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

Abstract

The present invention provides a lithium-sulfur battery composite positive electrode material based on a high-entropy rare earth metal oxide carrier and a preparation method thereof, and relates to the technical field of lithium-sulfur batteries. The lithium-sulfur battery composite positive electrode material based on a high-entropy rare earth metal oxide carrier of the present invention is prepared by mixing, grinding, and calcining a high-entropy rare earth metal oxide carrier and a sulfur element; the mass ratio of the HE-REO2 and the sulfur element is 1:(1-4); and the RE is La, Ce, Pr, Nd, and Sm. The present invention introduces four rare earth elements, La, Pr, Nd, and Sm, into the CeO2 lattice to form a nanofiber carrier with a single cubic fluorite structure, and utilizes its high oxygen vacancy concentration characteristics to significantly enhance the chemical adsorption and catalytic ability of lithium polysulfide, effectively suppress the shuttle effect, and make the sulfur-based composite material finally constructed show excellent comprehensive electrochemical performance.

Description

Technical Field

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

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

[0003] Lithium-sulfur batteries use sulfur as the positive electrode and metallic lithium as the negative electrode, with a theoretical energy density of up to 2600 Wh kg -1 However, its practical application still faces many challenges, such as: (1) the extremely low electronic conductivity of sulfur and the final reaction product lithium sulfide, which seriously hinders the electron transport of the electrode and leads to incomplete electrode conversion reaction; (2) the electrode reaction intermediate lithium polysulfide is easily soluble in ether-based electrolytes, forming a "shuttle effect", which leads to the loss of active materials and rapid decay of electrode discharge capacity; (3) the redox of sulfur involves a solid-liquid-solid multiphase transformation process, and the reaction kinetics are 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 and cycle performance of lithium-sulfur batteries.

[0004] The development of sulfur cathode carrier materials to effectively anchor lithium polysulfide has been proven to be an effective method to inhibit the shuttle effect of the system. Transition metals and their compound materials have been widely reported to be used to inhibit the shuttle effect and improve the electrode kinetics. Compared with transition metals, rare earth metals have unique 4f valence layer energy levels and can induce rich orbital coupling effects, which have gradually attracted widespread research interest in the fields of catalysis and energy. Among the many rare earth metal oxides, cerium dioxide has a dynamically reversible Ce 3+ / Ce 4+ Redox couples and oxygen vacancy defects have a strong adsorption effect on lithium polysulfide.

[0005] Furthermore, given the diversity of polysulfide intermediates and the complexity of sulfur species conversion pathways, metal compound catalysts with a single active site are unlikely to meet the catalytic requirements for all conversion steps. Therefore, the design and synthesis of catalysts with multiple catalytic sites and tunable electronic structures have greater application prospects. Summary of the Invention

[0006] In light of this, the present invention provides a lithium-sulfur battery composite cathode material based on a high-entropy rare earth metal oxide support (HE-REO2) and a preparation method thereof. This invention utilizes the strong chemical adsorption of HE-REO2 on polar lithium polysulfides to significantly inhibit the dissolution of lithium polysulfides in ether electrolytes, thereby slowing the shuttle effect. This composite material exhibits the characteristics of high sulfur content, high specific capacity, and high cycle stability.

[0007] The first aspect of the present invention provides a lithium-sulfur battery composite positive electrode material based on HE-REO2, which is prepared by mixing, grinding and calcining HE-REO2 and sulfur;

[0008] The mass ratio of HE-REO2 to elemental sulfur is 1:(1-4);

[0009] The rare earth elements RE are La, Ce, Pr, Nd, and Sm.

[0010] Preferably, the HE-REO2 is (La 0.2 Ce 0.2 Pr 0.2 Nd 0.2 Sm 0.2 )O2.

[0011] The second aspect of the present invention is to provide a method for preparing a composite positive electrode material for a lithium-sulfur battery based on HE-REO2, comprising the following steps:

[0012] S1. Preparation of HE-REO2:

[0013] The rare earth element precursor and the polymer are dissolved in DMF and stirred evenly to obtain a precursor solution, which is then electrospun, dried, and calcined to obtain HE-REO2;

[0014] S2. Preparation of composite cathode materials for lithium-sulfur batteries:

[0015] HE-REO2 is mixed with sulfur, ground, and heat-treated to obtain a composite positive electrode material for a lithium-sulfur battery;

[0016] Preferably, the RE is La, Ce, Pr, Nd, or Sm; the rare earth element precursor is a soluble salt of a rare earth, more preferably a 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; and the solid content of the precursor solution is 0.11 g mL -1The electrospinning parameters were set as follows: fluid propulsion rate 2 mL h -1 The distance between the propeller and the outermost side is 80-120 cm, the moving speed is 150 cm / min, the electrostatic field potential is 20 kV, and the distance between the needle tip and the metal collecting plate is 15 cm; the drying temperature is 60℃-120℃, the drying time is 12℃-24 h, preferably 12 h; the roasting heating rate 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 heat treatment heating rate 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.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] The present invention introduces four rare earth elements, La, Pr, Nd, and Sm, into the CeO2 lattice to form a nanofiber carrier with a single cubic fluorite structure, and utilizes its high oxygen vacancy concentration characteristics to significantly enhance the chemical adsorption and catalytic ability of lithium polysulfide, effectively inhibiting the shuttle effect.

[0019] The present invention adopts electrospinning to prepare HE-REO2 nanofibers and then heat-treats them to form composites with sulfur. The process ensures high sulfur content (about 80%) and high tap density (>1.7 g·cm -3 ) while achieving excellent specific capacity and cycle stability.

[0020] The present invention successfully solves the problems of sulfur cathode dissolution and kinetic retardation through structural design and preparation process innovation, so that the final constructed sulfur-based composite material shows excellent comprehensive electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 This is a scanning electron microscope image of the HE-REO2 material prepared in Example 1;

[0023] Figure 2 This is a scanning electron microscope image of the CeO2 carrier material prepared in Comparative Example 1;

[0024] Figure 3 The figure is a rate performance diagram of the composite positive electrode materials prepared in Example 1 and Comparative Examples 1-4;

[0025] Figure 4 The charge and discharge curves of the composite cathode materials prepared in Example 1 and Comparative Example 1 at a rate of 0.1-5C;

[0026] Figure 5 The cycle performance curves of the lithium-sulfur battery composite cathode materials prepared in Example 1 and Comparative Example 1 at a 1C rate;

[0027] Figure 6 This is the cycle performance curve of the lithium-sulfur battery composite positive electrode material prepared in Example 1 at a 0.2C rate. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The first aspect of the present invention provides a lithium-sulfur battery composite positive electrode material based on HE-REO2, which is prepared by mixing, grinding and calcining HE-REO2 and sulfur;

[0030] The mass ratio of HE-REO2 to elemental sulfur is 1:(1-4);

[0031] The HE-REO2 is RE x O2;

[0032] The rare earth elements RE are La, Ce, Pr, Nd, and Sm.

[0033] 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.

[0034] In some preferred embodiments of the present invention, the mass ratio of HE-REO2 to elemental sulfur is 1:4.

[0035] The second aspect of the present invention is to provide a method for preparing a composite positive electrode material for a lithium-sulfur battery based on HE-REO2, comprising the following steps:

[0036] S1. Preparation of HE-REO2:

[0037] The rare earth element precursor and the polymer are dissolved in DMF and stirred evenly to obtain a precursor solution, which is then electrospun, dried, and calcined to obtain HE-REO2;

[0038] The rare earth elements are La, Ce, Pr, Nd, and Sm; the rare earth element precursor is a soluble salt of a rare earth, preferably a 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 were set as follows: fluid propulsion rate 2 mL h -1 The distance between the propeller and the outermost side is 80-120 cm, the moving speed is 150 cm / min, the electrostatic field potential is 20 kV, and the distance between the needle tip and the metal collecting 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;

[0039] In some preferred embodiments of the present invention, the drying time is 12 h, the roasting heating rate is 2°C / min, the roasting temperature is 750°C, and the roasting holding time is 2 h;

[0040] S2. Preparation of composite cathode materials for lithium-sulfur batteries:

[0041] HE-REO2 is mixed with sulfur, ground, and heat-treated to obtain a composite positive electrode material for a lithium-sulfur battery;

[0042] The heat treatment heating rate 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;

[0043] In some preferred embodiments of the invention, the heating rate of the heat treatment is 2°C / min, and the holding time of the heat treatment is 12 h.

[0044] In order to further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0045] Example 1 A method for preparing a composite cathode material for a lithium-sulfur battery based on a HE-REO2 polar carrier, comprising the following steps:

[0046] S1. Preparation of HE-REO2 materials

[0047] To 10 mL of DMF, 0.2 mmol La(NO3)3·6H2O, 0.2 mmol Ce(NO3)3·6H2O, 0.2 mmol Pr(NO3)3·6H2O, 0.2 mmol Nd(NO3)3·9H2O, and 0.2 mmol Sm(NO3)3·9H2O were added and stirred until the added substances were completely dissolved. Then, 1 g of polyacrylonitrile was added and stirred for 12 h to obtain a polymer viscous fluid.

[0048] 10 mL of the obtained polymer viscous fluid was drawn into the propulsion tank of the electrospinning system using a syringe, and the spinning parameters were set, where the fluid propulsion rate was 2 mL h -1 The propeller moves left and right within a range of 80-120 cm from the outermost side, at a moving speed of 150 cm / min, the electrostatic field potential is 20 kV, the distance between the needle tip and the metal collecting plate is 15 cm, spinning begins, and the precursor is collected by the metal collecting plate; after the spinning is completed, the collected precursor is dried in a drying oven for 12 h; and in a muffle furnace, the temperature is raised to 750 ° C at a rate of 2 ° C / min, kept at this temperature for 2 h, and finally cooled to room temperature to obtain HE-REO2;

[0049] S2, HE-REO2 and sulfur composite

[0050] HE-REO2 and sulfur were mixed in a mass ratio of 1:4, ground to obtain a mixture of HE-REO2 and sulfur, and placed in a crucible for later use; the crucible containing the mixture of HE-REO2 and sulfur was placed in a reactor under an argon atmosphere and sealed; the sealed reactor was transferred to a muffle furnace, heated to 155°C at a rate of 1°C / min, and kept warm for 12 h; and then cooled to room temperature to obtain a lithium-sulfur battery composite positive electrode material, recorded as S / HE-REO2.

[0051] Comparative Example 1 A method for preparing a composite positive electrode material for a lithium-sulfur battery based on a CeO2 carrier, comprising the following steps:

[0052] S1. Preparation of CeO2 carrier material:

[0053] Add 1 mmol of Ce(NO3)3·6H2O to 10 mL of DMF and stir until the added substance is completely dissolved; then add 1 g of polyacrylonitrile and stir for 12 h to obtain a polymer viscous fluid;

[0054] The remaining steps are the same as those in Example S1;

[0055] Composite of S2, CeO2 carrier materials and sulfur:

[0056] The same as step S2 of Example 1 was performed to obtain a lithium-sulfur battery composite positive electrode material, which was recorded as S / CeO2.

[0057] Comparative Example 2 A method for preparing a lithium-sulfur battery composite positive electrode material based on a rare earth metal oxide polar carrier, comprising the following steps:

[0058] S1、(La 1 / 3 Ce 1 / 3 Pr 1 / 3 ) Preparation of O2 carrier materials

[0059] To 10 mL of DMF, 0.33 mmol of La(NO3)3·6H2O, 0.33 mmol of Ce(NO3)3·6H2O, and 0.33 mmol of Pr(NO3)3·6H2O were added and stirred until the added substances were completely dissolved. Then, 1 g of polyacrylonitrile was added and stirred for 12 h to obtain a polymer viscous fluid.

[0060] The remaining steps are the same as those in Example S1;

[0061] S2、(La 1 / 3 Ce 1 / 3 Pr 1 / 3 ) O2 carrier material and sulfur composite

[0062] The same as step S2 of Example 1, the lithium-sulfur battery composite positive electrode material is obtained, which is recorded as S / (La 1 / 3 Ce 1 / 3 Pr 1 / 3 )O2.

[0063] Comparative Example 3 A method for preparing a lithium-sulfur battery composite positive electrode material based on a rare earth metal oxide polar carrier, comprising the following steps:

[0064] S1、(La 1 / 3 Ce 1 / 3 Nd 1 / 3 ) Preparation of O2 carrier materials

[0065] To 10 mL of DMF, 0.33 mmol of La(NO3)3·6H2O, 0.33 mmol of Ce(NO3)3·6H2O, and 0.33 mmol of Nd(NO3)3·6H2O were added and stirred until the added substances were completely dissolved. Then, 1 g of polyacrylonitrile was added and stirred for 12 h to obtain a polymer viscous fluid.

[0066] The remaining steps are the same as those in Example S1;

[0067] S2、(La 1 / 3 Ce 1 / 3 Nd 1 / 3 ) O2 carrier material and sulfur composite

[0068] The same as step S2 of Example 1, the lithium-sulfur battery composite positive electrode material is obtained, which is recorded as S / (La 1 / 3 Ce 1 / 3 Nd 1 / 3 )O2.

[0069] Comparative Example 4 A lithium-sulfur battery composite positive electrode material based on a rare earth metal oxide polar carrier, the steps are as follows:

[0070] S1、(La 1 / 3 Ce 1 / 3 Sm 1 / 3 ) Preparation of O2 carrier materials

[0071] To 10 mL of DMF, 0.33 mmol of La(NO3)3·6H2O, 0.33 mmol of Ce(NO3)3·6H2O, and 0.33 mmol of Sm(NO3)3·6H2O were added and stirred until the added substances were completely dissolved. Then, 1 g of polyacrylonitrile was added and stirred for 12 h to obtain a polymer viscous fluid.

[0072] The remaining steps are the same as those in Example S1;

[0073] S2、(La 1 / 3 Ce 1 / 3 Sm 1 / 3 ) O2 carrier material and sulfur composite

[0074] The same as step S2 of Example 1, the lithium-sulfur battery composite positive electrode material is obtained, which is recorded as S / (La 1 / 3 Ce 1 / 3 Sm 1 / 3 )O2.

[0075] Test Example 1

[0076] The composite positive electrode materials prepared in Example 1 and Comparative Examples 1-4 were used to make electrode sheets and assemble batteries. The process is detailed as follows:

[0077] (1) Electrode sheet production

[0078] The composite positive electrode materials prepared in Example 1 and Comparative Examples 1-4 were mixed with a conductive agent (aligned carbon nanotubes, with an average tube diameter of 10-30 nm and a tube length greater than 2 μm, purchased from Nanjing Pioneer Nanomaterial Technology Co., Ltd.) and PVdF in a mass ratio of 7:2:1 and dispersed in NMP. The mass volume ratio of the composite positive electrode material to NMP was 0.2 g:2.0 mL. The slurry was then coated on a current collector aluminum foil and dried in a drying oven at 60°C for 24 h for later use. The obtained positive electrode sheet was then cut to obtain a positive electrode disc with a diameter of 12 mm. The area loading of sulfur was 1.3 mg / cm 2 ;

[0079] (2) Battery assembly

[0080] Button cells (2032) were used to assemble the battery and test its performance. The assembly sequence was negative electrode shell – spring – gasket – lithium sheet – electrolyte – diaphragm – electrolyte – positive electrode sheet – positive electrode shell, and then the battery was packaged. The entire process was completed in a glove box filled with argon.

[0081] The obtained 2032 button cell was placed on the battery test system and after standing for 24 h, the charge and discharge test was carried out at a rate of 0.1-5 C, with the voltage cutoff range set at 1.7-2.8 V. The results are as follows: Figure 2-5 shown.

[0082] Compared with other materials, the material obtained in Example 1 has the highest specific capacity and capacity retention rate. Specifically, the discharge specific capacity of the composite positive electrode material obtained in Example 1 at 0.1C and 5C rates is 1264.6 mAh g -1 and 698.2 mAh g -1 , which is significantly better than the composite positive electrode materials obtained in the comparative examples, among which Example 1 and Comparative Examples 2-4 perform better than Comparative Example 1; the material in Example 1 has a first discharge capacity of 935.4 mAh g at a rate of 1 C. -1 After 1000 cycles, the capacity can still be maintained at 459.9 mAh g -1 The average capacity decay rate is 0.051%.

[0083] Furthermore, the composite cathode material obtained in Example 1 exhibited excellent electrochemical performance under high sulfur loading conditions. The discharge capacity of the corresponding sulfur electrode at a rate of 0.2 C was 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), and the corresponding area specific capacities are 3.5 mAh cm -2 , 4.2 mAh cm -2 and 4.8 mAh cm -2 After 100 cycles, the area specific capacity remains at 2.4 mAh cm -2 , 2.7 mAh cm -2 and 2.9 mAh cm -2 , the capacity retention rates were 68.5%, 64.2% and 60.4% respectively.

[0084] Since 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.

[0085] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A lithium-sulfur battery composite cathode material based on a high-entropy rare earth metal oxide support, characterized in that: The material is prepared by mixing, grinding and calcining a high entropy rare earth metal oxide carrier HE-REO2 and sulfur. The mass ratio of HE-REO2 to elemental sulfur is 1:(1-4); The rare earth elements RE are La, Ce, Pr, Nd, and Sm; The preparation method of the HE-REO2 is as follows: The rare earth element precursor and the polymer are dissolved in DMF and stirred evenly to obtain a precursor solution, which is then electrospun, dried, and calcined to obtain HE-REO2; The molar ratio of La, Ce, Pr, Nd and Sm in the precursor solution is 1:1:1:1:

1.

2. The method for preparing a lithium-sulfur battery composite cathode material based on a high-entropy rare earth metal oxide support according to claim 1, characterized in that: The following steps are involved: S1. Preparation of HE-REO2: The rare earth element precursor and polymer are dissolved in N,N-dimethylformamide (DMF), stirred evenly to obtain a precursor solution, and then electrospun, dried, and calcined to obtain HE-REO2; S2. Preparation of composite cathode materials for lithium-sulfur batteries: HE-REO2 is mixed with sulfur, ground, and heat-treated to obtain a lithium-sulfur battery composite positive electrode material.

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

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, characterized in that The electrospinning parameters were set as follows: fluid propulsion rate 2 mL / h -1 The distance between the propeller and the outermost side is 80-120 cm, the moving speed is 150 cm / min, the electrostatic field potential is 20 kV, and the distance between the needle tip and the metal collecting plate is 15 cm.

8. The preparation method according to claim 2, characterized in that The roasting heating rate is 2° C. / min, the roasting temperature is 750° C., and the roasting holding time is 2 h.

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

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