is 1:1:1:1:1; the molar mass ratio of the rare-earth element precursor to the polymer is 1 mol:1 g; the stirring temperature is 50°C - 80°C, preferably 60°C; the solid content of the precursor solution is 0.11 g mL -1 ; the electrospinning parameters are set as follows: fluid propulsion rate 2 mL h -1, the distance of the left - right movement of the thruster from the outermost side is 80 - 120 cm, the movement rate is 150 cm / min, the potential of the electrostatic field is 20 kV, and the distance between the needle tip and the metal collection plate is 15 cm; the drying temperature is 60℃ - 120℃, the drying time is 12℃ - 24 h, preferably 12 h; the heating rate of roasting is 1 - 5℃ / min, preferably 2℃ / min, the roasting temperature is 550 - 850℃, preferably 750℃, and the roasting holding time is 1 - 3 h, preferably 2 h; the heating rate of heat treatment is 1 - 5℃ / min, preferably 2℃ / min, the heat treatment temperature is 155℃, and the heat treatment holding time is 6 - 24 h, preferably 12 h.

[0010] Compared with the prior art, the beneficial technical effects of the present invention are as follows: In the present invention, four rare - earth elements, La, Pr, Nd, and Sm, are introduced into the CeO2 lattice to form a nanofiber support with a single - cubic fluorite structure. By utilizing its high oxygen - vacancy concentration characteristics, the chemical adsorption and catalytic ability for polysulfide lithium are significantly enhanced, effectively inhibiting the shuttle effect.

[0011] The present invention adopts the process of preparing HE - REO2 nanofibers by electrospinning and then sulfur - compounding through heat treatment. While ensuring a high sulfur content (about 80%) and a high tap density (>1.7 g·cm -3 ), excellent specific capacity and cycle stability are achieved.

[0012] Through structural design and innovation of the preparation process, the present invention successfully solves problems such as sulfur cathode dissolution and kinetic sluggishness, enabling the finally constructed sulfur - based composite material to exhibit excellent comprehensive electrochemical performance. Brief Description of the Drawings

[0013] The present invention will be further described below in conjunction with the drawings.

[0014] Figure 1 It is the scanning electron microscope image of the HE - REO2 material prepared in Example 1; Figure 2 It is the scanning electron microscope image of the CeO2 support material prepared in Comparative Example 1; Figure 3 It is the rate performance graph of the composite cathode materials prepared in Example 1 and Comparative Examples 1 - 4; Figure 4 It is the charge - discharge curve of the composite cathode materials prepared in Example 1 and Comparative Example 1 at 0.1 - 5C rates; Figure 5 It is the cycle performance curve of the lithium - sulfur battery composite cathode materials prepared in Example 1 and Comparative Example 1 at 1C rate; Figure 6Cycling performance curve of the composite cathode material for lithium-sulfur batteries prepared in Example 1 at a rate of 0.2C. Detailed implementation mode

[0015] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0016] The first aspect of the present invention provides a composite cathode material for lithium-sulfur batteries based on HE-REO2, which is prepared by mixing, grinding, and roasting HE-REO2 and sulfur; The mass ratio of HE-REO2 to sulfur is 1:(1-4); The HE-REO2 is RE x O2; The rare earth element RE is La, Ce, Pr, Nd, Sm.

[0017] In some specific embodiments of the present invention, the HE-REO2 is (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )O2.

[0018] In some preferred embodiments of the present invention, the mass ratio of HE-REO2 to sulfur is 1:4.

[0019] The second aspect of the present invention is to provide a preparation method for a composite cathode material for lithium-sulfur batteries based on HE-REO2, including the following steps: S1. Preparation of HE-REO2: Dissolve the rare earth element precursor and the polymer in DMF, stir evenly to obtain a precursor solution, then carry out electrospinning, dry after electrospinning, and calcine to obtain HE-REO2; The rare earth element is La, Ce, Pr, Nd, Sm, the rare earth element precursor is a soluble salt of rare earth, preferably rare earth nitrate; the polymer is polyacrylonitrile (molecular weight ≤ 150000); the molar ratio of La, Ce, Pr, Nd, Sm in the precursor solution is 1:1:1:1:1; the molar mass ratio of the rare earth element precursor to the polymer is 1 mol:1 g; the stirring temperature is 50°C - 80°C, preferably 60°C; the solid content of the precursor solution is 0.11 g mL -1; The electrospinning parameters are set as follows: the fluid propulsion rate is 2 mL h -1 , the distance of the thruster moving left and right from the outermost side is 80 - 120 cm, the moving rate is 150 cm / min, the electrostatic field potential is 20 kV, and the distance between the needle tip and the metal collection plate is 15 cm; the drying temperature is 60°C - 120°C, and the drying time is 12°C - 24 h; the calcination heating rate is 1 - 5°C / min, the calcination temperature is 550 - 850°C, and the calcination holding time is 1 - 3 h; In some preferred embodiments of the present invention, the drying time is 12 h, the calcination heating rate is 2°C / min, the calcination temperature is 750°C, and the calcination holding time is 2 h; S2. Preparation of the composite cathode material for lithium-sulfur battery: Mix HE-REO2 with sulfur, grind, and perform heat treatment to obtain the composite cathode material for lithium-sulfur battery; The heating rate of the heat treatment is 1 - 5°C / min, preferably 2°C / min, the heat treatment temperature is 155°C, and the heat treatment holding time is 6 - 24 h, preferably 12 h; In some preferred embodiments of the invention, the heating rate of the heat treatment is 2°C / min, and the heat treatment holding time is 12 h.

[0020] To further illustrate the present invention, the following examples are used for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0021] Example 1 A preparation method of a composite cathode material for lithium-sulfur battery based on HE-REO2 polar carrier, the steps are as follows: S1. Preparation of HE-REO2 material Add 0.2 mmol of La(NO3)3·6H2O, 0.2 mmol of Ce(NO3)3·6H2O, 0.2 mmol of Pr(NO3)3·6H2O, 0.2 mmol of Nd(NO3)3·9H2O, and 0.2 mmol of Sm(NO3)3·9H2O to 10 mL of DMF, stir until the added substances are completely dissolved, and then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid; Use a syringe to suck 10 mL of the obtained polymer viscous fluid and place it in the propulsion tank of the electrospinning system, and set the spinning parameters, where the fluid propulsion rate is 2 mL h -1, the left - right movement range of the thruster is 80 - 120 cm from the outermost side, the movement rate is 150 cm / min, the electrostatic field potential is 20 kV, the distance between the tip and the metal collection plate is 15 cm. Start electrospinning and collect the precursor with the metal collection plate; after electrospinning ends, dry the collected precursor in an oven for 12 h; then heat it in a muffle furnace at a rate of 2 °C / min to 750 °C, hold for 2 h, and finally cool to room temperature to obtain HE - REO2; S2. Composite of HE - REO2 and sulfur Mix HE - REO2 and sulfur in a mass ratio of 1:4, grind to obtain a mixture of HE - REO2 and sulfur, and place it in a crucible for standby; put the crucible with the mixture of HE - REO2 and sulfur into a reaction kettle under an argon atmosphere, seal it; transfer the sealed reaction kettle to a muffle furnace, heat it at a rate of 1 °C / min to 155 °C, hold for 12 h; then cool to room temperature to obtain the composite cathode material for lithium - sulfur batteries, denoted as S / HE - REO2.

[0022] Comparative Example 1. A preparation method of a composite cathode material for lithium - sulfur batteries based on CeO2 carrier, the steps are as follows: S1. Preparation of CeO2 carrier material: Add 1 mmol Ce(NO3)3·6H2O to 10 mL DMF, stir until the added substances are completely dissolved; then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid; The remaining steps are the same as those in Example S1; S2. Composite of CeO2 carrier material and sulfur Same as step S2 in Example 1 to obtain the composite cathode material for lithium - sulfur batteries, denoted as S / CeO2.

[0023] Comparative Example 2. A preparation method of a composite cathode material for lithium - sulfur batteries based on rare - earth metal oxide polar carrier, the steps are as follows: S1. Preparation of (La 1 / 3 Ce 1 / 3 Pr 1 / 3 )O2 carrier material Add 0.33 mmol La(NO3)3·6H2O, 0.33 mmol Ce(NO3)3·6H2O and 0.33 mmol Pr(NO3)3·6H2O to 10 mL DMF, stir until the added substances are completely dissolved; then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid; The remaining steps are the same as those in Example S1; S2. (La 1 / 3 Ce 1 / 3 Pr 1 / 3)Composite of O2 carrier material and elemental sulfur Following the steps of S2 in Example 1, a composite cathode material for lithium-sulfur battery was obtained, denoted as S / (La 1 / 3 Ce 1 / 3 Pr 1 / 3 )O2.

[0024] Comparative Example 3 A preparation method of a composite cathode material for lithium-sulfur battery based on rare earth metal oxide polar carrier is as follows: S1. Preparation of (La 1 / 3 Ce 1 / 3 Nd 1 / 3 )O2 carrier material Add 0.33 mmol La(NO3)3·6H2O, 0.33 mmol Ce(NO3)3·6H2O and 0.33 mmol Nd(NO3)3·6H2O to 10 mL of DMF, stir until the added substances are completely dissolved; then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid; The remaining steps are the same as those in Example S1; S2. Composite of (La 1 / 3 Ce 1 / 3 Nd 1 / 3 )O2 carrier material and elemental sulfur Following the steps of S2 in Example 1, a composite cathode material for lithium-sulfur battery was obtained, denoted as S / (La 1 / 3 Ce 1 / 3 Nd 1 / 3 )O2.

[0025] Comparative Example 4 A composite cathode material for lithium-sulfur battery based on rare earth metal oxide polar carrier is as follows: S1. Preparation of (La 1 / 3 Ce 1 / 3 Sm 1 / 3 )O2 carrier material Add 0.33 mmol La(NO3)3·6H2O, 0.33 mmol Ce(NO3)3·6H2O and 0.33 mmol Sm(NO3)3·6H2O to 10 mL of DMF, stir until the added substances are completely dissolved; then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid; The remaining steps are the same as those in Example S1; S2. Composite of (La 1 / 3 Ce 1 / 3 Sm 1 / 3 )O2 carrier material and elemental sulfur Following the steps of S2 in Example 1, a composite cathode material for lithium-sulfur battery was obtained, denoted as S / (La 1 / 3 Ce1 / 3 Sm 1 / 3 )O2。

[0026] Test Example 1

[0027] The composite cathode materials prepared in Example 1 and Comparative Examples 1-4 were used to fabricate electrode sheets and assemble batteries. The process is described in detail as follows: (1) Electrode sheet fabrication The composite cathode materials prepared in Example 1 and Comparative Examples 1-4 were mixed evenly with a conductive agent (oriented carbon nanotubes, average tube diameter 10-30 nm, tube length > 2 μm, purchased from Nanjing Pioneer Nano Materials Technology Co., Ltd.) and PVdF in a mass ratio of 7:2:1, and dispersed in NMP. The mass-volume ratio of the composite cathode material to NMP was 0.2 g:2.0 mL; then the slurry was coated on the current collector aluminum foil and dried in a drying oven at 60 °C for 24 h for standby; then the obtained positive electrode sheet was cut to obtain a positive electrode disc with a diameter of 12 mm, and the areal sulfur loading was 1.3 mg / cm 2 ; (2) Battery assembly A coin cell (2032) was used to assemble the battery and test its performance. The assembly sequence was negative electrode case – spring piece – gasket – lithium sheet – electrolyte – separator – electrolyte – positive electrode sheet – positive electrode case, and then the battery was encapsulated; the whole process was completed in a glove box filled with argon.

[0028] The obtained 2032 coin cell was placed on a battery testing system. After standing for 24 h, charge-discharge tests were carried out at a rate of 0.1-5 C, and the voltage cut-off range was set to 1.7-2.8 V. The results are as Figure 2-5 shown.

[0029] Compared with other materials, the material obtained in Example 1 had the highest specific capacity and capacity retention rate. Specifically, the discharge specific capacities of the composite cathode material obtained in Example 1 at 0.1C and 5C rates were 1264.6 mAh g -1 and 698.2 mAh g -1 respectively, which were significantly better than the composite cathode materials obtained in the comparative examples. Among them, the performance of Example 1 and Comparative Examples 2-4 was better than that of Comparative Example 1; the first discharge specific capacity of the material in Example 1 at 1 C rate was 935.4 mAh g -1 , and the capacity could still be maintained at 459.9 mAh g -1 after 1000 cycles, and the average capacity decay rate per cycle was 0.051%.

[0030] Furthermore, the composite cathode material obtained in Example 1 exhibits excellent electrochemical performance under high sulfur loading conditions. The discharge specific capacities of the corresponding sulfur electrodes are 931.5 mAh g -1 (3.8 mg cm -2 electrode), 756.4 mAh g -1 (5.5 mg cm -2 electrode), and 661.0 mAh g -1 (7.3 mg cm -2 electrode) at a rate of 0.2 C, and the corresponding areal specific capacities are 3.5 mAh cm -2 , 4.2 mAh cm -2 , and 4.8 mAh cm -2 . After 100 cycles, the areal specific capacities are maintained at 2.4 mAh cm -2 , 2.7 mAh cm -2 , and 2.9 mAh cm -2 , respectively, and the capacity retention rates are 68.5%, 64.2%, and 60.4%, respectively.

[0031] In view of the fact that the rate performance of Comparative Examples 2-4 is worse than that of Example 1, the cycle performance comparison of Examples 3-5 is not given.

[0032] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A composite cathode material for lithium-sulfur batteries based on a high-entropy rare-earth metal oxide support, characterized in that, This material is prepared by mixing, grinding, and calcining a high-entropy rare-earth metal oxide support HE-REO2 and sulfur; The mass ratio of the HE-REO2 to sulfur is 1:(1-4); The rare-earth element RE is La, Ce, Pr, Nd, or Sm.

2. The preparation method of a composite cathode material for a lithium-sulfur battery based on a high-entropy rare-earth metal oxide support according to claim 1, characterized in that, It includes the following steps: S1. Preparation of HE-REO2: Dissolve a rare-earth element precursor and a polymer in N,N-dimethylformamide DMF, stir evenly to obtain a precursor solution, then perform electrospinning, dry after electrospinning, and calcine to obtain HE-REO2; S2. Preparation of the composite cathode material for a lithium-sulfur battery: Mix HE-REO2 with sulfur, grind, and perform heat treatment to obtain the composite cathode material for a lithium-sulfur battery.

3. The preparation method according to claim 2, characterized in that, The rare-earth element precursor is a soluble salt of a rare-earth element.

4. The preparation method according to claim 2, characterized in that, The polymer is polyacrylonitrile.

5. The preparation method according to claim 2, characterized in that, The molar ratio of La, Ce, Pr, Nd, and Sm in the precursor solution is 1:1:1:1:

1.

6. The preparation method according to claim 2, characterized in that, The molar mass ratio of the rare-earth element precursor to the polymer is 1 mol:1 g.

7. The preparation method according to claim 2, wherein, The electrospinning parameters are set as follows: the fluid propulsion rate is 2 mL / h -1 , the distance of the thruster moving left and right from the outermost side is 80 - 120 cm, the moving rate is 150 cm / min, the electrostatic field potential is 20 kV, and the distance between the needle tip and the metal collection plate is 15 cm.

8. The preparation method according to claim 2, wherein The heating rate of the calcination is 2 °C / min, the calcination temperature is 750 °C, and the calcination holding time is 2 h.

9. The preparation method according to claim 2, wherein, The heating rate of the heat treatment is 1 °C / min, the heat treatment temperature is 155 °C, and the heat treatment holding time is 12 h.

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