Method for regulating oxygen vacancies of layered positive electrode material based on rapid cooling

Abstract

The application discloses a method for regulating oxygen vacancies of layered positive electrode materials based on rapid cooling, and belongs to the technical field of lithium battery electrode materials. The method comprises the following steps: S1, placing a mixture of a transition metal salt or a hydroxide precursor for preparing lithium ion positive electrode materials and a lithium source in a muffle furnace for stage high-temperature calcination; S2, after the calcination is completed, taking out the powder material from the muffle furnace and immediately cooling the powder material in deionized water at room temperature to obtain a lithium-rich layered powder material suspension; and S3, performing suction filtration on the suspension and then placing the suspension in an oven for drying to obtain the lithium ion positive electrode material. In the preparation process, the method does not need to wait for natural cooling after heat treatment is completed, can retain a lithium-rich layered phase of the material under a high-temperature state, reduces an alkali metal interlayer spacing, and has high reversible specific capacity and good rate performance of the material after treatment.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a method for regulating oxygen vacancies in layered cathode materials based on rapid cooling. Background Technology

[0002] With the ever-increasing demand for energy and the growing emphasis on renewable energy, adjusting the existing energy structure and promoting the development of new energy technologies are crucial strategies for the sustainable development of the nation and society. Lithium-ion batteries, in particular, are high-performance batteries widely used in electronic devices and electric vehicles. They not only possess numerous technological advantages but also play a vital role in promoting environmental protection, economic development, and industrial upgrading.

[0003] The performance of the cathode material is a key factor determining the overall battery performance. In the design and development of cathode materials for lithium-ion batteries, layered lithium-rich materials that partially replace transition metals with lithium exhibit excellent specific capacity and energy density, and are considered one of the most commercially promising cathode materials for next-generation high-energy-density lithium-ion batteries. The high capacity of these materials is attributed to the unique redox reaction involving their unique anionic oxygen, which enables additional charge storage during charge and discharge, thereby increasing their capacity. Therefore, they have been extensively studied. However, the redox mechanism of the anionic oxygen remains unclear due to limitations in current characterization techniques, and lithium-rich cathode materials still suffer from problems such as low coulombic efficiency and low reversible capacity.

[0004] The introduction and regulation of oxygen vacancies is one of the important methods for modifying lithium-ion cathode materials, which helps to improve the overall performance of the battery. However, the number and distribution of oxygen vacancies need to be precisely controlled, as excessive oxygen vacancies may lead to material instability and a decline in electrochemical performance. Existing technologies mostly regulate high-temperature heat treatment by controlling heating time and heating rate, but research on regulating the formation of oxygen vacancies and their impact on material properties during the cooling process is equally important. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for regulating oxygen vacancies in layered cathode materials based on rapid cooling. This method can significantly shorten the material production cycle and solve the problems of low first-cycle coulombic efficiency and low reversible capacity of existing materials mentioned in the background.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for regulating oxygen vacancies in layered cathode materials based on rapid cooling, comprising the following steps:

[0007] S1. The mixture of transition metal salt or hydroxide precursor used to prepare lithium-ion cathode material and lithium source is placed in a muffle furnace for staged high-temperature calcination.

[0008] S2. After calcination, the powder material is removed from the muffle furnace and immediately placed in deionized water at room temperature to cool, thus obtaining a suspension of lithium-rich layered powder material.

[0009] S3. The above suspension is filtered to obtain a wetted powder material, which is then dried in an oven to obtain the lithium-ion cathode material.

[0010] Furthermore, the transition metal salt or hydroxide precursor used to prepare lithium-ion cathode materials is prepared by any of the following methods: co-precipitation, sol-gel, solid-state sintering, etc.

[0011] Furthermore, the transition metal salt used to prepare lithium-ion cathode materials includes any one or a combination of several of nickel carbonate, manganese carbonate, cobalt carbonate, nickel acetate, manganese acetate, cobalt acetate, nickel nitrate, manganese nitrate, and cobalt nitrate; the hydroxide includes any one or a combination of several of nickel hydroxide, manganese hydroxide, and cobalt hydroxide; and the lithium source includes any one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate.

[0012] Furthermore, in step S1, the staged high-temperature calcination process is as follows: first, the temperature is increased to 400-500℃ at a heating rate of 5℃ / min and held for 4-6 hours, and then the temperature is increased to 850-950℃ at a heating rate of 5℃ / min and held for 10-18 hours.

[0013] Furthermore, in step S2, after calcination, the powder material is removed from the muffle furnace and immediately placed in deionized water at room temperature to cool, thereby obtaining a suspension of lithium-rich layered powder material. Here, deionized water at room temperature refers to deionized water at 20-25°C. To ensure the cooling effect, at least 1000 ml of deionized water is added for every 4-5 g of powder material. In order to enable the powder material to cool rapidly in deionized water, the deionized water is stirred. The stirring method can be magnetic stirring, ultrasonic vibration, or propeller stirring.

[0014] Furthermore, in step S3, the suspension is poured into a sand core funnel for filtration to obtain a wetted powder material. The material is then placed in an oven and dried at 120°C for 12 hours to remove excess moisture, thus obtaining the lithium-ion cathode material.

[0015] Compared with the prior art, the method for regulating oxygen vacancies in layered cathode materials based on rapid cooling described in this invention has the following beneficial effects:

[0016] 1. Through rapid cooling treatment, the morphology and crystal structure of the layered lithium-rich material at high temperature are preserved, resulting in a wider lattice spacing and the formation of an appropriate amount of oxygen vacancies in the material. This effectively improves the cycle reversible capacity and rate performance of the lithium-rich cathode material, and it has high versatility.

[0017] 2. This invention does not employ furnace cooling, thus reducing the occurrence of side reactions during the slow cooling process. Attached Figure Description

[0018] Figure 1 The Li prepared in Example 1 of this invention 1.2 Ni 0.2 Mn 0.6 FIB-SEM image of O2 material.

[0019] Figure 2 These are XRD comparison images of the samples prepared in Example 1 and Comparative Examples 1 to 4 of the present invention.

[0020] Figure 3 The above are XPS O2p comparison images of the samples prepared in Example 1 and Comparative Examples 1 to 4 of this invention.

[0021] Figure 4 The images show the EPR comparison of the samples prepared in Example 1 and Comparative Examples 1 to 4 of this invention.

[0022] Figure 5 The first charge-discharge curves of the samples prepared in Example 1 and Comparative Examples 1 to 4 of this invention are shown at a current of 0.1C.

[0023] Figure 6 This is a comparison chart of the cycling performance of the samples prepared in Example 1 and Comparative Examples 1 to 4 of the present invention at a 1C rate for 100 cycles.

[0024] Figure 7 This is a comparison chart of the rate performance of the samples prepared in Example 1 and Comparative Examples 1 to 4 of the present invention after 5 cycles at various rate currents of 0.1C, 0.5C, 1C, 2C, 5C, and 10C. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] In this invention, the term "stirring" includes, but is not limited to, magnetic stirring, ultrasonic oscillation, and propeller stirring, because the amount of material to be prepared is small, and stirring is required to ensure that the material and the cooling medium are in full contact and achieve rapid cooling; the term "immediately" means that the residence time of the high-temperature powder material in room temperature air should not be too long, and the temperature of the powder material should be kept above 850°C before rapid cooling.

[0028] Here, a detailed description is provided through one embodiment and four comparative examples.

[0029] Example 1:

[0030] (1) Preparation of Li 1.2 Ni 0.2 Mn 0.6 O2 material: 0.25 mol NiSO4·6H2O and 0.75 mol MnSO4·H2O were dissolved in 500 ml of deionized water and stirred at a constant temperature of 50 °C for 1 hour in a magnetic stirrer to obtain a sulfate mixed solution.

[0031] (2) Dissolve 1 mol of sodium carbonate in 500 ml of deionized water and stir at a constant temperature in a magnetic stirrer to obtain a precipitant;

[0032] (3) Dissolve 37 ml of ammonia in 500 ml of deionized water to obtain a complexing agent. Slowly pump the above sulfate mixed solution, complexing agent and precipitant into the reaction vessel. Heat the vessel to 50°C and stir at 600 rpm to carry out a co-precipitation reaction. After the reaction is completed, filter the precipitate three times and dry it in an oven at 100°C for 12 hours to obtain the carbonate precursor, which is the precursor of the positive electrode material.

[0033] (4) The carbonate precursor and lithium carbonate obtained in step (3) are added to a mortar in a molar ratio of 0.8:0.66 according to the chemical formula of the layered lithium-rich material. Anhydrous ethanol is used as the grinding agent. The mixture is immersed in the mortar and baked under an experimental baking lamp. The mixture is ground until the material is uniform in color and the ethanol is completely evaporated to obtain a granular mixture.

[0034] (5) Place the above mixture in a muffle furnace, heat it up in stages and keep it at a high temperature. First, heat it up at a heating rate of 5℃ / min and keep it at 500℃ for 5 hours. Then, heat it up at a heating rate of 5℃ / min and keep it at 900℃ for 12 hours.

[0035] (6) When the calcination reaches the predetermined time, the high-temperature bright red powder material obtained in step (5) is immediately taken out and poured into 1000ml of room temperature deionized water within 5s to cool it fully, so as to obtain a suspension of lithium-rich layered powder material.

[0036] (7) Pour the layered lithium-rich cathode material suspension obtained in step (6) into a sand core funnel for washing and filtration to obtain wetted powder material, place it in an oven and dry it at 120°C for 12 hours to obtain the cathode material.

[0037] Comparative Example 1:

[0038] Compared with Example 1, the difference lies in the cooling medium; liquid nitrogen is used as the cooling medium, while the other steps are the same as in Example 1.

[0039] Comparative Example 2:

[0040] Compared with Example 1, the difference lies in the cooling medium; a copper plate is used as the cooling medium. The remaining steps are the same as in Example 1. The specific steps are as follows:

[0041] Once the calcination reaches the predetermined time, immediately remove the high-temperature bright red powder material, pour it onto a clean copper plate, and cover the powder material with another clean copper plate. Press the copper plate to ensure the powder material is evenly compressed until the powder material temperature drops to room temperature.

[0042] Comparative Example 3:

[0043] Compared with Example 1, the difference lies in the cooling medium. An ice-water mixture (around 0°C) is used as the cooling medium, while the other steps are the same as in Example 1.

[0044] Comparative Example 4:

[0045] Compared with Example 1, the difference lies in the cooling medium. In Example 1, air is used as the cooling medium for furnace cooling. The remaining steps are the same as in Example 1.

[0046] Material characterization and testing

[0047] (1) Material characterization

[0048] (a) FIB-SEM characterization tests of the materials in Example 1 are shown in [reference needed]. Figure 1 Obvious cracks appeared inside the lithium-ion cathode material after rapid cooling with deionized water.

[0049] (b) XRD patterns of the materials in Example 1, Comparative Examples 1 to 4 are shown below. Figure 2 Compared with the material of Comparative Example 4, which was cooled in the furnace, the main peak of the materials of Example 1 and Comparative Examples 1 to 3, which underwent rapid cooling treatment, shifted to the left, indicating that the interlayer spacing of the alkali metal layers of the layered oxides was larger after rapid cooling treatment.

[0050] (c) XPS characterization spectra of O1s of materials from Comparative Examples 1 to 4 in Example 1 are shown below. Figure 3The peak near 529.5 eV represents oxygen in the crystal lattice, and the peak near 531.5 eV represents oxygen vacancies. In Example 1, which underwent rapid cooling treatment, the oxygen vacancy content on the surface of the materials in Comparative Examples 1 to 3 was significantly higher than that of the furnace-cooled material in Comparative Example 4.

[0051] (d) EPR characterization spectra of materials from Example 1, Comparative Examples 1 to 4 are shown below. Figure 4 The materials of Example 1 and Comparative Examples 1 to 3, which underwent rapid cooling treatment, showed stronger signal strength compared to the material of Comparative Example 4, which was cooled in the furnace. This indicates that the materials contained more oxygen vacancies, with Comparative Example 1 having the highest oxygen vacancy content.

[0052] (2) Materials Testing

[0053] The main steps of the test are as follows:

[0054] (a) The powder materials obtained in Example 1 and Comparative Examples 1 to 4 were used as active materials and ground with conductive carbon black and PVDF binder in a mass ratio of 8:1:1. After thorough mixing, NMP was added to form a uniform slurry, which was coated on aluminum foil and dried at 80 to 120°C for 6 to 24 hours as a test electrode (diameter 12 nm). Then, lithium metal (diameter 14 nm) was used as the counter electrode. The battery case was model 2032, the electrolyte was lithium high voltage electrolyte, and the separator was Celgard 2400 separator (diameter 16 nm). The battery was assembled in a glove box.

[0055] (b) After a resting period of 8 hours, a low-current charge-discharge program was set up with a rate of 0.1C (1C = 200mA / g), a voltage range of 2V-4.8V, and one cycle at 0.1C. The charge-discharge curves are shown below. Figure 5 Among them, Example 1 showed the highest first-cycle discharge capacity, greater than 250 mAh / g, and all rapid cooling materials were superior to the furnace cooling materials. A charge-discharge program with a rate of 1C, a voltage range of 2V-4.8V, and 100 cycles was set. The specific capacity-cycle curves are shown below. Figure 6 Among them, Example 1 had the highest initial capacity, but its capacity retention rate was lower than that of Comparative Example 3. A set of charge-discharge programs was set with rates of 0.1C, 0.5C, 1C, 5C, 10C, and 0.1C, and each rate current was cycled 5 times. The specific capacity-cycle curves are shown in the figure. Figure 7 In Example 1, the material exhibited a significant capacity advantage at low magnification rates, while the advantage diminished at high magnification rates. The material that underwent rapid cooling was superior to the material that was cooled in the furnace.

Claims

1. A method for regulating oxygen vacancies in layered cathode materials based on rapid cooling, characterized in that, Includes the following steps: S1. The mixture of transition metal salt or hydroxide precursor used to prepare lithium-ion cathode material and lithium source is placed in a muffle furnace for staged high-temperature calcination. S2. After calcination, the powder material is removed from the muffle furnace and immediately placed in deionized water at room temperature to cool, thus obtaining a suspension of lithium-rich layered powder material. S3. The above suspension is filtered and then dried in an oven to obtain the lithium-ion cathode material.

2. The method as described in claim 1, characterized in that, Transition metal salts or hydroxide precursors used to prepare lithium-ion cathode materials are prepared by any of the following methods: co-precipitation, sol-gel, or solid-state sintering.

3. The method as described in claim 1, characterized in that, The transition metal salts used to prepare lithium-ion cathode materials include any one or a combination of nickel carbonate, manganese carbonate, cobalt carbonate, nickel acetate, manganese acetate, cobalt acetate, nickel nitrate, manganese nitrate, and cobalt nitrate; the hydroxides include any one or a combination of nickel hydroxide, manganese hydroxide, and cobalt hydroxide; and the lithium source includes any one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate.

4. The method as described in claim 1, characterized in that, In step S1, the staged high-temperature calcination process is as follows: first, the temperature is increased to 400~500℃ at a heating rate of 5℃ / min and held for 4~6h, and then the temperature is increased to 850~950℃ at a heating rate of 5℃ / min and held for 10~18h.

5. The method as described in claim 1, characterized in that, In step S2, after calcination, the powder material is removed from the muffle furnace and immediately placed in deionized water at room temperature to cool, thereby obtaining a suspension of lithium-rich layered powder material. Here, deionized water at room temperature refers to deionized water at 20~25℃. At least 1000ml of deionized water is added for every 4~5g of powder material. The deionized water is stirred by magnetic stirring, ultrasonic vibration or propeller stirring.

6. The method as described in claim 1, characterized in that, In step S3, the suspension is poured into a sand core funnel for filtration to obtain a wetted powder material. The material is then placed in an oven and dried at 120°C for 12 hours to remove excess moisture, thus obtaining the lithium-ion cathode material.

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