A hard carbon-molybdenum sulfide heterojunction material and a light charging sodium ion battery based on the material

Abstract

The application discloses a hard carbon-molybdenum sulfide heterojunction material and a light charging sodium ion battery based on the material. The synthesis method of the hard carbon-molybdenum sulfide heterojunction material comprises the following steps: 1) mixing water and ethanol to obtain a mixed solvent; 2) adding HC into the mixed solvent to obtain a carbon sphere dispersion liquid; adding MoO3 and CH4N2S into the mixed solvent, and dissolving to obtain a MoO3 / thiourea solution; 3) adding the MoO3 / thiourea solution into the carbon sphere dispersion liquid to obtain a mixed solution; and 4) heating the mixed solution at 180-220 DEG C, and washing, drying and calcining the product after cooling to obtain the HC-MoS2 heterojunction material. The application designs a bifunctional electrode material HC-MoS2 in which few-layer MoS2 nanosheets are uniformly anchored on hard carbon. The PSIBs based on the HC-MoS2 composite material exhibit excellent light charging performance, including stable cycle performance and high energy storage capacity under light.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a hard carbon-molybdenum sulfide heterojunction material and a photochargeable sodium-ion battery based on the material. Background Technology

[0002] In the context of the global energy transition, solar power, as a clean and renewable energy source, plays a crucial role in reducing carbon emissions and decreasing reliance on traditional energy sources. However, its intermittency and instability limit its large-scale application. Combining solar power generation with electrochemical energy storage systems is an effective way to address this issue. However, existing photovoltaic (PV) and energy storage systems still face challenges such as large space requirements and low integration, limiting their large-scale use and making them unsuitable for the urgent needs of emerging fields such as the Internet of Things (IoT), flexible electronics, and wearable devices for integrated PV-energy storage systems. Therefore, photovoltaic rechargeable batteries with dual-functional electrode systems have emerged. These batteries integrate photovoltaic energy capture and electrochemical energy storage functions on the same electrode, achieving in-situ conversion of "photogenerated carriers to ion embedding." By simplifying the structure, they effectively reduce material usage and system volume, significantly improving space utilization and providing a new path for constructing compact, low-cost distributed photovoltaic-energy storage systems.

[0003] Currently, various forms of photovoltaic-rechargeable or photovoltaic-assisted integrated devices have been reported, such as solar redox flow batteries, photovoltaic-chargeable lithium metal batteries, photovoltaic-assisted sodium-ion batteries, photovoltaic-chargeable zinc metal batteries, and photovoltaic-chargeable supercapacitors. Although new breakthroughs are constantly emerging in the field of photovoltaic-chargeable batteries, the photovoltaic charging voltage of most current research results is still relatively low (most are around 1V, and there is no photovoltaic-rechargeable sodium-ion battery with a photovoltaic charging voltage exceeding 2V), and the discharge current after photovoltaic charging is too small, which is still difficult to meet the needs of practical applications. Summary of the Invention

[0004] The purpose of this invention is to provide a hard carbon-molybdenum sulfide heterojunction material and a photochargeable sodium-ion battery based on the material.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for synthesizing a hard carbon-molybdenum sulfide heterojunction material includes the following steps:

[0007] 1) Mix water and ethanol to obtain a mixed solvent;

[0008] 2) Add HC to the mixed solvent and sonicate to obtain a carbon ball dispersion; add MoO3 and CH4N2S to the mixed solvent and stir to dissolve to obtain a MoO3 / thiourea solution;

[0009] 3) Add the MoO3 / thiourea solution to the carbon ball dispersion and sonicate under stirring conditions to obtain a mixed solution;

[0010] 4) Transfer the above mixed solution into a Teflon-lined stainless steel autoclave, heat at 180~220℃ for 20~26 hours, cool to room temperature, wash and dry the product, and then calcine at 750~850℃ for 1.8~2.5 hours under N2 atmosphere to obtain HC-MoS2 heterojunction material.

[0011] In step 1), the volume ratio of water to ethanol in the mixed solvent is 1:1.

[0012] In step 2), the mass ratio of HC, MoO3, and CH4N2S is 1:1.8~2.2:11.5~12.5, preferably 1:2:12.

[0013] In step 3), the product is washed with ethanol and water.

[0014] In step 3), the drying process involves drying at 75-85°C for 12-16 hours.

[0015] In step 4), the heating rate during calcination is 4.5~5.5℃ / min.

[0016] The prepared HC-MoS2 heterojunction material can be used as a photoelectrode in photochargeable sodium-ion batteries.

[0017] This invention designs a bifunctional electrode material (HC-MoS2) consisting of few-layer MoS2 nanosheets uniformly anchored on hard carbon and applies it to photochargeable sodium-ion batteries (PSIBs). This unique structure forms a heterojunction of hard carbon and molybdenum sulfide, which not only enhances the conductivity and structural stability of MoS2 but also achieves efficient light absorption and charge separation under illumination. Hard carbon, as a classic sodium storage material, provides a continuous electron transport channel and promotes ion diffusion in its composite material with molybdenum sulfide due to its excellent conductivity, while the MoS2 nanosheets serve as active centers for light capture and charge storage. Experimental results show that PSIBs based on the HC-MoS2 composite material exhibit excellent photocharging performance, including stable cycling performance and efficient energy storage capacity under illumination. This invention provides a promising bifunctional electrode material design strategy for developing next-generation self-charging battery systems. Attached Figure Description

[0018] Figure 1 These are SEM images of the original HC(a) and HC-MoS2(b).

[0019] Figure 2 The XRD results of HC and HC-MoS2 are shown in (a), the UV-Vis absorption spectrum of HC-MoS2 is shown in (b), and the corresponding band gap diagram is shown in (c).

[0020] Figure 3 The diagram shows the band distribution (a) and work function comparison (b) before and after the formation of the heterostructure of HC and MoS2, and a schematic diagram (c) of constructing PSIBs using HC-MoS2 photoanode.

[0021] Figure 4 The photocharging performance (a) and photocharging cycle stability (b) of PSIBs constructed from HC-MoS2 photoanodes are shown.

[0022] Figure 5 The comparison shows the charge-discharge curves of PSIBs at current densities of 200 (a) and 500 mA / g (b) under light and dark conditions, as well as the cycle stability of PSIBs under switching between light and dark conditions (c). Detailed Implementation

[0023] Example 1

[0024] Synthesis of hard carbon-molybdenum sulfide (HC-MoS2) heterojunction materials

[0025] 1) Mix equal volumes of DI (deionized water) and ethanol to obtain a mixed solvent;

[0026] 2) Add 100 mg HC to 40 mL of mixed solvent and sonicate for 30 min to obtain carbon sphere dispersion; add 0.2 g MoO3 and 1.2 g CH4N2S to 40 mL of mixed solvent in sequence, stir vigorously to dissolve completely to obtain MoO3 / thiourea solution;

[0027] 3) Add the MoO3 / thiourea solution to the carbon ball dispersion and sonicate under stirring conditions to obtain a mixed solution;

[0028] 4) The above mixed solution was transferred into a 100 mL Teflon-lined stainless steel autoclave and heated at 200 °C for 24 hours. After cooling to room temperature, the black product was washed with ethanol and DI and dried at 80 °C for 12 hours. Then, under N2 atmosphere, the temperature was increased to 800 °C at a heating rate of 5 °C / min and calcined for 2 hours to obtain the HC-MoS2 composite material.

[0029] Example 2

[0030] Fabrication and performance testing of photoelectric charging sodium-ion batteries (PSIBs)

[0031] Electrochemical performance tests of PSIBs were conducted using a CR2032 coin cell system. Cell assembly was performed in an argon-filled glove box (O2 and H2O concentrations were both below 0.01 ppm). The electrolyte was a 1.0 M sodium hexafluorophosphate (NaPF6) solution dissolved in dimethyl ethylene glycol (DME).

[0032] (1) Electrode preparation: Porous foam copper is cut into circular pieces with a diameter of 12 mm. The active material (HC-MoS2 composite material), Super P conductive agent and sodium carboxymethyl cellulose (CMC) are mixed in deionized water at a mass ratio of 8:1:1 and thoroughly ground into a negative electrode slurry. The negative electrode slurry is coated on the above porous foam copper as the photoelectrode of PSIBs.

[0033] (2) Battery assembly

[0034] PSIBs Assembly: An 8 mm diameter through-hole is made in the center of the CR2032 positive electrode shell as a light window. The photoelectrode is aligned with the inner side of the positive electrode shell light window, and the hole is sealed with epoxy resin. After curing, the positive electrode shell light window-electrode component is formed. The gasket is also pre-drilled. Then, the following components are assembled in sequence: negative electrode shell, sodium foil, electrolyte addition, diaphragm, electrolyte addition again, positive electrode shell light window-electrode component, gasket, and spring. The positive electrode shell and negative electrode shell are aligned, and the assembly is carried out in a glove box at 50 kg / cm². -2 Pressure sealing.

[0035] For PSIBs, a light source system needs to be configured at the light window position during testing to evaluate their photocharging performance. The light field refers to testing PSIBs under illumination, while the dark field refers to testing PSIBs under no-light (dark) conditions.

[0036] Example 1 uses a hydrothermal method to grow molybdenum disulfide (MoS2) nanosheets in situ on the surface of carbon spheres, successfully achieving uniform loading of MoS2 on hard carbon spheres. Figure 1 SEM images of the original hard carbon (HC) and HC-MoS2 composites are shown. Compared with the original HC, the HC-MoS2 exhibits significant changes in surface morphology, with molybdenum sulfide growing uniformly on the HC surface without obvious agglomeration. This indicates that during the synthesis process, well-dispersed carbon spheres diffuse uniformly in the solvent, serving as a loading material for molybdenum sulfide and forming a spherical HC-MoS2 heterostructure.

[0037] Figure 2 The XRD results of HC and HC-MoS2 are shown, along with the UV-Vis absorption and band gap width of HC-MoS2. Based on... Figure 2 XRD pattern analysis (a) shows that the HC-MoS2 composite material contains phase characteristics of both HC and MoS2. Except for the weak diffraction peak at 24.9° belonging to the HC(002) crystal plane, the other diffraction peaks of HC-MoS2 are consistent with those of pure MoS2. Figure 2 (b) The UV-Vis absorption spectrum shows that the absorption edge of HC-MoS2 is located at 620 nm. Based on this, the band gap of HC-MoS2 is calculated to be 2.0 eV. Figure 2 (c) indicates that it has good semiconductor properties.

[0038] To further verify that HC-MoS2 is suitable as a photoanode for constructing PSIBs, this invention calculates the work function of the most exposed crystal plane (001) of MoS2 and HC. For example... Figure 3 As shown in (a), the work function of HC(001) is 3.766 eV, which is significantly lower than that of MoS2(001) at 5.185 eV, indicating that the interface between the two forms a typical ohmic contact. Figure 3 The band alignment results in (b) indicate that after interfacial contact, electrons tend to be injected into HC from the MoS2 side and enriched on the HC side, while holes are more easily enriched on the MoS2 side, thus achieving space charge separation. These interfacial charge transport and separation characteristics provide a theoretical basis for their working mechanism as a bifunctional electrode in PSIBs, see [reference needed]. Figure 3 (c).

[0039] To investigate the photocharging performance of PSIBs assembled using HC-MoS2 as the cathode, the battery was discharged to 0.05V and then photocharged under no external bias. Figure 4 (a) It can be seen that after 1 hour of illumination, the voltage rises to over 1 V, and reaches 2.2 V after 18 hours. Subsequently, in the dark, at 200 mA g... -1 Constant current discharge was performed at a current density that resulted in a discharge specific capacity of 360 mAh g. -1 It can stably operate for three photocharging cycles, totaling nearly 60 hours, without external bias, and can be used for this purpose. Figure 4 (b).

[0040] To evaluate the cycling stability of the PSIB under dark and light field conditions, this invention conducted constant current charge-discharge tests within a voltage range of 0.05–2.8 V. Figure 5 (a) and (b) compared 200 mA g -1 and 500 mA g -1 Charge-discharge curves under dark and illuminated conditions at current densities. 200 mA g -1 At current density, the battery charging capacity increased from 551.99 mAh g in the dark field. -1 The capacity has been increased to 651.34 mAh g for light fields. -1 500 mA g -1 At current density, the battery charging capacity increased from 469.38 mAh g⁻¹. -1 Increased to 562.20 mAh g -1 . Figure 5 (c) Demonstrates PSIBs at 500 mA g -1Cyclic stability at current density was verified by alternating illumination conditions, demonstrating the battery's stable operation under different environments. These results showcase the high capacity, long cycle life, and continuous photocharging capability of PSIBs assembled using HC-MoS2 as the cathode, proving the feasibility of HC-MoS2 composite materials as a self-powered photochargeable battery system.

Claims

1. A method for synthesizing a hard carbon-molybdenum sulfide heterojunction material, characterized in that, Includes the following steps: 1) Mix water and ethanol to obtain a mixed solvent; 2) Add HC to the mixed solvent and sonicate to obtain a carbon ball dispersion; add MoO3 and CH4N2S to the mixed solvent and stir to dissolve to obtain a MoO3 / thiourea solution; 3) Add the MoO3 / thiourea solution to the carbon ball dispersion and sonicate under stirring conditions to obtain a mixed solution; 4) Heat the above mixed solution at 180~220℃ for 20~26 hours, cool to room temperature, wash and dry the product, and then calcine it at 750~850℃ for 1.8~2.5 hours under N2 atmosphere to obtain HC-MoS2 heterojunction material.

2. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 1, characterized in that, In step 1), the volume ratio of water to ethanol in the mixed solvent is 1:

1.

3. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 1, characterized in that, In step 2), the mass ratio of HC, MoO3, and CH4N2S is 1:1.8~2.2:11.5~12.

5.

4. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 3, characterized in that, The mass ratio of HC, MoO3, and CH4N2S is 1:2:

12.

5. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 1, characterized in that, In step 3), the product is washed with ethanol and water.

6. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 1, characterized in that, In step 3), the drying process involves drying at 75-85°C for 12-16 hours.

7. The method for synthesizing a hard carbon-molybdenum sulfide heterojunction material according to claim 1, characterized in that, In step 4), the heating rate during calcination is 4.5~5.5℃ / min.

8. The HC-MoS2 heterojunction material obtained by the synthesis method according to any one of claims 1 to 7.

9. The application of the HC-MoS2 heterojunction material as described in claim 8 in a rechargeable sodium-ion battery.

10. A photoelectric charging sodium-ion battery, characterized in that, It uses the HC-MoS2 heterojunction material as described in claim 8 as the photoelectrode.

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