Sodium ion battery negative electrode material, preparation method thereof and sodium ion battery

Abstract

The application provides a kind of sodium ion battery negative material and its preparation method and sodium ion battery, belong to secondary battery technical field.The preparation method takes loquat skin as carrier, iron salt and nickel salt as raw material, synthesizes iron salt / nickel salt / loquat skin composite by using hydrothermal method, then obtains iron / nickel / biomass carbon precursor after washing, freeze-drying, then carbonizes through two-stage calcination, loquat skin carbonizes into graphite carbon, graphite carbon reduces iron salt and nickel salt at high temperature to form iron and nickel, obtains iron / nickel / biomass carbon, then uses chemical vapor deposition technology to generate carbon nanotubes, finally obtains phosphide / biomass carbon / carbon nanotube composite material through sealed tube gas phase phosphorization.The composite material constructed as sodium ion battery negative material has excellent capacity, rate performance and stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field, and particularly relates to a sodium ion battery negative electrode material and a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] The massive consumption of traditional non-renewable energy sources such as petroleum not only exacerbates the "energy crisis", but also leads to increasingly serious environmental pollution. Therefore, exploring efficient and long-lasting and inexpensive clean energy storage methods is an important goal for the sustainable development of contemporary society. In recent years, electrochemical energy storage devices have attracted widespread attention from the academic community due to their high energy conversion efficiency and high energy density. Among them, lithium ion batteries, as the most common secondary batteries, have high working voltage, long service life and large energy density, but their application is limited due to the shortage of lithium resources and high cost. In order to reduce the over-reliance on lithium resources, researchers found that Na and Li, which belong to the same alkali metal main group, have similar chemical properties and the same energy storage mechanism, and sodium is abundant. However, the growing market demand poses greater challenges to sodium ion batteries, and exploring new electrode materials is a key way to achieve higher performance sodium ion batteries.

[0003] The negative electrode material is a key link to determine whether the sodium ion battery has excellent performance. At present, conversion-type materials (phosphides, selenides, sulfides, etc.) are considered as extremely potential negative electrode materials due to their high theoretical specific capacity. Among them, phosphides have greater advantages in high theoretical capacity, cycle stability, low potential platform and conductivity compared to selenides and sulfides, which makes them become a candidate for sodium ion battery negative electrode materials with great potential, but phosphides also have the common problem of serious volume expansion.

[0004] So far, researchers have taken various means to improve and optimize the foregoing problems. For example, patent application file CN118572059A designs a carbon-coated phosphide material with an embedded structure, and the special carbon layer structure can effectively buffer the volume expansion of the phosphide, and the rich carbon layer can increase the conductivity of the electrode. In addition, Liu Shuling et al. used a coprecipitation method to dope Fe ions into cobalt phosphide, and the conductivity was significantly improved [1] . In addition, patent application file CN117720076A compounding phosphide with carbon obtains excellent lithium storage performance. However, the above modification methods are relatively single, and the performance improvement of phosphide is also relatively limited.

[0005] [1] Zeyi Wang, Shuling Liu, Jinyu Du, Yichuang Xing, Yanling Hu, Yujie Ma, Xinyi Lu, Chao Wang. Iron-doped nickel phosphide hollow nanospheres synthesized by solvothermal phosphidization of layered double hydroxides for electrocatalytic oxygen evolution, Green Chemistry, 2024, 26: 7779-7788. SUMMARY

[0006] The present application is based on the findings and recognitions of the inventors on the following facts and problems: In order to further expand the application of phosphides in sodium ion batteries, it is necessary to build a comprehensive modification means to overcome the above problems, so as to significantly improve the performance of phosphides.

[0007] The present application aims to at least partially solve one of the technical problems in the related art. To this end, embodiments of the present application propose a sodium ion battery negative electrode material, a preparation method thereof, and a sodium ion battery.

[0008] In a first aspect, embodiments of the present application provide a preparation method of a sodium ion battery negative electrode material, comprising the following steps:

[0009] S1. Washing the loquat skin with water and then pre-freezing it in a refrigerator, and then freeze-drying to obtain dried loquat skin;

[0010] S2. Configuring a mixed aqueous solution of iron salt and nickel salt, and then soaking the dried loquat skin in the mixed aqueous solution of iron salt and nickel salt to obtain a composite of iron salt / nickel salt / loquat skin;

[0011] S3. Washing the composite of iron salt / nickel salt / loquat skin with water and ethanol, and then freeze-drying to obtain an iron / nickel / biomass carbon precursor;

[0012] S4. Two-stage calcining the iron / nickel / biomass carbon precursor to obtain a composite of iron / nickel / biomass carbon;

[0013] S5. Chemical vapor deposition of carbon nanotubes on the composite of iron / nickel / biomass carbon to obtain a composite of iron / nickel / biomass carbon / carbon nanotubes;

[0014] S6. The iron / nickel / biomass charcoal / carbon nanotube composite is subjected to tube-sealing gas phase phosphorization to obtain a composite metal phosphide / biomass charcoal / carbon nanotube composite material.

[0015] The preparation method of the embodiment of the present application has the following advantages and technical effects:

[0016] (1) The preparation method of the embodiment of the present application uses loquat skin as a carrier, iron salt and nickel salt as raw materials, and adopts a hydrothermal method to synthesize an iron salt / nickel salt / loquat skin composite. After cleaning and freeze-drying, an iron / nickel / biomass charcoal precursor is obtained. Subsequently, carbonization is performed through two-stage calcination. The loquat skin is carbonized into graphite charcoal, and the graphite charcoal reduces the iron salt and the nickel salt at high temperature to form iron and nickel, thereby obtaining iron / nickel / biomass charcoal. Then, carbon nanotubes are generated using chemical vapor deposition (CVD) technology. Finally, tube-sealing gas phase phosphorization is performed to obtain a phosphide / biomass charcoal / carbon nanotube composite material. The composite material constructed as a sodium ion battery negative electrode material has excellent capacity, rate performance, and stability.

[0017] (2) The phosphide / biomass charcoal / carbon nanotube composite material prepared by the preparation method of the embodiment of the present application has the advantages of each composite phase. It not only has excellent stability of biomass charcoal, but also has high reversible capacity of phosphide. At the same time, the biomass charcoal can act as a buffer layer to slow down the volume expansion of the phosphide during sodium storage, and has a certain chemical adsorption effect on the sodium phosphide generated during the charging and discharging process, thereby prolonging the service life of the electrode. In addition, the external three-dimensional network constructed by the highly conductive carbon nanotubes promotes the rapid transmission of electrons, and the large specific surface area provides favorable conditions for electrolyte infiltration and ion exchange. Therefore, the composite material is not a simple superposition of the three components, and exhibits better electrochemical performance than any single component.

[0018] In some embodiments, in step S1, the freeze-drying time is 14 hours or more.

[0019] In some embodiments, in step S2, the soaking temperature is 50-90℃, and the soaking time is 10-24 hours.

[0020] In some embodiments, in step S2, the mass of the dried loquat skin is 1-3g, and the volume of the mixed aqueous solution of the iron salt and the nickel salt is 60-150mL; and / or, in the mixed aqueous solution of the iron salt and the nickel salt, the concentration of the iron salt is 0.35-0.7mol / L, and the concentration of the nickel salt is 0.35-0.7mol / L; and / or, in step S2, the iron salt is at least one of ferric nitrate, ferric sulfate, and ferric chloride; and / or, the nickel salt is at least one of nickel nitrate, nickel sulfate, and nickel chloride.

[0021] In some embodiments, in step S3, the washing is performed 3-5 times with water and ethanol, respectively, and / or, in step S3, the freeze-drying is performed for 14-24 h.

[0022] In some embodiments, in step S4, the first-stage calcination is performed under a protective atmosphere of nitrogen or argon, at a temperature of 300-400℃ for 1-4 h, and the second-stage calcination is performed at a temperature of 600-900℃ for 1-4 h.

[0023] In some embodiments, in step S5, the carbon source for the chemical vapor deposition is ethanol or acetylene, and the flow rate of the carbon source is 10-30 sccm; and / or, the chemical vapor deposition is performed under a protective atmosphere of nitrogen or argon, and the flow rate of the protective atmosphere is 100-300 sccm; and / or, the chemical vapor deposition is performed under a reducing atmosphere of hydrogen, and the flow rate of the reducing atmosphere is 10-30 sccm; and / or, the chemical vapor deposition is performed at a temperature of 600-800℃ for 0.5-3 h.

[0024] In some embodiments, in step S6, the mass ratio of the iron / nickel / biomass carbon / carbon nanotube composite to red phosphorus is 3:1-1:1, and the phosphating reaction is performed at a temperature of 500-600℃ for 3-5 h.

[0025] In a second aspect, the embodiments of the present application also provide a sodium-ion battery negative electrode material obtained by the preparation method of the first aspect.

[0026] The sodium-ion battery negative electrode material according to the embodiments of the present application has the following advantages and technical effects:

[0027] (1) The introduction of the iron diphosphide / nickel diphosphide heterostructure has a synergistic effect, provides more active sites, and reduces the migration energy barrier of Na+.

[0028] (2) The porous wrinkled lamellar structure of the loquat peel has abundant pores and a large specific surface area, so the unique structure of the biomass carbon in the phosphide / biomass carbon / carbon nanotube composite not only has abundant pores and a high specific surface area, ensuring sufficient contact between the active material and the electrolyte, thereby generating more electrochemical reaction active sites; and at the same time, the volume expansion in the process of sodium extraction from the phosphide is relieved, and the stability is significantly improved.

[0029] (3) In addition to forming a unique structure, the addition of biomass carbon also successfully performs nitrogen doping on the phosphide. Nitrogen doping can bring abundant oxygen vacancies, effectively optimize the electronic structure of the phosphide, improve the internal conductivity of the phosphide, and at the same time, the increased defects are beneficial to the transmission of sodium ions and accelerate the reaction kinetics.

[0030] (4) The carbon nanotubes are compounded with the phosphide, and the conductivity and structural stability are improved. The carbon nanotube network structure can form a three-dimensional conductive framework, and the overall performance of the negative electrode material is improved.

[0031] In a third aspect, the embodiments of the present application provide a sodium ion battery, comprising a negative electrode current collector and a negative electrode active layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active layer comprises the negative electrode material of the second aspect.

[0032] The sodium ion battery provided by the embodiments of the present application has the following advantages and technical effects:

[0033] Due to the use of the negative electrode material of the sodium ion battery provided by the embodiments of the present application, the sodium ion battery provided by the embodiments of the present application has excellent capacity, rate performance and stability. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM images of the phosphide / biomass charcoal / carbon nanotube composite material of Example 1 at different magnifications.

[0035] Figure 2 XRD diffraction pattern of the phosphide / biomass charcoal / carbon nanotube composite material of Example 1.

[0036] Figure 3 XPS pattern of the N element in the phosphide / biomass charcoal / carbon nanotube composite material of Example 1.

[0037] Figure 4 SEM image of the phosphide / biomass charcoal composite material of Comparative Example 1.

[0038] Figure 5 Rate performance comparison chart of the composite materials of Example 1 and Comparative Example 1.

[0039] Figure 6 Impedance comparison chart of the composite materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0040] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0041] In a first aspect, the embodiments of the present application provide a preparation method of a sodium ion battery negative electrode material, comprising the following steps:

[0042] S1. Washing loquat peel with water and then pre-freezing in a refrigerator, and then freeze-drying to obtain dried loquat peel;

[0043] S2. A mixed aqueous solution of iron and nickel salts is configured, and then the dried loquat peels are soaked in the mixed aqueous solution of iron and nickel salts to obtain an iron salt / nickel salt / loquat peel composite;

[0044] S3. The iron salt / nickel salt / loquat peel composite is washed with water and ethanol, and then freeze-dried to obtain an iron / nickel / biomass carbon precursor;

[0045] S4. The iron / nickel / biomass carbon precursor is subjected to two-stage calcination to obtain an iron / nickel / biomass carbon composite;

[0046] S5. The iron / nickel / biomass carbon composite is subjected to chemical vapor deposition of carbon nanotubes to obtain an iron / nickel / biomass carbon / carbon nanotube composite;

[0047] S6. The iron / nickel / biomass carbon / carbon nanotube composite is subjected to tube-sealing gas-phase phosphidation to obtain a composite metal phosphide / biomass carbon / carbon nanotube composite material.

[0048] The preparation method of the embodiment of the present application uses loquat peels as a carrier, iron and nickel salts as raw materials, and uses a hydrothermal method to synthesize an iron salt / nickel salt / loquat peel composite, and then after washing and freeze-drying, an iron / nickel / biomass carbon precursor is obtained. Subsequently, after carbonization, an iron / nickel / biomass carbon composite is obtained. Then, using chemical vapor deposition technology, carbon nanotubes are generated to obtain an iron / nickel / biomass carbon / carbon nanotube composite. Finally, tube-sealing gas-phase phosphidation is performed to obtain a phosphide / biomass carbon / carbon nanotube composite material embedded in a porous carbon with a folded sheet structure. The composite material constructed as a sodium ion battery negative electrode material has excellent capacity, rate performance, and stability.

[0049] The sodium ion battery negative electrode material prepared by the preparation method of the embodiment of the present application can increase active sites and improve reversible capacity due to the synergistic effect between the bimetallic heterostructure. Secondly, the porous folded structure of the biomass carbon (LPC) can buffer the volume expansion of the phosphide, thereby improving the cycle stability of the electrode material. At the same time, the folded structure has abundant pores, which can provide more reaction active sites and ion / electron rapid transmission channels. Finally, the external three-dimensional network constructed by the highly conductive carbon nanotubes can overall improve the conductivity of the composite material.

[0050] In some embodiments, in step S1, the freeze-drying time is 14 hours or more, for example, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc. The freeze-drying time in step S1 is within the above range, which can remove the water in the fresh loquat peels and maintain the structure of the loquat peel solid material.

[0051] In some embodiments, in step S2, the soaking temperature is 50-90℃, such as 50℃, 60℃, 70℃, 80℃, 90℃, etc., and the soaking time is 10-24h, such as 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc. The hydrothermal reaction can be used to synthesize the complex of iron / nickel / peel, and the soaking temperature and soaking time in the above range can make the iron, nickel and peel fully complex.

[0052] In some embodiments, in step S2, the mass of the dried peel is 1-3g, and the volume of the mixed aqueous solution of the iron and nickel salts is 60-150mL; and / or, in the mixed aqueous solution of the iron and nickel salts, the concentration of the iron salt is 0.35-0.7mol / L, such as 0.35mol / L, 0.4mol / L, 0.45mol / L, 0.5mol / L, 0.55mol / L, 0.6mol / L, 0.65mol / L, 0.7mol / L, etc., and the concentration of the nickel salt is 0.35-0.7mol / L, such as 0.35mol / L, 0.4mol / L, 0.45mol / L, 0.5mol / L, 0.55mol / L, 0.6mol / L, 0.65mol / L, 0.7mol / L, etc. The ratio of the peel, iron salt and nickel salt in the above range can make the iron, nickel and peel fully complex.

[0053] In some embodiments, in step S2, the nickel salt is at least one of nickel nitrate, nickel sulfate and nickel chloride; and / or, the iron salt is at least one of iron nitrate, iron sulfate and iron chloride. The above iron and nickel salts are easily soluble in water, which is beneficial for the hydrothermal reaction with the peel to form the complex.

[0054] In some embodiments, in step S3, the washing with water and ethanol is performed for 3-5 times, respectively. This is beneficial for removing the residual substances on the surface of the complex of iron / nickel / peel.

[0055] In some embodiments, in step S3, the freeze-drying time is 14-24h, such as 14h, 16h, 18h, 20h, 22h, 24h, etc. The freeze-drying of the washed complex of iron / nickel / peel in this step can remove the solvent introduced in the washing process while not damaging the structure of the peel, which is beneficial for obtaining the biomass charcoal with the porous and wrinkled structure after carbonization.

[0056] In some embodiments, in step S4, the nitrogen or argon is used as the protective atmosphere. The protective atmosphere is used to avoid the oxidation of iron and nickel.

[0057] In some embodiments, in step S4, the reaction temperature of the first-stage calcination is 300-400°C, such as 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, etc., the reaction time of the first-stage calcination is 1-4h, such as 1h, 2h, 3h, 4h, etc., the reaction temperature of the second-stage calcination is 600-900°C, such as 600°C, 350°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc., and the reaction time of the second-stage calcination is 1-4h, such as 1h, 2h, 3h, 4h, etc. In the first-stage calcination, the cellulose and other organic matters contained in the iron / nickel / biomass carbon precursor can be removed, and in the second-stage calcination, the loquat skin can be carbonized to form amorphous biomass carbon with sodium storage activity, and the electrical conductivity of the composite material can be increased.

[0058] In some embodiments, in step S5, the carbon source for chemical vapor deposition is ethanol or acetylene, and the flow rate of the carbon source is 10-30sccm. The chemical vapor deposition under the above conditions can form a three-dimensional network structure of carbon nanotubes on the surface of the phosphide / biomass carbon.

[0059] In some embodiments, in step S5, the chemical vapor deposition is carried out in a protective atmosphere of nitrogen or argon, and the flow rate of the protective atmosphere is 100-300sccm; and / or, the chemical vapor deposition is carried out in a reducing atmosphere of hydrogen, and the flow rate of the reducing atmosphere is 10-30sccm. The protective atmosphere and the reducing atmosphere are used to avoid oxidation of the biomass carbon.

[0060] In some embodiments, in step S5, the reaction temperature for chemical vapor deposition is 600-800°C, such as 600°C, 650°C, 700°C, 850°C, 800°C, etc., and the reaction time is 0.5-3h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc. The reaction temperature and the reaction time of the chemical vapor deposition are beneficial to improve the electrical conductivity of the carbon nanotubes.

[0061] In some embodiments, in step S6, the mass ratio of the iron / nickel / biomass carbon / carbon nanotube composite to red phosphorus is 3:1-1:1, such as 3:1, 2.5:1, 2:1, 1.5:1, 1:1, etc. The tube sealing is to put the iron / nickel / biomass carbon / carbon nanotube composite and red phosphorus into a quartz tube, and to seal the quartz tube by a tube sealing machine. The gas-phase phosphorization is then carried out in a vacuum state.

[0062] In some embodiments, in step S6, the phosphating reaction temperature is 500-600℃, such as 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, etc., and the phosphating reaction time is 3-5h, such as 3h, 3.5h, 4h, 4.5h, 5h, etc. The above phosphating reaction temperature and time are conducive to fully phosphating the iron, nickel in the composite of iron / nickel / biomass charcoal / carbon nanotube to generate metal phosphides.

[0063] In a second aspect, the embodiments of the present application provide a sodium ion battery negative electrode material obtained by the preparation method of the first aspect.

[0064] Due to the use of the preparation method of the embodiments of the present application, the sodium ion battery negative electrode material of the embodiments of the present application has the advantages of each composite phase. Among them, the iron diphosphide / nickel diphosphide greatly improves the reversible capacity of the composite material as a substance with high theoretical capacity; in addition, the heterostructure formed by the two phosphides has a synergistic effect to increase the active sites and improve the reversible capacity; and the unique structure of the biomass charcoal not only has abundant pores and high specific surface area, but also can effectively increase the contact area of the active material and the electrolyte, thereby accelerating the electron transfer. At the same time, the external three-dimensional network constructed by the high-conductivity carbon nanotubes can overall improve the conductivity of the composite material. The above various modification methods can optimize the practical application value of the phosphide from the aspects of electrochemical performance and electrode reaction kinetics.

[0065] In a third aspect, the embodiments of the present application provide a sodium ion battery, which comprises a negative electrode current collector and a negative electrode active layer arranged on at least one side surface of the negative electrode current collector, and the negative electrode active layer comprises the negative electrode material of the second aspect.

[0066] Due to the use of the negative electrode material of the embodiments of the present application, the sodium ion battery of the embodiments of the present application has excellent capacity, rate performance and stability.

[0067] The present application will be described in detail below with reference to the embodiments and the accompanying drawings.

[0068] Embodiment 1

[0069] (1) The peel of loquat was peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze drying for 14h;

[0070] (2) A mixed aqueous solution of 70mL of 0.35mol / L iron chloride and 0.35mol / L nickel chloride was prepared, and after being stirred uniformly, it was kept at 50℃, and 3g of loquat peel obtained in step (1) was soaked therein for 24h;

[0071] (3) The loquat peel obtained in step (2) was washed three times with water and three times with ethanol to remove surface residues. It was then transferred to a freeze dryer for freeze drying. After freeze drying for 14 hours, yellow-green slices α were obtained.

[0072] (4) Black sheet β was obtained by calcining yellow-green sheet α in two stages. Argon was used as the protective atmosphere. The reaction temperature and time of the first stage of calcination were 400℃ and 1h, respectively. The reaction temperature and time of the second stage of calcination were 900℃ and 1h, respectively.

[0073] (5) Under an argon-hydrogen mixture, carbon source ethanol was introduced by bubbling ethanol and carbon nanotubes were grown on the black sheet β by chemical vapor deposition (CVD) at 650°C for 2.5 h to obtain a composite γ of iron / nickel / biochar / carbon nanotubes; wherein, argon was used as a protective atmosphere with an argon flow rate of 200 sccm and hydrogen was used as a reducing atmosphere with a hydrogen flow rate of 20 sccm.

[0074] (6) The iron / nickel / biochar / carbon nanotube composite γ was subjected to encapsulated gas-phase phosphating under the following conditions: a mass ratio of iron / nickel / biochar / carbon nanotubes to red phosphorus of 1:1, a phosphating temperature of 600℃, and a phosphating time of 3 hours, to obtain the final product, a phosphide / biochar / carbon nanotube composite material. Based on the total mass of the composite material as 100%, the content of iron diphosphide was 25%, the content of nickel diphosphide was 25%, the content of CNTs was 15%, and the remainder was biochar of 35%.

[0075] Figure 1 The images are SEM images of the phosphide / biochar / carbon nanotube composite material of Example 1 at different magnifications. It can be seen that there are many phosphide nanoparticles after phosphating, and carbon nanotubes are clearly grown on the surface of the phosphide particles after CVD technology. Figure 2 The XRD diffraction pattern of the phosphide / biochar / carbon nanotube composite material in Example 1 is shown below. Figure 2 As can be seen, the phase of the phosphide / biochar / carbon nanotube composite material was further identified by X-ray diffraction as a mixture of iron phosphide / nickel phosphide (JCPDS 74-1383, JCPDS 71-2234), and the presence of carbon nanotubes was confirmed by the above SEM images. The valence state of nitrogen on the surface of the phosphide / biochar / carbon nanotube composite material in Example 1 was determined by X-ray photoelectron spectroscopy (XPS). Figure 3 The high-resolution N 1s spectrum revealed the presence of characteristic peaks of pyridine N (397.8 eV), pyrrole N (400.2 eV) and graphite N (402.8 eV), indicating that N is clearly present in the composite material, proving the successful incorporation of N.

[0076] Example 2

[0077] The preparation method of the embodiment of the present application is the same as that of example 1, except that the phosphating temperature of step (6) is different, and the specific method is as follows:

[0078] (1) The peel of loquat was peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze drying for 14 hours;

[0079] (2) A mixed aqueous solution of 70 mL of 0.35 mol / L iron sulfate and 0.35 mol / L nickel sulfate was prepared, and after being stirred uniformly, it was kept at 50°C, and 3g of loquat peel obtained in step (1) was soaked therein for 24 hours;

[0080] (3) The loquat peel obtained in step (2) was washed with water and ethanol for 3 times respectively to remove the surface residual substances, and then transferred to a freeze dryer for freeze drying, and after freeze drying for 14 hours, a yellow-green sheet alpha was obtained;

[0081] (4) The yellow-green sheet alpha was calcined by two-stage temperature calcination to obtain a black sheet beta, wherein argon gas was used as a protective atmosphere, the reaction temperature and time of the first-stage calcination were 400°C and 1 hour respectively, and the reaction temperature and time of the second-stage calcination were 900°C and 1 hour respectively;

[0082] (5) Under argon-hydrogen mixed gas, carbon source ethanol was bubbled into the black sheet beta by ethanol bubbling method, and carbon nanotubes were grown on the black sheet beta by chemical vapor deposition (CVD) method at 650°C for 2.5 hours to obtain a composite gamma of iron / nickel / biomass charcoal / carbon nanotubes; wherein argon gas was used as a protective atmosphere, the argon gas flow was 200sccm, and hydrogen gas was used as a reducing atmosphere, and the hydrogen gas flow was 20sccm;

[0083] (6) The composite gamma of iron / nickel / biomass charcoal / carbon nanotubes was subjected to sealed tube gas phase phosphating, and the conditions were as follows: the mass ratio of the composite gamma to red phosphorus was 1:1, the phosphating temperature was 500°C, and the phosphating time was 3 hours, to obtain a final product of phosphide / biomass charcoal / carbon nanotube composite material. Based on the total mass of the composite material being 100%, the content of iron phosphide was 25%, the content of nickel phosphide was 25%, the content of CNTs was 15%, and the remaining was biomass charcoal 35%.

[0084] Example 3

[0085] The preparation method of the embodiment of the present application is the same as that of example 1, except that the types and concentrations of iron salt and nickel salt of step (3) are different, and the specific method is as follows:

[0086] (1) The peel of loquat was peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze drying for 14 hours;

[0087] (2) 70 mL of a mixed aqueous solution of ferric nitrate with a concentration of 0.53 mol / L and nickel nitrate with a concentration of 0.18 mol / L was configured, and after being stirred uniformly, it was kept at 50℃, and 3 g of the loquat peel obtained in step (1) was soaked therein for 24 h;

[0088] (3) The loquat peel obtained in step (2) was washed with water and ethanol for 3 times respectively to remove the surface residual substances, and was transferred to a freeze dryer for freeze drying, and yellow-green sheet α was obtained after freeze drying for 14 h;

[0089] (4) The yellow-green sheet α was calcined by adopting a two-stage temperature calcination to obtain black sheet β, wherein argon was used as a protective atmosphere, the reaction temperature and time of the first-stage calcination were 400℃ and 1 h respectively, and the reaction temperature and time of the second-stage calcination were 900℃ and 1 h respectively;

[0090] (5) The carbon source ethanol was introduced by an ethanol bubbling method under an argon-hydrogen mixed gas, and the black sheet β was subjected to a chemical vapor deposition (CVD) growth of carbon nanotubes for 2.5 h at 650℃ to obtain a composite γ of iron / nickel / biomass charcoal / carbon nanotubes; wherein argon was used as a protective atmosphere, the argon flow rate was 200 sccm, and hydrogen was used as a reducing atmosphere, and the hydrogen flow rate was 20 sccm;

[0091] (6) The composite γ of iron / nickel / biomass charcoal / carbon nanotubes was subjected to a sealed tube gas phase phosphorization, and the conditions were as follows: the mass ratio to red phosphorus was 1:1, the phosphorization temperature was 600℃, and the phosphorization time was 3 h, to obtain a final product of phosphide / biomass charcoal / carbon nanotube composite material. In the composite material, the content of iron phosphide was 37.5%, the content of nickel phosphide was 12.5%, the content of CNTs was 15%, and the remaining was biomass charcoal 35%, with the total mass of the composite material being 100%.

[0092] Example 4

[0093] The preparation method of the embodiment of the application is the same as that of Example 1, and the difference lies in that the nickel salt is omitted in step (3), and the specific method is as follows:

[0094] (1) The peel of loquat was peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze drying for 14 h;

[0095] (2) 70 mL of an aqueous solution of ferric chloride with a concentration of 0.7 mol / L was configured, and after being stirred uniformly, it was kept at 50℃, and 3 g of the loquat peel obtained in step (1) was soaked therein for 24 h;

[0096] (3) The loquat peel obtained in step (2) was washed with water and ethanol for 3 times respectively to remove the surface residual substances, and was transferred to a freeze dryer for freeze drying, and yellow-green sheet α was obtained after freeze drying for 14 h;

[0097] (4) Two-stage temperature calcination is used to obtain black sheet β from yellow-green sheet α, wherein argon is used as the protective atmosphere, the reaction temperature and time of the first-stage calcination are 400 DEG C and 1 h respectively, and the reaction temperature and time of the second-stage calcination are 900 DEG C and 1 h respectively;

[0098] (5) Carbon source ethanol is introduced into black sheet β by ethanol bubbling method under argon-hydrogen mixed gas, and carbon nanotubes are grown on black sheet β by chemical vapor deposition (CVD) at 650 DEG C for 2.5 h to obtain a composite of iron / biomass carbon / carbon nanotubes γ; wherein argon is used as the protective atmosphere, the argon flow rate is 200 sccm, and hydrogen is used as the reducing atmosphere, the hydrogen flow rate is 20 sccm;

[0099] (6) The composite of iron / biomass carbon / carbon nanotubes γ is subjected to sealed tube gas phosphorization, the conditions are that the mass ratio of the composite to red phosphorus is 1:1, and the phosphorization temperature is 600 DEG C, to obtain a final product of phosphide / biomass carbon / carbon nanotube composite material. In the composite material, the content of ferrous phosphide is 50%, the content of CNTs is 15%, and the remaining is biomass carbon 35% based on the total mass of the composite material.

[0100] Example 5

[0101] The preparation method of the embodiment of the present application is the same as that of Example 1, except that the iron salt is omitted in step (3), and the specific method is as follows:

[0102] (1) The peel of loquat is peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze drying for 14 h;

[0103] (2) A 70 mL aqueous solution of nickel chloride with a concentration of 0.7 mol / L is prepared, and 3 g of the loquat peel obtained in step (1) is soaked in the solution for 24 h after stirring uniformly;

[0104] (3) The loquat peel obtained in step (2) is washed with water and ethanol for 3 times respectively to remove the surface residual substances, and then transferred to a freeze dryer for freeze drying, and yellow-green sheet α is obtained after freeze drying for 14 h;

[0105] (4) Two-stage temperature calcination is used to obtain black sheet β from yellow-green sheet α, wherein argon is used as the protective atmosphere, the reaction temperature and time of the first-stage calcination are 400 DEG C and 1 h respectively, and the reaction temperature and time of the second-stage calcination are 900 DEG C and 1 h respectively;

[0106] (5) Carbon source ethanol is introduced into black sheet β by ethanol bubbling method under argon-hydrogen mixed gas, and carbon nanotubes are grown on black sheet β by chemical vapor deposition (CVD) at 650 DEG C for 2.5 h to obtain a composite of iron / biomass carbon / carbon nanotubes γ; wherein argon is used as the protective atmosphere, the argon flow rate is 200 sccm, and hydrogen is used as the reducing atmosphere, the hydrogen flow rate is 20 sccm;

[0107] (6) The nickel / biomass charcoal / carbon nanotube composite γ is subjected to tube-sealing gas-phase phosphorization under conditions of a mass ratio of 1:1 with red phosphorus, a phosphorization temperature of 600°C, and a phosphorization time of 3h, to obtain a final product of phosphide / biomass charcoal / carbon nanotube composite material. In terms of the total mass of the composite material being 100%, the content of nickel phosphide is 50%, the content of CNTs is 15%, and the remainder is biomass charcoal 35%.

[0108] Comparative Example 1

[0109] According to the procedure of Example 1, while removing the CVD process of step (5), the remaining steps are unchanged to obtain a phosphide / biomass charcoal composite material. The specific method is as follows:

[0110] (1) The peel of loquat is peeled off, washed with deionized water, and then pre-frozen in a refrigerator, and then transferred to a freeze dryer for freeze-drying for 14h;

[0111] (2) A mixed aqueous solution of 70mL of 0.35mol / L ferric chloride and 0.35mol / L nickel chloride is prepared, and after being stirred uniformly, it is kept at 50°C, and 3g of the loquat peel obtained in step (1) is soaked therein for 24h;

[0112] (3) The loquat peel obtained in step (2) is washed with water and ethanol for 3 times respectively to remove the surface residual substances, and then transferred to a freeze dryer for freeze-drying, and after freeze-drying for 14h, a yellow-green sheet α is obtained;

[0113] (4) The yellow-green sheet α is calcined by a two-stage temperature calcination to obtain a black sheet β, wherein argon gas is used as the protective atmosphere, the reaction temperature and time of the first-stage calcination are 400°C and 1h respectively, and the reaction temperature and time of the second-stage calcination are 900°C and 1h respectively;

[0114] (5) The black sheet β is subjected to tube-sealing gas-phase phosphorization under conditions of a mass ratio of 1:1 of the black sheet β and red phosphorus, a phosphorization temperature of 600°C, and a phosphorization time of 3h, to obtain a final product of phosphide / biomass charcoal composite material. In terms of the total mass of the composite material being 100%, the content of iron phosphide is 18.5%, the content of nickel phosphide is 18.5%, and the remainder is biomass charcoal 63%.

[0115] Figure 4 The SEM image of the phosphide / biomass charcoal composite material of Comparative Example 1 can be seen that in the sample without CVD, there are only phosphide nanoparticles on the surface of the wrinkled carbon layer, and no roughness phenomenon occurs, indicating that there is no carbon nanotube.

[0116] The final powdery composite material obtained in the above examples and comparative examples was mixed with Super P and polyvinylidene fluoride (PVDF) by repeated grinding and stirring to form a slurry, which was coated on a copper foil, dried thoroughly, and punched into a round sheet as a sodium-ion battery electrode to be assembled. A coin-type sodium-ion battery was assembled with a sodium sheet as a negative electrode, the above electrode sheet as a positive electrode, and a glass fiber as a separator, and an electrolyte was added to both sides of the separator. The electrolyte was prepared by dissolving NaPF6 as a solute in a solvent composed of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:1. The assembled sodium-ion battery was allowed to stand and then subjected to electrochemical tests. -1 The final powdery composite material obtained in the above examples and comparative examples was mixed with Super P and polyvinylidene fluoride (PVDF) by repeated grinding and stirring to form a slurry, which was coated on a copper foil, dried thoroughly, and punched into a round sheet as a sodium-ion battery electrode to be assembled. A coin-type sodium-ion battery was assembled with a sodium sheet as a negative electrode, the above electrode sheet as a positive electrode, and a glass fiber as a separator, and an electrolyte was added to both sides of the separator. The electrolyte was prepared by dissolving NaPF6 as a solute in a solvent composed of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1:1. The assembled sodium-ion battery was allowed to stand and then subjected to electrochemical tests.

[0117] The sodium-ion batteries assembled with the composite materials of examples 1-5 and comparative example 1 as negative electrode materials showed different electrochemical performances with changes in chemical components and parameters in the preparation process. The maximum discharge capacities of the batteries at different current densities are shown in Table 1.

[0118] Table 1. Maximum discharge capacities of the batteries assembled with the composite materials of examples 1-5 and comparative example 1 as negative electrode materials at different current densities

[0119]

[0120] It can be seen that the changes in the parameters in the preparation process have a relatively large effect on the electrochemical performance of the sodium-ion batteries. The changed parameters include phosphating temperature and iron / nickel ratio. When the phosphating temperature is reduced to 500°C (example 2), the capacity at a small current is relatively high, but the capacity at a large current decays relatively fast. When the iron / nickel ratio is changed (example 3), the proportion of iron is appropriately increased, although the capacity at each current density shows a decrease, the overall stability of the composite material still exists. When a single metal salt is used (examples 4 and 5), the overall capacity of the composite material is greatly reduced, because the synergistic effect of the heterogeneous structure in the composite material no longer exists. In the absence of carbon nanotubes, the specific capacity of comparative example 1 at different current densities is lower than that of examples 1-3, which shows that the presence of carbon nanotubes can significantly improve the poor conductivity in the composite material, thereby improving the rate performance. Figure 5 The rate performance comparison chart of the composite materials of example 1 and comparative example 1 is shown in FIG. 1. Figure 6 The impedance comparison chart of the composite materials of example 1 and comparative example 1 is shown in FIG. 2. Combined with FIG. 1, Figure 5 and Figure 6 It is not difficult to see that the presence of carbon nanotubes not only improves the electrochemical performance of the composite material, but also reduces the interface impedance, increases the sodium ion migration rate, and accelerates the reaction kinetics.

[0121] In this disclosure, the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" mean that a particular feature, structure, material, or characteristic is included in at least one embodiment or example of the present disclosure. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, the terminology "comprising" is used in the disclosure as comprising but not limited to, that is, it is open-ended and does not exclude the presence of additional features, structures, materials, or characteristics.

[0122] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above-described embodiments are exemplary, and are not to be interpreted as limiting the present disclosure, and the ordinary skilled in the art can make changes, modifications, replacements, and variations to the above-described embodiments within the scope of the present disclosure.

Claims

1. A method for preparing a sodium-ion battery anode material, characterized in that, The method comprises the following steps: S1. washing loquat peel with water and then pre-freezing in a refrigerator, and then freeze-drying to obtain dried loquat peel; S2. configuring a mixed aqueous solution of iron salt and nickel salt, and then soaking the dried loquat peel in the mixed aqueous solution of iron salt and nickel salt to obtain an iron salt / nickel salt / loquat peel composite; S3. washing the iron salt / nickel salt / loquat peel composite with water and ethanol, and then freeze-drying to obtain an iron / nickel / biomass carbon precursor; S4. two-stage calcining the iron / nickel / biomass carbon precursor to obtain an iron / nickel / biomass carbon composite; S5. chemical vapor deposition of carbon nanotubes on the iron / nickel / biomass carbon composite to obtain an iron / nickel / biomass carbon / carbon nanotube composite; S6. tube-sealing gas-phase phosphorization of the iron / nickel / biomass carbon / carbon nanotube composite to obtain a composite metal phosphide / biomass carbon / carbon nanotube composite material.

2. The production method according to claim 1, characterized by, In step S1, the freeze-drying time is 14 hours or more.

3. The preparation method according to claim 1, characterized in that, In step S2, the soaking temperature is 50-90 DEG C, and the soaking time is 10-24 hours.

4. The production method according to claim 1, characterized by, In step S2, the mass of the dried loquat peel is 1-3 g, and the volume of the mixed aqueous solution of iron salt and nickel salt is 60-150 mL; and / or, in the mixed aqueous solution of iron salt and nickel salt, the concentration of the iron salt is 0.35-0.7 mol / L, and the concentration of the nickel salt is 0.35-0.7 mol / L; and / or, in step S2, the iron salt is at least one of ferric nitrate, ferric sulfate and ferric chloride; and / or, the nickel salt is at least one of nickel nitrate, nickel sulfate and nickel chloride.

5. The method of claim 1, wherein, In step S3, the washing with water and ethanol is performed 3-5 times, and / or, the freeze-drying time in step S3 is 14-24 hours.

6. The method of claim 1, wherein, In step S4, nitrogen or argon is used as the protective atmosphere, and / or, the reaction temperature of the first-stage calcining is 300-400 DEG C, the reaction time of the first-stage calcining is 1-4 hours, the reaction temperature of the second-stage calcining is 600-900 DEG C, and the reaction time of the second-stage calcining is 1-4 hours.

7. The preparation method according to claim 1, characterized in that, In step S5, the carbon source for the chemical vapor deposition is ethanol or acetylene, and the flow rate of the carbon source is 10-30 seem; and / or, nitrogen or argon is used as the protective atmosphere for the chemical vapor deposition, and the flow rate of the protective atmosphere is 100-300 seem; and / or, hydrogen is used as the reducing atmosphere for the chemical vapor deposition, and the flow rate of the reducing atmosphere is 10-30 seem; and / or, the reaction temperature for the chemical vapor deposition is 600-800 DEG C, and the reaction time is 0.5-3 hours.

8. The method of claim 1, wherein, In step S6, the mass ratio of the iron / nickel / biomass carbon / carbon nanotube composite to red phosphorus is 3:1-1:1, and the phosphorization reaction temperature and time are 500-600 DEG C and 3-5 hours, respectively.

9. A sodium-ion battery anode material, characterized in that, The method is obtained by any one of claims 1-8.

10. A sodium-ion battery comprising a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector, characterized in that, The negative electrode active layer comprises the negative electrode material of claim 9.

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