Controllable construction method for carbon layer structure on hard carbon surface and application of controllable construction method

Abstract

The invention provides a controllable construction method of a hard carbon surface carbon layer structure and application thereof, and belongs to the field of new energy materials. The preparation method comprises the following steps: carrying out high-temperature heat treatment on a hard carbon precursor to obtain a hard carbon sample, dissolving coated asphalt in a toluene solution, centrifugally throwing out insoluble substances to obtain a toluene soluble asphalt solution, and drying the toluene soluble asphalt solution to obtain a toluene soluble asphalt component; carrying out mixing-drying treatment on the asphalt component and a hard carbon sample in a liquid phase solution to obtain an asphalt coated hard carbon sample; and performing hydrogen reduction treatment on the obtained asphalt coated sample at low temperature to obtain a hard carbon sample coated with a low-defect-degree surface carbon layer, and then performing instant Joule heat treatment on the hard carbon sample coated with the low-defect-degree surface carbon layer to obtain a high-rate surface carbon layer modified hard carbon sample. The carbon layer constructed in the invention improves the stability of the solid electrolyte membrane in the sodium ion battery, reduces the internal resistance of sodium ion transmission, and promotes the rate property and cycle property of the sodium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy battery materials, and specifically relates to a method for controllably constructing a carbon layer structure on a hard carbon surface and its application. Background Art

[0002] Sodium-ion batteries have significant advantages in cost and safety due to their abundant and evenly distributed reserves of available sodium resources and the use of aluminum foil as the negative electrode current collector, allowing them to rapidly capture the new energy market. As the market develops, the fast-charging properties of sodium-ion batteries are increasingly unable to meet the growing market demand. The fundamental reason lies in the randomly curved microcrystalline structure and complex surface and interface structure within the hard carbon negative electrode material. As the primary active surface that contacts and reacts with sodium ions, the properties of the hard carbon surface interface determine the structure and composition of the solid electrolyte membrane (SEI), the diffusion and transport behavior of Na+, and the stability of the interface structure, directly affecting the long-term cycling, rate properties, and environmental applicability of sodium-ion batteries. Therefore, how to improve the surface and interface structural properties of hard carbon is one of the key points to improve the kinetics of hard carbon.

[0003] Coating the surface of hard carbon with an asphalt-derived carbon layer can effectively improve the interfacial properties of hard carbon, and this method has been deeply studied by many researchers. For example, patents CN111900400A, CN117963885A, and CN118183739A coat the surface of phenolic resin, biomass hard carbon, and coal-based hard carbon with asphalt to obtain hard carbon with an ordered carbon layer on the surface. However, for asphalt, its composition is complex, and not all carbon layers formed by asphalt components are beneficial to the fast charging properties of sodium ion batteries. In addition, there are random functional group structures distributed on the molecular structure of asphalt polycyclic aromatic hydrocarbons. This structure is randomly rearranged under the influence of thermal stress during the subsequent carbonization process, which causes the asphalt-derived carbon layer to develop randomly and is uncontrollable. Therefore, there are differences in the properties of the carbon layer on the surface of hard carbon prepared by different researchers using the same method.

[0004] Therefore, it is urgent to develop a method to achieve controllable design of the carbon layer structure on the hard carbon surface to further improve the fast charging properties of sodium ion batteries. Summary of the Invention

[0005] In order to solve the problem of uncontrollable carbon layer structure caused by complex coating asphalt components and random distribution of defect structures in condensed ring aromatic hydrocarbon molecules in asphalt, the present invention provides a method for controllable construction of carbon layer structure on hard carbon surface and its application.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for controllably constructing a carbon layer structure on a hard carbon surface comprises the following steps:

[0008] Step 1, subjecting a hard carbon precursor to high-temperature carbonization treatment to obtain a hard carbon sample;

[0009] Step 2: dissolving the coated asphalt in a toluene solvent, and after sufficient dissolution, centrifuging to remove solid residual particles, and then drying to remove the toluene solvent, thereby obtaining a toluene-soluble asphalt component;

[0010] Step 3, mixing the toluene-soluble asphalt component and the hard carbon sample in a liquid phase in proportion and then drying the mixture to obtain an asphalt-coated hard carbon sample;

[0011] Step 4, reducing the asphalt-coated hard carbon sample in hydrogen at low temperature to obtain a hard carbon sample coated with a low-defect surface carbon layer;

[0012] Step 5: subjecting the hard carbon sample coated with the low-defect surface carbon layer to a flash Joule heat treatment to obtain a hard carbon sample modified with a high-magnification surface carbon layer.

[0013] Furthermore, the hard carbon precursor is one or more of a biomass series, a coal series, an asphalt series or a polymer series;

[0014] The biomass series is one or more of bamboo, coconut shell, apricot shell, walnut shell, wood, nut shell, rice husk, straw, bagasse, cellulose, lignin or starch;

[0015] The coal series is one or more of long flame coal, lignite, peat, lean coal and lean coal;

[0016] The asphalt series is one or more of medium-temperature asphalt, modified asphalt, coal-coated asphalt, oil-coated asphalt, and liquefied residue asphalt;

[0017] The polymer series is one or more of phenolic resin, epoxy resin and polyacrylonitrile.

[0018] Furthermore, the treatment temperature of the high-temperature carbonization in step 1 is 1200-1500° C., the treatment time is 1-5 hours, and the heating rate is 2-5° C. / min.

[0019] Furthermore, the coating asphalt in step 2 is one or more of coal-based coating asphalt having a softening point of 150°C to 280°C and oil-based coating asphalt having a softening point of 150°C to 280°C; the ratio of coating asphalt to toluene solvent is 1g:20-100mL; the rotation speed of the centrifugal treatment in step 2 is 500-5000r / min, and the centrifugation time is 10-60min; the temperature of the drying treatment in step 2 is 60-100°C, and the drying time is 4-8h.

[0020] Furthermore, in step 3, the weight ratio of the toluene-soluble asphalt component to the hard carbon sample is 1 to 6:100;

[0021] The liquid phase solvent involved in the liquid phase mixing-drying process in step 3 is one or more of toluene, tetrahydrofuran, and N,N-dimethylacetamide;

[0022] In step 3, the ratio of the liquid phase solvent to the toluene-soluble asphalt component and the hard carbon sample is 20-100 mL: 1 g;

[0023] The liquid phase mixing time in step 3 is 2 to 10 hours, and the stirring speed is 200 to 1000 r / min;

[0024] The drying temperature in step 3 is 80-100° C., and the drying time is 4-8 hours.

[0025] Furthermore, in the step 4, the low-temperature hydrogen reduction is specifically performed at a flow rate ratio of hydrogen to inert gas of 2 to 5:100; the hydrogen reduction temperature is 350°C to 550°C, the reduction time is 1 to 5 hours, and the heating rate is 2 to 10°C / min; and the inert gas includes one or both of nitrogen and argon.

[0026] Furthermore, in step 5, the flash Joule heat treatment is performed at a temperature of 1500-2000° C., with a residence time of 100 ms-10 s; and the temperature of the Joule heat treatment is greater than or equal to the temperature of the high-temperature heat treatment of the hard carbon precursor.

[0027] A hard carbon material coated with a high-rate surface carbon layer, wherein the surface carbon layer of the hard carbon material has a thickness of 5 to 10 nm and an interlayer spacing of 0.35 to 0.40 nm;

[0028] The specific surface area of the hard carbon material is less than 5 m 2 / g, at a current density of 0.1A / g, the gram capacity of sodium ion batteries is higher than 220mAh / g.

[0029] A hard carbon negative electrode plate coated with a high-rate surface carbon layer, the negative electrode plate comprising the hard carbon material coated with the high-rate surface carbon layer.

[0030] A sodium ion battery comprises the above-mentioned negative electrode plate.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) Different from directly modifying the hard carbon surface with coated asphalt, the present invention is based on the principle of like dissolves like. The coated asphalt components are refined by toluene, and components that are more beneficial to the surface and interfacial properties of the hard carbon are extracted for modification, thus avoiding the influence of adverse components in the coated asphalt. On the one hand, the toluene-soluble asphalt components are mostly small-layer molecular structures, which are easy to form short-range carbon layer structures during the subsequent carbonization process, providing more embedding sites for sodium ion transport. On the other hand, the carbon layer structure derived from toluene-soluble asphalt has strong toughness, which can effectively alleviate the surface damage caused by the expansion of hard carbon at high rates.

[0033] (2) By reducing the functional groups on the molecular structure of polycyclic aromatic hydrocarbons in toluene-soluble asphalt with hydrogen, the defects on the edges of the polycyclic aromatic hydrocarbons are repaired, making them more flat and reducing the random bending of the carbon layer caused by the shedding of functional groups. Under the premise of being lower than the high-temperature heat treatment temperature of hard carbon, the low-defect carbon layer structure on the surface of hard carbon is regulated within milliseconds by using flash Joule heating technology. This process does not affect the structural properties of the hard carbon itself. By combining hydrogen low-temperature reduction and instantaneous Joule heating technology, the carbon layer structure on the surface of hard carbon is effectively controlled, thereby contributing to the fast charging properties of sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0035] Figure 1 A method for controllable construction of carbon layer structure on hard carbon surface and its application flow chart;

[0036] Figure 2 A method for controllable construction of carbon layer structure on hard carbon surface and SEM images of its application;

[0037] Figure 3 A method for controllable construction of carbon layer structure on hard carbon surface and its application TEM image;

[0038] Figure 4 A method for controllable construction of carbon layer structure on hard carbon surface and rate property diagram of its application. DETAILED DESCRIPTION

[0039] To gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description thereof. However, the present invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a comprehensive understanding of the present disclosure.

[0040] Example 1

[0041] This embodiment provides a method for controllably constructing a carbon layer structure on a hard carbon surface and its application. The process flow chart is as follows: Figure 1 As shown, the preparation method comprises the following steps:

[0042] Step 1: heat-treating the hard carbon precursor (coconut shell) at 1300° C. for 2 h at a heating rate of 2° C. / min to obtain a hard carbon sample;

[0043] Step 2: Dissolve the oil-based coated asphalt with a softening point of 200°C in a ratio of 1g:50mL of coated asphalt to toluene solvent. After sufficient dissolution, discard the solid insoluble matter under the conditions of a centrifugal speed of 1000r / min and a centrifugal time of 10min to obtain a liquid-soluble asphalt solution; dry the liquid-soluble asphalt solution in an oven at a temperature of 80°C and a time of 8h to obtain a toluene-soluble asphalt component.

[0044] Step 3: The toluene-soluble asphalt component and the hard carbon are mixed in a weight ratio of 3:100, and mixed and dissolved in an N,N-dimethylacetamide liquid solvent, wherein the ratio of the N,N-dimethylacetamide liquid solvent to (toluene-soluble asphalt component + hard carbon sample) is 100 mL:1 g, the mixing and dissolving time is 5 h, and the stirring speed is 1000 r / min; after the mixing and dissolving is completed, the above-mentioned liquid mixture is dried in an oven at a temperature of 80°C for 4 h to obtain an asphalt-coated hard carbon sample;

[0045] Step 4: The asphalt-coated hard carbon sample is subjected to defect repair treatment under the conditions of a hydrogen to inert gas flow ratio of 2:100, a hydrogen reduction temperature of 500°C, a reduction time of 2h, and a heating rate of 2°C / min to obtain a hard carbon sample coated with a low-defect surface carbon layer.

[0046] Step 5: heat-treating the hard carbon sample coated with the low-defect surface carbon layer in a flash Joule heating instrument at a reaction temperature of 1600° C. and a residence time of 1 s to obtain a hard carbon sample modified with a high-rate surface carbon layer.

[0047] Example 2

[0048] This embodiment provides a method for controllably constructing a carbon layer structure on a hard carbon surface and its application, comprising the following steps:

[0049] Step 1: subjecting a hard carbon precursor, long flame coal, to a high temperature heat treatment at a temperature of 1400° C. for 3 h and a heating rate of 5° C. / min to obtain a hard carbon sample;

[0050] Step 2: dissolve the coal-based coated asphalt with a softening point of 150°C in a ratio of 1g:100mL of coated asphalt to toluene solvent. After sufficient dissolution, discard the solid insoluble matter under the conditions of a centrifugal speed of 2000r / min and a centrifugal time of 20min to obtain a liquid-soluble asphalt solution; dry the liquid-soluble asphalt solution in an oven at a temperature of 100°C and a time of 4h to obtain a toluene-soluble asphalt component.

[0051] Step 3: The toluene-soluble asphalt component and the hard carbon are mixed in a weight ratio of 5:100, and mixed and dissolved in a toluene liquid phase solvent, wherein the ratio of the toluene liquid phase solvent to (toluene-soluble asphalt component + hard carbon sample) is 80 mL:1 g, the mixing and dissolving time is 10 h, and the stirring speed is 5000 r / min; after the mixing and dissolving is completed, the above-mentioned liquid phase mixture is dried in an oven at a temperature of 60°C for 8 h to obtain an asphalt-coated hard carbon sample;

[0052] Step 4: The asphalt-coated hard carbon sample is subjected to defect repair treatment under the conditions of a hydrogen to inert gas flow ratio of 5:100, a hydrogen reduction temperature of 400°C, a reduction time of 5h, and a heating rate of 10°C / min to obtain a hard carbon sample coated with a low-defect surface carbon layer.

[0053] Step 5: heat-treating the hard carbon sample coated with the low-defect surface carbon layer in a flash Joule heating instrument at a reaction temperature of 2000° C. and a residence time of 100 ms to obtain a hard carbon sample modified with a high-rate surface carbon layer.

[0054] Example 3

[0055] This embodiment provides a method for controllably constructing a carbon layer structure on a hard carbon surface and its application, comprising the following steps:

[0056] Step 1: heat-treating the hard carbon precursor (phenolic resin) at 1400° C. for 5 h at a heating rate of 3° C. / min to obtain a hard carbon sample;

[0057] Step 2: dissolve the oil-based coated asphalt with a softening point of 280°C in a ratio of 1g:20mL of coated asphalt to toluene solvent. After sufficient dissolution, discard the solid insoluble matter under the conditions of a centrifugal speed of 5000r / min and a centrifugal time of 60min to obtain a liquid-soluble asphalt solution; dry the liquid-soluble asphalt solution in an oven at a temperature of 60°C and a time of 8h to obtain a toluene-soluble asphalt component.

[0058] Step 3: The toluene-soluble asphalt component and the hard carbon are mixed in a weight ratio of 6:100, and mixed and dissolved in a tetrahydrofuran liquid solvent, wherein the ratio of the tetrahydrofuran liquid solvent to (toluene-soluble asphalt component + hard carbon sample) is 20 mL:1 g, the mixing and dissolving time is 6 h, and the stirring speed is 500 r / min; after the mixing and dissolving is completed, the above-mentioned liquid mixture is dried in an oven at a temperature of 100°C for 5 h to obtain a asphalt-coated hard carbon sample;

[0059] Step 4: The asphalt-coated hard carbon sample is subjected to defect repair treatment under the conditions of a hydrogen to inert gas flow ratio of 4:100, a hydrogen reduction temperature of 550°C, a reduction time of 1 hour, and a heating rate of 6°C / min to obtain a hard carbon sample coated with a low-defect surface carbon layer.

[0060] Step 5: heat-treating the hard carbon sample coated with the low-defect surface carbon layer in a flash Joule heating instrument at a reaction temperature of 1800° C. and a residence time of 500 ms to obtain a hard carbon sample modified with a high-rate surface carbon layer.

[0061] Example 4

[0062] The difference between this embodiment and embodiment 1 is that in step 2, the coated asphalt is not subjected to toluene component refinement treatment and the solid insoluble matter is not thrown out.

[0063] The rest of the preparation methods and parameters remained the same as in Example 1.

[0064] Example 5

[0065] The difference between this embodiment and embodiment 1 is that the asphalt-coated hard carbon sample is not subjected to low-temperature hydrogen reduction treatment in step 4.

[0066] The rest of the preparation methods and parameters remained the same as in Example 1.

[0067] Example 6

[0068] The difference between this embodiment and embodiment 1 is that in step 4, the hard carbon sample coated with the low-defect surface carbon layer is heated to 1600° C. at a slow heating rate (2° C. / min) and held for 1 second.

[0069] The rest of the preparation methods and parameters remained the same as in Example 1.

[0070] Example 7

[0071] The difference between this embodiment and embodiment 1 is that no flash Joule heat treatment is performed in step (3).

[0072] The rest of the preparation methods and parameters remained the same as in Example 1.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that no asphalt liquid phase coating is performed, and only subsequent hydrogen reduction and flash Joule heat treatment are performed to prepare high-rate hard carbon.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that no asphalt liquid phase coating is performed, and only subsequent flash Joule heat treatment is performed to prepare high-rate hard carbon.

[0077] Comparative Example 3

[0078] This comparative example differs from Example 1 in that no asphalt liquid phase coating is performed, and only subsequent hydrogen reduction treatment is performed to prepare high-rate hard carbon.

[0079] The microstructure of the hard carbon material prepared in Example 1 was characterized, and its SEM and TEM images are shown in FIG. Figure 2 and Figure 3 As shown; the hard carbon prepared in Example 1 was tested for rate properties, and the rate diagram was as shown Figure 4 shown.

[0080] The specific surface area of high-rate hard carbon is tested by a nitrogen adsorption-desorption instrument (the test conditions are vacuum pretreatment at 150°C for 5 hours, and the specific surface area of hard carbon is only tested in a liquid nitrogen environment), and the powder conductivity is tested by a powder resistivity meter (a certain amount of sample powder is placed in a powder resistivity tester, and the conductivity test is performed at different pressures of 0-26MPa, and the value at 20MPa is taken as the conductivity of the sample).

[0081] The surface carbon layer modified hard carbon negative electrode material provided in the above examples and comparative examples is made into a negative electrode sheet, and is assembled with a commercial sodium sheet, a separator and an electrolyte to obtain a sodium ion button battery. The specific steps include:

[0082] A slurry prepared by mixing pitch-based hard carbon material, Super P, 1.5% carboxymethyl cellulose (CMC), and 45% styrene-butadiene rubber (SBR) in a mass ratio of 91:2:2:5 was coated onto aluminum foil. A commercial sodium sheet was used as the positive electrode. Glass fiber (Whatman, GF / D) and 1 M NaClF₂ were used as the separator and electrolyte, respectively. CR2032 coin cells were assembled in a glove box (H₂O, O₂ <0.1 ppm). Charge-discharge tests at 0–2 V and cycling stability were performed using a LAND CT2001 battery tester (LAND, Wuhan, China).

[0083] The above sodium ion batteries were subjected to capacity performance tests and cycle stability tests.

[0084] The conditions for the rate performance test are: charge and discharge three times at a low current of 0.1C (30 mAh / g), then test the gram capacity at 0.5C (150 mAh / g) discharge and 30 mAh / g charge. The voltage window is set to 0~2 V, and the rate properties are calculated according to 0.5C / 0.1C, as shown in the following example: Figure 4 shown.

[0085] The conditions for the cycle stability test are: charge and discharge the button for 3 cycles at a current of 30 mA / g, and then charge and discharge at a current density of 100 mA / g. The current window is set to 0~2V, and the number of cycles is 500.

[0086] The test results are shown in Table 1.

[0087]

[0088] Any matters not described in detail in this specification are prior art known to those skilled in the art. Although the above description of the present invention is based on specific embodiments to facilitate understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the specific embodiments. As long as various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, such modifications will be obvious to those skilled in the art, and all inventions and creations utilizing the concepts of the present invention are protected.

Claims

1. A method for controllably constructing a carbon layer structure on a hard carbon surface, characterized by: The following steps are involved: Step 1, subjecting a hard carbon precursor to high-temperature carbonization treatment to obtain a hard carbon sample; Step 2: dissolving the coated asphalt in a toluene solvent, and after sufficient dissolution, centrifuging to remove solid residual particles, and then drying to remove the toluene solvent, thereby obtaining a toluene-soluble asphalt component; Step 3, mixing the toluene-soluble asphalt component and the hard carbon sample in a liquid phase in proportion and then drying the mixture to obtain an asphalt-coated hard carbon sample; Step 4, reducing the asphalt-coated hard carbon sample in hydrogen at low temperature to obtain a hard carbon sample coated with a low-defect surface carbon layer; Step 5: subjecting the hard carbon sample coated with the low-defect surface carbon layer to a flash Joule heat treatment to obtain a hard carbon sample modified with a high-magnification surface carbon layer.

2. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: The hard carbon precursor is one or more of a biomass series, a coal series, an asphalt series or a polymer series; The biomass series is one or more of bamboo, coconut shell, apricot shell, walnut shell, wood, nut shell, rice husk, straw, bagasse, cellulose, lignin or starch; The coal series is one or more of long flame coal, lignite, peat, lean coal and lean coal; The asphalt series is one or more of medium-temperature asphalt, modified asphalt, coal-coated asphalt, oil-coated asphalt, and liquefied residue asphalt; The polymer series is one or more of phenolic resin, epoxy resin and polyacrylonitrile.

3. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: The high-temperature carbonization treatment temperature in step 1 is 1200-1500° C., the treatment time is 1-5 hours, and the heating rate is 2-5° C. / min.

4. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: The coating asphalt in step 2 is one or more of coal-based coating asphalt having a softening point of 150°C to 280°C and oil-based coating asphalt having a softening point of 150°C to 280°C; the ratio of coating asphalt to toluene solvent is 1g:20-100mL; the rotation speed of the centrifugal treatment in step 2 is 500-5000r / min, and the centrifugation time is 10-60min; the temperature of the drying treatment in step 2 is 60-100°C, and the drying time is 4-8h.

5. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: In step 3, the weight ratio of the toluene-soluble asphalt component to the hard carbon sample is 1 to 6:100; The liquid phase solvent involved in the liquid phase mixing-drying process in step 3 is one or more of toluene, tetrahydrofuran, and N,N-dimethylacetamide; In step 3, the ratio of the liquid phase solvent to the toluene-soluble asphalt component and the hard carbon sample is 20-100 mL: 1 g; The liquid phase mixing time in step 3 is 2 to 10 hours, and the stirring speed is 200 to 1000 r / min; The drying temperature in step 3 is 80-100° C., and the drying time is 4-8 hours.

6. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: In the step 4, the low-temperature hydrogen reduction is specifically performed at a hydrogen to inert gas flow ratio of 2 to 5:100; the hydrogen reduction temperature is 350° C. to 550° C., the reduction time is 1 to 5 hours, and the heating rate is 2 to 10° C. / min; and the inert gas includes one or both of nitrogen and argon.

7. The method for controllably constructing a carbon layer structure on a hard carbon surface according to claim 1, characterized in that: In step 5, the flash Joule heat treatment is performed at a temperature of 1500-2000° C., with a residence time of 100 ms-10 s; and the temperature of the Joule heat treatment is greater than or equal to the temperature of the high-temperature heat treatment of the hard carbon precursor.

8. A hard carbon material coated with a high-rate surface carbon layer, prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The thickness of the surface carbon layer of the hard carbon material is 5-10 nm, and the interlayer spacing of the surface carbon layer is 0.35-0.40 nm; The specific surface area of the hard carbon material is less than 5 m 2 / g, at a current density of 0.1A / g, the gram capacity of sodium ion batteries is higher than 220mAh / g.

9. A hard carbon negative electrode plate coated with a high-rate surface carbon layer, characterized in that: The negative electrode plate includes the hard carbon material coated with the high-rate surface carbon layer as claimed in claim 8.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the negative electrode sheet as claimed in claim 9.

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