Nano-particle assembled submicron spherical ferric fluoride / cobalt fluoride heterostructure material as well as preparation method and application of nano-particle assembled submicron spherical ferric fluoride / cobalt fluoride heterostructure material

Abstract

The invention belongs to the technical field of energy storage materials, and particularly relates to a nano-particle assembled submicron spherical ferric fluoride / cobalt fluoride heterostructure material as well as a preparation method and application of the nano-particle assembled submicron spherical ferric fluoride / cobalt fluoride heterostructure material. Fe (NO3) 3.9 H2O, Co (NO3) 2.6 H2O, HF, absolute ethyl alcohol and polyethylene glycol are subjected to solvothermal reaction, after the reaction, the FeF3. 33H2O / CoF2 material is obtained through heat treatment, and the material is in a nano-particle assembled submicron spherical shape, has high structural stability, large specific surface area and short ion / electron transmission distance, and can be used for preparing a nano-particle assembled submicron spherical material. Therefore, higher capacity, more excellent cycling stability and more excellent rate capability can be provided for the lithium ion / sodium ion battery, and the material can be applied to the field of high-performance low-cost positive electrode materials of the lithium ion / sodium ion battery and has outstanding application prospects and industrial potential. The preparation method is simple, easy to control, non-toxic, harmless, low in cost and suitable for large-scale production and popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage materials, and in particular relates to a nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material, a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries (LIBs) play a vital role in portable electronic devices, electric vehicles, and renewable energy storage due to their excellent energy density, long cycle life, and good environmental compatibility. The basic components of LIBs include positive electrode, negative electrode, electrolyte, and separator, among which the active components of electrode materials dominate the electrochemical performance of batteries. + ) donor, the cathode material directly determines the capacity of the battery and affects the cost of the battery to a certain extent. Since the performance of the cathode material largely limits the overall design and capacity of LIBs, the development of new high-performance cathode materials has become the key to improving the performance of LIBs.

[0003] However, the limited resources of lithium and the increasing demand have led to an increasing production cost of LIBs, which has restricted their application in large-scale energy storage systems. In this context, sodium-ion batteries (SIBs), as an energy storage system with a similar working principle, have gradually become a potential alternative technology to LIBs due to their abundant sodium resources and low cost. Although sodium-ion batteries are generally lower in energy density than lithium-ion batteries, partly because of the high sodium content of SIBs, the energy density of SIBs is much higher than that of lithium-ion batteries. + The ionic radius is larger (Na + for And Li + for ), which significantly affects the ion transport, solid phase structure transformation and interface properties of electrode materials. In addition, the relatively high atomic mass of sodium (23 g·mol -1 , lithium is 6.9 g·mol -1 ) and the higher standard electrode potential also make SIBs have certain disadvantages in terms of energy density. However, since the mass of lithium or sodium accounts for only a small part of the total mass of the battery, the capacity of the battery is mainly determined by the performance of the electrode material, which means that the transition from LIBs to SIBs does not necessarily lead to a significant decrease in energy density.

[0004] The key components of SIBs include positive electrode materials, negative electrode materials, electrolytes, separators, and adhesives. In early studies, although the electrode materials developed for SIBs, such as MoS2, TiS2, and NaxMO2, have certain research value, they have obvious defects in electrochemical performance, so the application research of these materials has progressed slowly. With the deepening of research, the development of electrode materials that can meet the performance requirements of SIBs has become a key task in promoting the commercialization of sodium-ion battery technology. Researchers have explored a variety of new positive and negative electrode materials, which have made significant progress in improving battery capacity and extending cycle life.

[0005] Currently, the cathode materials of commercial LIBs (such as LiFePO4, LiCoO2 and LiNi x Mn y Co 1-x-y O2) mainly rely on intercalation / non-intercalation reaction mechanisms, and usually only one electron transfer occurs during the charge and discharge process, which limits the energy density of these materials. x , M=Fe,Ni,Co,Cu) as conversion cathode materials, because each redox center can achieve multi-electron transfer, it has a higher theoretical capacity. Compared with traditional intercalation cathode materials, transition metal fluorides not only provide higher electrochemical capacity, but also have lower cost and better environmental friendliness.

[0006] Among all metal fluorides, FeF3·0.33H2O is considered to be one of the most promising cathode materials. FeF3·0.33H2O has a high theoretical specific capacity and a high discharge voltage platform, which is mainly attributed to its unique hexagonal tungsten bronze (HTB) structure. The structure of FeF3·0.33H2O is composed of large hexagonal cavities, which provide channels for the rapid diffusion of lithium or sodium ions. In addition, water molecules are embedded in the structure of FeF3·0.33H2O, acting as powerful structural stabilizers in electrochemical reactions, which helps to maintain its structural stability during multiple charge and discharge processes, improve cycle stability, and show good lithium / sodium storage potential. Therefore, iron-based fluorides are regarded as one of the most attractive cathode materials and have received widespread attention in the research of lithium-ion batteries and sodium-ion batteries.

[0007] Although FeF3·0.33H2O has many advantages as a battery positive electrode material, its performance in practical applications still faces certain challenges. Specifically, FeF3·0.33H2O exhibits significant volume expansion during the electrochemical cycle, which will lead to increased mechanical stress in the material, thereby affecting the rate performance and cycle stability of the battery. In order to overcome these problems, researchers have adopted a variety of strategies to improve the performance of FeF3·0.33H2O. Nanostructure design is one of the effective methods. Nanosizing can effectively accommodate the volume changes of the material during the charge and discharge process and shorten the diffusion path of ions. In addition, the composite of carbon-based materials can significantly improve the electrical conductivity of FeF3·0.33H2O, thereby improving its rate performance and cycle stability. Heteroatom doping is also an effective means to improve the performance of FeF3·0.33H2O batteries. Metal ions (such as Mn 2+ 、Co 2+ 、Ni 2+ , Cu 2+ , Zn) doping can introduce more active sites, thereby enhancing the energy storage performance.

[0008] In general, iron fluoride (FeF3·0.33H2O), as a cathode material with high energy density and good stability, has broad application prospects in lithium-ion batteries and sodium-ion batteries. Although it has problems of volume expansion and insufficient kinetic performance during the electrochemical cycle, its electrochemical performance can be significantly improved through methods such as nano-design, carbon material composite and heterogeneous atom doping, promoting its widespread application in battery technology. In the future, with the continuous advancement of material design and battery technology, iron fluoride-based materials are expected to become high-performance, low-cost cathode materials, providing strong technical support for the commercial application of lithium-ion batteries and sodium-ion batteries. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material, a preparation method and an application thereof.

[0010] In a first aspect of the present invention, a method for preparing a nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material is provided, which comprises the following steps:

[0011] S1: Mix polyethylene glycol and ethanol in a solution to obtain solution A;

[0012] S2: Add ferric nitrate nonahydrate, cobalt nitrate hexahydrate and hydrofluoric acid to solution A under continuous stirring, and continue stirring; then place the solution in a high pressure reactor for solvothermal reaction;

[0013] S3: washing the solid product after the solvothermal reaction in step S2 repeatedly with anhydrous ethanol, centrifuging and vacuum drying;

[0014] S4: heat-treating the obtained gray powder material under an inert gas atmosphere to remove part of the crystal water, thereby obtaining the FeF3·0.33H2O / CoF2 material, namely the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material.

[0015] The present invention proposes an effective preparation method, which can overcome the problems of easy agglomeration and poor conductivity of FeF3·0.33H2O materials in the prior art. The obtained iron fluoride / cobalt fluoride heterostructure material is assembled into a submicron spherical structure by nanoparticles, and Co 2+ Doping can significantly improve the electrochemical performance of FeF3·0.33H2O by expanding the hexagonal cavity and reducing the band gap. In addition, aliovalent doping effectively promotes the growth of nanocrystals and improves the conductivity of the material by introducing defects and inducing phase transition or composition change.

[0016] Specifically, Co 2+ Doping can not only enhance the structural stability of lithium-ion battery cathode materials and improve specific capacity, but also extend the battery life. 2+ Doping helps promote the embedding and de-embedding process of sodium ions, thereby improving the overall performance of the battery. This material has a wide range of application prospects, especially in the field of high-performance, low-cost cathode materials for lithium-ion and sodium-ion batteries, showing great industrial potential.

[0017] In addition, the preparation method adopted is simple, easy to control, non-toxic, harmless and low-cost, and is very suitable for large-scale production and promotion and application.

[0018] Preferably, in step S1, the volume ratio of polyethylene glycol to ethanol is 1:1-4, for example, 1:1, 1:2, 1:3 or 1:4, wherein 1:1 is most preferred.

[0019] Preferably, in step S2, the molar ratio of ferric nitrate nonahydrate to cobalt nitrate hexahydrate may be 1:0, 0.98:0.02, 0.96:0.04, 0.94:0.06, 0.92, 0.08:0.9:0.1, and most preferably 0.92:0.08.

[0020] Preferably, in step S2, the solvothermal reaction temperature is 100-200°C, for example, 100°C, 120°C, 150°C, 160°C, 180°C, 200°C, and most preferably 150°C.

[0021] Preferably, in step S2, the solvent thermal reaction time is 10-16 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, and most preferably 12 hours.

[0022] Preferably, in step S4, the temperature of the heat treatment is 200-400°C, for example, 200°C, 240°C, 280°C, 300°C, 340°C, 380°C or 400°C, most preferably 300°C.

[0023] Preferably, in step S4, the heat treatment time is 1-3 hours, for example, 1 hour, 2 hours or 3 hours.

[0024] Preferably, in step S4, the inert gas is nitrogen or argon.

[0025] The second aspect of the present invention provides a nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material prepared by the preparation method described above.

[0026] The inventors have found that the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material provided by the present invention has excellent electrochemical properties, and can be applied to the field of electrode materials, especially the field of battery positive electrode materials, and has good application prospects and industrialization potential.

[0027] Therefore, the third aspect of the present invention provides the use of the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material as described above in the preparation of lithium ion / sodium ion battery positive electrode materials.

[0028] The submicron spherical iron fluoride / cobalt fluoride heterostructure material assembled by the nanoparticles as described above can be directly used as a positive electrode material for lithium ion / sodium ion batteries or mixed with other existing positive electrode materials to prepare a composite positive electrode material for preparing lithium / sodium electrodes and further preparing lithium / sodium batteries.

[0029] A fourth aspect of the present invention provides an iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material, which is obtained by mixing the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material and graphite through ball milling.

[0030] The present invention finds that by mixing the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material and graphite through ball milling, the layered graphite can wrap the FeF3·0.33H2O / CoF2 nanoparticle material. Through the above means, the volume expansion problem of the electrode material during the charge and discharge process can be effectively alleviated, the structure can be kept stable, and the cycle life can be improved.

[0031] Therefore, the fifth aspect of the present invention provides the use of the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite as described above in the preparation of lithium ion / sodium ion battery positive electrode materials.

[0032] In summary, the present invention provides a method for preparing iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite. The FeF3·0.33H2O / CoF2 high-performance lithium / sodium storage material prepared by the method has excellent electrical properties and can be used to prepare electrode materials, thereby being used in the battery industry, and has great application potential and industrial value in the electrical field. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0034] Figure 1 It is an X-ray diffraction diagram of the iron fluoride / cobalt fluoride heterostructure nanosphere material prepared in Example 1 of the present invention and a comparison diagram thereof with the standard data of FeF3·0.33H2O crystal (PDF#76-1262) and the standard data of CoF2 crystal (PDF#81-2033);

[0035] Figure 2 is a scanning electron microscope image (SEM) of the iron fluoride / cobalt fluoride heterostructure nanosphere material of Example 1 of the present invention;

[0036] Figure 3 is a scanning electron microscope image (SEM) of the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material of Example 2 of the present invention;

[0037] Figure 4 TEM images and element distribution maps (Mapping) of the iron fluoride / cobalt fluoride heterostructure nanosphere material composite graphite material of Example 2 of the present invention, (a) is a TEM image, and (b-f) are element distribution maps (Mapping) of Fe, Co, F, O and C elements respectively;

[0038] Figure 5 It is a lithium battery charge and discharge curve diagram of different cycle numbers using the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material of Example 2 of the present invention;

[0039] Figure 6 This is a comparison chart of constant current charge and discharge of lithium battery at a current density of 100 mA / g using the materials prepared in Comparative Example 1 and Examples 1-2 of the present invention;

[0040] Figure 7 This is a comparison chart of sodium battery constant current charge and discharge at a current density of 50 mA / g using the materials prepared in Comparative Example 1 and Examples 1-2 of the present invention;

[0041] Figure 8 It is a comparison diagram of sodium battery constant current charge and discharge at a current density of 200 mA / g using the materials prepared in Comparative Example 1 and Examples 1-2 of the present invention;

[0042] Fig. 9 This is a sodium electric cycle rate performance diagram at different current densities using the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material of Example 2 of the present invention;

[0043] Fig.10 It is a sodium charge-discharge curve diagram of the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material of Example 2 of the present invention at different cycle numbers;

[0044] Fig.11 It is a constant current charge and discharge diagram at a current density of 100 mA / g using Example 1 and Examples 3-6 of the present invention. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0046] Embodiment 1:

[0047] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol (i.e., the volume ratio of polyethylene glycol to anhydrous ethanol is 1:1) and add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic stirrer at a speed of 900 r / min, and react for 30 minutes;

[0048] S2: Under continuous stirring, weigh 1.86 g of ferric nitrate nonahydrate, 0.116 g of cobalt nitrate hexahydrate (molar ratio 0.92:0.08) and 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place the mixture in a high pressure reactor and react at 150° C. for 12 hours;

[0049] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample FeF3·0.33H2O / CoF2;

[0050] S4: The FeF3·0.33H2O / CoF2 precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300°C at a heating rate of 2°C / min at room temperature for 3 hours, thereby obtaining a nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material.

[0051] S5: Weigh iron fluoride / cobalt fluoride material, Ketjen black, and polyvinylidene fluoride (PVDF) (the volume ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0052] Embodiment 2:

[0053] 80 mg of the iron fluoride / cobalt fluoride heterostructure nanosphere material prepared in Example 1 and 20 mg of graphite (the volume ratio of FeF3·0.33H2O / CoF2:G=8:2) were weighed and placed in an agate ball mill, with a ball-to-material ratio of 10:1. 1.6 g of agate balls were also added to the agate mill, and the mill was sealed; during the ball milling process, the ball milling speed was 300 rpm. To ensure that the material is not deposited at the bottom as much as possible. After the ball milling is completed, the temperature is cooled to room temperature, and the material is collected and sealed to obtain a nanoparticle assembly submicron spherical iron fluoride composite graphite material.

[0054] Weigh iron fluoride / cobalt fluoride composite graphite material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to an aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0055] Embodiment 3:

[0056] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol and add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic rod at a speed of 900 r / min, and react for 30 minutes;

[0057] S2: Under continuous stirring, weigh 1.980 g of ferric nitrate nonahydrate, 0.0291 g of cobalt nitrate hexahydrate (molar ratio 0.98:0.02) and 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place the mixture in a high pressure reactor and react at 150° C. for 12 hours;

[0058] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample named FC1;

[0059] S4: The FC1 precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300° C. at room temperature at a heating rate of 2° C. / min for 3 hours, thereby obtaining a nanoparticle-assembled submicron spherical FC1 material.

[0060] S5: Weigh nanoparticle-assembled submicron spherical FC1 material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0061] Embodiment 4:

[0062] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol and add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic rod at a speed of 900 r / min, and react for 30 minutes;

[0063] S2: Under continuous stirring, weigh 1.939 g of ferric nitrate nonahydrate, 0.0582 g of cobalt nitrate hexahydrate (molar ratio 0.96:0.04) and 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place the mixture in a high pressure reactor and react at 150° C. for 12 hours;

[0064] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample FC2;

[0065] S4: The FC2 precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300° C. at room temperature at a heating rate of 2° C. / min for 3 hours, thereby obtaining a nanoparticle-assembled submicron spherical FC2 material.

[0066] S5: Weigh nanoparticle-assembled submicron spherical FC2 material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0067] Embodiment 5:

[0068] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol and add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic rod at a speed of 900 r / min, and react for 30 minutes;

[0069] S2: Under continuous stirring, weigh 1.899 g of ferric nitrate nonahydrate, 0.0873 g of cobalt nitrate hexahydrate (molar ratio 0.94:0.06) and 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place the mixture in a high pressure reactor and react at 150° C. for 12 hours;

[0070] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample FC3;

[0071] S4: The FC3 precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300° C. at room temperature at a heating rate of 2° C. / min for 3 hours, thereby obtaining a nanoparticle-assembled submicron spherical FC3 material.

[0072] S5: Weigh nanoparticle-assembled submicron spherical FC3 material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0073] Embodiment 6:

[0074] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol, add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic stirrer at 900 r / min, and react for 30 minutes;

[0075] S2: Under continuous stirring, weigh 1.818 g of ferric nitrate nonahydrate, 0.1455 g of cobalt nitrate hexahydrate (molar ratio 0.90:0.1) and 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place the mixture in a high pressure reactor and react at 150° C. for 12 hours;

[0076] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample FC4;

[0077] S4: The FC4 precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300° C. at room temperature at a heating rate of 2° C. / min for 3 hours, thereby obtaining a nanoparticle-assembled submicron spherical FC4 material.

[0078] S5: Weigh nanoparticle-assembled submicron spherical FC4 material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0079] Comparative Example 1:

[0080] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol and add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic rod at a speed of 900 r / min, and react for 30 minutes;

[0081] S2: Under continuous stirring, weigh 2.02 g of ferric nitrate nonahydrate, measure 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place it in a high pressure reactor and react at 150 ° C for 12 hours;

[0082] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample FeF3·0.33H2O;

[0083] S4: The FeF3·0.33H2O precursor obtained in step S3 is placed in an argon atmosphere, put into a tube furnace, and heated to 300°C at a heating rate of 2°C / min at room temperature for 3 hours to obtain a nanoparticle-assembled submicron spherical iron fluoride material.

[0084] S5: Weigh nanoparticle-assembled submicron spherical ferric fluoride material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to an aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0085] Comparative Example 2:

[0086] S1: Measure 20 ml of polyethylene glycol and 20 ml of anhydrous ethanol, add them to 100 ml of polytetrafluoroethylene liner, stir in a water bath, stir with a magnetic stirrer at 900 r / min, and react for 30 minutes;

[0087] S2: Under continuous stirring, weigh 1.46 g of cobalt nitrate hexahydrate, measure 1 ml of 40 wt% HF solution, and continue stirring for 2 h; then place it in a high pressure reactor and react at 150 ° C for 12 hours;

[0088] S3: After the reaction is completed, the pressure is released to normal pressure and naturally cooled to room temperature. The obtained solid is fully washed with anhydrous ethanol for 2-4 times and vacuum dried at 80°C for 10 hours to obtain a dry sample CoF2;

[0089] S4: placing the cobalt fluoride precursor obtained in step S3 in an argon atmosphere, placing it in a tube furnace, heating it to 300° C. at room temperature at a heating rate of 2° C. / min for 3 hours, thereby obtaining a cobalt fluoride material.

[0090] S5: Weigh cobalt fluoride material, Ketjen black, and polyvinylidene fluoride (PVDF) (the mass ratio of the three is 80:10:10), add a certain amount of N-methylpyrrolidone (NMP), mix, and continuously stir until it becomes a paste, and then apply it to the aluminum foil current collector; dry, bake, and press the current collector coated with the composite material to obtain a battery.

[0091] Microscopic characterization

[0092] Depend on Figure 1 It can be seen that the positions and intensities of the diffraction peaks of the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material prepared in Example 1 are basically consistent with the standard diffraction cards (FeF3·0.33H2O JCPDS No.76-1262 and CoF2 JCPDS No.81-2033), and the diffraction peak intensity is relatively strong, indicating that the material has a high degree of crystallinity. The XRD pattern of the material prepared in Example 2 is consistent with Figure 1 are similar and are therefore omitted here.

[0093] Depend on Figure 2 It can be seen that the iron fluoride / cobalt fluoride heterostructure nanosphere material prepared in Example 1 has a spherical structure with a relatively smooth surface. It is an aggregate composed of tiny nanoparticles with a particle size of about 1-2 μm.

[0094] Depend on Figure 3 It can be seen that the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material prepared in Example 2 has a surface of layered graphite wrapped with FeF3·0.33H2O / CoF2 nanoparticle material, which effectively alleviates the volume expansion problem of the electrode material during the charging and discharging process, maintains structural stability, and improves the cycle life.

[0095] Depend on Figure 4(af) It can be seen that the TEM images and mapping element distribution diagrams of the FeF3·0.33H2O / CoF2 / G heterostructure nanosphere composite graphite material prepared in Example 1 show that most of the FeF3·0.33H2O / CoF2 / G nanospheres have a diameter of only about 200nm, and graphite is evenly coated on the nanospheres, indicating that the cobalt fluoride heterostructure and graphite will effectively improve the electronic conductivity of the composite positive electrode material. In addition, the element distribution diagram confirms that Fe, Co, F, O and C elements are evenly present in the entire FeF3·0.33H2O / CoF2 / G crystal.

[0096] Electrical performance test

[0097] (1) Lithium-ion battery testing was performed at 289K using the Xinwei multi-channel CT-4008-5V-20mA test system. In the 2-4.5V voltage range, 100mAh g -1 At current density of 1000mAh g -1 The cycle capacity and coulombic efficiency of the assembled batteries were tested at current density.

[0098] (2) Sodium ion battery testing was performed at 289K using the Xinwei multi-function channel CT-4008-5V-20mA test system, with a voltage range of 1.5-4V, 100mAh g -1 The cycle capacity and coulombic efficiency of the assembled battery were tested at the current density;

[0099] (3) Tested at 289K using the Xinwei multi-function channel CT-4008-5V-20mA test system. In the voltage range of 1.5-4V, at 20mA g -1 , 50mA g -1 , 100mA g -1 , 200mA g -1 , 500mA g -1 , 50mA g -1 and 20mA g -1 The reaction was cycled 10 times at a current density of , and the rate performance test was carried out.

[0100] In lithium-ion batteries, the cycle stability test results of the FeF3·0.33H2O / CoF2 composite material prepared in Example 1 are as follows: Figure 6 As shown. At 100mA g -1 At the current density, the first discharge capacity is 150 mAh g -1 , the first coulombic efficiency reached 111.7%. After 100 charge and discharge cycles, the discharge capacity of the battery was 112 mAh g -1, the capacity retention rate is 74.4%. Compared with Comparative Example 1 and Comparative Example 2, the electrochemical performance of the material has been significantly improved. Since the ionic radius of cobalt and iron is similar, replacing Fe atoms with Co atoms can effectively reduce structural distortion and maintain the stable structure of iron fluoride. This further shows that when the two materials form a heterostructure, they can complement each other, iron fluoride provides a higher theoretical capacity, while cobalt fluoride improves conductivity and enhances reaction rate. This synergistic effect helps to improve the rate performance and cycle life of the battery and reduce capacity decay.

[0101] In addition, Examples 3-6 are iron fluoride / cobalt fluoride materials doped with different cobalt contents, and the lithium ion cycle stability test results further verify the improvement of electrochemical performance by cobalt fluoride. Fig.11 As shown, at 100mA g -1 Under current density, as the cobalt content increases, the electrochemical performance of the lithium-ion battery continues to increase, especially when the molar ratio of Fe to Co is 0.92:0.08 (Example 1), the material shows the best performance. When the cobalt content is increased to 0.9:0.1 (Example 6), the electrochemical performance shows a downward trend.

[0102] Comparative Example 2 Preparation of Iron Fluoride / Cobalt Fluoride Heterostructure Nanosphere Composite Graphite Material Cyclic Stability Test ( Figure 7 ), at 100mA g -1 At the current density, the first discharge capacity of Example 2 is 175 mAh g -1 , the first coulombic efficiency is close to 100%. After 100 cycles, the battery capacity rises to 180mAh g -1 Compared with Example 1, the FeF3·0.33H2O / CoF2 composite graphite material prepared in Example 2 performs better in terms of cycle stability and electrochemical capacity, showing that cobalt fluoride significantly improves the performance of iron fluoride materials.

[0103] In summary, the test results of Example 1 and Example 2 show that the formation of cobalt fluoride can not only improve the cycle stability of FeF3·0.33H2O material, but also significantly improve the electrochemical capacity, further demonstrating the potential of heterostructure composite materials of cobalt and iron in lithium-ion batteries.

[0104] The sodium battery cycle stability test results of the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material prepared in Example 2 are as follows: Figure 7-9 As shown. At 50mA g -1 At the current density, the first discharge capacity reaches 135 mAh g -1 After 100 charge and discharge cycles, the battery capacity is 168 mAh g -1, showing excellent cycle stability. It is obvious that there is a capacity increase process in the first 20 cycles. This is mainly because the electrode material needs to undergo an activation process in the initial stage. During this process, the active sites inside the electrode material are gradually activated, and sodium ions can be embedded and removed faster, which makes the number of active substances participating in the electrochemical reaction gradually increase, which in turn manifests as an increase in capacity. As the number of cycles increases further, its capacity slowly shows a decay trend. However, even in the decay stage, the electrochemical capacity exhibited by the heterostructure composite material is still higher than that of FeF3·0.33H2O. From Fig. 9 It can be seen that the electrochemical capacity of the FeF3·0.33H2O / CoF2 / G composite material prepared in Example 2 at different current densities is 163 mAh g -1 , 185mAh g -1 , 177mAh g -1 , 165mAh g -1 and 160mAh g -1 When the current density returns to 20 mA g -1 The battery reversible capacity is 184 mAh g -1 , far exceeding the initial capacity, further indicating that the battery has excellent reversible cyclability. Compared with the material in Comparative Example 1, the FeF3·0.33H2O / CoF2 / G composite material exhibits a significantly longer cycle life, which indicates that the composite carbon material enhances the cycle stability of the electrode material to a certain extent and improves its electrochemical capacity.

[0105] Further analysis Fig.10 The test results show that at 50mA g -1 Under the current density, the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material prepared in Example 2 has an obvious activation process in the initial charge and discharge process, and the charge and discharge curve does not show an obvious platform. This shows that the material has a high electrochemical reaction activity in the initial charge and discharge process, and can maintain stable electrochemical performance in subsequent cycles, fully demonstrating its excellent electrochemical cycle stability.

[0106] In summary, the iron fluoride / cobalt fluoride heterostructure nanosphere composite graphite material prepared in Example 2 not only has a high initial capacity at low current density, but also maintains excellent capacity retention rate in multiple cycles and has strong cycle stability, showing great potential as a negative electrode material for sodium batteries.

[0107] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a submicron spherical iron fluoride / cobalt fluoride heterostructure material assembled by nanoparticles, characterized in that It includes the following steps: S1: Mix polyethylene glycol and ethanol in a solution to obtain a clear solution A; S2: Add ferric nitrate nonahydrate, cobalt nitrate hexahydrate and hydrofluoric acid to solution A under continuous stirring, and continue stirring; then place the solution in a high pressure reactor for solvothermal reaction; S3: washing the solid product after the solvothermal reaction in step S2 repeatedly with anhydrous ethanol, centrifuging and vacuum drying; S4: heat-treating the obtained gray powder material under an inert gas atmosphere to remove part of the crystal water, thereby obtaining the FeF3·0.33H2O / CoF2 material, namely the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material.

2. The preparation method according to claim 1, characterized in that: In step S1, the volume ratio of polyethylene glycol to ethanol is 1:

1.

3. The preparation method according to claim 1, characterized in that: In step S2, the molar ratio of ferric nitrate nonahydrate to cobalt nitrate hexahydrate is 1-0.9:0-0.

1.

4. The preparation method according to claim 1, characterized in that: In step S2, the solvent thermal reaction temperature is 100-200°C, and the reaction time is 10-16 hours.

5. The preparation method according to claim 1, characterized in that: In step S4, the temperature of the heat treatment is 200-400°C.

6. The nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material as claimed in claim 6 in the preparation of positive electrode materials for lithium ion / sodium ion batteries.

8. An iron fluoride / cobalt fluoride heterostructure composite graphite material, characterized in that: It is obtained by mixing the nanoparticle-assembled submicron spherical iron fluoride / cobalt fluoride heterostructure material and graphite through ball milling.

9. Use of the iron fluoride / cobalt fluoride heterostructure material composite graphite material as claimed in claim 8 in preparing positive electrode materials for lithium ion / sodium ion batteries.

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