Sodium-ion battery negative electrode material and preparation method and application thereof

Abstract

The application provides a kind of sodium ion battery negative electrode material and its preparation method and application.The negative electrode material includes black phosphorus, carbon carrier and sodium salt;The morphology of the carbon carrier is the morphology of LDH template;The black phosphorus and sodium salt are compounded in the carbon carrier;The carbon carrier is also doped with double metal ions, and the double metal is the double metal element in the LDH template.The negative electrode material provided by the application has multiple bonding effects between the carbon carrier, phosphoric acid, double metal ions and sodium salt, which ensures the stability of the material interface and effectively inhibits the volume expansion of black phosphorus during the cycle process;And the interaction between each substance, synergistic effect, makes the negative electrode material have excellent cycle stability and high reversible capacity, and also has good rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a sodium-ion battery anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries boast advantages such as high energy density, long cycle life, and low pollution, making them dominant in portable electronic devices and power equipment. However, the scarcity and high price of lithium resources will limit the cost and application scope of lithium-ion batteries in the foreseeable future. Meanwhile, the high natural abundance and low price of sodium resources make sodium-ion batteries the most promising alternative to lithium batteries in large-scale energy storage and low-cost equipment.

[0003] Black phosphorus is the most stable of the three isoforms of phosphorus, and it can interconvert with white phosphorus and red phosphorus under certain conditions. Compared to red phosphorus (10...), black phosphorus... -12 S / m), with high carrier mobility (10 2 Black phosphorus exhibits high theoretical sodium storage capacity (2596 mAh / g), good thermal stability, and high anisotropy. As a negative electrode material for secondary batteries, its excellent high charge mobility gives it unique electronic properties as an energy storage electrode material.

[0004] Although the conductivity of black phosphorus meets the basic requirements of electrode materials, it also suffers from significant volume expansion after sodium storage, and its two-dimensional structure is difficult to restore upon sodium removal. Therefore, black phosphorus still needs to be combined with other materials to improve material utilization and cycle stability. Carbon materials are inexpensive, readily available, have good conductivity, rich structures, and great potential for surface modification, making them ideal for composite modification of black phosphorus. For example, using highly conductive carbon materials for coating is possible; however, the usual coating method involves mixing the carbon source and black phosphorus material through ball milling, followed by drying the dispersant and then high-temperature carbonization. For instance, CN108336340A discloses a method for preparing carbon-coated black phosphorus anode material for sodium-ion batteries. Using black phosphorus material as a substrate, a low-molecular-weight A-type carbon source and a high-molecular-weight B-type carbon source are combined, and the two types of carbon sources are uniformly mixed and coated onto the surface of black phosphorus nanosheets via a phase transfer method. After carbonization, a carbon-coated black phosphorus anode material for sodium-ion batteries is obtained. However, this method cannot guarantee that the carbon coating layer is evenly coated on the surface of black phosphorus, and its structure is too simple, which causes the carbon outer layer to be broken when the black phosphorus expands. Therefore, it cannot provide a long-term improvement effect on the capacity of black phosphorus.

[0005] Therefore, how to improve the specific capacity of black phosphorus-based anode materials while ensuring the cycle stability of the battery is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a sodium-ion battery anode material, its preparation method, and its applications. The anode material provided by this invention exhibits multiple bonding interactions between the carbon support, phosphoric acid, bimetallic ions, and sodium salt, ensuring the stability of the material interface and effectively suppressing the volume expansion of black phosphorus during cycling. Furthermore, the interactions and synergistic cooperation among these substances result in excellent cycle stability and high reversible capacity, along with good rate performance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a sodium-ion battery anode material, the anode material comprising black phosphorus, a carbon support, and a sodium salt; the morphology of the carbon support is the morphology of an LDH template; the black phosphorus and the sodium salt are composited in the carbon support; the carbon support is also doped with bimetallic ions, the bimetal being a bimetallic element in the LDH template.

[0009] In the negative electrode material provided by the present invention, the morphology of the carbon support is the same as that of the LDH template, that is, the carbon layer structure is obtained by using LDH as a template, thereby preserving the morphology of LDH. Moreover, black phosphorus and sodium salt are not only located on the surface of the carbon support, but also inside the carbon support support structure; and bimetallic ions are doped in the carbon support.

[0010] In this invention, the metal ions and sodium salt in black phosphorus and the carbon support are bonded to each other, forming CP, MP, and MOP bonds. The inter-elemental bonding ensures the stability of the material interface, reduces the volume expansion of black phosphorus during cycling, provides more active sites, and improves the electrode specific capacity, thereby improving the electron transfer rate and the utilization rate of the active material. Furthermore, the introduction of bimetals also enhances the overall electronic and ionic conductivity of the material, accelerates the reaction kinetics of the anode material, and the lattice change can alleviate the internal stress during cycling. The interaction of metal covalent bonds and van der Waals forces provides strong interaction between different components, ensuring the structural stability and long-cycle performance of this sodium-loving black phosphorus-metal-carbon composite material. The pre-doping of sodium salt also helps to accelerate the adsorption and deintercalation of sodium ions by the anode material during cycling. The LDH-morphological carbon support has a larger interlayer spacing, which is more suitable for the deintercalation of sodium ions in carbon. The in-situ doped metal ions also benefit the cycling stability of the carbon material. As a result, this anode material exhibits excellent electrochemical performance in sodium-ion batteries, with superior cycling stability, high reversible capacity, and good rate performance.

[0011] In this invention, if the morphology of the carbon support is that of conventional carbon particles, high rate and high capacity performance cannot be achieved; and if it does not conform to sodium salt, rapid ion transport cannot be achieved.

[0012] Preferably, the morphology of the carbon support includes a lamellar morphology and / or a petal-like morphology, with a petal-like morphology being more preferred.

[0013] The carbon support morphology provided by this invention, with its sheet-like and petal-like morphologies, is conducive to rapid ion transport and adsorption of active sites; and the petal-like morphology is more conducive to obtaining more active sites.

[0014] Preferably, the lamellar and petal-like morphologies have hollow structures, and the hollow structures contain black phosphorus, sodium salts, and bimetallic ions.

[0015] In this invention, the carbon support microstructure has a hollow structure. The black phosphorus, sodium salt and bimetallic ions in the hollow structure not only improve the electrochemical performance, but also play a supporting role, stabilizing the morphology of the carbon support and preventing its structural collapse.

[0016] Preferably, the mass percentage of the black phosphorus in the negative electrode material is 30% to 70%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0017] Preferably, the mass percentage of the carbon support in the negative electrode material is 30% to 70%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%.

[0018] In a second aspect, the present invention provides a method for preparing a sodium-ion battery anode material as described in the first aspect, the method comprising the following steps:

[0019] The LDH template was carbon-coated to obtain LDH-C;

[0020] LDH-C, black phosphorus, and sodium salt are mixed, and the template is removed to obtain the sodium-ion battery anode material.

[0021] The preparation method provided by this invention involves coating an LDH template with a carbon layer. After template removal, the original morphology of the LDH template is retained. During template removal, black phosphorus and sodium salt can enter the hollow structure after template removal, achieving the embedding of sodium salt and black phosphorus. On the one hand, this effectively suppresses the volume expansion of black phosphorus. On the other hand, the sodium salt forms a bond with the bimetallic compound formed by black phosphorus, carbon support, and LDH template, thereby improving the structural stability of the anode material and exposing more active sites. This achieves effective composite of black phosphorus and carbon and greatly suppresses the volume expansion of black phosphorus. As a result, the cycle performance, capacity, and rate performance of the anode material are improved. Moreover, the preparation method is simple and efficient, requiring no complex processing.

[0022] Preferably, the median particle size of the LDH template is ≤10μm, such as 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm.

[0023] In this invention, if the median particle size of the LDH template is too large, exceeding 10 μm, it will lead to a decrease in specific surface area, a reduction in active sites, and a decrease in rate performance.

[0024] Preferably, the bimetallic element in the LDH template includes any two of magnesium, aluminum, nickel, cobalt, iron, or zinc, with nickel and cobalt being the most preferred.

[0025] In this invention, nickel and cobalt are selected as bimetallic elements for LDH templates, which can better obtain petal-shaped LDH templates with high specific surface area.

[0026] Preferably, the method for preparing the LDH template includes: mixing a first metal salt, a second metal salt, an alkaline solution, and a solvent, reacting the mixture, and then drying it under vacuum to obtain the LDH template.

[0027] In this invention, no special limitation is made on the type of alkaline solution. Any type of alkaline solution used for preparing LDH that can be known to those skilled in the art within a reasonable range is applicable to this invention, including but not limited to ammonia, 0.5-5 mol / L NaOH or KOH or urea.

[0028] Preferably, the mass ratio of the first metal salt to the second metal salt is 1:2 to 3:1, for example, 1:2, 1:1, 2:1 or 3:1.

[0029] Preferably, the total mass ratio of the first metal salt and the second metal salt to the mass ratio of the alkaline solution is 1:(4-12), for example, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11 or 1:12, etc.

[0030] Preferably, the reaction includes a hydrothermal reaction, an oil bath heating reaction, or a microwave reaction.

[0031] Optionally, during the preparation of the LDH template, when using a hydrothermal reaction, the hydrothermal temperature is 120–180℃, such as 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, or 180℃, and the hydrothermal time is 6–18h, such as 6h, 8h, 10h, 12h, 15h, or 18h.

[0032] When the reaction is heated in an oil bath, the reaction temperature is 60-90℃, such as 60℃, 70℃, 80℃ or 90℃, and the reaction time is 12-24h, such as 12h, 15h, 18h, 20h or 24h.

[0033] Microwave reactions are continuous, and the specific parameters of the microwaves can be adjusted adaptively according to different equipment.

[0034] It should be noted that the LDH template can be prepared by the preparation method provided above. As for the specific reaction and the control of reaction time and temperature, those skilled in the art can make adaptive adjustments according to actual needs. Within a reasonable range, all LDH template preparation methods known to those skilled in the art are applicable to this invention. At the same time, if the LDH template is available for purchase, commercially available LDH templates can also be used directly.

[0035] Preferably, the carbon coating method includes any one or a combination of at least two of the following: gas phase carbon coating, liquid phase carbon coating, or solid phase carbon coating, with gas phase carbon coating being the preferred method.

[0036] Carbon coating is a conventional technique used by those skilled in the art, and specific carbon coating methods are also conventional choices for those skilled in the art. Regarding the types of carbon sources, preparation processes, preparation conditions, and parameters under different preparation methods, those skilled in the art can make adaptive adjustments according to specific needs.

[0037] Optionally, when using the gas-phase carbon coating method, the specific process, exemplarily, includes:

[0038] LDH carbon coating is performed by chemical vapor deposition (CVD). LDH template powder is heated to 800–1200°C in a tube furnace. Hydrogen / inert gas is introduced for protection throughout the heating process. After reaching the predetermined temperature, a carbon source is introduced to coat the LDH to obtain LDH-C.

[0039] Optionally, during the CVD deposition process, the heating rate is 1–10 °C / min, the inert gas is one or a mixture of nitrogen, helium, neon, and argon, and the gas flow rate is 50–200 sccm; the hydrogen flow rate is 5–50 sccm; the carbon source includes at least one of methane, ethane, ethylene, and acetylene, and the carbon source gas flow rate is 5–100 sccm during CVD.

[0040] Optionally, when liquid-phase carbon coating is used, the specific preparation process, exemplarily, includes:

[0041] LDH powder and carbon source powder are mixed and stirred evenly in the liquid phase, dried, and heated to 600-1300℃ in a tube furnace and held for 2-6 hours. The entire process is completed under the protection of inert gas and hydrogen.

[0042] Optionally, in the liquid phase process, the heating rate is 1–10 °C / min, the inert gas is one or a mixture of nitrogen, helium, neon, and argon, the gas flow rate is 50–200 sccm, and the hydrogen flow rate is 5–50 sccm. When natural asphalt, coal tar pitch, petroleum asphalt, melamine, and melamine analogues are selected as carbon sources, hydrocarbon solvents such as sulfur dioxide, ethanol, carbon tetrachloride, and N,N-dimethylformamide are selected. When water-soluble carbon sources such as glucose, ethylenediaminetetraacetic acid, and polyvinyl alcohol are selected, deionized water is used for thorough dissolution.

[0043] Preferably, the thickness of the carbon layer after carbon coating is 0.1 to 2 μm, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm.

[0044] In this invention, if the carbon layer is too thick, it will affect the ion transport rate; if it is too thin, it will lead to instability in the material structure.

[0045] Preferably, the sodium salt comprises any one or a combination of at least two of sodium titanate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium dioxolaneborate, sodium perchlorate, sodium nitrate, or sodium chloride.

[0046] Preferably, the amount of sodium salt added is 1% to 10% of the total mass of the mixed substance, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0047] Preferably, the method for removing the template includes: mixing the mixed substance with an alkaline solution again, and then carrying out a second hydrothermal reaction and acid leaching.

[0048] The present invention performs a second hydrothermal reaction, which, on the one hand, is combined with the subsequent acid leaching to remove the LDH template; on the other hand, through the second hydrothermal reaction, the black phosphorus and sodium salt mixed in the early stage can also enter the internal structure of the carbon layer. Under high temperature and high pressure, the black phosphorus / carbon / doped metal react fully and form bonds.

[0049] Preferably, the concentration of the alkaline solution is 5 to 15 mol / L, such as 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, 11 mol / L, 12 mol / L, 13 mol / L, 14 mol / L, or 15 mol / L.

[0050] Preferably, the temperature of the hydrothermal reaction is 100-180°C, such as 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C.

[0051] Preferably, the hydrothermal reaction time is 6 to 18 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, or 18 hours.

[0052] Preferably, the substance after the hydrothermal reaction is washed with water before acid leaching.

[0053] Preferably, the concentration of acid in the acid leaching is 1 to 10 mol / L, such as 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, or 10 mol / L.

[0054] Preferably, the acid leaching time is 12 to 48 hours, such as 12 hours, 15 hours, 18 hours, 20 hours, 23 hours, 25 hours, 28 hours, 30 hours, 33 hours, 35 hours, 38 hours, 40 hours, 43 hours, 45 hours, or 48 hours.

[0055] Preferably, the acid leaching is followed by washing and drying.

[0056] As a preferred technical solution, the preparation method includes the following steps:

[0057] LDH templates with a median particle size ≤10μm were carbon-coated to obtain LDH-C with a carbon layer thickness of 0.1~2μm;

[0058] LDH-C, black phosphorus, and sodium salt are mixed, and the mixture is then mixed again with an alkaline solution. The mixture is then subjected to a hydrothermal reaction at 100–180°C for 6–18 hours, followed by water washing, acid leaching for 12–48 hours, washing, and drying to obtain the sodium-ion battery anode material.

[0059] Thirdly, the present invention also provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery negative electrode material as described in the first aspect.

[0060] The negative electrode material provided by this invention can be used as a negative electrode active material in the preparation of negative electrode sheets. It can be used alone as a negative electrode active material, or it can be mixed and used in combination with other substances besides the negative electrode material provided by this invention. Those skilled in the art can make adaptive choices according to actual needs.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] (1) In this invention, the metal ions and sodium salt in black phosphorus and carbon support are bonded to each other to form CP, MP, MOP bond relationships. The mutual bonding between elements ensures the stability of the material interface, reduces the volume expansion of black phosphorus during cycling, provides more active sites, and improves the specific capacity of the electrode, thereby improving the electron transfer rate and the utilization rate of the active material. The introduction of bimetal ensures the structural stability and long-cycle performance of the sodium-loving black phosphorus-metal-carbon anode material. The early doping of sodium salt is also beneficial to accelerating the adsorption and deintercalation of sodium ions by the anode material during cycling. The LDH-shaped carbon support has a larger interlayer spacing, which is more suitable for the deintercalation of sodium ions in carbon. The in-situ doped metal ions are also beneficial to the cycle stability of the carbon material. Thus, the anode material exhibits excellent electrochemical performance in sodium-ion batteries, with superior cycle stability, high reversible capacity, and good rate performance.

[0063] (2) The preparation method provided by the present invention involves a carbon layer coating the surface of an LDH template. After template removal, the original morphology of the LDH template is retained. During the template removal process, black phosphorus and sodium salt can enter the hollow structure after template removal, realizing the embedding of sodium salt and black phosphorus. On the one hand, the volume expansion of black phosphorus is effectively suppressed. On the other hand, the sodium salt forms a bond with the bimetallic compound formed by black phosphorus, carbon support and LDH template, thereby improving the structural stability of the anode material and exposing more active sites. This achieves effective composite of black phosphorus and carbon and greatly suppresses the volume expansion of black phosphorus. This improves the cycle performance, capacity and rate performance of the anode material. Moreover, the preparation method is simple and efficient, without the need for complicated processing. Attached Figure Description

[0064] Figure 1 The image shown is a SEM image of LDH-C-1 provided in Example 1.

[0065] Figure 2 The image is a SEM image of C-BP-2 provided in Example 2.

[0066] Figure 3 The image shows a SEM image of LDH-C-3 provided in Example 3. Detailed Implementation

[0067] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0068] In one specific embodiment, the present invention provides a process for preparing an LDH template, the process comprising:

[0069] (1) LDH-1:

[0070] Weigh 15g magnesium nitrate, 10g aluminum nitrate, and 20g urea, add them to a mixed solution of 160g ethanol / 40g deionized water, and stir continuously at 50℃ until dissolved. Transfer the solution to a hydrothermal reactor and react at 120℃ in an oven for 24h. After the reaction is complete, filter repeatedly, wash, and freeze dry under vacuum to obtain LDH-1 with a median particle size of 5μm.

[0071] (2) LDH-2:

[0072] Weigh 14.35g of nickel nitrate, 19.87g of cobalt nitrate, and 23.52g of urea, and add them to a mixed solution of 80g of ethylene glycol and 120g of deionized water. Stir continuously at 60°C until dissolved. Transfer the solution to a hydrothermal reactor and react at 160°C in an oven for 6 hours. After the reaction is complete, filter repeatedly, wash, and freeze dry under vacuum to obtain LDH-2 with a median particle size of 8μm.

[0073] The following examples and comparative examples all use the LDH templates provided above (LDH templates with different particle sizes were obtained by adaptively adjusting the reaction conditions).

[0074] Example 1

[0075] This embodiment provides a sodium-ion battery anode material, which includes black phosphorus, a carbon support, and a sodium salt; the carbon support has a layered morphology; the black phosphorus and sodium salt are composited in the carbon support; the carbon support is also doped with bimetallic ions (magnesium and aluminum), and the bimetallic ions are bimetallic elements in the LDH template.

[0076] The sodium-ion battery is prepared as follows, based on the preparation method provided in the above specific embodiments:

[0077] LDH-1 was placed in a ceramic crucible and transferred to a single-zone tube furnace. The temperature was increased at a rate of 5 °C / min until it reached 1050 °C, while maintaining a protective atmosphere of 160 sccm argon and 20 sccm hydrogen. After reaching 1050 °C, the temperature was held, and 50 sccm of methane was introduced for 30 min. The methane was then stopped, and the mixture was allowed to cool naturally to obtain the desired product. Figure 1 The LDH-C-1 shown has a carbon layer thickness of 150 nm.

[0078] In an inert gas glove box, 16g of LDH-C-1, 5g of black phosphorus, and 1g of NaFSI were weighed and placed in an agate ball mill jar. 120g of agate beads of different sizes were added, and the mixture was dry-milled for 4 hours. The ground powder was sieved and placed in a hydrothermal reactor. 100mL of 8mol / L NaOH solution was added, and the mixture was hydrothermally heated at 120℃ for 12 hours. The mixture was then filtered and repeatedly washed until the pH was <9. The powder was then transferred to 50mL of 3mol / L nitric acid and soaked for 12 hours. The mixture was then filtered and repeatedly washed until the pH was >6. After freeze-drying, the sodium-ion battery anode material (C-BP-1) was obtained.

[0079] Example 2

[0080] This embodiment provides a sodium-ion battery anode material, which includes black phosphorus, a carbon support, and a sodium salt; the carbon support has a layered morphology; the black phosphorus and sodium salt are composited in the carbon support; the carbon support is also doped with bimetallic ions (magnesium and aluminum), and the bimetallic ions are bimetallic elements in the LDH template.

[0081] The sodium-ion battery is prepared as follows, based on the preparation method provided in the above specific embodiments:

[0082] 5g of LDH-1 was placed in a ceramic crucible. 10g of glucose was weighed and dissolved in 20mL of deionized water. After complete dissolution, the solution was poured into the ceramic crucible. The crucible was placed on a 100℃ heating platform and stirred continuously to volatilize, resulting in LDH-glucose sol. The solution was then transferred to a single-temperature zone tube furnace. The heating rate was 8℃ / min. The temperature was increased to 400℃ and held for 1 hour. The temperature was then increased to 800℃ and held for 2 hours. During this period, 160sccm of argon and 20sccm of hydrogen were used for protection. After natural cooling, LDH-C-2 (carbon layer thickness of 1.2μm) was obtained.

[0083] In an inert gas glove box, 26g of LDH-C-, 8g of black phosphorus, and 1g of NaCl were weighed and placed in an agate ball mill jar. 150g of agate beads of different sizes were added, and the mixture was dry-milled for 4 hours. The ground powder was sieved and placed in a hydrothermal reactor. 100mL of 10mol / L NaOH solution was added, and the mixture was hydrothermally heated at 180℃ for 6 hours. After filtration, the powder was repeatedly washed until pH < 9. The powder was then transferred to 50mL of 10mol / L nitric acid and soaked for 12 hours. After filtration and repeated washing until pH > 6, the mixture was freeze-dried to obtain the sodium-ion battery anode material (e.g., ...). Figure 2 (as shown in C-BP-2).

[0084] Example 3

[0085] This embodiment provides a sodium-ion battery anode material, which includes black phosphorus, a carbon support, and a sodium salt; the carbon support has a petal-like morphology; the black phosphorus and sodium salt are composited in the carbon support; the carbon support is also doped with bimetallic ions (nickel and cobalt), and the bimetallic ions are bimetallic elements in the LDH template.

[0086] The sodium-ion battery is prepared as follows, based on the preparation method provided in the above specific embodiments:

[0087] 5g of LDH-2 was placed in a ceramic crucible and transferred to a single-zone tube furnace. The temperature was increased at a rate of 5℃ / min until it reached 1100℃, while maintaining a protective atmosphere of 160 sccm argon and 20 sccm hydrogen. After reaching 1050℃, the temperature was maintained, and ethylene was introduced at 20 sccm for 60 min. The ethylene was then stopped, and the furnace was allowed to cool naturally to obtain the desired product. Figure 3 The LDH-C-3 shown has a carbon layer thickness of 200 nm.

[0088] In an inert gas glove box, 38g of LDH-C-3, 12g of black phosphorus, and 1.5g of NaNO3 were weighed and placed in an agate ball mill jar. 215g of agate beads of different sizes were added, and the mixture was dry-milled for 4 hours. The ground powder was sieved and placed in a hydrothermal reactor. 100mL of 10mol / L NaOH solution was added, and the mixture was hydrothermally heated at 120℃ for 12 hours. After filtration, the powder was repeatedly washed until pH < 9. The powder was then transferred to 50mL of 4mol / L nitric acid and soaked for 12 hours. After filtration and repeated washing until pH > 6, the powder was freeze-dried to obtain the sodium-ion battery anode material (C-BP-3).

[0089] Example 4

[0090] The difference between this embodiment and embodiment 3 is that the median particle size of the LDH template in this embodiment is 10 μm, and the hydrothermal time is controlled to 10 h during the preparation of the LDH template, and the CVD time is extended so that the thickness of the carbon coating layer of the material is the same as that in embodiment 3, which is 200 nm.

[0091] The remaining preparation methods and parameters are consistent with those in Example 3.

[0092] Example 5

[0093] The difference between this embodiment and embodiment 3 is that the median particle size of the LDH template in this embodiment is 15 μm, and the hydrothermal time is controlled to 24 h during the preparation of the LDH template, and the CVD time is extended so that the thickness of the carbon coating layer of the material is the same as that in embodiment 3, which is 200 nm.

[0094] The remaining preparation methods and parameters are consistent with those in Example 3.

[0095] Example 6

[0096] The difference between this embodiment and Embodiment 2 is that the thickness of the carbon layer in the LDH-C in this embodiment is approximately 2 μm; and the amount of glucose added is controlled during the preparation of the carbon coating.

[0097] The remaining preparation methods and parameters are consistent with those in Example 2.

[0098] Example 7

[0099] The difference between this embodiment and embodiment 3 is that the thickness of the carbon layer in the LDH-C in this embodiment is 100 nm; and the CVD time is controlled to 15 min during the carbon coating preparation process.

[0100] The remaining preparation methods and parameters are consistent with those in Example 3.

[0101] Example 8

[0102] The difference between this embodiment and Embodiment 1 is that the methane is introduced for 60 minutes in this embodiment, and the thickness of the carbon layer after carbon coating is 320 nm.

[0103] The remaining preparation methods and parameters are consistent with those in Example 1.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 3 is that the negative electrode material provided in this comparative example does not contain sodium salt; and no NaNO3 is added in the preparation method.

[0106] The remaining preparation methods and parameters are consistent with those in Example 3.

[0107] Comparative Example 2

[0108] This comparative example provides a negative electrode material, which includes commercial hard carbon negative electrode material and black phosphorus;

[0109] The preparation method of the negative electrode material is as follows:

[0110] Commercial sodium-ionized hard carbon mixed with black phosphorus was ball-milled at a 1:1 ratio and subjected to a hydrothermal reaction (hydrothermal at 120°C for 12 hours in an oven) to obtain CC-BP.

[0111] Comparative Example 3

[0112] This comparative example provides an anode material comprising commercially available hard carbon anode material, black phosphorus, and NaFSI.

[0113] The preparation method of the negative electrode material is as follows:

[0114] Commercial hard carbon anode material, black phosphorus, and NaFSI were ball-milled in a mass ratio of 6:5:1. The ground powder was sieved, placed in a hydrothermal reactor, and heated in an oven at 120°C for 12 hours. After washing and drying, the anode material was obtained.

[0115] Figure 1 The SEM image of LDH-C-1 provided in Example 1 is shown. Figure 1 It can be seen that the LDH template provided in Example 1 has a lamellar structure, and thus the LDH-C-1 after carbon coating also has a lamellar structure.

[0116] Figure 2 SEM images of C-BP-2 provided in Example 2, from Figure 2 It can be seen that when using liquid phase carbon coating method for LDH coating, the coating effect is poor and the uniformity is poor.

[0117] Figure 3 The SEM image of LDH-C-3 provided in Example 3 is from... Figure 3 It can be seen that NiCo-LDH, when assembled into a petal shape under a certain water-to-alcohol ratio, and uniformly coated with a carbon layer, has a morphology with a larger specific surface area and better active sites, resulting in a more superior electrochemical performance of the obtained anode material.

[0118] The negative electrode materials provided in Examples 1-8 and Comparative Examples 1-3 were used to prepare negative electrode sheets, and coin cells were assembled for electrochemical performance testing and analysis, as detailed below:

[0119] S1: Prepare the negative electrode sheet.

[0120] The negative electrode materials provided in Examples 1-8 and Comparative Examples 1-3 were used as negative electrode active materials. The three substances were weighed according to the mass ratio of active material: conductive agent (Super-P) and sodium alginate (CMC) = 8:1:1, mixed in the solvent NMP, and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was coated on copper foil and vacuum dried at 120°C for 12 hours to obtain a negative electrode sheet.

[0121] S2: Assemble the battery

[0122] Using a sodium metal sheet as the counter electrode, and with an electrolyte of 1 mol / L NaPF6 (PC:DMC = 4:6 vol%) + 2% VC and a glass fiber separator, CR2016 coin cells were assembled in a glove box filled with Ar gas, where the contents of H2O and O2 were kept below 0.1 ppm.

[0123] S3: Electrochemical Performance Testing and Analysis

[0124] Electrochemical performance was tested at room temperature using a LAND CT2001A battery testing system. The charge / discharge capacity of each coin cell was tested at 0.05C / 0.05C, with a test voltage range of 0.001–2V. Rate performance was tested at 1C / 0.2C, and cycle performance was tested at 0.2C / 0.2C. The test results are listed in Table 1 below.

[0125] Table 1

[0126]

[0127]

[0128] The thickness and thickness change rate of the electrode before and after cycling were tested using scanning electron microscopy. The specific test results are shown in Table 2.

[0129] Table 2

[0130]

[0131] Depend on Figures 1-3 From Tables 1 and 2, we can obtain:

[0132] The data results from Examples 1 and 3 show that when the carbon support has a petal-like morphology, the anode material with this morphology has a large specific surface area, better active sites, and superior electrochemical performance.

[0133] The data from Examples 3 and 4-5 show that when the particle size of the LDH template is too large, exceeding 10 μm, the ionic conductivity decreases, thus affecting the rate capability and cycling stability.

[0134] The data results from Examples 6 and 7, and Examples 1 and 8, show that if the carbon layer thickness after carbon coating is too thin, the structural stability deteriorates, leading to a decrease in cycle stability; while if the thickness is too thick, it will affect ionic conductivity and deteriorate rate performance.

[0135] The data from Example 3 and Comparative Example 1 show that without sodium salt composite in the negative electrode material, the specific capacity, ionic conductivity, and rate performance of the material are reduced.

[0136] The data results from Examples 1-3 and Comparative Examples 2-3 show that only by using the anode material provided by the present invention can high specific capacity, high rate capability, and high cycle stability be achieved. However, the conventional combination of hard carbon anode material and black phosphorus, even with the addition of sodium salt, cannot solve the volume expansion problem during the black phosphorus cycle, resulting in poor cycle stability.

[0137] In summary, in this invention, the metal ions and sodium salts in black phosphorus and the carbon support are bonded to each other, forming CP, MP, and MOP bonds. The inter-elemental bonding ensures the stability of the material interface, reduces the volume expansion of black phosphorus during cycling, provides more active sites, and improves the electrode specific capacity, thereby improving the electron transfer rate and the utilization rate of the active material. Furthermore, the introduction of bimetals ensures the structural stability and long-cycle performance of this sodium-loving black phosphorus-metal-carbon anode material. The pre-doping of sodium salt also helps to accelerate the adsorption and deintercalation of sodium ions by the anode material during cycling. The LDH-shaped carbon support has a larger interlayer spacing, which is more suitable for the deintercalation of sodium ions in carbon. The in-situ doping of metal ions also benefits the cycle stability of the carbon material. As a result, this anode material exhibits excellent electrochemical performance in sodium-ion batteries, with superior cycle stability, high reversible capacity, and good rate performance.

[0138] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A sodium-ion battery anode material, characterized in that, The negative electrode material includes black phosphorus, a carbon support, and a sodium salt; the morphology of the carbon support is the same as that of the LDH template; the black phosphorus and sodium salt are composited in the carbon support; the carbon support is also doped with bimetallic ions, and the bimetallic element is a bimetallic element in the LDH template; the bimetallic element in the LDH template includes any combination of two of magnesium, aluminum, nickel, cobalt, iron, or zinc. The morphology of the carbon support includes a lamellar morphology and / or a petal-like morphology; the lamellar and petal structures in the lamellar and petal-like morphologies have hollow structures, and the hollow structures contain black phosphorus, sodium salts and bimetallic ions; The sodium-ion battery anode material is prepared by the following method, which includes the following steps: LDH templates with a median particle size ≤10μm were carbon-coated to obtain LDH-C with a carbon layer thickness of 0.1~2μm; LDH-C, black phosphorus, and sodium salt are mixed, and the mixture is then mixed again with an alkaline solution. The mixture is then subjected to a hydrothermal reaction at 100-180°C for 6-18 hours, followed by water washing, acid leaching for 12-48 hours, washing, and drying to obtain the sodium-ion battery anode material.

2. The sodium-ion battery anode material according to claim 1, characterized in that, The carbon support has a petal-like morphology.

3. The sodium-ion battery anode material according to claim 1, characterized in that, The mass percentage of black phosphorus in the anode material is 30-70%.

4. The sodium-ion battery anode material according to claim 1, characterized in that, The mass of the carbon support accounts for 30-70% of the mass of the anode material.

5. A method for preparing a sodium-ion battery negative electrode material as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: LDH templates with a median particle size ≤10μm were carbon-coated to obtain LDH-C with a carbon layer thickness of 0.1~2μm; LDH-C, black phosphorus, and sodium salt are mixed, and the mixture is then mixed again with an alkaline solution. The mixture is then subjected to a hydrothermal reaction at 100-180°C for 6-18 hours, followed by water washing, acid leaching for 12-48 hours, washing, and drying to obtain the sodium-ion battery anode material.

6. The preparation method according to claim 5, characterized in that, The bimetallic elements in the LDH template are nickel and cobalt.

7. The preparation method according to claim 5, characterized in that, The method for preparing the LDH template includes: mixing a first metal salt, a second metal salt, an alkaline solution, and a solvent, reacting the mixture, and then drying it under vacuum to obtain the LDH template.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the first metal salt to the second metal salt is 1:2 to 3:

1.

9. The preparation method according to claim 7, characterized in that, The total mass ratio of the first metal salt and the second metal salt to the mass ratio of the alkaline solution is 1:(4~12).

10. The preparation method according to claim 7, characterized in that, The reaction includes hydrothermal reaction, oil bath heating reaction, or microwave reaction.

11. The preparation method according to claim 5, characterized in that, The carbon coating method includes any one or a combination of at least two of the following: gas phase carbon coating, liquid phase carbon coating, or solid phase carbon coating.

12. The preparation method according to claim 11, characterized in that, The carbon coating method is a gas-phase carbon coating method.

13. The preparation method according to claim 5, characterized in that, The sodium salt includes any one or a combination of at least two of sodium titanate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium dioxolaneborate, sodium perchlorate, sodium nitrate, or sodium chloride.

14. The preparation method according to claim 5, characterized in that, The amount of sodium salt added is 1 to 10% of the total mass of the mixed substance.

15. The preparation method according to claim 5, characterized in that, The concentration of the alkaline solution is 5~15 mol / L.

16. The preparation method according to claim 5, characterized in that, The concentration of acid in the pickling process is 1~10 mol / L.

17. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery negative electrode material as described in any one of claims 1-4.

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