Hard carbon material for battery negative electrode, preparation method of hard carbon material and battery

Abstract

The invention provides a hard carbon material for a battery negative electrode, a preparation method of the hard carbon material and a battery. The preparation method of the hard carbon material comprises the following steps: step 1, adding a saccharide aqueous solution into a hydrothermal kettle for hydrothermal reaction; 2, filtering a hydrothermal reaction product obtained in the step 1, separating filtrate and filter residues, and drying the filter residues to obtain a spherical carbon precursor; and 3, carrying out pre-carbonization treatment on the spherical carbon precursor obtained in the step 2 in a pore-forming atmosphere, introducing nitrogen or inert gas, and carrying out high-temperature annealing treatment in a nitrogen or inert gas atmosphere to obtain the hard carbon material. According to the preparation method of the hard carbon material, the battery capacity is further improved by improving the oxygen content or the specific surface area, the porosity and the like.

Description

Technical Field

[0001] The present invention relates to the field of battery negative electrode materials, in particular to a hard carbon material for battery negative electrode and a preparation method thereof, and a battery. Background Art

[0002] Sodium-ion batteries are considered the core direction of the post-lithium era due to their high abundance of sodium resources (2.3% in the earth's crust, only 0.006% in lithium), low cost (the price of sodium carbonate is less than 1 / 10 of that of lithium carbonate), excellent low-temperature performance (capacity retention rate at -20°C > 80%), and fast charging potential (charging rate can reach more than 5C). However, the technology of negative electrode materials for sodium-ion batteries is not yet mature. Traditional graphite (interlayer spacing 0.335nm) fails because the radius of sodium ions (0.102nm) is much larger than the radius of lithium ions (0.076nm). Hard carbon materials have become the only negative electrode system that can be commercialized due to their disordered layered structure (interlayer spacing 0.38nm to 0.42nm) and abundant defect sites.

[0003] Hard carbon is the preferred material for the negative electrode of sodium-ion batteries. It can also be used for the negative electrode of lithium-ion batteries and potassium-ion batteries, and has excellent fast-charging performance. The hard carbon products currently on the market have large particle sizes and irregular edges. Due to the tip discharge effect, the fast-charging performance is poor and sodium metal is easily precipitated during fast charging and discharging, which leads to safety problems such as short circuit and thermal runaway. There are also problems such as unstable performance between batches, rapid capacity drop during fast charging, low long-cycle performance and first-cycle coulomb efficiency (less than 90%), and poor conductivity. The morphology and performance of hard carbon used in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries in the prior art need to be further optimized in order to find hard carbon with better electrochemical and safety performance.

[0004] There is a hard carbon material currently produced by hydrothermal reaction of glucose. Although it has good capacity and first-cycle coulombic efficiency, the oxygen content and porosity of the hard carbon produced under the original synthesis conditions are not high enough, which limits the battery capacity. Summary of the invention

[0005] The first object of the present invention is to provide a method for preparing a hard carbon material for a battery negative electrode, which can further improve the battery capacity by increasing the oxygen content or specific surface area, porosity, etc.

[0006] The second object of the present invention is to provide a hard carbon material for battery negative electrode prepared by the above preparation method.

[0007] A third object of the present invention is to provide a battery having a battery negative electrode made of the above hard carbon material.

[0008] To achieve the above-mentioned first purpose, the present invention provides a method for preparing a hard carbon material for a battery negative electrode, comprising: step one, adding a sugar aqueous solution to a hydrothermal kettle for a hydrothermal reaction; step two, filtering the product of the hydrothermal reaction obtained in step one, separating the filtrate and the filter residue, and drying the filter residue to obtain a spherical carbon precursor; step three, pre-carbonizing the spherical carbon precursor obtained in step two in a pore-forming atmosphere, introducing nitrogen or an inert gas, and performing a high-temperature annealing treatment in a nitrogen or inert gas atmosphere to obtain a hard carbon material.

[0009] It can be seen from the above scheme that the present invention obtains a spherical carbon precursor by hydrothermal reaction of a sugar aqueous solution, and then performs a preliminary pre-carbonization treatment in a pore-forming atmosphere, and then performs a high-temperature annealing treatment in a nitrogen atmosphere. The pore-forming atmosphere can play a pore-forming role, increase the oxygen content, specific surface area and porosity, and thus greatly increase the battery capacity.

[0010] A preferred solution is that in step three, the heating rate during the pre-carbonization treatment is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 200°C to 500°C, and the insulation time is in the range of 1 hour to 3 hours.

[0011] A further solution is that in step three, during the high temperature annealing treatment, the heating rate is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 800°C to 1900°C, and the holding time is in the range of 1 hour to 3 hours.

[0012] It can be seen that by controlling the heating rate, carbonization temperature and holding time of the pre-carbonization process and the high-temperature annealing process, the oxygen content, specific surface area and porosity can be reasonably controlled, thereby ensuring that the battery capacity is maximized.

[0013] A preferred solution is that the pore-forming atmosphere is an air atmosphere or an ammonia atmosphere.

[0014] It can be seen from this that pores can be formed by pre-oxidation with air or by using ammonia.

[0015] A preferred solution is that the raw material of the sugar aqueous solution includes at least one of glucose, sucrose, syrup and sugarcane juice.

[0016] It can be seen that the use of at least one of glucose, sucrose, syrup, and sugarcane juice as the sugar aqueous solution is easier to obtain and cheaper than the existing method of preparing the precursor by pre-treating the biomass precursor and directly calcining it at high temperature. In addition, after the hydrothermal reaction, due to the interface pressure difference, a layer of flaky hard shell will form on the liquid surface. This flaky hard shell has a poor ability to store sodium ions after pre-carbonization treatment, which affects the uniformity of the hard carbon and limits the electrochemical performance.

[0017] A preferred solution is that the atmosphere of the hydrothermal reaction is air, nitrogen or argon.

[0018] It can be seen that there are some large particles in the products after the hydrothermal reaction, and there will also be flaky hard shells on the surface, which limit the improvement of the electrochemical performance. By controlling the atmosphere of the hydrothermal reaction to nitrogen or argon and controlling the reaction rate, the particles are more uniform, the battery cycle performance is significantly improved, and there is no oxygen in the reactor, which reduces the oxygen content of the hard carbon obtained in step three and increases the first-cycle coulomb efficiency.

[0019] A preferred solution is that during the hydrothermal reaction, the reaction solution is stirred within a preset time period.

[0020] It can be seen that after the hydrothermal reaction, a layer of flaky hard shell will be formed on the liquid surface due to the interface pressure difference. The ability of this flaky hard shell to store sodium ions after pre-carbonization treatment is very poor, which affects the uniformity of the hard carbon and limits the electrochemical performance. The present invention stirs the reaction solution during the hydrothermal reaction to destroy the interface pressure difference and avoid the formation of a flaky hard shell on the liquid surface, thereby ensuring the uniformity of the product particles and improving the capacity and the first-cycle coulomb efficiency.

[0021] A preferred solution is that in step 2, during the process of filtering the product of the hydrothermal reaction, an organic solution is used to wash the filter residue.

[0022] It can be seen that in step 2, the surface of the spherical carbon precursor obtained after filtration still contains organic acid impurities, which will affect the electrochemical performance of the battery. By washing the filter residue with an organic solution, impurities such as organic acid can be reduced and the battery capacity can be improved.

[0023] To achieve the above second purpose, the present invention provides a hard carbon material for battery negative electrode, which is prepared by the above preparation method.

[0024] To achieve the third objective, the present invention provides a battery, including a negative electrode, wherein the material of the negative electrode includes the hard carbon material described above. DETAILED DESCRIPTION

[0025] The preparation method of the hard carbon material for the negative electrode of the battery comprises the following steps:

[0026] Step 1: Add a saccharide aqueous solution with a concentration of 2.5% to 50% to a hydrothermal kettle for hydrothermal reaction. Preferably, the raw material of the saccharide aqueous solution includes at least one of glucose, sucrose, syrup, and sugarcane juice; the hydrothermal kettle is a high-pressure reactor; and the atmosphere of the hydrothermal reaction can be air, nitrogen, or argon. During the hydrothermal reaction, the heating rate is in the range of 1°C / min to 20°C / min, the reaction temperature is in the range of 180°C to 250°C, and the insulation time is in the range of 4 hours to 24 hours.

[0027] Step 2: Filter the product of the hydrothermal reaction obtained in step 1, separate the filtrate and the filter residue, and dry the filter residue to obtain a spherical carbon precursor.

[0028] Step three, after pre-carbonizing the spherical carbon precursor obtained in step two in a pore-forming atmosphere, nitrogen or an inert gas is introduced, and high-temperature annealing is performed in a nitrogen or inert gas atmosphere to obtain a hard carbon material. Among them, the heating rate during the pre-carbonization treatment is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 200°C to 500°C, and the insulation time is in the range of 1 hour to 3 hours. During the high-temperature annealing treatment, the heating rate is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 800°C to 1900°C, and the insulation time is in the range of 1 hour to 3 hours. By controlling the heating rate, carbonization temperature and insulation time of the pre-carbonization treatment process and the high-temperature annealing process, the oxygen content, specific surface area and porosity can be reasonably controlled, thereby ensuring that the battery capacity is maximized. Optionally, the pore-forming atmosphere is an air atmosphere or an ammonia atmosphere.

[0029] Embodiment 1:

[0030] The preparation method of the hard carbon material in this embodiment comprises the following steps:

[0031] Step 1: 600 g of glucose was stirred and dissolved in 2.4 L of deionized water to obtain a 20% glucose aqueous solution, and the dissolved solution was placed in a 4 L autoclave, the atmosphere in the autoclave was air atmosphere, the autoclave was heated to 200 ° C at a heating rate of 2 ° C / min, and kept at this temperature for 6 hours for hydrothermal reaction.

[0032] Step 2: After the hydrothermal reaction is completed, the product of the hydrothermal reaction obtained in step 1 is filtered, the filtrate and the filter residue are separated, and the filter residue is dried at a temperature of 65° C. to obtain a spherical carbon precursor.

[0033] Step three, place the spherical carbon precursor obtained in step two in a tubular furnace or a box furnace, heat it to 300°C at a rate of 5°C / min in an air atmosphere, keep it warm for 1 hour, stop heating and introduce nitrogen for 30 minutes, then heat it to 1300°C at a rate of 5°C / min in a nitrogen atmosphere, keep it warm for 1 hour, wait for the temperature to naturally cool to room temperature, and obtain air-pre-oxidized spheroidized hard carbon material.

[0034] Embodiment 2:

[0035] As an explanation of the second embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0036] In this embodiment, the carbonization temperature of the pre-carbonization process in step three is 200°C.

[0037] Embodiment 3:

[0038] As an explanation of the third embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0039] In this embodiment, the carbonization temperature of the pre-carbonization process in step three is 400°C.

[0040] Embodiment 4:

[0041] As an explanation of the fourth embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0042] In this embodiment, the holding time of the pre-carbonization process in step 3 is 2 hours.

[0043] Embodiment 5:

[0044] As an explanation of the fifth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0045] In this embodiment, the pore-forming atmosphere in step three is an ammonia atmosphere, and what is finally obtained is a spheroidized hard carbon material with ammonia pores.

[0046] Embodiment 6:

[0047] As an explanation of the sixth embodiment of the present invention, only the differences from the fifth embodiment described above will be described below.

[0048] In this embodiment, in the pore-forming stage of step three, the carbonization temperature of the pre-carbonization process is 400°C.

[0049] Embodiment 7:

[0050] As an explanation of the seventh embodiment of the present invention, only the differences from the fifth embodiment described above will be described below.

[0051] In this embodiment, in the pore-forming stage of step three, the heat preservation time of the pre-carbonization process is 2 hours.

[0052] Embodiment 8:

[0053] As an explanation of the eighth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0054] In this embodiment, step one is to stir and dissolve 600 g of glucose in 2.4 L of deionized water to obtain a 20% glucose aqueous solution, and the dissolved solution is charged into a 4 L high-pressure reactor, and nitrogen is introduced into the high-pressure reactor for 30 minutes to replace the air in the high-pressure reactor. Then, the high-pressure reactor is heated to 200° C. at a heating rate of 2° C. / min, and kept at this temperature for 6 hours for hydrothermal reaction.

[0055] Embodiment 9:

[0056] As an explanation of the ninth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0057] In this embodiment, mechanical stirring is added throughout step 1, and the stirring speed is in the range of 10 rpm to 400 rpm. Preferably, the stirring speed in this embodiment is 100 rpm. In addition, in other embodiments, mechanical stirring can also be added at the beginning of the hydrothermal reaction, and the stirring can be turned off after 4 hours of insulation, that is, the last 2 hours of insulation in the hydrothermal reaction are not stirred, and the upper effect can also be achieved.

[0058] Embodiment 10:

[0059] As an explanation of the tenth embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0060] In step 2, the product of the hydrothermal reaction is filtered, and after the filtrate and the filter residue are separated, the filter residue is washed with isopropanol and dried at 65° C. to obtain a spherical carbon precursor. In other embodiments, an organic solution such as ethanol or acetone may also be used for washing.

[0061] Embodiment 11:

[0062] As an explanation of Example 11 of the present invention, only the differences from the above-mentioned Example 1 are described below.

[0063] In this embodiment, mechanical stirring is added throughout the step 1, and the stirring speed is in the range of 10 rpm to 400 rpm. Preferably, the stirring speed in this embodiment is 100 rpm.

[0064] In addition, in step 2, the product of the hydrothermal reaction is filtered, and after the filtrate and the filter residue are separated, the filter residue is washed with isopropanol, and the filter residue is dried at a temperature of 65° C. to obtain a spherical carbon precursor. In other embodiments, an organic solution such as ethanol or acetone may also be used for washing.

[0065] Comparative Example:

[0066] The only difference between this comparative example and Example 1 is that in step 3, no pore-forming atmosphere is used, and a nitrogen atmosphere is used throughout the process.

[0067] That is, in this embodiment, step three is to place the spherical carbon precursor obtained in step two in a tubular furnace or a box furnace, heat it to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere, keep it warm for 1 hour, and wait for the temperature to naturally cool to room temperature to obtain a spheroidized hard carbon material.

[0068] Performance Testing

[0069] The spheroidized hard carbon materials obtained in the above embodiments and comparative examples were coated on aluminum foil to make electrodes, which were then assembled into CR2032 button batteries. The electrochemical properties of the batteries were tested to obtain electrochemical performance comparison tables shown in Tables 1 to 3.

[0070] Table 1 Comparison of electrochemical performance of Examples 1 to 4 and Comparative Examples

[0071]

[0072] Table 2 Comparison of electrochemical performance of Examples 5 to 7 and Comparative Examples

[0073]

[0074] Table 3 Comparison of electrochemical performance of Examples 8 to 11 and Comparative Examples

[0075]

[0076] As can be seen from Table 1, the present invention obtains a spherical carbon precursor by hydrothermal reaction of a sugar aqueous solution, and then performs pre-oxidation to form pores in an air atmosphere. After pre-carbonization treatment, annealing treatment is performed in a nitrogen atmosphere. Air as a pore-forming atmosphere can play a pore-forming role, increase the oxygen content and porosity, and thus greatly increase the battery capacity. The specific capacity at 0.1C in each embodiment reaches about 380 mAh / g, and although the first-cycle coulomb efficiency is lower than that of the comparative example, it can also reach more than 90%.

[0077] It can be seen from Table 2 that ammonia can also play a pore-forming role, which can increase the specific surface area and porosity, thereby greatly increasing the battery capacity. The specific capacity at 0.1C in each embodiment reaches about 370 mAh / g, and although the first-cycle coulomb efficiency is lower than that of the control example, it can also reach or approach 90%.

[0078] It can be seen from Table 3 that in Example 8, the atmosphere of the hydrothermal reaction is replaced with nitrogen or other inert gases such as argon to control the reaction rate, making the particles more uniform and the battery cycle performance significantly improved. In addition, there is no oxygen in the reactor, which can reduce the oxygen content of the hard carbon obtained in step three, thereby increasing the first-cycle coulomb efficiency.

[0079] In Example 9, mechanical stirring is added throughout the hydrothermal reaction process to destroy the interfacial pressure difference and avoid the formation of a flaky hard shell on the liquid surface, thereby ensuring the uniformity of the product particles and improving the capacity and the first-cycle coulomb efficiency.

[0080] In Example 10, by washing the filter residue with an organic solution, impurities such as organic acid on the surface of the spherical carbon precursor can be reduced, thereby improving the battery capacity.

[0081] In Example 11, mechanical stirring is added throughout the hydrothermal reaction process to avoid the formation of a flaky hard crust on the liquid surface, thereby improving the capacity and the first-cycle coulombic efficiency. At the same time, the filter residue is washed with an organic solution to reduce impurities such as organic acids on the surface of the spherical carbon precursor, thereby further improving the battery capacity.

[0082] In addition, the hard carbon prepared in each embodiment has a nano-spherical microstructure, the isotropic nanoparticles provide excellent conductivity, can better withstand volume expansion and is not easy to break during the cycle, the spheroidized morphology is not easy to generate sodium metal dendrites, the cycle performance is excellent, and the safety performance of the battery is guaranteed.

[0083] Examples of hard carbon materials for battery negative electrodes:

[0084] The hard carbon material for the battery negative electrode of this embodiment is prepared by the preparation method of the above preparation method embodiment.

[0085] Battery Example:

[0086] The battery of this embodiment includes a negative electrode, and the material of the negative electrode includes the hard carbon material of the hard carbon material embodiment. Optionally, the battery can be a lithium ion battery, a sodium ion battery or a potassium ion battery.

[0087] Finally, it should be emphasized that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a hard carbon material for a battery negative electrode, characterized in that: include: Step 1, adding a sugar aqueous solution into a hydrothermal kettle for hydrothermal reaction; Step 2, filtering the product of the hydrothermal reaction obtained in step 1, separating the filtrate and the filter residue, and drying the filter residue to obtain a spherical carbon precursor; Step three, pre-carbonizing the spherical carbon precursor obtained in step two in a pore-forming atmosphere, introducing nitrogen or an inert gas, and performing high-temperature annealing in a nitrogen or inert gas atmosphere to obtain a hard carbon material.

2. The preparation method according to claim 1, characterized in that: In step three, the heating rate during the pre-carbonization treatment is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 200°C to 500°C, and the insulation time is in the range of 1 hour to 3 hours.

3. The preparation method according to claim 2, characterized in that: In step three, during the high temperature annealing treatment, the heating rate is in the range of 2°C / min to 10°C / min, the carbonization temperature is in the range of 800°C to 1900°C, and the holding time is in the range of 1 hour to 3 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The pore-forming atmosphere is an air atmosphere or an ammonia atmosphere.

5. The preparation method according to any one of claims 1 to 3, characterized in that: The raw material of the sugar aqueous solution includes at least one of glucose, sucrose, syrup and sugarcane juice.

6. The preparation method according to any one of claims 1 to 3, characterized in that: The atmosphere of the hydrothermal reaction is air, nitrogen or argon.

7. The preparation method according to any one of claims 1 to 3, characterized in that: During the hydrothermal reaction, the reaction solution is stirred within a preset time period.

8. The preparation method according to any one of claims 1 to 3, characterized in that: In the step 2, during the filtering of the product of the hydrothermal reaction, the filter residue is washed with an organic solution.

9. A hard carbon material for a negative electrode of a battery, characterized in that: The method is as described in any one of claims 1 to 8.

10. A battery comprising a negative electrode, characterized in that The material of the negative electrode includes the hard carbon material as claimed in claim 9.

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