Bashkiria-based porous carbon material for positive electrode of aqueous zinc-iodine battery and preparation method thereof

Abstract

The application discloses a Bashan-based porous carbon material for a positive electrode of a water-based zinc-iodine battery and a preparation method of the Bashan-based porous carbon material for the positive electrode of the water-based zinc-iodine battery. The preparation method comprises the following steps: mixing Bashan, a first pore-forming agent and a nitrogen source, pre-carbonizing to obtain a pre-carbonized product, wherein the first pore-forming agent is at least one of a bicarbonate, an oxalate and a carbonate; mixing the pre-carbonized product and a second pore-forming agent, high-temperature carbonizing to obtain a high-temperature carbonized product, wherein the second pore-forming agent is a hydroxide pore-forming agent; obtaining a porous carbon material based on the high-temperature carbonized product; mixing the porous carbon material and elemental iodine, placing the mixture in a sealed container, heating at 60-100 DEG C under an inert atmosphere for 3-5 hours to obtain the Bashan-based porous carbon material for the positive electrode of the water-based zinc-iodine battery. The water-based zinc-iodine battery prepared from the Bashan-based porous carbon material for the positive electrode of the water-based zinc-iodine battery has excellent high-rate cycle stability and is suitable for application scenarios of high-rate charging and discharging.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery and its preparation method. Background Technology

[0002] Aqueous zinc-iodine batteries, with zinc as the negative electrode and iodine-based materials as the positive electrode, have advantages such as wide availability of raw materials, simple battery structure, high safety, high energy density, low manufacturing cost, and environmental friendliness. They have shown great application potential in large-scale energy storage systems, low-speed electric vehicles, and power batteries, and have become one of the current research hotspots for new rechargeable batteries.

[0003] As a core component of aqueous zinc-iodine batteries, the cathode material's performance directly determines key electrochemical indicators such as specific capacity, cycle stability, and rate performance. Porous carbon materials, due to their large specific surface area, abundant pore structure, stable physicochemical properties, provision of sufficient sites for iodine adsorption and loading, accelerated ion transport in the electrolyte, low preparation cost, and renewability, play a crucial supporting role in the cathode of aqueous zinc-iodine batteries and have become a highly promising cathode carrier material.

[0004] In the preparation of porous carbon materials, using biomass as a natural carbon source not only has advantages such as wide availability of raw materials, low carbon emissions, and low price, but also enables the high-value utilization of biomass resources. However, in existing technologies, when applying biomass porous carbon materials to the positive electrode carrier of aqueous zinc-iodine batteries, there are still many unresolved technical bottlenecks. These bottlenecks directly result in the overall electrochemical performance of aqueous zinc-iodine batteries failing to meet practical application requirements, seriously hindering their industrialization. The specific technical defects are as follows:

[0005] 1. Poor matching between pore structure and iodine molecule size, resulting in insufficient iodine loading and iodine fixation stability: In existing technologies, porous carbon materials prepared using conventional biomass carbon sources (such as sawdust, straw, shells, etc.) and traditional pore-forming processes (single physical activation or chemical activation) can achieve a large specific surface area and a well-developed pore system. However, the pore size distribution range is relatively wide (usually 0.3-50 nm), and the proportion of microporous structures (pore size 0.5-1 nm) that are highly matched with the size of iodine molecules (molecular diameter approximately 0.56 nm) is relatively low, resulting in a limited effective loading of iodine molecules. Furthermore, iodine molecules mainly adhere to the surface of porous carbon materials and the macropores and mesopores through physical adsorption, and the adsorption force is weak. During battery charge-discharge cycles, iodine species are easily dissolved from the electrode material into the electrolyte, causing a severe "shuttle effect," which directly leads to rapid capacity decay and a significant decrease in cycle stability.

[0006] 2. Poor pore connectivity and limited ion transport efficiency: In traditional pore-forming processes, the distribution of pore-forming agents is uneven, and pores are prone to collapse or blockage during carbonization. This results in the formation of closed or semi-closed pores in the prepared biomass porous carbon materials, making it difficult to construct a continuous and interconnected porous network structure. This type of structure not only hinders the rapid migration and diffusion of zinc ions in the electrolyte, but also limits the effective contact and reaction between iodine species and zinc ions, thus leading to poor rate performance and low charge and discharge efficiency of the battery, which cannot meet the application requirements of high-power scenarios.

[0007] 3. Weak mechanical properties and insufficient electrode structure stability: Existing biomass porous carbon materials have a loose skeleton structure and low mechanical strength. During repeated charging and discharging of the battery, they are easily subjected to external forces such as electrolyte erosion and volume expansion and contraction, which can easily cause phenomena such as pore structure collapse, electrode pulverization, and detachment. This will damage the integrity of the electrode structure and cause the continuous degradation of the battery's electrochemical performance, making it unable to meet the requirements of long-term cycle use.

[0008] 4. Lack of active sites and slow kinetics of iodine redox reaction: The surface chemical properties of the pore walls (especially the inner pore walls) of existing biomass porous carbon materials are simple and lack sufficient active sites (such as nitrogen doping sites, defect sites, etc.), which cannot effectively catalyze the redox reaction of iodine. This results in a slow redox reaction rate of iodine species and a large charge transfer resistance, which further restricts the rate performance and energy efficiency of the battery, making it difficult to achieve both high capacity and high power output. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing balsa wood-based porous carbon materials for the positive electrode of aqueous zinc-iodine batteries.

[0010] Another object of the present invention is to provide a balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery obtained by the above preparation method.

[0011] The objective of this invention is achieved through the following technical solution.

[0012] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0013] Step 1: Mix powdered balsa wood, the first pore-forming agent, and the nitrogen source evenly, and pre-carbonize at 150~350℃ for at least 2 hours in an air atmosphere. Cool to room temperature to obtain a pre-carbonized product. The first pore-forming agent is at least one of bicarbonate, oxalate, and carbonate, and the nitrogen source is one or a mixture of nitrogen-containing organic compounds and ammonium salts. The ratio of balsa wood, the first pore-forming agent, and the nitrogen source by mass is 10:(1~5):(0.5~2).

[0014] In step 1, the bicarbonate is potassium bicarbonate (KHCO3), the oxalate is potassium oxalate (K2C2O4), and the carbonate is potassium carbonate (K2CO3).

[0015] In step 1, the nitrogen-containing organic compound is either melamine or urea.

[0016] In step 1, the ammonium salt is ammonium bicarbonate.

[0017] In step 1, the pre-carbonization time is 5~12 h.

[0018] In step 1, balsa wood needs to be pretreated before use. The pretreatment includes: washing with water under ultrasonic conditions, drying, and pulverizing into powder.

[0019] Step 2: Mix the pre-carbonized product and the second pore-forming agent evenly, and carbonize at a high temperature of 700~900℃ for at least 3 hours under a nitrogen or inert gas atmosphere, and cool to room temperature to obtain a high-temperature carbonized product. The second pore-forming agent is a hydroxide-based pore-forming agent, and the ratio of the pre-carbonized product to the second pore-forming agent by mass is 10:(2~5).

[0020] In step 2, the preferred temperature for high-temperature carbonization is 700~750℃, and the preferred ratio of the pre-carbonized product to the second pore-forming agent is 10:(4~5) by mass.

[0021] In step 2, the hydroxide-based pore-forming agent is one or a mixture of several of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0022] In step 2, the high-temperature carbonization time is 2~4 hours.

[0023] Step 3: The high-temperature carbonization product is subjected to acid washing, water washing (washing to neutral) and drying in sequence to obtain porous carbon material;

[0024] In step 3, the pickling is performed using hydrochloric acid.

[0025] Step 4: Mix the porous carbon material and elemental iodine evenly, place them in a sealed container, and heat at 60-100°C for 3-5 hours under an inert atmosphere (to sublimate the elemental iodine and allow it to be fully adsorbed by the porous carbon material) to obtain balsa wood-based porous carbon material (iodine-loaded balsa wood-based porous carbon composite material) for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine is 0.5:(1.0-2.0) by mass.

[0026] In step 4, the ratio of porous carbon material to elemental iodine is 0.5:(1.8-2.0) by mass.

[0027] The above preparation method yields a balsa-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery.

[0028] In the above technical solution, the balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes: porous carbon material and iodine element loaded in the porous carbon material, wherein the loading amount of iodine element in the balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery (balsa wood-based porous carbon composite material loaded with iodine) is 55-80 wt%.

[0029] In the above technical solution, the porous carbon material has a hierarchical pore structure, which includes micropores with a pore size of 0.5~1.0 nm and mesopores with a pore size of 2.0~4.0 nm.

[0030] In the above technical solution, the specific surface area of ​​the porous carbon material is 2000 m². 2 g -1 The above pore volume is greater than 0.70 cm³. 3 g -1 .

[0031] An aqueous zinc-iodine battery includes: a balsa-based porous carbon material used as the positive electrode of the aqueous zinc-iodine battery.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. This invention selects balsa wood, the fastest-growing and lightest tree in nature, as a carbon source. Its natural vessel and sieve structure is composed of cellulose, hemicellulose, and lignin. After high-temperature carbonization, the framework is retained, transforming it into a network porous carbon material with high specific surface area and high mechanical strength. This solves the defects of porous carbon materials prepared from conventional biomass carbon sources, such as weak mechanical properties and easy collapse of pore structure. Through a two-step carbonization and two-step pore-forming process, the first pore-forming agent, the second pore-forming agent, and the nitrogen source are confined within the pores of the balsa wood, preparing a porous carbon material with a multi-level pore structure and sufficient active sites. When used for iodine loading, this porous carbon material can effectively solve bottlenecks such as low iodine loading, shuttle effect caused by iodine species dissolution, and pore structure collapse, significantly improving iodine loading, optimizing reaction kinetics, and thus enabling aqueous zinc-iodine batteries to have high energy density, long cycle life, and green safety, with broad application prospects.

[0034] 2. The porous carbon material prepared by this invention has a high specific surface area and a precisely regulated hierarchical pore structure, forming an adsorption-confinement-diffusion synergistic effect. The hierarchical pore structure includes micropores and mesopores. Micropores that match iodine molecules can efficiently capture iodine molecules, achieving spatial confinement of iodine. This spatial confinement effect can inhibit the generation and dissolution of polyiodide ions, reduce the shuttle effect, and improve the cycle stability of the battery. Mesopores can serve as a fast diffusion channel for zinc ions, reducing transport resistance and significantly improving the rate performance of the battery.

[0035] 3. This invention introduces abundant nitrogen-doped active sites through a two-step carbonization and two-step pore-forming process, overcoming the bottleneck of insufficient active sites and slow reaction kinetics in existing biomass porous carbon materials. Nitrogen-doped sites enhance iodine adsorption capacity and increase iodine loading, while simultaneously catalyzing the redox reaction of iodine and reducing charge transfer resistance, achieving a balance between high capacity and high power in the battery and optimizing its overall electrochemical performance.

[0036] 4. At a current density of 20C, the initial discharge specific capacity of the aqueous zinc-iodine battery is 149.70 mAh g. -1 Even after 3000 cycles, the discharge specific capacity remains as high as 129.82 mAh g. -1 With a capacity retention rate of 86.72%, it exhibits excellent high-rate cycle stability and is highly adaptable to high-rate charge and discharge application scenarios. Attached Figure Description

[0037] Figure 1 The elemental distribution diagram is shown for the balsa-based porous carbon material used as the cathode of the aqueous zinc-iodine battery prepared in Example 1.

[0038] Figure 2 Thermogravimetric curves of the balsa-based porous carbon material used in the positive electrode of the aqueous zinc-iodine battery in Example 1, the porous carbon material in Example 1, and elemental iodine;

[0039] Figure 3 Nitrogen adsorption-desorption isotherms of the porous carbon material prepared in Example 1 and the balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery;

[0040] Figure 4 Pore ​​size distribution diagrams of the porous carbon material prepared in Example 1 and the balsa-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery;

[0041] Figure 5 The cyclic voltammogram of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 1 using balsa wood-based porous carbon material;

[0042] Figure 6 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 1 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0043] Figure 7 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 1 using balsa wood-based porous carbon material at a current density of 1 C.

[0044] Figure 8The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 1 using balsa wood-based porous carbon material at a current density of 5 C.

[0045] Figure 9 The rate performance diagram is shown for the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material of the aqueous zinc-iodine battery in Example 1.

[0046] Figure 10 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 1 using balsa wood-based porous carbon material at a current density of 10 C.

[0047] Figure 11 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 2 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0048] Figure 12 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 3 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0049] Figure 13 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 4 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0050] Figure 14 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 5 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0051] Figure 15 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 6 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0052] Figure 16 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 7 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0053] Figure 17 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 8 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0054] Figure 18 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 9 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0055] Figure 19 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 10 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0056] Figure 20 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 11 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0057] Figure 21 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 12 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0058] Figure 22 The charge-discharge curves of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery of Example 13 using balsa wood-based porous carbon material are shown at a current density of 1 C.

[0059] Figure 23 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 13 using balsa wood-based porous carbon material at a current density of 1 C.

[0060] Figure 24 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 8 using balsa wood-based porous carbon material at a current density of 1 C.

[0061] Figure 25 Electrochemical impedance spectroscopy (Nyquist plot) of aqueous zinc-iodine batteries prepared by using balsa wood-based porous carbon material for the positive electrode of aqueous zinc-iodine batteries in Examples 1 and 14-15 and iodine supported on biomass porous carbon material in Example 16.

[0062] Figure 26 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 1 using balsa wood-based porous carbon material at a current density of 20 C.

[0063] Figure 27 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 14 using balsa wood-based porous carbon material at a current density of 20 C.

[0064] Figure 28 The graph shows the cycling performance of the aqueous zinc-iodine battery prepared from the positive electrode of the aqueous zinc-iodine battery in Example 15 using balsa wood-based porous carbon material at a current density of 20 C.

[0065] Figure 29The graph shows the cycling performance of an aqueous zinc-iodine battery prepared by loading iodine onto the biomass porous carbon material of Example 16 at a current density of 20 C. Detailed Implementation

[0066] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0067] The raw material information involved in the following examples is as follows:

[0068]

[0069] Balsa wood needs to be pretreated before use. The pretreatment includes: crushing the balsa wood purchased from Zhejiang Youwei New Material Co., Ltd. into wood chips, ultrasonically dispersing it with deionized water for 30 minutes at a power of 220 W and an ultrasonic frequency of 40 kHz, drying it at 120℃ to constant weight, pulverizing it into powder with a pulverizer, and passing it through a 60-mesh standard sieve to obtain balsa wood powder with uniform particle size.

[0070] Thermogravimetric test: The material is heated from room temperature to 500℃ at a rate of 5℃ / min.

[0071] Iodine, porous carbon materials, and balsamic-based porous carbon materials (iodine-loaded balsamic-based porous carbon composite materials) used as cathodes in aqueous zinc-iodine batteries were subjected to thermogravimetric analysis (TGA) tests, and the iodine loading in the balsamic-based porous carbon materials for aqueous zinc-iodine battery cathodes was calculated. The formula for calculating the iodine loading in the balsamic-based porous carbon materials for aqueous zinc-iodine battery cathodes is as follows:

[0072] Iodine loading = (Mass of porous carbon material at T℃ to its mass at room temperature) (%) - (Mass of balsa wood-based porous carbon material for the positive electrode of aqueous zinc-iodine batteries at T℃ to its mass at room temperature) (%). To make the iodine loading value more accurate, the iodine loading at T℃ = 300℃, 350℃, 400℃, 450℃ and 500℃ was calculated and the average value was taken.

[0073] The following embodiments illustrate the assembly method of an aqueous zinc-iodine battery (CR2032 button cell): a zinc sheet (16 mm in diameter) is used as the negative electrode, a glass fiber membrane (Whatman) is used as the separator, and the electrolyte is an aqueous ZnSO4 solution (prepared from zinc sulfate heptahydrate) with a ZnSO4 concentration of 1M. The method for preparing the positive electrode includes: mixing positive electrode material, acetylene black, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, and deionized water (by mass, the ratio of positive electrode material, acetylene black, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, and deionized water is 800:100:50:50:3000), stirring until homogeneous to obtain a positive electrode slurry, coating the positive electrode slurry onto titanium foil, drying at room temperature for 12 hours, and cutting it into small circular pieces with a diameter of 16 mm using a cutting machine to obtain the positive electrode. The loading of the positive electrode material on the positive electrode is 3.5 mg / cm³. 2 The cathode material is one of the balsa wood-based porous carbon materials for aqueous zinc-iodine batteries prepared in Examples 1-15 and the iodine-loaded biomass porous carbon material prepared in Example 16.

[0074] The electrochemical performance of aqueous zinc-iodine batteries was tested in the voltage range of 0.8–1.6 V using the Shanghai Chenhua CHI660E electrochemical workstation and the Blue Battery testing system.

[0075] Examples 1-7

[0076] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0077] Step 1: Add the pretreated balsa wood (powder), the first pore-forming agent, and the nitrogen source to a mortar and grind manually for 30 minutes until uniformly mixed. Place the mixture in a tube furnace and heat it to 200°C at a rate of 10°C / min under an air atmosphere. Pre-carbonize the mixture at 200°C for 5 hours (to remove moisture and some tar from the balsa wood). Cool to room temperature to obtain the pre-carbonized product. The first pore-forming agent is potassium bicarbonate (KHCO3), and the nitrogen source is melamine. The ratio of balsa wood, the first pore-forming agent, and the nitrogen source by mass is 10:5:2.

[0078] Step 2: Add the pre-carbonized product and the second pore-forming agent to a mortar and grind manually for 30 minutes until they are evenly mixed. Place the mixture in a tube furnace and heat it to X℃ at a rate of 5℃ / min under an argon atmosphere. Carbonize at X℃ for 3 hours (during the high-temperature carbonization process, the first pore-forming agent and the second pore-forming agent work together to form pores). Cool to room temperature to obtain the high-temperature carbonized product. The second pore-forming agent is potassium hydroxide (KOH). The ratio of the pre-carbonized product to the second pore-forming agent by mass is Y.

[0079] Step 3: The high-temperature carbonization product is sequentially acid-washed, water-washed (washed to neutral), and dried to obtain porous carbon material. Specifically, the high-temperature carbonization product is immersed in excess hydrochloric acid (HCl concentration in hydrochloric acid is 1 mol / L), acid-washed for 6 hours at room temperature and stirring speed of 500 r / min (to remove metal ion impurities), then washed with deionized water until neutral, and finally dried at 120℃ to constant weight.

[0080] Step 4: Mix the porous carbon material and elemental iodine, and dry ball mill at 200 r / min for 2 h (ball-to-material mass ratio of 20:1). Transfer the mixture to a reaction vessel and heat it to 100°C under a sealed argon atmosphere. o C causes elemental iodine to sublimate at 100°C. o The material is kept at temperature C for 4 hours to allow iodine to be fully adsorbed by the porous carbon material, thus obtaining balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine is Z by mass.

[0081] X, Y, and Z are shown in Table 1.

[0082] Table 1

[0083]

[0084] Example 8 (as a comparison)

[0085] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0086] Step 1: Add the pretreated balsa wood, the first pore-forming agent, and the nitrogen source to a mortar and grind manually for 30 minutes until the mixture is uniform. Place the mixture in a tube furnace and heat it to 200°C at a rate of 10°C / min under an air atmosphere. Pre-carbonize the mixture at 200°C for 5 hours and then cool it to room temperature to obtain the pre-carbonized product. The first pore-forming agent is potassium bicarbonate (KHCO3), and the nitrogen source is melamine. The ratio of balsa wood, the first pore-forming agent, and the nitrogen source by mass is 10:5:2.

[0087] Step 2: Add the pre-carbonized product to a mortar and grind manually for 30 minutes until it is evenly mixed. Place it in a tube furnace and heat it to 900°C at a rate of 5°C / min under an argon atmosphere. Carbonize it at 900°C for 3 hours and cool it to room temperature to obtain the high-temperature carbonized product.

[0088] Step 3: The high-temperature carbonization product is sequentially acid-washed, water-washed (washed to neutral), and dried to obtain porous carbon material. Specifically, the high-temperature carbonization product is immersed in excess hydrochloric acid, acid-washed for 6 hours at room temperature and stirring speed of 500 r / min, then washed with deionized water until neutral, and finally dried at 120℃ to constant weight. The concentration of HCl in the hydrochloric acid is 1 mol / L.

[0089] Step 4: Mix the porous carbon material and elemental iodine, and dry ball mill at 200 r / min for 2 h (ball-to-material mass ratio of 20:1). Transfer the mixture to a reaction vessel and heat it to 100°C under a sealed argon atmosphere. o C causes elemental iodine to sublimate at 100°C. o The material was kept at temperature C for 4 hours to allow iodine to be fully adsorbed by the porous carbon material, thus obtaining balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine was 0.5:1 by mass.

[0090] Example 9 (as a comparison)

[0091] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery is basically the same as that in Example 8, except that the phrase "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:2" is replaced with "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:1".

[0092] Example 10 (as a comparison)

[0093] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery is basically the same as that in Example 8, except that the phrase "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:2" is replaced with "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:0.5".

[0094] Example 11 (for comparison)

[0095] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery is basically the same as that in Example 8, except that the phrase "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:2" is replaced with "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:3:0.5".

[0096] Example 12 (as a comparison)

[0097] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery is basically the same as that in Example 8, except that the phrase "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:5:2" is replaced with "by mass parts, the ratio of balsa wood, the first pore-forming agent and the nitrogen source is 10:1:0.5".

[0098] Example 13 (for comparison)

[0099] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0100] Step 1: Add the pretreated balsa wood to a mortar and grind manually for 30 minutes until it is evenly mixed. Place it in a tube furnace and heat it to 200°C at a rate of 10°C / min in an air atmosphere. Pre-carbonize it at 200°C for 5 hours and then cool it to room temperature to obtain the pre-carbonized product.

[0101] Step 2: Add the pre-carbonized product to a mortar and grind manually for 30 minutes until it is evenly mixed. Place it in a tube furnace and heat it to 900°C at a rate of 5°C / min under an argon atmosphere. Carbonize it at 900°C for 3 hours and cool it to room temperature to obtain the high-temperature carbonized product.

[0102] Step 3: The high-temperature carbonization product is sequentially acid-washed, water-washed (washed to neutral), and dried to obtain porous carbon material. Specifically, the high-temperature carbonization product is immersed in excess hydrochloric acid, acid-washed for 6 hours at room temperature and stirring speed of 500 r / min, then washed with deionized water until neutral, and finally dried at 120℃ to constant weight. The concentration of HCl in the hydrochloric acid is 1 mol / L.

[0103] Step 4: Mix the porous carbon material and elemental iodine, and dry ball mill at 200 r / min for 2 h (ball-to-material mass ratio of 20:1). Transfer the mixture to a reaction vessel and heat it to 100°C under a sealed argon atmosphere. o C causes elemental iodine to sublimate at 100°C. o The material was kept at temperature C for 4 hours to allow iodine to be fully adsorbed by the porous carbon material, thus obtaining balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine was 0.5:1 by mass.

[0104] Example 14 (for comparison)

[0105] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0106] Step 1: Add the pretreated balsa wood, the first pore-forming agent, the second pore-forming agent, and the nitrogen source to a mortar and grind manually for 30 min until uniformly mixed. Place the mixture in a tube furnace and heat it to 200 ℃ at a rate of 10 ℃ / min under an air atmosphere. Pre-carbonize the mixture at 200 ℃ for 5 h and then cool it to room temperature to obtain the pre-carbonized product. The first pore-forming agent is potassium bicarbonate (KHCO3), the second pore-forming agent is potassium hydroxide (KOH), and the nitrogen source is melamine. The mass ratio of balsa wood, the first pore-forming agent, the second pore-forming agent, and the nitrogen source is 10:5:5:2 (the mass retention rate of balsa wood after pre-carbonization is 97 wt% to 98 wt%, and the mass change of balsa wood before and after pre-carbonization is very small).

[0107] Step 2: Place the pre-carbonized product in a tube furnace, heat it to 700 ℃ at a rate of 5 ℃ / min under an argon atmosphere, and carbonize it at 700 ℃ for 3 h. Cool it to room temperature to obtain the high-temperature carbonized product.

[0108] Step 3: The high-temperature carbonization product is sequentially acid-washed, water-washed (washed to neutral), and dried to obtain porous carbon material. Specifically, the high-temperature carbonization product is immersed in excess hydrochloric acid (HCl concentration in hydrochloric acid is 1 mol / L), acid-washed for 6 hours at room temperature and stirring speed of 500 r / min (to remove metal ion impurities), then washed with deionized water until neutral, and finally dried at 120℃ to constant weight.

[0109] Step 4: Mix the porous carbon material and elemental iodine, and dry ball mill at 200 r / min for 2 h (ball-to-material mass ratio of 20:1). Transfer the mixture to a reaction vessel and heat it to 100°C under a sealed argon atmosphere. o C causes elemental iodine to sublimate at 100°C. o The material was kept at temperature C for 4 hours to allow iodine to be fully adsorbed by the porous carbon material, thus obtaining balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine was 0.5:2 by mass.

[0110] Example 15 (as a comparison)

[0111] A method for preparing a balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery includes the following steps:

[0112] Step 1: Add the pretreated balsa wood and nitrogen source to a mortar and grind manually for 30 min until evenly mixed. Place the mixture in a tube furnace and heat it to 200 ℃ at a rate of 10 ℃ / min under an air atmosphere. Pre-carbonize the mixture at 200 ℃ for 5 h and cool it to room temperature to obtain the pre-carbonized product. The nitrogen source is melamine, and the ratio of balsa wood to nitrogen source by mass is 10:2.

[0113] Step 2: Add the pre-carbonized product, the first pore-forming agent, and the second pore-forming agent to a mortar and grind manually for 30 min until uniformly mixed. Place the mixture in a tube furnace and heat it to 700 ℃ at a rate of 5 ℃ / min under an argon atmosphere. Carbonize at 700 ℃ for 3 h and cool to room temperature to obtain the high-temperature carbonized product. The first pore-forming agent is potassium bicarbonate (KHCO3), and the second pore-forming agent is potassium hydroxide (KOH). The ratio of the pre-carbonized product, the first pore-forming agent, and the second pore-forming agent by mass is 10:5:5 (the mass retention rate of balsa wood after pre-carbonization is 97 wt% to 98 wt%, and the mass change of balsa wood before and after pre-carbonization is very small).

[0114] Step 3: The high-temperature carbonization product is sequentially acid-washed, water-washed (washed to neutral), and dried to obtain porous carbon material. Specifically, the high-temperature carbonization product is immersed in excess hydrochloric acid (HCl concentration in hydrochloric acid is 1 mol / L), acid-washed for 6 hours at room temperature and stirring speed of 500 r / min (to remove metal ion impurities), then washed with deionized water until neutral, and finally dried at 120℃ to constant weight.

[0115] Step 4: Mix the porous carbon material and elemental iodine, and dry ball mill at 200 r / min for 2 h (ball-to-material mass ratio of 20:1). Transfer the mixture to a reaction vessel and heat it to 100°C under a sealed argon atmosphere. o C causes elemental iodine to sublimate at 100°C. o The material was kept at temperature C for 4 hours to allow iodine to be fully adsorbed by the porous carbon material, thus obtaining balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to elemental iodine was 0.5:2 by mass.

[0116] Example 16 (for comparison)

[0117] Iodine-loaded biomass porous carbon material is the biomass porous carbon material prepared in Example 4 of the invention patent with publication number CN121341997A.

[0118] The iodine loading amounts in the balsa wood-based porous carbon materials used for the positive electrodes of aqueous zinc-iodine batteries prepared in Examples 1-15 and the biomass porous carbon materials prepared in Example 16 were 62.61 wt%, 60.06 wt%, 58.68 wt%, 60.08 wt%, 60.84 wt%, 58.36 wt%, 57.14 wt%, 54.64 wt%, 54.44 wt%, 54.52 wt%, 52.08 wt%, 49.72 wt%, 40.44 wt%, 54.56 wt%, 56.78 wt%, and 62.2 wt%, respectively.

[0119] Elemental analysis of the balsa-based porous carbon material used in the aqueous zinc-iodine battery cathode prepared in Example 1 was performed using scanning electron microscopy and energy dispersive spectroscopy. The results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the balsa wood-based porous carbon material used in the positive electrode of the aqueous zinc-iodine battery includes four elements: carbon (C), nitrogen (N), oxygen (O) and iodine (I), and the four elements are evenly distributed.

[0120] Figure 2 Balsamic wood-based porous carbon material for the positive electrode of the aqueous zinc-iodine battery in Example 1 ( Figure 2 The "iodine-carbon composite" in Example 1 and the porous carbon material in Example 1 ( Figure 2 Thermogravimetric curves of porous carbon and elemental iodine, from Figure 2 It can be seen that the iodine loading in the balsa wood-based porous carbon material used as the positive electrode of the aqueous zinc-iodine battery prepared in Example 1 is 62.61 wt%. The thermogravimetric curve of elemental iodine shows that it loses weight rapidly in the range of about 100~200℃, which directly reflects the thermal behavior of elemental iodine's easy sublimation and volatilization, proving that iodine exists in the carbon support in a molecular state through physical adsorption.

[0121] The porous carbon material prepared in Example 1 ( Figure 3 and Figure 4 "Porous carbon" and balsa wood-based porous carbon materials for the positive electrode of aqueous zinc-iodine batteries ( Figure 3 and Figure 4 The BET test was performed on the "iodine-carbon composite" and the results were obtained. Figure 3 Nitrogen adsorption-desorption isotherms and Figure 4 Aperture distribution diagram. For example... Figure 3 As shown, under low relative pressure (P / P0 < 0.1), the nitrogen adsorption-desorption isotherm of the porous carbon material points vertically upwards, indicating the presence of micropores in the porous carbon material. The specific surface area of ​​the porous carbon material is 2019.156 m². 2 g -1 The pore volume is 0.74 cm³. 3 g -1 The specific surface area of ​​the balsa wood-based porous carbon material used in the positive electrode of an aqueous zinc-iodine battery is 293.378 m². 2 g -1 .like Figure 4 As shown, the pore size of the porous carbon material is concentrated in the range of 0.5–2 nm, with a small amount distributed in the range of 2–4 nm, indicating that the porous carbon material contains abundant micropores and mesopores. The peak intensity of the balsa wood-based porous carbon material used as the cathode in an aqueous zinc-iodine battery is significantly lower than that of the porous carbon material. These results indicate that iodine is not only attached to the surface of the porous carbon material, but a large amount of iodine is trapped in the abundant micropores of the porous carbon material.

[0122] On the Shanghai Chenhua CHI660E electrochemical workstation, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode in Example 1 was subjected to cyclic voltammetry testing within a voltage window of 0.8V to 1.6V, with a scan rate of 0.1 mV / s. The voltage-current response data for the first cycle were recorded, as shown below. Figure 5 The cyclic voltammetry curves shown are as follows: Figure 5As shown, the voltage corresponding to the reduction peak of the aqueous zinc-iodine battery is 1.201V, and the voltage corresponding to the oxidation peak is 1.264V. The difference between the voltages corresponding to the reduction peak and the oxidation peak is 0.063V, indicating excellent redox reversibility and low polarization. This suggests that the use of balsa wood-based porous carbon material in the cathode of the aqueous zinc-iodine battery can effectively accelerate charge transfer and iodine species diffusion rate, significantly suppress polyiodide ion shuttle, and thus significantly improve the charge-discharge stability, rate performance, and cycle life of the aqueous zinc-iodine battery.

[0123] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode of Example 1 was subjected to its first charge-discharge test, and the results were as follows: Figure 6 The charge-discharge curves shown are derived from... Figure 6 It can be seen that the small potential difference between the charging and discharging platforms indicates that its electrode polarization is small; the specific capacity of the first charge and the specific capacity of the first discharge are both close to the theoretical specific capacity of iodine, 211 mAh g. -1 This indicates that under the confinement of the micropore space, the dispersion and utilization of iodine are significantly improved, and the vast majority of the loaded iodine effectively participates in the electrochemical reversible reaction of the battery, thereby ensuring the high specific capacity of the battery.

[0124] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 1 was subjected to charge-discharge tests and 200 cycles, yielding the following results: Figure 7 The cycle performance graph shown is from Figure 7 It can be seen that its initial discharge specific capacity is 211.67 mAh g. -1 After 200 cycles, it has 211.54 mAh g. -1 The discharge specific capacity has a capacity retention rate of 99.94%.

[0125] At a current density of 5C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode of Example 1 was subjected to charge-discharge tests and 10,000 cycles, yielding the following results: Figure 8 The cycle performance graph shown is from Figure 8 It can be seen that its initial discharge specific capacity is 174.80 mAh g. -1 After 10,000 cycles, it has 162.30 mAh g. -1 The discharge specific capacity has a capacity retention rate of 92.85%.

[0126] The aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode of the aqueous zinc-iodine battery in Example 1 was subjected to discharge tests at different current densities, and the results were as follows: Figure 9The rate performance diagram shown illustrates the discharge specific capacity obtained after 11 cycles at each current density, with each cycle yielding one discharge specific capacity. The current density increases from 0.2C, 0.5C, 1C, 2C, 3C to 5C, then sequentially decreases back to 3C, 2C, 1C, 0.5C, and 0.2C. Figure 9 It can be seen that the discharge specific capacity (average value) corresponding to the current density increasing from 0.2C, 0.5C, 1C, 2C, 3C to 5C, and then decreasing back to 3C, 2C, 1C, 0.5C, and 0.2C is 235.64 mAh g⁻¹. -1 220.20 mAhg -1 209.73 mAh g -1 190.53 mAh g -1 173.29 mAh g -1 154.59mAh g -1 174.59mAh g -1 184.72mAh g -1 202.70mAh g -1 211.98mAh g -1 228.95mAh g -1 .

[0127] At a current density of 10C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode of Example 1 was subjected to charge-discharge tests and 11,000 cycles, yielding the following results: Figure 10 The cycle performance graph shown is from Figure 10 It can be seen that its initial discharge specific capacity is 164.06 mAh g. -1 After 11,000 cycles, it has 147.65 mAh g. -1 The discharge specific capacity has a capacity retention rate of 89.99%.

[0128] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 2 was subjected to its first charge-discharge test, and the results were as follows: Figure 11 The charge-discharge curves shown are derived from... Figure 11 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 2 has a first-cycle charge specific capacity of 211.60 mAh g. -1 The first discharge specific capacity is 208.04 mAh g. -1 .

[0129] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 3 was subjected to its first charge-discharge test, and the results were as follows: Figure 12 The charge-discharge curves shown are derived from... Figure 12 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 3 has a first-cycle charge specific capacity of 203.09 mAh g. -1 The first discharge specific capacity is 202.80 mAh g. -1 .

[0130] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 4 was subjected to its first charge-discharge test, and the results were as follows: Figure 13 The charge-discharge curves shown are derived from... Figure 13 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 4 has a first-cycle charge specific capacity of 196.12 mAh g. -1 The first discharge specific capacity was 192.11 mAh g. -1 .

[0131] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 5 was subjected to its first charge-discharge test, and the results were as follows: Figure 14 The charge-discharge curves shown are derived from... Figure 14 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 5 has a first-cycle charge specific capacity of 192.11 mAh g. -1 The first discharge specific capacity was 191.67 mAh g. -1 .

[0132] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 6 was subjected to its first charge-discharge test, and the results were as follows: Figure 15 The charge-discharge curves shown are derived from... Figure 15 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 6 has a first-cycle charge specific capacity of 193.75 mAh g. -1 The first discharge specific capacity is 189.64 mAh g. -1 .

[0133] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 7 was subjected to its first charge-discharge test, and the results were as follows: Figure 16 The charge-discharge curves shown are derived from... Figure 16It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 7 has a first-cycle charge specific capacity of 189.16 mAh g. -1 The first discharge specific capacity is 187.15 mAh g. -1 .

[0134] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 8 was subjected to its first charge-discharge test, and the results were as follows. Figure 17 The charge-discharge curves shown are derived from... Figure 17 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 8 has a first-cycle charge specific capacity of 185.12 mAh g. -1 The first discharge specific capacity was 183.48 mAh g. -1 .

[0135] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 9 was subjected to its first charge-discharge test, and the results were as follows: Figure 18 The charge-discharge curves shown are derived from... Figure 18 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 9 has a first-cycle charge specific capacity of 180.12 mAh g. -1 The first discharge specific capacity is 177.63 mAh g. -1 .

[0136] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 10 was subjected to its first charge-discharge test, and the results were as follows: Figure 19 The charge-discharge curves shown are derived from... Figure 19 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 10 has a first-cycle charge specific capacity of 178.55 mAh g. -1 The first discharge specific capacity was 178.41 mAh g. -1 .

[0137] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 11 was subjected to its first charge-discharge test, and the results were as follows: Figure 20 The charge-discharge curves shown are derived from... Figure 20 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 11 has a first-cycle charge specific capacity of 175.08 mAh g.-1 The first discharge specific capacity is 174.66 mAh g. -1 .

[0138] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 12 was subjected to its first charge-discharge test, and the results were as follows: Figure 21 The charge-discharge curves shown are derived from... Figure 21 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode in Example 12 has a first-cycle charge specific capacity of 172.93 mAh g. -1 The first discharge specific capacity was 170.43 mAh g. -1 .

[0139] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 13 was subjected to its first charge-discharge test, and the results were as follows: Figure 22 The charge-discharge curves shown are derived from... Figure 22 It can be seen that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode in Example 13 has a first-cycle charge specific capacity of 144.81 mAh g. -1 The first discharge specific capacity is 143.80 mAh g. -1 .

[0140] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 13 was subjected to charge-discharge tests and 200 cycles, yielding the following results: Figure 23 The cycle performance graph shown is from Figure 23 It can be seen that its initial discharge specific capacity is 156.61 mAh g. -1 After 200 cycles, it has 92.34 mAh g. -1 The discharge specific capacity has a capacity retention rate of 58.96%.

[0141] At a current density of 1 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 8 was subjected to charge-discharge tests and 200 cycles, yielding the following results: Figure 24 The cycle performance graph shown is from Figure 24 It can be seen that its initial discharge specific capacity is 181.31 mAh g. -1 After 200 cycles, it has 173.67 mAh g. -1 The discharge specific capacity has a capacity retention rate of 95.79%.

[0142] The specific capacity of the first charge and the specific capacity of the first discharge corresponding to the charge-discharge curves are plotted in Table 2.

[0143] Table 2

[0144]

[0145] By comparing the first-cycle charge specific capacity and first-cycle discharge specific capacity corresponding to Examples 1-13, it can be seen that the first-cycle charge-discharge specific capacity of the aqueous zinc-iodine battery prepared with balsa wood-based porous carbon material as the cathode in Examples 1-12 is at a high level, and the difference between the first-cycle charge specific capacity and the first-cycle discharge specific capacity is extremely small. This indicates that the iodine loaded on the porous carbon material can fully and effectively participate in the redox electrochemical reaction of the battery, and the iodine utilization rate is high. Among them, the first-cycle charge-discharge specific capacity of the aqueous zinc-iodine battery prepared with balsa wood-based porous carbon material as the cathode in Examples 1-7 is higher than that in Examples 8-12. This shows that the two-step pore-forming can precisely control the pore structure of balsa wood and construct a hierarchical porous system, which not only increases the iodine loading sites but also shortens the ion transport path, thereby effectively improving the first-cycle charge-discharge specific capacity of the aqueous zinc-iodine battery.

[0146] Using a Princeton electrochemical workstation, under open-circuit voltage conditions, AC impedance tests were performed on aqueous zinc-iodine batteries prepared using balsa wood-based porous carbon material as the positive electrode in Examples 1 and 14-15, and on an aqueous zinc-iodine battery prepared using iodine-loaded biomass porous carbon material as described in Example 16. The results were as follows: Figure 25 The Nyquist curve shown is from... Figure 25 It can be seen that the order of charge transfer resistance (semicircle diameter) for Examples 1 and Examples 14-16 is: Example 1 < Example 15 < Example 14 < Example 16. Example 1 has the smallest semicircle diameter and the lowest charge transfer resistance, indicating that its electrode interface charge transfer rate is the fastest and ion transport resistance is the lowest. This is due to the stepwise pore-forming strategy: the first pore-forming agent (KHCO3) constructs preliminary pores in the pre-carbonization stage, and the second pore-forming agent (KOH) further expands the pores and forms a hierarchical pore structure in the high-temperature carbonization stage. The pore connectivity is good, the specific surface area is high, and the iodine element is highly dispersed, effectively reducing the electrode-electrolyte interface impedance and improving the reaction kinetics. Example 1, by adding the first and second pore-forming agents stepwise, precisely controls the hierarchical pore structure of the porous carbon material, achieving high dispersion and efficient utilization of iodine element, significantly reducing the electrode interface impedance, and improving charge transfer kinetics. Therefore, it exhibits the best electrochemical performance in an aqueous zinc-iodine battery.

[0147] At a current density of 20 C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the positive electrode of Example 1 was subjected to charge-discharge tests and 3000 cycles, yielding the following results: Figure 26 The cycle performance graph shown is from... Figure 26 It can be seen that, at a high current density of 20C, the initial discharge specific capacity of the aqueous zinc-iodine battery is 149.70 mAh g. -1 Even after 3000 cycles, the discharge specific capacity remains as high as 129.82 mAh g. -1 The capacity retention rate reached 86.72%, and the average coulombic efficiency after 3000 cycles was 99.47%, demonstrating extremely excellent long-term cycling stability and structural durability. This is attributed to the natural continuous and mechanically strong vessel and sieve skeleton of Balsa wood, which, after pre-carbonization, high-temperature carbonization, and two-step pore-forming, forms a stable and non-collapse-resistant hierarchical porous carbon network. At the same time, by precisely controlling the 0.5~1.0 nm micropores and 2~4 nm mesopore structure, efficient adsorption and spatial confinement of iodine molecules are achieved, significantly suppressing iodine species dissolution and shuttle effects. In addition, the catalytic effect of nitrogen-doped active sites on the iodine redox reaction significantly reduces the electrode charge transfer resistance, thereby achieving an ultra-long cycle life and stable coulombic efficiency at high current densities.

[0148] At a current density of 20C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 14 was subjected to charge-discharge tests and 3000 cycles, yielding the following results: Figure 27 The cycle performance graph shown is from Figure 27 It can be seen that its initial discharge specific capacity is 140.04 mAh g. -1 After 3000 cycles, it has 97.82 mAh g. -1 The discharge specific capacity was 69.85%, with a capacity retention rate of 69.85% and an average coulombic efficiency of 99.14% after 3000 cycles. In Example 14, both the first and second pore-forming agents were added during the pre-carbonization stage, without employing the stepwise pore-forming strategy of this invention. During pre-carbonization, the carbon skeleton had not yet formed. The simultaneous addition of the first and second pore-forming agents led to excessive etching of the balsa wood skeleton, resulting in disordered pores, decreased connectivity, and even localized collapse. A stable hierarchical porous structure could not be formed, and the uniformity of iodine loading and the iodine fixation effect were significantly reduced. This fully demonstrates the crucial role of the stepwise pore-forming strategy of this invention.

[0149] At a current density of 20C, the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode material in Example 15 was subjected to charge-discharge tests and 3000 cycles, yielding the following results: Figure 28 The cycle performance graph shown is from Figure 28 It can be seen that its initial discharge specific capacity is 144.54 mAh g.-1 After 3000 cycles, it has 93.24 mAh g. -1 The discharge specific capacity was 64.50%, and the average coulombic efficiency after 3000 cycles was 97.28%. In Example 15, the first and second pore-forming agents were added simultaneously during the high-temperature carbonization stage. This resulted in excessive etching intensity, severely damaging the integrity of the balsa wood carbon skeleton, leading to poor pore connectivity and insufficient structural stability. This prevented effective anchoring of iodine, exacerbated the shuttle effect, and consequently reduced the cycle stability of the aqueous zinc-iodine battery. This further confirms the necessity of the two-step pore-forming process of this invention.

[0150] At a current density of 20C, an aqueous zinc-iodine battery prepared by loading iodine onto biomass porous carbon material as described in Example 16 was subjected to charge-discharge tests and cycled 3000 times, yielding the following results: Figure 29 The cycle performance graph shown is from Figure 29 It can be seen that its initial discharge specific capacity is 129.80 mAh g. -1 After 3000 cycles, it has 76.70 mAh g. -1 The discharge specific capacity was 59.09%, and the average coulombic efficiency after 3000 cycles was 98.74%. Example 16 did not use balsa wood as a carbon source, nor did it employ the stepwise pore-forming strategy of this invention. This resulted in the iodine-loaded biomass porous carbon material prepared in Example 4 of CN121341997A failing to form a hierarchical pore structure, exhibiting poor matching between the pore structure and iodine molecules, and lacking efficient iodine fixation sites and catalytic sites. Consequently, the aqueous zinc-iodine battery experienced rapid capacity decay during high current density cycling.

[0151] Depend on Figures 26-29 As can be seen, after 3000 cycles at an ultra-high current density of 20C, the capacity retention rate of the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode in Example 1 is significantly higher than that in Examples 14-16. These results fully demonstrate that the aqueous zinc-iodine battery prepared using balsa wood-based porous carbon material as the cathode in Example 1 exhibits excellent long-cycle performance at a high current density of 20C, effectively solving the problems of short cycle life and severe shuttle effect in aqueous zinc-iodine batteries.

[0152] This invention selects Balsa wood, which has the fastest growth rate and lightest density in nature, as a biomass carbon source. It innovatively designs a two-step carbonization and pore-forming process of "low-temperature pre-carbonization and high-temperature carbonization," successfully preparing Balsa wood-based porous carbon materials suitable for the cathode requirements of aqueous zinc-iodine batteries. Its core advantages are as follows:

[0153] (1) Balsa wood has a well-developed natural pore system and excellent mechanical properties. Its rich and strong internal vessels and sieves are composed of cellulose, hemicellulose and lignin. During the high-temperature carbonization pore-forming process, its skeleton structure can be retained and transformed into a porous carbon material with high mechanical strength, high specific surface area and interconnected pore structure. It is an ideal biomass carbon source for preparing porous carbon materials for the positive electrode of water-based zinc-iodine batteries.

[0154] (2) The present invention employs two-step carbonization and two-step pore-forming. Specifically, in the pre-carbonization stage, a first pore-forming agent is added to perform mild pre-pore-forming. By uniformly dispersing the first pore-forming agent and nitrogen source in the natural channels such as vessels and sieves of balsa wood in the low-temperature pre-carbonization stage, preliminary pore opening and framework stability are achieved. In the high-temperature carbonization stage, a second pore-forming agent is added to perform deep activation pore-forming. Under the premise of maintaining the stability of the original framework structure of balsa wood, uniform pore-forming can be achieved, and an interconnected network porous carbon framework structure can be constructed. At the same time, the introduction of nitrogen source can form abundant nitrogen-doped active sites on the inner surface of porous carbon, achieving multiple effects of "pore-forming, nitrogen fixation, and enhanced structural stability", achieving the technical effect of "killing multiple birds with one stone".

[0155] Porous carbon materials prepared by combining balsa wood as a carbon source with a two-step carbonization and two-step pore-forming process possess a stable, non-collapse-prone, interconnected network framework structure, high specific surface area, abundant nitrogen-doped active sites, and a sufficient number of micropores matching iodine molecules. Using it as an iodine-carrying material can significantly enhance the adsorption capacity and loading of iodine molecules, effectively inhibit the dissolution of iodine species in the electrolyte, accelerate the electrode reaction kinetics rate, and thus significantly improve the specific capacity, rate performance, charge-discharge stability, and cycle life of aqueous zinc-iodine batteries, providing technical support for the industrial application of aqueous zinc-iodine batteries.

[0156] The preparation method proposed in this invention is simple, easy to operate, and low in cost; the porous carbon material has good conductivity, effectively binds iodine, and has a high iodine loading. Aqueous zinc-iodine batteries prepared using balsa-based porous carbon materials as the cathode exhibit excellent electrochemical performance.

[0157] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery, characterized in that, Includes the following steps: Step 1: Mix the powdered balsa wood, the first pore-forming agent, and the nitrogen source evenly, and pre-carbonize at 150~350℃ for at least 2 hours in an air atmosphere. Cool to room temperature to obtain the pre-carbonized product. The first pore-forming agent is bicarbonate, the nitrogen source is melamine, and the ratio of balsa wood, the first pore-forming agent, and the nitrogen source by mass is 10:(1~5):(0.5~2). Step 2: Mix the pre-carbonized product and the second pore-forming agent evenly, and carbonize at a high temperature of 700~900℃ for at least 3 hours under a nitrogen or inert gas atmosphere, and cool to room temperature to obtain a high-temperature carbonized product. The second pore-forming agent is a hydroxide-based pore-forming agent. The ratio of the pre-carbonized product to the second pore-forming agent by mass is 10:(2~5). The hydroxide-based pore-forming agent is potassium hydroxide. Step 3: The high-temperature carbonization product is subjected to acid washing, water washing and drying in sequence to obtain porous carbon material; Step 4: Mix the porous carbon material and iodine evenly, place them in a sealed container, and heat at 60-100°C for 3-5 hours under an inert atmosphere to obtain balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery. The ratio of porous carbon material to iodine is 0.5:(1.0-2.0) by mass.

2. The preparation method according to claim 1, characterized in that, In step 1, the bicarbonate is potassium bicarbonate.

3. Balsamic-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery obtained by the preparation method according to any one of claims 1 to 2.

4. The balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery according to claim 3, characterized in that, The balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery comprises: porous carbon material and iodine element loaded in the porous carbon material, wherein the loading amount of the iodine element in the balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery is 55-80 wt%.

5. The balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery according to claim 4, characterized in that, The porous carbon material has a hierarchical pore structure, which includes micropores with a pore size of 0.5~1.0 nm and mesopores with a pore size of 2.0~4.0 nm.

6. The balsa wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery according to claim 4, characterized in that, The specific surface area of ​​porous carbon materials is 2000 m² 2 g -1 The above pore volume is greater than 0.70 cm³. 3 g -1 .

7. An aqueous zinc-iodine battery, characterized in that, include: Balsamic wood-based porous carbon material for the positive electrode of an aqueous zinc-iodine battery as described in claim 3.

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