CN115377391A - A metal oxide composite material and its preparation method and application, a negative electrode material - Google Patents

Abstract

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a metal oxide composite material, a preparation method and application thereof, and a negative electrode material. The invention provides a metal oxide composite material, the metal oxide composite material is a rod-like structure composed of a plurality of submicron spheres connected in series; the chemical composition of the submicron spheres is CoFe ₂ O ₄ ·xFe ₂ O ₃ , the value range of x is 1≤x≤4. In the present invention, the rod-shaped structure composed of submicron spheres is more conducive to the diffusion of lithium ions in the composite material and improves the diffusion speed of lithium ions; at the same time, the metal oxide composite material with rod-shaped structure can be better when preparing negative electrodes. It is mixed with the conductive agent and the binder, which together improve the specific capacity and cycle stability of the lithium battery at high current density.

Description

A metal oxide composite material and its preparation method and application, a negative electrode Material

technical field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a metal oxide composite material, a preparation method and application thereof, and a negative electrode material.

Background technique

Lithium-ion batteries mainly include positive electrodes, electrolytes, and negative electrodes, and work mainly by moving lithium ions between the positive and negative electrodes. During the charging and discharging process, lithium ions intercalate and deintercalate back and forth between the two electrodes: during charging, lithium ions are deintercalated from the positive electrode, inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge.

Anode materials are an important part of lithium-ion batteries, which directly affect the electrochemical performance of lithium-ion batteries. Excellent anode materials can improve the reversible capacity, rate performance and cycle performance of batteries. At present, the negative electrode material is mainly graphite, its theoretical specific capacity is only 372mAh/g, and its lithium storage capacity is low; in contrast, transition metal oxides have become the current lithium-ion battery negative electrode materials because of their high theoretical specific capacity. However, due to the low electronic conductivity of metal oxides and the huge volume change of the material during the cycle, it is easy to cause material pulverization, resulting in a decrease in the cycle life of the battery.

The study found that the complex formed by multiple metal oxides exhibited better electrochemical performance than single oxides due to their synergistic effect. However, the obtained composite still has the defects of low charge-discharge capacity and poor cycle stability at high current density.

Contents of the invention

The purpose of the present invention is to provide a metal oxide composite material and its preparation method and application, and a negative electrode material. The metal oxide composite material provided by the present invention is applied to the negative electrode of lithium ion batteries, which can improve the performance of lithium ion batteries at high currents. Density charge-discharge capacity and cycle stability.

In order to achieve the above object, the present invention provides the following technical solutions:

The invention provides a metal oxide composite material, the metal oxide composite material is a rod-shaped structure composed of a plurality of submicron spheres connected in series;

The chemical composition of the submicron sphere is CoFe ₂ O ₄ ·xFe ₂ O ₃ , and the value range of x is 1≤x≤4.

Preferably, the diameter of the submicron sphere is 200-1000 nm;

The length of the rod-like structure is 2-20 μm.

Preferably, the submicron sphere has a porous structure;

The pore diameter of the submicron sphere is 2-30nm;

The specific surface area of the metal oxide composite material is 10-30m ² /g.

The present invention also provides a method for preparing the metal oxide composite material described in the above technical solution, comprising the following steps:

Mixing water-soluble cobalt salt, water-soluble iron salt, sodium citrate, urea and water, the obtained alkaline mixed salt solution undergoes hydrothermal reaction to obtain a precursor;

The precursor is thermally decomposed to obtain the metal oxide composite material.

Preferably, the water-soluble cobalt salt includes one or more of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride;

The water-soluble iron salt includes one or more of ferrous sulfate, ferric nitrate and ferric chloride.

Preferably, the molar ratio of the water-soluble cobalt salt, water-soluble iron salt, sodium citrate and urea is 0.03-0.12:0.06-0.24:0.02-0.48:0.12-0.48;

The molar concentration of the water-soluble cobalt salt in the alkaline mixed salt solution is 0.03-0.12 mol/L.

Preferably, the temperature of the hydrothermal reaction is 150-190° C., and the holding time is 4-8 hours.

Preferably, the thermal decomposition temperature is 400-600° C., the heating rate to the thermal decomposition temperature is 2-5° C./min, and the holding time is 2-4 hours.

The present invention also provides the application of the metal oxide composite material described in the above technical solution or the metal oxide composite material prepared by the preparation method described in the above technical solution in lithium ion batteries.

The present invention also provides a negative electrode material, including an active material, a conductive agent and a binder, and the active material is the metal oxide composite material described in the above technical solution or the metal oxide prepared by the preparation method described in the above technical solution. oxide composites.

The invention provides a metal oxide composite material, the metal oxide composite material is a rod-like structure composed of a plurality of submicron spheres connected in series; the chemical composition of the submicron spheres is CoFe ₂ O ₄ ·xFe ₂ O ₃ , the value range of x is 1≤x≤4. The metal oxide composite material provided by the present invention includes CoFe ₂ O ₄ and Fe ₂ O ₃ two metal oxides, due to the synergistic effect of the two, compared with a single metal oxide, it has more excellent electrochemical properties; The rod-shaped structure composed of microspheres is more conducive to the diffusion of lithium ions in the composite material and increases the diffusion speed of lithium ions; at the same time, the metal oxide composite material with rod-shaped structure can better bond with the conductive agent and bond when preparing the negative electrode. Agents are mixed together to improve the specific capacity and cycle stability of lithium-ion batteries at high current densities.

Description of drawings

Fig. 1 is the XRD figure of the metal oxide composite material that embodiment 1 obtains;

Fig. 2 is the SEM picture of the metal oxide composite material that embodiment 1 obtains;

Fig. 3 is the TEM figure of the metal oxide composite material that embodiment 1 obtains;

Fig. 4 is the rate performance figure of the button cell that application example 1 obtains;

Fig. 5 is the cycle performance figure of the button cell that application example 1 obtains;

Fig. 6 is the SEM figure of the metal oxide composite material that comparative example 1 obtains;

Fig. 7 is the SEM picture of the pure phase CoFe ₂ O ₄ material that comparative example 2 obtains;

FIG. 8 is a graph of the rate performance of button batteries prepared using the materials obtained in Comparative Examples 1-2 as electrode materials.

Detailed ways

The invention provides a metal oxide composite material, the metal oxide composite material is a rod-shaped structure composed of a plurality of submicron spheres connected in series;

The chemical composition of the submicron sphere is CoFe ₂ O ₄ ·xFe ₂ O ₃ , and the value range of x is 1≤x≤4.

In the present invention, the diameter of the submicron sphere is preferably 200-1000 nm, more preferably 300-900 nm, more preferably 400-800 nm. In the present invention, the submicron sphere preferably has a porous structure; the pore diameter of the submicron sphere is preferably 2-30 nm, more preferably 3-19 nm, and more preferably 4-18 nm.

In the present invention, the length of the rod-like structure is preferably 2-20 μm, more preferably 3-19 μm, and more preferably 4-18 μm.

In the present invention, the specific surface area of the metal oxide composite material is preferably 10-30 m ² /g, more preferably 12-28 m ² /g, more preferably 15-25 m ² /g.

The submicron spheres provided by the present invention have a porous structure and are applied to the negative electrode of a lithium-ion battery. In the process of charging and discharging, the rich pore structure is conducive to the full penetration of the electrolyte in the material, thereby accelerating the reaction speed and improving the lithium-ion battery. The rate performance of the battery.

The present invention also provides a method for preparing the metal oxide composite material described in the above technical solution, comprising the following steps:

Mixing water-soluble cobalt salt, water-soluble iron salt, sodium citrate, urea and water, the obtained alkaline mixed salt solution undergoes hydrothermal reaction to obtain a precursor;

The precursor is thermally decomposed to obtain the metal oxide composite material.

In the present invention, unless otherwise specified, all preparation materials are commercially available products well known to those skilled in the art.

The invention mixes water-soluble cobalt salt, water-soluble iron salt, sodium citrate, urea and water, and undergoes hydrothermal reaction to obtain a precursor.

In the present invention, the water-soluble cobalt salt preferably includes one or more of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride; when the water-soluble cobalt salt is preferably two or more of the above options , the present invention has no special limitation on the proportion of specific substances, and they can be mixed in any proportion. In the present invention, the cobalt nitrate is preferably added in the form of cobalt nitrate hexahydrate; the cobalt sulfate is preferably added in the form of cobalt sulfate heptahydrate; the cobalt acetate is preferably added in the form of cobalt acetate tetrahydrate; The cobalt chloride is preferably added in the form of cobalt chloride hexahydrate.

In the present invention, the water-soluble iron salt preferably includes one or more of ferrous sulfate, ferric nitrate and ferric chloride; when the water-soluble iron salt is preferably two or more of the above selections, the present invention The invention has no special limitation on the proportion of specific substances, and they can be mixed in any proportion. In the present invention, the ferrous sulfate is preferably added in the form of ferrous sulfate heptahydrate; the ferric nitrate is preferably added in the form of ferric nitrate nonahydrate; the ferric chloride is preferably added in the form of ferric chloride hexahydrate form to add.

In the present invention, the water is preferably deionized water.

In the present invention, the molar ratio of the water-soluble cobalt salt, water-soluble iron salt, sodium citrate and urea is preferably 0.03-0.12:0.06-0.24:0.02-0.48:0.12-0.48, more preferably 0.04-0.11: 0.07-0.23: 0.03-0.47: 0.13-0.47, more preferably 0.05-0.10: 0.08-0.22: 0.04-0.46: 0.14-0.46. In the present invention, the molar concentration of the water-soluble cobalt salt in the alkaline mixed salt solution is preferably 0.03-0.12 mol/L, more preferably 0.04-0.11 mol/L, more preferably 0.05-0.10 mol/L.

In the present invention, the mixing is preferably performed under stirring conditions. In the present invention, there is no special limitation on the conditions and parameters of the stirring, and those well-known by those skilled in the art can be used. In a specific embodiment of the present invention, the order of mixing is preferably adding water-soluble cobalt salt, water-soluble iron salt, sodium citrate and urea to deionized water in sequence.

In the present invention, the temperature of the hydrothermal reaction is preferably 150-190°C, more preferably 160-180°C, more preferably 165-170°C; the holding time is preferably 4-8h, more preferably 5-7h, More preferably 6h. In the present invention, the hydrothermal reaction is preferably carried out in a polytetrafluoroethylene-lined hydrothermal reactor.

After the hydrothermal reaction is completed, the present invention preferably further includes sequentially cooling, filtering, washing and drying the obtained feed liquid.

The present invention has no special limitation on the cooling process, it can be cooled to room temperature naturally. In the present invention, there is no special limitation on the filtering process, which can be carried out by adopting a process well known to those skilled in the art. In the present invention, the washing is preferably deionized water washing; the number of times of washing is preferably 3-5 times. In the present invention, the drying temperature is preferably 60-90°C, more preferably 70-80°C. In the present invention, the precursor is preferably brown.

In the present invention, through the combined use of sodium citrate and urea, the morphology of the product can be regulated in the hydrothermal process, and then a rod-like structure composed of submicron spheres can be obtained.

After the precursor is obtained, the present invention thermally decomposes the precursor to obtain the metal oxide composite material.

In the present invention, the thermal decomposition temperature is preferably 400-600°C, more preferably 450-550°C, more preferably 480-500°C; the heating rate to the thermal decomposition temperature is preferably 2-5°C /min, more preferably 3-4°C/min; the holding time is preferably 2-4h, more preferably 3h. In the present invention, the thermal decomposition is preferably performed in an air atmosphere. In the present invention, the thermal decomposition is preferably carried out in a tube furnace. In the present invention, gas can be released during thermal decomposition, and a porous structure can be formed on the basis of maintaining the rod-like shape.

In the present invention, the metal oxide composite material is preferably black.

The invention uses water as a solvent without adding other organic solvents, and the raw materials are simple and easy to obtain, and the cost is low; the preparation process is simple and operable, the conditions are mild, and the requirements for equipment safety are low; no pollutants are produced, and the obtained product is green and environmentally friendly; The product has strong consistency and has a good industrial application prospect.

The present invention also provides the application of the metal oxide composite material described in the above technical solution or the metal oxide composite material prepared by the preparation method described in the above technical solution in lithium ion batteries.

The present invention also provides a negative electrode material, including an active material, a conductive agent and a binder, and the active material is the metal oxide composite material described in the above technical solution or the metal oxide prepared by the preparation method described in the above technical solution. oxide composites.

In the present invention, there is no special limitation on the types of the conductive agent and the binder, and those known to those skilled in the art can be used. In a specific embodiment of the present invention, the conductive agent is acetylene black; the binder is polyvinylidene fluoride.

In a specific embodiment of the present invention, the mass ratio of the active material, conductive agent and binder is 75:15:10.

In order to further illustrate the present invention, a metal oxide composite material provided by the present invention, its preparation method and application, and a negative electrode material are described in detail below in conjunction with the accompanying drawings and examples, but they cannot be understood as limiting the protection scope of the present invention. limit.

Example 1

Add 2mmol cobalt nitrate hexahydrate, 4mmol ferrous sulfate heptahydrate, 8mmol sodium citrate and 8mmol urea to 35mL deionized water in sequence, stir and dissolve to obtain an alkaline mixed salt solution;

Then transfer the solution to a reaction kettle lined with polytetrafluoroethylene, heat it to 160°C for hydrothermal reaction, and keep it warm for 6 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 550° C. in an air atmosphere at a heating rate of 2° C./min for thermal decomposition, and keep the temperature for 2 hours to obtain the metal oxide composite material.

Example 2

Add 2mmol cobalt nitrate hexahydrate, 4mmol ferrous sulfate heptahydrate, 6mmol sodium citrate and 8mmol urea to 35mL deionized water in sequence, stir and dissolve to obtain an alkaline mixed salt solution;

Then transfer the solution to a reaction kettle with a polytetrafluoroethylene liner, heat it to 150°C for hydrothermal reaction, and keep it warm for 6 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 500° C. in an air atmosphere at a heating rate of 1° C./min for thermal decomposition, and keep the temperature for 2 hours to obtain the metal oxide composite material.

Example 3

Add 2mmol cobalt nitrate hexahydrate, 4mmol ferrous sulfate heptahydrate, 4mmol sodium citrate and 8mmol urea to 35mL deionized water in sequence, stir and dissolve to obtain an alkaline mixed salt solution;

Then transfer the solution to a reaction kettle lined with polytetrafluoroethylene, heat it to 170°C for hydrothermal reaction, and keep it warm for 8 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 550° C. in an air atmosphere at a heating rate of 5° C./min for thermal decomposition, and keep the temperature for 2 hours to obtain the metal oxide composite material.

Example 4

Add 1mmol cobalt nitrate hexahydrate, 2mmol ferrous sulfate heptahydrate, 1mmol sodium citrate and 3mmol urea to 35mL deionized water in sequence, stir and dissolve to obtain an alkaline mixed salt solution;

Then transfer the solution to a reaction kettle lined with polytetrafluoroethylene, heat it to 180°C for hydrothermal reaction, and keep it warm for 10 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 600° C. in an air atmosphere at a heating rate of 2° C./min for thermal decomposition, and keep the temperature for 2 hours to obtain the metal oxide composite material.

Comparative example 1

Add 2mmol of cobalt nitrate hexahydrate, 4mmol of ferrous sulfate heptahydrate and 8mmol of sodium citrate to 35mL of deionized water in sequence, stir and dissolve to form a uniform solution;

Then transfer the solution to a reaction kettle lined with polytetrafluoroethylene, heat it to 160°C for hydrothermal reaction, and keep it warm for 6 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 550°C in an air atmosphere at a heating rate of 2°C/min for thermal decomposition, and keep it warm for 2 hours to obtain a metal oxide composite material.

Comparative example 2

Add 2mmol cobalt nitrate hexahydrate, 4mmol ferrous sulfate heptahydrate and 8mmol urea to 35mL deionized water in sequence, stir and dissolve to form a uniform solution;

Then transfer the solution to a reaction kettle lined with polytetrafluoroethylene, heat it to 160°C for hydrothermal reaction, and keep it warm for 6 hours; after the reaction kettle is naturally cooled to room temperature, filter and collect the precipitate, and wash the obtained precipitate with deionized water 3 times, drying at 80°C to obtain a brown precursor solid powder;

Then put the obtained precursor solid powder into a tube furnace, heat up to 550°C in an air atmosphere at a heating rate of 2°C/min for thermal decomposition, and keep it for 2 hours to obtain a pure-phase CoFe ₂ O ₄ material.

Application example 1

The metal oxide composite material obtained in Example 1 is used as an active material to prepare a lithium-ion battery;

The preparation method is:

Mix the metal oxide composite material, acetylene black, and polyvinylidene fluoride binder at a mass ratio of 75:15:10, add an appropriate amount of N-methylpyrrolidone solvent and stir evenly, and coat it on the copper foil. The negative electrode sheet was obtained by vacuum drying. The lithium sheet is used as the counter electrode, the polypropylene porous membrane is used as the diaphragm, and the solution obtained by dissolving 1 mol of lithium hexafluorophosphate in 1 L of ethylene carbonate and dimethyl carbonate (volume ratio 1:1) is used as the electrolyte, and assembled into a CR2016 button Battery.

Performance Testing

test case 1

Carry out X-ray diffraction test to the metal oxide composite material obtained in Example 1, the obtained XRD pattern is shown in Figure 1, as can be seen from Figure 1, the metal oxide composite material obtained in this embodiment contains CoFe ₂ O ₄ and Fe ₂ O ₃ two-phase, high crystallinity;

According to elemental analysis, the molar ratio of CoFe ₂ O ₄ and Fe ₂ O ₃ is about 1:2.6.

test case 2

The metal oxide composite material obtained in Example 1 is subjected to a scanning electron microscope test, and the obtained SEM image is shown in Figure 2. As can be seen from Figure 2, the metal oxide composite material obtained in this embodiment is composed of a plurality of submicron spheres A rod-like structure formed in series.

Test case 3

The metal oxide composite material obtained in Example 1 was tested by a transmission electron microscope, and the obtained TEM image is shown in FIG. 3 . It can be seen from FIG. 3 that the metal oxide composite material obtained in this embodiment has abundant pores inside.

Test case 4

The rate performance of the CR2016 button battery obtained in Application Example 1 was tested on the CT2001A battery test system, and the obtained rate performance diagram is shown in Figure 4. The capacity is as high as 1007mAh/g, and there is still an average discharge capacity of 444mAh/g at a high current density of 6A/g, showing excellent high-rate performance;

The CR2016 button battery obtained in Application Example 1 was subjected to a constant current charge and discharge test on the CT2001A battery test system, and the voltage cut-off range was 0.01 to 3V. After 600 cycles at a current density of A/g, there is still a discharge capacity of 880mAh/g, indicating that the metal oxide composite material provided by the invention can improve the cycle stability of the lithium-ion battery.

Test case 5

A scanning electron microscope test was performed on the metal oxide composite material obtained in Comparative Example 1, and the obtained SEM image is shown in FIG. 6 . It can be seen from Figure 6 that the obtained metal oxide composite material is in the shape of nanospheres.

Test case 6

The pure-phase CoFe ₂ O ₄ material obtained in Comparative Example 2 was tested by a scanning electron microscope, and the obtained SEM image is shown in FIG. 7 . It can be seen from Figure 7 that the obtained CoFe ₂ O ₄ material has an irregular granular morphology.

Test case 7

The materials obtained in Comparative Examples 1 and 2 were prepared according to the method of Application Example 1 to obtain a button battery, and then the rate performance test was performed. The obtained rate performance diagram is shown in Figure 8. As can be seen from Figure 8, at 0.1A/g current The average discharge capacities of the comparative examples 1 and 2 materials under the density are 590mAh/g and 857mAh/g respectively, and the average discharge capacities under the high current density of 6A/g are respectively 258mAh/g and 356mAh/g, which are obviously lower than those obtained in Example 1 The average discharge capacity of the material.

Although the foregoing embodiment has described the present invention in detail, it is only a part of the embodiments of the present invention, rather than all embodiments, and other embodiments can also be obtained according to the present embodiment without inventive step, and these embodiments are all Belong to the protection scope of the present invention.

Claims (10)

1. The metal oxide composite material is characterized in that the metal oxide composite material is a rod-shaped structure formed by connecting a plurality of submicron spheres in series;

the chemical composition of the submicron spheres is CoFe ₂ O ₄ ·xFe ₂ O ₃ And the value range of x is more than or equal to 1 and less than or equal to 4.

2. The metal oxide composite material according to claim 1, wherein the submicron spheres have a diameter of 200 to 1000nm;

the length of the rod-shaped structure is 2-20 mu m.

3. The metal oxide composite of claim 2, wherein the submicron spheres have a porous structure;

the aperture of the submicron sphere is 2-30 nm;

the specific surface area of the metal oxide composite material is 10-30 m ² /g。

4. A method for producing a metal oxide composite material according to any one of claims 1 to 3, characterized by comprising the steps of:

mixing water-soluble cobalt salt, water-soluble iron salt, sodium citrate, urea and water to obtain an alkaline mixed salt solution, and carrying out hydrothermal reaction on the alkaline mixed salt solution to obtain a precursor;

and carrying out thermal decomposition on the precursor to obtain the metal oxide composite material.

5. The preparation method according to claim 4, wherein the water-soluble cobalt salt comprises one or more of cobalt nitrate, cobalt sulfate, cobalt acetate and cobalt chloride;

the water-soluble ferric salt comprises one or more of ferrous sulfate, ferric nitrate and ferric chloride.

6. The preparation method according to claim 4 or 5, wherein the molar ratio of the water-soluble cobalt salt to the water-soluble iron salt to the sodium citrate to the urea is 0.03-0.12: 0.06-0.24: 0.02 to 0.48:0.12 to 0.48;

the molar concentration of the water-soluble cobalt salt in the alkaline mixed salt solution is 0.03-0.12 mol/L.

7. The preparation method according to claim 6, wherein the temperature of the hydrothermal reaction is 150-190 ℃ and the holding time is 4-8 h.

8. The method according to claim 6 or 7, wherein the thermal decomposition temperature is 400 to 600 ℃, the heating rate of the temperature to the thermal decomposition temperature is 2 to 5 ℃/min, and the holding time is 2 to 4 hours.

9. Use of the metal oxide composite material according to any one of claims 1 to 3 or the metal oxide composite material prepared by the preparation method according to any one of claims 4 to 8 in a lithium ion battery.

10. A negative electrode material comprising an active material, a conductive agent and a binder, wherein the active material is the metal oxide composite material according to any one of claims 1 to 3 or the metal oxide composite material prepared by the preparation method according to any one of claims 4 to 8.

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