Hard carbon composite, preparation method and sodium ion battery

Abstract

The present application relates to the technical field of battery material preparation, and particularly relates to a hard carbon composite material, a preparation method and a sodium ion battery. The preparation method comprises the following steps: providing a carbon source, sodium peroxide and phytic acid in a preset ratio to be mixed to obtain a mixture; performing a reduction reaction and a first heating in the mixture to obtain a porous hard carbon precursor; introducing borane gas into a reaction space in which the porous hard carbon precursor is located, and performing a second heating and a deposition reaction to obtain the hard carbon composite material. The present application further provides a hard carbon composite material and a sodium ion battery. The problems of low energy density and poor fast charging performance of the hard carbon used in the sodium ion battery are solved.

Description

[Technical Field]

[0001] This invention relates to the field of battery material preparation technology, and in particular to a hard carbon composite material, its preparation method, and a sodium-ion battery. [Background Technology]

[0002] Hard carbon, a type of carbon that is difficult to graphitize, possesses a highly disordered, isotropic, stable structure and a large interlayer spacing, allowing for rapid diffusion of sodium ions. Furthermore, hard carbon exhibits good compatibility with electrolytes, a high diffusion coefficient, and a wide lithium / sodium intercalation potential range, which facilitates rapid ion insertion and prevents the deposition of dendritic lithium / sodium, making it suitable for high-current charge-discharge operations. However, due to its disordered layer structure, hard carbon has poor electronic conductivity, affecting its rate performance. Additionally, the low specific capacity and low compaction density of hard carbon used in batteries hinder the improvement of its energy density.

[0003] Current technologies for improving the electronic conductivity and energy density of hard carbon materials mainly involve doping the core and shell with materials possessing high electronic or ionic conductivity, or creating pores to enhance sodium storage capacity. However, these methods can reduce fast-charging performance. Therefore, developing materials that simultaneously improve the energy density and fast-charging performance of hard carbon materials is essential. [Summary of the Invention]

[0004] To address the issues of low energy density and poor fast-charging performance of hard carbon used in sodium-ion batteries, this invention provides a hard carbon composite material, a preparation method, and a sodium-ion battery.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a hard carbon composite material, wherein the prepared hard carbon composite material can be applied in sodium-ion batteries, comprising the following steps:

[0006] Provide a preset ratio of carbon source, sodium peroxide and phytic acid to mix and obtain a mixture;

[0007] A reduction reaction and a first heating were carried out in the mixture to obtain a porous hard carbon precursor;

[0008] Hard carbon composite materials are obtained by introducing borane gas into the reaction space containing the porous hard carbon precursor and then subjecting it to a second heating and deposition reaction.

[0009] Preferably, the preset ratio is: carbon source: sodium peroxide: phytic acid = 100: (1-5): (1-5).

[0010] Preferably, before carrying out the reduction reaction in the mixture, the process includes: introducing an inert gas into the mixture to place the mixture in an inert gas environment.

[0011] Preferably, the reduction reaction in the mixture specifically includes: introducing carbon dioxide gas into the inert gas environment in which the mixture is located, so that the mixture undergoes a reduction reaction to obtain oxygen for pore formation.

[0012] Preferably, the first heating of the mixture specifically includes:

[0013] The mixture is first heated to 500-700℃ for pyrolysis for 1-6 hours to obtain a porous carbon framework. The porous carbon framework is then subjected to oxygen to form pores to obtain a porous hard carbon precursor.

[0014] Preferably, introducing borane gas into the reaction space containing the porous hard carbon precursor includes:

[0015] The borane gas is one of diborane or butorane;

[0016] The flow rate of the borane gas is 100-500 ml / min.

[0017] Preferably, the porous hard carbon precursor is introduced with borane gas and undergoes a second heating and deposition reaction, specifically including:

[0018] The porous hard carbon precursor was heated to 1000-1400℃ for a second time under borane gas and then subjected to vapor deposition for 1-6 hours to obtain a hard carbon composite material.

[0019] Preferably, the carbon source is any one of xylose, glucose, sucrose, trehalose, lactose, maltose, chitosan, and mannan.

[0020] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: a hard carbon composite material, which is prepared by the hard carbon composite material preparation method described above.

[0021] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: a sodium-ion battery, comprising a positive electrode, a positive electrode current collector, an electrolyte layer, a negative electrode current collector, and a negative electrode stacked sequentially; the negative electrode material includes the hard carbon composite material as described above.

[0022] Compared with the prior art, the hard carbon composite material, preparation method, and sodium-ion battery provided by the present invention have the following beneficial effects:

[0023] 1. This invention provides a method for preparing a hard carbon composite material, comprising the following steps: providing a carbon source, sodium peroxide, and phytic acid in a predetermined ratio to mix and obtain a mixture; performing a reduction reaction and a first heating in the mixture to obtain a porous hard carbon precursor; and obtaining the hard carbon composite material by introducing borane gas into the reaction space containing the porous hard carbon precursor and then performing a second heating and deposition reaction. This method solves the problem of poor fast-charging performance of hard carbon materials when used in batteries to improve energy density in existing designs. By adjusting the raw materials and their ratios, a reaction occurs, transforming the carbon source into a porous hard carbon material, and the doping of phosphorus increases the specific capacity of the material. Furthermore, by introducing borane gas, the borane gas is decomposed and deposited onto the porous hard carbon precursor during the second heating, resulting in a boron-doped amorphous carbon coating on its outer shell, reducing surface defects and improving the initial efficiency and fast-charging performance of the porous hard carbon composite material.

[0024] 2. The preset ratio in this embodiment of the invention is: carbon source: sodium peroxide: phytic acid = 100:(1-5):(1-5). This embodiment selectively adjusts the components of the raw materials to ensure that the preset ratio of carbon source, sodium peroxide and phytic acid is fully mixed, and the phosphorus doping provided by phytic acid can improve the specific capacity of the porous hard carbon composite material.

[0025] 3. In this embodiment of the invention, before the reduction reaction in the mixture, an inert gas is introduced into the mixture to create an inert gas environment. By venting air, oxidation is prevented from occurring during pyrolysis and reduction, which helps to obtain the desired porous hard carbon precursor.

[0026] 4. The reduction reaction in the mixture in this embodiment of the invention specifically includes: introducing carbon dioxide gas into the inert gas environment in which the mixture is located, so that the mixture undergoes a reduction reaction to obtain oxygen for pore formation, Na2O2+CO2=NaCO3+1 / 2O2↑, the oxygen performs a pore formation on the hard carbon, and porous hard carbon can be obtained.

[0027] 5. The first heating of the mixture in this embodiment specifically includes: heating the mixture to 500-700℃ for pyrolysis for 1-6 hours to obtain a porous carbon framework. The porous carbon framework forms pores under the action of oxygen to obtain a porous hard carbon precursor. After the first heating, the organic matter and carbon source in the mixture undergo pyrolysis, changing the material structure and forming a porous structure containing many micropores and mesopores. These pores are crucial for sodium storage active sites; that is, the carbon source also undergoes pore formation during pyrolysis. Furthermore, at high temperatures, the carbon source and organic matter decompose and volatilize, leaving behind the carbon framework. In other words, pyrolysis helps remove excess organic matter and impurities, thereby improving the purity of the material.

[0028] 6. In this embodiment of the invention, borane gas is introduced into the reaction space containing the porous hard carbon precursor. The borane gas is either diborane or butorane; the flow rate of the borane gas is 100-500 ml / min. If the flow rate of the borane gas is too high, the amorphous carbon formed may not have enough time to coat the outer surface of the porous hard carbon composite material, making it difficult to form a stable and uniform coating layer. This may lead to the formation of pores or surface defects on the surface of the porous hard carbon composite material, reducing its tap density.

[0029] 7. The embodiment of the present invention, which involves introducing borane gas into the porous hard carbon precursor and subjecting it to a second heating and deposition reaction, specifically includes: heating the porous hard carbon precursor to 1000-1400°C under borane gas and obtaining a hard carbon composite material through vapor phase deposition for 1-6 hours. Depositing carbon borides (borane) on the surface of the porous hard carbon precursor can reduce surface defects, improve initial efficiency, and enhance the electronic conductivity of the material. Furthermore, boron doping exhibits good compatibility with the electrolyte, improving cycle life and high-temperature storage performance.

[0030] 8. The carbon source in this embodiment of the invention is any one of xylose, glucose, sucrose, trehalose, lactose, maltose, chitosan, and mannan. The wide availability of carbon sources makes the raw materials for preparing hard carbon composite materials using the method in this embodiment readily available and economically viable.

[0031] 9. The present invention also provides a hard carbon composite material, which has the same beneficial effects as the preparation method of the above-mentioned hard carbon composite material, and will not be described in detail here.

[0032] 10. This invention also provides a sodium-ion battery that has the same beneficial effects as the aforementioned hard carbon composite material, which will not be described in detail here. [Attached Image Description]

[0033] Figure 1 This is a flowchart of the preparation method of hard carbon composite material provided in the first embodiment of the present invention.

[0034] Figure 2 This is a scanning image obtained by scanning electron microscopy testing of the hard carbon composite material prepared in Experiment 1 according to the present invention.

Detailed Implementation Methods

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] In the embodiments provided by this invention, it should be understood that "B corresponding to A" means that B is associated with A, and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B solely based on A; B can also be determined based on A and / or other information.

[0037] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Those skilled in the art should also recognize that the embodiments described in the specification are optional embodiments, and the actions and modules involved are not necessarily essential to the invention.

[0038] In various embodiments of the present invention, it should be understood that the sequence number of each process does not necessarily imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0039] Because hard carbon has a disordered layer structure, it has poor electronic conductivity, which affects its rate performance. Furthermore, the hard carbon used in batteries has a low specific capacity and low compaction density, which affects the improvement of its energy density.

[0040] Current technologies for improving the electronic conductivity and energy density of hard carbon materials mainly involve doping the core and shell with materials possessing high electronic or ionic conductivity, or creating pores to enhance sodium storage capacity. However, these methods can reduce fast-charging performance. Therefore, developing materials that simultaneously improve the energy density and fast-charging performance of hard carbon materials is essential.

[0041] To address the issue of poor fast-charging performance of hard carbon materials in existing battery designs when used to increase energy density, please refer to... Figure 1 The first embodiment of the present invention provides a method for preparing a hard carbon composite material, the prepared hard carbon composite material being applicable in sodium-ion batteries, comprising the following steps:

[0042] S1 provides a preset ratio of carbon source, sodium peroxide and phytic acid to mix and obtain a mixture;

[0043] S2, undergoes reduction reaction and first heating in the mixture to obtain porous hard carbon precursor;

[0044] S3, a hard carbon composite material is obtained by introducing borane gas into the reaction space containing the porous hard carbon precursor and then subjecting it to a second heating and deposition reaction.

[0045] Understandably, this invention first provides a carbon source, sodium peroxide, and phytic acid in a predetermined ratio to obtain a mixture. The carbon source serves as the matrix, primarily for the subsequent preparation of hard carbon in the battery structure, compared to the traditional use of graphite materials. The advantage of hard carbon is that it has shorter graphene layers, sometimes a single layer, but more often formed by stacking two or three graphene layers to create the basic structure. This interlaced layered structure allows sodium ions to be inserted and extracted from various angles of the material, accelerating the diffusion rate and enabling rapid charging and discharging. However, its disadvantage is that hard carbon itself has a disordered layered structure, resulting in poor electronic conductivity and affecting its rate performance. Sodium peroxide acts as an oxidant, releasing oxygen and contributing to the formation of a porous hard carbon precursor. Phytic acid provides phosphorus, which is incorporated into the porous hard carbon precursor, thereby increasing the specific capacity of the precursor. Simultaneously, the -POC chemical bonds formed in this embodiment prevent the collapse of the carbon skeleton during carbonization, thus improving the material's strength.

[0046] It should be understood that this embodiment selectively adjusts the components of the raw materials to obtain a mixture by mixing carbon source, sodium peroxide, and phytic acid in a preset ratio. Since this embodiment is mainly applied to sodium-ion batteries, sodium peroxide is selectively selected as one of the raw materials. The sodium peroxide in the mixture can be reduced to obtain oxygen that can be used for pore formation, which can perform a first pore formation on the hard carbon structure to obtain a porous hard carbon. Furthermore, after the first heating, the organic matter and carbon source in the mixture can be pyrolyzed to produce the carbon skeleton of hard carbon. The carbon skeleton will undergo a second pore formation during the formation process, producing a carbon skeleton with channels. After two pore formations, a porous hard carbon precursor can be formed. After borane gas is introduced into the reaction space where the porous hard carbon precursor is located, boron doped amorphous carbon is generated after a second high-temperature pyrolysis. Specifically, the hard carbon composite material has a core-shell structure, and its outer shell is coated with boron doped amorphous carbon, which can improve the electronic conductivity of the hard carbon composite material. In this embodiment, the reaction occurs after adjusting the raw materials and their proportions, transforming the carbon source into a porous hard carbon material. Furthermore, the doping with phosphorus increases the material's specific capacity. Additionally, by introducing borane gas, it undergoes a second heating and pyrolysis process, depositing onto the porous hard carbon precursor. This coats the precursor with boron-doped amorphous carbon, reducing surface defects and improving the initial efficiency and fast-charging performance of the porous hard carbon composite material.

[0047] Specifically, the preset ratio is: carbon source: sodium peroxide: phytic acid = 100:(1-5):(1-5). Optionally, the ratio of carbon source: sodium peroxide: phytic acid can also be: 100:(1-2):(1-3), 100:(2-3):(2-4), 100:(3-5):(4-5), or 100:(1-3):(2-5). It should be understood that this embodiment selectively adjusts the components of the raw materials to ensure that the preset ratio of carbon source, sodium peroxide, and phytic acid is fully mixed, and the phosphorus doping provided by phytic acid can improve the specific capacity of the porous hard carbon composite material.

[0048] Furthermore, in step S2 above, before the reduction reaction in the mixture, an inert gas is introduced into the mixture to create an inert gas environment. It should be understood that the primary purpose of introducing an inert gas (typically nitrogen or argon) to purge air is to create a moisture-free environment. At high temperatures, moisture and oxygen in the air can adversely affect the reaction products. By purging air, ensuring that oxidation does not occur during pyrolysis and reduction helps obtain the desired porous hard carbon precursor.

[0049] Specifically, in step S2 above, the reduction reaction in the mixture includes: introducing carbon dioxide gas into the inert gas environment containing the mixture for 30-300 minutes to allow the mixture to undergo a reduction reaction and obtain oxygen for pore formation. The first heating in the mixture includes: heating the mixture to 500-700℃ for pyrolysis for 1-6 hours to obtain a porous carbon framework, and then forming pores in the porous carbon framework under the action of oxygen to obtain a porous hard carbon precursor.

[0050] It should be understood that when a carbon source, sodium peroxide, and phytic acid are mixed and then introduced into carbon dioxide gas, the carbon dioxide reacts with the sodium peroxide:

[0051] Reaction 1: Na₂O₂ + CO₂ = Na₂CO₃ + 1 / 2O₂↑;

[0052] further:

[0053] Reaction 2: 2C6HOP6 + 3O2 = 4CO2↑ + 12P + 8C;

[0054] It should be understood that since this embodiment uses a sodium-ion battery, sodium peroxide is selected as the raw material, meaning that no other cationic impurities will enter the system during the reaction. In reaction one, carbon dioxide reacts with sodium peroxide to generate oxygen, which then creates pores in the hard carbon, resulting in porous hard carbon. Specifically, the reduction reaction time is controlled to ensure that carbon dioxide and sodium peroxide react completely. Carbon dioxide is a relatively mild reducing agent, unlike some stronger reducing agents which are highly reactive, which helps control the reaction conditions. Furthermore, carbon dioxide can promote the decomposition and conversion of the carbon source at high temperatures, contributing to the formation of the porous hard carbon precursor.

[0055] Specifically, in reaction two, after the first heating, the organic matter and carbon source in the mixture undergo pyrolysis, altering the material's structure and forming a porous structure containing numerous micropores and mesopores. These pores are crucial for sodium storage active sites; in other words, the carbon source also undergoes pore-forming during pyrolysis. That is, oxygen creates pores, and pyrolysis creates pores again; the combined effect of these two processes results in excellent porosity of the hard carbon. Furthermore, at high temperatures, the carbon source and organic matter decompose and volatilize, leaving behind a carbon skeleton. Pyrolysis helps remove excess organic matter and impurities, thereby improving the material's purity. It should be noted that by controlling the pyrolysis conditions—specifically, the temperature range and time—the pore structure and properties of the porous hard carbon material can be adjusted to meet user needs.

[0056] Furthermore, in reaction two, the pyrolysis of phytic acid allows for phosphorus doping onto the porous hard carbon, forming a phosphorus-doped amorphous porous structure, thereby improving the material's specific capacity. Additionally, this embodiment selectively uses phytic acid as a raw material. Firstly, phytic acid offers better fast-charging performance compared to phosphoric acid; that is, when the hard carbon composite material prepared in this embodiment is applied to the anode of a sodium-ion battery, its rate performance and constant current ratio are improved compared to existing technologies. Secondly, during the first heating process, after the phytic acid decomposes, the -POC chemical bonds in the reaction system prevent the collapse of the carbon skeleton during carbonization, thus improving the material's strength.

[0057] It should be noted that the reduction reaction by introducing carbon dioxide and the heating of the mixture can be carried out simultaneously. This allows the carbon source to form a porous carbon framework at high temperatures, and oxygen can further create pores in the carbon framework to achieve a better pore-forming effect.

[0058] Furthermore, the introduction of borane gas into the reaction space containing the porous hard carbon precursor includes the use of either diborane or butorane. This allows for a variety of borane gas options. The flow rate of the borane gas is 100-500 ml / min. It should be understood that depositing carbon borides (boranes) on the surface of the porous hard carbon precursor can reduce surface defects, improve initial efficiency, and enhance the electronic conductivity of the material. Furthermore, boron doping exhibits good compatibility with the electrolyte, improving cycle life and high-temperature storage performance. Optionally, the flow rate of the borane gas can also be 100-200 ml / min, 150-300 ml / min, 200-400 ml / min, or 300-500 ml / min. It should be understood that if the flow rate of the borane gas is too high, the formed amorphous carbon may not have sufficient time to coat the outer surface of the porous hard carbon composite material, thus failing to form a uniform material. This can lead to the formation of pores or surface defects on the surface of porous hard carbon composites, reducing their true density.

[0059] Specifically, the porous hard carbon precursor is introduced into a borane gas, and undergoes a second heating and deposition reaction, which specifically includes: the porous hard carbon precursor is heated a second time to 1000-1400°C under borane gas and subjected to vapor phase deposition for 1-6 hours to obtain a hard carbon composite material. Specifically, chemical vapor deposition (CVD) is a process used to grow thin films, coatings, or nanomaterials. It deposits materials onto a solid substrate by reacting chemical substances in the gas phase. Its principle is to introduce one or more gaseous precursor compounds into a reaction chamber, causing them to react chemically and grow a material film or coating on the surface of a solid substrate. These precursor compounds produce the desired material through decomposition, deposition, or reaction. Reaction conditions (including temperature, pressure, gas flow rate, etc.) can be adjusted according to the desired material properties.

[0060] In the second heating process of this embodiment, after borane undergoes cracking, boron dops the amorphous carbon in the reaction system and then deposits it on the surface of the porous hard carbon precursor, coating it to form a hard carbon composite material. This embodiment controls the temperature of the second heating and the vapor deposition time to ensure that the boron-doped carbon fully encapsulates the shell of the hard carbon composite material. It should be understood that this embodiment uses vapor deposition of cracked borane gas onto the surface of the porous hard carbon precursor to obtain the hard carbon composite material. The vapor deposition method allows for better control of the introduction of boron, as the flow rate and concentration of the borane gas can be precisely controlled. This allows for more uniform boron doping in the material to achieve the desired properties.

[0061] It should be understood that porous hard carbon composite materials have a core-shell structure. The boron-doped amorphous carbon in the outer shell of the material improves the electronic conductivity and fast-charging performance. At the same time, the porous structure can increase the specific surface area of ​​the hard carbon material, improve the adsorption capacity, and enhance the specific capacity of the material.

[0062] Optionally, the carbon source is any one of xylose, glucose, sucrose, trehalose, lactose, maltose, chitosan, and mannan. It should be understood that the wide availability of carbon sources makes the raw materials for preparing hard carbon composite materials using the method in this embodiment readily available and economically viable.

[0063] To address the aforementioned problems, the second embodiment of this invention also provides a hard carbon composite material, characterized in that it is prepared by the aforementioned method for preparing hard carbon composite materials.

[0064] This invention also provides a hard carbon composite material, which has the same beneficial effects as the preparation method of the hard carbon composite material described above, and will not be repeated here.

[0065] To address the aforementioned issues, a third embodiment of the present invention also provides a sodium-ion battery, comprising a positive electrode, a positive electrode current collector, an electrolyte layer, a negative electrode current collector, and a negative electrode stacked sequentially; the negative electrode material comprises the hard carbon composite material described above.

[0066] Specifically, to demonstrate that the hard carbon composite material prepared according to the embodiments of the present invention can improve both energy density and fast-charging performance when applied to batteries, the following experimental examples are conducted:

[0067] Experimental Example 1:

[0068] Step S1:

[0069] Mix 100g maltose, 5g sodium peroxide and 5g phytic acid evenly. First, argon inert gas is introduced to purge the air in the tube. Then, carbon dioxide (flow rate 100ml / min) is introduced to carry out the reduction reaction for 30min. After that, the temperature is raised to 700℃ for pyrolysis for 1h to obtain a porous hard carbon precursor.

[0070] Step S2:

[0071] The porous hard carbon precursor was transferred to a tube furnace, and then diborane gas (flow rate 500 ml / min) was introduced by vapor deposition and the temperature was raised to 1400 °C. After deposition for 1 h, a hard carbon composite material formed by boron-doped amorphous carbon coating was obtained.

[0072] Experimental Example 2:

[0073] Step S1:

[0074] Mix 100g glucose, 1g sodium peroxide and 1g phytic acid evenly. First, argon inert gas is introduced to purge the air in the tube. Then, carbon dioxide gas (flow rate 10ml / min) is introduced to carry out the reduction reaction for 300min. After that, the temperature is raised to 500℃ for pyrolysis for 6h to obtain a porous hard carbon precursor.

[0075] Step S2:

[0076] The porous hard carbon precursor was transferred to a tube furnace, and then borane gas (flow rate 100 ml / min) was introduced by vapor deposition and the temperature was raised to 1000 °C. After deposition for 6 h, a hard carbon composite material formed by boron-doped amorphous carbon coating was obtained.

[0077] Example 3:

[0078] Step S1:

[0079] Mix 100g maltose, 5g sodium peroxide and 5g phytic acid evenly. First, argon inert gas is introduced to purge the air in the tube. Then, carbon dioxide (flow rate 100ml / min) is introduced to carry out the reduction reaction for 30min. After that, the temperature is raised to 700℃ for pyrolysis for 1h to obtain a porous hard carbon precursor.

[0080] Step S2:

[0081] The porous hard carbon precursor was transferred to a tube furnace, and then diborane gas (flow rate 500 ml / min) was introduced by vapor deposition and the temperature was raised to 1400 °C. After deposition for 1 h, a hard carbon composite material formed by boron-doped amorphous carbon coating was obtained.

[0082] Comparative Example 2: Unlike Experimental Example 1, sodium peroxide was not added, but all other steps and conditions were the same as in Example 1.

[0083] Comparative Example 2: Unlike Example 1, phytic acid was not added, but all other steps and conditions were the same as in Example 1.

[0084] Comparative Example 3: Unlike Example 1, no vapor deposition was performed.

[0085] Now, scanning electron microscopy (SEM) tests will be performed on the above experimental example 1:

[0086] Specifically, please refer to Figure 2 The hard carbon composite material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 2 As shown, from Figure 2 As can be seen from the above, the hard carbon material prepared in Example 1 has a granular structure with a uniform size distribution and a particle size of 5-10 μm.

[0087] Furthermore, the physicochemical properties and coin cell performance of the above-mentioned experimental examples 1-3 and comparative examples 1-3 were tested:

[0088] Based on GB / T-24533-2019 "Graphite-based Anode Materials for Lithium-ion Batteries"; the diffusion coefficient of the material was tested by GITT, and the interlayer spacing was tested by X-ray diffraction (XRD). Specifically, the boron-doped amorphous carbon-coated hard carbon composite materials obtained in Examples 1-3 and Comparative Examples 1-3 were assembled into coin cells A1, A2, A3, B1, B2, and B3, respectively.

[0089] Specifically, the preparation process of the coin cell battery is as follows: a binder, a conductive agent, and a solvent are added to the negative electrode material, stirred to form a slurry, coated onto copper foil, and then dried and rolled. The binder used is LA132 binder, the conductive agent is SP, the negative electrode material is the hard carbon material prepared in Examples 1-3 and Comparative Examples 1-2, and the solvent is double-distilled water. The ratio is: negative electrode material: SP: LA132: double-distilled water = 94g: 2g: 4g: 220mL, and a negative electrode sheet is prepared. The electrolyte is NaPF6 / EC+DEC (volume ratio 1:1, concentration 1.1mol / L), the sodium metal sheet is used as the counter electrode, and the separator is made of polyethylene (PE), polypropylene (PP), or polyethylene propylene (PEP) composite membrane. The simulated battery assembly is carried out in an argon-filled glove box, and the electrochemical performance is tested on a battery tester. The charge and discharge voltage range is 0.00V to 2.0V, and the charge and discharge rate is 0.1C. The rate capability (1C / 0.1C) and cycle performance (0.2C / 0.2C, 100 cycles) of its button cells were also tested. The test results are shown in Table 1 below:

[0090] Table 1. Physical and Chemical Properties and Button Cell Test Table

[0091]

[0092]

[0093] As shown in Table 1, compared with Comparative Example 1, the boron-doped amorphous carbon-coated hard carbon composite materials prepared in Examples 1-3 exhibit significantly improved initial discharge capacity, initial efficiency, rate performance, and cycle performance. This is because the reaction of carbon dioxide with sodium peroxide forms a porous structure and achieves phosphorus doping, thereby enhancing the specific capacity of the material. Simultaneously, the boron-doped amorphous carbon in the outer shell enhances the electronic conductivity of the material, improving both rate performance and cycle performance.

[0094] Furthermore, pouch cell battery tests were conducted on the aforementioned experimental examples 1-3 and comparative examples 1-3:

[0095] The hard carbon composite materials from Examples 1-3 and Comparative Examples 1-3 were used as negative electrodes, and negative electrode sheets were prepared by slurry mixing and coating, using layered oxides (NaFe) 1 / 3 Mn 1 / 3 Ni 1 / 3 A 2Ah pouch cell was prepared using O2 as the positive electrode, NaPF6 (solvent EC+DEC, volume ratio 1:1, concentration 1.3mol / L) as the electrolyte, and Celegard 2400 as the separator.

[0096] Cyclic performance test: charge / discharge current 1.0C / 1.0C, voltage range 1-4.0V, number of cycles 500.

[0097] Rate performance testing: Testing the initial cycle DCR and constant current ratio under 2C charging conditions of the pouch battery.

[0098] The test results are shown in Table 2:

[0099] Table 2. Test Table for Soft Pack Batteries

[0100]

[0101] As shown in Table 2, the cycle retention rate, cycle charge, and constant current ratio of Examples 1-3 are significantly better than those of Comparative Examples 1-3. This indicates a significant improvement in cycle performance in Examples 1-3. The reason for this is that the materials in these examples have a high specific surface area, which improves the liquid retention performance and thus the cycle performance. Simultaneously, the boron-doped amorphous carbon coating on the outer shell enhances the fast-charging performance of the material.

[0102] In summary, it can be seen that the hard carbon composite material prepared by the method of preparing hard carbon composite material provided in this invention, when applied to sodium-ion batteries, can improve energy density while solving the problem of poor fast charging performance, and improve fast charging performance in one step.

[0103] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: a hard carbon composite material, which is prepared by the hard carbon composite material preparation method described above.

[0104] To solve the above-mentioned technical problems, the present invention provides another technical solution as follows: a sodium-ion battery, comprising a positive electrode, a positive electrode current collector, an electrolyte layer, a negative electrode current collector, and a negative electrode stacked sequentially; the negative electrode material includes the hard carbon composite material as described above.

[0105] Compared with the prior art, the hard carbon composite material, preparation method, and sodium-ion battery provided by the present invention have the following beneficial effects:

[0106] 1. This invention provides a method for preparing a hard carbon composite material, comprising the following steps: providing a carbon source, sodium peroxide, and phytic acid in a predetermined ratio to mix and obtain a mixture; performing a reduction reaction and a first heating in the mixture to obtain a porous hard carbon precursor; and obtaining the hard carbon composite material by introducing borane gas into the reaction space containing the porous hard carbon precursor and then performing a second heating and deposition reaction. This method solves the problem of poor fast-charging performance of hard carbon materials when used in batteries to improve energy density in existing designs. By adjusting the raw materials and their ratios, a reaction occurs, transforming the carbon source into a porous hard carbon material, and the doping of phosphorus increases the specific capacity of the material. Furthermore, by introducing borane gas, the borane gas is decomposed and deposited onto the porous hard carbon precursor during the second heating, resulting in a boron-doped amorphous carbon coating on its outer shell, reducing surface defects and improving the initial efficiency and fast-charging performance of the porous hard carbon composite material.

[0107] 2. The preset ratio in this embodiment of the invention is: carbon source: sodium peroxide: phytic acid = 100:(1-5):(1-5). This embodiment selectively adjusts the components of the raw materials to ensure that the preset ratio of carbon source, sodium peroxide and phytic acid is fully mixed, and the phosphorus doping provided by phytic acid can improve the specific capacity of the porous hard carbon composite material.

[0108] 3. In this embodiment of the invention, before the reduction reaction in the mixture, an inert gas is introduced into the mixture to create an inert gas environment. By venting air, oxidation is prevented from occurring during pyrolysis and reduction, which helps to obtain the desired porous hard carbon precursor.

[0109] 4. The reduction reaction in the mixture according to the embodiments of the present invention specifically includes: introducing carbon dioxide gas into the inert gas environment containing the mixture to cause the mixture to undergo a reduction reaction to obtain oxygen for pore formation. The oxygen performs a single pore formation on the hard carbon, resulting in porous hard carbon.

[0110] 5. The first heating of the mixture in this embodiment specifically includes: heating the mixture to 500-700℃ for pyrolysis for 1-6 hours to obtain a porous carbon framework. The porous carbon framework forms pores under the action of oxygen to obtain a porous hard carbon precursor. After the first heating, the organic matter and carbon source in the mixture undergo pyrolysis, changing the material structure and forming a porous structure containing many micropores and mesopores. These pores are crucial for sodium storage active sites; that is, the carbon source also undergoes pore formation during pyrolysis. Furthermore, at high temperatures, the carbon source and organic matter decompose and volatilize, leaving behind the carbon framework. In other words, pyrolysis helps remove excess organic matter and impurities, thereby improving the purity of the material.

[0111] 6. In this embodiment of the invention, borane gas is introduced into the reaction space containing the porous hard carbon precursor. The borane gas is either diborane or butorane; the flow rate of the borane gas is 100-500 ml / min. If the flow rate of the borane gas is too high, the formed amorphous carbon may not have enough time to coat the outer surface of the porous hard carbon composite material, thus failing to form a uniform material. This may lead to the formation of pores or surface defects on the surface of the porous hard carbon composite material, reducing its true density.

[0112] 7. The embodiment of the present invention, which involves introducing borane gas into the porous hard carbon precursor and subjecting it to a second heating and deposition reaction, specifically includes: heating the porous hard carbon precursor to 1000-1400°C under borane gas and obtaining a hard carbon composite material through vapor phase deposition for 1-6 hours. Depositing carbon borides (borane) on the surface of the porous hard carbon precursor can reduce surface defects, improve initial efficiency, and enhance the electronic conductivity of the material. Furthermore, boron doping exhibits good compatibility with the electrolyte, improving cycle life and high-temperature storage performance.

[0113] 8. The carbon source in this embodiment of the invention is any one of xylose, glucose, sucrose, trehalose, lactose, maltose, chitosan, and mannan. The wide availability of carbon sources makes the raw materials for preparing hard carbon composite materials using the method in this embodiment readily available and economically viable.

[0114] 9. The present invention also provides a hard carbon composite material, which has the same beneficial effects as the preparation method of the above-mentioned hard carbon composite material, and will not be described in detail here.

[0115] 10. This invention also provides a sodium-ion battery that has the same beneficial effects as the aforementioned hard carbon composite material, which will not be described in detail here.

[0116] The foregoing has provided a detailed description of a hard carbon composite material, its preparation method, and a sodium-ion battery disclosed in the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon composite material, wherein the prepared hard carbon composite material is used in a sodium-ion battery, characterized in that: Includes the following steps: A carbon source, sodium peroxide, and phytic acid are provided to be mixed to obtain a mixture, wherein the mass ratio of carbon source, sodium peroxide, and phytic acid is carbon source: sodium peroxide: phytic acid = 100: (1~5): (1~5); An inert gas is introduced into the mixture to make the mixture in an inert gas environment. Carbon dioxide gas is introduced into the inert gas environment of the mixture to make the mixture undergo a reduction reaction to form a first pore. The mixture is then heated to 500-700℃ for pyrolysis for 1-6 hours to form a second pore, so as to obtain a porous hard carbon precursor. Phytic acid is used to provide phosphorus doping into the porous hard carbon precursor to form -POC chemical bonds. Hard carbon composite materials are obtained by introducing borane gas into the reaction space containing the porous hard carbon precursor, heating it a second time to 1000-1400℃ under borane gas, and then performing vapor deposition for 1-6 hours.

2. The method for preparing hard carbon composite material as described in claim 1, characterized in that: By introducing borane gas into the reaction space containing the porous hard carbon precursor, including: The borane gas is one of diborane or butorane; The flow rate of the borane gas is 100-500 ml / min.

3. The method for preparing hard carbon composite material as described in claim 1, characterized in that: The carbon source is any one of xylose, glucose, sucrose, trehalose, lactose, maltose, chitosan, and mannan.

4. A hard carbon composite material, characterized in that: It is prepared by the method for preparing hard carbon composite material as described in any one of claims 1-3.

5. A sodium-ion battery, characterized in that: The method includes a positive electrode, a positive electrode current collector, an electrolyte layer, a negative electrode current collector, and a negative electrode stacked in sequence; the negative electrode material includes the hard carbon composite material as described in claim 4.

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