A sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material and its preparation method

Abstract

The invention discloses a sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material and a preparation method thereof, and relates to the technical field of composite electrode materials. The preparation method comprises the following steps: adding citrus pulp to deionized water, heating, soaking in a glucose aqueous solution of transition metal chloride, performing a replacement reaction and a hydrothermal reaction; freeze drying, preheating, sintering into a phase, cooling to room temperature; mixing with sulfur element, performing a hydrothermal reaction, and then cooling to room temperature to obtain a sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material. The composite electrode material prepared by the invention has a hierarchical porous structure, has a high specific surface area, a high high cycle stability, a rate performance and a coulombic efficiency, and is suitable as a lithium-sulfur battery positive electrode material to solve the problems of poor conductivity and poor electrochemical performance of the active substance of the electrode material in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of composite electrode materials, and particularly to a sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material and a preparation method thereof. Background Art

[0002] So far, lithium - ion batteries are still the most widely commercialized batteries. However, with the development and progress of society, their relatively low energy density (200 - 250 Wh / kg) can no longer meet the requirements of society for high - energy - density batteries. Therefore, it is urgent to explore new high - energy - density battery systems. Among various battery systems, lithium - sulfur batteries have received the most attention. Their high energy density (2600 Wh / kg) and volumetric density (2800 Wh / L) are twice that of commercial lithium - ion batteries. The sulfur cathode has a theoretical capacity of 1675 mAh / g and is also inexpensive and environmentally friendly, thus also attracting much attention. However, lithium - sulfur batteries have some inherent defects that hinder their further development: 1) The shuttle effect of intermediate products (polysulfides) leads to the generation of irreversible capacity, reduces the Coulombic efficiency, and greatly limits their cycle stability; 2) The poor electron / ion conductivity of active materials sulfur and lithium sulfide reduces the electro - chemical reaction kinetics, resulting in low utilization rate of active materials and rate performance; 2) During the process of converting elemental sulfur into lithium sulfide, the volume expansion rate is about 80%, which easily causes the destruction and pulverization of the cathode structure, reducing its cycle performance. To address the above problems, the following several strategies are mainly adopted to modify the sulfur cathode: 1) Composite sulfur with highly conductive substances such as carbon materials to improve the electron conductivity of active materials; 2) Composite with polar compounds such as metals, oxides, carbides, sulfides, etc. to adsorb soluble polysulfides, thereby inhibiting their shuttle effect; 3) Construct a porous structure to increase the reaction area between active materials and electrolytes, improve their utilization rate, and thus improve their electro - chemical performance. Among them, composite the active material sulfur with highly conductive porous carbon materials is a relatively effective modification method. Therefore, it is very necessary to invent a new type of porous carbon material suitable for large - scale production and with high conductivity, which is also a good way to improve the electro - chemical performance of the sulfur cathode. Summary of the Invention

[0003] To solve the above - mentioned technical problems, the purpose of the present invention is to provide a sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material and a preparation method thereof, so as to solve the problems of poor conductivity of active materials and poor electro - chemical performance of electrode materials in the prior art.

[0004] The technical solution of the present invention to solve the above - mentioned technical problems is as follows: Provide a preparation method of a sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material, including the following steps:

[0005] (1) adding peeled citrus pulp into deionized water, heating at 120-180° C. for 10-30 min, then soaking in a glucose aqueous solution of a transition metal chloride salt, performing a replacement reaction for 10-16 h, and then performing a hydrothermal reaction to obtain a citrus pulp precursor;

[0006] (2) freeze-drying the citrus pulp precursor obtained in step (1), preheating it under an inert gas at 400-600° C. for 3-6 h, sintering it into a phase, and cooling it to room temperature to obtain a citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material;

[0007] (3) The citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material obtained in step (3) and sulfur are uniformly mixed, subjected to a hydrothermal reaction, and then cooled to room temperature to obtain a sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material.

[0008] The beneficial effects of the present invention are as follows: the composite electrode material of the present invention is composited by sulfur, citrus pulp-derived carbon and transition metal nanoparticles, wherein the citrus pulp-derived carbon is obtained by high-temperature carbonization after hydrothermal crosslinking of ordinary citrus pulp, and the transition metal nanoparticles are uniformly embedded in the citrus pulp-derived carbon. The metal content of the composite electrode material and the chemical composition and microstructure of the citrus pulp-derived carbon can be controlled by precursor concentration and reaction conditions.

[0009] The sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material prepared by the present invention has a hierarchical porous structure, high porosity and specific surface area, can greatly increase the sulfur storage space of active substance sulfur, improve the utilization rate of active substance, shorten the transmission distance of electrons and ions, and accelerate the overall electrochemical reaction kinetics; at the same time, the presence of metal nanoparticles can effectively anchor polysulfides, inhibit their shuttle effect, reduce the loss of active substances, enhance their cycle performance and Coulomb effect, and contribute to the development of new sulfur positive electrode materials with high energy density and high rate performance. The composite electrode material of the present invention has high discharge capacity, high energy density and long cycle life, and can be widely used in the fields of transportation, aerospace and aviation.

[0010] On the basis of the above technical solution, the present invention can also be improved as follows:

[0011] Further, in step (1), the citrus fruit is grapefruit or orange

[0012] Furthermore, in step (1), the mass volume ratio of citrus pulp and deionized water is 8-12 g:100 mL.

[0013] Further, it is characterized in that in step (1), the glucose aqueous solution of the transition metal chloride is prepared by the following method: mixing the transition metal chloride, glucose and deionized water to obtain the glucose aqueous solution of the transition metal chloride; wherein, the mass-volume ratio of the transition metal chloride, glucose and deionized water is 0.2 - 0.5 g: 2 - 4 g: 100 mL.

[0014] Further, in step (1), the transition metal is at least two of nickel, cobalt, iron, copper and zinc.

[0015] Further, the diameter of the transition metal is 10 - 50 nm.

[0016] Further, in steps (1) and (3), the conditions of the hydrothermal reaction are both: reacting at 160 - 200 °C for 12 - 16 h.

[0017] Further, in step (2), sintering is carried out at 600 - 900 °C for 2 - 4 h to form a phase.

[0018] Further, in step (2), the inert gas is argon.

[0019] Further, in step (3), the mass ratio of the citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material to sulfur is 1: 1 - 1.5.

[0020] The present invention also provides a composite electrode material prepared by the preparation method of the above sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material.

[0021] Further, the sulfur content in the composite electrode material is 50 - 60 wt%, the citrus fruit pulp-derived carbon content is 48 - 35 wt%, and the metal alloy content is 2 - 5 wt%.

[0022] The present invention also provides the application of the above sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material in the preparation of a lithium-sulfur battery positive electrode.

[0023] The present invention has the following beneficial effects:

[0024] 1. The present invention uses the citrus fruit pulp-derived carbon as the sulfur host material, and prepares the citrus fruit pulp-derived carbon / metal alloy nanoparticle composite material by solution replacement, hydrothermal reaction and in combination with carbothermal reduction method, and then composites the active substance sulfur with it by the sulfur infiltration method. The whole preparation process is relatively simple, the cost is low, and it has extremely strong versatility.

[0025] 2. The sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material prepared by the present invention can effectively improve the conductivity of the electrode, accelerate the electro - chemical reaction kinetics, has good polar interactions with polysulfides, improve its anchoring effect on polysulfides, and relieve volume expansion and other advantages, strengthening the electro - chemical performance of the sulfur cathode from all aspects.

[0026] 3. The sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material prepared by the present invention has a hierarchical porous structure, with a high specific surface area, high cycle stability, rate performance and Coulomb efficiency, etc. It is suitable as a cathode material for lithium - sulfur batteries. This composite cathode improves the rate performance and cycle performance of lithium - sulfur batteries, contributing to the development of high - energy - density and high - stability lithium - sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a scanning electron microscope image of the composite electrode material prepared in Example 1;

[0028] Figure 2 It is a scanning electron microscope image of the composite electrode material prepared in Example 1;

[0029] Figure 3 It is a transmission electron microscope image of the composite electrode material prepared in Example 1;

[0030] Figure 4 It is a galvanostatic charge - discharge test chart of the composite electrode materials prepared in Example 1 and Comparative Examples 1 - 2;

[0031] Figure 5 It is a cycle performance chart of the composite electrode materials prepared in Example 1 and Comparative Examples 1 - 2. DETAILED DESCRIPTION OF THE INVENTION

[0032] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0033] Example 1:

[0034] A sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material, and its preparation method includes the following steps:

[0035] (1) Mix nickel chloride, cobalt chloride, glucose and deionized water to prepare an aqueous glucose solution of transition metal chloride; wherein, the mass - to - volume ratio of transition metal chloride, glucose and deionized water is 0.3 g: 3 g: 100 mL, and the diameter of the transition metal is 30 nm;

[0036] (2) Add 10 g of peeled pomelo pulp to 100 mL of deionized water, heat it at 160 °C for 20 min, take it out, and obtain inactivated pomelo pulp. Then soak it in the glucose aqueous solution of transition metal chloride prepared in step (1) for a displacement reaction for 14 h to obtain pomelo pulp with a glucose aqueous solution of transition metal chloride filled inside. Transfer the above pomelo pulp and the glucose aqueous solution of transition metal chloride outside the pulp to a hydrothermal reaction kettle, and carry out hydrothermal reaction at 180 °C for 14 h to obtain a citrus fruit pulp precursor;

[0037] (3) Freeze the citrus fruit pulp precursor prepared in step (2) at -60 °C for 12 h, then carry out freeze-drying, then preheat it at argon and 500 °C for 4 h, and then sinter it at 800 °C for 3 h, and cool it to room temperature to obtain a citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material;

[0038] (4) Mix the citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material prepared in step (4) and sulfur in a mass ratio of 1:1 evenly, carry out hydrothermal reaction at 180 °C for 13 h, and then cool it to room temperature to prepare a sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material.

[0039] Example 2:

[0040] A sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material, and its preparation method includes the following steps:

[0041] (1) Mix nickel chloride, iron chloride, glucose and deionized water to prepare a glucose aqueous solution of transition metal chloride; wherein, the mass-volume ratio of transition metal chloride, glucose and deionized water is 0.2 g: 2 g: 100 mL, and the diameter of the transition metal is 10 nm;

[0042] (2) Add 8 g of peeled orange pulp to 100 mL of deionized water, heat it at 120 °C for 30 min, take it out, and obtain inactivated orange pulp. Then soak it in the glucose aqueous solution of transition metal chloride prepared in step (1) for a displacement reaction for 10 h to obtain orange pulp with a glucose aqueous solution of transition metal chloride filled inside. Transfer the above orange pulp and the glucose aqueous solution of transition metal chloride outside the pulp to a hydrothermal reaction kettle, and carry out hydrothermal reaction at 160 °C for 16 h to obtain a citrus fruit pulp precursor;

[0043] (3) After freezing the citrus fruit pulp precursor obtained in step (2) at -60 °C for 12 h, freeze-dry it, then preheat it under argon and at 400 °C for 6 h, and then sinter it into a phase at 600 °C for 4 h, and cool it to room temperature to obtain a citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material;

[0044] (4) Mix the citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material obtained in step (4) and sulfur in a mass ratio of 1:1.2 evenly, carry out a hydrothermal reaction at 160 °C for 16 h, and then cool it to room temperature to obtain a sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material.

[0045] Example 3:

[0046] A sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material, and its preparation method includes the following steps:

[0047] (1) Mix copper chloride, zinc chloride, glucose and deionized water to prepare an aqueous glucose solution of transition metal chloride; wherein, the mass-volume ratio of transition metal chloride, glucose and deionized water is 0.5 g: 4 g: 100 mL, and the diameter of the transition metal is 50 nm;

[0048] (2) Add 12 g of peeled pomelo pulp to 100 mL of deionized water, heat it at 180 °C for 10 min, take it out to obtain inactivated pomelo pulp, then soak it in the aqueous glucose solution of transition metal chloride prepared in step (1), carry out a displacement reaction for 16 h to obtain pomelo pulp filled with the aqueous glucose solution of transition metal chloride inside, transfer the above pomelo pulp and the aqueous glucose solution of transition metal chloride outside the pulp to a hydrothermal reaction kettle, and carry out a hydrothermal reaction at 200 °C for 1 h to obtain a citrus fruit pulp precursor;

[0049] (3) After freezing the citrus fruit pulp precursor obtained in step (2) at -60 °C for 12 h, freeze-dry it, then preheat it under argon and at 600 °C for 3 h, and then sinter it into a phase at 900 °C for 2 h, and cool it to room temperature to obtain a citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material;

[0050] (4) Mix the citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material obtained in step (4) and sulfur in a mass ratio of 1:1.5 evenly, carry out a hydrothermal reaction at 200 °C for 12 h, and then cool it to room temperature to obtain a sulfur-citrus fruit pulp-derived carbon / metal alloy nanoparticle composite electrode material. Comparative Example 1:

[0051] A sulfur - citrus pulp - derived carbon / metal nanoparticle composite electrode material, and its preparation method includes the following steps: In step (1), there is only nickel chloride and no cobalt chloride, and the rest is the same as in Example 1.

[0052] Comparative Example 2:

[0053] A sulfur - citrus pulp - derived carbon composite electrode material, and its preparation method includes the following steps: The inactivated pomelo pulp is subjected to a displacement reaction in an aqueous glucose solution not soaked with transition metal chloride, and the rest is the same as in Example 1.

[0054] Test Example

[0055] I. The sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material prepared in Example 1 is subjected to scanning electron microscopy and transmission electron microscopy tests, and the results are shown in Figures 1-3 . It can be seen from Figures 1-3 that the electrode material prepared by the present invention has a hierarchical porous structure. The present invention increases the loading amount of the active substance sulfur and also increases the contact area between the electrode surface and the electrolyte; both the citrus pulp - derived carbon and the metal nanoparticles have high electronic conductivity, which improves the conductivity of the electrode and accelerates the interfacial reaction; the citrus pulp - derived carbon has in - situ doped phosphorus and nitrogen elements, providing adsorption sites for polysulfides, and synergistically with the polar metal nanoparticles to inhibit the shuttle effect of polysulfides, thereby improving the rate and cycle performance of the electrode.

[0056] II. Performance Test

[0057] The electrode materials prepared in Example 1 and Comparative Examples 1 - 2 are subjected to discharge capacity, rate performance, and long - cycle performance tests. The specific detection method is as follows: The prepared electrode material is used as the positive electrode, metallic lithium is used as the negative electrode, and Celgard 2400 cellulose membrane is used as the separator. They are assembled into a CR2025 coin - type battery. The electrolyte used is a 1 mol / L LiTFSI solution (the solvent is a mixed solution of 1,3 - dioxolane and ethylene glycol dimethyl ether with a volume ratio of 1:1), and then a constant - current charge - discharge test is carried out on a Neware battery test system. The voltage window is 1.7 - 2.8 V (vs Li / Li + ), the rate performance current density range is 0.1 - 3 C, and the cycling test current is 0.1 C. The results are shown in Figures 4-5 .

[0058] It can be seen from Figure 4 that at a high current density of 5 C, the discharge capacity of the electrode material prepared in Example 1 is 741 mAh / g; while the discharge capacities of the electrode materials prepared in Comparative Example 1 and Comparative Example 2 are 625 mAh / g and 371 mAh / g respectively. It can be seen that the electrode material prepared by the present invention has high high - rate performance and excellent electrochemical performance at high currents.

[0059] It can be seen fromFigure 5 As can be seen from (Example 1, Comparative Example 1, and Comparative Example 2 from bottom to top), at a current density of 2C, the discharge capacity of the electrode material prepared in Example 1 is 868 mAh / g, and after 200 cycles, the capacity retention rates are 73.1%; while the discharge capacities of the electrode materials prepared in Comparative Example 1 and Comparative Example 2 are 655 mAh / g and 511 mAh / g respectively, and after 200 cycles, the capacity retention rates are 59.6% and 50.9% respectively. It can be seen that the electrode material prepared by the present invention has good long-cycle performance, greatly improving the cycle life of the battery.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material, characterized in that, The following steps are involved: (1) adding the peeled citrus pulp into deionized water, heating it at 120-180° C. for 10-30 min, then soaking it in a glucose aqueous solution of a transition metal chloride, performing a replacement reaction for 10-16 h, and then performing a hydrothermal reaction to obtain a citrus pulp precursor; (2) freeze-drying the citrus pulp precursor obtained in step (1), preheating it under an inert gas at 400-600° C. for 3-6 hours, sintering it into a phase, and cooling it to room temperature to obtain a citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material; (3) mixing the citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material and sulfur obtained in step (2) evenly, performing a hydrothermal reaction, and then cooling to room temperature to obtain a sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material; In step (1), the transition metal is at least two of nickel, cobalt, iron, copper and zinc; In step (1), the conditions of the hydrothermal reaction are: 160-200° C. for 12-16 h.

2. The preparation method of the sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to claim 1, characterized in that, In step (1), the citrus fruit is grapefruit or orange.

3. The preparation method of the sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to claim 1, characterized in that, In step (1), the mass volume ratio of citrus pulp and deionized water is 8-12 g:100 mL.

4. The preparation method of the sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material according to claim 1, characterized in that, In step (1), the glucose aqueous solution of transition metal chloride is prepared by the following method: mixing transition metal chloride, glucose and deionized water to prepare the glucose aqueous solution of transition metal chloride; wherein the mass volume ratio of transition metal chloride, glucose and deionized water is 0.2-0.5g:2-4g:100mL.

5. The preparation method of the sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to claim 1, characterized in that In step (3), the conditions of the hydrothermal reaction are: 160-200° C. for 12-16 h.

6. The preparation method of the sulfur - citrus pulp - derived carbon / metal alloy nanoparticle composite electrode material according to claim 1, characterized in that, In step (3), the mass ratio of the citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material to sulfur is 1:1-1.

5.

7. Sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material prepared according to the preparation method of sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to any one of claims 1 to 6.

8. The sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to claim 7, wherein, The composite electrode material has a sulfur content of 50-60wt%, a citrus pulp-derived carbon content of 48-35wt%, and a metal alloy content of 2-5wt%.

9. Use of the sulfur-citrus pulp-derived carbon / metal alloy nanoparticle composite electrode material according to claim 7 or 8 in preparing a positive electrode for a lithium-sulfur battery.

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