Preparation Method of Porous Hard Carbon Composite Material and Negative Electrode of Sodium Ion Battery

Abstract

The present application provides a method for preparing a porous hard carbon composite material and a negative electrode for a sodium ion battery. The method for preparing the porous hard carbon composite material includes the following steps: performing a calcination operation on epoxy resin powder to obtain porous hard carbon; performing a first deposition operation on the porous hard carbon to obtain a material coated with a thin layer of deposited carbon; placing the material coated with the thin layer of deposited carbon in a transition metal salt solution to obtain a mixed slurry; performing a pH adjustment operation on the mixed slurry until the pH value of the mixed slurry is 5-6; performing an ultrasonic operation on the mixed slurry after pH adjustment to break the thin layer of deposited carbon blocking between the macropores and mesopores in the porous hard carbon and attach transition metal compounds to the pore peripheries to obtain a transition metal composite hard carbon material; and performing a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and particularly to a method for preparing a porous hard carbon composite material and a negative electrode of a sodium-ion battery. Background Art

[0002] Hard carbon is considered to be the most promising commercial negative electrode material due to its rich reserves, low cost, and low working potential. However, the rate performance and the first Coulombic efficiency (initial efficiency) of hard carbon materials are still not satisfactory in practical applications. The first Coulombic efficiency is a performance index for measuring the negative electrode materials of batteries. Many strategies have been proposed to improve the rate performance of hard carbon, such as doping heteroatoms (N, F, P, and S) and designing structures with a large specific surface area. However, this kind of hard carbon material with a large specific surface area or heteroatom doping has a high average working voltage and a low initial efficiency (usually lower than 70%), which also hinders its application in full batteries. In contrast, hard carbon materials with a low specific surface area and limited defect sites can obtain a high initial efficiency, but cannot enhance the diffusion kinetics of Na+, resulting in poor cycle performance of the battery. Therefore, it is necessary to develop an effective method to achieve fast Na+ storage kinetics and a high initial efficiency. Coating the material by physical or chemical methods can effectively improve the initial efficiency and cycle performance of the hard carbon negative electrode sodium-ion battery. Among them, the hard carbon material can be modified by coating, and the coating can be physical coating or chemical coating. Chemical coating methods include sol-gel method, chemical deposition method, etc. Among them, the coating film obtained by the chemical deposition method is more uniform and the film thickness is controllable.

[0003] However, whether it is chemical vapor deposition or electrochemical deposition method, it is easy to block the pores in the structure of the hard carbon material, resulting in a reduction in the pores of the hard carbon material, thereby leading to a decrease in the sodium storage capacity of the negative electrode. At the same time, the migration and diffusion of sodium ions in the hard carbon negative electrode material are also severely hindered. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a porous hard carbon composite material and a negative electrode of a sodium-ion battery, which can increase the pores of the hard carbon material and achieve high initial efficiency and high cycle performance of the battery.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A method for preparing a porous hard carbon composite material, comprising the following steps:

[0007] Calcining epoxy resin powder to obtain porous hard carbon;

[0008] Performing a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material;

[0009] Place the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry;

[0010] Adjust the pH of the mixed slurry until the pH value of the mixed slurry is 5 - 6;

[0011] Perform an ultrasonic operation on the mixed slurry after pH adjustment to break the deposited carbon thin layer between the macropores and mesopores in the porous hard carbon and attach the transition metal compound to the pore periphery to obtain a transition metal composite hard carbon material;

[0012] Perform a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material.

[0013] In one embodiment, before the operation of calcining the epoxy resin powder, the following steps are further included:

[0014] Place the epoxy resin powder in a tube furnace and continuously introduce a first gas.

[0015] In one embodiment, the specific operation steps for performing the first deposition operation on the porous hard carbon to obtain the deposited carbon thin layer coating material are as follows:

[0016] Stop introducing the first gas;

[0017] Continuously introduce a second gas into the tube furnace to perform a vapor deposition operation to obtain the deposited carbon thin layer coating material.

[0018] In one embodiment, after performing the first deposition operation on the porous hard carbon to obtain the deposited carbon thin layer coating material and before placing the deposited carbon thin layer coating material in the transition metal salt solution to obtain the mixed slurry, the following steps are further included:

[0019] Stop introducing the second gas and cool the tube furnace to room temperature.

[0020] In one embodiment, the first gas is argon, helium, or nitrogen.

[0021] In one embodiment, the second gas is methane, ethane, or ethylene.

[0022] In one embodiment, the specific operation steps for performing an ultrasonic operation on the mixed slurry after pH adjustment to break the deposited carbon thin layer between the macropores and mesopores in the porous hard carbon and attach the transition metal compound to the pore periphery to obtain the transition metal composite hard carbon material are as follows:

[0023] Perform an ultrasonic operation on the mixed slurry after pH adjustment;

[0024] Filter the mixed slurry after ultrasonic treatment to obtain a filtered mixture;

[0025] Dry the filtered mixture to obtain a transition metal composite hard carbon material.

[0026] In one embodiment, the specific operation steps for subjecting the transition metal composite hard carbon material to a second deposition operation to obtain a porous hard carbon composite material are as follows:

[0027] Grind the transition metal composite hard carbon material;

[0028] Place the ground transition metal composite hard carbon material in the tubular furnace;

[0029] Continuously introduce the second gas into the tubular furnace to perform the vapor deposition operation to obtain the porous hard carbon composite material.

[0030] In one embodiment, the filtered metal salt solution is one or more of iron chloride, copper chloride, nickel chloride, and titanium chloride.

[0031] A negative electrode of a sodium ion battery, which is the porous hard carbon composite material prepared by using the preparation method of the porous hard carbon composite material described in any one of the above embodiments.

[0032] Compared with the prior art, the present invention has at least the following advantages:

[0033] The preparation method of the porous hard carbon composite material of the present application obtains a deposited carbon thin layer coating material through the first deposition operation on the porous hard carbon, so that a deposited carbon thin layer is formed on the surface of the porous hard carbon. Then, the deposited carbon thin layer coating material is placed in an excessive metal salt solution, and the pH value is adjusted to a weak acid condition of 5-6. At this time, the pores of the porous hard carbon are blocked by the deposited thin carbon layer. Therefore, it is necessary to break the blocked pore part of the thin layer through ultrasonic operation. Ultrasonic waves under the weak acid condition with a pH value of 5-6 can break the deposited thin carbon layer blocking the pores of the porous hard carbon. The periphery of the broken pores is attached with transition metal compounds, which can effectively prevent the pores from being blocked during the second deposition carbon coating process, and the formation of the deposition layer is more uniform and compact under the catalysis of the transition metal. In this way, the structural stability of the porous hard carbon composite material can be effectively improved, and at the same time, the problem that chemical deposition easily causes pore blockage of the hard carbon material can be effectively solved. In this way, the sodium storage capacity of the porous hard carbon composite material is effectively improved when it is applied to the negative electrode of a sodium ion battery. Further, since the hard carbon material has a high first efficiency when applied to the negative electrode of a sodium ion battery, the porous hard carbon composite material can have a high first efficiency and high cycle performance when used for the negative electrode of a sodium ion battery, that is, the first efficiency and cycle performance of the hard carbon negative electrode sodium ion battery can be effectively improved by coating the material through the preparation method of the porous hard carbon composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a schematic flow chart of the preparation method of the porous hard carbon composite material in an embodiment;

[0036] Figure 2 It is a SEM diagram of the porous hard carbon composite material of Example 1;

[0037] Figure 3 It is a schematic diagram of the negative electrode plate of the sodium ion battery of Example 1;

[0038] Figure 4 It is a data comparison diagram of Example 1 and Comparative Example 4;

[0039] Figure 5 It is a curve graph of the test results of the ultrasonic condition variables of Example 1;

[0040] Figure 6 It is a curve graph of the test results of the ultrasonic condition variables of Example 1;

[0041] Figure 7 It is a graph of the test results of the ultrasonic condition variables in Example 1. Detailed implementation manners

[0042] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided so that the disclosure of the present invention can be understood more thoroughly and comprehensively.

[0043] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there can also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0045] The preparation method of the porous hard carbon composite material provided by this application includes the following steps: calcining epoxy resin powder to obtain porous hard carbon; performing a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material; placing the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry; adjusting the pH of the mixed slurry until the pH value of the mixed slurry is 5-6; performing an ultrasonic operation on the mixed slurry after adjusting the pH to break the deposited carbon thin layer between the macropores and mesopores blocked in the porous hard carbon and make the transition metal compound adhere to the pore periphery to obtain a transition metal composite hard carbon material; performing a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material.

[0046] The preparation method of the above-mentioned porous hard carbon composite material obtains a deposited carbon thin layer coating material through the first deposition operation on the porous hard carbon, so that a deposited carbon thin layer is formed on the surface of the porous hard carbon. Then, the deposited carbon thin layer coating material is placed in an excessive metal salt solution, and the pH value is adjusted to a weak acid condition of 5-6. At this time, the pores of the porous hard carbon are blocked by the deposited thin carbon layer. Therefore, it is necessary to break the blocked pores of the thin layer through ultrasonic operation. Ultrasonic waves under the weak acid condition with a pH value of 5-6 can break the deposited thin carbon layer blocking the pores of the porous hard carbon. The periphery of the broken pores is attached with a transition metal compound, which can effectively prevent the pores from being blocked during the second deposition carbon coating process. And under the catalysis of the transition metal, the formation of the deposition layer is more uniform and compact, so that the structural stability of the porous hard carbon composite material can be effectively improved. At the same time, it can also effectively solve the problem that chemical deposition easily causes pore blockage of the hard carbon material, so that the sodium storage capacity of the porous hard carbon composite material is effectively improved when it is applied to the negative electrode of a sodium-ion battery. Further, since the hard carbon material has a high initial efficiency when applied to the negative electrode of a sodium-ion battery, the porous hard carbon composite material can have a high initial efficiency and high cycle performance when used as the negative electrode of a sodium-ion battery, that is, the material coating by the preparation method of the porous hard carbon composite material can effectively improve the initial efficiency and cycle performance of the hard carbon negative electrode sodium-ion battery.

[0047] Please refer to Figure 1 , in order to better understand the preparation method of the porous hard carbon composite material of the present application, the following further explains the preparation method of the porous hard carbon composite material:

[0048] The preparation method of the porous hard carbon composite material in one embodiment includes the following steps:

[0049] S100, calcine the epoxy resin powder to obtain porous hard carbon.

[0050] In this embodiment, after weighing a certain amount of epoxy resin powder and performing high-temperature calcination, the epoxy resin powder is carbonized to form porous hard carbon, that is, a hard carbon material with pores, so as to ensure that the negative electrode has a porous structure when applied to the negative electrode of a sodium-ion battery, so that the sodium storage capacity of the negative electrode material can be improved, thereby effectively improving the cycle performance of the sodium-ion battery. At the same time, the hard carbon material has a high initial efficiency when applied to a sodium-ion battery.

[0051] S200, perform the first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material.

[0052] In this embodiment, through the first deposition operation on the porous hard carbon, that is, a short first carbon deposition coating on the porous hard carbon, a thin layer of deposited carbon is coated on the surface of the porous hard carbon structure, which not only achieves the effect of pre-deposition, but also lays a solid "foundation" for the deposition coating layer to ensure the stability of the deposition coating layer, and further ensure the structural stability of the porous hard carbon composite material.

[0053] S300, Place the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry.

[0054] In this embodiment, the transition metal salt can not only make the formation of the deposition layer more uniform and compact, but also easily adhere to the periphery of the pores, playing a role in preventing pore blockage. Therefore, under the catalysis of the transition metal, the structural stability of the deposition coating layer is effectively improved, and at the same time, there will be no pore blockage, so that the sodium storage capacity can be effectively improved, and the cycle performance of the battery can be effectively improved when applied to the negative electrode of a sodium-ion battery.

[0055] S400, Adjust the pH of the mixed slurry so that the pH value of the mixed slurry is 5-6.

[0056] Since the gas-phase deposition or electrochemical deposition method is prone to pore blockage in the hard carbon material structure, but ultrasonic treatment under weak acid conditions can break the thin layer blocking the macropores and mesopores to ensure the porous structure of the hard carbon material. Therefore, in this embodiment, the pH of the mixed slurry is adjusted so that the pH value of the mixed slurry is 5-6 to make the mixed slurry reach the weak acid condition.

[0057] S500, Perform ultrasonic treatment on the mixed slurry after pH adjustment to break the deposited carbon thin layer between the macropores and mesopores blocked in the porous hard carbon and make the transition metal compound adhere to the periphery of the pores to obtain a transition metal composite hard carbon material.

[0058] In this embodiment, through ultrasonic oscillation of the mixed slurry, the carbon thin layer blocking between the macropores and mesopores is broken, and then the transition metal compound adheres to the periphery of the broken pores, so that there will be no pore blockage in the subsequent deposition operation, thus ensuring the porous structure of the hard carbon material and further ensuring the sodium storage capacity when applied to the negative electrode of a sodium-ion battery.

[0059] It should be particularly noted that pores with a diameter greater than 50 nm are called macropores, and pores with a diameter between 2-50 nm are called mesopores (or medium pores). Therefore, the macropore and mesopore structures in this application are defined as a mixed pore structure. Here, the pore periphery refers to the periphery of the mixed pores, that is, the peripheries of both the macropores and mesopores are adhered to by the transition metal compound.

[0060] S600, perform a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material.

[0061] In this embodiment, under the catalysis of the transition metal compound, the deposition coating layer of the porous hard carbon formed in the second deposition is more uniform and compact, effectively improving the structural stability of the porous hard carbon composite material. At the same time, the characteristic of having pores in the structure is also retained. Therefore, the stability performance and cycling performance of the porous hard carbon composite material are effectively improved when applied to the negative electrode of a sodium ion battery. Combining with the high initial efficiency performance of the hard carbon material in battery applications, such a porous hard carbon composite material can enable the battery to achieve high cycling performance and high initial efficiency.

[0062] In one embodiment, before the operation of calcining the epoxy resin powder, the following steps are further included:

[0063] Place the epoxy resin powder in a tube furnace and continuously introduce a first gas.

[0064] It should be noted that the first gas is an inert gas. Continuously introducing the first gas into the tube furnace makes the tube furnace filled with the inert gas. At the same time, under the environmental conditions of the inert gas atmosphere, the epoxy resin powder is calcined at a high temperature to form a porous hard carbon material. Further, the calcination temperature is 1200 °C. The epoxy resin can be calcined and converted into a porous hard carbon material at 1200 °C. Further, the calcination time is 6 h. Since the epoxy resin belongs to a flame-retardant organic resin and the time required for complete conversion into a porous hard carbon under anaerobic conditions is relatively long

[0065] In one embodiment, the specific operation steps for performing a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material are as follows:

[0066] Stop introducing the first gas;

[0067] Continuously introduce a second gas into the tube furnace to perform a vapor deposition operation to obtain a deposited carbon thin layer coating material.

[0068] It should be noted that the second gas is a gas for vapor deposition. Continuously introducing the second gas into the tube furnace, the second gas is deposited on the porous hard carbon material at a high temperature to form a deposited carbon thin layer and coat the surface of the porous hard carbon material. Further, the first deposition temperature is 1200 °C. By continuously introducing the vapor deposition gas, that is, the second gas, under high temperature conditions, a thin carbon deposition layer is formed on the surface of the porous hard carbon structure. Further, the first deposition time is 0.5 h. Since it lays the "foundation" for the deposition coating layer, the first deposition is a short carbon deposition, forming a thin carbon deposition layer on the surface of the porous hard carbon structure for subsequent ultrasonic breaking.

[0069] In one embodiment, after the first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material, and before placing the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry, the following steps are further included:

[0070] Stop introducing the second gas and cool the tubular furnace to room temperature.

[0071] It should be noted that stopping the introduction of the second gas means completing the first deposition of the porous hard carbon. After the tubular furnace is cooled to room temperature, the deposited carbon thin layer coating material can be taken out of the tubular furnace to facilitate subsequent processes.

[0072] In one embodiment, the first gas is argon, helium or nitrogen. It should be noted that argon, helium or nitrogen are all inert gases. By continuously introducing the first gas, an inert gas atmosphere is formed in the tubular furnace, so as to ensure the carbonization of the epoxy resin powder to form a porous hard carbon material.

[0073] In one embodiment, the second gas is methane, ethane or ethylene. It should be noted that methane, ethane or ethylene can be rapidly decomposed into carbon under high temperature and transition metal catalysis, so that the distance between carbon atoms becomes smaller, and the speed of stacking to form a carbon deposition layer is relatively consistent. In this way, the formed deposition coating layer is more uniform and compact, and the structural stability of the porous hard carbon composite material is further improved.

[0074] In one embodiment, the specific operation steps for subjecting the mixed slurry after pH adjustment to ultrasonic treatment to break the deposited carbon thin layer between the macropores and mesopores in the porous hard carbon and attach the transition metal compound to the pore periphery to obtain a transition metal composite hard carbon material are as follows:

[0075] Subject the mixed slurry after pH adjustment to ultrasonic treatment;

[0076] Perform a filtration operation on the ultrasonicated mixed slurry to obtain a filtered mixture;

[0077] Perform a drying operation on the filtered mixture to obtain a transition metal composite hard carbon material.

[0078] It should be noted that after subjecting the mixed slurry after pH adjustment to ultrasonic treatment, the transition metal compound adheres to the porous hard carbon. At this time, only the liquid phase part needs to be filtered out from the mixed slurry, and the solid phase part is dried to obtain a transition metal composite hard carbon material. Under the attachment of the transition metal, the pores of the hard carbon material are not easily blocked, so that the porous structure of the hard carbon material can be effectively guaranteed.

[0079] Furthermore, the vibration frequency of the ultrasonic operation is 28 kHz - 40 kHz. In this frequency range, the mixture of the porous hard carbon and the transition metal compound is more uniform. Meanwhile, during the ultrasonic oscillation, the hard carbon material can obtain more surface pore structures, which can further improve the sodium intercalation and deintercalation capacity of the hard carbon material, thereby effectively improving the reversible sodium storage capacity of the porous hard carbon composite material when applied to the negative electrode of the sodium-ion battery, and further effectively improving the cycle performance of the sodium-ion battery.

[0080] Furthermore, the temperature of the ultrasonic operation is 32°C - 40°C. In this temperature range, the transition metal compound adheres better to the porous hard carbon, which can effectively prevent the pore blockage during the subsequent deposition of the hard carbon material. In this way, the hard carbon material obtains more pore structures, enabling the porous hard carbon composite material to have better reversible sodium storage capacity when applied to the negative electrode of the sodium-ion battery, and further enabling the negative electrode of the sodium-ion battery to have high initial efficiency and high cycle performance.

[0081] Furthermore, the pressure of the ultrasonic operation is 25 MPa - 40 MPa. In this pressure range, the bonding degree between the transition metal compound and the porous hard carbon is effectively improved, making it easier for the transition metal compound to adhere to the porous hard carbon. Therefore, under the ultrasonic environmental conditions within this frequency range, temperature range, and pressure range, the hard carbon material and the transition metal compound are more likely to combine and mix evenly, so that the hard carbon material obtains more pore structures, and further enabling the porous hard carbon composite material to have a relatively high reversible sodium storage capacity when applied to the negative electrode of the sodium-ion battery, making the sodium-ion battery have the characteristics of high initial efficiency and high cycle performance.

[0082] In one of the embodiments, the specific operation steps for performing the second deposition operation on the transition metal composite hard carbon material to obtain the porous hard carbon composite material are as follows:

[0083] Perform a grinding operation on the transition metal composite hard carbon material;

[0084] Place the ground transition metal composite hard carbon material in the tube furnace;

[0085] Continuously introduce the second gas into the tube furnace to perform the chemical vapor deposition operation to obtain the porous hard carbon composite material.

[0086] It should be noted that the ground transition metal composite hard carbon material is placed in a tube furnace, and a second gas is continuously introduced to perform a second deposition under high temperature conditions. Through grinding and catalysis by the transition metal, the formation of the deposition coating layer becomes more uniform and compact. Moreover, the second gas on the surface catalyzed by the transition metal can be decomposed into carbon more quickly, resulting in a smaller distance between carbon atoms and a relatively consistent stacking speed. In this way, the formation of the deposition layer is more uniform and compact, the structural stability of the porous hard carbon composite material is better, and at the same time, the structural stability of the periphery of the pores is also better, thus ensuring the stability of sodium ion storage and migration, and further effectively guaranteeing the safety performance and cycle performance of the sodium ion battery. Further, the second deposition temperature is 1200 °C. By continuously introducing the second gas at high temperature, a deposition coating layer is formed on the surface of the porous hard carbon, and at the same time, the formation of the deposition coating layer is more uniform and compact under the catalysis of the transition metal. Further, the second deposition time is 5 h. By forming the deposition coating layer through the second deposition time, the structural strength of the porous hard carbon composite material is effectively improved, and at the same time, the pores of the hard carbon material become larger, further improving the sodium storage capacity of the hard carbon material and making the process of sodium ion storage and migration smoother, thus effectively improving the cycle performance of the sodium ion battery.

[0087] In one embodiment, the filtered metal salt solution is one or more of ferric chloride, copper chloride, nickel chloride, and titanium chloride. It can be understood that ferric chloride, copper chloride, nickel chloride, and titanium chloride can all adhere to the pores of the hard carbon material and can all catalyze the formation of the deposition layer to be more uniform and compact.

[0088] This application also provides a negative electrode for a sodium ion battery, which is the porous hard carbon composite material prepared by using the preparation method of the porous hard carbon composite material described in any of the above embodiments.

[0089] In this embodiment, the porous hard carbon composite material prepared by the preparation method of the porous hard carbon composite material has high initial efficiency and high cycle performance when applied to the negative electrode of a sodium ion battery. At the same time, the porous hard carbon composite material also has good structural stability, thus effectively guaranteeing the safety performance of the sodium ion battery.

[0090] The following are examples listed, but it should be noted that the following examples do not exhaust all possible situations, and the materials used in the following examples can be obtained from commercial channels without special instructions.

[0091] Example 1

[0092] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop gas supply and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in a mixed solution of 0.5 M ferric chloride and 0.5 M titanium chloride, adjust the pH to 5, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0093] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to an NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0094] Example 2

[0095] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop gas supply and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in 1 M nickel chloride solution, adjust the pH to 5, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0096] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to an NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0097] Example 3

[0098] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace the argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop the gas supply and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in 1 M ferric chloride solution, adjust the pH to 5, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0099] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to the NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0100] Comparative Example 1

[0101] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace the argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop the gas supply and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in a mixed solution of 0.5 M ferric chloride and 0.5 M titanium chloride, adjust the pH to 8, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0102] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to the NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0103] Comparative Example 2

[0104] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop ventilation and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in a mixed solution of 0.5 M ferric chloride and 0.5 M titanium chloride, adjust the pH to 7, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0105] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to an NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0106] Comparative Example 3

[0107] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace argon gas with methane gas and carry out carbon deposition at 1200 °C for 0.5 h. Stop ventilation and cool to room temperature with the furnace. Place the carbon-deposited thin film hard carbon in deionized water, adjust the pH to 5, stir for 30 min, then ultrasonicate for 1 h, filter and dry. Grind the dried transition metal composite hard carbon for 30 min, place it in a tubular furnace, introduce methane gas, and carry out carbon deposition at 1200 °C for 5 h to obtain a porous hard carbon composite material.

[0108] (2) Weigh the porous hard carbon composite material, PVDF and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to an NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on the aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0109] Comparative Example 4

[0110] (1) Take 10 g of epoxy resin powder in a tubular furnace, introduce argon gas, heat up to 1200 °C and calcine for 6 h to obtain porous hard carbon. Replace argon gas with methane gas and carry out carbon deposition at 1200 °C for 5.5 h to obtain porous hard carbon.

[0111] (2) Weigh porous hard carbon, PVDF, and conductive carbon black according to a mass ratio of 8:1:1, mix them evenly, add them to an NMP solution to form a uniform slurry, and the total solid content of the slurry is 40%. Then coat the slurry on aluminum foil and vacuum dry it at 80 °C to obtain a hard carbon electrode sheet. Finally, cut it into circular pieces with a diameter of 12 mm, use sodium as the counter electrode, and 1 M NaPF6-EC / DEC (volume ratio 1:1) as the electrolyte to assemble a button cell.

[0112] Perform electron microscopy scanning on the porous hard carbon composite material in Example 1 to obtain an electron micrograph Figure 2 .

[0113] Perform the first discharge test on Examples 1-3 and Comparative Examples 1-4, and the results are shown in Table 1.

[0114] Table 1

[0115] Example Specific surface area m2 / g First efficiency % Initial discharge capacity mAh / g Example 1 15.7 95.2 247.6 Example 2 16.2 93.6 221.4 Example 3 15.3 88.9 198.5 Comparative example 1 15.1 90.1 204.0 Comparative example 2 16.4 92.5 219.8 Comparative example 3 15.9 80.2 186.5 Comparative example 4 16.3 77.9 164.3

[0116] Perform cyclic charge and discharge tests on Example 1 and Comparative Example 4, and the results are as Figure 4 .

[0117] As can be seen from Table 1, Example 1 is the optimal example. Example 1 has a relatively high first discharge capacity and high first efficiency in the first discharge test. Therefore, when the porous hard carbon composite material of the present application is applied to the sodium ion electron negative electrode, the sodium ion battery has a high first efficiency.

[0118] From Figure 4 it can be seen that the top first and second lines represent the change of the Coulomb efficiency of Example 1 and Comparative Example 4 with the number of cycles; the bottom third and fourth lines represent the change of the specific capacity of Example 1 and Comparative Example 4 with the number of cycles. Figure 4 The difference between Example 1 and Comparative Example 4 is that the cycle stability of Example 1 is significantly better than that of Comparative Example 4. Specifically, after 100 cycles, the specific capacity and Coulomb efficiency of Example 1 are basically unchanged, but the Coulomb efficiency of Comparative Example 4 has started to show a significant decline at 95 cycles, and the specific capacity of Comparative Example 4 has also decreased to 94.3% of the first specific capacity. When the porous hard carbon composite material of the present application is applied to the sodium ion electron negative electrode, the sodium ion battery has a relatively high first efficiency and good cycle performance.

[0119] In summary, the porous hard carbon composite material of the present application has a high first efficiency and good cycle performance when applied to the negative electrode of a sodium ion battery.

[0120] Furthermore, for variable test 1 of the ultrasonic conditions, set the temperature in the ultrasonic conditions of Example 1 to 30 °C, the pressure to 0.1 MPa, and the frequency as the variable. Prepare an assembled button cell for the first discharge test to obtain the results Figure 5 .

[0121] Variable test 2 of ultrasonic conditions: Set the frequency in the ultrasonic conditions in Example 1 to 33 kHz, the pressure to 0.1 MPa, and the temperature as a variable. Fabricate an assembled button battery for the first discharge test and obtain the results Figure 6 .

[0122] Variable test 3 of ultrasonic conditions: Set the temperature in the ultrasonic conditions in Example 1 to 35 °C, the frequency to 33 kHz, and the pressure as a variable. Fabricate an assembled button battery for the first discharge test and obtain the results Figure 7

[0123] It can be seen from Figure 5 that the optimal frequency range of the ultrasonic frequency is 28 kHz - 40 kHz, and the most preferred frequency is 33 kHz. When the porous hard carbon composite material obtained by ultrasonic vibration at 33 kHz is applied to the negative electrode of a sodium-ion battery, the battery has a high initial efficiency.

[0124] It can be seen from Figure 6 that the optimal temperature range of the ultrasonic temperature is 32 °C - 40 °C, and the most preferred temperature is 35 °C. When the porous hard carbon composite material obtained by ultrasonic treatment at 35 °C is applied to the negative electrode of a sodium-ion battery, the battery has a high initial efficiency.

[0125] It can be seen from Figure 7 that the optimal pressure range of the ultrasonic pressure is 25 MPa - 40 MPa, and the most preferred pressure is 30 MPa. When the ultrasonic temperature is 35 °C, the frequency is 33 kHz, and the pressure is 30 MPa, the first Coulombic efficiency of the battery can reach 95.2%.

[0126] In summary, the most preferred ultrasonic conditions are a temperature of 35 °C, a frequency of 33 kHz, and a pressure of 30 MPa. When the porous hard carbon composite material obtained under the most preferred ultrasonic conditions is applied to the negative electrode of a sodium-ion battery, it exhibits high initial efficiency and high cycle performance.

[0127] Compared with the prior art, the present invention has at least the following advantages:

[0128] The preparation method of the porous hard carbon composite material of the present application obtains a deposited carbon thin layer coating material through the first deposition operation on the porous hard carbon, so that a deposited carbon thin layer is formed on the surface of the porous hard carbon. Then, the deposited carbon thin layer coating material is placed in an excessive metal salt solution, and the pH value is adjusted to a weak acid condition of 5-6. At this time, the pores of the porous hard carbon are blocked by the deposited thin carbon layer. Therefore, ultrasonic operation is required to break the pores blocked by the thin layer. Ultrasonic waves in the weak acid condition with a pH value of 5-6 can break the deposited thin carbon layer blocking the pores of the porous hard carbon. The periphery of the broken pores is attached with transition metal compounds, which can effectively prevent the pores from being blocked during the second deposition carbon coating process, and the formation of the deposition layer is more uniform and compact under the catalysis of the transition metal. In this way, the structural stability of the porous hard carbon composite material can be effectively improved, and at the same time, the problem that chemical deposition easily leads to pore blockage of the hard carbon material can be effectively solved. In this way, the sodium storage capacity of the porous hard carbon composite material is effectively improved when it is applied to the negative electrode of a sodium-ion battery. Further, since the hard carbon material has a high first efficiency when applied to the negative electrode of a sodium-ion battery, the porous hard carbon composite material can have a relatively high first efficiency and relatively high cycle performance when used as the negative electrode of a sodium-ion battery. That is, the first efficiency and cycle performance of the sodium-ion battery with a hard carbon negative electrode can be effectively improved by coating the material through the preparation method of the porous hard carbon composite material.

[0129] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of a porous hard carbon composite material, characterized in that, it includes the following steps: Calcine the epoxy resin powder to obtain porous hard carbon; Perform a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material; Place the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry; Adjust the pH of the mixed slurry until the pH value of the mixed slurry is 5 - 6; Perform an ultrasonic operation on the mixed slurry after adjusting the pH to break the deposited carbon thin layer between the macropores and mesopores in the porous hard carbon and make the transition metal compound adhere to the pore periphery to obtain a transition metal composite hard carbon material; Perform a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material.

2. The preparation method of the porous hard carbon composite material according to claim 1, characterized in that, before the step of calcining the epoxy resin powder, the preparation method further includes the following steps: Place the epoxy resin powder in a tubular furnace and continuously introduce a first gas.

3. The preparation method of the porous hard carbon composite material according to claim 2, characterized in that, the step of performing a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material includes: Stop introducing the first gas; Continuously introduce a second gas into the tubular furnace to perform a vapor deposition operation to obtain a deposited carbon thin layer coating material.

4. The preparation method of the porous hard carbon composite material according to claim 3, characterized in that, after the step of performing a first deposition operation on the porous hard carbon to obtain a deposited carbon thin layer coating material and before the step of placing the deposited carbon thin layer coating material in a transition metal salt solution to obtain a mixed slurry, the preparation method further includes the following steps: Stop introducing the second gas and cool the tubular furnace to room temperature.

5. The preparation method of the porous hard carbon composite material according to claim 4, characterized in that, the first gas is argon, helium or nitrogen.

6. The preparation method of the porous hard carbon composite material according to claim 5, characterized in that, the second gas is methane, ethane or ethylene.

7. The preparation method of the porous hard carbon composite material according to claim 1, characterized in that, the specific operation steps of performing an ultrasonic operation on the mixed slurry after adjusting the pH to break the deposited carbon thin layer between the macropores and mesopores in the porous hard carbon and make the transition metal compound adhere to the pore periphery to obtain a transition metal composite hard carbon material are as follows: Perform an ultrasonic operation on the mixed slurry after adjusting the pH; Perform a filtration operation on the ultrasonicated mixed slurry to obtain a filtered mixture; Perform a drying operation on the filtered mixture to obtain a transition metal composite hard carbon material.

8. The preparation method of the porous hard carbon composite material according to claim 4, characterized in that, the specific operation steps of performing a second deposition operation on the transition metal composite hard carbon material to obtain a porous hard carbon composite material are as follows: Perform a grinding operation on the transition metal composite hard carbon material; Place the ground transition metal composite hard carbon material into the tubular furnace; Continuously introduce the second gas into the tubular furnace to perform the vapor deposition operation to obtain the porous hard carbon composite material.

9. The method for preparing the porous hard carbon composite material according to claim 1, characterized in that, The transition metal salt solution is at least one of ferric chloride, copper chloride, nickel chloride or titanium chloride.

10. A negative electrode for a sodium ion battery, characterized in that, The porous hard carbon composite material prepared by using the method for preparing the porous hard carbon composite material according to any one of claims 1-9.

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