Preparation method of high-cycling-stability biomass charcoal / magnesium composite material negative pole piece

Abstract

The invention discloses a preparation method of a high-cycling-stability biomass charcoal / magnesium composite material negative pole piece, and relates to a preparation method of a biomass charcoal / magnesium composite material negative pole piece. The problems that when biomass charcoal serves as an artificial protection interface of the magnesium metal surface, the circulation stability of a biomass charcoal / magnesium composite material is not high, and a battery is prone to failure in a short time in the working process are solved. The potassium hydroxide and the phosphoric acid are used for carrying out chemical activation treatment on the biomass charcoal, the natural biomass charcoal is subjected to modification treatment, the conjugate structure of the natural biomass charcoal is destroyed, the modified biomass charcoal playing an artificial SEI role in the magnesium ion battery solves the problem that an electrolyte / solvent is difficult to select, and the cycle stability in the working process of the battery is effectively improved. The raw materials are rich in source, the production cost is low, the process is simple, ecological safety is achieved, the performance can be greatly improved through simple modification treatment, and industrial production and application are met.

Description

Technical Field

[0001] The invention relates to a method for preparing a biomass carbon / magnesium composite material negative electrode sheet. Background Art

[0002] As future applications have higher and higher requirements for energy density, high safety and environmental pollution, the demand for large and medium-sized batteries in electric vehicles and energy storage is increasing, and the current lithium-ion batteries are not expected to be sufficient to meet the needs of this rapidly growing market. Magnesium batteries are a promising candidate for super lithium-ion battery anodes because they have significant theoretical advantages in energy density through divalent ion reactions.

[0003] In conventional organic electrolytes, the SEI (solid electrolyte interface) layer formed directly in magnesium batteries hinders the conduction of magnesium ions and passivates the surface, which has an adverse effect on performance. Therefore, reversible deposition / stripping chemistry can only be achieved in kinetically slow solid electrolytes and highly corrosive and oxidatively unstable ether electrolytes (such as Grignard reagents). 2+ The artificial magnesium ion conductive interface of deposition / stripping has attracted the attention of more and more scientific researchers, and has been realized through polymer coating, alloying, inorganic halogen compound modification and gas phase chemical adsorption. Studies have shown that natural biochar can be used as a medium for magnesium ion conduction and has the potential to be an artificial magnesium ion battery SEI. However, when natural biochar is directly used as an artificial protective interface on the surface of magnesium metal, due to the high electronic conductivity of the biochar / magnesium composite material and poor wettability with the electrolyte, the battery cycle stability is not high, and the battery is prone to failure during operation as the cycle progresses. Summary of the invention

[0004] In order to solve the problem that when biochar is used as an artificial protective interface on the surface of magnesium metal, the cycle stability of the biochar / magnesium composite material is not high and it is easy to fail in a short time during battery operation, the present invention proposes a method for preparing a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0005] The method for preparing the negative electrode sheet of the biomass carbon / magnesium composite material with high cycle stability of the present invention is carried out according to the following steps:

[0006] 1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials;

[0007] 2. Potassium hydroxide chemical activation treatment:

[0008] The biochar weighed in step 1 and potassium hydroxide powder are mixed to obtain a mixture of biochar and potassium hydroxide; or the weighed potassium hydroxide is used to prepare a potassium hydroxide aqueous solution, and then the biochar is placed in the potassium hydroxide solution and stirred, and then the biochar is filtered and placed in a vacuum oven to dry, to obtain a mixture of biochar and potassium hydroxide;

[0009] The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide;

[0010] 3. Biomass carbon phosphating treatment:

[0011] The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried;

[0012] 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet:

[0013] Under a protective atmosphere, the activated biochar obtained in step three is subjected to pressure infiltration to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

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

[0015] 1. The present invention provides a method for preparing a negative electrode sheet of a biochar / magnesium composite material with high cycle stability, using potassium hydroxide and phosphoric acid to chemically activate the biochar to achieve the modification of natural biochar and destroy the conjugated structure of natural biochar, so as to better meet the performance requirements of artificial SEI. At the same time, the modified biochar / magnesium composite material is synthesized by self-exhaust pressure infiltration technology. The modified biochar that plays the role of artificial SEI in magnesium ion batteries has better optimized electronic conductivity and better interface wettability, and solves the problem of electrolyte / solvent selection difficulties, so that it can be used in more antioxidant conventional electrolytes, and the cycle stability is effectively improved during the battery operation process, and the overpotential is effectively reduced during the rate performance test.

[0016] 2. As we all know, biomass waste can cause serious environmental problems. Therefore, it is urgent to find suitable applications for this waste. The present invention realizes the transformation of a variety of biomass precursors into an important component of energy storage materials. Using natural biomass materials as raw materials, a simple process for preparing modified hard carbon is studied. By chemically activating the biomass hard carbon material, the modified hard carbon material effectively exerts its functional material properties and plays a role in magnesium metal batteries. 2+ Interface protection.

[0017] 3. The present invention has abundant raw material sources, low production cost, simple process, and ecological safety. Simple modification treatment can achieve significant improvement in performance, meeting the requirements of industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a SEM image of the modified biomass carbon / magnesium composite material obtained in Example 1;

[0019] Figure 2 These are the experimental results of the symmetric battery rate performance test of the modified biomass carbon / magnesium composite material obtained in Example 1. DETAILED DESCRIPTION

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

[0021] Specific implementation method 1: The preparation method of the negative electrode sheet of the biomass carbon / magnesium composite material with high cycle stability in this implementation method is carried out according to the following steps:

[0022] 1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials;

[0023] 2. Potassium hydroxide chemical activation treatment:

[0024] The biochar weighed in step 1 and potassium hydroxide powder are mixed to obtain a mixture of biochar and potassium hydroxide; or the weighed potassium hydroxide is used to prepare a potassium hydroxide aqueous solution, and then the biochar is placed in the potassium hydroxide solution and stirred, and then the biochar is filtered and placed in a vacuum oven to dry, to obtain a mixture of biochar and potassium hydroxide;

[0025] The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide;

[0026] 3. Biomass carbon phosphating treatment:

[0027] The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried;

[0028] 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet:

[0029] Under a protective atmosphere, the activated biochar obtained in step three is subjected to pressure infiltration to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0030] 1. This embodiment provides a method for preparing a negative electrode sheet of a biochar / magnesium composite material with high cycle stability, using potassium hydroxide and phosphoric acid to chemically activate the biochar to achieve the modification of natural biochar and destroy the conjugated structure of natural biochar, so as to better meet the performance requirements of artificial SEI. At the same time, the modified biochar / magnesium composite material is synthesized by self-exhaust pressure infiltration technology. The modified biochar that plays the role of artificial SEI in magnesium ion batteries has better optimized electronic conductivity and better interface wettability, and solves the problem of electrolyte / solvent selection difficulties, so that it can be used in more antioxidant conventional electrolytes, and the cycle stability is effectively improved during the battery operation process, and the overpotential is effectively reduced during the rate performance test.

[0031] 2. As we all know, biomass waste can cause serious environmental problems. Therefore, it is urgent to find suitable applications for this waste. This embodiment realizes the conversion of a variety of biomass precursors into an important component of energy storage materials. Using natural biomass materials as raw materials, a simple process for preparing modified hard carbon is studied, and by chemically activating the biomass hard carbon material, the modified hard carbon material effectively exerts its functional material properties and plays a role in magnesium metal batteries. 2+ Interface protection.

[0032] 3. This implementation method has abundant raw material sources, low production costs, simple processes, and ecological safety. Simple modification treatment can achieve significant performance improvements, meeting the requirements of industrial production and application.

[0033] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the mass ratio of the biochar and potassium hydroxide powder in step 2 is 1:1-30.

[0034] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: the concentration of the potassium hydroxide solution in step two is 1 to 20 mol / L, and the stirring time of the biochar in the potassium hydroxide solution is 2 to 48 hours.

[0035] Specific embodiment 4: This embodiment differs from any one of specific embodiments 1 to 3 in that the heating rate of the heat treatment of the biochar and potassium hydroxide mixture described in step 2 is 1 to 20°C / min, the insulation temperature is 450 to 950°C, and the insulation time is 1 to 4h.

[0036] Specific implementation mode 5: This implementation mode is different from any one of specific implementation modes 1 to 4 in that the protective atmosphere described in step 2, step 3 and step 4 is helium, nitrogen or argon.

[0037] Specific implementation method 6: This implementation method is different from any one of specific implementation methods 1 to 5 in that the concentration (mass fraction) of phosphoric acid in step 3 is 85% to 98%.

[0038] Specific implementation method 7: This implementation method is different from any one of specific implementation methods 1 to 6 in that the mass ratio of the biochar to the phosphoric acid in step 3 is 1:10-50.

[0039] Specific implementation eight: This implementation differs from one of specific implementations one to six in that: the biochar described in step three is immersed in the phosphoric acid solution for 1 to 10 hours.

[0040] Specific embodiment nine: This embodiment differs from any one of specific embodiments one to seven in that the heating rate of the heat treatment of the biochar and phosphoric acid mixture described in step three is 1 to 20°C / min, the insulation temperature is 450 to 1000°C, and the insulation time is 1 to 6h.

[0041] Specific embodiment ten: This embodiment differs from any one of specific embodiments one to nine in that: the method for preparing modified biochar / magnesium composite materials by pressure infiltration as described in step four is: preparing pure magnesium metal into a magnesium melt, and then preheating the activated biochar, and then pressure infiltrating the activated biochar into the magnesium melt after preheating to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 600-650°C, and the pressure infiltration temperature is 800-890°C.

[0042] The following examples are used to verify the beneficial effects of the present invention:

[0043] Embodiment 1:

[0044] The preparation method for improving the cycle stability of the biomass carbon / magnesium composite negative electrode sheet in this embodiment is carried out according to the following steps:

[0045] 1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials;

[0046] 2. Potassium hydroxide chemical activation treatment:

[0047] After preparing a potassium hydroxide aqueous solution with weighed potassium hydroxide, the biomass charcoal is placed in the potassium hydroxide solution and stirred, and then the biomass charcoal is filtered and placed in a vacuum oven for drying to obtain a mixture of biomass charcoal and potassium hydroxide;

[0048] The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide;

[0049] The concentration of the potassium hydroxide solution is 4 mol / L, and the biochar is placed in the potassium hydroxide solution and stirred for 24 hours;

[0050] The heating rate of the biochar and potassium hydroxide mixture heat treatment is 5°C / min, the holding temperature is 800°C, and the holding time is 1h;

[0051] The protective atmosphere is nitrogen;

[0052] 3. Biomass carbon phosphating treatment:

[0053] The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried;

[0054] The phosphoric acid concentration is 98% (w / w);

[0055] The mass ratio of the biochar to the phosphoric acid is 1:30;

[0056] The biochar is immersed in the phosphoric acid solution for 5 hours;

[0057] The heat treatment rate of the biochar and phosphoric acid mixture is 10°C / min, the holding temperature is 600°C, and the holding time is 2h;

[0058] The protective atmosphere is nitrogen;

[0059] 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet:

[0060] Under a protective atmosphere, the activated biochar obtained in step three is subjected to pressure infiltration to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0061] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is: preparing pure magnesium metal into a magnesium melt, then preheating the activated biochar, and after preheating, pressure infiltrating the magnesium melt to completely fill the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 640°C, and the pressure infiltration temperature is 880°C.

[0062] The protective atmosphere is nitrogen.

[0063] Comparative Example 1:

[0064] The preparation method of the unmodified biomass carbon / magnesium composite material prepared in the comparative example is:

[0065] 1. Weighing materials: weigh biomass charcoal and pure magnesium metal as raw materials;

[0066] 2. Preparation of unmodified biomass carbon / magnesium composite materials:

[0067] The biochar was pressure infiltrated under a protective atmosphere to obtain a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0068] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is as follows: preparing pure magnesium metal into a magnesium melt, then preheating the biochar, and then pressure infiltrating the magnesium melt to fill all three-dimensional interconnected pores in the biochar; the preheating temperature is 640° C., and the pressure infiltration temperature is 880° C. The protective atmosphere is nitrogen.

[0069] Figure 1 This is the SEM image of the modified biomass carbon / magnesium composite material negative electrode sheet obtained in Example 1; as can be seen from Figure 1, the overall morphology of the modified biomass carbon / magnesium composite material negative electrode sheet is basically unchanged during the pressure infiltration process, and the interface bonding with the metal magnesium is good. Figure 2 The symmetrical battery assembled with the modified biomass carbon / magnesium composite negative electrode obtained in Example 1 and the unmodified biomass carbon / magnesium composite prepared in Comparative Example 1 was subjected to a rate performance test experiment in an acetonitrile (ACN) electrolyte containing 0.5 mol / L Mg(TFSI)2. It can be seen that the modified biomass carbon / magnesium composite negative electrode obtained in Example 1 has a rate performance of 2 uA cm -2 、10uA cm -2 、20uA cm -2 The deposition / stripping overpotential under the current density cycle is still lower than 0.4V, while the overpotential of the unmodified biomass carbon / magnesium composite material (Comparative Example 1) is close to 0.85V after cycling under the same conditions. The rate performance of the modified biomass carbon / magnesium composite material negative electrode sheet obtained in Example 1 is effectively improved.

[0070] Embodiment 2:

[0071] The preparation method for improving the cycle stability of the biomass carbon / magnesium composite negative electrode sheet in this embodiment is carried out according to the following steps:

[0072] 1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials;

[0073] 2. Potassium hydroxide chemical activation treatment:

[0074] After preparing a potassium hydroxide aqueous solution with weighed potassium hydroxide, the biomass charcoal is placed in the potassium hydroxide solution and stirred, and then the biomass charcoal is filtered and placed in a vacuum oven for drying to obtain a mixture of biomass charcoal and potassium hydroxide;

[0075] The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide;

[0076] The concentration of the potassium hydroxide solution is 3 mol / L, and the biochar is placed in the potassium hydroxide solution and stirred for 20 hours;

[0077] The heating rate of the biochar and potassium hydroxide mixture heat treatment is 10°C / min, the holding temperature is 600°C, and the holding time is 2h;

[0078] The protective atmosphere is nitrogen;

[0079] 3. Biomass carbon phosphating treatment:

[0080] The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried;

[0081] The phosphoric acid concentration is 85% (w / w);

[0082] The mass ratio of the biochar to the phosphoric acid is 1:40;

[0083] The biochar is immersed in the phosphoric acid solution for 8 hours;

[0084] The heating rate of the heat treatment of the biochar and phosphoric acid mixture is 5°C / min, the holding temperature is 500°C, and the holding time is 3h;

[0085] The protective atmosphere is nitrogen;

[0086] 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet:

[0087] Under a protective atmosphere, the activated biochar obtained in step three is subjected to pressure infiltration to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0088] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is: preparing pure magnesium metal into a magnesium melt, then preheating the biochar, and then pressure infiltrating the magnesium melt after preheating to fill all the three-dimensional interconnected pores in the biochar; the preheating temperature is 630°C, and the pressure infiltration temperature is 860°C.

[0089] The protective atmosphere is nitrogen.

[0090] Comparative Example 2:

[0091] The preparation method of the unmodified biomass carbon / magnesium composite material prepared in the comparative example is:

[0092] 1. Weighing materials: weigh biomass charcoal and pure magnesium metal as raw materials;

[0093] 2. Preparation of unmodified biomass carbon / magnesium composite materials:

[0094] The biochar was pressure infiltrated under a protective atmosphere to obtain a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0095] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is as follows: preparing pure magnesium metal into a magnesium melt, then preheating the biochar, and then pressure infiltrating the magnesium melt to fill all three-dimensional interconnected pores in the biochar; the preheating temperature is 630° C., and the pressure infiltration temperature is 860° C. The protective atmosphere is nitrogen.

[0096] After testing, the polarization potential test of the symmetrical battery assembled with the modified biomass carbon / magnesium composite electrode and the unmodified biomass carbon / magnesium composite electrode (Comparative Example 2) found that in 0.5 mol / L Mg(TFSI)2 / ACN electrolyte, the rate performance of the modified biomass carbon / magnesium composite electrode was improved, the overpotential was effectively reduced, and the number of reversible deposition / stripping cycles was increased. The modified biomass carbon / magnesium composite negative electrode obtained in Example 2 was subjected to 2 uAcm -2 、10uA cm -2 、20uA cm -2The deposition / stripping overpotential under the current density cycle is still lower than 0.5V, while the overpotential of the unmodified biomass carbon / magnesium composite material after cycling under the same conditions (Comparative Example 2) is close to 0.9V. The overpotential of the negative electrode sheet of the modified biomass carbon / magnesium composite material obtained in Example 2 is effectively reduced.

[0097] Embodiment 3:

[0098] The preparation method for improving the cycle stability of the biomass carbon / magnesium composite negative electrode sheet in this embodiment is carried out according to the following steps:

[0099] 1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials;

[0100] 2. Potassium hydroxide chemical activation treatment:

[0101] The biochar and potassium hydroxide powder weighed in step 1 are mixed to obtain a mixture of biochar and potassium hydroxide;

[0102] The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide;

[0103] The mass ratio of the biochar to the potassium hydroxide powder is 1:5;

[0104] The heating rate of the biochar and potassium hydroxide mixture heat treatment is 15°C / min, the holding temperature is 650°C, and the holding time is 3h;

[0105] The protective atmosphere is nitrogen;

[0106] 3. Biomass carbon phosphating treatment:

[0107] The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried;

[0108] The phosphoric acid concentration is 90% (w / w);

[0109] The mass ratio of the biochar to the phosphoric acid is 1:50;

[0110] The biochar is immersed in the phosphoric acid solution for 10 hours;

[0111] The heating rate of the heat treatment of the biochar and phosphoric acid mixture is 20°C / min, the holding temperature is 800°C, and the holding time is 5h;

[0112] The protective atmosphere is nitrogen;

[0113] 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet:

[0114] Under a protective atmosphere, the activated biochar obtained in step three is subjected to pressure infiltration to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0115] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is: preparing pure magnesium metal into a magnesium melt, then preheating the biochar, and after preheating, pressure infiltrating the magnesium melt to completely fill the three-dimensional interconnected pores in the biochar; the preheating temperature is 610°C, and the pressure infiltration temperature is 850°C.

[0116] The protective atmosphere is nitrogen;

[0117] Comparative Example 3:

[0118] The preparation method of the unmodified biomass carbon / magnesium composite material prepared in the comparative example is:

[0119] 1. Weighing materials: weigh biomass charcoal and pure magnesium metal as raw materials;

[0120] 2. Preparation of unmodified biomass carbon / magnesium composite materials:

[0121] The biochar was pressure infiltrated under a protective atmosphere to obtain a biochar / magnesium composite negative electrode sheet with high cycle stability.

[0122] The method for preparing the modified biochar / magnesium composite material by pressure infiltration is as follows: preparing pure magnesium metal into a magnesium melt, then preheating the biochar, and then pressure infiltrating the magnesium melt to fill all three-dimensional interconnected pores in the biochar; the preheating temperature is 610° C., and the pressure infiltration temperature is 850° C. The protective atmosphere is nitrogen.

[0123] After testing, the polarization potential test of the symmetrical battery assembled with the modified biomass carbon / magnesium composite electrode piece and the unmodified biomass carbon / magnesium composite electrode piece (Comparative Example 3) found that in 0.5 mol / L Mg(TFSI)2 / ACN electrolyte, the rate performance of the modified biomass carbon / magnesium composite electrode piece was improved, the overpotential was effectively reduced, and the number of reversible deposition / stripping cycles was increased. The modified biomass carbon / magnesium composite negative electrode piece obtained in Example 3 was subjected to 2 uAcm -2 、10uA cm -2 、20uA cm -2The deposition / stripping overpotential under the current density cycle is still lower than 0.5V, while the overpotential of the unmodified biomass carbon / magnesium composite material (Comparative Example 3) is close to 1V after cycling under the same conditions. The rate performance of the modified biomass carbon / magnesium composite material negative electrode sheet obtained in Example 3 is effectively improved.

Claims

1. A method for preparing a biomass carbon / magnesium composite negative electrode sheet with high cycle stability, characterized in that: The preparation method for improving the cycle stability of the biomass carbon / magnesium composite negative electrode sheet is carried out according to the following steps:

1. Weighing materials: weigh biochar, potassium hydroxide, phosphoric acid and pure magnesium metal as raw materials; 2. Potassium hydroxide chemical activation treatment: The biochar weighed in step 1 and potassium hydroxide powder are mixed to obtain a mixture of biochar and potassium hydroxide; or the weighed potassium hydroxide is used to prepare a potassium hydroxide aqueous solution, and then the biochar is placed in the potassium hydroxide solution and stirred, and then the biochar is filtered and placed in a vacuum oven to dry, to obtain a mixture of biochar and potassium hydroxide; The obtained mixture of biomass charcoal and potassium hydroxide is heat-treated under a protective atmosphere, and finally cooled with the furnace to room temperature to obtain biomass charcoal chemically activated with potassium hydroxide; 3. Biomass carbon phosphating treatment: The biochar chemically activated with potassium hydroxide obtained in step 2 is immersed in phosphoric acid, filtered and transferred to a vacuum drying oven for drying, and then transferred to a vacuum box furnace for heat treatment again under a protective atmosphere, and after completion, cooled to room temperature to obtain activated biochar, and the activated biochar is washed in deionized water until the pH is neutral, and finally dried; 4. Preparation of high cycle stability biomass carbon / magnesium composite negative electrode sheet: Under a protective atmosphere, the activated biochar obtained in step three and pure magnesium metal are pressure infiltrated to prepare a biochar / magnesium composite negative electrode sheet with high cycle stability.

2. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The mass ratio of the biochar to the potassium hydroxide powder in step 2 is 1:1 to 30.

3. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The concentration of the potassium hydroxide solution in step 2 is 1 to 20 mol / L, and the biochar is placed in the potassium hydroxide solution and stirred for 2 to 48 hours.

4. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The heating rate of the heat treatment of the biochar and potassium hydroxide mixture in step 2 is 1-20°C / min, the insulation temperature is 450-950°C, and the insulation time is 1-4h.

5. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The protective atmosphere described in step 2, step 3 and step 4 is helium, nitrogen or argon.

6. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The phosphoric acid concentration in step 3 is 85% to 98%.

7. The method for preparing a negative electrode sheet of a biomass carbon / magnesium composite material with high cycle stability according to claim 1, characterized in that: The mass ratio of the biochar to the phosphoric acid in step three is 1:10-50.

8. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The biochar described in step 3 is immersed in the phosphoric acid solution for 1 to 10 hours.

9. The method for preparing a negative electrode sheet of a biomass carbon / magnesium composite material with high cycle stability according to claim 1, characterized in that: The heating rate of the heat treatment of the biochar and phosphoric acid mixture in step 3 is 1-20°C / min, the insulation temperature is 450-1000°C, and the insulation time is 1-6h.

10. The method for preparing the biomass carbon / magnesium composite negative electrode sheet with high cycle stability according to claim 1, characterized in that: The method for preparing the modified biochar / magnesium composite material by pressure infiltration described in step 4 is: preparing pure magnesium metal into a magnesium melt, then preheating the activated biochar, and after preheating, pressure infiltrating the magnesium melt to fill all the three-dimensional interconnected pores in the activated biochar; the preheating temperature is 600-650°C, and the pressure infiltration temperature is 800-890°C.

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