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

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to an iron-based bimetallic oxide composite material and a preparation method and application thereof. The composite material provided by the application comprises an iron-based bimetallic oxide and coated carbon 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. In the application, the composite material with the solid microrod structure is beneficial to the diffusion of lithium ions in the composite material and has a high tap density. Meanwhile, the surface-coated carbon can further improve the conductivity of the composite material, and is beneficial to the maintenance of the structural integrity of the microrod in the cycle process. When applied to a lithium ion battery, the lithium ion battery can further improve the charge-discharge capacity and cycle stability of the lithium ion battery under a high current density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a Fe-based double-metal oxide composite material and a preparation method and application thereof. BACKGROUND

[0002] The Fe-based double-metal oxide has a wide application prospect as a negative electrode material in a lithium ion battery. The Fe-based double-metal oxide (MFe2O4, M=Zn, Co, Ni, etc.) is considered to be one of ideal choices for replacing traditional carbon materials due to its low price, non-toxicity, environmental friendliness, and high theoretical specific capacity (900-1000 mAh / g), which is much higher than that of a commercial graphite negative electrode material (372 mAh / g).

[0003] However, the existing Fe-based double-metal oxide is in a porous, nanoparticle or fibrous form, has a low tap density, and is prone to structural collapse in the charging and discharging process, thereby reducing the specific capacity, rate performance and cycle stability of the battery under high current density. SUMMARY

[0004] The Fe-based double-metal oxide provided by the application can be applied to a lithium ion battery, and can improve the charging and discharging capacity, rate performance and cycle stability of the lithium ion battery under high current density.

[0005] In order to achieve the above-mentioned purpose, the application provides the following technical scheme:

[0006] The application provides a Fe-based double-metal oxide composite material, which comprises a Fe-based double-metal oxide and coated carbon on the surface of the Fe-based double-metal oxide.

[0007] The Fe-based double-metal oxide composite material has a solid microrod structure; and the cross section of the solid microrod structure is circular.

[0008] The Fe-based double-metal oxide composite material is in a monodisperse state and does not form clusters.

[0009] Preferably, the chemical composition of the Fe-based double-metal oxide is MFe2O4, and the M is Zn, Co, Ni or Cu.

[0010] The mass percentage content of the coated carbon in the Fe-based double-metal oxide composite material is 8-15%.

[0011] Preferably, the length of the solid microrod structure is 0.5-1.5 pm, and the diameter is 0.3-0.5 pm.

[0012] The application further provides a preparation method of the iron-based bimetallic oxide composite material.

[0013] The water-soluble iron salt, the auxiliary metal salt, polyvinylpyrrolidone, ethylenediamine and water are mixed to perform a hydrothermal reaction to obtain the iron-based bimetallic oxide, and the auxiliary metal salt comprises at least one of a water-soluble zinc salt, a water-soluble cobalt salt, a water-soluble nickel salt or a water-soluble copper salt.

[0014] The iron-based bimetallic oxide and the water solution containing a carbon source are mixed, and then drying and carbonization are sequentially performed to obtain the iron-based bimetallic oxide composite material.

[0015] Preferably, the iron salt is ferric ammonium oxalate trihydrate.

[0016] The water-soluble zinc salt comprises at least one of zinc nitrate, zinc sulfate, zinc acetate and zinc chloride.

[0017] The water-soluble cobalt salt comprises at least one of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride.

[0018] The water-soluble nickel salt comprises at least one of nickel nitrate, nickel sulfate, nickel acetate and nickel chloride.

[0019] The water-soluble copper salt comprises at least one of copper nitrate, copper sulfate, copper acetate and copper chloride.

[0020] Preferably, the molar ratio of the water-soluble iron salt and the auxiliary metal salt is 2:1.

[0021] The mass ratio of the water-soluble iron salt and polyvinylpyrrolidone is 1:0.4-0.8.

[0022] The molar ratio of the water-soluble iron salt and ethylenediamine is 1:25-50.

[0023] The molar concentration of the water-soluble iron salt is 0.05-0.5 mol / L.

[0024] Preferably, the temperature of the hydrothermal reaction is 150-180 DEG C, and the holding time is 5-9 h.

[0025] Preferably, the carbon source in the water solution containing a carbon source comprises at least one of gluconolactone, sucrose, glucose and polyacrylic acid.

[0026] The concentration of the water solution containing a carbon source is 10-20 g / L.

[0027] The mass ratio of the iron-based bimetallic oxide and the water solution containing a carbon source is 1:40-100.

[0028] Preferably, the carbonization temperature is 400-600 DEG C, the temperature rising rate for rising to the carbonization temperature is 2-5 DEG C / min, and the holding time is 2-4 h.

[0029] The carbonization is performed under a protective atmosphere.

[0030] The application further provides the application of the iron-based double-metal oxide composite material or the iron-based double-metal oxide composite material prepared by the preparation method as a negative material of a lithium ion battery.

[0031] The application provides an iron-based double-metal oxide composite material, which comprises iron-based double-metal oxide and coated carbon on the surface of the iron-based double-metal oxide; the iron-based double-metal oxide composite material has a solid microrod structure; the cross section of the solid microrod structure is circular; and the iron-based double-metal oxide composite material is in a monodisperse state and does not form clusters. In the application, the composite material with the solid microrod structure is beneficial to the rapid diffusion of lithium ions in the composite material, improves the utilization rate of active materials, and has large tap density; meanwhile, the surface-coated carbon can further improve the conductivity of the composite material, the coating effect can make the microrod keep the structure intact in the cycle process, and when applied to a lithium ion battery, the lithium ion battery can further improve the charge and discharge capacity, rate performance and cycle stability under high current density. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The XRD pattern of the ZnFe2O4 material and the ZnFe2O4 / C composite material obtained in Example 1;

[0033] Figure 2 The SEM pattern of the ZnFe2O4 material obtained in Example 1;

[0034] Figure 3 The SEM pattern of the ZnFe2O4 / C composite material obtained in Example 1;

[0035] Figure 4 The TEM pattern of the ZnFe2O4 / C composite material obtained in Example 1;

[0036] Figure 5 The rate performance diagram of the button cell prepared from the ZnFe2O4 / C composite material obtained in Example 1;

[0037] Figure 6 The cycle performance diagram of the button cell prepared from the ZnFe2O4 / C and ZnFe2O4 materials obtained in Example 1;

[0038] Figure 7 The SEM pattern of the CoFe2O4 material obtained in Example 2;

[0039] Figure 8 SEM image of the NiFe2O4 material obtained in Example 3;

[0040] Figure 9 SEM image of the CuFe2O4 material obtained in Example 4;

[0041] Figure 10 SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 1;

[0042] Figure 11 SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 2;

[0043] Figure 12 SEM image of the ZnFe2O4 / C composite material obtained in Comparative Example 3. DETAILED DESCRIPTION

[0044] The present application provides a Fe-based double metal oxide composite material, comprising a Fe-based double metal oxide and coated carbon on the surface of the Fe-based double metal oxide.

[0045] The Fe-based double metal oxide composite material has a solid microrod structure; the cross section of the solid microrod structure is circular.

[0046] The Fe-based double metal oxide composite material is in a monodisperse state and does not form clusters.

[0047] In the present application, the chemical composition of the Fe-based double metal oxide is preferably MFe2O4, and the M is Zn, Co, Ni or Cu. In the present application, the mass percentage of the coated carbon in the Fe-based double metal oxide composite material is preferably 8-15%, and specifically can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%. In the present application, the coated carbon is preferably amorphous carbon.

[0048] In the present application, 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 application, the tap density of the Fe-based double metal oxide composite material is preferably 1.3-1.6 g / cm 3 .

[0049] The present application also provides a preparation method of the Fe-based double metal oxide composite material described in the above technical solution, comprising the following steps:

[0050] Mixing water-soluble iron salt, auxiliary metal salt, polyvinylpyrrolidone, ethylenediamine and water, and carrying out hydrothermal reaction to obtain iron-based bimetallic oxide, wherein the auxiliary metal salt comprises water-soluble zinc salt, water-soluble cobalt salt, water-soluble nickel salt or water-soluble copper salt;

[0051] Mixing the iron-based bimetallic oxide and water solution containing carbon source, and sequentially carrying out drying and carbonization to obtain the iron-based bimetallic oxide composite material.

[0052] The application mixes water-soluble iron salt, auxiliary metal salt, polyvinylpyrrolidone, ethylenediamine and water, and carries out hydrothermal reaction to obtain iron-based bimetallic oxide, wherein the auxiliary metal salt comprises water-soluble zinc salt, water-soluble cobalt salt, water-soluble nickel salt or water-soluble copper salt.

[0053] In the application, the water-soluble iron salt is preferably ferric ammonium oxalate trihydrate; the water-soluble zinc salt preferably comprises 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 comprises 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 comprises 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 comprises at least one of copper nitrate, copper sulfate, copper acetate and copper chloride, and the copper sulfate is preferably copper sulfate pentahydrate. In the application, the water is preferably deionized water.

[0054] In the application, the molar ratio of the water-soluble iron salt to the auxiliary metal salt is preferably 2:1; the mass ratio of the water-soluble iron salt to polyvinylpyrrolidone is preferably 1:0.4-0.8, and specifically can be 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8; the molar ratio of the water-soluble iron salt to ethylenediamine is preferably 1:25-50, and specifically can be 1:25, 1:30, 1:35, 1:40, 1:45 or 1:50; the molar concentration of the water-soluble iron salt is 0.05-0.5 mol / L, and specifically can be 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L.

[0055] In the application, the mixing is preferably carried out under stirring. In the application, the temperature of the hydrothermal reaction is preferably 150-180℃, and specifically can be 150℃, 160℃, 170℃ or 180℃, and the holding time is preferably 5-9 h, and specifically can be 5 h, 6 h, 7 h, 8 h or 9 h. In the application, the hydrothermal reaction is preferably carried out in a hydrothermal reaction kettle with a polytetrafluoroethylene lining.

[0056] In the present application, after the hydrothermal reaction, the obtained system is preferably cooled to room temperature, and then the precipitate is collected by filtration, and the obtained precipitate is sequentially subjected to repeated water washing and drying. In the present application, the drying temperature is preferably 80℃.

[0057] After obtaining the iron-based bimetallic oxide, the iron-based bimetallic oxide is mixed with an aqueous solution containing a carbon source, and sequentially subjected to drying and carbonization to obtain the iron-based bimetallic oxide composite material.

[0058] In the present application, the carbon source in the aqueous solution containing a carbon source preferably includes at least one of gluconolactone, sucrose, glucose and polyacrylic acid; and the solvent in the aqueous solution containing a carbon source is preferably deionized water. In the present application, the aqueous solution containing a carbon source is preferably obtained by dissolving a carbon source in water. In the present application, the concentration of the aqueous solution containing a carbon source is preferably 10-20 g / L, and can be specifically 10 g / L, 15 g / L or 20 g / L; and the mass ratio of the iron-based bimetallic oxide to the aqueous solution containing a carbon source is preferably 1:40-100, and can be specifically 1:40, 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100.

[0059] In the present application, the drying method is preferably stirring under heating until the water is completely evaporated. In the present application, the heating temperature is preferably 80℃. In the present application, the carbonization temperature is preferably 400-600℃, and can be specifically 400℃, 500℃ or 600℃; the temperature rising rate for rising to the carbonization temperature is preferably 2-5℃ / min, and can be specifically 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min; and the holding time is preferably 2-4 h, and can be specifically 2 h, 3 h or 4 h; the carbonization is preferably carried out in a protective atmosphere, and the protective atmosphere is preferably argon. In the present application, the carbonization is preferably carried out in a tube furnace.

[0060] The present application 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 of a lithium ion battery.

[0061] Unless otherwise specified, the materials and equipment used in the present application are commercially available in the art.

[0062] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0063] Example 1

[0064] 1 mmol of zinc sulfate heptahydrate, 2 mmol of ferric ammonium oxalate trihydrate, 0.5 g of polyvinylpyrrolidone (k30) and 5 mL of ethylenediamine were sequentially added to 30 mL of deionized water, stirred to dissolve and form a uniform solution;

[0065] The above solution was transferred to a reaction kettle with a polytetrafluoroethylene lining, heated to 160°C for hydrothermal reaction, and kept for 8 h; after the reaction kettle was cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water, and dried at 80°C to obtain ZnFe2O4 powder material;

[0066] Then 0.11 g of gluconolactone was dissolved in 10 mL of deionized water, 0.2 g of ZnFe2O4 material was added and stirred vigorously at 80°C, and after the water was completely evaporated, it was transferred to a tube furnace, heated to 500°C at a heating rate of 4°C / min in an argon atmosphere for carbonization, and kept for 2 h to obtain ZnFe2O4 / C composite material (the carbon content in the composite material was tested by an elemental analyzer Unicube, and the mass percentage of coated carbon was 11.1%; the tap density of the composite material was tested by a tap density tester GP-01, and the result was 1.45 g / cm 3 ).

[0067] Example 2

[0068] 1 mmol of cobalt sulfate heptahydrate, 2 mmol of ferric ammonium oxalate trihydrate, 0.5 g of polyvinylpyrrolidone (k30) and 5 mL of ethylenediamine were sequentially added to 30 mL of deionized water, stirred to dissolve and form a uniform solution;

[0069] The above solution was transferred to a reaction kettle with a polytetrafluoroethylene lining, heated to 160°C for hydrothermal reaction, and kept for 6 h; after the reaction kettle was cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water, and dried at 80°C to obtain CoFe2O4 powder material;

[0070] The composite material was prepared in the manner of Example 1, and was recorded as CoFe2O4 / C composite material (the carbon content in the composite material was tested by an elemental analyzer Unicube, and the mass percentage of coated carbon was 10.9%; the tap density of the composite material was tested by a tap density tester GP-01, and the result was 1.42 g / cm 3 ).

[0071] Example 3

[0072] 1 mmol nickel sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine were added sequentially to 30 mL of deionized water and stirred to dissolve and form a homogeneous solution.

[0073] The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 170°C for hydrothermal reaction, and kept at the temperature for 6 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain NiFe2O4 powder material.

[0074] The composite material was prepared according to the method in Example 1, denoted as NiFe2O4 / C composite material. (The carbon content in the composite material was tested using a Unicube elemental analyzer, and the mass percentage of coated carbon was found to be 11.0%; the tap density of the composite material was tested using a GP-01 tap density tester, and the result was 1.40 g / cm³.) 3 ).

[0075] Example 4

[0076] 1 mmol copper sulfate pentahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine were added sequentially to 30 mL of deionized water and stirred to dissolve and form a homogeneous solution.

[0077] The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 160°C for hydrothermal reaction, and kept at the temperature for 8 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain CuFe2O4 powder material.

[0078] The composite material was prepared according to the method in Example 1, denoted as CuFe2O4 / C composite material. (The carbon content in the composite material was tested using a Unicube elemental analyzer, and the mass percentage of coated carbon was found to be 11.2%; the tap density of the composite material was tested using a GP-01 tap density tester, and the result was 1.37 g / cm³.) 3 ).

[0079] Comparative Example 1

[0080] Zinc acetate, iron acetate and citric acid were mixed in a 100 mL distilled water in a measured ratio, then the pH value of the solution was accurately controlled at 7 with ammonia water. Citric acid was used as a chelating agent and carbon source at the same time. The resulting solution was placed in a stirrer and heated to 80°C until the water was completely evaporated. During the drying process, the xerogel formed fluffy powder after being kept at 120°C for 12 hours. Finally, the sample was calcined at 600°C for 4 hours to obtain ZnFe2O4 / C composite (see Alam M W, BaQais A, Rahman M M, et al. Investigation on In Situ Carbon-Coated ZnFe2O4 as Advanced Anode Material for Li-Ion Batteries[J]. Gels, 2022, 8, 305.).

[0081] The SEM image of the obtained composite is shown in Figure 10 It can be seen that due to the combustion process caused by carbon agglomeration, irregular particles of different sizes, different stacking modes and uneven distribution are formed.

[0082] The obtained composite was assembled into a button cell for rate performance test, and the current density was increased from 100 mAh·g -1 to 8000 mAh·g -1 , and then decreased to 500 mAh·g -1 . At different current densities of 100, 200, 500, 2000, 4000 and 8000 mA·g -1 , the discharge capacity reached about 1312, 1059, 806, 471, 207 and 119 mAh·g -1 , respectively.

[0083] Comparative Example 2

[0084] ZnFe2O4 / C composite microspheres were prepared by a hydrothermal method. 8 mmol of zinc chloride, 16 mmol of iron chloride hexahydrate and 45 mmol of ammonium acetate were dissolved in a mixture of ethylene glycol and deionized water, and stirred for 1 hour. Then 2.6 mmol of citric acid was added to the mixed solution. The uniform solution was transferred to a polytetrafluoroethylene-lined stainless steel autoclave and hydrothermally treated at 200°C for 24 hours to obtain a ZnFe2O4 particle precipitate. Finally, the obtained ZnFe2O4 particles were sintered at 600°C for 5 hours under a nitrogen atmosphere to form mesoporous ZnFe2O4 / C composite microspheres (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).

[0085] The SEM image of the obtained mesoporous ZnFe2O4 / C composite microspheres is shown in Figure 11 It can be seen that the obtained composite material is a secondary particle composed of nano-sized particles, and has a porous structure.

[0086] The obtained composite material was assembled into a button cell for rate performance testing. The specific capacity of the ZnFe2O4 / C electrode was 1050, 920, 870 and 600 mAh·g -1 at a specific current of 0.1, 0.2, 0.5 and 1.0 A·g -1 , respectively.

[0087] Comparative Example 3

[0088] Into a 20 mL sample bottle, 10 mL of N,N-dimethylformamide was poured, and 1.2 g of polyacrylonitrile was dissolved. After a transparent colloidal solution was formed, 2 mmol of iron acetylacetone and 1 mmol of anhydrous zinc acetate were dissolved into the solution under magnetic stirring, and the reaction was continued for 12 hours. Subsequently, the solution was transferred to a 5 mL syringe. Using an electrospinning device, ZnFe2O4 / C nanofiber precursors were prepared under the condition of negative voltage -5 kV to positive voltage 15 kV, with a sample injection speed of 0.01 mL / min. Subsequently, the nanofiber precursors were heated to 550°C at a heating rate of 1°C / min under an argon atmosphere, and finally ZnFe2O4 / C nanofibers were obtained (see Xiao Y, Zhang Z, Ma Z, et al. Synthesis and electrochemical properties of ZnFe2O4 / C as novel anode material for lithium ion battery [J]. Ionics, 2021, 27: 1377-1384.).

[0089] The SEM image of the obtained ZnFe2O4 / C nanofiber is shown in Figure 12 , and it can be seen that its morphology presents a fibrous shape.

[0090] The obtained composite material was assembled into a button cell for rate performance and cycle performance tests. When the current density was 2 A·g -1 , the specific capacity was only 261.8 mAh·g -1 . When a higher current density of 0.5 A·g -1 was applied, after 500 cycles, the specific capacity was only maintained at 479.3 mAh·g -1 .

[0091] Performance test

[0092] Test Example 1

[0093] The ZnFe2O4 material and ZnFe2O4 / C composite material obtained in Example 1 were subjected to X-ray diffraction test, and the obtained XRD image is shown in Figure 1 . It can be seen from Figure 1 that the ZnFe2O4 material and ZnFe2O4 / C composite material obtained in this example are both single-phase ZnFe2O4, and the carbon in the ZnFe2O4 / C composite material is amorphous.

[0094] Test Example 2

[0095] The ZnFe2O4 material and ZnFe2O4 / C composite material obtained in Example 1 were subjected to scanning electron microscope test, and the obtained SEM images areFigure 2 and Figure 3 It can be seen from Figure 2 that the ZnFe2O4 material obtained in the embodiment presents a monodisperse microrod morphology. Figure 3 It can be seen from

[0096] The CoFe2O4 material obtained in Example 2 was subjected to scanning electron microscope test, and the obtained SEM image is shown in Figure 7 It can be seen from Figure 7 that the obtained CoFe2O4 material presents a monodisperse microrod morphology.

[0097] The NiFe2O4 material obtained in Example 3 was subjected to scanning electron microscope test, and the obtained SEM image is shown in Figure 8 It can be seen from Figure 8 that the obtained NiFe2O4 material presents a monodisperse microrod morphology.

[0098] The CuFe2O4 material obtained in Example 4 was subjected to scanning electron microscope test, and the obtained SEM image is shown in Figure 9 It can be seen from Figure 9 that the obtained CuFe2O4 material presents a monodisperse microrod morphology.

[0099] Test Example 3

[0100] The ZnFe2O4 / C composite material obtained in Example 1 was subjected to transmission electron microscope test, and the obtained TEM image is shown in Figure 4 It can be seen from Figure 4 that the ZnFe2O4 / C composite material obtained in the embodiment is a solid microrod, and the surface of the rod is coated with a carbon layer.

[0101] Test Example 4

[0102] The material obtained in the embodiment was used as an active material to prepare a lithium ion battery;

[0103] The preparation method is as follows:

[0104] The active material, Super P conductive carbon and polyvinylidene fluoride binder were mixed in a mass ratio of 75:15:10, an appropriate amount of N-methyl pyrrolidone solvent was added and stirred uniformly, coated on a copper foil, and vacuum dried at 70°C to obtain a negative electrode sheet. A lithium sheet was used as a counter electrode, a polypropylene porous membrane was used as a separator, and a solution obtained by dissolving 1 mol of lithium hexafluorophosphate in 1L of a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:1) was used as an electrolyte to assemble a CR2016 button cell.

[0105] The CR2016 button cell obtained by taking the ZnFe2O4 / C composite material as the active material was subjected to rate performance test on a CT2001A battery test system, and the obtained rate performance graph is shown in Figure 5 As can be seen from Figure 5 , the average discharge capacity at a current density of 0.1 A / g is as high as 1055 mAh / g, the average discharge capacity at a current density of 0.2 A / g is 999 mAh / g, the average discharge capacity at a current density of 0.5 A / g is 818 mAh / g, the average discharge capacity at a current density of 1 A / g is 698 mAh / g, the average discharge capacity at a current density of 2 A / g is 588 mAh / g, and the average discharge capacity at a large current density of 4 A / g is still 489 mAh / g, which shows excellent high-rate performance.

[0106] The CR2016 button cell obtained by taking the ZnFe2O4 and ZnFe2O4 / C composite material was subjected to constant current charge-discharge test on a CT2001A battery test system, and the voltage cutoff range was 0.01-3 V; the first three cycles were activated at a current density of 0.1 A / g, and the obtained cycle performance curve is shown in Figure 6 As can be seen from Figure 6 , the ZnFe2O4 / C composite material still maintains a discharge capacity of 803 mAh / g after 900 cycles at a current density of 0.5 A / g, and the capacity retention rate is 106%, which shows that the composite material provided by the application can improve the cycle stability of the lithium ion battery. The ZnFe2O4 material only maintains a discharge capacity of 204 mAh / g after 900 cycles at a current density of 0.5 A / g, and the capacity retention rate is 26%, which shows that the cycle stability of the single ZnFe2O4 material is far worse than that of the ZnFe2O4 / C composite material.

[0107] The CoFe2O4 / C composite material obtained in Example 2 was subjected to battery test in the above manner, and the average discharge capacity at a current density 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, and the capacity retention rate was 90%.

[0108] The NiFe2O4 / C composite material obtained in Example 3 was subjected to battery test in the above manner, and the average discharge capacity at a current density 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%.

[0109] The CuFe2O4 / C composite material obtained in Example 4 was subjected to battery test in the above manner, and the average discharge capacity reached 1032 and 462 mAh / g at current densities of 0.1 and 4 A / g, respectively, and remained 762 mAh / g after 900 cycles at a current density of 0.5 A / g, with a capacity retention rate of 86%.

[0110] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. An iron-based bimetallic oxide composite material, characterized in that, It consists of an iron-based bimetallic oxide and a carbon coating 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 length of the solid microrod structure is 0.5~1.5μm and the diameter is 0.3~0.5μm; The iron-based bimetallic oxide composite material is monodisperse and does not form clusters; The steps of the preparation method of the iron-based bimetallic oxide composite material are as follows: 1 mmol zinc sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine were added sequentially to 30 mL of deionized water and stirred to dissolve and form a homogeneous solution. The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 160°C for hydrothermal reaction, and kept at the temperature for 8 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain ZnFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g ZnFe2O4 material was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain the ZnFe2O4 / C composite material. Alternatively, add 1 mmol cobalt sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL of deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner and heated to 160°C for hydrothermal reaction, and kept at the temperature for 6 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water and dried at 80°C to obtain CoFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g CoFe2O4 powder was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain the CoFe2O4 / C composite material. Alternatively, add 1 mmol nickel sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 170°C for hydrothermal reaction, and kept at the temperature for 6 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain NiFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g NiFe2O4 powder was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain NiFe2O4 / C composite material. Alternatively, add 1 mmol copper sulfate pentahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 160°C for hydrothermal reaction, and kept at the temperature for 8 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain CuFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g CuFe2O4 powder was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain CuFe2O4 / C composite material. The iron-based bimetallic oxide composite material is used as a negative electrode material for lithium-ion batteries.

2. The method for preparing the iron-based bimetallic oxide composite material according to claim 1, characterized in that, The steps are as follows: 1 mmol zinc sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine were added sequentially to 30 mL of deionized water and stirred to dissolve and form a homogeneous solution. The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 160°C for hydrothermal reaction, and kept at the temperature for 8 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain ZnFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g ZnFe2O4 material was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain the ZnFe2O4 / C composite material. Alternatively, add 1 mmol cobalt sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL of deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner and heated to 160°C for hydrothermal reaction, and kept at the temperature for 6 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water and dried at 80°C to obtain CoFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g CoFe2O4 powder was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain the CoFe2O4 / C composite material. Alternatively, add 1 mmol nickel sulfate heptahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 170°C for hydrothermal reaction, and kept at the temperature for 6 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain NiFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g NiFe2O4 powder was added and stirred vigorously at 80 °C. After the water was completely evaporated, it was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The temperature was held for 2 h to obtain NiFe2O4 / C composite material. Alternatively, add 1 mmol copper sulfate pentahydrate, 2 mmol ferric ammonium oxalate trihydrate, 0.5 g polyvinylpyrrolidone and 5 mL ethylenediamine sequentially to 30 mL deionized water, stir to dissolve and form a homogeneous solution; The above solution was transferred to a reaction vessel with a polytetrafluoroethylene liner, heated to 160°C for hydrothermal reaction, and kept at the temperature for 8 hours. After the reaction vessel cooled to room temperature, the precipitate was collected by filtration and repeatedly washed with deionized water. It was then dried at 80°C to obtain CuFe2O4 powder material. Then, 0.11 g gluconolactone was dissolved in 10 mL of deionized water, 0.2 g CuFe2O4 powder was added, and the mixture was stirred vigorously at 80 °C. After the water was completely evaporated, the mixture was transferred to a tube furnace and carbonized at 500 °C in an argon atmosphere at a heating rate of 4 °C / min. The mixture was held at this temperature for 2 h to obtain the CuFe2O4 / C composite material.

3. The application of the iron-based bimetallic oxide composite material according to claim 1 or the iron-based bimetallic oxide composite material prepared by the preparation method according to claim 2 as a negative electrode material for lithium-ion batteries.

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