A carbon-coated lithium iron oxide material

Abstract

The application discloses a carbon-coated lithium ferrite material and belongs to the technical field of material preparation. First, nano Fe2O3 and LiNO3 are mixed, deionized water is added, and a uniform mixed solution is prepared through magnetic stirring, then the mixed solution is subjected to spray drying, the obtained precursor powder is mixed with graphite, and the mixture is placed in a muffle furnace for twice calcination, then inert gas is introduced into an atmosphere furnace to create a low-oxygen and low-humidity environment, and carbon source gas and auxiliary carbonization mixed gas are introduced to perform CVD treatment, so that a 2-10nm carbon coating layer is formed on the surface of the lithium ferrite material, and finally the carbon-coated lithium ferrite material is obtained. The material can be used as an electrode lithium supplement agent to improve the electrochemical performance of a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, in particular to a carbon-coated lithium ferrite material. BACKGROUND

[0002] In the field of energy storage and conversion, the development of high-performance electrode materials has become a key factor in promoting the progress of various battery technologies. Li5FeO4, as a material with unique crystal structure and electrochemical properties, has shown great application potential in the field of lithium-ion batteries and other fields.

[0003] Li5FeO4 has a high theoretical specific capacity, which can provide stronger energy output for batteries; at the same time, it has a relatively stable structure during charging and discharging, which helps to improve the cycle life and safety performance of the battery. Therefore, Li5FeO4 is highly concerned in electric vehicles, portable electronic devices, and large-scale energy storage systems.

[0004] However, in practical applications, the performance of Li5FeO4 material is limited by various factors. On the one hand, the original Li5FeO4 material has a large particle size, resulting in a small specific surface area and insufficient active sites, which makes the diffusion path of lithium ions inside the material longer, thereby affecting the charging and discharging rate and rate performance of the battery. On the other hand, the electronic conductivity of Li5FeO4 itself is low, which greatly limits its charging and discharging efficiency in the battery, resulting in serious polarization and large energy loss when the battery works at high current density.

[0005] In order to overcome these problems, researchers have tried various methods to modify Li5FeO4. Traditional preparation methods often have difficulty in accurately controlling the particle size and microstructure of the material, resulting in poor consistency and stability of the material performance. For example, Li5FeO4 prepared by some simple mixing and calcination processes has uneven particle size distribution, which cannot fully develop its potential performance.

[0006] In addition, pure Li5FeO4 material is prone to side reactions with electrolyte during charging and discharging, leading to the destruction of the material structure and the degradation of the battery performance. Therefore, it is necessary to form an effective coating layer on the surface of Li5FeO4 to improve the chemical stability and interface compatibility of the material.

[0007] In view of the above problems, the present technical scheme proposes a new Li5FeO4 material preparation method, which aims to prepare Li5FeO4 material with small particle size and carbon coating layer by accurately controlling the preparation of precursor, calcination conditions and surface coating process, to improve its electronic conductivity, lithium ion diffusion performance and chemical stability, thereby improving its comprehensive performance in the field of energy storage. SUMMARY

[0008] The application aims to provide a carbon-coated lithium ferrite material, and prepare a Li5FeO4 material with small particle size and a carbon coating layer to improve its electronic conductivity, lithium ion diffusion performance and chemical stability.

[0009] To achieve the above-mentioned purpose, the application provides a carbon-coated lithium ferrite material, comprising the following preparation steps:

[0010] Step one, mixing nano Fe2O3 and LiNO3, then adding deionized water and performing magnetic stirring to obtain a mixed solution;

[0011] Step two, performing spray drying on the mixed solution obtained in step one to obtain a precursor powder;

[0012] Step three, mixing the precursor powder obtained in step two with graphite, then placing them in a muffle furnace and performing twice calcination to obtain a lithium ferrite material;

[0013] Step four, introducing inert gas into the atmosphere furnace to make the oxygen content in the furnace less than 1 ppm and the humidity less than 5%, then introducing carbon source gas and auxiliary carbonization gas to perform CVD treatment, forming a 2-10 nm carbon coating layer on the surface of the lithium ferrite material obtained in step three to obtain a carbon-coated lithium ferrite material.

[0014] Preferably, in step one, the nano Fe2O3 and LiNO3 are mixed in a Li / Fe atomic ratio of 6:1-12:1, and the magnetic stirring time is 1-24 h.

[0015] Preferably, in step two, when performing spray drying, the inlet air temperature is 150-180℃ and the outlet air temperature is 80-120℃.

[0016] Preferably, in step three, the two-step calcination steps are as follows:

[0017] First calcination: heating to 300-400℃ and calcining for 1-5 h to obtain a first calcined precursor;

[0018] Second calcination: grinding the first calcined precursor, then placing it in the muffle furnace again, heating to 600-1000℃ and calcining for 5-30 h to obtain a lithium ferrite material.

[0019] Preferably, in step four, the carbon source gas is one or more of acetylene, methane, coal gas and natural gas, and the auxiliary carbonization gas is one or more of argon, nitrogen and hydrogen; when introducing the carbon source gas and the auxiliary carbonization gas, the carbon source gas flow is 10-100 ml / min and the auxiliary carbonization gas flow is 20-200 ml / min.

[0020] Preferably, in step four, the CVD treatment time is 5-30 min.

[0021] Preferably, in step three, the heating rate is 1-15℃ / min during the primary calcination and the secondary calcination; the mass ratio of the precursor powder to the graphite is 13-25:0.3-1.

[0022] Preferably, in step three, the graphite includes one or more of natural graphite, expanded graphite, oxidized graphite, and artificial graphite.

[0023] The material prepared according to the above can be used in lithium ion batteries as an electrode material or a composite material of an electrode material.

[0024] Therefore, the present application provides a carbon-coated lithium ferrite material, which has the following beneficial effects:

[0025] (1) During the primary calcination, the graphite is mixed with the precursor, which can better refine the particle size of the precursor and prepare for the formation of small-particle-size Li5FeO4. Smaller particle size can increase the specific surface area of the material and improve the reactivity and performance of the material.

[0026] (2) During the secondary calcination, the precursor can be further reacted completely to obtain small-particle-size Li5FeO4, which ensures the purity of the product and the integrity of the crystal structure.

[0027] (3) By introducing inert gas to create an oxygen-free and low-humidity environment, and then introducing a specific flow of carbon source gas and carbonization aid gas for CVD treatment for 5-30 min, a dense carbon coating layer of 2-10 nm is formed on the surface of Li5FeO4. The carbon coating layer can improve the electronic conductivity of the material, enhance the structural stability of the material, and effectively improve the charge-discharge performance and cycle stability of Li5FeO4. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of the obtained carbon-coated Li5FeO4;

[0029] Figure 2 XRD image of the obtained carbon-coated Li5FeO4 of the present application;

[0030] Figure 3 TEM image of the obtained carbon-coated Li5FeO4 of the present application;

[0031] Figure 4 First charge-discharge curve of the obtained carbon-coated Li5FeO4 of the present application;

[0032] Figure 5 First charge-discharge curve of the LiFePO4 half-cell before and after the addition of Li5FeO4 obtained in Example 1;

[0033] Figure 6First charge-discharge curve of LiFePO4 half-cell before and after adding Li5FeO4 in Example 2;

[0034] Figure 7 First charge-discharge curve of LiFePO4 half-cell before and after adding Li5FeO4 in Example 3;

[0035] Figure 8 SEM image of Comparative Example 1;

[0036] Figure 9 First charge-discharge curve of Comparative Example 1;

[0037] Figure 10 XRD image of Comparative Example 2;

[0038] Figure 11 First charge-discharge curve of Comparative Example 2;

[0039] Figure 12 First charge-discharge curve of Comparative Example 3;

[0040] Figure 13 Impedance image of Comparative Example 3. DETAILED DESCRIPTION

[0041] The technical solutions of the present application are further illustrated by the following examples.

[0042] Example 1

[0043] Step one, preparation of precursor: mix nano Fe2O3 and LiNO3 according to the atomic ratio of Li / Fe at a ratio of 6:1, 2.8g of Fe2O3, 14.5g of LiNO3, add 150ml of deionized water, magnetically stir for 24h to obtain a mixed solution;

[0044] Step two, spray drying: spray dry the mixed solution obtained in step one, with an inlet temperature of 150℃ and an outlet temperature of 100℃, to obtain a precursor powder;

[0045] Step three, primary calcination: mix about 13g of the precursor powder obtained in step two with 0.3g of natural graphite and place them in a muffle furnace, heat to 300℃ at a heating rate of 5℃ / min, and calcine for 3h.

[0046] Secondary calcination: take out the precursor obtained after primary calcination and grind it thoroughly, then place it again in a muffle furnace, heat to 600℃ at a heating rate of 5℃ / min, and calcine for 18h. At a high temperature of 600℃, the precursor can be further reacted completely to obtain small-particle-size Li5FeO4;

[0047] Step four, the precursor powder is put into a tube furnace, inert gas is introduced into the tube, the air in the tube is removed, the oxygen content in the tube furnace is ensured to be less than 1 ppm, the humidity is less than 5%, acetylene and argon-hydrogen mixed gas are introduced, the acetylene flow is 20 ml / min, the argon-hydrogen mixed gas flow is 60 ml / min, the CVD treatment is performed for 5 min, a dense 2-10 nm carbon coating layer is formed on the surface of Li5FeO4, and small-particle-size Li5FeO4 coated with carbon is obtained.

[0048] Li5FeO4 is mixed with positive electrode material lithium iron phosphate, super p, binder PVDF and solvent NMP and the like to be uniform, wherein the amount of Li5FeO4 added is 3% of the positive electrode material lithium iron phosphate, and a LiFePO4 (LFO) half-cell is formed with lithium metal, and the first charge specific capacity of the LiFePO4 half-cell before and after the addition of Li5FeO4 is tested at 2.5-4.2V. Figure 5 The first charge-discharge curves of LPO and LPO (LFO) half-cells are shown in the figure. It can be seen from the figure that the first charge specific capacity of the LPO half-cell after adding Li5FeO4 is improved, reaching 188.52 mAh / g, which is 23.54 mAh / g higher than the first charge specific capacity of the LPO half-cell of 164.98 mAh / g, and an additional lithium extraction platform appears, which is provided by Li5FeO4.

[0049] Example 2

[0050] Step one, precursor preparation: nano-Fe2O3 and LiNO3 are mixed in a ratio of 9:1 according to the Li / Fe atomic ratio, 2.8g of Fe2O3, 21.8g of LiNO3, 150ml of deionized water is added, and magnetic stirring is carried out for 24h to obtain a mixed solution.

[0051] Step two, spray drying: the mixed solution obtained in step one is subjected to spray drying, the inlet air temperature is 160℃, and the outlet air temperature is 110℃, to obtain a precursor powder.

[0052] Step three, primary calcination: about 20g of the precursor powder obtained in step two is mixed with 0.5g of expanded graphite and put into a muffle furnace, the temperature is raised to 350℃ at a rate of 10℃ / min, and calcination is carried out for 4h.

[0053] Secondary calcination: the precursor obtained after primary calcination is taken out and ground thoroughly, and then put into a muffle furnace again, the temperature is raised to 800℃ at a rate of 10℃ / min, and calcination is carried out for 24h, small-particle-size Li5FeO4 is obtained at a high temperature of 800℃;

[0054] Step four, inert gas is introduced into the tube to remove air in the tube, ensuring that the oxygen content in the tube furnace is less than 1 ppm and the humidity is less than 5%, methane and high-purity nitrogen are introduced, the methane flow is 50 ml / min, the high-purity nitrogen flow is 100 ml / min, and CVD treatment is performed for 20 min to form a dense 2-10 nm carbon coating layer on the surface of Li5FeO4, thereby obtaining small-particle-size Li5FeO4 coated with carbon.

[0055] Li5FeO4 is mixed with positive electrode material lithium iron phosphate, super p, binder PVDF, and solvent NMP and other materials, and the amount of Li5FeO4 added is 3% of the positive electrode material lithium iron phosphate, and a LiFePO4 (LFO) half-cell is formed with lithium metal. The first charge specific capacity of the LiFePO4 half-cell before and after the addition of Li5FeO4 is tested at 2.5-4.2V. Figure 6 The first charge-discharge curves of LPO and LPO (LFO) half-cells are shown in the figure. It can be seen from the figure that the first charge specific capacity of the LPO half-cell after adding Li5FeO4 is improved, reaching 202.97 mAh / g, which is 37.99 mAh / g higher than the first charge specific capacity of the LPO half-cell of 164.98 mAh / g, and an additional lithium removal platform appears, which is provided by Li5FeO4.

[0056] Example 3

[0057] Step one, preparation of the precursor: mix nano-Fe2O3 and LiNO3 in a ratio of 12:1 according to the Li / Fe atomic ratio, 2.8g of Fe2O3 is added to 150ml of deionized water, and after magnetic stirring for 24h, a mixed solution is obtained.

[0058] Step two, spray drying: the mixed solution obtained in step one is subjected to spray drying, the inlet air temperature is 180℃, and the outlet air temperature is 120℃, thereby obtaining a precursor powder.

[0059] Step three, primary calcination: about 25g of the precursor powder obtained in step two is mixed with 1g of graphite oxide and placed in a muffle furnace, the temperature is raised to 400℃ at a rate of 15℃ / min, and calcination is performed for 5h.

[0060] Secondary calcination: the precursor obtained after primary calcination is taken out and ground thoroughly, and then placed in a muffle furnace again, the temperature is raised to 1000℃ at a rate of 15℃ / min, and calcination is performed for 30h. At a high temperature of 1000℃, the precursor is further reacted completely to obtain small-particle-size Li5FeO4.

[0061] Step four, inert gas is introduced into the tube to remove air in the tube, ensuring that the oxygen content in the tube furnace is less than 1 ppm, the humidity is less than 5%, the coal gas and nitrogen hydrogen mixed gas are introduced, the coal gas flow is 60 ml / min, the nitrogen hydrogen mixed gas flow is 150 ml / min, the CVD treatment is carried out for 30 min, a dense 2-10 nm carbon coating layer is formed on the surface of Li5FeO4, and small particle size Li5FeO4 after carbon coating is obtained.

[0062] Li5FeO4 is mixed with positive electrode material lithium iron phosphate, super p, binder PVDF and solvent NMP and other materials, wherein the amount of Li5FeO4 added is 3% of the positive electrode material lithium iron phosphate, and a LiFePO4 (LFO) half battery is formed with lithium metal. The first charge specific capacity of LiFePO4 half battery before and after adding Li5FeO4 is tested at 2.5-4.2V. Figure 7 The first charge-discharge curves of LPO and LPO (LFO) half battery are shown in the figure. It can be seen from the figure that the first charge specific capacity of LPO half battery after adding Li5FeO4 is improved, reaching 187.5 mAh / g, which is 22.52 mAh / g higher than the first charge specific capacity of LPO half battery 164.98 mAh / g, and an additional delithiation platform appears, which is provided by Li5FeO4.

[0063] Comparative example 1

[0064] Comparative example 1 has no first calcination step, and the rest of the operations and steps are the same as example 1. Without the first calcination, the graphite cannot play a role. From Figure 8 It can be seen that the prepared Li5FeO4 has large particle size and uneven size, and Figure 9 It can be seen that the first charge specific capacity of Li5FeO4 is 602.62 mAh / g, and the performance is relatively low.

[0065] Comparative example 2

[0066] Comparative example 2 has no second calcination step, and the rest of the operations and steps are the same as example 1. Without the second calcination, the reaction is insufficient, and there are more impurities and residual graphite, which affects the performance. From Figure 10 It can be seen that the diffraction peak contains other impurities in addition to Li5FeO4, and Figure 11 It can be seen that the first charge specific capacity is 538.63 mAh / g, and the performance of Li5FeO4 is affected due to the presence of impurities.

[0067] Comparative example 3

[0068] Comparative Example 3, which was prepared without carbon coating in step four, has poor air stability and general performance and a large impedance. From Figure 12 It can be seen that the Li5FeO4 without carbon coating has a first charge specific capacity of 638.65 mAh / g, which is poorer than the carbon-coated Li5FeO4, and from Figure 13 It can be seen that the Li5FeO4 after carbon coating has a significantly reduced impedance.

[0069] Therefore, the present application provides a carbon-coated lithium iron oxide material, which improves its electronic conductivity, lithium ion diffusion performance and chemical stability.

[0070] In the description of the present specification, the description referring to the terms "one experimental example", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the experimental example or example are included in at least one experimental example or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same experimental example or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more experimental examples or examples in a suitable manner.

[0071] Finally, it should be noted that: the above experimental examples are only used to illustrate the technical solutions of the present application rather than limit them, and although the present application has been described in detail with reference to the preferred experimental examples, those skilled in the art should understand that: it can still modify or equivalently replace the technical solutions of the present application, and these modifications or equivalent replacements also cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A carbon-coated lithium ferrite material, characterized in that, The preparation steps include the following: Step 1: Mix nano Fe2O3 and LiNO3, add them to deionized water, and stir magnetically to obtain a mixed solution; Step 2: Spray dry the mixed solution obtained in Step 1 to obtain precursor powder; Step 3: Mix the precursor powder obtained in Step 2 with graphite, and then place it in a muffle furnace for two calcinations to obtain lithium ferrite material. In step three, the two calcination steps are as follows: First calcination: Heat to 300-400℃ and calcine for 1-5 hours to obtain the precursor after first calcination; Secondary calcination: After the precursor is ground after the first calcination, it is placed in a muffle furnace again and heated to 600-1000℃ for 5-30 hours to obtain lithium ferrite material. In step three, the heating rate during the initial calcination and the second calcination is 1-15℃ / min; the mass ratio of precursor powder to graphite is 13-25:0.3-1. Step 4: Inert gas is introduced into the atmosphere furnace to make the oxygen content in the furnace less than 1 ppm and the humidity less than 5%. Then, carbon source gas and auxiliary carbonization gas are introduced to perform CVD treatment. A carbon coating layer of 2-10 nm is formed on the surface of the lithium ferrite material obtained in step 3, and the carbon-coated lithium ferrite material is obtained.

2. The carbon-coated lithium ferrite material according to claim 1, characterized in that, In step one, nano Fe2O3 and LiNO3 are mixed in a Li / Fe atomic ratio of 6:1 to 12:1; the magnetic stirring time is 1-24 hours.

3. The carbon-coated lithium ferrite material according to claim 1, characterized in that, In step two, during spray drying, the inlet air temperature is 150-180℃ and the outlet air temperature is 80-120℃.

4. The carbon-coated lithium ferrite material according to claim 1, characterized in that, In step four, the carbon source gas is one or more of acetylene, methane, coal gas, and natural gas, and the auxiliary carbonizing gas is one or more of argon, nitrogen, and hydrogen. When the carbon source gas and auxiliary carbonizing gas are introduced, the flow rate of the carbon source gas is 10-100 ml / min, and the flow rate of the auxiliary carbonizing gas is 20-200 ml / min.

5. The carbon-coated lithium ferrite material according to claim 1, characterized in that, In step four, the CVD processing time is 5-30 minutes.

6. The carbon-coated lithium ferrite material according to claim 1, characterized in that, In step three, graphite includes one or more of the following: natural graphite, expanded graphite, graphite oxide, and artificial graphite.

7. The carbon-coated lithium ferrite material according to claim 1, characterized in that, The prepared materials can be used as electrode materials or composite materials of electrode materials in lithium-ion batteries.

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