Iron-based bimetallic oxide composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an iron-based bimetallic oxide composite material as well as a preparation method and application thereof. The composite material provided by the invention comprises an iron-based bimetallic oxide and coating carbon located on the surface of the iron-based bimetallic oxide, the iron-based bimetallic oxide composite material has a solid microrod structure; the section of the solid microrod structure is circular; the iron-based bimetallic oxide composite material is in a monodisperse state and does not form clusters. According to the invention, the composite material with the solid microrod structure is beneficial to diffusion of lithium ions in the composite material, and the tap density is large; and meanwhile, the carbon coated on the surface can further improve the conductivity of the composite material, so that the microrod can maintain the structural integrity in the cycle process, and the charge-discharge capacity and the cycle stability of the lithium ion battery under high current density can be further improved when the microrod is applied to the lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to an iron-based bimetallic oxide composite material and a preparation method and application thereof. Background Art

[0002] Iron-based bimetallic oxides (MFe2O4, M = Zn, Co, Ni, etc.) have broad application prospects as anode materials in lithium-ion batteries. Due to their low cost, non-toxicity, and environmental friendliness, they also possess high theoretical specific capacity (900-1000 mAh / g), significantly exceeding the 372 mAh / g of commercial graphite anode materials. They are considered an ideal alternative to traditional carbon materials.

[0003] However, existing iron-based bimetallic oxides are porous, nanoparticle or fibrous, have low tap density, and are prone to structural collapse during the charge and discharge process, which in turn leads to reduced specific capacity, rate performance and cycle stability of the battery at high current density. Summary of the Invention

[0004] The purpose of the present invention is to provide an iron-based bimetallic oxide composite material and its preparation method and application. The iron-based bimetallic oxide provided by the present invention is applied to lithium-ion batteries to improve the charge and discharge capacity, rate performance and cycle stability of lithium-ion batteries at high current density.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides an iron-based bimetallic oxide composite material, comprising an iron-based bimetallic oxide and coated carbon located on the surface of the iron-based bimetallic oxide; The iron-based bimetallic oxide composite material has a solid microrod structure; the cross section of the solid microrod structure is circular; The iron-based bimetallic oxide composite material is in a monodisperse state and does not form clusters.

[0006] Preferably, the chemical composition of the iron-based bimetallic oxide is MFe2O4, and M is Zn, Co, Ni or Cu; The mass percentage of the coated carbon in the iron-based bimetallic oxide composite material is 8-15%.

[0007] Preferably, the solid microrod structure has a length of 0.5-1.5 μm and a diameter of 0.3-0.5 μm.

[0008] The present invention also provides a method for preparing the iron-based bimetallic oxide composite material described in the above technical solution, comprising the following steps: Mixing a water-soluble iron salt, an auxiliary metal salt, polyvinyl pyrrolidone, ethylenediamine and water, and performing a hydrothermal reaction to obtain an iron-based bimetallic oxide, wherein the auxiliary metal salt includes a water-soluble zinc salt, a water-soluble cobalt salt, a water-soluble nickel salt or a water-soluble copper salt; The iron-based bimetallic oxide and an aqueous solution containing a carbon source are mixed, and dried and carbonized in sequence to obtain the iron-based bimetallic oxide composite material.

[0009] Preferably, the iron salt is ammonium ferric oxalate trihydrate; The water-soluble zinc salt includes at least one of zinc nitrate, zinc sulfate, zinc acetate and zinc chloride; The water-soluble cobalt salt includes at least one of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride; The water-soluble nickel salt includes at least one of nickel nitrate, nickel sulfate, nickel acetate and nickel chloride; The water-soluble copper salt includes at least one of copper nitrate, copper sulfate, copper acetate and copper chloride.

[0010] Preferably, the molar ratio of the water-soluble iron salt to the auxiliary metal salt is 2:1; The mass ratio of the water-soluble iron salt to polyvinyl pyrrolidone is 1:0.4-0.8; The molar ratio of the water-soluble iron salt to ethylenediamine is 1:25-50; The molar concentration of the water-soluble iron salt is 0.05-0.5 mol / L.

[0011] Preferably, the temperature of the hydrothermal reaction is 150-180° C., and the holding time is 5-9 hours.

[0012] Preferably, the carbon source in the aqueous solution containing a carbon source comprises at least one of gluconolactone, sucrose, glucose and polyacrylic acid; The concentration of the aqueous solution containing the carbon source is 10-20 g / L; The mass ratio of the iron-based bimetallic oxide to the aqueous solution containing a carbon source is 1:40-100.

[0013] Preferably, the carbonization temperature is 400-600°C, the heating rate to the carbonization temperature is 2-5°C / min, and the holding time is 2-4h; The carbonization is carried out under a protective atmosphere.

[0014] The present invention also provides the use of the iron-based bimetallic oxide composite material described in the above technical solution or the iron-based bimetallic oxide composite material prepared by the preparation method described in the above technical solution as a negative electrode material for a lithium-ion battery.

[0015] The present invention provides an iron-based bimetallic oxide composite material, comprising an iron-based bimetallic oxide and a carbon coating located on the surface of the iron-based bimetallic oxide; the iron-based bimetallic oxide composite material has a solid microrod structure; the cross-section of the solid microrod structure is circular; and the iron-based bimetallic oxide composite material is monodispersed and does not form clusters. In the present invention, the composite material having a solid microrod structure facilitates rapid diffusion of lithium ions within the composite material, improves active material utilization, and has a high tap density. Furthermore, the carbon coating further enhances the composite material's conductivity, and its coating enables the microrods to maintain structural integrity during cycling. Application to lithium-ion batteries can further improve the charge-discharge capacity, rate capability, and cycling stability of lithium-ion batteries at high current densities. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 XRD patterns of the ZnFe2O4 material and the ZnFe2O4 / C composite material obtained in Example 1; Figure 2 This is the SEM image of the ZnFe2O4 material obtained in Example 1; Figure 3 This is a SEM image of the ZnFe2O4 / C composite material obtained in Example 1; Figure 4 TEM image of the ZnFe2O4 / C composite material obtained in Example 1; Figure 5 This is a rate performance diagram of a button cell prepared from the ZnFe2O4 / C composite material obtained in Example 1; Figure 6 This is a cycle performance diagram of button batteries prepared with ZnFe2O4 / C and ZnFe2O4 materials obtained in Example 1; Figure 7 This is the SEM image of the CoFe2O4 material obtained in Example 2; Figure 8 This is the SEM image of the NiFe2O4 material obtained in Example 3; Figure 9 This is the SEM image of the CuFe2O4 material obtained in Example 4; Figure 10 This is the SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 1; Figure 11 This is the SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 2; Figure 12 This is the SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 3. DETAILED DESCRIPTION

[0017] The present invention provides an iron-based bimetallic oxide composite material, comprising an iron-based bimetallic oxide and coated carbon located on the surface of the iron-based bimetallic oxide; The iron-based bimetallic oxide composite material has a solid microrod structure; the cross section of the solid microrod structure is circular; The iron-based bimetallic oxide composite material is in a monodisperse state and does not form clusters.

[0018] In the present invention, the chemical composition of the iron-based bimetallic oxide is preferably MFe2O4, where M is Zn, Co, Ni, or Cu. In the present invention, the mass percentage of the coated carbon in the iron-based bimetallic oxide composite material is preferably 8-15%, specifically 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. In the present invention, the coated carbon is preferably amorphous carbon.

[0019] In the present invention, the length of the solid microrod structure is preferably 0.5-1.5 μm, and the diameter is preferably 0.3-0.5 μm. In the present invention, the tap density of the iron-based bimetallic oxide composite material is preferably 1.3-1.6 g / cm 3 .

[0020] The present invention also provides a method for preparing the iron-based bimetallic oxide composite material described in the above technical solution, comprising the following steps: Mixing a water-soluble iron salt, an auxiliary metal salt, polyvinyl pyrrolidone, ethylenediamine and water, and performing a hydrothermal reaction to obtain an iron-based bimetallic oxide, wherein the auxiliary metal salt includes a water-soluble zinc salt, a water-soluble cobalt salt, a water-soluble nickel salt or a water-soluble copper salt; The iron-based bimetallic oxide and an aqueous solution containing a carbon source are mixed, and dried and carbonized in sequence to obtain the iron-based bimetallic oxide composite material.

[0021] The invention mixes water-soluble iron salt, auxiliary metal salt, polyvinyl pyrrolidone, ethylenediamine and water, and performs hydrothermal reaction to obtain iron-based bimetallic oxide, wherein the auxiliary metal salt includes water-soluble zinc salt, water-soluble cobalt salt, water-soluble nickel salt or water-soluble copper salt.

[0022] In the present invention, the water-soluble iron salt is preferably ammonium ferric oxalate trihydrate; the water-soluble zinc salt preferably includes at least one of zinc nitrate, zinc sulfate, zinc acetate, and zinc chloride, and the zinc sulfate is preferably zinc sulfate heptahydrate; the water-soluble cobalt salt preferably includes at least one of cobalt nitrate, cobalt sulfate, cobalt acetate, and cobalt chloride, and the cobalt sulfate is preferably cobalt sulfate heptahydrate; the water-soluble nickel salt preferably includes at least one of nickel nitrate, nickel sulfate, nickel acetate, and nickel chloride, and the nickel sulfate is preferably nickel sulfate heptahydrate; the water-soluble copper salt preferably includes at least one of copper nitrate, copper sulfate, copper acetate, and copper chloride, and the copper sulfate is preferably copper sulfate pentahydrate. In the present invention, the water is preferably deionized water.

[0023] In the present invention, the molar ratio of the water-soluble iron salt and the auxiliary metal salt is preferably 2:1; the mass ratio of the water-soluble iron salt and polyvinylpyrrolidone is preferably 1:0.4~0.8, specifically 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8; the molar ratio of the water-soluble iron salt and ethylenediamine is preferably 1:25~50, specifically 1:25, 1:30, 1:35, 1:40, 1:45, 1:50; the molar concentration of the water-soluble iron salt is 0.05~0.5 mol / L, specifically 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L.

[0024] In the present invention, the mixing is preferably carried out under stirring. In the present invention, the temperature of the hydrothermal reaction is preferably 150-180°C, specifically 150°C, 160°C, 170°C, or 180°C, and the holding time is preferably 5-9 hours, specifically 5 hours, 6 hours, 7 hours, 8 hours, or 9 hours. In the present invention, the hydrothermal reaction is preferably carried out in a hydrothermal reactor with a polytetrafluoroethylene lining.

[0025] In the present invention, after the hydrothermal reaction, the obtained system is preferably cooled to room temperature, and the precipitate is collected by filtration, and the obtained precipitate is repeatedly washed with water and dried. In the present invention, the drying temperature is preferably 80°C.

[0026] After obtaining the iron-based bimetallic oxide, the present invention mixes the iron-based bimetallic oxide with an aqueous solution containing a carbon source, and sequentially performs drying and carbonization to obtain the iron-based bimetallic oxide composite material.

[0027] In the present invention, the carbon source in the aqueous solution containing a carbon source preferably includes at least one of gluconolactone, sucrose, glucose, and polyacrylic acid; the solvent in the aqueous solution containing a carbon source is preferably deionized water. In the present invention, the aqueous solution containing a carbon source is preferably obtained by dissolving a carbon source in water. In the present invention, the concentration of the aqueous solution containing a carbon source is preferably 10-20 g / L, specifically 10 g / L, 15 g / L, or 20 g / L; the mass ratio of the iron-based bimetallic oxide to the aqueous solution containing a carbon source is preferably 1:40-100, specifically 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1:100.

[0028] In the present invention, the drying method is preferably: stirring under heating conditions until the water is completely evaporated. In the present invention, the heating temperature is preferably 80°C. In the present invention, the carbonization temperature is preferably 400~600°C, specifically 400°C, 500°C, 600°C; the heating rate to the carbonization temperature is preferably 2~5°C / min, specifically 2°C / min, 3°C / min, 4°C / min, 5°C / min; the holding time is preferably 2~4h, specifically 2h, 3h, 4h; the carbonization is carried out under a protective atmosphere, and the protective atmosphere is preferably argon. In the present invention, the carbonization is preferably carried out in a tube furnace.

[0029] The present invention also provides the use of the iron-based bimetallic oxide composite material described in the above technical solution or the iron-based bimetallic oxide composite material prepared by the preparation method described in the above technical solution as a negative electrode material for a lithium-ion battery.

[0030] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] Example 1 1 mmol of zinc sulfate heptahydrate, 2 mmol of ammonium ferric oxalate trihydrate, 0.5 g of polyvinyl pyrrolidone (k30), and 5 mL of ethylenediamine were added to 30 mL of deionized water in sequence, and stirred to dissolve to form a uniform solution; The above solution was transferred to a reactor with a polytetrafluoroethylene lining, heated to 160°C for hydrothermal reaction, and kept warm for 8 hours; after the reactor was cooled to room temperature, the precipitate was collected by filtration, repeatedly washed with deionized water, and dried at 80°C to obtain ZnFe2O4 powder material; Then, 0.11 g of gluconolactone was dissolved in 10 mL of deionized water, 0.2 g of ZnFe2O4 material was added, and the mixture was vigorously stirred at 80 ° C. After the water was completely evaporated, the mixture was transferred to a tube furnace and heated to 500 ° C at a heating rate of 4 ° C / min in an argon atmosphere for carbonization. The temperature was kept for 2 h to obtain a ZnFe2O4 / C composite material (the carbon content in the composite material was tested using the elemental analyzer Unicube, and the mass percentage of the coated carbon was 11.1%; the tap density of the composite material was tested using the tap density tester GP-01, and the result was 1.45 g / cm 3 ).

[0033] Example 2 1 mmol of cobalt sulfate heptahydrate, 2 mmol of ammonium ferric oxalate trihydrate, 0.5 g of polyvinyl pyrrolidone (k30), and 5 mL of ethylenediamine were added to 30 mL of deionized water in sequence, and stirred to dissolve to form a uniform solution; The above solution was transferred to a reactor with a polytetrafluoroethylene lining, heated to 160°C for hydrothermal reaction, and kept warm for 6 hours. After the reactor was cooled to room temperature, the precipitate was collected by filtration, repeatedly washed with deionized water, and dried at 80°C to obtain CoFe2O4 powder material; A composite material was prepared in the manner of Example 1 and was designated as CoFe2O4 / C composite material. (The carbon content in the composite material was tested using an elemental analyzer, Unicube, and the mass percentage of the coated carbon was 10.9%. The tap density of the composite material was tested using a tap density tester, GP-01, and the result was 1.42 g / cm 3 ).

[0034] Example 3 1 mmol of nickel sulfate heptahydrate, 2 mmol of ammonium ferric oxalate trihydrate, 0.5 g of polyvinyl pyrrolidone, and 5 mL of ethylenediamine were added to 30 mL of deionized water in sequence, and stirred to dissolve to form a uniform solution; The above solution was transferred to a reactor with a polytetrafluoroethylene lining, heated to 170°C for hydrothermal reaction, and kept warm for 6 hours. After the reactor was cooled to room temperature, the precipitate was collected by filtration, repeatedly washed with deionized water, and dried at 80°C to obtain NiFe2O4 powder material; A composite material was prepared in the manner of Example 1 and was designated as NiFe2O4 / C composite material. (The carbon content in the composite material was tested using an elemental analyzer, Unicube, and the mass percentage of the coated carbon was 11.0%. The tap density of the composite material was tested using a tap density tester, GP-01, and the result was 1.40 g / cm 3 ).

[0035] Example 4 1 mmol of copper sulfate pentahydrate, 2 mmol of ammonium ferric oxalate trihydrate, 0.5 g of polyvinylpyrrolidone, and 5 mL of ethylenediamine were added to 30 mL of deionized water in sequence and stirred to dissolve to form a uniform solution; The above solution was transferred to a reactor with a polytetrafluoroethylene lining, heated to 160°C for hydrothermal reaction, and kept warm for 8 hours; after the reactor was cooled to room temperature, the precipitate was filtered and collected, and repeatedly washed with deionized water, and dried at 80°C to obtain CuFe2O4 powder material; A composite material was prepared in the manner of Example 1 and was designated as CuFe2O4 / C composite material. (The carbon content in the composite material was tested using an elemental analyzer, Unicube, and the mass percentage of the coated carbon was 11.2%. The tap density of the composite material was tested using a tap density tester, GP-01, and the result was 1.37 g / cm 3 ).

[0036] Comparative Example 1 Zinc acetate, ferric acetate, and citric acid were mixed in 100 mL of distilled water according to the stoichiometric ratio. The pH of the solution was then precisely controlled at 7 using aqueous ammonia. The citric acid served as both a chelating agent and a carbon source. The resulting solution was heated continuously to 80°C in a stirrer until the water evaporated completely. During the drying process, the xerogel formed a fluffy powder after being kept at 120°C for 12 hours. Finally, the sample was calcined at 600°C for 4 hours to obtain the ZnFe2O4 / C composite material (for details, see Alam MW, BaQaisA, Rahman MM, et al. Investigation on In Situ Carbon-Coated ZnFe2O4 as Advanced Anode Material for Li-Ion Batteries[J]. Gels, 2022, 8, 305).

[0037] The SEM images of the obtained composite materials are shown in Figure 10 As shown, it can be seen that due to the combustion process triggered by carbon agglomeration, irregular particles with different sizes, different stacking methods and uneven distribution are formed.

[0038] The obtained composite material was assembled into a button battery for rate performance test. The current density was from 100 mAh g -1 Gradually increase to 8000mAh·g -1 , then dropped back to 500mAh·g -1 At 100, 200, 500, 2000, 4000 and 8000mA·g -1 At different current densities, the discharge capacities reached approximately 1312, 1059, 806, 471, 207, and 119 mAh·g, respectively. -1 .

[0039] Comparative Example 2 8 mmol of zinc chloride, 16 mmol of ferric chloride hexahydrate, and 45 mmol of ammonium acetate were dissolved in a mixture of ethylene glycol and deionized water and stirred continuously for 1 hour. 2.6 mmol of citric acid was then added to the mixture. The homogeneous solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally treated at 200°C for 24 hours to precipitate ZnFe2O4 particles. Finally, the resulting ZnFe2O4 particles were sintered at 600°C for 5 hours under a nitrogen atmosphere to form mesoporous ZnFe2O4 / C composite microspheres (for details, see Yao L, Hou X, Hu S, et al. Green synthesis of mesoporous ZnFe2O4 / C composite microspheres as superior anode materials for lithium-ion batteries [J]. Journal of Power Sources, 2014, 258(jul.15):305-313).

[0040] The SEM images of the obtained mesoporous ZnFe2O4 / C composite microspheres are shown in Figure 2. Figure 11 As shown, it can be seen that the obtained composite material is secondary particles composed of nano-scale particles and has a porous structure.

[0041] The obtained composite materials were assembled into button batteries for rate performance testing at 0.1, 0.2, 0.5 and 1.0 A·g -1 At specific currents, the specific capacities of the ZnFe2O4 / C electrodes are 1050, 920, 870, and 600 mAh·g, respectively. -1 .

[0042] Comparative Example 3 10 mL of N,N-dimethylformamide was poured into a 20 mL sample vial, and 1.2 g of polyacrylonitrile was added and dissolved. After a transparent colloidal solution was formed, 2 mmol of ferric acetylacetonate and 1 mmol of anhydrous zinc acetate were dissolved in the solution under magnetic stirring. The reaction was continued for 12 hours. The solution was then transferred to a 5 mL syringe. ZnFe2O4 / C nanofiber precursors were prepared using an electrospinning apparatus operating at a negative voltage of -5 kV to a positive voltage of 15 kV at a feed rate of 0.01 mL / min. The nanofiber precursors were then heated to 550°C under an argon atmosphere at a heating rate of 1°C / min to obtain ZnFe2O4 / C nanofibers (see Xiao Y, Zhang Z, Ma Z, et al. Synthesis and electrochemical properties of ZnFe2O4 / C as a novel anode material for lithium ion battery[J]. Ionics, 2021, 27:1377-1384).

[0043] The SEM images of the obtained ZnFe2O4 / C nanofibers are shown in Figure 2. Figure 12 As shown, it can be seen that its morphology is fibrous.

[0044] The obtained composite materials were assembled into button batteries for rate performance and cycle performance tests. -1 When the specific capacity is only 261.8 mAh g -1 At a higher current density of 0.5 A g -1 After 500 cycles, the battery capacity only remained at 479.3 mAh g -1 Specific capacity.

[0045] Performance Testing Test Example 1 The ZnFe2O4 material and ZnFe2O4 / C composite material obtained in Example 1 were subjected to X-ray diffraction test, and the obtained XRD patterns were as follows: Figure 1 As shown. Figure 1 It can be seen that the ZnFe2O4 material and the ZnFe2O4 / C composite material obtained in this embodiment are both ZnFe2O4 single phase, and the carbon in the ZnFe2O4 / C composite material is amorphous.

[0046] Test Example 2 The ZnFe2O4 material and ZnFe2O4 / C composite material obtained in Example 1 were tested by scanning electron microscopy, and the obtained SEM images were as follows: Figure 2 and Figure 3 As shown. Figure 2It can be seen that the ZnFe2O4 material obtained in this embodiment presents a monodisperse microrod morphology. Figure 3 It can be seen that the ZnFe2O4 / C composite material obtained in this example also presents a monodisperse microrod morphology.

[0047] The CoFe2O4 material obtained in Example 2 was subjected to scanning electron microscopy testing, and the obtained SEM image was as follows: Figure 7 As shown. Figure 7 It can be seen that the obtained CoFe2O4 material has a monodisperse microrod morphology.

[0048] The NiFe2O4 material obtained in Example 3 was subjected to scanning electron microscopy testing, and the obtained SEM images are as follows: Figure 8 As shown. Figure 8 It can be seen that the obtained NiFe2O4 material has a monodisperse microrod morphology.

[0049] The CuFe2O4 material obtained in Example 4 was subjected to scanning electron microscopy testing, and the obtained SEM images are as follows: Figure 9 As shown. Figure 9 It can be seen that the obtained CuFe2O4 material has a monodisperse microrod morphology.

[0050] Test Example 3 The ZnFe2O4 / C composite material obtained in Example 1 was tested by transmission electron microscopy, and the obtained TEM image is as follows: Figure 4 As shown, from Figure 4 It can be seen that the ZnFe2O4 / C composite material obtained in this embodiment is a solid micron rod, and the surface of the rod is covered with a carbon layer.

[0051] Test Example 4 The material obtained in the embodiment is used as active material to prepare a lithium ion battery; The preparation method is: The active material, Super P conductive carbon, and polyvinylidene fluoride binder were mixed in a mass ratio of 75:15:10, and an appropriate amount of N-methylpyrrolidone solvent was added and stirred evenly. The mixture was then coated on copper foil and dried in a vacuum at 70°C to produce the negative electrode. A CR2016 coin cell battery was assembled using a lithium sheet as the counter electrode, a polypropylene porous membrane as the separator, and a solution of 1 mol lithium hexafluorophosphate dissolved in 1 L of a mixed solvent of ethylene carbonate and dimethyl carbonate (1:1 by volume).

[0052] The CR2016 button battery obtained by using ZnFe2O4 / C composite material as active material was tested on the CT2001A battery test system for rate performance. The rate performance diagram is shown in the figure below. Figure 5 As shown. Figure 5It can be seen that the average discharge capacity at a current density of 0.1A / g is as high as 1055mAh / g, the average discharge capacity at a current density of 0.2A / g is 999mAh / g, the average discharge capacity at a current density of 0.5A / g is 818mAh / g, the average discharge capacity at a current density of 1A / g is 698mAh / g, the average discharge capacity at a current density of 2A / g is 588mAh / g, and the average discharge capacity at a high current density of 4A / g is still 489mAh / g, showing excellent high-rate performance.

[0053] The CR2016 button cell obtained from ZnFe2O4 and ZFe2O4 / C composite materials was subjected to constant current charge and discharge tests on a CT2001A battery test system. The voltage cutoff range was 0.01~3V. The battery was activated at a current density of 0.1A / g for the first three cycles. The cycle performance curves are shown in the figure. Figure 6 As shown. Figure 6 It can be seen that after 900 cycles at a current density of 0.5 A / g, the ZnFe2O4 / C composite material still maintained a discharge capacity of 803 mAh / g, with a capacity retention rate of 106%, indicating that the composite material provided by the present invention can improve the cycling stability of lithium-ion batteries. After 900 cycles at a current density of 0.5 A / g, the ZnFe2O4 material only maintained a discharge capacity of 204 mAh / g, with a capacity retention rate of 26%, indicating that the cycling stability of the single ZnFe2O4 material is far inferior to that of the ZnFe2O4 / C composite material.

[0054] The CoFe2O4 / C composite material obtained in Example 2 was subjected to battery testing in the above manner. The average discharge capacities at current densities of 0.1 and 4 A / g reached 1045 and 478 mAh / g, respectively. After 900 cycles at a current density of 0.5 A / g, the discharge capacity was still maintained at 785 mAh / g, with a capacity retention rate of 90%.

[0055] The NiFe2O4 / C composite material obtained in Example 3 was subjected to battery testing in the above manner. The average discharge capacities at current densities of 0.1 and 4 A / g reached 1025 and 455 mAh / g, respectively. After 900 cycles at a current density of 0.5 A / g, the discharge capacity was still maintained at 750 mAh / g, and the capacity retention rate was 82%.

[0056] The CuFe2O4 / C composite material obtained in Example 4 was subjected to battery testing in the above manner. The average discharge capacities at current densities of 0.1 and 4 A / g reached 1032 and 462 mAh / g, respectively. After 900 cycles at a current density of 0.5 A / g, the discharge capacity was still maintained at 762 mAh / g, and the capacity retention rate was 86%.

[0057] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. An iron-based bimetallic oxide composite material, characterized in that: It comprises an iron-based bimetallic oxide and coated carbon located on the surface of the iron-based bimetallic oxide; The iron-based bimetallic oxide composite material has a solid microrod structure; the cross section of the solid microrod structure is circular; The iron-based bimetallic oxide composite material is in a monodisperse state and does not form clusters; The preparation method of the iron-based bimetallic oxide composite material comprises the following steps: Mixing a water-soluble iron salt, an auxiliary metal salt, polyvinyl pyrrolidone, ethylenediamine and water, and performing a hydrothermal reaction to obtain an iron-based bimetallic oxide; The iron-based bimetallic oxide and an aqueous solution containing a carbon source are mixed, and dried and carbonized in sequence to obtain the iron-based bimetallic oxide composite material.

2. The iron-based bimetallic oxide composite material according to claim 1, characterized in that The chemical composition of the iron-based bimetallic oxide is MFe2O4, and M is Zn, Co, Ni or Cu; The mass percentage of the coated carbon in the iron-based bimetallic oxide composite material is 8-15%.

3. The iron-based bimetallic oxide composite material according to claim 1, characterized in that The length of the solid microrod structure is 0.5-1.5 μm, and the diameter is 0.3-0.5 μm.

4. The method for preparing the iron-based bimetallic oxide composite material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Mixing a water-soluble iron salt, an auxiliary metal salt, polyvinyl pyrrolidone, ethylenediamine and water, and performing a hydrothermal reaction to obtain an iron-based bimetallic oxide, wherein the auxiliary metal salt includes a water-soluble zinc salt, a water-soluble cobalt salt, a water-soluble nickel salt or a water-soluble copper salt; The iron-based bimetallic oxide and an aqueous solution containing a carbon source are mixed, and dried and carbonized in sequence to obtain the iron-based bimetallic oxide composite material.

5. The preparation method according to claim 4, characterized in that The iron salt is ammonium ferric oxalate trihydrate; The water-soluble zinc salt includes at least one of zinc nitrate, zinc sulfate, zinc acetate and zinc chloride; The water-soluble cobalt salt includes at least one of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride; The water-soluble nickel salt includes at least one of nickel nitrate, nickel sulfate, nickel acetate and nickel chloride; The water-soluble copper salt includes at least one of copper nitrate, copper sulfate, copper acetate and copper chloride.

6. The preparation method according to claim 4 or 5, characterized in that The molar ratio of the water-soluble iron salt to the auxiliary metal salt is 2:1; The mass ratio of the water-soluble iron salt to polyvinyl pyrrolidone is 1:0.4-0.8; The molar ratio of the water-soluble iron salt to ethylenediamine is 1:25-50; The molar concentration of the water-soluble iron salt is 0.05-0.5 mol / L.

7. The preparation method according to claim 4, characterized in that The temperature of the hydrothermal reaction is 150-180° C., and the insulation time is 5-9 hours.

8. The preparation method according to claim 4, characterized in that The carbon source in the aqueous solution containing a carbon source comprises at least one of gluconolactone, sucrose, glucose and polyacrylic acid; The concentration of the aqueous solution containing the carbon source is 10-20 g / L; The mass ratio of the iron-based bimetallic oxide to the aqueous solution containing a carbon source is 1:40-100.

9. The preparation method according to claim 4, characterized in that The carbonization temperature is 400-600°C, the heating rate to the carbonization temperature is 2-5°C / min, and the holding time is 2-4h; The carbonization is carried out under a protective atmosphere.

10. Use of the iron-based bimetallic oxide composite material according to any one of claims 1 to 3 or the iron-based bimetallic oxide composite material prepared by the preparation method according to any one of claims 4 to 9 as a negative electrode material for lithium-ion batteries.

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