Preparation Method and Application of Asphalt-Based Edge-Rich Carbon Nanoplates

Abstract

The present application discloses a preparation method and application of asphalt-based edge-rich carbon nanosheets, belonging to the technical field of carbon material preparation. The preparation method includes: 1. Ball-milling coal tar pitch and sodium chloride in a ball-milling tank; 2. Placing the mixture obtained in step 1 in a corundum boat and adding a certain amount of organic solvent for ultrasonic treatment; 3. Placing the mixture obtained in step 2 in a tube furnace, under the protection of an inert gas, and evaporating the organic solvent at a low temperature; 4. Performing high-temperature carbonization treatment on the mixture obtained in step 3; 5. Taking out the mixture obtained after carbonization in step 4 after cooling, washing with deionized water, and drying to obtain asphalt-based edge-rich carbon nanosheets. The preparation method of the present invention is simple and feasible, and sodium chloride can be recycled after being washed away with deionized water; the production cost is low, and the raw material uses coal tar pitch with rich sources, which is easy to obtain and has a low price; using the edge-rich carbon nanosheets as a zinc metal negative electrode protection material has a long cycle life and excellent rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon material preparation, and particularly relates to a preparation method and application of asphalt-based carbon nanosheets rich in edges. Background Art

[0002] Carbon materials include carbon quantum dots, carbon nanotubes, carbon fibers, graphene, carbon nanosheets, porous carbon, etc. Among them, carbon nanosheets, as novel two-dimensional carbon-based materials, have received increasing attention. Carbon nanosheets are two-dimensional sheet-like structures with a horizontal size exceeding 100 nm or several micrometers or even larger, but a thickness of only a few or a dozen atomic layers. Therefore, carbon nanosheets have broad application prospects in fields such as secondary batteries, supercapacitors, catalysts, adsorption, and electromagnetic wave absorption materials. However, a series of defects such as low chemical activity, poor ion affinity, and low electron transfer rate of traditional carbon nanosheets limit their development and application.

[0003] Patent CN108163832A uses medium-temperature coal tar pitch as a carbon source and sodium chloride obtained by dissolution and precipitation as a template, and carbonizes it at 600 - 1000 °C to obtain coal tar pitch-based smooth carbon nanosheets. Patent CN105788885A uses camellia flower petals as raw materials, mixes them evenly with an initiator, and then places them in a reactor and continuously reacts at 700 - 900 °C for 1 - 3 h to obtain biomass-based wrinkled carbon nanosheets. The above technologies have problems such as complex preparation processes and low efficiency, and most of the prepared carbon nanosheets are smooth carbon nanosheets with a low edge concentration, so it is difficult to further improve the quality of advanced carbon materials for high-performance electrochemical energy storage. Summary of the Invention

[0004] Technical Problems to be Solved:

[0005] In view of the deficiencies of the prior art, the present application provides a preparation method and application of asphalt-based carbon nanosheets rich in edges, which solve a series of defects such as low chemical activity, poor ion affinity, and low electron transfer rate of traditional carbon nanosheets that limit their development and application, as well as problems such as complex preparation processes, low efficiency, low edge concentration, and difficulty in further improving the quality of advanced carbon materials for high-performance electrochemical energy storage; and proposes an asphalt-based carbon nanosheet with rich raw material sources, simple preparation process, low cost, high edge concentration, and excellent performance, its preparation method and application.

[0006] Technical Solutions:

[0007] To achieve the above object, the present application is realized through the following technical solutions:

[0008] A preparation method of asphalt-based carbon nanosheets rich in edges, the specific steps are as follows:

[0009] Step 1: Put coal tar pitch with a softening point of 120 - 260 °C and sodium chloride into a ball mill jar and ball mill and crush for 0.5 - 1 h. Control the rotation speed of the ball mill at 500 revolutions per minute to obtain a uniformly mixed mixture A;

[0010] Step 2: Transfer the mixture A prepared in Step 1 into a quartz boat, add 5 - 20 mL of organic solvent, and put it into an ultrasonic cleaner for ultrasonic treatment for 15 - 30 min to mix evenly and obtain a uniformly mixed mixture B;

[0011] Step 3: Transfer the mixture B prepared in Step 2 into a tubular furnace, introduce inert gas for protection, and heat it at a heating rate of 1 - 5 °C / min to 150 - 350 °C for constant temperature evaporation of the organic solvent. Control the constant temperature time at 0.2 - 2 h to obtain a uniformly mixed mixture C;

[0012] Step 4: Perform carbonization treatment on the mixture C obtained in Step 3, that is, under the protection of inert gas, heat it at a heating rate of 5 - 10 °C / min to 600 - 1200 °C for carbonization treatment to obtain a mixture D, and control the carbonization time at 1 - 3 h;

[0013] Step 5: After cooling the mixture D obtained after carbonization in Step 4 to room temperature, take it out, wash it with deionized water and filter it by suction, then transfer it to a vacuum drying oven and dry it at 80 - 110 °C for 8 - 12 h to obtain the target material, asphalt-based edge-rich carbon nanosheets.

[0014] Further, in Step 1, the mass ratio of coal tar pitch to sodium chloride is 1:10 - 30, and the coal tar pitch is coal tar asphalt.

[0015] Further, in Step 2, the organic solvent is N,N-dimethylacetamide / water mixed solvent (m / m, 9:1), N,N-dimethylacetamide, N-methylpyrrolidone or toluene.

[0016] Further, the ultrasonic frequency in Step 2 is 53 kHz.

[0017] Further, the inert gas in Step 3 and Step 4 is argon or nitrogen.

[0018] Further, the cooling in Step 5 is air cooling.

[0019] This application also discloses the application of the asphalt-based edge-rich carbon nanosheets prepared by the above preparation method in zinc metal anode protection materials.

[0020] Further, the asphalt-based edge-rich carbon nanosheets and a polyvinylidene fluoride binder are prepared into a protection material according to a mass ratio of 9:1, and then coated on the surface of zinc foil by a coating method to make a zinc metal anode protection material with a carbon coating on the surface.

[0021] Further, the zinc metal anode protection material containing a carbon coating is cut into electrode sheets with a diameter of 14 mm, a CR2025 type battery case is used, Whatman 934-AH type glass fiber membrane is used as the separator material, and γ-manganese dioxide is used as the counter electrode. 2M ZnSO 4 is used as the electrolyte to prepare the battery.

[0022] Further, the electrochemical performance of the battery is tested on a Land CT2001A type battery test system. The charge-discharge voltage range is set to 0.9 - 1.8 V, and the reversible capacity of the asphalt-based edge-rich carbon nanosheets is measured under the condition of a charge-discharge current density of 3C.

[0023] Principle explanation: This application adopts an improved salt template method. According to the different solubilities of sodium chloride in different solvents, the partial dissolution and recrystallization of sodium chloride are controlled by the introduction and evaporation of organic solvents to form a salt template with edges, and then the edge concentration of carbon nanosheets is controlled by template replication. At 25 °C, the solubilities of sodium chloride in N,N-dimethylacetamide / water mixed solvent (m / m, 9:1), N,N-dimethylacetamide, N-methylpyrrolidone, and toluene are 1830.2 mg / 100 g, 7.4 mg / 100 g, 15.8 mg / 100 g, and <1.0 mg / 100 g, respectively.

[0024] Beneficial effects:

[0025] This application provides a preparation method and application of asphalt-based edge-rich carbon nanosheets, which have the following beneficial effects: Compared with the existing technology, the preparation method provided by the present invention is simple and efficient. The edge concentration of carbon nanosheets can be controlled only by the introduction and evaporation of organic solvents, and its maximum edge concentration can reach 28 edges / μm, with simple and efficient operation. The sodium chloride template agent can be removed by washing with water and can be recycled, reducing production costs; the raw materials and template agents are rich in sources and are easy to realize large-scale production; the asphalt-based edge-rich carbon nanosheets prepared by the present invention have the characteristics of long cycle life and excellent rate performance as the protection material for zinc metal anodes. The surface of the traditional asphalt-based carbon nanosheets prepared without adding organic solvents is smooth, and its maximum edge concentration is only 1 max edge / μm, and the cycle life and rate performance of the assembled zinc metal anode are poor. Description of the drawings

[0026] Figure 1 It is a scanning electron microscope photo of the asphalt-based edge-rich carbon nanosheets prepared in Example 1 of this application;

[0027] Figure 2 It is a transmission electron microscope photo of the asphalt-based edge-rich carbon nanosheets prepared in Example 1 of this application;

[0028] Figure 3 X-ray diffraction pattern of the asphalt-based edge-rich carbon nanosheets prepared in Example 1 of this application;

[0029] Figure 4 Cycling performance graph of the all-solid-state battery assembled with the asphalt-based edge-rich carbon nanosheets prepared in Example 1 of this application as the zinc metal anode protection material;

[0030] Figure 5 Rate performance graph of the all-solid-state battery assembled with the asphalt-based edge-rich carbon nanosheets prepared in Example 1 of this application as the zinc metal anode protection material. Detailed implementation manners

[0031] Next, the preferred embodiments of the present invention will be described in detail in conjunction with the drawings in the specification.

[0032] Example 1:

[0033] A preparation method of asphalt-based edge-rich carbon nanosheets, the specific steps are as follows:

[0034] Step 1: Place 1 g of coal tar pitch with a softening point of 220 °C and 20 g of sodium chloride in a ball mill jar and ball mill and crush for 0.5 h. The rotation speed of the ball mill is controlled at 500 revolutions per minute to obtain a uniformly mixed mixture A;

[0035] Step 2: Transfer the mixture A obtained in Step 1 into a quartz boat, add 15 mL of N,N-dimethylacetamide / water mixed solvent (m / m, 9:1), and place it in an ultrasonic cleaner for ultrasonic treatment for 15 min. The ultrasonic frequency is 53 kHz. Mix uniformly to obtain a uniformly mixed mixture B;

[0036] Step 3: Transfer the mixture B obtained in Step 2 into a tubular furnace, introduce an inert gas argon for protection, and heat it at a heating rate of 2 °C / min to 280 °C for constant temperature evaporation of the organic solvent. The constant temperature time is controlled at 1 h to obtain a uniformly mixed mixture C;

[0037] Step 4: Carbonize the mixture C obtained in Step 3, that is, under the protection of an inert gas argon, heat it at a heating rate of 5 °C / min to 800 °C for carbonization treatment to obtain a mixture D, and the carbonization time is controlled at 2 h;

[0038] Step 5: Take out the mixture D obtained after carbonization in Step 4, air-cool it to room temperature, wash it with deionized water and filter it by suction, then transfer it to a vacuum drying oven and dry it at 80 °C for 12 h to obtain the target material asphalt-based edge-rich carbon nanosheets.

[0039] Through low-magnification transmission electron microscopy ( Figure 1 ) and high-magnification transmission electron microscopy characterization ( Figure 2)It can be seen that the prepared material exhibits a nanorod array structure with edge enrichment, and the edge concentration can reach 28 edges / μm. X-ray diffraction characterization reveals that the carbon layer spacing of the asphalt-based edge-rich carbon nanosheets can reach 0.350 nm, as Figure 3 shown.

[0040] The obtained asphalt-based edge-rich carbon nanosheets and polyvinylidene fluoride binder are used to prepare a protective material according to a mass ratio of 9:1, and then it is coated on the surface of zinc foil by a coating method to form a zinc metal negative electrode protective material with a carbon coating on the surface. The zinc metal negative electrode protective material with a carbon coating is cut into electrode sheets with a diameter of 14 mm, a CR2025 type battery case is used, Whatman 934-AH type glass fiber membrane is used as the separator material, γ-manganese dioxide is used as the counter electrode, and 2M ZnSO 4 is used as the electrolyte. The electrochemical performance of the battery is tested on a Land CT2001A type battery test system. The charge-discharge voltage range is set to 0.9 - 1.8 V. It is measured that the reversible capacity of the asphalt-based edge-rich carbon nanosheets reaches 158 mAh·g -1 . Its rate performance and cycling performance are respectively as Figure 4 and Figure 5 shown.

[0041] Example 2:

[0042] A preparation method of asphalt-based edge-rich carbon nanosheets, the specific steps are as follows:

[0043] Step 1: Put 1 g of coal tar pitch with a softening point of 260 °C and 30 g of sodium chloride into a ball mill jar and ball mill and crush for 1 h. The rotation speed of the ball mill is controlled at 500 revolutions per minute to obtain a uniformly mixed mixture A;

[0044] Step 2: Transfer the mixture A prepared in Step 1 into a quartz boat, add 20 mL of organic solvent N-methylpyrrolidone, and put it into an ultrasonic cleaner for ultrasonic treatment for 30 min. The ultrasonic frequency is 53 kHz. Mix evenly to obtain a uniformly mixed mixture B;

[0045] Step 3: Transfer the mixture B prepared in Step 2 into a tube furnace, introduce inert gas argon for protection, and heat it at a heating rate of 3 °C / min to 350 °C for constant temperature to evaporate the organic solvent. The constant temperature time is controlled at 2 h to obtain a uniformly mixed mixture C;

[0046] Step 4: Carbonize the mixture C obtained in Step 3, that is, under the protection of inert gas argon, heat it at a heating rate of 5 °C / min to 1000 °C for carbonization treatment to obtain mixture D, and the carbonization time is controlled at 3 h;

[0047] Step 5: Take out the mixture D obtained after carbonization in Step 4, air-cool it to room temperature, wash it with deionized water and filter it by suction, then transfer it to a vacuum drying oven and dry it at 100 °C for 8 h to obtain the target material, asphalt-based edge-rich carbon nanosheets.

[0048] Prepare a protective material by mixing the obtained asphalt-based edge-rich carbon nanosheets and a polyvinylidene fluoride binder in a mass ratio of 9:1, and then coat it on the surface of zinc foil by the coating method to make a zinc metal negative electrode protective material with a carbon coating on the surface. Cut the zinc metal negative electrode protective material with a carbon coating into electrode sheets with a diameter of 14 mm, use a CR2025 type battery case, Whatman 934-AH type glass fiber membrane as the separator material, γ-manganese dioxide as the counter electrode, and 2M ZnSO 4 as the electrolyte. Perform electrochemical performance tests on the battery using a Land CT2001A type battery test system. Set the charge-discharge voltage range to 0.9 - 1.8 V. It is measured that the reversible capacity of the asphalt-based edge-rich carbon nanosheets reaches 142 mAh·g under the condition of a charge-discharge current density of 3C. -1

[0049] Example 3:

[0050] A preparation method of asphalt-based edge-rich carbon nanosheets, the specific steps are as follows:

[0051] Step 1: Put 1 g of coal tar pitch with a softening point of 120 °C and 10 g of sodium chloride into a ball mill jar and ball mill and crush for 0.5 h. Control the rotation speed of the ball mill at 500 revolutions per minute to obtain a uniformly mixed mixture A;

[0052] Step 2: Transfer the mixture A prepared in Step 1 into a quartz boat, add 10 mL of the organic solvent N,N-dimethylacetamide, and put it into an ultrasonic cleaner for ultrasonic treatment for 20 min. The ultrasonic frequency is 53 kHz. Mix evenly to obtain a uniformly mixed mixture B;

[0053] Step 3: Transfer the mixture B prepared in Step 2 into a tubular furnace, introduce an inert gas argon for protection, and heat it at a heating rate of 1 °C / min to 250 °C for constant temperature evaporation of the organic solvent. Control the constant temperature time at 0.5 h to obtain a uniformly mixed mixture C;

[0054] Step 4: Perform carbonization treatment on the mixture C obtained in Step 3, that is, under the protection of an inert gas argon, heat it at a heating rate of 5 °C / min to 1200 °C for carbonization treatment to obtain a mixture D, and control the carbonization time at 1 h;

[0055] Step 5: Take out the mixture D obtained after carbonization in Step 4, air-cool it to room temperature, wash it with deionized water, filter it by suction, then transfer it to a vacuum drying oven and dry it at 110 °C for 8 h to obtain the target material, asphalt-based edge-rich carbon nanosheets.

[0056] Prepare a protective material by mixing the obtained asphalt-based edge-rich carbon nanosheets and a polyvinylidene fluoride binder at a mass ratio of 9:1, and then coat it on the surface of the zinc foil by the coating method to make a zinc metal negative electrode protective material with a carbon coating on the surface. Cut the zinc metal negative electrode protective material with a carbon coating into electrode sheets with a diameter of 14 mm, use a CR2025 type battery case, Whatman 934-AH type glass fiber membrane as the separator material, γ-manganese dioxide as the counter electrode, and 2M ZnSO 4 as the electrolyte. Perform electrochemical performance tests on the battery using a Land CT2001A type battery test system. Set the charge-discharge voltage range to 0.9 - 1.8 V, and measure that the reversible capacity of the asphalt-based edge-rich carbon nanosheets reaches 137 mAh·g under the condition of a charge-discharge current density of 3C. -1 .

[0057] Example 4:

[0058] A preparation method of asphalt-based edge-rich carbon nanosheets, the specific steps are as follows:

[0059] Step 1: Place 1 g of coal tar pitch with a softening point of 180 °C and 25 g of sodium chloride in a ball mill jar and ball mill and crush for 1 h. Control the rotation speed of the ball mill at 500 revolutions per minute to obtain a uniformly mixed mixture A;

[0060] Step 2: Transfer the mixture A prepared in Step 1 into a quartz boat, add 20 mL of organic solvent toluene, and place it in an ultrasonic cleaner for ultrasonic treatment for 30 min. The ultrasonic frequency is 53 kHz. Mix evenly to obtain a uniformly mixed mixture B;

[0061] Step 3: Transfer the mixture B prepared in Step 2 into a tubular furnace, introduce inert gas nitrogen for protection, and heat it at a heating rate of 5 °C / min to 150 °C for constant temperature evaporation of the organic solvent. Control the constant temperature time at 0.2 h to obtain a uniformly mixed mixture C;

[0062] Step 4: Perform carbonization treatment on the mixture C obtained in Step 3, that is, under the protection of inert gas argon, heat it at a heating rate of 5 °C / min to 600 °C for carbonization treatment to obtain mixture D, and control the carbonization time at 3 h;

[0063] Step 5: Take out the mixture D obtained after carbonization in Step 4, air-cool it to room temperature, wash it with deionized water, filter it by suction, then transfer it to a vacuum drying oven and dry it at 80 °C for 12 h to obtain the target material, asphalt-based edge-rich carbon nanosheets.

[0064] The obtained asphalt-based edge-rich carbon nanosheets and polyvinylidene fluoride binder were used to prepare a protective material according to a mass ratio of 9:1, and then it was coated on the surface of zinc foil by a coating method to make a zinc metal negative electrode protective material with a carbon coating on the surface. The zinc metal negative electrode protective material with a carbon coating was cut into electrode sheets with a diameter of 14 mm, a CR2025 type battery case was used, Whatman 934-AH type glass fiber membrane was used as the separator material, γ-manganese dioxide was used as the counter electrode, and 2M ZnSO 4 was used as the electrolyte. The electrochemical performance of the battery was tested on a Land CT2001A type battery test system. The charge-discharge voltage range was set to 0.9 - 1.8 V, and the reversible capacity of the asphalt-based edge-rich carbon nanosheets was measured to reach 131 mAh·g -1 .

[0065] Comparative example:

[0066] A preparation method of asphalt-based smooth carbon nanosheets, the specific steps are as follows:

[0067] Step 1: 1 g of coal tar pitch with a softening point of 220 °C and 20 g of sodium chloride were placed in a ball milling tank and ball milled for 0.5 h, and the rotation speed of the ball mill was controlled at 500 revolutions per minute to obtain a uniformly mixed mixture;

[0068] Step 2: The mixture A prepared in Step 1 was transferred to a quartz boat;

[0069] Step 3: The mixture was transferred to a tubular furnace, protected by introducing inert gas argon, and heated to 800 °C at a heating rate of 5 °C / min for carbonization treatment, and the carbonization time was controlled at 2 h;

[0070] Step 4: The mixture obtained after carbonization was air-cooled to room temperature and then taken out, washed with deionized water and filtered by suction, and then transferred to a vacuum drying oven and dried at 80 °C for 12 h to obtain the target material asphalt-based smooth carbon nanosheets.

[0071] The obtained asphalt-based smooth carbon nanosheets and polyvinylidene fluoride binder were used to prepare a protective material according to a mass ratio of 9:1, and then it was coated on the surface of zinc foil by a coating method to make a zinc metal negative electrode material with a carbon coating on the surface. The material obtained after coating was cut into electrode sheets with a diameter of 14 mm, a CR2025 type battery case was used, Whatman 934-AH type glass fiber membrane was used as the separator material, γ-manganese dioxide was used as the counter electrode, and 2M ZnSO 4As the electrolyte. The electrochemical performance of the battery was tested using a Land CT2001A battery test system. The charge-discharge voltage range was set to 0.9 - 1.8 V, and the reversible capacity of the asphalt-based rich-edge carbon nanosheets was measured to reach 125 mAh·g under the condition of a charge-discharge current density of 3C. -1 .

[0072] Compared with Example 1, in this comparative example, no organic solvent was added, and the surface of the prepared asphalt-based carbon nanosheets was smooth, with a maximum edge concentration of only 1 max edge / μm. The initial reversible capacity of the all-battery assembled with this asphalt-based carbon nanosheet as the zinc metal anode protection material was significantly reduced under the same test conditions.

[0073] The examples proposed in the present invention are examples under relatively optimal conditions, but are not limited to the content proposed above. Those skilled in the relevant art can easily reproduce the above examples and further extend and vary the solutions, but as long as they do not depart from the spirit of the present invention, they are within the protection scope of the present invention.

Claims

1. A method for preparing pitch-based edge-rich carbon nanosheets, characterized in that: The specific steps are: Step 1, placing coal tar pitch with a softening point of 120-260° C. and sodium chloride in a ball mill and grinding them for 0.5-1 h, with the speed of the ball mill controlled at 500 rpm to obtain a uniformly mixed mixture A; Step 2, transfer the mixture A obtained in step 1 into a quartz boat, add 5-20 mL of an organic solvent, put it into an ultrasonic cleaning machine for ultrasonic treatment for 15-30 min, mix well, and obtain a well-mixed mixture B; Step 3, the mixture B obtained in step 2 is transferred into a tube furnace, an inert gas is introduced for protection, and the temperature is increased to 150-350°C at a heating rate of 1-5°C / min to evaporate the organic solvent at a constant temperature, and the constant temperature time is controlled at 0.2-2 h to obtain a uniformly mixed mixture C; Step 4, carbonizing the mixture C obtained in step 3, i.e., heating the mixture to 800°C at a heating rate of 5-10°C / min under inert gas protection to obtain a mixture D, and the carbonization time is controlled within 1-3 h; Step 5, the mixture D obtained after carbonization in step 4 is cooled to room temperature, taken out, washed with deionized water, filtered, and then transferred to a vacuum drying oven and dried at 80-110° C. for 8-12 h to obtain the target material asphalt-based edge-rich carbon nanosheets; The organic solvent in step 2 is a mixed solvent of N, N-dimethylacetamide and water in a mass ratio of 9:1, N, N-dimethylacetamide, N-methylpyrrolidone or toluene.

2. The method for preparing a pitch-based edge-rich carbon nanosheet according to claim 1, characterized in that: In the step 1, the mass ratio of coal tar pitch to sodium chloride is 1:10-30, and the coal tar pitch is coal tar pitch.

3. The method for preparing a pitch-based edge-rich carbon nanosheet according to claim 1, characterized in that: The ultrasonic frequency in step 2 is 53 kHz.

4. The method for preparing a pitch-based edge-rich carbon nanosheet according to claim 1, characterized in that: The inert gas in step 3 and step 4 is argon or nitrogen.

5. The method for preparing a pitch-based edge-rich carbon nanosheet according to claim 1, characterized in that: The cooling in step 5 is air cooling.

6. Use of asphalt-based edge-rich carbon nanosheets prepared by the preparation method according to any one of claims 1 to 5 in zinc metal negative electrode protective materials.

7. The use according to claim 6, characterized in that: The protective material is prepared by mixing asphalt-based edge-rich carbon nanosheets and polyvinylidene fluoride binder in a mass ratio of 9:1, and then coated on the surface of zinc foil by a coating method to prepare a zinc metal negative electrode protective material with a carbon coating on the surface.

8. The use according to claim 7, characterized in that: The zinc metal negative electrode protection material containing a carbon coating was cut into electrode sheets with a diameter of 14 mm, and a battery was prepared using a CR2025 battery case, a Whatman 934-AH glass fiber membrane as a separator material, γ-manganese dioxide as a counter electrode, and 2M ZnSO4 as an electrolyte.

9. The use according to claim 8, characterized in that: The electrochemical performance of the battery was tested on a Land CT2001A battery testing system with the charge and discharge voltage range set to 0.9-1.8 V. The reversible capacity of the asphalt-based edge-rich carbon nanosheets was measured at a charge and discharge current density of 3 C.

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