Kara gum-based biopolymer electrolyte for magnesium-air battery and preparation method and application thereof

Abstract

This invention provides a carrageenan-based biopolymer electrolyte for magnesium-air batteries, its preparation method, and its applications. By introducing lithium bromide into a κ-carrageenan matrix and co-doping with magnesium acetate, this invention prepares a biopolymer gel electrolyte that possesses high ionic conductivity, excellent discharge performance, and good mechanical properties. This electrolyte can replace aqueous electrolytes to solve the problems of self-corrosion and leakage in magnesium-air batteries, meeting the needs of flexible energy storage. It also significantly improves the discharge time, discharge efficiency, and discharge specific capacity of magnesium-air batteries, making it suitable for flexible solid-state power supplies in wearable devices. The electrolyte preparation method of this invention is simple, low-cost, and environmentally friendly and biodegradable.

Description

Technical Field

[0001] This invention belongs to the field of magnesium-air battery technology, and relates to biopolymer electrolytes for magnesium-air batteries, specifically to carrageenan-based biopolymer electrolytes for magnesium-air batteries, their preparation methods, and applications. Background Technology

[0002] With the continuous growth of global energy demand and the increasing prominence of environmental problems, the development of new clean energy sources and efficient energy storage and conversion technologies has become a critical issue that urgently needs to be addressed. Traditional energy storage technologies, such as lithium-ion batteries, generally face problems such as high cost, insufficient safety, and poor environmental compatibility. Against this backdrop, metal-air batteries, due to their significant advantages such as high energy density, low cost, safety, reliability, and environmental friendliness, have gradually become a research hotspot for next-generation electrochemical energy storage systems. This type of battery adopts an open structure, directly utilizing oxygen from the air as the cathode active material, while the anode can be selected from metals or alloys abundant in the Earth's crust, such as aluminum, magnesium, and lithium. The discharge products are environmentally friendly, aligning with the concept of green and sustainable development.

[0003] Among numerous metal-air battery systems, the magnesium-air battery (Mg-O2 battery) has attracted considerable attention due to its unique performance advantages. This system boasts a theoretical operating voltage as high as 3.1 V and a power output of 3910 Wh·kg⁻¹. -1 With its theoretical energy density, low cost, and environmental friendliness, the magnesium-air battery shows broad application prospects in areas with clear demands for flexible energy storage, such as portable electronic devices and smart wearable products. Meanwhile, the development of high-performance magnesium-air batteries is also expected to alleviate the current problems of lithium-ion batteries, such as their dependence on rare metals and high manufacturing energy consumption, providing a feasible path for building a diversified electrochemical energy storage system.

[0004] As a core component of magnesium-air batteries, the electrolyte's composition and properties directly affect the battery's energy conversion efficiency, operational life, and safety. Currently, magnesium-air batteries commonly use aqueous electrolytes (such as 3.5 wt% NaCl solution). While these electrolytes offer the advantage of high ionic conductivity, a series of key technological bottlenecks severely restrict their practical application. On one hand, magnesium anodes in aqueous systems are highly susceptible to severe self-corrosion and hydrogen evolution side reactions, leading to reduced anode utilization and significant voltage hysteresis. This results in the battery's actual operating voltage being far lower than the theoretical value, with an open-circuit voltage of only about 1.6 V, further decreasing to around 1.2 V after current loading. Simultaneously, the "negative differential effect" during discharge further exacerbates anode losses, resulting in an actual specific energy density less than 10% of the theoretical value. On the other hand, aqueous electrolytes, due to their high fluidity, easily penetrate porous air electrodes, posing a leakage risk and failing to meet the basic requirements of flexible, wearable devices for safe and deformable power systems. Therefore, developing novel electrolyte systems has become one of the core breakthroughs for improving the overall performance of magnesium-air batteries.

[0005] In recent years, polymer electrolytes have gained widespread attention in energy storage device research. However, most existing polymer electrolytes are based on synthetic polymers such as polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF), whose raw materials are derived from fossil fuels, are difficult to biodegrade, and have high costs, thus falling short of the requirements for green and sustainable development. In contrast, biopolymer electrolytes based on natural polymers such as agar, starch, carrageenan, and chitosan are gradually becoming the forefront of polymer electrolyte research. Existing bio-based electrolyte systems struggle to maintain high ionic conductivity while simultaneously achieving excellent discharge performance and mechanical strength, hindering their practical application in magnesium-air batteries. Therefore, developing a bio-based gel polymer electrolyte that combines high ionic conductivity, good discharge performance, and excellent mechanical properties is of significant scientific and practical value for overcoming the performance bottlenecks of magnesium-air batteries and promoting their practical and large-scale application. Summary of the Invention

[0006] To address the problems in the prior art, this invention provides a carrageenan-based biopolymer gel electrolyte for magnesium-air batteries, its preparation method, and its application.

[0007] The present invention adopts the following technical solution: A carrageenan-based biopolymer gel electrolyte for magnesium-air batteries, characterized in that 1-3% w / v κ-carrageenan is first added to a 0.4-0.7 mol·L⁻¹ solution at 70-90℃. -1The LiBr solution was stirred until homogeneous, and then magnesium acetate was added and mixed until homogeneous to obtain a κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution, wherein the mass ratio of magnesium acetate to κ-carrageenan was 1-7:3-9; then, a biopolymer gel electrolyte was prepared by solution casting.

[0008] The present invention also provides a method for preparing the above-mentioned carrageenan-based biopolymer gel electrolyte for magnesium-air batteries.

[0009] A method for preparing a carrageenan-based biopolymer gel electrolyte for magnesium-air batteries includes the following steps: (1) Add 1.5-3% w / v κ-carrageenan to a 0.4-0.7 mol·L⁻¹ thermometer at 70-90℃. -1 The LiBr solution was stirred until homogeneous, and then magnesium acetate was added and mixed until homogeneous to obtain a κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution, wherein the mass ratio of magnesium acetate to κ-carrageenan was 1-7:3-9. (2) The obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution was poured into a container at 70-90℃ and cooled to obtain a biopolymer gel electrolyte.

[0010] According to one embodiment of the present invention, the amount of magnesium acetate doped is 10%-50% (based on the total mass of magnesium acetate and κ-carrageenan being 100%); preferably 10-30%.

[0011] According to one embodiment of the present invention, the κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution is stirred at 50-80 °C for 1-3 h before being poured into the container.

[0012] According to one embodiment of the present invention, the cooling is room temperature cooling for 20-60 minutes.

[0013] According to one embodiment of the present invention, the product is dried after cooling at room temperature, with a drying temperature of 50-70 °C and a drying time of 1-5 h.

[0014] According to one embodiment of the present invention, the obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution is stirred at 70-80 °C for 1-3 h and then poured into a container while hot. After cooling at room temperature for 20-40 min, a carrageenan-based biopolymer gel electrolyte is obtained.

[0015] According to one embodiment of the present invention, the obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution is poured into a container at 60-80 °C, cooled for 20-40 min, dried at 50-70 °C for 1-5 h, and then cooled to room temperature for 20-40 min to obtain carrageenan-based biopolymer gel electrolyte.

[0016] According to one embodiment of the present invention, the magnesium acetate doping amount is 10-30 wt%, and the product is dried for 1-4 h.

[0017] According to one embodiment of the present invention, the magnesium acetate doping amount is 10-20 wt%, and the product is dried for 4 h.

[0018] This invention relates to a biopolymer gel electrolyte based on κ-carrageenan, used to replace the traditional aqueous electrolyte in primary magnesium-air batteries. This electrolyte not only possesses high ionic conductivity but also significantly extends the discharge time, improves discharge efficiency and capacity of primary magnesium-air batteries, while also exhibiting excellent mechanical properties. Therefore, it effectively solves the problems of severe anodic corrosion, leakage safety hazards, and low energy density in existing magnesium-air batteries, meeting the urgent need for safe and efficient electrolyte materials in flexible energy storage devices.

[0019] This invention provides a carrageenan-based biopolymer electrolyte for magnesium-air batteries, its preparation method, and its applications. By introducing lithium bromide into a κ-carrageenan matrix and co-doping with magnesium acetate, this invention prepares a biopolymer gel electrolyte that possesses high ionic conductivity, excellent discharge performance, and good mechanical properties. This electrolyte can replace aqueous electrolytes to solve the problems of self-corrosion and leakage in magnesium-air batteries, meeting the needs of flexible energy storage, and can also significantly improve the discharge time, discharge efficiency, and discharge specific capacity of magnesium-air batteries. The electrolyte preparation method of this invention is simple, low-cost, and environmentally friendly and biodegradable.

[0020] Specifically, the present invention has the following beneficial effects: (1) Undried electrolyte significantly improves basic discharge performance This invention significantly improves the ionic conductivity of the electrolyte by introducing lithium bromide into a κ-carrageenan matrix and co-doping with magnesium acetate. The electrolyte ionic conductivity increased from 3.91 × 10⁻⁶ to 3.91 × 10⁻⁶. -2 S·cm -1 Increased to 4.44×10 -2 S·cm -1 (14% increase), the discharge specific capacity of the assembled magnesium-air battery increased from 1033.77 mAh·g -1 The discharge capacity was increased to 1336.37 mAh·g⁻¹, and the discharge efficiency increased from 46.87% to 60.59% (both increases of 29%). This indicates that LiBr combined with magnesium acetate (40-70 wt%) can effectively improve the discharge performance of magnesium-air batteries while extending the discharge time by 1.54-6.76 h, and the specific discharge capacity of magnesium-air batteries is increased by 372-394 mAh·g⁻¹. -1 Discharge efficiency is improved by 36-38%.

[0021] (2) The dried electrolyte combines high discharge performance with excellent mechanical properties The mechanical properties of undried polymer electrolytes are poor. This invention further optimizes the electrolyte performance through drying treatment (60℃, 1-4 h). After drying, the electrolyte maintains high ionic conductivity (4.81×10⁻⁶). -2 -5.47×10 -2 S·cm -1 Simultaneously, the mechanical strength is significantly enhanced. When the magnesium acetate doping content is 10-30 wt% and drying time is 1-4 h, the discharge time of the magnesium-air battery is further increased by 48%-139% compared to the undried state, reaching a maximum of 23.40 h (10 wt% magnesium acetate, dried for 4 h), and the discharge specific capacity reaches 1315.02-1414.27 mAh·g. -1 The discharge efficiency remained between 61.19% and 64.23%. Mechanical property tests showed that the electrolyte could undergo tensile testing after drying; when the magnesium acetate doping content was 20 wt% and drying time was 4 h, the tensile strength reached 4.63 × 10⁻⁶. -1 MPa can effectively meet the mechanical performance requirements of wearable devices for flexible solid-state power supplies.

[0022] (3) Green environmental protection and process economy This invention uses κ-carrageenan, a natural and renewable resource, as the matrix. The raw material is widely available, inexpensive, and biodegradable. The electrolyte preparation process employs an aqueous solution casting method, requiring no organic solvents or complex equipment, making it simple to operate and easy to scale up for production. Furthermore, by systematically controlling the mass ratio of κ-carrageenan to magnesium acetate, this invention screens out the optimal composition range that combines high conductivity with good film-forming properties, providing a clear technical path for the composition optimization of biopolymer electrolytes for magnesium-air batteries. Attached Figure Description

[0023] Figure 1 These are electrochemical impedance spectroscopy spectra of κ-carrageenan-based biopolymer electrolytes doped with different amounts of magnesium acetate; Figure 2 The discharge performance (2.5 mA·cm⁻¹) of magnesium-air batteries doped with different amounts of magnesium acetate is shown. -2 Resulting figure; Figure 3 The images show the electrochemical impedance spectroscopy of κ-carrageenan-lithium bromide-magnesium acetate biopolymer electrolytes with different drying times, where (a) is 10% magnesium acetate; (b) is 30% magnesium acetate; (c) is 20% magnesium acetate; and (d) is 50% magnesium acetate. Figure 4 The discharge performance (2.5 mA·cm⁻¹) of magnesium-air batteries with different drying times. -2 Resulting figure; Figure 5This is a graph showing the compressive stress-strain curves of biopolymer electrolytes with different drying times. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments.

[0025] Unless otherwise specified, any range described in this invention includes the endpoint, any value between the endpoints, and any subrange formed by the endpoint or any value between the endpoints. Unless otherwise specified, all percentages mentioned in this invention are mass percentages. The following examples further illustrate the content of this invention, but are not intended to limit the invention.

[0026] All raw materials and reagents used in this invention are commercially available products. Unless otherwise specified, all ratios mentioned in this invention are mass ratios.

[0027] Comparative Example 1 The electrolyte used in this comparative example was prepared from κ-carrageenan and a 3.5 wt% sodium chloride aqueous solution commonly used in magnesium-air batteries. 2% w / v κ-carrageenan was added to a 3.5 wt% NaCl solution at 70°C and stirred for 2 h to obtain a homogeneous polymer electrolyte solution. While still hot, this solution was poured into a pre-washed and dried petri dish and cooled to room temperature for 30 min to obtain a κ-carrageenan-NaCl gel polymer electrolyte with a thickness of 6 mm. This was then cut into 30 mm × 10 mm rectangular electrolyte samples for later use. These electrolyte samples were sandwiched between stainless steel sheets to assemble an SS|PE|SS structure test cell. Electrochemical impedance spectroscopy was used to measure its ionic conductivity under open-circuit potential conditions, with a scan frequency range of 10. 5 The excitation signal was 10mV, ranging from Hz to 0.1Hz. An AZ31B magnesium alloy sample measuring 50 mm × 10 mm × 1 mm was prepared by progressively polishing its surface with 200#, 400#, 600#, 800#, and 1000# metallographic sandpaper. A magnesium-air battery was assembled using this polymer electrolyte, the AZ31B magnesium alloy sample, and an air cathode (M248 type air cathode from Changzhou Youteke New Energy Technology Co., Ltd.), operating at 2.5 mA / cm². 2 The discharge performance was tested by constant current discharge at a current density of κ-carrageenan-NaCl biopolymer electrolyte. The ionic conductivity of the electrolyte was 3.91 × 10⁻⁶. -2 S·cm -1 The assembled magnesium-air battery did not exhibit a discharge plateau, but showed rapid voltage decay, a discharge time of only 9.92 h, and a discharge specific capacity of 1033.77 mAh·g. -1 Discharge efficiency η The percentage is 46.87%. This electrolyte has poor mechanical properties and cannot be stretched.

[0028] Example 1 Preparation of polymer electrolytes In this embodiment, 0.5 mol·L -1 κ-carrageenan-lithium bromide-magnesium acetate biopolymer electrolytes doped with different masses of magnesium acetate were prepared by replacing 3.5 wt% NaCl solution with LiBr. The preparation steps are as follows: 2% w / v κ-carrageenan was added to 0.5 mol·L⁻¹ solution at 70℃. -1 A homogeneous solution was obtained by stirring the LiBr solution for 30 min, followed by the sequential addition of magnesium acetate in different mass ratios. The mass ratios of κ-carrageenan to magnesium acetate were 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, and 30:70. The solution was stirred at 70 °C for 2 h to obtain a homogeneous κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution. This solution was then poured into a pre-washed and dried petri dish while still hot and cooled to room temperature for 30 min to obtain a κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte with a thickness of 6 mm. This electrolyte was then cut into 30 mm × 10 mm rectangular electrolyte pieces for later use.

[0029] Experimental results Electrochemical impedance spectroscopy of polymer electrolytes with different concentrations of κ-carrageenan-lithium bromide-magnesium acetate is shown below. Figure 1 As shown in Table 1, the resistance and ionic conductivity obtained through data processing are presented. Polymer dielectrics of varying concentrations were assembled into magnesium-air batteries. Figure 2 Table 2 shows the voltage-time and voltage-specific capacity plots for the magnesium-air battery, along with the discharge performance results. As can be seen from Tables 1 and 2, compared to Comparative Example 1, with 0.5 mol·L⁻¹… -1 Replacing 3.5 wt% NaCl with LiBr increased the ionic conductivity of the polymer electrolyte by 14%, and improved the discharge specific capacity and discharge efficiency of the magnesium-air battery by 29%, indicating that using lithium bromide as a dopant is beneficial for improving the discharge performance of magnesium-air batteries. Furthermore, doping with 10-70 wt% magnesium acetate further improved the ionic conductivity of the polymer electrolyte and the discharge performance of the magnesium-air battery, resulting in a discharge time of 8.34-16.68 h and a discharge specific capacity of 1406.30-1455.12 mAh·g. -1 The discharge efficiency was 63.25-65.78%. Compared to Comparative Example 1, when the magnesium acetate content was 40wt%-70wt%, the discharge time of the magnesium-air battery was extended by 1.54-6.76 h, and the discharge specific capacity was increased by 372-394 mAh·g. -1The discharge efficiency is improved by 36-38%. Therefore, this concentration range is the optimal addition amount.

[0030] Table 1. Effect of magnesium acetate content on the ionic conductivity of κ-carrageenan-based biopolymer electrolytes. .

[0031] Table 2. Effect of magnesium acetate content on the discharge performance of magnesium-air batteries .

[0032] Example 2 In the experiment of Example 1, it was found that as the magnesium acetate content increased, the mechanical properties of the polymer electrolyte gradually decreased, failing to meet the flexibility requirements.

[0033] Therefore, this embodiment first follows the steps of Example 1, obtaining κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solutions with magnesium acetate doping contents of 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, and 70 wt% at 70℃. These solutions were poured into petri dishes while hot and cooled to room temperature for 30 min. Then, they were dried in a forced-air drying oven at 60℃ for 1 h, 2 h, 4 h, and 5 h respectively, and then cooled to room temperature for 30 min to obtain κ-carrageenan-LiBr polymer electrolytes with a thickness of approximately 0.6~5 mm. The electrolytes were then cut into 30 mm × 10 mm rectangles for later use. During the experiment, it was found that when the magnesium acetate content was higher than 50 wt%, salting out or failure to form occurred during the drying process. Therefore, only samples with magnesium acetate doping contents of 10-50 wt% were subsequently tested. The mechanical properties of the dried polymer electrolyte samples were tested using a microcomputer-controlled electronic universal testing machine, with a tensile speed set to 40 mm·min. -1 The sensor has a range of 5 kN.

[0034] Experimental results Electrochemical impedance spectroscopy of κ-carrageenan-lithium bromide-magnesium acetate polymer electrolytes with different drying times is shown below. Figure 3 As shown in Table 3, the resistance and ionic conductivity obtained through data processing are presented. Polymer dielectrics obtained at different drying times were assembled into magnesium-air batteries. Figure 4 Table 4 shows the voltage-time and voltage-specific capacity plots for the magnesium-air battery, and the discharge performance results. The compressive stress-strain curves of the biopolymer electrolyte at different drying times are also shown. Figure 5 As shown.

[0035] Table 3. Effect of drying time on the ionic conductivity of biopolymer electrolytes with different magnesium acetate doping contents. .

[0036] Table 4. Effect of drying time on the discharge performance of magnesium-air batteries with different magnesium acetate doping contents. .

[0037] As shown in Table 3, drying for different times can further improve the ionic conductivity of the κ-carrageenan-based polymer electrolytes doped with different magnesium acetates in Example 1.

[0038] As shown in Table 4, compared with Example 1, when the drying time does not exceed 4 hours, the discharge time of magnesium-air batteries assembled with polymer electrolytes doped with 10-50 wt% magnesium acetate is significantly improved, while the discharge specific capacity and discharge efficiency show little change. In particular, when the magnesium acetate doping amount is 10-30 wt% and the drying time is 1-4 hours, the discharge time can be further improved by 48%-139%, and the discharge specific capacity is 1315.02-1414.27 mAh·g. -1 The discharge efficiency remained at 61.19-64.23%, which was significantly higher than that of Comparative Example 1. When the magnesium acetate doping amount was 10 wt% and the drying time was 4 h, the polymer electrolyte exhibited the best overall performance in terms of ionic conductivity and magnesium-air battery discharge, with a discharge time of 23.40 h and a discharge specific capacity and discharge efficiency of 1395.19 mAh·g⁻¹. -1 And 63.26%. When the magnesium acetate doping amount is 20 wt% and the drying time is 2 h, the polymer electrolyte exhibits the best overall performance in terms of ionic conductivity and magnesium-air battery discharge, with a battery discharge time of 18.28 h, and a discharge specific capacity and discharge efficiency of 1410.28 mAh·g. -1 And 64.23%. When the magnesium acetate doping content is 30 wt%, the optimal drying time is 1 hour.

[0039] Therefore, when evaluating the discharge performance of magnesium-air batteries, the optimal drying time gradually decreases as the magnesium acetate content (10-30 wt%) increases. Experiments showed that the mechanical properties of the dried polymer electrolyte samples increased, allowing for tensile testing. Furthermore, the mechanical properties improved with increasing drying time. The polymer electrolyte with a magnesium acetate content of 20% and dried for 5 hours exhibited the highest tensile strength, 4.63 × 10⁻⁶. -1 MPa.

Claims

1. A carrageenan-based biopolymer gel electrolyte for magnesium-air batteries, characterized in that, First, add 1.5-3% w / v κ-carrageenan to a solution heated to 70-90℃ at a concentration of 0.4-0.7 mol·L⁻¹. -1 The LiBr solution was stirred until homogeneous, and then magnesium acetate was added and mixed until homogeneous to obtain a κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution, wherein the mass ratio of magnesium acetate to κ-carrageenan was 1-7:3-9; then, a biopolymer gel electrolyte was prepared by solution casting.

2. A method for preparing a carrageenan-based biopolymer gel electrolyte for magnesium-air batteries, comprising the following steps: (1) Add 1.5-3% w / v κ-carrageenan to a 0.4-0.7 mol·L⁻¹ thermometer at 70-90℃. -1 The LiBr solution was stirred until homogeneous, and then magnesium acetate was added and mixed until homogeneous to obtain a κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution, wherein the mass ratio of magnesium acetate to κ-carrageenan was 1-7:3-9. (2) The obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution was poured into a container at 70-90℃ and cooled to obtain a biopolymer gel electrolyte.

3. The method as described in claim 2, characterized in that: The doping amount of magnesium acetate is 10%-50%, based on the total mass of magnesium acetate and κ-carrageenan being 100%.

4. The method as described in claim 3, characterized in that: The doping amount of magnesium acetate is 10-30%.

5. The method as described in claim 2, characterized in that: The κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution was stirred at 70-90°C for 1-3 h before being poured into the container.

6. The method according to any one of claims 2-5, characterized in that: The cooling process involves cooling to room temperature for 20-60 minutes.

7. The method as described in claim 6, characterized in that: After cooling to room temperature, the product is dried at a temperature of 50-70°C for 1-5 hours.

8. The method as described in claim 6, characterized in that: After stirring the obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution at 70-80 °C for 1-3 h, pour it into a container while hot and cool it at room temperature for 20-40 min to obtain carrageenan-based biopolymer gel electrolyte.

9. The method as described in claim 6, characterized in that: The obtained κ-carrageenan-lithium bromide-magnesium acetate polymer electrolyte solution was poured into a container at 70-80℃, cooled for 20-40 min, dried at 50-70℃ for 1-5 h, and then cooled to room temperature for 20-40 min to obtain carrageenan-based biopolymer gel electrolyte.

10. The method as described in claim 9, characterized in that: The magnesium acetate doping amount is 10-30 wt%, and the product is dried for 1-4 h; preferably, the magnesium acetate doping amount is 10-20 wt%, and the product is dried for 4 h.

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