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 high-temperature annealing treatment on the spherical carbon precursor obtained in the step 2 to obtain the hard carbon material. According to the preparation method of the hard carbon material, the raw materials are easy to obtain, the cost is low, meanwhile, a nanospherical microstructure can be formed, and the hard carbon material has excellent cycle performance and battery capacity.

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, the existing method of preparing precursors usually adopts methods such as direct high-temperature calcination of biomass precursors after pretreatment. The acquisition of raw materials is related to the season and is not easy to obtain. It also requires complex processing technology and is costly. 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, the raw materials of which are easy to obtain and low in cost, and a nano-spherical microstructure can be formed, which has excellent cycle performance and battery capacity.

[0006] The second object of the present invention is to provide another method for preparing hard carbon materials for battery negative electrodes. The raw materials of this preparation method are easy to obtain and have low cost. At the same time, it can form a nano-spherical microstructure with excellent cycle performance and battery capacity. At the same time, the hard carbon obtained has a high compaction density, which is beneficial to increase the loading capacity of the electrode sheet.

[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: 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, high-temperature annealing treatment of the spherical carbon precursor obtained in step two to obtain a hard carbon material.

[0010] As can be seen from the above scheme, the present invention obtains a spherical carbon precursor by hydrothermal reaction of a sugar aqueous solution, and then performs high-temperature annealing 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 access to 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.

[0011] A preferred solution is that the raw material of the sugar aqueous solution includes at least one of glucose, sucrose, syrup and sugarcane juice.

[0012] It can be seen that using at least one of glucose, sucrose, syrup, and sugarcane juice as the sugar aqueous solution is easier to obtain and has lower cost than the existing method of preparing the precursor by directly calcining the biomass precursor at high temperature after pretreatment, and the performance of the prepared precursor is also better.

[0013] A preferred solution is that the atmosphere of the hydrothermal reaction is air, nitrogen or argon.

[0014] It can be seen that 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 hard carbon and limits the electrochemical performance. 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 electrochemical performance. By controlling the atmosphere of the hydrothermal reaction to nitrogen or argon, the reaction rate is controlled, the particles are more uniform, and the battery cycle performance is significantly improved. In addition, 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.

[0015] A preferred solution is that 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.

[0016] A preferred solution is that during the hydrothermal reaction, the reaction solution is stirred within a preset time period.

[0017] 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.

[0018] A preferred solution is that in step 2, after filtering the product of the hydrothermal reaction, the filter residue is washed with an organic solution.

[0019] 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.

[0020] 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; 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, dispersing the spherical carbon precursor obtained in step two in an organic solution, and then filtering and drying; step four, subjecting the dried product obtained in step three to a high-temperature annealing treatment to obtain a hard carbon material.

[0021] As can be seen from the above scheme, the preparation method of the hard carbon material of the present invention is not only easy to obtain raw materials and low in cost, but also has a simple preparation process. In addition, since the compaction density of the hard carbon produced under the original synthesis conditions is low, it is not conducive to increasing the load of the electrode sheet, which 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 to increase the compaction density of the hard carbon produced.

[0022] 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.

[0023] 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

[0024] 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.

[0025] The present invention is further described below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0026] The preparation method of the hard carbon material for the negative electrode of the battery comprises the following steps:

[0027] 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.

[0028] 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.

[0029] Step 3: subjecting the spherical carbon precursor obtained in step 2 to high temperature annealing to obtain a hard carbon material. In the high temperature annealing step, the heating rate is in the range of 0.5°C / min to 15°C / min, the reaction 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.

[0030] Embodiment 1:

[0031] The preparation method of the hard carbon material in this embodiment comprises the following steps:

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Embodiment 2:

[0036] As an explanation of the second embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0037] In this embodiment, the set temperature of the hydrothermal reaction in step 1 is 180°C.

[0038] Embodiment 3:

[0039] As an explanation of the third embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0040] In this embodiment, the set temperature of the hydrothermal reaction in step 1 is 250°C.

[0041] Embodiment 4:

[0042] As an explanation of the fourth embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0043] In this embodiment, in step 1, 1028 g of glucose is stirred and dissolved in 2.4 L of deionized water, that is, in this embodiment, the concentration of the glucose aqueous solution is 30%.

[0044] Embodiment 5:

[0045] As an explanation of the fifth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0046] In this embodiment, in step 1, 267 g of glucose is stirred and dissolved in 2.4 L of deionized water, that is, in this embodiment, the concentration of the glucose aqueous solution is 10%.

[0047] Embodiment 6:

[0048] As an explanation of the sixth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0049] In this embodiment, step three is to heat the temperature to 1700°C at a heating rate of 5°C / min in a tubular furnace or a box furnace under a nitrogen atmosphere, keep the temperature for 1 hour, and wait for the temperature to naturally cool to room temperature to obtain a spheroidized hard carbon material.

[0050] Embodiment 7:

[0051] As an explanation of the seventh embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0052] In this embodiment, in step 1, the high pressure reactor is heated to 200° C. at a heating rate of 2° C. / min and then kept at this temperature for 4 hours for hydrothermal reaction.

[0053] Embodiment 8:

[0054] As an explanation of the eighth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0055] 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.

[0056] Embodiment 9:

[0057] As an explanation of the ninth embodiment of the present invention, only the differences from the first embodiment described above will be described below.

[0058] 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.

[0059] Embodiment 10:

[0060] As an explanation of the tenth embodiment of the present invention, only the differences from the above-mentioned first embodiment will be described below.

[0061] 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.

[0062] Embodiment 11:

[0063] As an explanation of Example 11 of the present invention, only the differences from the above-mentioned Example 1 are described below.

[0064] 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.

[0065] Performance Testing

[0066] 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 an electrochemical performance comparison table as shown in Table 1.

[0067] Table 1 Comparison of electrochemical performance of Examples 1 to 7

[0068]

[0069] Table 2 Comparison of electrochemical performance of Examples 1 and 8

[0070]

[0071] Table 3 Comparison of electrochemical performance of Examples 9 and 10

[0072] Specific capacity (mAh / g) First cycle coulomb efficiency (%) Example 9 363 94.7 Example 10 367 93.9

[0073] Table 4 Comparison of electrochemical performance of Examples 1 and 11

[0074] <![CDATA[Apparent density of hard carbon (g / cm 3 )]]> Specific capacity (mAh / g) First cycle coulomb efficiency (%) Example 1 1.5 352 92.3 Embodiment 11 1.7 360 92.6

[0075] As can be seen from Table 1, 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 access to 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 can also reach more than 90%.

[0076] 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.

[0077] It can be seen from Table 2 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, which is increased from 92.3% to 95.6% relative to Example 1.

[0078] It can be seen from Table 3 that 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. 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%.

[0079] 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, and the battery capacity is increased from 352 mAh / g to 367 mAh / g compared with Example 1.

[0080] As shown in Table 4, in Example 11, 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 .

[0081] Examples of hard carbon materials for battery negative electrodes:

[0082] The hard carbon material for the battery negative electrode of this embodiment is prepared by the preparation method of the above preparation method embodiment.

[0083] Battery Example:

[0084] 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.

[0085] 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 negative electrode of a battery, 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, subjecting the spherical carbon precursor obtained in step two to high temperature annealing to obtain a hard carbon material.

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

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

4. The preparation method according to any one of claims 1 to 3, characterized in that: 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.

5. 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.

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

7. A method for preparing a hard carbon material for a negative electrode of a battery, 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 3, dispersing the spherical carbon precursor obtained in step 2 in an organic solution, and then filtering and drying; Step 4: subjecting the dried product obtained in step 3 to high temperature annealing to obtain a hard carbon material.

8. The preparation method according to claim 7, characterized in that: The spherical carbon precursor is dispersed in the organic solution for a preset time by using ultrasound.

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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