Preparation method of low electron conductance biomass charcoal / magnesium composite material

Abstract

The application relates to a preparation method of a low-electronic-conductivity biomass charcoal / magnesium composite material, and relates to a preparation method of a biomass charcoal / magnesium composite material. In order to solve the problem that the electronic conductivity of biomass charcoal makes the artificial protection interface of magnesium ions easy to fail in the battery cycle process. Method: biomass charcoal is mixed with potassium hydroxide, and the mixture is heat-treated under a protective atmosphere; the sample after heat treatment is washed and dried to obtain activated biomass charcoal; the activated biomass charcoal is pressure-infiltrated with magnesium metal and magnesium alloy to obtain an activated biomass charcoal / magnesium composite material. The conjugated structure of the material is destroyed by activating the biomass charcoal with potassium hydroxide, the electronic conductivity of the biomass charcoal is reduced, the electronic conductivity of the biomass charcoal / magnesium composite material is reduced, the reduction decomposition when the biomass charcoal / magnesium composite material is used as a negative electrode sheet is alleviated, and the cycle stability and the charge-discharge efficiency of the biomass charcoal / magnesium composite material negative electrode sheet are improved.

Description

Technical Field

[0001] This invention relates to the modification of a novel composite material and its preparation method. Background Technology

[0002] Developing high-energy-density and environmentally friendly rechargeable batteries has become a major focus for many researchers. With future applications demanding increasingly higher energy density and safety, and given the current limited lithium resources, current lithium-ion batteries are expected to be insufficient to meet the needs of this rapidly growing market. Magnesium metal is a promising candidate for ultra-high-energy-density lithium-ion battery anodes because the capacity of magnesium metal anodes in rechargeable magnesium batteries (2230 mAh g⁻¹) is... -1 ) is almost a commercially available lithium battery (graphite, 372mAh g) -l Magnesium has a reduction potential six times higher than that of lithium and a lower reduction potential (-2.37V vs. standard hydrogen electrode). Furthermore, magnesium exhibits less dendrite formation under electrochemical conditions, a stark contrast to lithium, and its high safety, high energy density, low price, and environmental friendliness are attracting increasing attention.

[0003] In conventional electrolytes, the ion passivation interface layer formed by the reduction of chemically unstable solvates typically hinders the formation of Mg. 0 / Mg 2+ The reaction. One solution is to reduce Mg. 2+ The interaction with the solvent prevents Mg 2+ Reduction, however, requires reversible magnesium deposition / stripping chemistry that can only be achieved with solid electrolytes that provide a wide voltage window but have slow kinetics, or with highly corrosive and oxidically unstable electrolytes such as Grignard reagents. Another solution is to construct a high magnesium ion conductivity interface, which allows reversible Mg deposition / stripping. 2+ Deposition / stripping, which has recently been achieved through polymer coating, alloying, inorganic halogen compound modification, and gas-phase chemisorption, is crucial for the effectiveness of this artificial magnesium ion conductive interface. High electronic conductivity at the interface layer can easily lead to reduction and decomposition at the electrolyte-artificial protective layer interface, forming a new passivation layer and causing the artificial protective interface to fail. Numerous studies have confirmed the potential of biochar as a magnesium ion conductive interface. However, due to its inherent electronic conductivity, biochar is prone to failure during battery cycling when used as an artificial magnesium ion protective interface. Therefore, a simple and cost-effective method is urgently needed to further reduce the electronic conductivity of biochar, thereby ensuring that modified biochar can function as an artificial magnesium ion protective interface layer. Summary of the Invention

[0004] To address the problem that biochar's electronic conductivity makes it prone to failure during battery cycling when used as an artificial protective interface for magnesium ions, this invention proposes a method for preparing a biochar / magnesium composite material with low electronic conductivity.

[0005] The preparation method of the low electronic conductivity biochar / magnesium composite material of the present invention is carried out according to the following steps:

[0006] 1. Weighing: Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials;

[0007] II. Preparation of a mixture of biochar and potassium hydroxide:

[0008] After thoroughly mixing the biochar and potassium hydroxide powder solid weighed in step one, place them in a crucible to prepare for the preparation of activated biochar.

[0009] Alternatively, the potassium hydroxide weighed in step one can be prepared into an aqueous solution of potassium hydroxide, and then the biochar can be immersed in the potassium hydroxide solution and stirred. The biochar can then be filtered and dried in a vacuum oven to obtain a dry mixture of biochar and potassium hydroxide, which can then be placed in a crucible.

[0010] III. Preparation of activated biochar:

[0011] The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar.

[0012] IV. Preparation of modified biochar / magnesium composite materials:

[0013] The activated biochar obtained in step three was washed until the pH was neutral, and then dried in a vacuum oven. Finally, the modified biochar / magnesium composite material was prepared by pressure impregnation under a protective atmosphere.

[0014] The present invention has the following beneficial effects:

[0015] 1. This invention provides a method for preparing a low electronic conductivity biochar / magnesium composite material. The biochar is chemically activated with potassium hydroxide, which disrupts the conjugated structure of the material and effectively reduces its electronic conductivity. The modified biochar / magnesium composite material is then synthesized using a self-venting pressure infiltration technique. As an artificial magnesium ion conductive interface, the modified biochar significantly improves the reversible deposition / stripping cycle count of the magnesium metal negative electrode in conventional electrolytes, effectively enhancing cycle stability and charge / discharge efficiency.

[0016] 2. As is well known, large quantities of waste wood and biomass waste are used for incineration power generation, discarded as garbage, or buried for agricultural purposes. This invention enables the conversion of inexpensive natural biomass materials into high-performance magnesium-ion battery anode materials. This invention improves the electronic conductivity properties of natural biomass materials, allowing them to more effectively fulfill their functional material properties.

[0017] 3. This invention is low in cost, uses renewable and environmentally friendly raw materials, and has a simple process. Its performance can be greatly improved through simple activation treatment, which meets the requirements of industrial production and application. Attached Figure Description

[0018] Figure 1 The image shows the XRD pattern of the modified biochar obtained in Example 1.

[0019] Figure 2 The electronic conductivity test results are for the modified biochar / magnesium composite material and the unmodified biochar / magnesium composite material obtained in Example 1. Detailed Implementation

[0020] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0021] Specific Implementation Method 1: The preparation method of the low electronic conductivity biochar / magnesium composite material in this implementation method is carried out according to the following steps:

[0022] 1. Weighing: Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials;

[0023] II. Preparation of a mixture of biochar and potassium hydroxide:

[0024] After thoroughly mixing the biochar and potassium hydroxide powder solid weighed in step one, place them in a crucible to prepare for the preparation of activated biochar.

[0025] Alternatively, the potassium hydroxide weighed in step one can be prepared into an aqueous solution of potassium hydroxide, and then the biochar can be immersed in the potassium hydroxide solution and stirred. The biochar can then be filtered and dried in a vacuum oven to obtain a dry mixture of biochar and potassium hydroxide, which can then be placed in a crucible.

[0026] III. Preparation of activated biochar:

[0027] The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar.

[0028] IV. Preparation of modified biochar / magnesium composite materials:

[0029] The activated biochar obtained in step three was washed until the pH was neutral, and then dried in a vacuum oven. Finally, the modified biochar / magnesium composite material was prepared by pressure impregnation under a protective atmosphere.

[0030] 1. This embodiment provides a method for preparing a low electronic conductivity biochar / magnesium composite material. The biochar is chemically activated with potassium hydroxide, which disrupts the conjugated structure of the material and effectively reduces its electronic conductivity. The modified biochar / magnesium composite material is then synthesized using a self-venting pressure infiltration technique. As an artificial magnesium ion conductive interface, the modified biochar significantly improves the reversible deposition / stripping cycle count of the magnesium metal negative electrode in conventional electrolytes, effectively enhancing cycle stability and charge / discharge efficiency.

[0031] 2. As is well known, large quantities of waste wood and biomass waste are used for incineration power generation, discarded as garbage, or buried for agricultural purposes. This embodiment realizes the transformation of inexpensive natural biomass materials into high-performance magnesium-ion battery anode materials. This embodiment improves the electronic conductivity properties of natural biomass materials, enabling them to more effectively fulfill their functional material properties.

[0032] 3. This implementation method is low in cost, uses renewable and environmentally friendly raw materials, and has a simple process. It can achieve a significant improvement in performance through simple activation treatment, which meets the requirements of industrial production and application.

[0033] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mass ratio of biochar and potassium hydroxide powder solid in step two is 1:1 to 20.

[0034] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the concentration of the potassium hydroxide solution in step 2 is 1-20 mol / L.

[0035] Specific Implementation Method Four: This implementation method differs from one of the specific implementation methods one to three in that the crucible type mentioned in step two is a graphite crucible or a nickel crucible.

[0036] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that: in step 2, the stirring speed of placing the biochar in the potassium hydroxide solution is 100-600 rpm, and the time is 2-24 hours.

[0037] Specific Implementation Method Six: This implementation method differs from one of Specific Implementation Methods One to Five in that the heating rate of the heat treatment of the biochar and potassium hydroxide mixture in step three is 2 to 10 °C / min.

[0038] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the heat treatment temperature of the biochar and potassium hydroxide mixture described in step three is 450-1000°C, and the protective atmosphere is helium, nitrogen, or argon.

[0039] Specific Implementation Method Eight: This implementation method differs from one of Specific Implementation Methods One to Seven in that the heat treatment time for the mixture of biochar and potassium hydroxide described in step three is 1 to 6 hours.

[0040] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the method for washing the activated biochar in step four is as follows: first soak it in a hydrochloric acid solution with a concentration of 1-10 mol / L, and then wash it thoroughly with deionized water until the pH test shows neutrality.

[0041] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that: the method for preparing modified biochar / magnesium composite material by pressure impregnation in step 4 is as follows: pure magnesium is prepared into magnesium melt, then activated biochar is preheated, and after preheating, pressure impregnation is performed into the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 600-650℃, and the pressure impregnation temperature is 800-890℃.

[0042] The beneficial effects of the present invention are verified using the following embodiments:

[0043] Example 1: The preparation method of the low electronic conductivity biochar / magnesium composite material in this example is carried out according to the following steps:

[0044] 1. Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials;

[0045] II. Preparation of a mixture of biochar and potassium hydroxide:

[0046] Prepare an aqueous solution of potassium hydroxide by weighing the potassium hydroxide in step one. Then, immerse the biochar in the potassium hydroxide solution and stir. Subsequently, filter the biochar and dry it in a vacuum oven to obtain a dry mixture of biochar and potassium hydroxide, and place it in a crucible.

[0047] The concentration of the potassium hydroxide solution is 4 mol / L;

[0048] The crucible in question is a nickel crucible;

[0049] The biochar was placed in a potassium hydroxide solution and stirred at a speed of 400 rpm for 24 hours.

[0050] III. Preparation of activated biochar:

[0051] The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar.

[0052] The heating rate of the heat treatment of the biochar and potassium hydroxide mixture is 5℃ / min, the holding temperature is 800℃, the protective atmosphere is nitrogen, and the holding time is 1h.

[0053] IV. Preparation of modified biochar / magnesium composite materials:

[0054] The activated biochar obtained in step three was washed until the pH was neutral, and then dried in a vacuum oven. Finally, the modified biochar / magnesium composite material was prepared by pressure impregnation under a protective atmosphere.

[0055] The method for washing the activated biochar is as follows: first soak it in a 2 mol / L hydrochloric acid solution, then wash it thoroughly with deionized water until the pH test shows neutrality;

[0056] The method for preparing modified biochar / magnesium composite material by pressure impregnation is as follows: pure magnesium is prepared into magnesium melt, then activated biochar is preheated, and after preheating, pressure impregnation is performed into the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 640℃, and the pressure impregnation temperature is 880℃.

[0057] Comparative example:

[0058] The preparation method of unmodified biochar / magnesium composite material is carried out according to the following steps:

[0059] 1. Weigh out the block biochar and pure magnesium as raw materials;

[0060] II. Preparation of biochar / magnesium composite materials:

[0061] Unmodified biochar / magnesium composite materials were prepared by pressure infiltration under a protective atmosphere. The method was as follows: pure magnesium was prepared into magnesium melt, and then block biochar was preheated. After preheating, pressure infiltration was performed into the magnesium melt to fill all the three-dimensional interconnected pores in the block biochar. The preheating temperature was 640℃, and the pressure infiltration temperature was 880℃.

[0062] Figure 1 The image shows the XRD pattern of the modified biochar obtained in Example 1. As can be seen from Figure 1, the broad diffraction peaks observed at a relatively low diffraction angle of 2θ = 20-23° belong to the 002 Bragg diffraction of the graphite domain, indicating that the activated hard carbon sample has small graphite domains, which is a typical feature of hard carbon phases. Figure 2The electronic conductivity test results for the modified biochar / magnesium composite material and the unmodified biochar / magnesium composite material obtained in Example 1 are shown. The electronic resistance of the two systems was obtained by calculating the slope of the voltage-current curves. The electronic conductivity of the modified biochar / magnesium composite material system was 3.25 × 10⁻⁶. -7 S cm -1 The electronic conductivity of the unmodified biochar / magnesium composite material is 1.09 × 10⁻⁶. -4 S cm -1 The system's electronic conductivity was reduced by three orders of magnitude, effectively preventing the reduction of conventional electrolytes at the artificial SEI interface and effectively limiting the occurrence of side reactions at the electrolyte and interface.

[0063] Example 2: The preparation method of the low electronic conductivity biochar / magnesium composite material in this example is carried out according to the following steps:

[0064] 1. Weighing: Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials;

[0065] II. Preparation of a mixture of biochar and potassium hydroxide:

[0066] After thoroughly mixing the biochar and potassium hydroxide powder solid weighed in step one, place them in a crucible to prepare for the activation heat treatment of the biochar.

[0067] The mass ratio of the biochar to potassium hydroxide powder is 1:3;

[0068] The crucible in question is a graphite crucible;

[0069] III. Preparation of activated biochar:

[0070] The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar.

[0071] The heating rate of the heat treatment of the biochar and potassium hydroxide mixture is 10℃ / min, the holding temperature is 450℃, the holding time is 1.5h, and the protective atmosphere is argon.

[0072] IV. Preparation of modified biochar / magnesium composite materials:

[0073] The activated biochar obtained in step three was washed until the pH was neutral, and then dried in a vacuum oven. Finally, the modified biochar / magnesium composite material was prepared by pressure impregnation under a protective atmosphere.

[0074] The method for washing the activated biochar is as follows: first soak it in a 3 mol / L hydrochloric acid solution, then wash it thoroughly with deionized water until the pH test shows neutrality;

[0075] The method for preparing modified biochar / magnesium composite material by pressure infiltration is as follows: pure magnesium is prepared into magnesium melt, then activated biochar is preheated, and after preheating, pressure infiltration is performed into the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 630℃, and the pressure infiltration temperature is 860℃.

[0076] Testing revealed that the electronic resistance of the modified biochar / magnesium composite system, obtained by calculating the slope of the voltage-current curves for both systems, was 2.06 × 10⁻⁶. -6 S cm -1 Compared to the unmodified biochar / magnesium composite system (comparative example), it reduced by at least two orders of magnitude.

[0077] Example 3: The preparation method of the low electronic conductivity biochar / magnesium composite material in this example is carried out according to the following steps:

[0078] 1. Weighing: Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials;

[0079] II. Preparation of a mixture of biochar and potassium hydroxide:

[0080] After thoroughly mixing the biochar and potassium hydroxide powder solid weighed in step one, place them in a crucible to prepare for the activation heat treatment of the biochar.

[0081] The mass ratio of the biochar to potassium hydroxide powder is 1:4;

[0082] The crucible in question is a nickel crucible;

[0083] III. Preparation of activated biochar:

[0084] The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar.

[0085] The heating rate of the heat treatment of the biochar and potassium hydroxide mixture is 2℃ / min, the holding temperature is 600℃, the holding time is 2h, and the protective atmosphere is nitrogen.

[0086] IV. Preparation of modified biochar / magnesium composite materials:

[0087] The activated biochar obtained in step three was washed until the pH was neutral, and then dried in a vacuum oven. Finally, the modified biochar / magnesium composite material was prepared by pressure impregnation under a protective atmosphere.

[0088] The method for washing the activated biochar is as follows: first soak it in a 6 mol / L hydrochloric acid solution, then wash it thoroughly with deionized water until the pH test shows neutrality;

[0089] The method for preparing modified biochar / magnesium composite material by pressure impregnation is as follows: pure magnesium is prepared into magnesium melt, then activated biochar is preheated, and after preheating, pressure impregnation is performed into the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 620℃, and the pressure impregnation temperature is 870℃.

[0090] Testing revealed that the electronic resistance of the modified biochar / magnesium composite system, obtained by calculating the slope of the voltage-current curves for both systems, was 5.35 × 10⁻⁶. -6 S cm -1 Compared to the unmodified biochar / magnesium composite system (comparative example), it reduced by at least two orders of magnitude.

Claims

1. A method for preparing a biomass char / magnesium composite material with low electronic conductivity for magnesium metal anodes, characterized in that: The preparation method of the biochar / magnesium composite material with low electronic conductivity for magnesium metal anode is carried out according to the following steps:

1. Weighing: Weigh out the block biochar, potassium hydroxide and pure magnesium as raw materials; II. Preparation of a mixture of biochar and potassium hydroxide: After thoroughly mixing the biochar and potassium hydroxide powder solid weighed in step one, place them in a crucible to prepare for the preparation of activated biochar. Alternatively, the potassium hydroxide weighed in step one can be prepared into an aqueous solution of potassium hydroxide, and then the biochar can be immersed in the potassium hydroxide solution and stirred. The biochar can then be filtered and dried in a vacuum oven to obtain a dry mixture of biochar and potassium hydroxide, which can then be placed in a crucible. III. Preparation of activated biochar: The mixture of biochar and potassium hydroxide obtained in step two is heated and kept at a temperature under a protective atmosphere. The potassium hydroxide activates the biochar during the heat treatment process. Then, it is cooled in the furnace under a protective atmosphere until room temperature to obtain activated biochar. The heat treatment temperature of the biochar and potassium hydroxide mixture is 450~1000℃, and the protective atmosphere is helium, nitrogen or argon. The heat treatment time for the mixture of biochar and potassium hydroxide is 1-6 h; IV. Preparation of modified biochar / magnesium composite materials: The activated biochar obtained in step three was washed until the pH was neutral, then dried in a vacuum oven. Finally, the activated biochar and pure magnesium were pressure impregnated under a protective atmosphere to prepare a modified biochar / magnesium composite material. The method for preparing modified biochar / magnesium composite material by pressure impregnation is as follows: pure magnesium is prepared into magnesium melt, then activated biochar is preheated, and after preheating, pressure impregnation is performed into the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 600~650℃, and the pressure impregnation temperature is 800~890℃.

2. The method for preparing the low electronic conductivity biomass char / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: The mass ratio of biochar and potassium hydroxide powder solid mentioned in step two is 1:1 to 20.

3. The method for preparing the low electronic conductivity biomass char / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: The concentration of the potassium hydroxide solution mentioned in step two is 1~20 mol / L.

4. The method for preparing the low electronic conductivity biomass char / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: The crucible mentioned in step two is a graphite crucible or a nickel crucible.

5. The method for preparing the low electronic conductivity biomass char / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: In step two, the biochar is placed in a potassium hydroxide solution and stirred at a speed of 100-600 rpm for 2-24 hours.

6. The method for preparing the low electronic conductivity biomass char / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: The heating rate for the heat treatment of the biochar and potassium hydroxide mixture in step three is 2~10℃ / min.

7. The method for preparing the low electronic conductivity biochar / magnesium composite material for magnesium metal anodes according to claim 1, characterized in that: The method for washing the activated biochar in step four is as follows: first soak it in a hydrochloric acid solution with a concentration of 1~10 mol / L, and then wash it thoroughly with deionized water until the pH test shows neutrality.

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