A sulfur-iron flow battery and self-supporting electrodes, preparation and use thereof

Abstract

This invention belongs to the field of batteries, specifically relating to a sulfur-iron flow battery and its self-supporting electrode, its preparation, and its application. The self-supporting electrode includes a base electrode and an array of active materials grown in situ on its surface; wherein the chemical formula of the active material is Co. x Ni y (CO3)2(OH)2, x / y is 1~2.5; x+y=3; the active material has an orthorhombic crystal structure. This invention innovatively demonstrates that forming an array of active materials with the aforementioned special phases and structures in situ on the substrate electrode can adapt to the charge-discharge characteristics of sulfur-iron flow batteries, achieving excellent energy density, power density, and energy storage efficiency even at low loads. Furthermore, it can also adapt to high-rate, long-cycle requirements.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials research, and in particular relates to the field of sulfur-iron flow battery technology. Background Technology

[0002] Polysulfide-iron / ferrocyanide (sulfur-iron) flow batteries are an emerging type of flow battery, containing S2 2- / S4 2- and [Fe(CN)6] 3- / [Fe(CN)6] 4- The solutions of the redox couple serve as the negative and positive electrolytes, respectively, and are charged and discharged through the reversible redox reaction of the two couples on the electrode surface.

[0003] The carbon felt electrode is a crucial component of the sulfur-iron flow battery stack, its main function being to provide [Fe(CN)6] with carbon. 3- / [Fe(CN)6] 4- and S2 2- / S4 2- The redox reactions of the two electron couples provide a site for these reactions. The interconversion of polysulfides at the negative electrode involves multi-electron processes, resulting in slow redox kinetics, which limits the energy density, power density, and energy storage efficiency of sulfur-iron flow batteries. Therefore, it is necessary to improve the redox rate of polysulfides on the negative electrode side. However, the carbon felt itself has low catalytic activity for polysulfide redox reactions, leading to slow reaction kinetics and severe polarization at the negative electrode, significantly limiting the overall performance improvement of sulfur-iron flow batteries. Therefore, it is necessary to load a catalyst onto the carbon felt to address the low activity of the original carbon felt. Summary of the Invention

[0004] To address the unsatisfactory electrochemical performance of existing sulfur-iron flow batteries, including electrode activity, capacity, efficiency, and high-rate long-cycle performance, the primary objective of this invention is to provide a self-supporting electrode for sulfur-iron flow batteries, its preparation method, and its application in sulfur-iron flow batteries.

[0005] A second objective of the present invention is to provide a sulfur-iron flow battery comprising the self-supporting electrode.

[0006] A self-supporting electrode for a sulfur-iron flow battery includes a base electrode and an array of active materials grown in situ on its surface; wherein the chemical formula of the active material is Co. x Ni y (CO3)2(OH)2, x / y is 1~2.5; x+y=3;

[0007] The active material has an orthorhombic crystal structure.

[0008] This invention innovatively demonstrates that forming an array of active materials with the special phase and structure in situ on the substrate electrode can adapt to the charge and discharge characteristics of sulfur-iron flow batteries, achieving excellent energy density, power density, and energy storage efficiency even under low load. Furthermore, it can also adapt to high-rate, long-cycle requirements.

[0009] In this invention, the substrate electrode is a carbon felt.

[0010] Preferably, the x / y ratio is 1.5 to 2.2; more preferably, it is 1.9 to 2.1:1. At these preferred ratios, superior flow battery performance can be achieved.

[0011] In this invention, the total loading of Co and Ni in the self-supporting electrode is 5~25 Wt.%.

[0012] The present invention also provides a method for preparing the self-supporting electrode of the sulfur-iron flow battery, wherein a water-soluble cobalt source, a water-soluble Ni source, and Formula 1 are dispersed in water to obtain a mixed solution, the mixed solution is mixed with a substrate electrode and sealed in a pressure-resistant container, and then heated to construct a subcritical state; and then subjected to heat and pressure treatment in this state, and then separated to obtain the self-supporting electrode.

[0013] Formula 1;

[0014] The total concentration of the water-soluble cobalt source and the water-soluble Ni source is 0.15~0.3M; the ratio of the total molar amount of the water-soluble cobalt source and the water-soluble Ni source to the molar amount of Formula 1 is 1:0.8~2;

[0015] The total weight ratio of the water-soluble cobalt source and the water-soluble Ni source to the weight ratio of the substrate electrode is 0.15~0.4:1;

[0016] The temperature for heating to construct the subcritical state is 170~220℃; the holding time is 18~30h.

[0017] This invention pre-treats the raw materials under subcritical conditions with heat and pressure, and through the combined control of parameters such as raw materials, proportions, subcritical temperature, and heat and pressure holding time during the processing, synergistic effects can be achieved. This enables the in-situ growth of the active array with the special physicochemical structure on the substrate electrode. Moreover, this active array is adapted to the characteristics of sulfur-iron flow batteries, and can effectively catalyze polysulfides in sulfur-iron flow batteries, enabling them to achieve excellent capacity, efficiency, energy density, and long-cycle performance at high rates.

[0018] In the mixed solution of the present invention, the total molar concentration of cobalt and nickel is 0.15~0.25M, and more specifically 0.19~0.21M.

[0019] The ratio of the total molar amount of the water-soluble cobalt source and the water-soluble Ni source to the molar amount of Formula 1 is 1:0.95~1.05.

[0020] The total weight ratio of the water-soluble cobalt source and the water-soluble Ni source to the weight of the substrate electrode is 0.25~0.35:1.

[0021] In this invention, the mixed solution can be sealed in a pressure-resistant container and then heated to create a subcritical state.

[0022] The filling volume of the mixed solution in the pressure-resistant container can be adjusted as needed, for example, it can be 30~60v.

[0023] In this invention, the heating temperature is 180~200℃.

[0024] In this invention, the heat preservation and pressure holding time is 22~26h.

[0025] The present invention also provides an application of a self-supporting electrode, which is used as a negative electrode to prepare a sulfur-iron flow battery, wherein the self-supporting electrode is the self-supporting electrode described in the present invention.

[0026] The present invention also provides a sulfur-iron flow battery, wherein the negative electrode is the self-supporting electrode described in the present invention.

[0027] In this invention, the active material of the positive electrode includes at least one of carbon felt, graphite felt, nickel foam, and carbon paper;

[0028] The sulfur-iron flow battery of the present invention, except for the self-supporting electrode described in the present invention, may have known components and structural relationships.

[0029] Beneficial effects

[0030] This invention provides a self-supporting electrode with the aforementioned special active array formed in situ, which is adapted to the characteristics of flow batteries and is suitable for S2. 2- / S4 2- The redox reaction exhibits excellent electrocatalytic activity, which enables the flow battery to exhibit excellent energy density, power density, and energy storage efficiency. In addition, it can significantly improve its structural stability and effectively improve its long-cycle performance at high rates.

[0031] The sulfur-iron flow battery assembled by the method of this invention achieves a speed of 80 mA / cm². 2 At the current density, the battery energy efficiency reaches 79.03% (as in Example 1); at the current density returning to 20 mA / cm², the energy efficiency is as high as 79.03% (as in Example 1). 2 At that time, the battery energy efficiency hardly decreased, remaining at around 92.14%. Attached Figure Description

[0032] Figure 1 Scanning electron microscope images of the active material / carbon felt electrode prepared in Example 1: (a) CF; (b) CF-01.

[0033] Figure 2 The image shows the X-ray diffraction pattern of the active material / carbon felt electrode prepared in Example 1.

[0034] Figure 3 The diagram shows the energy efficiency and coulombic efficiency of the active material / carbon felt electrode and the blank carbon felt electrode prepared in Example 1 during long-cycle operation.

[0035] Figure 4 The diagrams show the energy efficiency (a), coulombic efficiency, and voltage efficiency (b) of the active material / carbon felt electrode prepared in Example 1 and the carbon felt electrode in the experimental group.

[0036] Figure 5 The infrared spectrum of the active material / carbon felt electrode prepared in Example 1 is shown. Detailed Implementation

[0037] The process method of the present invention will be further described below through specific embodiments.

[0038] The battery assembly structure includes end plates, current collectors (copper sheets), bipolar plates (carbon plates), flow frames, electrodes, and separators. Battery performance (rate capability, long-cycle life, etc.) in this invention was tested at room temperature and pressure using the Xinwei Battery Testing System. The separator used in this invention is Nafion 212, which was soaked in 2M NaOH for 12 hours before use. The sulfur-side electrolyte for electrochemical testing was 0.5M Na₂S₂ + NaOH, and the iron-side electrolyte was 0.3M K₃[Fe(CN)₆] + 2M NaOH. The positive electrode was a blank carbon felt (CF) without any loaded material, and the negative electrode was the self-supporting electrode (carbon felt loaded with material) described in this invention. The carbon felt was from Liaoning Jingu Carbon Materials Co., Ltd., and all sizes used were 4 cm × 4 cm.

[0039] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0040] Example 1

[0041] Using cobalt nitrate as the cobalt source and nickel nitrate as the Ni source (nickel nitrate in this case), a mixed salt solution was prepared according to Formula 1, wherein the total concentration of cobalt and Ni ions was 0.2 M (the molar ratio of Co to Ni was 2:1), and the concentration of Formula 1 was 0.2 mol / L. 60 mL of the prepared mixed salt solution and a piece of carbon felt CF (the total metal salts of Co and Ni were 0.3 times the weight of the carbon felt) were placed in a 100 mL pressure-resistant reactor. The reactor was sealed (the filling volume of the solution in the sealed reactor was 50 v%), then heated to 180 ℃ (subcritical reaction: temperature marked T) and held under this temperature and pressure for 24 hours (reaction time). After washing the active material / carbon felt electrode with deionized water, it was dried in an oven at 60 ℃ for 12 h to obtain the in-situ grown active material carbon felt electrode, designated CF-01. 80 mA / cm 2 The energy efficiency is 79.03%.

[0042] Example 2

[0043] Compared with Example 1, the only difference is that the reaction time is changed. Other operations and parameters are the same as in Example 1, and the operations and effects are as follows:

[0044] Group A: Reaction time was 18 h; the material obtained had an 80 mA / cm² concentration. 2 The energy efficiency is 77.3%.

[0045] Control group A: reaction time was 12 h; the material obtained had a strength of 80 mA / cm². 2 The energy efficiency is 74.72%.

[0046] Control group B: reaction time was 9 h; the material obtained had a strength of 80 mA / cm². 2 The energy efficiency is 74.15%.

[0047] Example 3

[0048] Compared with Example 1, the only difference is that, while keeping the total molar concentration of total metal ions in the total mixed solution constant, the molar ratio of cobalt to Ni is changed. All other operations and parameters are the same as in Example 1. The experiments and results are as follows:

[0049] Group A: Co / Ni molar ratio of 1:1; the resulting material has an 80 mA / cm² strength. 2 The energy efficiency is 76.69%.

[0050] Group B: Co / Ni molar ratio of 1.5:1; the resulting material has an efficiency of 80 mA / cm². 2 The energy efficiency is 77.96%.

[0051] Group C: Co / Ni molar ratio of 2.5:1; the material prepared from this group has an efficiency of 80 mA / cm².2 The energy efficiency is 76.94%.

[0052] Comparative group A: Co / Ni molar ratio of 3:1; the material prepared from this group has a strength of 80 mA / cm². 2 The energy efficiency is 73.2%.

[0053] Example 4

[0054] Compared to Example 1, the only difference is the change in subcritical reaction conditions; all other operations and parameters are the same as in Example 1. The operations and results are as follows:

[0055] Group A: In a nickel-cobalt metal solution, the total concentration of nickel and cobalt is 0.25 M, and the total volume of the metal solution and other operating conditions remain unchanged; the material obtained has an 80 mA / cm³ concentration. 2 The energy efficiency is 79.12%.

[0056] Group B: The ratio of the total molar amount of water-soluble cobalt source and water-soluble Ni source to the molar amount of Equation 1 is 1:1.2; the weight ratio of the total weight of water-soluble cobalt source and water-soluble Ni source to the weight of the substrate electrode is 0.25:1; the material prepared from this method has an efficiency of 80 mA / cm². 2 The energy efficiency is 77.52%.

[0057] Example 5

[0058] Compared to Example 1, the only difference is that the reaction temperature T is changed to 200°C; all other operations and parameters are the same as in Example 1. 80 mA / cm 2 Its energy efficiency is 79.1%.

[0059] Comparative Example 1

[0060] Compared to Example 1, the only difference is that in step 1, a Ni source is missing, and the missing Ni is supplemented by an equimolar amount of cobalt source. The amount of cobalt metal used is the same as the molar amount of Ni. All other operations and parameters are the same as in Example 1. The carbon felt obtained in Comparative Example 1 has a performance of 80 mA / cm². 2 The energy efficiency is 74.12%.

[0061] Comparative Example 2

[0062] Compared to Example 1, the only difference is that the electrode obtained in step 1 is calcined in air at 350°C for 3 hours to obtain the negative electrode. All other operations and parameters are the same as in Example 1. The carbon felt obtained in Comparative Example 2 has a specific temperature range of 80 mA / cm². 2 The energy efficiency is 73.9%.

[0063] Comparative Example 3

[0064] Compared with Example 1, the only difference is that in step 1, the processing temperature T is 120°C, and all other operations and parameters are the same as in Example 1. The carbon felt obtained in Comparative Example 3 is at 80 mA / cm 2 The energy efficiency is 74.24%.

[0065] Comparative Example 4

[0066] Compared to Example 1, the only difference is that in step 1, Ni is replaced with equimolar amounts of the following metals, and the experimental groups are as follows:

[0067] Group A: Zn replaced Ni; Result: 80 mA / cm 2 The energy efficiency is 71.65%.

[0068] Group B: Fe replaced Ni; Result: 80 mA / cm 2 The energy efficiency is 65.37%.

[0069] Preparation process and performance of the product of this invention: From the appendix Figure 1 It can be seen that the active material prepared using this invention is uniformly loaded on the surface of the carbon felt, arranged regularly and tightly in a needle-like morphology. (From the attached...) Figure 2 It can be seen that the synthesized material is a basic cobalt carbonate carbon felt electrode doped with metallic nickel. From the attached... Figure 3 It can be seen that the active material exhibits good cycling stability; after 200 cycles, the energy efficiency and coulombic efficiency do not decrease significantly, and its performance is significantly improved compared to the blank carbon felt. (From the attached...) Figure 4 It can be seen that the in-situ loaded active material carbon felt electrode material prepared by the present invention improves the energy density and energy storage efficiency of sulfur-iron flow battery.

[0070] From the appendix Figure 5 As can be seen from the infrared spectrum of the in-situ supported active material carbon felt electrode, an infrared spectrum appears at 3500 cm⁻¹. -1 The strong peak at [value] is attributed to the stretching vibration peak of -OH. ν(OCO2), ν(CO3) / CO, ν(C=O), δ(CO3), δ(OCO), and ρ(OCO) are at 1500, 1385, 1043, 831, 745, and 694 cm⁻¹, respectively. -1 The appearance of CO3 indicates 2- It exists in the sample as a ligand. 964 cm -1 The peak represents the bending vibration of Co / Ni-OH.

Claims

1. A self-supporting electrode for a sulfur-iron flow battery, characterized in that, This includes a base electrode and an array of active materials grown in situ on its surface; wherein the chemical formula of the active material is Co. x Ni y (CO3)2(OH)2,; x / y is 1~2.5:1; x+y=3; The active material has an orthorhombic crystal structure.

2. The self-supporting electrode of the sulfur-iron flow battery as described in claim 1, characterized in that, The substrate electrode is a carbon felt.

3. The self-supporting electrode of the sulfur-iron flow battery as described in claim 1, characterized in that, In the self-supporting electrode, the total loading of Co and Ni is 5~25 wt.%.

4. A method for preparing a self-supporting electrode for a sulfur-iron flow battery according to any one of claims 1 to 3, characterized in that, A water-soluble cobalt source, a water-soluble Ni source, and Formula 1 were dispersed in water to obtain a mixed solution. The mixed solution was then mixed with the substrate electrode and sealed in a pressure-resistant container, followed by heating to construct a subcritical state. The self-supporting electrode is then subjected to heat and pressure treatment under this condition and subsequently separated to obtain the self-supporting electrode. Formula 1; The total concentration of the water-soluble cobalt source and the water-soluble Ni source is 0.15~0.3M; the ratio of the total molar amount of the water-soluble cobalt source and the water-soluble Ni source to the molar amount of Formula 1 is 1:0.8~2; The total weight ratio of the water-soluble cobalt source and the water-soluble Ni source to the weight ratio of the substrate electrode is 0.15~0.4:1; The temperature for heating to construct the subcritical state is 170~220℃; the holding time is 18~30h.

5. The method for preparing the self-supporting electrode of the sulfur-iron flow battery as described in claim 4, characterized in that, In the mixed solution, the total molar concentration of cobalt and nickel is 0.15~0.25M, and even further, 0.19~0.21M.

6. The method for preparing the self-supporting electrode of the sulfur-iron flow battery as described in claim 4, characterized in that, The heating temperature is 180~200℃.

7. The method for preparing the self-supporting electrode of the sulfur-iron flow battery as described in claim 6, characterized in that, The heat preservation and pressure holding time is 22~26 hours.

8. An application of a self-supporting electrode as a negative electrode in the assembly of a sulfur-iron flow battery, characterized in that, The self-supporting electrode is the self-supporting electrode according to any one of claims 1 to 3, or the self-supporting electrode prepared by the preparation method according to any one of claims 4 to 7.

9. A sulfur-iron flow battery, characterized in that, The negative electrode is the self-supporting electrode according to any one of claims 1 to 3, or the self-supporting electrode prepared by the preparation method according to any one of claims 4 to 7.

10. The sulfur-iron flow battery as described in claim 9, characterized in that, The active material of the positive electrode includes at least one of carbon felt, graphite felt, nickel foam, and carbon paper.

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