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, and the preparation method of the hard carbon material comprises the following steps: adding a saccharide aqueous solution into a hydrothermal kettle to carry out hydrothermal reaction, and carrying out high-temperature annealing treatment on a product of the hydrothermal reaction to obtain the hard carbon material; and adding an alkaline substance into the filtrate which is filtered and collected after the hydrothermal reaction to neutralize, adding a saccharide aqueous solution into the neutralized filtrate, and carrying out hydrothermal reaction again. According to the preparation method, the waste liquid can be recycled, so that the water consumption and the discharge amount of the waste liquid are reduced, and meanwhile, the hydrothermal yield can be increased.

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] In addition, in the existing preparation method of hard carbon materials using glucose for hydrothermal reaction, the hydrothermal reaction consumes a large amount of water, and directly discharging it as wastewater will cause a waste of water resources. In addition, since soluble organic acids are produced during the hydrothermal reaction, the reaction rate is reduced and the reaction is incomplete, limiting the increase in yield. 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 realize the recycling and reuse of waste liquid, thereby reducing water consumption and waste liquid discharge, and can also improve hydrothermal yield.

[0006] The second object of the present invention is to provide another method for preparing a hard carbon material for a battery negative electrode which can improve the hydrothermal yield.

[0007] The third object of the present invention is to provide a hard carbon material for battery negative electrode prepared by the above preparation method.

[0008] A fourth object of the present invention is to provide a battery having a battery negative electrode made of the above hard carbon material.

[0009] 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: adding a sugar aqueous solution to a hydrothermal kettle for a hydrothermal reaction, and subjecting the product of the hydrothermal reaction to a high-temperature annealing treatment to obtain a hard carbon material; adding an alkaline substance to the filtrate collected by filtration after the above-mentioned hydrothermal reaction for neutralization, and then adding the sugar aqueous solution to the neutralized filtrate to perform a hydrothermal reaction again.

[0010] As can be seen from the above scheme, the present invention obtains a spherical carbon precursor by subjecting a sugar aqueous solution to a hydrothermal reaction, and then performs a high-temperature annealing treatment in an atmosphere such as nitrogen to obtain a hard carbon material. Since the hydrothermal reaction usually consumes a large amount of deionized water, directly discharging the filtrate as wastewater after the reaction will cause a waste of water resources. Since the filtrate after the hydrothermal reaction contains organic acids, the pH value of the waste liquid is 4, so it cannot be directly reused. The present invention adds an alkaline substance to the filtrate of the hydrothermal reaction for neutralization, and then performs a hydrothermal reaction again, thereby realizing the recycling of wastewater, reducing water consumption and waste liquid discharge, and saving water resources. At the same time, since soluble organic acids are generated during the hydrothermal process, the reaction rate will be reduced, and the reaction will be incomplete, limiting the increase in the hydrothermal yield. By adding alkaline substances to the filtrate, the pH value during the reaction can be increased, making the reaction more complete, thereby increasing the hydrothermal yield.

[0011] A preferred embodiment is that the neutralization step can be repeated less than or equal to 4 times.

[0012] It can be seen from this that the neutralization step cannot be repeated indefinitely. The reason is that, although the organic acid components in the filtrate of the hydrothermal reaction are neutralized, organic acid salts such as sodium formate will still be generated during the hydrothermal reaction. When they accumulate to a certain amount, they will hinder the reaction. By limiting the number of neutralization steps, while ensuring the performance of the hard carbon material, the recycling of wastewater is achieved to the greatest extent, saving water resources.

[0013] A preferred solution is that the pH value of the neutralized filtrate is in the range of 6 to 8.

[0014] It can be seen from this that, through experimental verification, when the pH value of the neutralized filtrate is in the range of 6 to 8, it will not affect the specific capacity of the battery prepared using the corresponding hard carbon material.

[0015] A preferred solution is that after the hydrothermal reaction, the product of the hydrothermal reaction is filtered, the filtrate and the filter residue are separated, the filter residue is dried to obtain a spherical carbon precursor, and then the spherical carbon precursor is subjected to high temperature annealing to obtain a hard carbon material.

[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 raw materials and has low cost, and the performance of the obtained precursor is also better than the existing method of preparing the precursor by pre-treating the biomass precursor and directly calcining it at high temperature. The preparation method of the hard carbon material of the present invention not only has easy-to-obtain raw materials and low cost, but also has a simple preparation process. At the same time, the prepared hard carbon has a microstructure of a nano-spherical structure, and the isotropic nanoparticles provide excellent conductivity. It 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, and the cycle performance is excellent, and the safety performance of the battery is guaranteed.

[0017] A preferred solution is to add the alkaline solution after the temperature of the hydrothermal reaction is raised to a set temperature and kept at that temperature for a preset time.

[0018] It can be seen that since soluble organic acids are produced during the hydrothermal reaction, which reduces the reaction rate and makes the reaction incomplete, limiting the increase in yield, an alkaline solution is added after a preset insulation time to neutralize the soluble organic acids produced during the hydrothermal process, thereby increasing the pH value during the reaction, making the reaction more complete and improving the hydrothermal yield.

[0019] A preferred solution is that the alkaline substance is NaOH powder or NaOH solution; and / or the atmosphere of the hydrothermal reaction is air, nitrogen or argon; and / or during the hydrothermal reaction, the reaction solution is stirred within a preset time period. and / or after filtering the product of the hydrothermal reaction, the filter residue is washed with an organic solution. and / or after filtering the product of the hydrothermal reaction, the filter residue is dried and then dispersed in an organic solution, filtered and dried, and then subjected to high temperature annealing.

[0020] It can be seen that after the hydrothermal reaction, due to the interface pressure difference, a layer of flaky hard shell will be formed 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 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 flaky hard shell on the liquid surface, thereby ensuring the uniformity of product particles and improving the capacity and the first-cycle coulomb efficiency. In addition, there are some large particles in the product after the hydrothermal reaction, and there will also be flaky hard shells on the surface, which limit the improvement of electrochemical performance. By controlling the atmosphere of the hydrothermal reaction to nitrogen or argon, the reaction rate is controlled, the particles are more uniform, the battery cycle performance is significantly improved, and there is no oxygen in the reactor, reducing the oxygen content of the hard carbon obtained in the high-temperature annealing step, and increasing the first-cycle coulomb efficiency. In addition, the surface of the spherical carbon precursor obtained after filtering the hydrothermal reaction product 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. In addition, the compaction density of the hard carbon produced under the original synthesis conditions is low, which is not conducive to increasing the loading capacity of the electrode sheet and limiting its application in industry. The spherical carbon precursor obtained by filtering and drying the hydrothermal reaction product is dispersed in an organic solution by ultrasound and other methods to avoid agglomeration. The hard carbon material is well dispersed in the organic solution, which is more conducive to ultrasonic dispersion operation. After dispersion, it is filtered and carbonized at high temperature, so that the compaction density of the hard carbon produced is increased.

[0021] To achieve the above-mentioned second purpose, the present invention provides another 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, and when the temperature of the hydrothermal reaction rises to a set temperature and is kept warm for a preset time, adding an alkaline solution; step two, filtering the product of the hydrothermal reaction obtained in step one, separating the filtrate and the residue, and drying the residue to obtain a spherical carbon precursor; step three, performing a high-temperature annealing treatment on the spherical carbon precursor obtained in step two to obtain a hard carbon material.

[0022] It can be seen from the above scheme that the preparation method of the hard carbon material of the present invention not only has easy-to-obtain raw materials and low cost, but also has a simple preparation process. In addition, since soluble organic acids will be produced during the hydrothermal reaction, the reaction rate will be reduced and the reaction will be incomplete, limiting the increase in yield. Therefore, an alkaline solution is added after a preset insulation time to neutralize the soluble organic acid produced during the hydrothermal process of step one, thereby increasing the pH value during the reaction process, making the reaction more complete and improving the hydrothermal yield.

[0023] A preferred solution is that the preparation method further includes: step four, after the hydrothermal reaction in step one is completed, an alkaline substance is added to the filtered and collected filtrate for neutralization, and then the sugar aqueous solution is added to the neutralized filtrate to perform a hydrothermal reaction again.

[0024] It can be seen that by adding alkaline substances to the filtrate of the hydrothermal reaction for neutralization and then conducting the hydrothermal reaction again, the recycling of waste water is achieved, the water consumption and the discharge of waste liquid are reduced, and water resources are saved.

[0025] To achieve the third objective, the present invention provides a hard carbon material for a negative electrode of a battery, which is prepared by the above-mentioned preparation method.

[0026] To achieve the fourth 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the hard carbon material prepared in Example 1 of the method for preparing the hard carbon material for the negative electrode of a battery of the present invention. DETAILED DESCRIPTION

[0028] The preparation method of the hard carbon material for the negative electrode of the battery comprises the following steps:

[0029] 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.

[0030] Step 2: Filter the product of the hydrothermal reaction, separate the filtrate and the filter residue, and dry the filter residue to obtain a spherical carbon precursor.

[0031] Step three, subjecting the spherical carbon precursor to high temperature annealing treatment to obtain a hard carbon material.

[0032] Step 4: add an alkaline substance to the filtrate collected in step 2 for neutralization, then add the sugar aqueous solution to the neutralized filtrate, and perform the hydrothermal reaction of step 1 again. Preferably, the alkaline substance is NaOH powder or NaOH solution.

[0033] Repeat steps 2 and 3.

[0034] The neutralization step can be repeated for less than or equal to 4 times, and the pH value of the filtrate after neutralization is in the range of 6 to 8.

[0035] Since soluble organic acids are produced during the hydrothermal reaction, which reduce the reaction rate and make the reaction incomplete, thus limiting the increase in yield, an alkaline solution can be added after the temperature of the hydrothermal reaction is raised to a set temperature and kept warm for a preset time to neutralize the soluble organic acids produced during the hydrothermal process, thereby increasing the pH value during the reaction, making the reaction more complete and improving the hydrothermal yield.

[0036] Embodiment 1:

[0037] The preparation method of the hard carbon material in this embodiment comprises the following steps:

[0038] 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.

[0039] 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.

[0040] Step three, placing the spherical carbon precursor obtained in step two in a tubular furnace or a box furnace, heating it to 1300°C at a heating rate of 5°C / min under a nitrogen atmosphere, keeping it warm for 1 hour, and waiting for the temperature to naturally cool to room temperature to obtain a spheroidized hard carbon material.

[0041] Embodiment 2:

[0042] In this embodiment, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected in step 2 of embodiment 1 for neutralization, the pH value of the neutralized filtrate is 6, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step 1 again, and the subsequent steps are the same as those in embodiment 1, that is, drying the filter residue after the hydrothermal reaction, and annealing the spherical carbon precursor obtained after drying at high temperature, and finally obtaining a spheroidized hard carbon material made using once-recycled wastewater.

[0043] Embodiment 3:

[0044] In this embodiment, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected after the hydrothermal reaction in Example 2 for neutralization, the pH value of the neutralized filtrate is 6, and then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step one again. The subsequent steps are the same as those in Example 1, that is, drying the filter residue after the hydrothermal reaction, and high-temperature annealing the spherical carbon precursor obtained after drying, and finally obtaining a spheroidized hard carbon material made using secondary recycled wastewater.

[0045] Embodiment 4:

[0046] In this embodiment, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected after the hydrothermal reaction in Example 3 for neutralization, the pH value of the neutralized filtrate is 6, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step one again, and the subsequent steps are the same as those in Example 1, that is, drying the filter residue after the hydrothermal reaction, and annealing the spherical carbon precursor obtained after drying at high temperature, and finally obtaining a spheroidized hard carbon material made using tertiary recycled wastewater.

[0047] Embodiment 5:

[0048] In this embodiment, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected in step 2 of embodiment 1 for neutralization, the pH value of the neutralized filtrate is 8, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step 1 again, and the subsequent steps are the same as those in embodiment 1, that is, drying the filter residue after the hydrothermal reaction, and annealing the spherical carbon precursor obtained after drying at high temperature, and finally obtaining a spheroidized hard carbon material made using once-recycled wastewater.

[0049] Embodiment 6:

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

[0051] In this embodiment, the atmosphere of the hydrothermal reaction in step 1 is nitrogen. Specifically, after the glucose aqueous solution is loaded into a 4L autoclave, nitrogen is introduced into the autoclave for 30 minutes to replace the air in the autoclave. Then, the autoclave is heated to 200°C at a heating rate of 2°C / min, and the hydrothermal reaction is carried out at this temperature for 6 hours.

[0052] Embodiment 7:

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

[0054] 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.

[0055] Embodiment 8:

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

[0057] 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.

[0058] Embodiment 9:

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

[0060] In this embodiment, the spherical carbon precursor obtained in step 2 is ultrasonically dispersed in an organic solution such as ethanol or isopropanol for 30 minutes, filtered and dried, and then the dried product is subjected to high temperature annealing to obtain a hard carbon material. The ultrasonic dispersion time can be changed as needed.

[0061] Embodiment 10:

[0062] As an explanation of the tenth embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0063] In this embodiment, in step one, after the temperature of the hydrothermal reaction is raised to the set temperature and kept warm for a preset time, an alkaline solution is added. Specifically, when the autoclave is heated to 200°C and kept warm at this temperature for 1 hour, a 20% NaOH aqueous solution is injected, and the volume ratio of the NaOH aqueous solution to the original solution in the autoclave is 1:10. Optionally, the volume ratio of the NaOH aqueous solution to the original solution in the autoclave can be in the range of (1-1.5):10. In addition, the concentration of the NaOH aqueous solution can be in the range of 5% to 20%, which can be changed as needed. The time for injecting the NaOH aqueous solution can be in the range of 1 hour to 3 hours of insulation, which is the best effect.

[0064] Comparative Example 1:

[0065] In this comparative example, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected in step 2 of Example 1 for neutralization, the pH value of the neutralized filtrate is 5, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step 1 again, and the subsequent steps are the same as those in Example 1, that is, drying the filter residue after the hydrothermal reaction, and annealing the spherical carbon precursor obtained after drying at high temperature, and finally obtaining a spheroidized hard carbon material made using once-recycled wastewater.

[0066] Comparative Example 2:

[0067] In this comparative example, the preparation method of the hard carbon material includes: adding NaOH powder to the filtrate collected in step 2 of Example 1 for neutralization, the pH value of the neutralized filtrate is 9, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction of step 1 again. After the reaction is completed, there is no solid product.

[0068] Performance Testing

[0069] The spheroidized hard carbon materials obtained in the above embodiments 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 various embodiments and comparative examples

[0071]

[0072] Table 2 Comparison of electrochemical performance of Examples 1 and 6

[0073] Hard carbon oxygen content (%) Specific capacity (mAh / g) First cycle coulomb efficiency (%) Example 1 1.6 352 92.3 Example 6 0.3 361 95.6

[0074] Table 3 Comparison of electrochemical performance of Examples 1 and 9

[0075] <![CDATA[Apparent density of hard carbon (g / cm 3 )]]> Specific capacity (mAh / g) First cycle coulomb efficiency (%) Example 1 1.5 352 92.3 Example 9 1.7 360 92.6

[0076] As can be seen from the above table, a spherical carbon precursor is obtained by hydrothermal reaction of a sugar aqueous solution, and then a high-temperature annealing treatment is performed in an atmosphere such as nitrogen to obtain a hard carbon material. The preparation method of the hard carbon material of the present invention not only has easy-to-obtain raw materials and low cost, but also has a simple preparation process. After the hard carbon material prepared in each embodiment is used to make a battery, the specific capacity at 0.1C in each embodiment is close to or reaches 340mAh / g or more, and the first-cycle coulomb efficiency is also close to or reaches 92% or more.

[0077] In Examples 2 to 4, after the filtrate is neutralized by adding an alkaline substance, the filtrate is reused. From the electrochemical performance test results, it can be seen that the battery made of spheroidized hard carbon material obtained by recycling wastewater has only a small decrease in specific capacity and first-cycle coulomb efficiency, but its specific capacity can still reach more than 330mAh / g, and the first-cycle coulomb efficiency can also reach more than 91%. Therefore, by recycling and reusing the waste liquid, the performance of the prepared material can be guaranteed while reducing the water consumption and the discharge of the waste liquid. In addition, according to testing, the hydrothermal yield in the hydrothermal reaction process of Example 1 is 52%, and the hydrothermal yield in Example 2 is 54%. Therefore, the hydrothermal yield in the hydrothermal reaction process can be increased by about 2%, and the reaction is more complete. The hydrothermal yield refers to the ratio of the mass of the spherical carbon precursor after filtration and drying in step 2 to the mass of the glucose and other sugars added in step 1.

[0078] It can be seen from the performance test data of Examples 1 to 5 and Comparative Examples 1 and 2 that the pH value of the neutralized filtrate is in the range of 6 to 8 to ensure that it will not affect the electrochemical performance of the battery. If the pH value of the filtrate is lower than 6, it will greatly affect the specific capacity and the first-cycle coulombic efficiency. If the pH value of the filtrate is higher than 8, the hydrothermal reaction cannot proceed.

[0079] in addition, Figure 1 This is a scanning electron microscope image of the hard carbon prepared in Example 1. It can be seen from the figure that the prepared hard carbon 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.

[0080] It can be seen from Table 2 that in Example 6, 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, which is increased from 92.3% to 95.6% relative to Example 1.

[0081] In Example 7, 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. The capacity and the first-cycle coulomb efficiency are both improved, with the specific capacity increased to 363 mAh / g and the first-cycle coulomb efficiency increased to 94.7%.

[0082] In Example 8, 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, and the battery capacity is increased from 352 mAh / g to 367 mAh / g compared with Example 1.

[0083] As shown in Table 3, in Example 9, the compaction density of the hard carbon produced by the original synthesis conditions is low, which is not conducive to increasing the loading capacity of the electrode sheet and limits its application in industry. By dispersing the spherical carbon precursor obtained in step 2 in an organic solution by ultrasound or other means to avoid agglomeration, the hard carbon material is well dispersed in the organic solution, which is more conducive to ultrasonic dispersion operation. After dispersion, filtration and high-temperature carbonization are performed, so that the compaction density of the hard carbon produced is increased. Compared with Example 1, under the premise of ensuring the specific capacity and the first-cycle coulomb efficiency, the compaction density of the hard carbon is increased from 1.5g / cm 3 Increased to 1.7 g / cm 3 .

[0084] In Example 10, since soluble organic acids are produced during the hydrothermal reaction, which reduce the reaction rate and make the reaction incomplete, limiting the increase in yield, an alkaline solution is added after the preset insulation time to neutralize the soluble organic acids produced during the hydrothermal process of step one, thereby increasing the pH value during the reaction, making the reaction more complete, and the hydrothermal yield is increased from 52% in Example 1 to 60%.

[0085] Examples of hard carbon materials for battery negative electrodes:

[0086] The hard carbon material for the battery negative electrode of this embodiment is prepared by the preparation method of the above preparation method embodiment.

[0087] Battery Example:

[0088] 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.

[0089] 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: Adding the sugar aqueous solution into a hydrothermal kettle for hydrothermal reaction, and subjecting the product of the hydrothermal reaction to high-temperature annealing to obtain a hard carbon material; After the hydrothermal reaction, an alkaline substance is added to the filtrate collected by filtration to neutralize it, and then the sugar aqueous solution is added to the neutralized filtrate to perform a hydrothermal reaction again.

2. The preparation method according to claim 1, characterized in that: The neutralization step may be repeated a number of times less than or equal to 4 times.

3. The preparation method according to claim 1, characterized in that: The pH value of the filtrate after neutralization is in the range of 6 to 8.

4. The preparation method according to any one of claims 1 to 3, characterized in that: After the hydrothermal reaction, the product of the hydrothermal reaction is filtered, the filtrate and the filter residue are separated, the filter residue is dried to obtain a spherical carbon precursor, and then the spherical carbon precursor is subjected to high temperature annealing to obtain a hard carbon material.

5. The preparation method according to any one of claims 1 to 3, characterized in that: When the temperature of the hydrothermal reaction rises to the set temperature and is kept for a preset time, the alkaline solution is added.

6. The preparation method according to any one of claims 1 to 3, characterized in that: The alkaline substance is NaOH powder or NaOH solution; and / or The atmosphere of the hydrothermal reaction is air, nitrogen or argon; and / or During the hydrothermal reaction, the reaction solution is stirred within a preset time period; and / or After filtering the product of the hydrothermal reaction, washing the filter residue with an organic solution; and / or After filtering the product of the hydrothermal reaction, the filter residue is dried and then dispersed in an organic solution, filtered and dried again, and then subjected to high-temperature annealing treatment.

7. A method for preparing a hard carbon material for a negative electrode of a battery, characterized in that: include: Step 1: Add the sugar aqueous solution into the hydrothermal kettle for hydrothermal reaction, and add the alkaline solution after the temperature of the hydrothermal reaction rises to the set temperature and is kept warm for a preset time; 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, subjecting the spherical carbon precursor obtained in step two to high temperature annealing to obtain a hard carbon material.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: step 4, after the hydrothermal reaction in step 1 is completed, adding alkaline substances to the filtered and collected filtrate for neutralization, then adding the sugar aqueous solution to the neutralized filtrate, and performing the hydrothermal reaction again.

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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