Preparation method of cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries, its products and applications

Abstract

The present invention discloses a preparation method of a cobalt-nitrogen-doped carbon cathode material for zinc-iodine batteries, its products, and applications. The formation of the cobalt-nitrogen coordination structure of the present invention can provide a stable anchoring site for iodine species, accelerate the rapid conversion of iodine redox reactions, and enhance reaction kinetics. The formation of this structure can significantly improve the catalytic activity of the iodine conversion reaction and enhance the cycle stability of the zinc-iodine battery. The capacity of Co-NC at a current of 5C is 185mAh g ‑1 , can maintain 102mAh g at a current of 50C ‑1 , and can stably cycle 20,000 times with a coulombic efficiency close to 100%. The present invention verifies that the cobalt-nitrogen coordination provides catalytic active sites and conductivity, has the function of accelerating the conversion of catalytic polyiodides and adsorbing iodine, and improves the reversible conversion of iodine through the physical and chemical constraint effect, thus achieving long-term cycling performance of zinc-iodine batteries under high current.

Description

Technical Field

[0001] The present invention belongs to the technical field of zinc-iodine battery materials, and specifically relates to a preparation method of a cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries, as well as its product and application. Background Art

[0002] The doping of sulfur (a non-metallic element) has high electrocatalytic activity. The doping of sulfur improves the electrochemical performance of zinc-iodine batteries, but there are still certain problems. The capacity provided by nitrogen-sulfur dual-doped carbon materials used in zinc-iodine batteries is relatively low.

[0003] Since the active material of Zn-I2 battery (ZIB) will be l3 - and I5 - The I3 is dissolved in the water-based electrolyte, resulting in a serious shuttle effect and reducing the cycling stability of the Zn negative electrode, thereby reducing the actual energy density of the battery and accelerating capacity degradation. - and I5 - The formation of I2 is mainly due to the slow kinetics of the iodine conversion reaction in zinc-iodine batteries, and the poor conductivity of iodine further exacerbates the charge transfer barrier of the electrochemical reaction. Due to its poor conductivity, the positive electrode usually relies on a conductive carrier (such as porous carbon, carbon cloth, graphene, etc.) to transport electrons.

[0004] Loading iodine on a conductive support can effectively enhance electron transfer and redox conversion. Traditional porous carbon materials only provide physical confinement for iodine and polyiodides. Although porous carbon materials can physically confine iodine in the positive electrode, the formation of soluble iodide species can reduce energy storage efficiency and cycling stability. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and to briefly introduce some preferred embodiments.

[0006] As one aspect of the present invention, the present invention provides a method for preparing a cobalt-nitrogen doped carbon positive electrode material for a zinc-iodine battery, which comprises:

[0007] (1) mixing a carbon source, a nitrogen source, and manganese carbonate uniformly, heating to 800-850°C, washing, and drying to obtain NC material;

[0008] (2) mixing the NC material obtained in step (1) with a cobalt salt, drying the obtained mixture, heating it to 800-850° C., filtering, washing, and drying to obtain a Co-NC material;

[0009] (3) The Co-NC material obtained in step (2) is mixed with iodine, ground, heated to 110-130° C. under an inert atmosphere for reaction, and then heated in air to remove the iodine to obtain a positive electrode material.

[0010] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries according to the present invention: in step (1), the carbon source includes methyl cellulose, and the nitrogen source includes urea.

[0011] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries according to the present invention: in step (1), the mass ratio of the carbon source, the nitrogen source and the manganese carbonate is 1:0.5 to 1:5 to 10.

[0012] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries of the present invention: in step (1), the temperature is raised at 5°C / min under an inert atmosphere. -1 Heat to 250℃ and keep warm for 1~2h, then heat at 5℃min -1 Heat to 800℃ and keep warm for 2 to 3 hours.

[0013] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries according to the present invention: in step (2), the cobalt salt includes cobalt nitrate hexahydrate, and the mass ratio of the NC material to the cobalt salt is 1:0.97.

[0014] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries of the present invention: in step (2), the heating is carried out at a temperature of 10°C / min under an inert atmosphere. -1 Heat to 130℃ and keep warm for 3~4h, then -1 Heat to 800℃ and keep warm for 2 to 3 hours.

[0015] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries according to the present invention: in step (3), the mass ratio of the Co-NC material to the iodine element is 1:1.

[0016] As a preferred embodiment of the method for preparing the cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries according to the present invention: in step (3), the inert atmosphere comprises argon; the heating to 110-130°C for reaction is heating to 120°C for reaction for 8-10 hours; the heating in air is heating to 100°C in air and keeping warm for 12-24 hours.

[0017] Beneficial effects of the present invention: The formation of the cobalt-nitrogen coordination structure of the present invention can provide a stable anchoring site for iodine species, accelerate the rapid conversion of iodine redox reaction, and enhance the reaction kinetics. Electrochemical tests show that the formation of this structure can significantly improve the catalytic activity of the iodine conversion reaction and enhance the cycle stability of the zinc-iodine battery. The capacity of Co-NC at a current of 5C is 185mAh g -1 , can maintain 102mAh g at a current of 50C -1 , and can stably cycle 20,000 times with a coulombic efficiency close to 100%. The present invention verifies that the cobalt-nitrogen coordination provides catalytic active sites and conductivity, has the function of accelerating the conversion of catalytic polyiodides and adsorbing iodine, and improves the reversible conversion of iodine through the physical and chemical constraint effect, thus achieving long-term cycling performance of zinc-iodine batteries under high current. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, wherein:

[0019] Figure 1 Flow chart for the preparation of Co-NC.

[0020] Figure 2 SEM images of C-I2, NC-l2 and Co-NC-l2; EDS element distribution image of Co-NC-l2.

[0021] Figure 3 LSV curves of the oxidation process of C, NC and Co-NC, the Tafel slope curve calculated from the LSV curve of the oxidation process, the LSV curve of the reduction process, and the Tafel slope curve calculated from the LSV curve of the reduction process.

[0022] Figure 4 CV curves of C, NC, and Co-NC at different scan rates; b value calculated from CV; Co-NC at 5 mV s -1 Capacitance contribution rate; Nyquist plots of C, NC and Co-NC.

[0023] Figure 5 is the adsorption capacity of C, NC and Co-NC in 2M ZnSO4+0.02M l2(2m M l3-) aqueous solution, and the intensity of UV-visible absorbance I3v after adsorption for 48 hours.

[0024] Figure 6 This is the in-situ Raman image at 0.3C.

[0025] Figure 7 SEM images of dendrites on the surface of zinc negative electrode after 1000 cycles of C-l2 and Co-NC-l2.

[0026] Figure 8 Schematic diagram of the principle of rechargeable Zn-I2 battery based on Co-NC positive electrode.

[0027] Figure 9 For C, NC and Co-NC at 0.5mV s -1 CV curve, the starting potential of the CV positive and negative electrode reactions, and the Tafel slope calculated based on the CV; at 0.5 mV s -1 The overlap test of the first four CV curves.

[0028] Figure 10 Rate performance of C, NC and Co-NC at different currents; charge and discharge curves of Co-NC at different currents.

[0029] Figure 11 The self-discharge time-voltage curves of C, NC and Co-NC after 48 hours of standing.

[0030] Figure 12 Figure 3 shows the cycling performance of C, NC and Co-NC at 5C, the charge-discharge curve of the 800th cycle at 5C, the long-cycle performance of Co-NC at 50C and the charge-discharge curves of different cycles at 5C. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0032] Preparation of Co-NC, NC, and C materials:

[0033] Preparation of material C: Methyl cellulose (product number: C03X006; viscosity: 15 cPs; molecular weight: 454.5; cas number: 9004-67-5) and manganese carbonate were mixed at a mass ratio of 1:5. The mixed mixture was heated at 5 °C min-1 in an argon atmosphere. -1 Heat to 250℃ and keep warm for 1h, then heat at 5℃min -1 The temperature was raised to 800°C and maintained for 2 hours. The obtained product was pickled with hydrochloric acid to remove manganese carbonate, then filtered and washed several times, and finally vacuum dried to obtain the product.

[0034] Preparation of NC materials: Methyl cellulose, urea and manganese carbonate were mixed in a mass ratio of 1:0.5:5, and the mixed mixture was placed in an argon atmosphere at 5 °C min -1 Heat to 250℃ and keep warm for 1h, then heat at 5℃min -1 The temperature was raised to 800°C and maintained for 2 hours. The obtained product was pickled with hydrochloric acid to remove manganese carbonate, and then filtered and washed several times, and finally vacuum dried to obtain the product.

[0035] Preparation of Co-NC material: NC and cobalt nitrate hexahydrate were mixed in deionized water at a mass ratio of 1:0.97 and stirred for 4 hours. The obtained mixture was evaporated to dryness using a rotary evaporator. The dried mixture was heated at 10 °C min under an argon atmosphere. -1 Heat to 130℃ and keep warm for 3h, then -1 The temperature was raised to 800°C and kept at this temperature for 2 hours. The obtained product was pickled with hydrochloric acid, filtered and washed several times, and finally vacuum dried to obtain the product.

[0036] Figure 1 Flow chart for the preparation of Co-NC.

[0037] Preparation of Co-NC-l2, NC-l2 and C-l2 materials:

[0038] like Figure 1 As shown, the prepared C, NC and Co-NC materials were mixed with iodine in a mass ratio of 1:1 and ground thoroughly. The ground mixture was placed in a 50 mL reactor liner under an argon atmosphere and placed in the reactor. The reactor was kept at 120°C for 8 hours. The obtained mixture was kept at 100°C in air for 12 hours to remove the iodine on its surface.

[0039] Electrode preparation:

[0040] The electrode sheets were prepared by wet method. The Co-NC-l2, NC-l2 or C-l2 active materials, conductive agent (conductive carbon black) and binder (polyvinylidene fluoride) prepared above were mixed in a mass ratio of 8:1:1 and added to the mixer in batches. Then, an appropriate amount of N-methylpyrrolidone solution was added (150 microliters of N-methylpyrrolidone solution was added to every 10 mg of the mixture). The mixture was degassed and mixed to form a uniform slurry. 15 microliters of slurry was pipetted and dropped onto the steel sheet. The active material loading of each electrode was 1.5 mg cm -2 , and placed it in a vacuum oven at 40 °C and dried for 12 h as the positive electrode material.

[0041] Battery Assembly:

[0042] Before use, the zinc sheet was carefully polished with fine sandpaper, then ultrasonically treated in anhydrous ethanol for half an hour. After drying, it was used as the negative electrode. A 2M ZnSO4 solution was used as the electrolyte. The positive electrode shell, the positive electrode material, the electrolyte, the diaphragm, the electrolyte, the zinc sheet, the gasket, the shrapnel, and the negative electrode shell were assembled in this order. For each battery, 30 microliters of electrolyte were placed above and below the diaphragm. After assembly, the battery was sealed with a sealing machine at a pressure of 50 MPa, and the assembly process was kept consistent each time.

[0043] Experimental results:

[0044] Morphology and structure characterization:

[0045] The cobalt-doped active sites were introduced into the porous carbon structure, which significantly promoted the adsorption and reduction kinetics of iodine. Scanning electron microscopy (SEM) images of C-l2, NC-l2 and Co-NC-l2 were used to study the SEM images. The morphology of the sample did not change significantly after the iodine was added, and there was no obvious iodine crystal distribution on the surface, indicating that iodine was diffused and deposited inside the pores instead of accumulating on the outer surface. EDS mapping images are shown in Figure 2. Figure 2 As shown in Figure d, the elements C, N, Co, and I are uniformly dispersed throughout the sample, indicating that iodine has been successfully loaded into the carbon material and is evenly distributed in the carbon material.

[0046] Figure 2 SEM images of (a) C-l2, (b) NC-l2 and (c) Co-NC-l2; (d) EDS element distribution image of Co-NC-l2.

[0047] Electrocatalytic activity characterization:

[0048] In order to further explore the profound influence of the electrocatalytic sites of cobalt-nitrogen doped carbon materials on the kinetics of redox reactions, the Tafel slopes of the reduction and oxidation reactions were compared and analyzed. According to the linear sweep voltammetry (LSV) test of Zn-l2 battery ( Figure 3 ) shows that during the iodine oxidation process ( Figure 3 a), the potential change of Co-NC-l2 is 1.08V, while that of C-l2 and NC-l2 is 1.19V and 1.13V respectively, indicating that Co-NC-l2 can undergo iodine oxidation reaction at a lower voltage. Figure 3 c), the overpotential of Co-NC-l2 is smaller. Figure 3 In b, in the iodine oxidation reaction, Co-NC-l2 (16.7mVdec -1 )'s Tafel slope Lower than Nc-I2(158.1mV dec -1 ) and C-l2(424.1mV dec -1 ), which is attributed to the excellent catalytic activity of the Co-NC active center. Similarly, in the iodine reduction reaction, Co-NC-l2 (98mV dec -1 ) has a lower Tafel slope than NC-l2 (189mV dec -1 ) and C-l2(204mV dec -1 ), Co-NC showed better catalytic performance in iodine oxidation reaction. These results indicate that Co-NC has a better catalytic effect on l2 / l -conversion with higher electrocatalytic activity.

[0049] Figure 3 (a) LSV curves of the oxidation process of C, NC, and Co-NC, (b) Tafel slope curves calculated from the LSV curves of the oxidation process, (c) LSV curves of the reduction-oxidation process, and (d) Tafel slope curves calculated from the LSV curves of the reduction process.

[0050] In order to evaluate the electrochemical performance of C-l2, NC-I2 and Co-NC-I2 cathodes, we assembled zinc-iodine batteries and conducted Figure 4 Cyclic voltammetry test with 0.5 to 5 mV s -1 The CV curves at different scan rates further analyzed the kinetics of the C-I2, NC-l2, and Co-NC-l2 cathodes. As the scan rate increased, the redox current also increased accordingly ( Figure 4 ac), the oxidation peak and reduction peak of the zinc-iodine battery assembled with the C-I2 positive electrode deviate with the increase of the scan rate, indicating that the polarization is enhanced. At the same time, the zinc-iodine battery assembled with the Co-NC-l2 positive electrode has the highest current response and the largest peak potential difference, indicating the superior kinetic conversion of iodine species in Co-NC. The type of electrochemical behavior can be determined by measuring the equation of scan rate (v) and current (i) to determine the parameters (i = a·v b ), where the b value represents the electrochemical process dominated by ion diffusion (when the b value is close to 0.5) or capacitance process (when the b value is close to 1). Figure 4 As shown in de, the b values ​​of the oxidation peak and reduction peak of the zinc-iodine battery assembled with C-l2 positive electrode are 0.65 and 0.87 ( Figure 4 d), the b values ​​of the oxidation peak and reduction peak of the zinc-iodine battery assembled with NC-I2 positive electrode are 0.82 and 0.84 respectively ( Figure 4 e), the b values ​​of the oxidation peak and reduction peak of the zinc-iodine battery assembled with Co-NC-l2 positive electrode are 0.82 and 0.84 respectively ( Figure 4 f), which means that C-I2, NC-l2 and Co-NC-l2 are affected by diffusion-controlled processes and surface capacitance control. Among them, the b value of Co-NC-l2 is the largest, which means that the capacitive reaction plays a greater dominant role in the charge storage mechanism. The pseudocapacitive contribution is given by Log i =b·Log v +Log a Calculation: where k1v is the pseudo capacity contribution, k2v 1 / 2 is a diffusion-controlled process. As the scan rate increases, the capacitive charge contribution becomes dominant. Figure 4 It can be seen that at 0.5, 0.8, 1.0, 2.0, and 5.0 mV s -1When , the capacitance contributions of Co-NC-l2 are 82%, 85%, 88%, 90% and 95%, respectively, indicating that Co-NC-l2 has high electrochemical kinetics. -1 At high scan rates, the capacitance contribution rate reaches about 95% ( Figure 4 g), indicating the excellent rate performance of Co-NC-l2. The strong capacitance contribution is derived from the rapid redox reaction of iodine caused by the porous carbon structure and electrocatalysis. Electrochemical impedance spectroscopy (EIS) tests were conducted to detect the charge transfer dynamics of the zinc-iodine battery. In the Nyquist plot ( Figure 4 i), in the original state, the charge transfer resistance (R Ct ) of Co-NC-l2 (55Ω) is lower than that of NC-I2 (65Ω) and C-l2 (234Ω), which indicates that Co-NC-l2 has higher catalytic activity.

[0051] Figure 4 CV curves of (a) C, (b) NC, and (c) Co-NC at different scan rates; b values ​​calculated from CV for (d) C, (e) NC, and (f) Co-NC; Co-NC (g) at 5 mV s -1 Capacitance contribution rate, (h) capacitance contribution rate statistics; (i) Nyquist plot of C, NC and Co-NC.

[0052] Adsorption test and iodine conversion kinetics study:

[0053] In order to observe the adsorption capacity of C, NC and Co-NC for polyiodide, the adsorption capacity of C, NC and Co-NC was studied by immersing them in 2MZnSO4+0.02M I2(2mM I3-) aqueous solution for 48 hours. Figure 5 As shown in a. Compared with other solutions, the Co-NC solution is almost transparent. The UV-visible absorbance spectrum shows that ( Figure 5 b) Co-NC has the weakest l3- signal, the smallest proportion of polyiodide in solution, and the strongest adsorption of polyiodide. Compared with C-l2 and NC-I2 cathodes, the Co-NC-I2 cathode exhibits the lowest peak intensity and the weakest yellow color after 48 h, indicating that the Co-NC host has a strong physical / chemical adsorption effect on l2.

[0054] Figure 5 For C, NC and Co-NC (a) in 2M ZnSO4+0.02M l2(2mM l3 - ) adsorption capacity of aqueous solution, (b) intensity of UV-visible absorbance l3- after 48 h of adsorption.

[0055] In order to explore the redox kinetics of Co-NC in Zn-L2 batteries, in situ Raman measurements were performed at 0.3 C. The in situ Raman spectrum of the Zn-L2 battery using Co-NC-L2 cathode showed two main peaks at 110 and 165 cm -1 ( Figure 6 ), which can be attributed to l3 - and I5 - The symmetric stretching mode of the battery is shown in Figure 2. During charging, the intensity of the two Raman peaks increases and reaches a maximum intensity at 1.7 V, demonstrating the highly reversible transformation of polyiodide. During discharge, the intensity of these Raman peaks decreases slightly until they disappear completely, indicating that polyiodide conversion occurs (l5 - →I3 - →I - ). The introduction of Co-NC successfully accelerated the reversible transformation of iodine species.

[0056] Due to the confinement of iodine and iodide by Co-NC, the polyiodide anions are firmly anchored on the positive electrode side during the cycle, thus preventing the shuttle effect and the corrosion of the zinc negative electrode by polyiodide, thereby increasing the cycle stability and battery life of the battery. Figure 7 As shown in a, in the SEM image of the negative electrode of the zinc-iodine battery assembled with C-l2 positive electrode after 1000 cycles, it can be seen that the surface of the zinc negative electrode has obvious corrosion, showing the serious shuttle effect of the C-l2 positive electrode. Figure 7 As shown in b, the SEM image of the zinc negative electrode of the zinc-iodine battery assembled with the Co-NC-l2 positive electrode shows a clean, flat surface and produces fewer by-products after 1000 cycles. The results show that the iodine host based on Co-NC-l2 can effectively suppress the shuttle effect, prevent the corrosion of the zinc negative electrode by polyiodides and the occurrence of side reactions, thereby realizing a very stable, long-lasting and shuttle-free Zn-I2 battery.

[0057] Figure 6 In-situ Raman at 0.3°C. Figure 7 SEM images of dendrites on the zinc negative electrode surface after (a) C-l2 and (b) Co-NC-I2 cycles 1000 times.

[0058] Therefore, the combination of electrochemistry and in situ Raman spectroscopy demonstrates that Co-NC can effectively confine polyiodides within the abundant micro-mesopores, thereby preventing their significant leakage and shuttling during the discharge / charge process. More impressively, the embedded Co can serve as an electrocatalytic site to promote the rapid redox reaction of iodine chemistry ( Figure 8 The synergistic effect of these two advantages contributes to the excellent electrochemical performance of Zn-L2 batteries.

[0059] Figure 8Schematic diagram of the principle of rechargeable Zn-l2 battery based on Co-NC positive electrode.

[0060] Electrochemical performance characterization:

[0061] The cyclic voltammetry (CV) curves of C-l2, NC-l2 and Co-NC-l2 are shown in Figure 2. Figure 9 The fast redox kinetics of the zinc-iodine battery was verified by using C as the conductive carrier and a scan rate of 0.5 mV s -1 A fuzzy redox peak with large voltage polarization was observed in the zinc-iodine battery assembled by C-l2, which demonstrated a slow dynamic process, while the redox peak polarization of the zinc-iodine battery assembled by Co-NC-l2 was small, with the redox peak center at approximately 1.26 / 1.31 V and the potential difference as small as 40 mV, showing better reversibility. Figure 9 b shows the starting potentials of the three electrodes according to the first CV curve. The positive electrode starting potential of the Co-NC-l2 electrode is 1.53V, which is greater than that of C-l2 (1.36V) and NC / I2 (1.50V). The zinc-iodine battery assembled by Co-NC-l2 has a smaller overpotential and faster reaction kinetics. In addition, the Tafel slopes of the three electrodes are like Figure 9 As shown in c, it is derived from the CV curve. The Tafel slopes of the zinc-iodine batteries assembled by C-I2, NC-l2 and Co-NC-l2 in the reduction reaction are 234, 114 and 105 mV dec, respectively. -1 During the cathode reaction, the Co-NC-l2 cathode has the lowest Tafel slope among the three electrodes. The above results show that Co-NC has the fastest reaction kinetics, the best reversibility, the smallest polarization voltage and the largest peak area, which indicates that it has the ability to increase the redox kinetics of polyiodides.

[0062] Figure 9 (a) C, NC and Co-NC at 0.5 mV s -1 CV curves, (b) the starting potentials of the positive and negative electrode reactions of CV, and (c) the Tafel slope calculated based on CV; at 0.5 mV s -1 Overlap test of the first 4 CV curves of (d) C, (e) NC and (f) Co-NC.

[0063] like Figure 9 As shown in df, the CV overlap experiment of zinc-iodine batteries assembled with C-l2, NC-l2 and Co-NC-l2 found that there was a pair of obvious redox peaks near 1.25V, and compared with the zinc-iodine battery assembled with C-I2, the zinc-iodine battery assembled with Co-NC-l2 had better overlap, proving that Co-NC has smaller polarization, better reversibility and faster reaction kinetics.

[0064] Influenced by the catalysis of cobalt-nitrogen doped carbon materials, we used zinc-iodine batteries assembled with C-l2, NC-I2 and Co-NC-I2 positive electrodes to conduct rate tests on the batteries. Figure 10 As shown in a, the Co-NC-I2 cathode reaches 201.1, 184.9, 177.1, 172.8, 157.3, 145.1, 133.2, and 121.8 mAh g at 2C, 5C, 8C, 10C, 20C, 30C, 40C, and 50C, respectively. -1 The high specific capacity of NC-l2 and C-l2 cathodes reached 160.4 and 64.8 mAh g at 10C. -1 The capacity of the NC-I2 cathode at a high rate of 50C is higher than that of the Co-NC-I2 cathode. We believe that this is because the iodine loading is too low, while the iodine loading of Co-NC-l2 is much higher than that of the NC-l2 cathode. In fact, the real capacity is partly provided by the carbon. Since we fill in the iodine loading mass when testing the amount of active material, the carbon provides a certain capacity even in the presence of trace iodine, which is higher than that of the Co-NC-I2 cathode. At high current rates, Co-NC-I2 achieves a stable high coulombic efficiency, which is higher than that of C-l2 and NC-l2, highlighting the importance of catalysis.

[0065] The constant current charge and discharge (GCD) curves of Co-NC-I2 batteries at different rates (2C-50C) are shown in Figure 2. Figure 10 As shown in Figure 2b, the specific capacity of the Co-NC-l2 cathode exhibits minimal attenuation with increasing rate, with a uniform and clear charge-discharge platform, consistent with the CV curves. This demonstrates that Co-NC-l2 has high reversibility and more efficient iodine redox conversion.

[0066] Figure 10 (a) Rate performance of C, NC and Co-NC at different currents; (b) Charge and discharge curves of Co-NC at different currents.

[0067] The self-discharge of the battery was explored by static tests. The open circuit voltage of Co-NC-l2 provided ultra-high stability for about 48 hours at a higher voltage, indicating that the dissolution and shuttling of polyiodides can be well suppressed. Figure 11 As shown, the voltage difference of the Co-NC-l2 battery is stable at 0.57 V, while the voltage differences of the C-l2 and NC-l2 batteries are 0.76 V and 0.62 V, indicating that the self-discharge of the Co-NC-l2 battery is well suppressed. In contrast, the C-l2 and NC-l2 batteries show significant self-discharge.

[0068] Figure 11 The self-discharge (time-voltage curve) of C, NC and Co-NC after 48 hours of standing.

[0069] Zn-iodine batteries assembled with C-l2, NC-l2, and Co-NC-l2 cathodes were tested at 5C to investigate the cycling stability ( Figure 12 a). Obviously, at a current of 5C, the -1 ) and NC-l2 (150.8mAh g -1 Compared with the zinc-iodine battery assembled with the positive electrode of Co-NC-l2, the zinc-iodine battery assembled with the positive electrode of Co-NC-l2 has a high efficiency of 183.6 mAh g -1 The Coulombic efficiency of 96% verifies the excellent reversibility of the Co-NC-l2 electrode. At the same time, the Co-NC-l2 electrode also has excellent stable cycle performance and high specific capacity. The charge and discharge curves of C-l2, NC-l2 and Co-NC-l2 batteries are shown in Figure 2. Figure 12 As shown in Figure b. After 1000 cycles, the charge and discharge platform of the zinc-iodine battery assembled with C and NC positive electrodes is significantly reduced. The voltage polarization of the zinc-iodine battery assembled with C positive electrode (159mV) and the voltage polarization of the zinc-iodine battery assembled with NC positive electrode (140mV) are much larger than that of the zinc-iodine battery assembled with Co-NC positive electrode (75mV), indicating that Co-NC has smaller polarization and faster redox reaction kinetics. Figure 12 As shown in c, Co-NC-l2 achieved 20,000 stable cycles at an ultra-high current of 50C, providing 102 mAh g -1 The reversible capacity of 1.5 GHz demonstrates its extraordinary cycling stability.

[0070] The constant current charge-discharge (GCD) curves of zinc-iodine batteries assembled with C-l2, NC-l2 and Co-NC-l2 positive electrodes at different cycle numbers (100, 200, 500, 800, 1000) are shown in Figure 2. Figure 12 As shown in Figure 3, the capacity decay of the zinc-iodine battery assembled with the Co-NC-l2 cathode is small at different cycle numbers, and the capacity decay is not obvious as the number of cycles increases. However, the zinc-iodine battery assembled with the NC-l2 cathode decays severely after 500 cycles, and the zinc-iodine battery assembled with the C-l2 cathode decays significantly from the beginning to the end. This shows that Co-NC-l2 has high reversibility and stable cyclability.

[0071] Figure 12 Cycling performance of C, NC and Co-NC (a) at 5C, (b) charge-discharge curve of the 800th cycle at 5C; (c) long-cycle performance of Co-NC at 50C; charge-discharge curves of different cycles at 5C (d) Co-NC, (e) NC and (f) C.

[0072] This invention addresses the problems of iodine's low conductivity, easy sublimation, and severe multi-iodide shuttle effect. By utilizing metal doping to enhance catalysis, a cobalt-nitrogen-doped carbon material was prepared, thereby accelerating the iodine redox conversion and improving electrochemical performance:

[0073] (1) A cobalt-nitrogen doped carbon material (Co-NC) was prepared by introducing a metal element with higher catalytic activity through a template method and applied to aqueous zinc-iodine batteries. The test results showed that the N-anchored Co active site exhibited high catalytic activity for the I2 / l- electrochemical reaction process, with the lowest Tafel slope (16.7 mV dec) in the oxidation / reduction process. -1 / 98mVdec -1 ), and CV showed that the voltage difference of Co-NC was only 40mV. The overlap degree of Co-NC in the overlapping CV experiment was the highest, which better confirmed its optimal reversible conversion.

[0074] (2) In situ Raman spectroscopy confirmed the reaction kinetics of iodine species conversion. Non-in situ SEM testing of the cycled battery revealed that the surface of the zinc negative electrode of the zinc-iodine battery assembled with Co-NC was smooth and flat, indicating that the material can inhibit the growth of zinc dendrites and the shuttle effect of multiple iodides, and enhance the adsorption and conversion of iodine species. The capacity of Co-NC at a current of 5C is 185mAh g -1 , it can stably cycle 20,000 times at a current of 50C, and the voltage drop is minimal in the 48h self-discharge experiment.

[0075] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries, characterized by: include, (1) Mix the carbon source, nitrogen source and manganese carbonate evenly, heat to 800-850°C, wash and dry to obtain NC material; (2) mixing the NC material obtained in step (1) with a cobalt salt, drying the obtained mixture, heating it to 800-850° C., filtering, washing, and drying it to obtain a Co-NC material; (3) mixing the Co-NC material obtained in step (2) with iodine, grinding, heating to 110-130°C under an inert atmosphere for reaction, and then heating in air to remove the iodine on the surface to obtain a positive electrode material; The carbon source is methylcellulose, and the nitrogen source is urea; The mass ratio of the carbon source, nitrogen source and manganese carbonate is 1:0.5~1:5~10; The cobalt salt is cobalt nitrate hexahydrate, and the mass ratio of the NC material to the cobalt salt is 1:0.97; The mass ratio of the Co-NC material to the iodine element is 1:

1.

2. The method for preparing the cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries according to claim 1, characterized in that: In step (1), the temperature is raised at 5 °C min under an inert atmosphere. -1 Heat to 250℃ and keep warm for 1~2 h, then heat at 5℃min -1 Heat to 800°C and keep warm for 2-3 hours.

3. The method for preparing a cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries according to claim 1 or 2, characterized in that: In step (2), the temperature is raised at 10 °C min under an inert atmosphere. -1 Heat to 130℃ and keep warm for 3~4h, then heat at 5℃min -1 Heat to 800°C and keep warm for 2-3 hours.

4. The method for preparing a cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries according to claim 1 or 2, characterized in that: In step (3), the inert atmosphere includes argon; the heating to 110-130°C for reaction is heating to 120°C for reaction for 8-10 hours; and the heating in air is heating to 100°C in air and keeping warm for 12-24 hours.

5. The cobalt-nitrogen doped carbon positive electrode material for zinc-iodine batteries prepared by the preparation method according to claim 1.

6. Use of the cobalt-nitrogen doped carbon cathode material for zinc-iodine batteries prepared by the preparation method according to claim 1 in zinc-iodine batteries.

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