Process for the preparation of a bi-active self-supporting electrode

Abstract

The application discloses a preparation method of a double-active-material self-supporting electrode, and the double-active-material self-supporting electrode is composed of a porous self-supporting active material and another active material filled in the pores of the former; the porous self-supporting active material is interlaced porous plate-shaped lithium vanadium phosphate obtained through biomass soft template derivation, and the active material filled in the pores is sulfur or a derivative thereof. The preparation steps comprise the following steps: taking biomass as a template, uniformly attaching active material lithium vanadium phosphate precursors on the template, performing freeze drying, and finally performing carbonization and template removal and crystallization processes through inert atmosphere sintering to obtain the porous self-supporting lithium vanadium phosphate; loading sulfur or derivative lithium polysulfide on the porous self-supporting lithium vanadium phosphate; and then the double-active-material self-supporting electrode can be applied to a lithium-sulfur battery. The method is simple and environment-friendly, has high sulfur loading density, good cycle performance and high mechanical strength, and the second active material lithium vanadium phosphate can also contribute to additional capacity, thereby effectively improving the energy density of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the technical field of energy storage electrode material preparation methods, specifically relating to a method for preparing a self-supporting electrode with dual active materials. Background Technology

[0002] Lithium-sulfur batteries, as one of the new energy storage devices, have an ultra-high theoretical energy density (2600Wh / kg). -1 2800Wh L -1 In contemporary society, where high-energy-density energy storage devices are highly sought after, elemental sulfur has significant application potential and is abundant and environmentally friendly, thus possessing natural advantages in terms of cost and energy density. However, the insulation, expansion, and polysulfide "shuttle" effect of sulfur as the active material increases with the increase of sulfur loading, severely limiting the improvement of energy density in traditional sulfur-coated cathodes. To address these issues and achieve higher energy density than traditional lithium-sulfur coated cathodes, researchers have proposed a modification strategy based on the traditional method of modifying active materials sulfur and carbon materials in coated cathodes. This strategy uses conductive materials as the framework structure, on which a large amount of active material sulfur is loaded, thereby further improving the performance indicators of lithium-sulfur batteries. However, at present, the main self-supporting materials are mostly carbon materials, meaning that the cathode material accounts for a very low proportion of the total cell mass. Furthermore, carbon materials contribute almost no capacity within the 1.7–2.8V operating voltage window of lithium-sulfur batteries, resulting in a decrease in the specific energy index, which is based on the total cell mass. In addition, traditional self-supporting carbon materials are mostly amorphous carbon, making it difficult to combine a porous structure with excellent structural strength. Therefore, the commercial application of self-supporting lithium-sulfur batteries is difficult to achieve.

[0003] Lithium vanadium phosphate, as one of the cathode materials for lithium-ion batteries, has a wider redox potential window (1.4–4.8 V) and a higher theoretical specific capacity (132 mAh g⁻¹) compared to currently commercialized electrode materials. -1 , 1.4~3.0V; 197mAh g -1Lithium vanadium phosphate (Livanadium phosphate) possesses a high-voltage (3.0–4.8V) and a highly covalent three-dimensional structure that provides a high-speed channel for lithium-ion insertion / extraction reactions. Furthermore, its excellent structural stability, safety, and low cost make it a significant advantage as a novel high-energy-density lithium-ion battery cathode material. However, Livanadium phosphate suffers from low intrinsic conductivity and unstable interfacial properties at high voltages (>4.5V), affecting its rate capability and cycle performance. To address these issues, researchers typically improve Livanadium phosphate's performance through modifications such as carbon material composites, metal ion doping, and particle size refinement. Among these, low-cost biomass-derived carbon materials offer advantages such as low density, excellent electrical and thermal conductivity, stable physicochemical properties, and ease of structural control. They can also act as reducing agents during carbonization to simplify the sintering atmosphere and serve as soft and hard templates to impart different structural morphologies to electrode materials. Currently, the application of biomass in the fabrication of environmentally friendly and sustainable novel energy storage devices has become a research hotspot. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a self-supporting electrode with dual active materials, which solves the problem of low energy density in traditional sulfur-loaded cathode materials.

[0005] The technical solution adopted in this invention is: a method for preparing a dual-active-material self-supporting electrode, which uses biomass as a template, uniformly attaches the active material lithium vanadium phosphate precursor onto the biomass template, and then freeze-dries it. Finally, the carbonization, template removal, and crystallization process is completed by sintering in an inert atmosphere to obtain porous self-supporting lithium vanadium phosphate. Sulfur or its derivative lithium polysulfide is loaded onto the porous self-supporting lithium vanadium phosphate to obtain a dual-active-material self-supporting electrode that can be applied to lithium-sulfur batteries.

[0006] The invention is further characterized in that,

[0007] The specific steps for preparing a self-supporting electrode with dual active materials are as follows:

[0008] Step 1: Disperse the biomass and lithium source in the solvent under constant temperature stirring, then add vanadium source and phosphorus source, and add lithium source again to adjust the pH;

[0009] Step 2: Add solvent to the solution obtained in Step 1 again, stir and evaporate, pre-freeze the obtained product and then freeze-dry it to obtain a porous self-supporting lithium vanadium phosphate precursor.

[0010] Step 3: Press the porous self-supporting lithium vanadium phosphate precursor obtained in Step 2 between two layers of graphite plates and sinter it in a reducing atmosphere furnace to obtain porous self-supporting lithium vanadium phosphate.

[0011] Step 4: Load sulfur into the porous self-supporting lithium vanadium phosphate obtained in Step 3 to obtain a dual-active-material self-supporting electrode.

[0012] Preferably, in step 1, the biomass includes, but is not limited to, glucomannan, amylose, and bacterial cellulose; the solvent includes, but is not limited to, deionized water, anhydrous ethanol, and ethyl acetate; the constant temperature stirring range is 50–100°C; the stirring time is 2–48 h; and the pH is adjusted to 6–8 after adding the lithium source.

[0013] Preferably, the stirring evaporation in step 2 refers to evaporating the solvent to 1 / 20 to 1 / 2 of the volume after adding the solvent again; the pre-freezing is pre-freezing at -30 to -10℃ for 12 to 24 hours; and the freeze drying is drying at -60 to -40℃ for 12 to 36 hours.

[0014] Preferably, step 2 loading includes starting loading before or during freeze-drying, and loading is performed by loading a weighted object on top of the product that has an adjusting effect on the thickness of the freeze-dried product.

[0015] Preferably, the heating rate in step 3 is 2-10℃ / min, the low-temperature pre-sintering is 200-400℃ for 3-6 hours, and the high-temperature sintering is 700-900℃ for 3-12 hours; the thickness of the porous self-supporting lithium vanadium phosphate is 400-1000μm.

[0016] Preferably, the sulfur loading method in step 4 is as follows: sulfur powder is coated onto porous self-supporting lithium vanadium phosphate, wherein the mass ratio of sulfur powder to porous self-supporting lithium vanadium phosphate is 0.1 to 2:1; the temperature is raised to 20 to 60°C above the melting point of sulfur and held for 12 to 24 hours, followed by cooling; or during battery assembly, a DOL / DME mixed solution containing 0.05 to 0.2 g / mL of Li₂S₈ is dropped into the porous self-supporting lithium vanadium phosphate; the carbon content of the dual-active material self-supporting electrode is in the range of 0 to 5 wt.%.

[0017] The beneficial effects of this invention are:

[0018] (1) This invention employs a liquid-phase preparation method, utilizing biomass as a carbon source to improve the conductivity of lithium vanadium phosphate while simultaneously increasing V 5+ Restore to V 3+ This method allows for the one-step preparation of porous, self-supporting lithium vanadium phosphate. The preparation method is simple and requires no additional reducing reagents. It boasts low production costs, widely available raw materials, and good biocompatibility, making it an effective example of achieving sustainable development using renewable biomaterials.

[0019] (2) This invention utilizes the special structural characteristics of biomass soft templates to form an interlocking porous plate-like structure after carbonization, so that the lithium vanadium phosphate grown on it has similar structural characteristics, providing an effective channel for electrolyte wetting and long-distance electron transport. The porous self-supporting lithium vanadium phosphate prepared in this way has good electrochemical performance.

[0020] (3) The framework of the dual-active-material self-supporting electrode designed in this invention—the porous self-supporting lithium vanadium phosphate—possesses excellent structural strength due to the high crystallinity imparted by the sintering process. Combined with its porous characteristics, it can serve as a self-supporting framework structure for high-density active material sulfur loading. The interconnected conductive network, due to its multi-channel and multi-active-site structure, will not be blocked by the highly insulating elemental sulfur or lithium sulfide during charging and discharging, thus providing sufficient electron supply for electrochemical reactions.

[0021] (4) Compared with traditional slurry-coated electrodes, the dual-active-material self-supporting electrode designed in this invention simplifies the electrode preparation process, avoids the addition of additional binders, conductive agents and current collectors, improves the energy density of the battery, and can load more sulfur active materials.

[0022] (5) The sulfur-loaded framework of the dual-active-material self-supporting electrode designed in this invention is a porous self-supporting lithium vanadium phosphate, which can undergo polar adsorption with the polysulfides generated during the charging and discharging of lithium-sulfur batteries, thereby suppressing the occurrence of the "shuttle" effect and effectively improving the cycle stability of lithium-sulfur batteries.

[0023] (6) The dual active material self-supporting electrode designed in this invention uses lithium vanadium phosphate as the framework material. Compared with the traditional carbon material self-supporting framework, the former can also provide capacity within the working voltage window of the lithium-sulfur battery, thus effectively improving the actual energy density of the lithium-sulfur battery. Attached Figure Description

[0024] Figure 1 Electrochemical performance of porous self-supporting lithium vanadium phosphate prepared in the embodiments of the present invention;

[0025] Figure 2(a) shows the morphology of the porous self-supporting lithium vanadium phosphate precursor prepared in the embodiment of the present invention at a scale bar of 1 cm.

[0026] Figure 2(b) shows the morphology of the porous self-supporting lithium vanadium phosphate precursor prepared in the embodiment of the present invention at a scale bar of 1 μm;

[0027] Figure 3(a) is a schematic diagram of the morphology of the porous self-supporting lithium vanadium phosphate prepared in the embodiment of the present invention before sintering.

[0028] Figure 3(b) is a schematic diagram of the morphology of the porous self-supporting lithium vanadium phosphate prepared in the embodiment of the present invention after sintering. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0030] Example 1

[0031] Step 1: Disperse amylose and lithium hydroxide in deionized water, stir at 50°C for 2 hours to form a sol, add vanadium pentoxide and ammonium dihydrogen phosphate and stir for 2 hours, and add an appropriate amount of lithium acetate to adjust the pH to about 6.0.

[0032] Step 2: Add ethanol to the solution obtained in Step 1 and stir for 6 hours. Then, stir and evaporate the solution to 1 / 20 of the volume after adding solvent again. Pre-freeze the product at -10℃ for 12 hours and then freeze-dry it at -60℃ for 48 hours to obtain a porous self-supporting lithium vanadium phosphate precursor.

[0033] Step 3: Press the porous self-supporting lithium vanadium phosphate precursor obtained in Step 2 between two graphite plates, and pre-decompose it at 200℃ for 6 hours and sinter it at 700℃ for 12 hours in an argon atmosphere furnace with a heating rate of 10℃ / min to obtain a porous self-supporting lithium vanadium phosphate with a thickness of about 400μm.

[0034] Electrochemical performance tests were conducted on the porous self-supporting lithium vanadium phosphate prepared in Example 1, demonstrating its excellent electrochemical performance as a framework material. The results are as follows: Figure 1 As shown, it exhibits excellent rate performance at current densities ranging from 0.1 to 10C. The initial discharge specific capacity at 0.1C without activation is as high as 128.12 mAh / g (97.06% of the theoretical specific capacity), and the discharge specific capacity at a current density 100 times higher than 0.1C (10C) is 78.88 mAh / g, with a capacity retention rate of 61.57%, and it remains basically stable after five cycles.

[0035] Example 2

[0036] Step 1: Disperse glucomannan and lithium acetate in deionized water, stir at 70°C for 48 hours to form a sol, add vanadium pentoxide and ammonium dihydrogen phosphate and stir for 6 hours, and add an appropriate amount of lithium hydroxide to adjust the pH to about 7.0.

[0037] Step 2: Add ethyl acetate to the solution obtained in Step 1 and stir for 6 hours. Then, stir and evaporate to 1 / 5 of the volume after adding solvent again. Pre-freeze the obtained product at -20℃ for 16 hours and then freeze-dry at -50℃ for 24 hours to obtain a porous self-supporting lithium vanadium phosphate precursor derived from glucomannan.

[0038] Step 3: Press the porous self-supporting lithium vanadium phosphate precursor obtained in Step 2 between two graphite plates, and pre-decompose it at 250℃ for 6 hours and sinter it at 800℃ for 6 hours in an argon atmosphere furnace with a heating rate of 5℃ / min to obtain a porous self-supporting lithium vanadium phosphate with a thickness of about 300μm.

[0039] Step 4: The porous self-supporting lithium vanadium phosphate is placed into a glove box, and 60 μL of a DOL / DME mixed solution containing 0.2 g / mL Li2S8 is added. After standing, a dual-active material self-supporting cathode is obtained.

[0040] The morphology of the porous self-supporting lithium vanadium phosphate precursor prepared in Example 2 is as follows: Figure 2(a)-Figure 2(b) As shown, the lithium vanadium phosphate precursor and biomass material together form an interwoven plate-like structure, and the changes in the skeleton before and after sintering are as follows: Figures 3(a)-3(b) As shown, biomass materials are carbonized at high temperatures, turning V... 5+ Restore to V 3+ Lithium vanadium phosphate is generated, and the framework shrinks. The electrochemical performance of the self-supporting cathode with dual active materials prepared in Example 2 was tested, and the first-cycle discharge specific capacity at 0.1C was 1472.2 mAh / g.

[0041] Example 3

[0042] Step 1: Disperse bacterial cellulose and lithium carbonate in deionized water, stir at 90°C for 12 hours to form a sol, add vanadium pentoxide and ammonium dihydrogen phosphate and stir for 12 hours, and add an appropriate amount of lithium hydroxide to adjust the pH to about 8.0.

[0043] Step 2: Add deionized water to the solution obtained in Step 1 and stir for 12 hours. Then, stir and evaporate the solution to half the volume after adding solvent again. Pre-freeze the product at -30°C for 24 hours and then freeze-dry it at -40°C for 12 hours to obtain a porous self-supporting lithium vanadium phosphate precursor derived from bacterial cellulose.

[0044] Step 3: Press the porous self-supporting lithium vanadium phosphate precursor obtained in Step 2 between two graphite plates, and pre-decompose it at 400℃ for 3 hours and sinter it at 900℃ for 3 hours in an argon atmosphere furnace with a heating rate of 2℃ / min to obtain a porous self-supporting lithium vanadium phosphate with a thickness of about 400μm.

[0045] Step 4: Put sulfur powder and porous self-supporting lithium vanadium phosphate into a sealed container at a mass ratio of 0.4, heat to 160℃ and keep warm for 12 hours, and obtain a dual-active-material self-supporting positive electrode after natural cooling.

[0046] The electrochemical performance of the self-supporting positive electrode with dual active materials prepared in Example 3 was tested. The discharge specific capacity after 200 cycles at 0.1C was 1201.2 mAh / g, and the discharge specific capacities at 0.1C, 0.2C, 0.5C and 1C were 1405.4 mAh / g, 1118.2 mAh / g, 972.8 mAh / g and 838.4 mAh / g, respectively.

[0047] The key innovation of this invention lies in:

[0048] 1. A self-supported electrode using lithium vanadium phosphate / sulfur dual active materials was constructed. Lithium vanadium phosphate, an active material with a wide voltage window and the ability to suppress the "shuttle" effect, was selected and constructed into a porous self-supporting material. Its electrochemical window was then adapted to that of sulfur, thus constructing a self-supported electrode using dual active materials. This electrode combines the high sulfur loading of a carbon-based self-supported sulfur-loaded cathode with the ability to provide additional capacity by replacing the carbon material, which cannot provide capacity within the operating voltage window of a lithium-sulfur battery, with lithium vanadium phosphate.

[0049] 2. A porous, self-supporting lithium vanadium phosphate with excellent electrochemical performance and mechanical strength was constructed. Inexpensive, readily available, environmentally friendly, and harmless biomass carbon sources such as glucomannan, amylose, and bacterial biomass were used as liquid-phase growth templates for lithium vanadium phosphate. Near-net-net removal of the biomass template was achieved during carbonization (carbon content controlled between 0 and 5 wt.%). Based on the original biomass template structure, the final structure was controlled through the preparation process, endowing the porous, self-supporting lithium vanadium phosphate with excellent electrochemical and mechanical properties.

[0050] 3. The reason why this invention uses glucomannan, amylose and bacterial cellulose as biomass carbon sources is: (1) the above biomass is cheap and readily available, and environmentally friendly and harmless; (2) the above biomass is dispersed in a solvent, which can provide attachment sites for lithium vanadium phosphate; (3) the above biomass can be removed in subsequent processes; (4) the above biomass has a modifying effect on the electrochemical performance of lithium vanadium phosphate; (5) the specific structure formed by the above biomass and lithium vanadium phosphate can be controlled by subsequent processes, and can achieve sulfur loading function while having excellent electrochemical performance.

[0051] 4. The key to forming a precursor suitable for a dual-active-material self-supporting electrode in the method of this invention lies in selecting a suitable biomass template and supplementing it with subsequent control processes. The structure of the material affects its performance. In this invention, the essence of steps 1-3 is to control the structure of the material: step 1 achieves the formation of the biomass template and the attachment of the lithium vanadium phosphate precursor; step 2 achieves the control and maintenance of the density of the specific structure formed in step 1; and step 3 achieves the final shaping of the specific structure.

Claims

1. A method for the preparation of a dual active species self-supporting electrode, characterized in that, Using biomass as a template, an active material lithium vanadium phosphate precursor is uniformly attached to the biomass template and then freeze-dried. Finally, carbonization, template removal, and crystallization are completed by sintering in an inert atmosphere to obtain porous self-supporting lithium vanadium phosphate. Sulfur or its derivative lithium polysulfide is loaded onto the porous self-supporting lithium vanadium phosphate to obtain a dual-active-material self-supporting electrode that can be used in lithium-sulfur batteries.

2. A method for the preparation of a bi-active self-supporting electrode, characterized in that, The specific steps are as follows: Step 1: Disperse the biomass and lithium source in the solvent under constant temperature stirring, then add vanadium source and phosphorus source, and add lithium source again to adjust the pH; Step 2: Add solvent to the solution obtained in Step 1 again, stir and evaporate, pre-freeze the obtained product and then freeze-dry it to obtain a porous self-supporting lithium vanadium phosphate precursor. Step 3: Press the porous self-supporting lithium vanadium phosphate precursor obtained in Step 2 between two layers of graphite plates and sinter it in a reducing atmosphere furnace to obtain porous self-supporting lithium vanadium phosphate. Step 4: Load sulfur into the porous self-supporting lithium vanadium phosphate obtained in Step 3 to obtain a dual-active-material self-supporting electrode.

3. The method for preparing a dual-active-material free-standing electrode according to claim 2, wherein The biomass in step 1 includes glucomannan, amylose, and bacterial cellulose; the solvent includes deionized water, anhydrous ethanol, and ethyl acetate; the constant temperature stirring range is 50–100°C; the stirring time is 2–48 h; and the pH is adjusted to 6–8 after adding the lithium source.

4. The method for preparing a dual-active-material free-standing electrode according to claim 2, wherein The stirring evaporation mentioned in step 2 refers to evaporating the solvent to 1 / 20 to 1 / 2 of the volume after adding the solvent again; the pre-freezing refers to pre-freezing at -30 to -10℃ for 12 to 24 hours; the freeze drying refers to drying at -60 to -40℃ for 12 to 36 hours.

5. The method for preparing a self-supporting electrode with dual active materials according to claim 2, characterized in that, The loading described in step 2 includes starting loading before or during freeze-drying, and loading in a manner that involves loading a weighted object on top of the product to adjust the thickness of the freeze-dried product.

6. The method for preparing a self-supporting electrode with dual active materials according to claim 2, characterized in that, The heating rate for the sintering in step 3 is 2-10℃ / min, the low-temperature pre-sintering is 200-400℃ for 3-6 hours, and the high-temperature sintering is 700-900℃ for 3-12 hours; the thickness of the porous self-supporting lithium vanadium phosphate is 400-1000μm.

7. The method for preparing a self-supporting electrode with dual active materials according to claim 5, characterized in that, The sulfur loading method in step 4 is as follows: sulfur powder is coated onto porous self-supporting lithium vanadium phosphate, wherein the mass ratio of sulfur powder to porous self-supporting lithium vanadium phosphate is 0.1 to 2:1; the temperature is raised to 20 to 60°C above the melting point of sulfur and held for 12 to 24 hours, then cooled; or during battery assembly, a DOL / DME mixed solution containing 0.05 to 0.2 g / mL of Li₂S₈ is dropped into the porous self-supporting lithium vanadium phosphate; the carbon content of the dual-active material self-supporting electrode ranges from 0 to 5 wt.%.

Images