Zinc-iodine battery with high-stability carbon-loaded iodine positive electrode

Abstract

The invention discloses a high-stability carbon-loaded iodine positive electrode zinc-iodine battery, which comprises a carbon-loaded iodine positive electrode, a diaphragm, an electrolyte and a negative electrode which are sequentially stacked from bottom to top, and the carbon-loaded iodine positive electrode is an iodine-loaded self-supporting hollow carbon sphere / poly (3, 4-ethylenedioxythiophene) composite film. C-S and C-O groups on a poly (3, 4-ethylenedioxythiophene) molecular chain in the carbon-supported iodine positive electrode are beneficial to chemical adsorption of polyiodide, and rapid conversion of iodine species is promoted; the hollow carbon spheres with the hollow structure and the high specific surface area are beneficial to storage of active iodine and can provide active sites; the self-supporting hollow carbon sphere / poly (3, 4-ethylenedioxythiophene) composite film synergistically inhibits the shuttle effect of multi-iodide through physical adsorption and chemical effects, and the iodine-loaded battery shows stable cycle life and good self-discharge inhibition behavior.

Description

Technical Field

[0001] The present invention belongs to the field of zinc-iodine batteries, and in particular relates to a zinc-iodine battery which uses a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film as a host material to load active iodine as a positive electrode. Background Art

[0002] With the rapid development of renewable energy technology, aqueous zinc-ion batteries have become a research hotspot in the field of large-scale energy storage due to their advantages such as high safety, environmental friendliness and low cost. Among them, zinc-iodine batteries have a high theoretical capacity of iodine positive electrode (211 mAh g -1 ), rich natural resources and stable zinc metal negative electrode, showing broad application prospects.

[0003] Although zinc-iodine batteries have many advantages, their practical application faces the following challenges: (1) The electrical conductivity of iodine and polyiodides is extremely low (about 10 -6 ~10 -9 S cm -1 ), iodine needs to be loaded on a highly conductive host material to improve the conductivity of the positive electrode, improve the redox kinetics and alleviate the electrode polarization phenomenon. However, excessive host material will reduce the energy density of the battery, so it is necessary to balance the quality of the host material with the battery performance. (2) The thermodynamic instability and easy sublimation of iodine increase the complexity of electrode preparation. During the electrode drying process, iodine is easy to sublimate, resulting in mass loss, which in turn affects the battery capacity and wastes raw materials. (3) The polyiodides generated during the cycle are easily soluble in the electrolyte, causing a "shuttle effect", that is, polyiodides shuttle between the positive and negative electrodes, resulting in active material loss, inducing self-discharge and reducing coulombic efficiency. (4) In order to improve energy density, it is necessary to increase the loading and utilization of active iodine, but this will bring new challenges, such as cracking of thick electrodes, slow reaction kinetics and aggravated shuttle effect. In addition, uneven deposition and side reactions of the zinc negative electrode will lead to zinc dendrite growth and surface corrosion, affecting the safety and electrochemical performance of zinc-iodine batteries.

[0004] Although traditional carbon materials have a high specific surface area and a rich porous structure, they have weak physical adsorption of iodine and limited ability to restrict the shuttling of polyiodides, resulting in poor electrochemical performance. Therefore, the current research focus of zinc-iodine batteries is on the development of high-performance iodine host materials, such as Prussian blue analogues, MXene, conductive polymers, metal organic compounds, starch and other materials. Among them, conductive polymers with both high conductivity and stability can effectively restrict the migration of polyiodides and have become ideal candidates for electrode materials of energy storage devices. The conjugated structure in the main chain of the conductive polymer gives it unique electronic properties, which forms a conductive path through delocalized π electrons. In addition, conductive polymers can achieve "semiconductor-conductor" transformation through p-type doping or n-type doping. Their reversible redox properties and flexible structure are conducive to the realization of high-performance zinc-iodine batteries.

[0005] In summary, the main problems faced by zinc-iodine battery cathode materials are poor conductivity, easy dissolution and formation of polyiodide (I3 - / I5 - ) leads to key problems such as loss of active materials, which seriously restricts the cycle stability and energy density of the battery. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems of poor conductivity and shuttle effect of iodine in zinc-iodine batteries, and to provide a carbon-supported iodine positive electrode zinc-iodine battery that can synergistically inhibit the shuttle effect of multiple iodides through physical adsorption and chemical action. The battery exhibits a stable cycle life and good self-discharge inhibition behavior.

[0007] To achieve the above-mentioned purpose, the zinc-iodine battery adopted in the present invention includes a carbon-iodine-loaded positive electrode, a diaphragm, an electrolyte, and a negative electrode stacked in sequence from bottom to top, wherein the carbon-iodine-loaded positive electrode is a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film loaded with iodine.

[0008] The preparation method of the above-mentioned carbon-supported iodine positive electrode is: placing a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film and iodine in a mass ratio of 1:0.5-10 in a sealed container filled with argon, heating at 80-150°C for 5-10 hours, and then heating at 40-80°C in air for 1-3 hours.

[0009] Furthermore, the preferred preparation method of the above-mentioned carbon-supported iodine positive electrode is: placing a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film and iodine in a mass ratio of 1:1 to 3 in a sealed container filled with argon, heating at 110 to 130°C for 5 to 6 hours, and then heating at 60 to 70°C in air for 1 to 2 hours.

[0010] Furthermore, the preparation method of the self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film is as follows: ultrasonically mixing the hollow carbon spheres and the methanol dispersion of poly(3,4-ethylenedioxythiophene) nanofibers, vacuum filtering to form a film, and then freeze-drying. Preferably, the mass ratio of the hollow carbon spheres to the poly(3,4-ethylenedioxythiophene) nanofibers is 1:1 to 10, and the concentration of the poly(3,4-ethylenedioxythiophene) nanofibers in the methanol dispersion of the poly(3,4-ethylenedioxythiophene) nanofibers is 1 to 10 mg mL -1 .

[0011] Furthermore, the preparation method of the above-mentioned hollow carbon spheres is: using spherical silica with a diameter of 100 to 300 nm as a template and ferrocene as a precursor, after chemical vapor deposition at 500 to 550°C for 30 to 60 minutes, annealing at 600 to 900°C for 60 to 90 minutes, and treating the obtained material with a 15% to 25% HF aqueous solution for 20 to 24 hours to remove the silica template, and then washing with deionized water and ethanol, and drying at 60 to 100°C.

[0012] Furthermore, the poly(3,4-ethylenedioxythiophene) nanofibers are prepared by dispersing ferric chloride and sodium dodecyl sulfate in deionized water, stirring at 50-100°C for 1-5 hours, then adding 3,4-ethylenedioxythiophene and continuing to stir and polymerize for 5-10 hours. After the reaction is complete, the fibers are washed with deionized water and methanol. Preferably, the mass ratio of ferric chloride to sodium dodecyl sulfate to 3,4-ethylenedioxythiophene is 1:1-5:0.1-2.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention prepares a self-supporting composite film by combining hollow carbon spheres and poly (3,4-ethylenedioxythiophene). The self-supporting composite film is used as the host material and loaded with active iodine as the positive electrode of the zinc-iodine battery. The CS and CO groups on the poly (3,4-ethylenedioxythiophene) molecular chain in the self-supporting composite film are conducive to the chemical adsorption of polyiodide and promote the rapid conversion of iodine species. The hollow carbon spheres with a high specific surface area of ​​the hollow structure are conducive to the storage of active iodine and can provide active sites. The self-supporting hollow carbon sphere / poly (3,4-ethylenedioxythiophene) composite film synergistically suppresses the shuttle effect of polyiodide through physical adsorption and chemical action. The iodine-loaded battery exhibits a stable cycle life and good self-discharge inhibition behavior. The battery is at 0.1 and 10Ag -1 At a current of 100 and 47,000 cycles, the capacities are 188 and 110 mAh g, respectively. -1 , the capacity retention rates were 88% and 90% respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 TEM images of the MCS prepared in Example 1 and SEM images of the PEDOT nanofibers and the self-supporting P-MCS-7 film.

[0016] Figure 2 These are the Raman graphs of the PEDOT nanofibers, self-supporting P-MCS-7 film, I2-P-MCS-7 prepared in Example 1, the I2-MCS prepared in Comparative Example 1, and the I2-PEDOT prepared in Comparative Example 2.

[0017] Figure 3 It is the XPS chart of I2-P-MCS-7 prepared in Example 1 and I2-MCS prepared in Comparative Example 1.

[0018] Figure 4 The MCS, PEDOT nanofibers and self-supporting P-MCS-7 film prepared in Example 1 adsorbed I3 - The subsequent UV-visible spectrum.

[0019] Figure 5 The MCS, PEDOT nanofibers and self-supporting P-MCS-7 film prepared in Example 1 adsorbed I3 - Optical photograph of the experiment.

[0020] Figure 6 The zinc-iodine battery in Example 1 and Comparative Examples 1-2 is 0.1Ag -1 Cycling performance at current density.

[0021] Figure 7 The zinc-iodine battery in Example 1 is 10Ag -1 Cycling performance at current density.

[0022] Figure 8 The zinc-iodine battery in Example 2 is 0.1Ag -1 Cycling performance at current density. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited to the following examples.

[0024] Example 1

[0025] Preparation of hollow carbon spheres (MCS): Spherical silica with a diameter of 200 nm was used as a template and ferrocene as a precursor. After chemical vapor deposition at 530°C for 60 minutes, it was annealed at 800°C for 90 minutes. The obtained material was treated with a 20% HF aqueous solution for 24 hours to remove the silica template, and then washed with deionized water and ethanol and dried at 80°C to obtain MCS.

[0026] Preparation of poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers: 4.05 g of FeCl₃·6H₂O and 8.65 g of sodium dodecyl sulfate (SDS) were dispersed in 100 mL of deionized water and stirred at 50°C for 2 h. Subsequently, 750 mg of EDOT was added, and polymerization with stirring was continued for 6 h. After the reaction, the product was washed with deionized water and methanol to remove unreacted chemicals and residual SDS, resulting in PEDOT nanofibers.

[0027] Preparation of self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film (P-MCS): PEDOT nanofibers were dispersed in methanol to obtain a concentration of 2 mg mL -1 The methanol dispersion of PEDOT nanofibers was prepared. Based on a mass ratio of MCS to PEDOT of 1:7, 6 mg of MCS and 21 mL of the methanol dispersion of PEDOT nanofibers were ultrasonically mixed. The membranes were then vacuum filtered and freeze-dried to obtain a self-supporting P-MCS-7 film.

[0028] Preparation of the carbon-supported iodine cathode: A self-supporting P-MCS-7 film was cut into 10 mm diameter electrodes. The electrodes were then placed in a sealed container filled with argon at a mass ratio of 1:1 with iodine particles. The electrodes were heated at 130°C for 6 hours. Subsequently, to remove excess iodine, the electrodes were heated in air at 60°C for 1 hour to obtain the carbon-supported iodine cathode (I2-P-MCS-7). The iodine loading on the I2-P-MCS-7 was 1.5-1.8 mg cm -2 .

[0029] Assembly of zinc-iodine battery: Zinc-iodine battery was assembled in an air environment. The assembly order was positive electrode shell, carbon-supported iodine positive electrode (I2-P-MCS-7), glass fiber separator, electrolyte, zinc negative electrode, gasket, shrapnel, and negative electrode shell. The battery shell model was CR2032 button battery. 90 μL of 2M ZnSO4 aqueous solution was added to each battery as electrolyte. The separator model was Whatman GF / A, and the thickness of the zinc negative electrode was 50 μm.

[0030] Example 2

[0031] Self-supporting films with MCS:PEDOT mass ratios of 1:1, 1:4, and 1:9 were prepared according to the method of Example 1 and named P-MCS-1, P-MCS-4, and P-MCS-9, respectively.

[0032] Carbon-supported iodine positive electrodes I2-P-MCS-1, I2-P-MCS-4, and I2-P-MCS-9 were prepared according to the method of Example 1, and zinc-iodine batteries were assembled according to the method of Example 1.

[0033] Comparative Example 1

[0034] Preparation of carbon-supported iodine positive electrode: MCS (prepared as in Example 1) and iodine particles were mixed in a mass ratio of 1:1 and heated at 80°C for 12 hours to obtain I2-MCS. I2-MCS was then ground evenly with Ketjen black and binder PVDF in a mass ratio of 8:1:1. The mixture was then stirred in NMP as a solvent for 4 hours and then coated on a stainless steel current collector. The mixture was dried at 40°C for 7 hours and then cut into 10 mm diameter electrode pieces. The active iodine loading on each electrode piece was 1.0-1.2 mg cm -2 .

[0035] The zinc-iodine battery was assembled according to the method of Example 1.

[0036] Comparative Example 2

[0037] Preparation of PEDOT self-supporting film: -1 The methanol dispersion of PEDOT nanofibers was ultrasonically homogenized, vacuum filtered to form a film, and then freeze-dried to obtain a PEDOT self-supporting film.

[0038] Preparation of the PEDOT-loaded iodine cathode: The PEDOT self-supporting film was cut into 10 mm diameter electrodes. The electrodes were then placed in a sealed container filled with argon gas with an iodine particle mass ratio of 1:1 and heated at 130°C for 6 h. Subsequently, to remove excess iodine, the electrodes were heated at 60°C in air for 1 h to obtain the PEDOT-loaded iodine cathode (I2-PEDOT). The iodine loading on I2-PEDOT was 1.5-1.8 mg cm -2 .

[0039] The zinc-iodine battery was assembled according to the method of Example 1.

[0040] The morphology of the MCS, PEDOT nanofibers and self-supporting P-MCS-7 films prepared in Example 1 was characterized. Figure 1 .Depend on Figure 1 As can be seen, compared to MCS, the fibrous PEDOT and hollow MCS structures in the self-supporting P-MCS-7 film intertwine to form a three-dimensional conductive network. The addition of MCS also significantly alleviates the agglomeration of PEDOT nanofibers, facilitating rapid ion transport. In the self-supporting P-MCS-7 film, the internal cavities of the MCS facilitate reactant storage and diffusion channels, while the PEDOT nanofiber conductive network provides a fast ion transport path.

[0041] Depend on Figure 2 It can be seen that the Raman spectrum is located at 1509cm -1 、1429cm -1 、1368cm -1 The peaks at correspond to PEDOT nanofibers Cα =C β Asymmetric stretching vibration, C α =C β Symmetric stretching vibration, C β =C β stretching vibration, which indicates that it has a high degree of conjugation. -1 and 213cm -1 The Raman signal peaks at correspond to I3 - and I5 - , indicating that there is a significant chemical reaction between iodine and PEDOT in Comparative Example 2 and P-MCS-7 in Example 1, and I3 - In comparative example 1, no polyiodide peaks were found in I2-MCS, indicating that iodine exists mainly in the form of physical adsorption in the carbon material. The above results show that MCS in the self-supporting P-MCS-7 film plays a physical adsorption role, while PEDOT plays a chemical adsorption role. The self-supporting P-MCS-7 film can achieve physical and chemical dual adsorption of iodine species as an iodine positive electrode carrier.

[0042] Depend on Figure 3 It can be seen that in the XPS spectrum, only I 0 , indicating that iodine exists in the carbon material mainly in the form of physical adsorption; while in Example 1, I2-P-MCS-7 has I 0 and I - , indicating that there is a significant chemical interaction between iodine and P-MCS-7, and iodine achieves physical and chemical dual adsorption of iodine species.

[0043] In order to explore the effects of MCS, PEDOT nanofibers and self-supporting P-MCS-7 films on I3 - To investigate the difference in adsorption capacity, different carriers of the same mass were immersed in Zn(I3)2 aqueous solution of the same concentration to conduct iodine adsorption experiments. The supernatants after 24 hours of adsorption on different carriers were analyzed by UV-visible absorption spectra. The absorption peaks at 287nm and 350nm correspond to I3 - .Depend on Figure 4 It can be seen that the supernatant I3 after the self-supporting P-MCS-7 film adsorption - The absorption peak is the weakest, followed by PEDOT, and the highest peak is MCS. This shows that the PEDOT component in the self-supporting P-MCS-7 film has a strong effect on I3 - Adsorption plays a dominant role. Figure 5The optical images also show that the solution in the self-supporting P-MCS film and the PEDOT sample bottle is almost colorless after 24 hours of adsorption, while the solution in the MCS sample bottle is still light yellow, which indicates that the self-supporting P-MCS-7 film has a stronger adsorption capacity for polyiodide. Therefore, I2-P-MCS-7 can effectively limit the adsorption of I3 as the positive electrode of zinc-iodine battery. - The shuttle of zinc-iodine can be reduced, and the utilization rate of active materials can be improved, which is conducive to the realization of stable shuttle-free zinc-iodine batteries.

[0044] Depend on Figure 6 It can be seen that compared with Comparative Examples 1 and 2, the zinc-iodine battery of Example 1 has a -1 At a current density of 1.5 GHz, the initial specific capacity reaches 213 mAh g -1 After 100 cycles, the capacity remains at 188 mAh g -1 , the capacity retention rate is as high as 88%, and the coulombic efficiency is close to 100%. This shows that I2-P-MCS-7 has good redox reversibility and high iodine utilization. The specific capacity of the zinc-iodine battery in comparative example 1 is only 28 mAh g after 100 cycles. -1 Although the zinc-iodine battery of Comparative Example 2 has a higher initial specific capacity, its cycle stability is poor.

[0045] Depend on Figure 7 It can be seen that the zinc-iodine battery of Example 1 has a -1 The initial specific capacity at high current density is 121 mAh g -1 , after more than 47,000 cycles, it still maintains 110mAh g -1 The discharge specific capacity is 100%, the capacity retention rate reaches 91%, the capacity decay rate per cycle is only 0.0002%, and the coulombic efficiency is close to 100%. This shows that the I2-P-MCS-7 of Example 1 has excellent cycling stability. This indicates that the multi-iodide shuttle effect is effectively suppressed. The above results show that I2-P-MCS-7 can still maintain its effectiveness and cycling stability under high mass loading conditions, and has great application potential.

[0046] In order to further confirm that the composite film of hollow carbon spheres and poly (3,4-ethylenedioxythiophene) is beneficial to the realization of high stability zinc-iodine batteries, Figure 8 The samples of Example 2 with different ratios are shown in 0.1Ag -1 Cycling curves of 100 cycles at the same current density. The three ratios of I2-P-MCS-1, I2-P-MCS-4, and I2-P-MCS-9 all showed relatively stable cycling performance, with initial specific capacities of 198 mAh g -1 , 200mAh g -1 , 102mAh g -1After 100 cycles, they maintained approximately 85%, 87%, and 80% of their capacity retention, respectively. This indicates that they have suppressed the shuttle effect of polyiodides to a certain extent and have good electrochemical performance.

Claims

1. A high-stability carbon-supported iodine cathode zinc-iodine battery, comprising a carbon-supported iodine cathode, a separator, an electrolyte, and a cathode stacked sequentially from bottom to top, characterized in that: The carbon-supported iodine positive electrode is a self-supporting hollow carbon sphere / poly (3,4-ethylenedioxythiophene) composite film loaded with iodine.

2. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 1, characterized in that: The preparation method of the carbon-supported iodine positive electrode is as follows: placing a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film and iodine in a mass ratio of 1:0.5-10 in a sealed container filled with argon, heating at 80-150°C for 5-10 hours, and then heating at 40-80°C in air for 1-3 hours.

3. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 1, characterized in that: The preparation method of the carbon-supported iodine positive electrode is as follows: placing a self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film and iodine in a mass ratio of 1:1-3 in a sealed container filled with argon, heating at 110-130°C for 5-6 hours, and then heating at 60-70°C in air for 1-2 hours.

4. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to any one of claims 1 to 3, characterized in that: The preparation method of the self-supporting hollow carbon sphere / poly(3,4-ethylenedioxythiophene) composite film comprises: uniformly mixing the hollow carbon spheres and a methanol dispersion of poly(3,4-ethylenedioxythiophene) nanofibers through ultrasonic mixing, vacuum filtering to form a film, and then freeze-drying; wherein the mass ratio of the hollow carbon spheres to the poly(3,4-ethylenedioxythiophene) nanofibers is 1:1 to 10.

5. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 4, characterized in that: The concentration of the poly(3,4-ethylenedioxythiophene) nanofiber in the methanol dispersion of the poly(3,4-ethylenedioxythiophene) nanofiber is 1 to 10 mg / mL. -1 .

6. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 4, characterized in that: The hollow carbon spheres are prepared by using spherical silica with a diameter of 100 to 300 nm as a template and ferrocene as a precursor. After chemical vapor deposition at 500 to 550° C. for 30 to 60 minutes, the material is annealed at 600 to 900° C. for 60 to 90 minutes. The obtained material is treated with an HF aqueous solution with a mass concentration of 15% to 25% for 20 to 24 hours to remove the silica template. The material is then washed with deionized water and ethanol and dried at 60 to 100° C.

7. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 4, characterized in that: The preparation method of the poly (3,4-ethylenedioxythiophene) nanofiber is as follows: ferric chloride and sodium dodecyl sulfate are dispersed in deionized water, stirred at 50-100° C. for 1-5 hours, then 3,4-ethylenedioxythiophene is added, and the stirring polymerization is continued for 5-10 hours; after the reaction is completed, the fibers are washed with deionized water and methanol.

8. The high-stability carbon-supported iodine positive electrode zinc-iodine battery according to claim 7, characterized in that: The mass ratio of the ferric chloride, sodium lauryl sulfate and 3,4-ethylenedioxythiophene is 1:1-5:0.1-2.

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