Method for preparing porous carbon coated lithium-rich lithium ferrite by sol-gel method and application of porous carbon coated lithium-rich lithium ferrite in lithium supplement

Abstract

The invention discloses a method for preparing porous carbon coated lithium-rich lithium ferrite by a sol-gel method and application of the porous carbon coated lithium-rich lithium ferrite in lithium supplement. According to the method, a means of dispersing metal salt by sol-gel is adopted, ferric salt and an organic carbon source are compounded before lithium salt is added, a ferric salt precursor substrate frame structure coated with a carbon precursor in situ is obtained, the substrate frame structure is stable and uniform in particle size distribution, and then the lithium salt is added into a system, so that the composite material is obtained. Lithium ions are gradually migrated from the outside to the inside and are finally uniformly distributed on the frame, so that the influence of non-uniform distribution of a solid-phase lithium source and an iron source on the particle size of a product is avoided, lithium and ferric salt react in the calcining process, and meanwhile, an organic carbon precursor on the outer layer of the ferric salt is gradually carbonized at a high temperature and is accompanied with gas generation to obtain a porous carbon material. The porous carbon coated lithium-rich lithium ferrite has the advantages that the particle size is small, and the particle size distribution is uniform.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery cathode lithium supplement materials, and more specifically, to a method for preparing lithium-rich lithium ferrite coated with porous carbon by a sol-gel method and its application in lithium supplement. Background Art

[0002] With the improvement of science and technology and the rapid growth of the energy market, the demand for lithium-ion batteries is increasing day by day. At the same time, the performance requirements for lithium-ion batteries are also gradually increasing. Among them, the demand for improving the energy density of lithium-ion batteries is urgent and crucial, and it is the focus of attention for researchers in future scientific research. However, one of the reasons limiting the key electrochemical performance parameter (energy density) of lithium-ion batteries is that during the charging process at the initial stage of battery charge and discharge, when lithium ions in the cathode material migrate to the anode, a solid electrolyte interphase (SEI) will be formed on the anode surface, resulting in irreversible loss of lithium ions in the cathode, and thus causing a certain capacity loss. Therefore, for this key problem, a strategy of supplementing lithium ions to the lithium-ion battery cathode material can be adopted to improve the electrochemical performance of the lithium-ion battery.

[0003] The main lithium supplement technologies include cathode lithium supplement and anode lithium supplement technologies. Among them, the strategy of supplementing lithium ions in the anode material is usually to add metallic lithium powder or lithium metal strip to the anode material. However, adding lithium metal to the anode material has high requirements for the production process and high requirements for the required environment, resulting in that the current production process line and the environment of the process of lithium-ion batteries are difficult to meet the requirements of this technology, and thus it is difficult to be applied in existing battery companies on the market. On the other hand, compared with the anode lithium supplement technology, the cathode lithium supplement technology has an obvious advantage that it does not need to design and modify the existing production process line of lithium-ion batteries, so it can be applied to battery manufacturers in the market.

[0004] Based on this, current scientific researchers have focused a lot on developing advanced cathode lithium supplement materials. The studied cathode lithium supplement materials include M / LiO, Li 6 CoO 4 、Li 2 NiO 2 and M / LiF, etc. Among them, the theoretical specific capacity of Li 5 FeO 4 is as high as 867 mAh g -1, and at the same time shows a high irreversible capacity. The main method for synthesizing lithium-rich lithium iron oxide is the high-temperature solid-state method. Lithium hydroxide is used as the lithium source, and iron oxide is used as the iron source. They are mixed in a high-speed mixer according to a certain ratio, and then ball-milled. The ball-milled mixture is placed in a high-temperature sintering furnace for calcination, and after calcination, it is pulverized to obtain. However, the intrinsic electronic conductivity of lithium-rich lithium iron oxide material is low and its stability in air is not high. It is easy to react with moisture and carbon dioxide in the air to produce lithium-containing compounds, which has a great impact on the electrochemistry of the material.

[0005] Existing methods for modifying the air stability and intrinsic electronic conductivity of lithium-rich lithium iron oxide materials usually involve carbon coating on lithium-rich lithium iron oxide. For example, the Chinese patent with the publication number CN115642232A provides a preparation method, the obtained product and application of carbon-coated lithium-rich lithium iron oxide. Carbon coating is carried out in-situ, the process is simple, and the prepared carbon-coated lithium-rich lithium iron oxide has good air stability, high capacity and conductivity. However, this method still has problems such as large and uneven particle sizes of the carbon-coated lithium-rich lithium iron oxide. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing porous carbon-coated lithium-rich lithium iron oxide by the sol-gel method and its application in lithium supplementation. The prepared porous carbon-coated lithium-rich lithium iron oxide has small particle size and uniform particle size distribution.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention:

[0008] The present invention provides a method for preparing porous carbon-coated lithium-rich lithium iron oxide by the sol-gel method, including the following steps:

[0009] (1) Dissolve an iron salt in a solvent to obtain an iron salt solution, and dissolve an organic carbon source in the same solvent to obtain an organic carbon source solution;

[0010] (2) Mix the iron salt solution and the organic carbon source solution obtained in step (1), stir and heat to obtain a mixed solution of iron salt precursor in-situ coated with a carbon precursor;

[0011] (3) Continuously stir the mixed solution obtained in step (2), then add a lithium salt and continue to stir, and heat to obtain a gel-like mixture;

[0012] (4) Calcinate the gel-like mixture obtained in step (3) in an inert gas environment to prepare porous carbon-coated lithium-rich lithium iron oxide.

[0013] As a preferred technical solution, in step (1), the iron salt is FeCl 2 , FeSO 4 , Fe(NO 3 ), Fe 2 O 3, C 6 H 8 O 7 Fe, Fe(C 5 H 5 ) 2 One or more of the above.

[0014] As a preferred technical solution, in the step (1), the organic carbon source is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polydopamine, cetyltrimethylammonium bromide, sodium dodecyl sulfate, sodium oleate and oleylamine.

[0015] As a preferred technical solution, in the step (2), the iron salt and the organic carbon source are mixed in a mass ratio of 1:0.2 - 3.

[0016] As a preferred technical solution, in the step (3), the lithium salt is one or more of Li 2 O, LiOH, Li 2 C 2 O 4 , Li 2 CO 3 , LiNO 3 One or more of the above.

[0017] As a preferred technical solution, in the step (3), the lithium salt is added in a molar ratio of lithium salt to iron salt of 5 - 6:1.

[0018] As a preferred technical solution, in the steps (2) and (3), the heating temperature is 30 - 120 °C.

[0019] As a preferred technical solution, in the step (4), the calcination temperature is controlled at 400 - 1000 °C, the heating rate is 2 - 30 °C / min, and the holding time is 2 - 36 h.

[0020] The present invention also provides lithium-rich lithium ferrite coated with porous carbon prepared by the above method.

[0021] The present invention also provides the application of the lithium-rich lithium ferrite coated with porous carbon in lithium supplementation for the positive electrode of a lithium-ion battery.

[0022] Advantages of the present invention:

[0023] The present invention uses the method of sol-gel to disperse metal salts. Before adding lithium salts, iron salts are first compounded with an organic carbon source to obtain a base framework structure of iron salt precursors in-situ coated with a carbon precursor. This base framework structure is stable and has a uniform particle size distribution. Then, lithium salts are added to the system, allowing lithium ions to gradually migrate from the outside to the inside of the framework and finally evenly distributed on the framework, so as to avoid uneven distribution of solid-phase lithium source and iron source affecting the particle size of the product. Finally, during the calcination process, lithium reacts with iron salts, and at the same time, the organic carbon precursor on the outer layer of the iron salts is gradually carbonized at high temperature with gas generation to obtain a porous carbon material, and lithium-rich lithium ferrite coated with porous carbon is prepared. The lithium-rich lithium ferrite coated with porous carbon has the advantages of small particle size and uniform particle size distribution. Description of the Drawings

[0024] Figure 1 Transmission electron microscope image of lithium-rich lithium ferrite coated with porous carbon prepared in Example 1;

[0025] Figure 2 XRD spectrum of lithium-rich lithium ferrite coated with porous carbon prepared in Example 1;

[0026] Figure 3 Charge-discharge curve of a full cell assembled with lithium-rich lithium ferrite coated with porous carbon prepared in Example 1 as a lithium supplement additive;

[0027] Figure 4 Charge-discharge curve of a full cell assembled without a lithium supplement additive;

[0028] Figure 5 Charge-discharge curves of full cells assembled with lithium-rich lithium ferrite coated with porous carbon prepared in Example 1, Example 2, and Comparative Example 1 as the cathode material. Detailed Embodiments

[0029] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings.

[0030] Example 1

[0031] (1) Dissolve ferric sulfate in a mixed solvent composed of water and glycerol in a mass ratio of 3:1 to obtain an iron salt solution; dissolve cetyltrimethylammonium bromide in a mixed solvent composed of water and glycerol in a mass ratio of 3:1 to obtain an organic carbon source solution;

[0032] (2) According to the mass ratio of iron salt to organic carbon source of 1:2.5, mix the iron salt solution and the organic carbon source solution obtained in step (1), and stir and heat at 50 °C in a heating stirrer to obtain a mixed solution of iron salt precursors in-situ coated with a carbon precursor;

[0033] (3) Continuously stir the mixed solution obtained in step (2), then add lithium nitrate (with a molar ratio 5.5 times that of the iron salt) and continue stirring, and then place it in a baking machine for heat treatment to obtain a gel-like mixture;

[0034] (4) Calcinate the gel-like mixture obtained in step (3) in an inert gas environment, with a heating rate of 20 °C / min, and hold at 800 °C for 5 h to prepare lithium-rich lithium iron oxide coated with porous carbon.

[0035] Figure 1 Fig. 7 is a transmission electron microscope image of the lithium-rich lithium iron oxide coated with porous carbon prepared in Example 1. It can be seen from the figure that the lithium-rich lithium iron oxide coated with porous carbon has small particle size and uniform particle size distribution.

[0036] Figure 2 Fig. 8 is an XRD pattern of the lithium-rich lithium iron oxide coated with porous carbon prepared in Example 1. Characteristic peaks of lithium-rich lithium iron oxide are found from the figure, which proves the successful preparation of lithium-rich lithium iron oxide.

[0037] Take the lithium-rich lithium iron oxide coated with porous carbon prepared in Example 1 as a lithium supplement additive, and add it to the slurry prepared by mixing lithium iron phosphate, PVDF and acetylene black in a mass ratio of 92:5:3 at a mass ratio of 8:1:1. The solvent of the slurry is N-methylpyrrolidone. Then coat the slurry on an aluminum foil, and cut the dried foil into pieces to obtain a positive electrode sheet.

[0038] The negative electrode is a slurry prepared by mixing graphite, PVDF and acetylene black in a mass ratio of 8:1:1, and the solvent is also N-methylpyrrolidone. Coat the obtained slurry on a copper foil, and then dry it in a drying oven. Cut the dried sheet to obtain a negative electrode sheet.

[0039] Assemble the positive electrode sheet added with the lithium supplement additive and the negative electrode sheet into a coin-type full cell for charge-discharge tests. The obtained charge-discharge curves are as Figure 3 shown.

[0040] Assemble the positive electrode sheet without adding the lithium supplement additive and the negative electrode sheet into a coin-type full cell for charge-discharge tests. The obtained charge-discharge curves are as Figure 4 shown.

[0041] Compare Figure 3 and Figure 4 It can be known that the lithium-rich lithium iron oxide coated with porous carbon prepared in Example 1 as a lithium supplement additive can improve the specific capacity.

[0042] Example 2

[0043] (1) Dissolve ferric sulfate in a mixed solvent composed of water, n - hexane, ethanol, and glycerol with a mass ratio of 1:3:1:1 to obtain an iron salt solution; dissolve sodium oleate in a mixed solvent composed of water, n - hexane, ethanol, and glycerol with a mass ratio of 1:3:1:1 to obtain an organic carbon source solution;

[0044] (2) According to the mass ratio of iron salt to organic carbon source of 1:0.25, mix the iron salt solution and the organic carbon source solution obtained in step (1), and stir and heat at 70 °C in a heating stirrer to obtain a mixed solution of iron salt precursor coated in - situ with a carbon precursor;

[0045] (3) Continuously stir the mixed solution obtained in step (2), then add lithium nitrate (with a molar ratio 5.5 times that of the iron salt) and continue to stir, and then place it in a baking machine for heat treatment to obtain a gel - like mixture;

[0046] (4) Calcinate the gel - like mixture obtained in step (3) in an inert gas environment, with a heating rate of 10 °C / min, and hold at 600 °C for 10 h to obtain lithium - rich lithium ferrite coated with porous carbon.

[0047] Comparative Example 1

[0048] (1) Dissolve ferric sulfate and lithium nitrate in a mixed solvent composed of water and glycerol with a mass ratio of 3:1 according to a molar ratio of 1:5.5, and at the same time add cetyltrimethylammonium bromide according to the mass ratio of iron salt to organic carbon source of 1:2.5, and stir and heat to form a gel - like mixture;

[0049] (2) Calcinate the gel - like mixture obtained in step (1) in an inert gas environment, with a heating rate of 20 °C / min, and hold at 800 °C for 5 h to obtain lithium - rich lithium ferrite coated with porous carbon.

[0050] Respectively use the lithium - rich lithium ferrite coated with porous carbon prepared in Example 1, Example 2, and Comparative Example 1 as the positive electrode material, and prepare slurries with PVDF and acetylene black according to a mass ratio of 8:1:1. The solvent of the slurry is N - methylpyrrolidone. Then coat the slurry on the aluminum foil, and cut the dried sheet to obtain a positive electrode sheet; the negative electrode is a lithium metal sheet.

[0051] Respectively assemble the positive electrode sheets of Example 1, Example 2, and Comparative Example 1 with the negative electrode sheets into coin - type full cells for charge - discharge tests, and the obtained charge - discharge curves are as Figure 5 shown. It can be seen from the figure that, compared with the lithium - rich lithium ferrite coated with porous carbon prepared in Comparative Example 1, the lithium - rich lithium ferrite coated with porous carbon prepared in Example 1 and Example 2 can release more lithium ions.

[0052] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method, characterized in that: It includes the following steps: (1) Dissolve iron salt in a solvent to obtain an iron salt solution, and dissolve an organic carbon source in the same solvent to obtain an organic carbon source solution; (2) Mix the iron salt solution and the organic carbon source solution obtained in step (1), stir and heat to obtain a mixed solution of iron salt precursor in-situ coated with carbon precursor; (3) Continuously stir the mixed solution obtained in step (2), then add lithium salt and continue to stir, and heat-treat to obtain a gel-like mixture; (4) Calcinate the gel-like mixture obtained in step (3) in an inert gas environment to prepare lithium-rich lithium ferrite coated with porous carbon.

2. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (1), the iron salt is FeCl 2 , FeSO 4 , Fe(NO 3 ), Fe 2 O 3 , C 6 H 8 O 7 Fe, Fe(C 5 H 5 ) 2 or more of them.

3. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (1), the organic carbon source is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polydopamine, cetyltrimethylammonium bromide, sodium dodecyl sulfate, sodium oleate and oleylamine.

4. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (2), the iron salt and the organic carbon source are mixed in a mass ratio of 1:0.2 - 3.

5. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (3), the lithium salt is Li 2 O, LiOH, Li 2 C 2 O 4 , Li 2 CO 3 , LiNO 3 or one or more of them.

6. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (3), the lithium salt is added in a molar ratio of lithium salt to iron salt of 5 - 6:

1.

7. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the steps (2) and (3), the heating temperature is 30 - 120 °C.

8. The method for preparing lithium-rich lithium ferrite coated with porous carbon by sol-gel method according to claim 1, characterized in that: In the step (4), the calcination temperature is controlled at 400 - 1000 °C, the heating rate is 2 - 30 °C / min, and the heat preservation time is 2 - 36 h.

9. Lithium-rich lithium ferrite coated with porous carbon prepared by the method according to any one of claims 1 to 8.

10. Application of the lithium-rich lithium ferrite coated with porous carbon according to claim 9 in lithium supplementation of the positive electrode of a lithium-ion battery.

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