WO2023173775A1

WO2023173775A1 - Modified lithium ion battery positive electrode material and preparation method therefor and application thereof

Info

Publication number: WO2023173775A1
Application number: PCT/CN2022/131587
Authority: WO
Inventors: 朱青林; 刘伟健; 缪建麟; 王雀乐; 阮丁山; 李长东
Original assignee: 广东邦普循环科技有限公司; 湖南邦普循环科技有限公司; 湖南邦普汽车循环有限公司
Priority date: 2022-03-18
Filing date: 2022-11-14
Publication date: 2023-09-21
Also published as: CN114709383A

Abstract

The present invention relates to the technical field of battery materials, and disclosed are a modified lithium ion battery positive electrode material and a preparation method therefor and an application thereof. The chemical formula of the modified lithium ion battery positive electrode material is Li₅FeO₄@C, the modified lithium ion battery positive electrode material is an agglomerate, and the agglomerate is formed by agglomerating sphere-like particles. According to the carbon-doped and coated agglomerate modified lithium ion positive electrode material prepared by the present invention, firstly, the conductivity of the material can be improved, the polarization performance of the material can be reduced, and the charging capacity of the material at high rate can be improved; and secondly, the surface of Li₅FeO₄ can be prevented from being in direct contact with water and carbon dioxide in the air, the "air sensitive effect" on the surface of the modified lithium ion positive electrode material is eliminated or mitigated, and the stability of the material in the air is improved.

Description

Modified lithium-ion battery cathode materials and preparation methods and applications thereof

Technical field

The invention belongs to the technical field of battery materials, and specifically relates to modified lithium-ion battery cathode materials and their preparation methods and applications.

Background technique

During the charging process of lithium-ion batteries, lithium ions are detached from the positive electrode and embedded in the negative electrode. When discharging, the lithium ions migrate from the negative electrode to the positive electrode. However, during the cycle, a CEI film (surface electrolyte interface film) will be formed on the surface of the positive electrode material and on the negative electrode material. An SEI film (solid electrolyte interface film) is formed on the surface. This process leads to the consumption of active lithium in the original material and reduces the charge and discharge efficiency. In order to improve charge and discharge efficiency, a modified lithium-ion battery material can be added to the positive or negative electrode, such as adding lithium powder and lithium foil to the negative electrode material and adding high-capacity lithium-containing oxides, including lithium-rich compounds, to the positive electrode material. , nanocomposites and binary lithium compounds based on conversion reactions, etc., to solve the irreversible capacity loss caused by the consumption of active lithium. Compared with the difficult and high-investment negative electrode process, the process of adding a modified lithium-ion battery material to the positive electrode is simple and convenient.

Among modified lithium-ion battery cathode materials, Li ₅ FeO ₄ is a safe, reliable, relatively low-cost material that can release a large amount of lithium ions during the first charge, and the product after releasing lithium ions has extremely low activity and will not occur again. Lithium insertion or dissolution can significantly improve the cycle efficiency and energy density of lithium-ion batteries, so it is an ideal modified lithium-ion cathode material with great potential. However, common Li ₅ FeO ₄ has low purity, large particle size differences, and is non-conductive, which seriously affects its electrochemical activity. It is also unstable in the air and needs to be stored and used in an inert atmosphere, and the preparation conditions are general. They are all liquid phase, chemical vapor deposition or solid phase sintering at high temperature and for a long time. The preparation process is complicated and difficult to be industrialized.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a modified lithium-ion battery cathode material and its preparation method and application. The material is an agglomerate-modified lithium-ion cathode material doped and coated with carbon, which can block the surface of Li ₅ FeO ₄ from the air. The direct contact between medium water and carbon dioxide eliminates or alleviates the "air sensitivity effect" on the surface of the modified lithium ion cathode material.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A modified lithium-ion battery cathode material, the chemical formula of which is Li ₅ FeO ₄ @C; the modified lithium-ion battery cathode material is an agglomerate, and the agglomerate is formed by agglomeration of spherical particles.

Agglomerates refer to step (1) in the preparation method where the pulverized material is sintered to form small spherical particles and then grow and aggregate together to form agglomerates.

Part of the carbon in Li ₅ FeO ₄ @C is doped in Li ₅ FeO ₄ , and the other part of the carbon is coated on the surface of Li ₅ FeO _4. This is because the carbon source is mixed on the surface of the crushed material. After the second sintering, the crushed material grows longer. Large, part of it is doped in Li ₅ FeO ₄ , and the other part of carbon is coated on the surface of Li ₅ FeO ₄ .

Preferably, the modified lithium ion cathode material has an average particle size of 1.0-10 μm and a specific surface area of 3.0-15.0 m ² /g.

Preferably, the particle size of the spherical particles is 10-500 nm.

Preferably, the modified lithium ion cathode material is charged and discharged at a charging voltage range of 2.8-4.25V and a current density of 0.23C, with a charge specific capacity of 645-655mAh/g and a discharge specific capacity of 2.1-2.6mAh/g.

Preferably, the mass percentage of carbon in the modified lithium ion cathode material is 1-18%.

A method for preparing modified lithium-ion battery cathode materials, including the following steps:

(1) Mix the lithium source and the iron source, perform sintering for the first time, and pulverize to obtain the pulverized material;

(2) Mix the pulverized material with a carbon source, perform a second sintering, pulverize, and sieve to obtain modified lithium-ion battery cathode material;

The molar ratio of lithium in the lithium source to iron in the iron source is (5.0-6.0):1; the temperature of the second sintering is 450-750°C; the particle size D50 of the pulverized material is 1.0-5.0 μm.

Preferably, in step (1), the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium acetate, lithium borate, lithium metaborate, lithium lactate, lithium nitrate, lithium oxalate or lithium oxide.

Preferably, in step (1), the iron source is ferric nitrate, ferrous nitrate, ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, ferric citrate, ferric oxide or ferric oxide. At least one.

Preferably, in step (1), the molar ratio of lithium in the lithium source and iron in the iron source is (5.0-6.0):1.

Preferably, in step (1), the first sintering atmosphere is at least one of oxygen, nitrogen, argon, helium, and neon.

Preferably, in step (2), the second sintering atmosphere is at least one of oxygen, nitrogen, argon, helium, and neon.

Preferably, in step (1), the temperature rise rate of the first sintering is 1°C-10°C/min, the temperature of the first sintering is 400-750°C, and the time of the first sintering is 4-20 h.

Further preferably, the temperature of the first sintering is 400-500°C, and the time of the first sintering is 4-15 hours.

Preferably, in step (1), the equipment used for crushing is one of a jet pulverizer and a mechanical mill.

Preferably, in step (2), the carbon source is polyethylene glycol, polyvinyl alcohol, polyacrylic acid, polypyrrole, fatty alcohol polyoxyethylene, glucose, sucrose, conductive graphite, acetylene black, carbon fiber, Ketjen black , at least one of carbon nanotubes and graphene.

Further preferably, the carbon source is at least one of polyethylene glycol, polyvinyl alcohol, polyacrylic acid, polypyrrole, fatty alcohol polyoxyethylene, glucose, and sucrose.

Preferably, in step (2), the content of the carbon source accounts for 1-25% by mass of the modified lithium ion cathode material.

Preferably, in step (2), the temperature rise rate of the second sintering is 1°C-10°C/min, the temperature of the second sintering is 450-750°C, and the time of the second sintering is 4-12 hours.

Further preferably, the temperature of the second sintering is 450-550°C, and the time of the second sintering is 4-10 hours.

Preferably, in step (2), the sieving is through a 300-mesh vibrating sieve.

A battery includes the above-mentioned modified lithium-ion battery cathode material.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) What the present invention prepares is an agglomerate-modified lithium ion cathode material doped and coated with carbon (since the particles of the crushed material are very small, 1.0-5.0 μm, the carbon source is mixed on the surface of the crushed material, and after a second sintering, The crushed material grows up, so part of the carbon is doped in the material, and the other part of the carbon is coated on the surface of the material). The coated carbon can block the surface of Li ₅ FeO ₄ (modified lithium ion cathode material) from water in the air. Direct contact with carbon dioxide eliminates or alleviates the "air sensitivity effect" on the surface of the modified lithium-ion cathode material, improving the stability of the material in the air; the doped carbon plays a conductive role. The secondary particles of the above-mentioned agglomerate are spherical with uniform size, and the spherical particles are smaller. When charging and discharging at a charging voltage range of 2.8-4.25V and a current density of 0.23C, the charging specific capacity is 645-655mAh/g, and the discharge specific capacity is 2.1-2.6mAh/g.

(2) The present invention improves the rate performance of the modified lithium ion cathode material by increasing the electronic conductivity of the material and shortening the migration distance of lithium ions. Electrical conductivity (electron conductivity) is achieved by growing a layer of carbon material in situ on the surface and middle of the modified lithium ion cathode material through sintering to improve the electronic conductivity of the material. Shortening the migration distance of lithium ions is mainly achieved by controlling the crushing and sintering processes to obtain agglomerated modified lithium ion cathode materials. The above method improves the conductivity and ion migration rate of the material. In the charging voltage range of 2.8-4.25V, 0.23C current density charge and discharge, the charge specific capacity is 645-655mAh/g, and the discharge specific capacity is 2.1-2.6mAh/g. The specific capacity is high, the discharge specific capacity is low, and the material is quickly deactivated after delithiation is completed. This effectively improves the active lithium consumed during the battery charge and discharge process, and improves the cycle performance of lithium-ion batteries.

Description of the drawings

Figure 1 is an XRD pattern of the modified lithium ion cathode material prepared in Example 1;

Figure 2 is an SEM image of the modified lithium ion cathode material prepared in Example 1;

Figure 3 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 1;

Figure 4 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 2;

Figure 5 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 3;

Figure 6 is a charging curve diagram of the modified lithium ion cathode material prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3.

Detailed ways

The concept of the present invention and the technical effects produced will be clearly and completely described below with reference to the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without exerting creative efforts are all protection scope of the present invention.

Example 1

The specific experimental steps for the preparation method of the modified lithium ion cathode material of this embodiment are as follows:

(1) Weigh lithium hydroxide monohydrate and iron oxide according to a Li:Fe molar ratio of 5.5:1, then put them into a mixer and mix them evenly to obtain a mixed material;

(2) The mixed material obtained in step (1) is sintered for the first time under oxygen conditions, and the temperature is raised to 450°C and kept for 4 hours. Then the temperature is raised to 480°C and kept for 12 hours. The heating rate is 5°C/min. The cooling procedure is to cool to room temperature with the furnace, and then grind it with an airflow mill to obtain fine powder with a particle size D50 of about 2 μm;

(3) Weigh the fine powder and glucose in step (2) according to a mass ratio of 10:1, mix them, and conduct the second sintering under nitrogen protection. Raise the temperature to 700°C and keep it warm for 6 hours. The heating rate is 5℃/min. The cooling program is to cool to room temperature with the furnace, and then pass through a 300-mesh sieve to obtain the carbon-doped and coated modified lithium ion cathode material. The phase XRD analysis is shown in Figure 1, and the morphology is shown in Figure 1. 2 shown.

Figure 1 is an XRD pattern of the carbon doped and coated modified lithium ion cathode material prepared in Example 1 of the present invention; it can be seen from Figure 1 that the main phase measured in the material corresponds to the PDF card of Li ₅ FeO ₄ , and the carbonic acid in the material The peak intensity of lithium is relatively weak, and the content of lithium carbonate by-product generated by the reaction between the carbon material and the lithium source is small, indicating that the sample prepared according to the protocol of Example 1 is a relatively pure substance.

Figure 2 is an SEM image of the carbon doped and coated modified lithium ion cathode material prepared in Example 1. It can be seen from the figure that the material mainly exists in the form of agglomerates, the particle size of the secondary particles is small, and the material's The surface is evenly coated with a layer of carbon material, which enables the material to have a higher specific capacity and lower charging voltage platform under high-rate charging. At the same time, the carbon is evenly coated on the surface of the material, which also increases the material's ability to absorb air in the air. stability under.

Example 2

(1) Weigh lithium hydroxide monohydrate and iron oxide according to a Li:Fe molar ratio of 6.0:1, then put them into a mixer and mix them evenly to obtain a mixed material;

(3) Weigh the fine powder and glucose in step (2) according to a mass ratio of 10:1, mix them, and conduct the second sintering under nitrogen protection. Raise the temperature to 700°C and keep it warm for 6 hours. The heating rate The temperature is 5°C/min. The cooling program is to cool to room temperature with the furnace, and then pass through a 300-mesh sieve to obtain a carbon-doped and coated modified lithium-ion cathode material.

Example 3

(1) Weigh lithium hydroxide monohydrate and iron oxide according to a Li:Fe molar ratio of 5.8:1, then put them into a mixer and mix them evenly to obtain a mixed material;

Comparative example 1

Comparing the step of Comparative Example 1 with that of Example 1, the Li:Fe molar ratio in step (1) of Example 1 was changed to 7:1.

The SEM of the modified lithium ion cathode material obtained by the method of Comparative Example 1 is shown in Figure 3.

Comparative example 2

Compared with the material preparation of Comparative Example 2 in Example 1, the crushing particle size D50 in step (2) of Example 1 was changed to 15 μm.

The SEM of the modified lithium ion cathode material obtained by the method of Comparative Example 2 is shown in Figure 4.

Comparative example 3

Compared with the preparation of the modified lithium ion cathode material of Comparative Example 3 in Example 1, the sintering temperature in step (3) of Example 1 was changed to 800°C and maintained for 12 hours.

Figure 3 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 1. It can be seen from the figure that the particle size of the material is larger and the surface carbon source of the material is less. The main reason is that excessive lithium reacts with the carbon source. More lithium carbonate will cause unfavorable situations such as reduced material specific capacity and slurry gelation.

Figure 4 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 2. Since it is not crushed, after sintering, the particles of the material are larger, the lithium ions of the material have greater resistance to escape from the interior of the material, and the charging specific capacity is low.

Figure 5 is an SEM image of the modified lithium ion cathode material prepared in Comparative Example 3. If the second sintering temperature is too high, the particles of the material will grow, and the carbon source on the surface of the material will become carbon dioxide, which will reduce the carbon content and lead to the ratio of the material. Capacity is significantly reduced.

Mix the modified lithium ion cathode material prepared in Example 1 and Comparative Examples 1-3, the conductive agent SP, the binder PVDF and the solvent NMP, and stir the mixture to obtain a slurry, which is evenly coated on the aluminum foil. After drying, cut into slices, assemble the cut positive electrode sheets, electrolyte and separator into a button battery. After standing still, test the electrochemical performance of the battery. The test reference current density is 1C=600mA/g.

Figure 6 is a buckle charge specific capacity-voltage curve of the materials prepared in Example 1 and Comparative Examples 1-3 (the abscissa is the specific capacity, the ordinate is the voltage), which also shows that the voltage platform of the sample prepared in Example 1 is lower than High capacity.

The test results of the first cycle of button half cells of the modified lithium ion cathode material of Example 1 and Comparative Examples 1-3 are shown in Table 1:

Table 1

Table 1 shows the charge specific capacity in the first cycle of the modified lithium ion cathode materials of Example 1 and Comparative Examples 1-3. The charge specific capacity of Example 1 measured at a voltage of 2.8-4.25V and a current density of 0.23C was 649.74. mAh/g, and the specific discharge capacity is 2.3mAh/g, which can better improve the cycle performance of lithium-ion batteries and is better than Comparative Examples 1-3. Modified lithium-ion battery materials are prepared by controlling processes such as lithium matching, sintering and pulverization to prepare carbon-containing modified lithium-ion battery cathode materials with a stable structure.

The present invention is not limited to the above-described embodiments. Various changes can be made within the knowledge scope of those of ordinary skill in the art without departing from the gist of the present invention. In addition, the embodiments of the present invention and the features in the embodiments may be combined with each other without conflict.

Claims

A modified lithium-ion battery cathode material, characterized in that the chemical formula of the modified lithium-ion battery cathode material is Li 5 FeO 4 @C; the modified lithium-ion battery cathode material is an agglomerate, and the Agglomerates are formed by agglomeration of spherical particles.
The modified lithium ion battery cathode material according to claim 1, characterized in that the modified lithium ion cathode material has an average particle size of 1.0-10 μm and a specific surface area of 3.0-15.0 m 2 /g.
The modified lithium ion battery cathode material according to claim 1, characterized in that, the modified lithium ion cathode material is charged and discharged in a charging voltage range of 2.8-4.25V, a current density of 0.23C, and the charging specific capacity is 645-655mAh. /g, the specific discharge capacity is 2.1-2.6mAh/g.
The modified lithium ion battery cathode material according to claim 1, wherein the mass percentage of carbon in the modified lithium ion cathode material is 1-18%.
The preparation method of modified lithium-ion battery cathode material according to any one of claims 1-4, characterized in that it includes the following steps:

(1) Mix the lithium source and the iron source, perform sintering for the first time, and pulverize to obtain the pulverized material;

(2) Mix the pulverized material with a carbon source, perform a second sintering, pulverize, and sieve to obtain modified lithium-ion battery cathode material;

The molar ratio of lithium in the lithium source to iron in the iron source is (5.0-6.0):1; the temperature of the second sintering is 450-750°C; the particle size D50 of the pulverized material is 1.0-5.0 μm.
The preparation method according to claim 5, characterized in that, in step (1), the lithium source is lithium hydroxide, lithium carbonate, lithium acetate, lithium borate, lithium metaborate, lithium lactate, lithium nitrate, lithium oxalate or at least one of lithium oxide.
The preparation method according to claim 5, characterized in that in step (1), the iron source is ferric nitrate, ferrous nitrate, ferric chloride, ferrous chloride, ferric sulfate, ferrous sulfate, citric acid At least one of iron, iron oxide or ferric oxide.
The preparation method according to claim 5, characterized in that in step (1), the temperature rise rate of the first sintering is 1°C-10°C/min, and the temperature of the first sintering is 400-750°C, The time of the first sintering is 4-20h; in step (2), the temperature rise rate of the second sintering is 1°C-10°C/min, and the time of the second sintering is 4-12h.
The preparation method according to claim 5, characterized in that in step (2), the carbon source is polyethylene glycol, polyvinyl alcohol, polyacrylic acid, polypyrrole, fatty alcohol polyoxyethylene, glucose, sucrose, At least one of conductive graphite, acetylene black, carbon fiber, Ketjen black, carbon nanotubes, and graphene.
A battery, characterized by comprising the modified lithium-ion battery cathode material according to any one of claims 1-4.