Preparation method of layered positive electrode material treated by reducing gas

Abstract

The invention discloses a preparation method of a reducing gas treatment layered positive electrode material, and belongs to the field of lithium ion batteries. The preparation method comprises the following steps: placing a layered positive electrode material in a reducing atmosphere, and carrying out high-temperature heat treatment to form the layered positive electrode material coated with surface oxygen vacancy defects and low-valence metal oxide. The preparation viscosity of the positive electrode material slurry can be reduced, the specific capacity of the layered positive electrode material is improved, the side reaction between the material and the electrolyte is reduced, the process is simple, and the operability is high.

Description

A method for preparing layered cathode materials treated with reducing gas Technical Field

[0001] This invention relates to the technical field of lithium-ion batteries, and in particular to a method for preparing a layered cathode material treated with reducing gas. Background Technology

[0002] Layered cathode materials are a class of important materials widely used in lithium-ion batteries, attracting widespread attention due to their superior electrochemical performance. The core characteristic of these materials is their layered crystal structure, which allows lithium ions to efficiently intercalate and deintercalate during charge and discharge, resulting in high energy density and excellent cycle stability. Layered cathode materials are typically composed of metal oxides, such as lithium cobalt oxide (LiCoO2), nickel-cobalt-manganese oxide (NCM), and lithium-rich manganese-based cathode materials (LLOs), which play a crucial role in the cathode of batteries. To further improve the performance of layered cathode materials, many researchers have focused on optimizing synthesis methods, improving their surface structure, and performing chemical modifications. These methods can effectively improve the conductivity, rate performance, and cycle stability of the materials, thereby meeting the needs of different application scenarios.

[0003] Given the limitations of traditional processing methods, current research focuses on developing novel and more efficient processing techniques. Heating layered cathode materials in a reducing atmosphere can induce the formation of oxygen vacancies on the material surface. Oxygen vacancies are defects in the crystal structure; their presence introduces additional electrons, thereby improving the material's conductivity. This enhanced electronic conductivity can effectively reduce the internal resistance of the battery during high-rate discharge, thus significantly improving the material's rate performance. Furthermore, a low-valence oxide coating layer forms on the material surface after reducing gas treatment. This coating layer forms due to the reduction reaction in the reducing atmosphere, converting the surface oxides of the material into low-valence oxides (such as CoO, NiO, etc.). Low-valence oxides possess higher ionic conductivity and chemical stability, further improving the electrode material's performance. Specifically, this coating layer can form a protective film, reducing direct contact between the electrolyte and the electrode material, thereby mitigating side reactions and improving the material's chemical stability and cycle life. Summary of the Invention

[0004] The first aspect of the present invention is to provide a method for preparing a layered cathode material by treating a reducing gas, wherein the layered cathode material is placed in a reducing atmosphere and subjected to high-temperature heat treatment to form a material coated with surface oxygen vacancy defects and low-valence metal oxides, thereby obtaining the layered cathode material.

[0005] The first aspect of this invention is to provide a method for preparing a layered cathode material treated with a reducing gas, specifically comprising the following steps:

[0006] Step (1) Place the layered cathode material into a crucible and then place it in a rotary furnace.

[0007] Step (2) introduce reducing gas into the rotary kiln described in step (1) to perform atmosphere replacement;

[0008] Step (3) involves heating the rotary furnace described in step (2) at a high temperature to obtain the layered cathode material.

[0009] Preferably, the layered cathode material is xLi2MnO3·(1-x)LiTMO2, wherein TM is selected from any one or at least a combination of two of Mn, Ni, Al, Co, Fe or Ti, and 0≤x≤1.

[0010] Preferably, the reducing gas in step (2) is an argon-hydrogen mixture, wherein the volume fraction of hydrogen is 1% to 20%.

[0011] Preferably, the number of atmosphere replacements in step (2) is 1-5 times, and the replacement time is 1-20 minutes each time;

[0012] Preferably, the heating rate of the high-temperature heating in step (3) is 0.5 to 10 °C / min;

[0013] Preferably, the high-temperature heating in step (3) is 100–700°C;

[0014] Preferably, the high-temperature heating time in step (3) is 0.1 to 12 hours.

[0015] Preferably, the coating thickness is 0.1–10 nm, and more preferably, the coating thickness is 0.1–5 nm.

[0016] The preparation method of this invention is simple and efficient, safe and pollution-free, and easy to industrialize. This method can form oxygen vacancies on the surface of layered cathode materials, reduce some high-valence oxides, and form a low-valence oxide coating layer, hindering direct contact between the active material and the electrolyte, thus improving the rate performance and cycle stability of the material. Attached Figure Description

[0017] Figure 1 is a HAADF-STEM image of the lithium-rich manganese-based cathode material particles coated with spinel surface obtained in Example 1 of the present invention.

[0018] Figure 2 shows the first charge-discharge curves of Example 1 and the comparative example under a working voltage of 2-4.8V;

[0019] Figure 3 shows the cycle curves of Example 1 and the comparative example at an operating voltage of 2-4.6V;

[0020] Figure 4 shows the first charge-discharge curves of Example 2 and the comparative example at a working voltage of 3-4.6V;

[0021] Figure 5 shows the cycle curves of Example 2 and the comparative example at a working voltage of 3-4.6V; Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0023] Comparative Example

[0024] The lithium-rich manganese-based cathode material has the chemical formula: 0.3Li₂MnO₃0.7LiNi 0.5 Mn 0.5 O2. The cycle performance of lithium-ion batteries assembled from the modified layered cathode material and the unmodified layered cathode material prepared in this embodiment was compared using a blue electric test system. The test temperature was 25℃, the test charge / discharge voltage range was 2.0-4.8V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity was 277.05mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the capacity retention rate after 200 cycles was 82.44%.

[0025] Example 1

[0026] In 2g of 0.3Li2MnO30.7LiNi 0.5 Mn 0.5 The O2-rich lithium-manganese-based layered cathode material was placed in a crucible and then in a rotary kiln. The kiln was purged three times with an argon-hydrogen mixture containing 5% hydrogen, each purging lasting 15 minutes. The temperature was increased from room temperature to 400°C at a rate of 5°C / min, held for 2 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium-manganese-based layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the charge / discharge voltage range was 2.0-4.8V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity, as shown in Figure 1, increased from 277.05mAh / g to 290.06mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 200-cycle discharge specific capacity, as shown in Figure 2, increased from 82.44% to 92.43%.

[0027] Example 2

[0028] Two g of LiCoO2 lithium cobalt oxide layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 5% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 200°C at a rate of 3°C / min, held at that temperature for 6 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium cobalt oxide layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the test charge / discharge voltage range was 3.0-4.6V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity, as shown in Figure 3, increased from 211.9mAh / g to 214.8mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 25-cycle discharge specific capacity, as shown in Figure 4, increased from 190.8mAh / g to 199.5mAh / g.

[0029] Example 3

[0030] In 2g of 0.3Li2MnO30.7LiNi 0.5 Mn 0.5 The O2-rich lithium-manganese-based layered cathode material was placed in a crucible and then in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 7% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 300°C at a rate of 5°C / min, held for 4 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium-manganese-based layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the charge / discharge voltage range was 2.0-4.8V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 277.05mAh / g to 286.41mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 200-cycle discharge specific capacity retention increased from 82.44% to 93.41%.

[0031] Example 4

[0032] In 2g of LiNi 0.8 Co 0.1 Mn 0.1The O2 ternary layered cathode material was placed in a crucible and then in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 5% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 200°C at a rate of 1°C / min, held for 8 hours, and then cooled to room temperature to obtain the hydrogen-reduced ternary layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the charge / discharge voltage range was 2.8-4.5V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 209.07mAh / g to 212.24mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 300-cycle discharge specific capacity retention increased from 65.2% to 85.4%.

[0033] Example 5

[0034] In 2g of LiNi 0.8 Co 0.1 Mn 0.1 The O2 ternary layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 7% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 300°C at a rate of 10°C / min, held for 2 hours, and then cooled to room temperature to obtain the hydrogen-reduced ternary layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the charge / discharge voltage range was 2.8-4.5V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 209.07mAh / g to 214.24mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 300-cycle discharge specific capacity retention rate increased from 65.2% to 87.1%.

[0035] Example 6

[0036] In 2g of 0.3Li2MnO30.7LiNi 0.5 Mn 0.5The O2-rich lithium-manganese-based layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 5% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 200°C at a rate of 1°C / min, held at that temperature for 12 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium-manganese-based layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the test charge / discharge voltage range was 2.0-4.8V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 277.05mAh / g to 286.41mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 100-cycle discharge specific capacity retention rate increased from 91.26% to 94.14%.

[0037] Example 7

[0038] In 2g of 0.3Li2MnO30.7LiNi 0.5 Mn 0.5 The O2-rich lithium-manganese-based layered cathode material was placed in a crucible and then in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 8% hydrogen, each purging lasting 15 minutes. The temperature was increased from room temperature to 600°C at a rate of 10°C / min, held for 1 hour, and then cooled to room temperature to obtain hydrogen-reduced lithium-manganese-based layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the charge / discharge voltage range was 2.0-4.8V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 277.05mAh / g to 291.38mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 100-cycle discharge specific capacity retention increased from 91.26% to 95.64%.

[0039] Example 8

[0040] Two g of LiCoO2 lithium cobalt oxide layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 5% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 400°C at a rate of 5°C / min, held at that temperature for 3 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium cobalt oxide layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the test charge / discharge voltage range was 3.0-4.6V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 211.9mAh / g to 216.2mAh / g. After activation, the charge / discharge current was changed to 100mA / g, and the 300-cycle discharge specific capacity retention rate increased from 68.1% to 74.8%.

[0041] Example 9

[0042] Two g of LiCoO2 lithium cobalt oxide layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 8% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 500°C at a rate of 10°C / min, held at that temperature for 2 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium cobalt oxide layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the test charge / discharge voltage range was 3.0-4.6V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 211.9mAh / g to 214.7mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 200-cycle discharge specific capacity retention rate increased from 78.6% to 89.4%.

[0043] Example 10

[0044] Two g of LiCoO2 lithium cobalt oxide layered cathode material was placed in a crucible and then placed in a rotary furnace. The furnace was purged three times with an argon-hydrogen mixture containing 7% hydrogen, each time for 15 minutes. The temperature was increased from room temperature to 450°C at a rate of 3°C / min, held at that temperature for 4 hours, and then cooled to room temperature to obtain hydrogen-reduced lithium cobalt oxide layered cathode material. The modified layered cathode material and the unmodified layered cathode material were compared in a cycle performance test using a Blue Electric testing system. The test temperature was 25°C, the test charge / discharge voltage range was 3.0-4.6V, and the charge / discharge current was 20mA / g. The initial discharge specific capacity increased from 211.9mAh / g to 215.9mAh / g. After activation, the charge / discharge current was changed to 200mA / g, and the 200-cycle discharge specific capacity retention rate increased from 78.6% to 90.2%.

[0045] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for preparing a layered cathode material treated with a reducing gas, characterized in that, The preparation method includes: placing the layered cathode material in a reducing atmosphere and subjecting it to high-temperature heat treatment to form a material coated with surface oxygen vacancy defects and low-valence metal oxides, thereby obtaining the layered cathode material.

2. The method for preparing a reducing gas-treated layered cathode material according to claim 1, characterized in that, Its structural formula is xLi2MnO3·(1-x)LiTMO2, where TM is selected from any one or at least two of Mn, Ni, Al, Co, Fe or Ti, and 0≤x≤1.

3. The method for preparing the layered cathode material according to claim 1, characterized in that, The reducing gas is an argon-hydrogen mixture, wherein the volume fraction of hydrogen is 1% to 20%.

4. The method for preparing a reducing gas-treated layered cathode material according to claim 1, characterized in that, The process includes the following steps: (1) placing the layered cathode material into a crucible and then into a rotary furnace; (2) introducing a reducing gas into the rotary furnace in step (1) to perform atmosphere replacement; and (3) heating the rotary furnace in step (2) at a high temperature to obtain the layered cathode material.

5. The method for preparing a reducing gas-treated layered cathode material according to claim 4, characterized in that, The number of atmosphere replacements in step (2) is 1-5 times; preferably, the atmosphere replacement time in step (2) is 1-20 minutes each time.

6. The preparation method according to claim 4, characterized in that, The heating rate of the high-temperature heating in step (3) is 0.5 to 10 °C / min; preferably, the temperature of the high-temperature heating in step (3) is 100 to 700 °C; preferably, the heating time of the high-temperature heating in step (3) is 0.1 to 12 h.

7. The preparation method according to claim 4, characterized in that, The reducing gas modification includes forming a surface oxygen vacancy defect and a low-valence metal oxide coating layer on the surface of the layered cathode material.

8. The preparation method according to claim 7, characterized in that, The thickness of the coating layer is 0.1–10 nm.

9. A layered cathode material, characterized in that, The layered cathode material is prepared by the preparation method of the layered cathode material as described in any one of claims 1-8.

10. An application of the layered cathode material as described in claim 9, characterized in that, The layered cathode material is used in the field of lithium-ion batteries.

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