Method for surface modification of a high-voltage layered oxide cathode material

Abstract

The application relates to the technical field of new energy, and discloses a method for surface modification of high-pressure layered oxide positive electrode materials. The method comprises the following steps: step a, taking a high-pressure layered oxide positive electrode material sample, heating the sample to 400-1000 DEG C, and then adding the sample into a prepared reducing solution for quenching treatment, wherein the mass ratio of the reducing solution to the high-pressure layered oxide positive electrode material sample is 1:(0.1-1); and step b, filtering, washing and drying the high-pressure layered oxide positive electrode material sample after the quenching treatment, so as to obtain a surface-modified high-pressure layered oxide positive electrode material. The surface structure of the high-pressure layered oxide positive electrode is adjusted by the reducing solution quenching method, oxygen vacancies and rock salt structures are generated on the particle surface, surface doping is realized, and the surface stability of the high-pressure layered oxide positive electrode material is improved.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a method for surface modification of high-voltage layered oxide cathode materials. Background Technology

[0002] Lithium-ion batteries boast advantages such as high energy density, long lifespan, and low cost. The performance of a lithium-ion battery largely depends on its cathode material, which not only stores most of the battery's energy but also determines its discharge voltage. Therefore, developing advanced cathode materials is crucial for improving lithium-ion battery performance. Layered oxide cathode materials, such as lithium cobalt oxide (LCO), high-nickel ternary cathode materials (e.g., NCM811), and lithium-rich manganese layered cathode materials (LLOs), are considered the cathode material systems with the greatest market potential due to their advantages in energy density and capacity. To meet the demands for higher energy density lithium-ion batteries, it is necessary to improve the specific capacity of cathode materials.

[0003] The high-voltage development of layered oxide cathode materials is crucial for advancing high-energy lithium-ion batteries. On the one hand, it involves lowering the upper cutoff potential of lithium cobalt oxide and high-nickel ternary cathode materials from 4.3V (vs. Li / Li). + Increasing the voltage to 4.6V can improve its specific capacity and energy density by more than 20-30%; on the other hand, due to the participation of lattice oxygen in charge compensation, lithium-rich manganese-based substrate cathode materials can exhibit 250 mAh g⁻¹ at a high upper limit cutoff potential of 4.6~4.8V. -1 The above-mentioned ultra-high specific capacity. When charged to a high potential, the lattice oxygen in the layered oxide cathode material becomes highly unstable and escapes from the particle surface, leading to continuous Li / O loss and surface densification. Subsequently, the released oxygen and unstable high-valence transition metal ions (such as Ni) generated during charging... 4+ and Co 4+ This exacerbates harmful interfacial side reactions, leading to severe electrolyte consumption, the formation of an unstable cathode electrolyte interface (CEI), and the dissolution of transition metals. Therefore, the severe instability of the surface of high-voltage layered oxide cathode materials results in short cycle life and reduced safety performance in high-energy lithium-ion batteries.

[0004] Currently, common methods for surface modification of high-voltage layered oxide cathode materials include surface coating, electrolyte design, and surface structure modulation. The first two neglect the fundamental cause of surface instability: surface structural instability. In contrast, adjusting the surface structure through various surface treatments (such as surface doping and surface reconstruction) has shown great potential in enhancing the surface stability of layered oxide cathodes. For example, high-temperature reducing gas treatment (such as PH3 and NH3) and wet chemical treatment followed by additional high-temperature calcination typically involve complex, expensive, and difficult-to-scale processes. Furthermore, the differences in properties among various layered oxide cathode materials limit the versatility of these treatment methods. Therefore, developing a simple, cost-effective, and universal strategy to modulate the surface structure of high-voltage layered oxide cathodes and improve their overall electrochemical performance is of great significance.

[0005] Therefore, there is an urgent need for a simple, low-cost, and scalable method for surface modification of high-voltage layered oxide cathode materials. Summary of the Invention

[0006] To address the problems that existing technologies involve complex, expensive, and difficult-to-scale processes, and that the differences in properties of various layered oxide cathode materials result in poor versatility of these treatment methods and difficulty in improving overall electrochemical performance, this disclosure provides a method for surface modification of high-voltage layered oxide cathode materials.

[0007] According to a first aspect of the present invention, a method for surface modification of a high-voltage layered oxide cathode material is provided, comprising:

[0008] Step a: Take a high-voltage layered oxide cathode material sample, heat it to 400~1000℃, and then add it to a pre-prepared reducing solution for quenching treatment. The mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be 1:(0.1~1).

[0009] Step b: After cooling the quenched high-pressure layered oxide cathode material sample, filter, wash and dry it to obtain surface-modified high-pressure layered oxide cathode material.

[0010] In some embodiments, step a is preceded by:

[0011] Prepare a reducing solution consisting of an aqueous solution of an organic compound with a concentration of 10–500 g / L and an aqueous solution of an inorganic compound with a molar concentration of 0.1–3 mol / L.

[0012] In some embodiments, the aqueous solution of the organic compound includes one or more of glucose, acetaldehyde, oxalic acid, urea, and ascorbic acid.

[0013] In some embodiments, the inorganic aqueous solution includes one or more of sodium sulfite, sodium bisulfite, ammonium sulfite, ferrous sulfate, sodium nitrite, sodium sulfide, potassium sulfide, sodium borohydride, and sodium ascorbate.

[0014] In some embodiments, step a includes:

[0015] Take a high-voltage layered oxide cathode material sample, add it to a muffle furnace, and heat it to 400-1000℃ in air at a heating rate of 2-8℃ / min. Then add it to a pre-prepared reducing solution for quenching treatment. The mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be 1:(0.1-1).

[0016] In some embodiments, step a further includes:

[0017] Take a high-voltage layered oxide cathode material sample, add it to a tube furnace, and heat it to 400-1000℃ at a heating rate of 2-8℃ / min under an oxygen atmosphere. Then add it to a pre-prepared reducing solution for quenching treatment, wherein the mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be 1:(0.1-1).

[0018] In some embodiments, step b includes:

[0019] The high-pressure layered oxide cathode material sample after quenching was cooled and filtered, then cleaned with deionized water and ethanol in sequence, and then placed in a vacuum drying oven for drying to obtain the surface-modified high-pressure layered oxide cathode material.

[0020] In some embodiments, step b further includes:

[0021] The high-pressure layered oxide cathode material sample after quenching was cooled and filtered, then washed twice with deionized water and then twice with ethanol. After that, it was placed in a vacuum drying oven and dried at 80°C for 6-12 hours to obtain the surface-modified high-pressure layered oxide cathode material.

[0022] In some embodiments, the high-voltage layered oxide cathode material includes lithium cobalt oxide cathode material, high-nickel ternary cathode material, and lithium-rich manganese layered cathode material.

[0023] In some embodiments, the molecular formula of the lithium-rich manganese-based substrate cathode material is Li. 1+x TM 1-x O2, wherein TM is at least two of Ni, Co, and Mn, and x is 0. <x<1。

[0024] The above-mentioned method for surface modification of high-pressure layered oxide cathode materials involves taking a high-pressure layered oxide cathode material sample, heating it to 400-1000℃, and then adding it to a pre-prepared reducing solution for quenching treatment. The mass ratio of the reducing solution to the high-pressure layered oxide cathode material sample is controlled at 1:(0.1-1). After quenching, the high-pressure layered oxide cathode material sample is cooled, filtered, washed, and dried to obtain the surface-modified high-pressure layered oxide cathode material. This invention's method for surface modification of high-pressure layered oxide cathode materials uses a reducing solution quenching method to adjust the surface structure of the high-pressure layered oxide cathode, generating oxygen vacancies and rock salt structures on the particle surface, achieving surface doping, and improving the surface stability of the high-pressure layered oxide cathode material. In the above process, the liquid-solid interface reaction ensures sufficient and uniform contact and reaction between the layered oxide cathode material and the reducing solution, resulting in complete and uniform surface structure regulation. This significantly improves the overall electrochemical performance of the lithium-ion battery (initial coulombic efficiency, high-voltage cycle stability). The above processing steps are simple and time-saving, and the reaction conditions are easy to control. They are suitable for continuous industrial production, which improves production efficiency and is applicable to large-scale production. The reducing solvents used are all common chemical raw materials, which are inexpensive and have low production costs. They are widely applicable to solving the surface instability of battery cathode materials, and can even be extended to the surface modification of lithium-ion battery cathode materials such as high-voltage spinel and other layered oxide cathode materials of sodium-ion batteries. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0026] Figure 1 A flowchart illustrating a method for surface modification of a high-voltage layered oxide cathode material according to an embodiment of the present invention;

[0027] Figure 2 Scanning electron microscope (SEM) morphology image of the surface-modified lithium-rich manganese-based substrate cathode material obtained in Example 5 of the present invention;

[0028] Figure 3 High-angle annular dark-field scanning transmission (HAADF-STEM) image of the particle surface region of the surface-modified lithium-rich manganese-based basal cathode material obtained in Example 5 of the present invention;

[0029] Figure 4The blank example provided by this invention is the original lithium-rich manganese-based substrate cathode material Li that has not undergone reducing solution quenching treatment. 1.2 Ni 0.2 Mn 0.6 Scanning electron microscope (SEM) morphology of O2;

[0030] Figure 5 The blank example provided by this invention is the original lithium-rich manganese-based substrate cathode material Li that has not undergone reducing solution quenching treatment. 1.2 Ni 0.2 Mn 0.6 High-angle annular dark-field scanning transmission (HAADF-STEM) image of the surface region of O2 particles;

[0031] Figure 6 Schematic diagrams of X-ray diffraction (XRD) patterns of Examples 5-6 and blank examples (original lithium-rich manganese-based substrate cathode material) provided for this invention;

[0032] Figure 7 Cycling performance diagrams of Examples 1-2, Blank Example (Lithium Cobalt Oxide), and Comparative Example 1 at 1C rate provided for the present invention;

[0033] Figure 8 Cycling performance diagrams of Examples 3-4, Blank Example (high-nickel ternary cathode material NCM811), and Comparative Example 2 at 1C rate provided for this invention;

[0034] Figure 9 Comparison of the first charge-discharge curves of Examples 5-7, Blank Example (Lithium-rich Manganese-based Layered Cathode Material), and Comparative Example 3 at 0.1C rate provided by the present invention;

[0035] Figure 10 Cycling performance diagrams of Examples 5-7, Blank Example (Lithium-rich Manganese-based Stereo cathode material), and Comparative Example 3 at 1C rate provided for this invention. Detailed Implementation

[0036] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0037] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0038] It should be noted that, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationship, are only for the convenience of describing this disclosure 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, and therefore should not be construed as a limitation of this disclosure. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0039] Furthermore, the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Terms such as "including" or "contains" mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility of covering other elements as well.

[0040] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure depending on the specific circumstances. When a particular device is described as being located between a first device and a second device, an intermediary device may or may not be present between the particular device and the first or second device.

[0041] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0042] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0043] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0044] Please refer to Figure 1 , Figure 1 The flowchart shown illustrates a method for surface modification of a high-voltage layered oxide cathode material according to an embodiment of the present invention. The method 100 for surface modification of a high-voltage layered oxide cathode material includes:

[0045] Step a: Take a high-voltage layered oxide cathode material sample, heat it to 400~1000℃, and then add it to a pre-prepared reducing solution for quenching treatment. The mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be 1:(0.1~1).

[0046] Specifically, quenching is a common heat treatment process in steel production, and its application has been extended to the preparation and modification of various functional materials.

[0047] Specifically, the pre-prepared reducing solutions include aqueous solutions of organic compounds with aldehyde groups / unsaturated bonds and aqueous solutions of inorganic compounds / organic salts containing low-valence elements. The aqueous solutions of organic compounds with aldehyde groups / unsaturated bonds include glucose, acetaldehyde, oxalic acid, urea, and ascorbic acid, while the aqueous solutions of inorganic compounds / organic salts containing low-valence elements include sodium sulfite, sodium bisulfite, ammonium sulfite, ferrous sulfate, sodium nitrite, sodium sulfide, potassium sulfide, sodium borohydride, and sodium ascorbate. These reducing solutions are all common, inexpensive chemical raw materials with low production costs.

[0048] Specifically, the concentration of the organic aqueous solution in the pre-prepared reducing solution is 10~500g / L, and the molar concentration of the inorganic aqueous solution is 0.1~3mol / L.

[0049] Specifically, oxygen vacancies and rock salt structures are generated on the surface of high-voltage layered oxide cathode material particles through a reducing solution quenching method, achieving surface doping and improving the surface stability of the high-voltage layered oxide cathode material under high pressure. Among these, surface oxygen vacancies can not only promote the Li-coated surface region... + Diffusion can also suppress the irreversible release of lattice oxygen; the surface rock salt structure shell has excellent chemical and electrochemical stability, which can significantly suppress the release of lattice oxygen, the dissolution of transition metal ions and interfacial side reactions, and improve interfacial stability; surface ion doping can also regulate the electronic structure of the material, and can suppress the damage to the material's crystal structure, irreversible phase transitions on the surface and the release of lattice oxygen.

[0050] Step b: After cooling the quenched high-pressure layered oxide cathode material sample, filter, wash and dry it to obtain surface-modified high-pressure layered oxide cathode material.

[0051] The surface structure of high-voltage layered oxide cathode materials was modulated using a reducing solution quenching method, utilizing the residual heat carried to ignite the Li / M particles on the surface. n+ Ion exchange reaction (M n+ Some cations present in reducing solutions, such as H+ + Na + Fe 3+ The reduction reaction of layered oxide cathode materials with transition metal ions generates oxygen vacancies and rock salt structures on the particle surface, achieving surface doping. Furthermore, the surface reconstruction layer can be precisely controlled by altering the temperature of the layered oxide cathode material, the type and concentration of the reducing solution, etc. The prepared surface-modified high-voltage layered oxide cathode material exhibits higher initial coulombic efficiency and discharge specific capacity, superior high-voltage cycle stability, and suppresses lattice oxygen release and transition metal ion dissolution compared to the original layered oxide cathode material.

[0052] The aforementioned method for surface modification of high-voltage layered oxide cathode materials utilizes a reducing solution quenching method to adjust the surface structure of the high-voltage layered oxide cathode, generating oxygen vacancies and rock salt structures on the particle surface, thus achieving surface doping and improving the surface stability of the high-voltage layered oxide cathode material. Specifically, the liquid-solid interface reaction in this process ensures sufficient and uniform contact and reaction between the layered oxide cathode material and the reducing solution, resulting in complete and uniform surface structure regulation. This significantly improves the overall electrochemical performance of the lithium-ion battery (initial coulombic efficiency and high-voltage cycle stability).

[0053] The above processing steps are simple and time-saving, and the reaction conditions are easy to control. They are suitable for continuous industrial production, which improves production efficiency and is applicable to large-scale production. They have wide applicability in solving the surface instability of battery cathode materials, and can even be extended to the surface modification of lithium-ion battery cathode materials such as high-voltage spinel and other layered oxide cathode materials of sodium-ion batteries.

[0054] According to several embodiments of the present invention, before step a, a reducing solution is further prepared, consisting of an organic aqueous solution with a concentration of 10-500 g / L and an inorganic aqueous solution with a molar concentration of 0.1-3 mol / L. By reasonably controlling the concentrations of the organic and inorganic aqueous solutions, a reducing solution meeting the requirements of the reducing solution quenching method can be precisely prepared. This is beneficial for the subsequent generation of oxygen vacancies and rock salt structures on the surface of the high-voltage layered oxide cathode material particles, achieving surface doping and improving the surface stability of the high-voltage layered oxide cathode material under high pressure.

[0055] According to several embodiments of the present invention, the aqueous solution of organic matter includes one or more of glucose, acetaldehyde, oxalic acid, urea, and ascorbic acid. The aforementioned glucose, acetaldehyde, oxalic acid, urea, and ascorbic acid are all commonly used industrial raw materials, readily available and inexpensive, suitable for continuous industrial production.

[0056] According to several embodiments of the present invention, the inorganic aqueous solution includes one or more of sodium sulfite, sodium bisulfite, ammonium sulfite, ferrous sulfate, sodium nitrite, sodium sulfide, potassium sulfide, sodium borohydride, and sodium ascorbate. The aforementioned sodium sulfite, sodium bisulfite, ammonium sulfite, ferrous sulfate, sodium nitrite, sodium sulfide, potassium sulfide, sodium borohydride, and sodium ascorbate are all commonly used industrial raw materials, readily available, and low in cost, suitable for continuous industrial production.

[0057] According to several embodiments of the present invention, step a includes: taking a high-voltage layered oxide cathode material sample, adding it to a muffle furnace, heating it to 400-1000°C at a heating rate of 2-8°C / min in an air atmosphere, and then adding it to a pre-prepared reducing solution for quenching treatment, wherein the mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be 1:(0.1-1). Alternatively, the high-voltage layered oxide cathode material sample can be added to a muffle furnace and heated using the air atmosphere inside the muffle furnace to a preset temperature range before being added to a pre-prepared reducing solution for quenching treatment, and the mass ratio of the reducing solution to the high-voltage layered oxide cathode material sample is controlled to be maintained at 1:(0.1-1), so that the reducing quenching treatment can be carried out to the maximum extent, and the layered oxide cathode material and the reducing solution can fully and uniformly contact and react, resulting in complete and uniform regulation of the surface structure, and significantly improving the overall electrochemical performance (initial coulombic efficiency, high-voltage cycle stability) of the lithium-ion battery.

[0058] According to several embodiments of the present invention, step a further includes: taking a high-pressure layered oxide cathode material sample, adding it to a tube furnace, heating it to 400-1000°C at a heating rate of 2-8°C / min under an oxygen atmosphere, and then adding it to a pre-prepared reducing solution for quenching treatment, wherein the mass ratio of the reducing solution to the high-pressure layered oxide cathode material sample is controlled to be 1:(0.1-1). Alternatively, the high-pressure layered oxide cathode material sample can be added to a tube furnace, heated using the oxygen atmosphere within the tube furnace, and then added to a pre-prepared reducing solution for quenching treatment after reaching a preset temperature range, while maintaining the mass ratio of the reducing solution to the high-pressure layered oxide cathode material sample at 1:(0.1-1). This allows the reducing quenching treatment to proceed to the maximum extent, ensuring sufficient and uniform contact and reaction between the layered oxide cathode material and the reducing solution, resulting in complete and uniform regulation of the surface structure, and significantly improving the overall electrochemical performance (initial coulombic efficiency, high-voltage cycle stability) of the lithium-ion battery.

[0059] According to several embodiments of the present invention, step b includes: cooling and filtering the quenched high-pressure layered oxide cathode material sample, then washing it successively with deionized water and ethanol, and then drying it in a vacuum drying oven to obtain a surface-modified high-pressure layered oxide cathode material. Washing with deionized water and ethanol successively ensures thorough cleaning and minimizes the impact of surface impurities on the subsequent surface modification process.

[0060] According to several embodiments of the present invention, step b further includes: cooling and filtering the quenched high-pressure layered oxide cathode material sample, then washing it twice with deionized water and twice with ethanol, and then placing it in a vacuum drying oven and drying it at 80°C for 6-12 hours to obtain the surface-modified high-pressure layered oxide cathode material. Reasonably controlling the number of times the deionized water and ethanol are used ensures thorough cleaning while reducing resource waste. Simultaneously, reasonably controlling the drying time after cleaning ensures that the surface-modified high-pressure layered oxide cathode material is fully dried.

[0061] According to several embodiments of the present invention, the high-voltage layered oxide cathode material includes lithium cobalt oxide cathode material, high-nickel ternary cathode material, and lithium-rich manganese layered cathode material.

[0062] According to several embodiments of the present invention, the molecular formula of the lithium-rich manganese-based substrate cathode material is Li. 1+x TM 1-x O2, where TM is at least two of Ni, Co, and Mn, and x takes the value 0. <x<1。

[0063] To further understand the method for surface modification of a high-voltage layered oxide cathode material according to the present invention, the following detailed description is provided in specific embodiments.

[0064] Example 1

[0065] A 100 g / L glucose solution was prepared. The original lithium cobalt oxide cathode material was placed in a muffle furnace and heated to 1000°C at a heating rate of 5°C / min. Then, it was directly poured into the glucose solution for quenching, with the mass ratio of glucose solution to lithium cobalt oxide controlled at 1:0.3. After the lithium cobalt oxide had completely cooled, it was filtered and washed, rinsed twice with deionized water, and then twice with ethanol. It was then dried in a vacuum drying oven at a temperature below 80°C for 12 hours to obtain the surface-modified high-voltage lithium cobalt oxide cathode material. In this embodiment, the original lithium cobalt oxide cathode material was a commercially available single-crystal lithium cobalt oxide with a size of approximately 10 μm, prepared using existing solid-state methods, which will not be described in detail here.

[0066] Example 2

[0067] A 2 mol / L sodium sulfite solution was prepared. The original lithium cobalt oxide cathode material was placed in a muffle furnace and heated to 1000°C at a heating rate of 5°C / min. Then, it was directly poured into the sodium sulfite solution for quenching, with the mass ratio of sodium sulfite solution to lithium cobalt oxide controlled at 1:0.1. After the lithium cobalt oxide had completely cooled, it was filtered and washed, first twice with deionized water, then twice with ethanol. Finally, it was dried in a vacuum drying oven at a temperature below 80°C for 12 hours to obtain the surface-modified high-voltage lithium cobalt oxide cathode material. The original lithium cobalt oxide cathode material used in Example 2 was the same as that in Example 1, and will not be described again.

[0068] Example 3

[0069] To prepare a urea solution with a concentration of 100 g / L, the original high-nickel ternary cathode material NCM811 (LiNi) was added. 0.8 Mn 0.1 Co 0.1O2 was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under an oxygen-flowing atmosphere (flow rate of 100 mL / min). Then, it was directly poured into a urea solution for quenching treatment, with a urea-to-NCM811 mass ratio of 1:1. After the NCM811 had completely cooled, it was filtered and washed, first twice with deionized water, then twice with ethanol. Finally, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain the surface-modified high-voltage NCM811 cathode material. The original NCM811 used in Example 2 was a commercially available polycrystalline high-nickel ternary cathode material, prepared by an existing co-precipitation method, which will not be described in detail here.

[0070] Example 4

[0071] Prepare a 2 mol / L sodium ascorbate solution and apply the original high-nickel ternary cathode material NCM811 (LiNi) to it. 0.8 Mn 0.1 Co 0.1 O2) was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under an oxygen-flowing atmosphere (flow rate of 100 mL / min). Then, it was directly poured into a sodium ascorbate solution for quenching treatment, with a mass ratio of sodium ascorbate solution to NCM811 cathode material of 1:0.2. After the NCM811 had completely cooled, it was filtered and washed, first twice with deionized water, then twice with ethanol. Finally, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain the surface-modified high-voltage NCM811 cathode material. The original NCM811 used in Example 4 was the same as that in Example 3, and will not be described again.

[0072] Example 5

[0073] Prepare a 100 g / L glucose solution and then apply the original lithium-rich manganese-based substrate cathode material Li. 1.2 Ni 0.2 Mn 0.6 O2 was placed in a muffle furnace and heated to 900°C at a heating rate of 5°C / min. It was then directly poured into a glucose solution for quenching, with the mass ratio of glucose solution to lithium-rich manganese-based crystalline cathode material being 1:0.3. After the lithium-rich manganese-based crystalline cathode material had completely cooled, it was filtered and washed, rinsed twice with deionized water and twice with ethanol, and then dried in a vacuum drying oven at 80°C for 12 hours to obtain a surface-modified high-voltage lithium-rich manganese-based crystalline cathode material. The lithium-rich manganese-based crystalline cathode material Li in Example 5... 1.2 Ni 0.2 Mn 0.6O2 was prepared in the laboratory using a sol-gel method, and consisted of single-crystal particles with a particle size of approximately 300 nm. The preparation process is based on existing technology and will not be described in detail here. The scanning electron microscope (SEM) morphology image of the surface-modified lithium-rich manganese-based substrate cathode material obtained in Example 5 is shown below. Figure 2 As shown, the high-angle annular dark-field scanning transmission (HAADF-STEM) image of the particle surface region of the surface-modified lithium-rich manganese-based substrate cathode material obtained in Example 5 is as follows. Figure 3 As shown.

[0074] Example 6

[0075] Prepare a 1 mol / L ferrous sulfate solution and then apply the original lithium-rich manganese-based substrate cathode material Li... 1.2 Ni 0.2 Mn 0.6 O2 was placed in a muffle furnace and heated to 900°C at a heating rate of 5°C / min. It was then directly poured into a ferrous sulfate solution for quenching, with the mass ratio of ferrous sulfate solution to lithium-rich manganese-based cathode material being 1:0.1. After the lithium-rich manganese-based cathode material had completely cooled, it was filtered and washed, first twice with deionized water, then twice with ethanol. Finally, it was dried in a vacuum drying oven at 80°C for 12 hours to obtain the surface-modified lithium-rich manganese-based cathode material. The original lithium-rich manganese-based cathode material used in Example 6 was the same as in Example 5 and will not be described again.

[0076] Example 7

[0077] Prepare a 2 mol / L sodium borohydride solution and then apply the original lithium-rich manganese-based substrate cathode material Li... 1.2 Ni 0.2 Mn 0.6 O2 was placed in a muffle furnace and heated to 900°C at a heating rate of 5°C / min. It was then directly poured into a sodium borohydride solution for quenching, with the mass ratio of sodium borohydride solution to lithium-rich manganese-based crystalline cathode material being 1:1. After the material had completely cooled, it was filtered and washed, first twice with deionized water, then twice with ethanol. It was then dried in a vacuum drying oven at 80°C for 12 hours to obtain the surface-modified lithium-rich manganese-based crystalline cathode material. The original lithium-rich manganese-based crystalline cathode material used in Example 7 was the same as in Example 5 and will not be described again.

[0078] Blank example

[0079] The original lithium cobalt oxide, the original high-nickel ternary cathode material NCM811, and the original lithium-rich manganese-based layered cathode material Li were not treated with reducing solution quenching. 1.2 Ni 0.2 Mn 0.6O2. Among them, the original lithium-rich manganese-based substrate cathode material Li, which has not undergone reducing solution quenching treatment, is... 1.2 Ni 0.2 Mn 0.6 The scanning electron microscope (SEM) morphology image of O2 is as follows: Figure 4 As shown, the original lithium-rich manganese-based substrate cathode material Li, which has not undergone reducing solution quenching treatment, is a prime example. 1.2 Ni 0.2 Mn 0.6 High-angle annular dark-field scanning transmission (HAADF-STEM) image of the O2 particle surface region as shown in the image. Figure 5 As shown.

[0080] Depend on Figure 2 and Figure 4 The comparison shows that the lithium-rich manganese-based substrate cathode materials in Example 5 and Blank Example 3 are both nanoparticles prepared by the sol-gel method, with a size of approximately 300 nm. Meanwhile, the surface of Example 5 is rougher, which may be due to surface structure modulation caused by the quenching process. Figure 5 It can be seen that the original lithium-rich manganese-based substrate cathode material Li, which has not undergone reducing solution quenching treatment, 1.2 Ni 0.2 Mn 0.6 The O2 surface region has a well-defined layered structure, consisting of... Figure 5 and Figure 3 The comparison shows that the lithium-rich manganese-based substrate cathode material in Example 5 exhibits a rock-salt shell with a thickness of approximately 4 nm on its surface, while maintaining a well-defined layered structure internally. This phenomenon indicates that quenching with a reducing solution can improve the Li / M... n+ Ion exchange reactions and reduction reactions of transition metal ions induce the formation of a protective rock salt structure shell, suppressing interfacial side reactions and lattice oxygen release, thereby achieving excellent high-pressure cycling stability.

[0081] Comparative Example 1

[0082] Comparative Example 1 is compared with Examples 1-2. In Comparative Example 1, deionized water (containing no reducing substances) was used as the quenching solution.

[0083] Comparative Example 2

[0084] Comparative Example 2 is compared with Examples 3-4. In Comparative Example 2, deionized water (containing no reducing substances) was used as the quenching solution.

[0085] Comparative Example 3

[0086] Comparative Example 3 is compared with Examples 5-7. In Comparative Example 3, deionized water (containing no reducing substances) was used as the quenching solution.

[0087] The X-ray diffraction (XRD) patterns of Examples 5-6, Comparative Example 1, and the blank example (original lithium-rich manganese-based substrate cathode material) are shown below. Figure 6 As shown, from Figure 6 It can be seen that the lithium-rich manganese-based layered cathode materials in Examples 5, 6 and Blank Example 3 all exhibit similar XRD patterns, with no additional diffraction peaks appearing, indicating that the reducing solution quenching process does not affect the crystal structure of the lithium-rich layered manganese-based cathode material.

[0088] The cycling performance graphs of Examples 1-2, Blank Example (Lithium Cobalt Oxide), and Comparative Example 1 at 1C rate are shown below. Figure 7 As shown, from Figure 7 As can be seen, compared with the blank example, Examples 1 and 2 achieve higher capacity retention rates. This is attributed to the surface modification of the material achieved through quenching with a reducing solution (including surface oxygen vacancies, rock salt structure shell, and surface doping), which suppresses interfacial side reactions such as electrolyte decomposition under high pressure, irreversible changes in surface structure, and dissolution of transition metals. In Comparative Example 1, since no reducing substance is involved in quenching, the degree of surface structure regulation is small, and the material surface is more susceptible to damage from water. Therefore, it has the lowest specific capacity and poor cycle performance.

[0089] The cycling performance of Examples 3-4, the blank example (high-nickel ternary cathode material NCM811), and Comparative Example 2 at 1C rate is shown in the graphs. Figure 8 As shown, from Figure 8 As can be seen, Examples 3 and 4 exhibit the highest capacity retention rates compared to the blank example. This is attributed to the surface modification of the material achieved through quenching with a reducing solution (including surface oxygen vacancies, rock salt structure shell, and surface doping), which suppresses interfacial side reactions such as electrolyte decomposition under high pressure, irreversible changes in surface structure, and transition metal dissolution. In Comparative Example 2, due to the absence of reducing substances during quenching, the degree of surface structure regulation is small. However, the deionized water quenching process and subsequent washing process partially remove residual alkali from the surface, thus partially alleviating interfacial side reactions. Therefore, its cycle stability is slightly better than the blank example, but still far inferior to Examples 3 and 4.

[0090] The comparison graphs of the first charge-discharge curves of Examples 5-7, the blank example (lithium-rich manganese-based substrate cathode material), and Comparative Example 3 at 0.1C rate are shown below. Figure 9 As shown, from Figure 9As can be seen, compared with the blank example and Comparative Example 3, Examples 5-7 can achieve higher initial coulombic efficiency and discharge specific capacity. This is due to the surface modification of the material (including surface oxygen vacancies, rock salt structure shell and surface doping), which can suppress lattice oxygen release and interfacial side reactions of lithium-rich manganese-based substrate cathode materials and improve the reversibility of oxygen oxidation-reduction process.

[0091] The cycling performance of Examples 5-7, the blank example (lithium-rich manganese-based substrate cathode material), and Comparative Example 3 at 1C rate is shown in the graphs. Figure 10 As shown, from Figure 10 As can be seen, compared with the blank example and Comparative Example 3, Examples 5-7 exhibit the best capacity retention and the lowest voltage decay rate. This is because the stable surface structure in subsequent cycles can significantly alleviate problems such as electrolyte decomposition, lattice oxygen release, irreversible phase transition from layered to spinel, and dissolution of transition metals, thereby improving the capacity retention and voltage retention.

[0092] The high-voltage layered oxide cathode materials obtained in Examples 1-7, the blank example, and Comparative Examples 1-3 were mixed with a conductive agent (super-P conductive carbon black) and a binder (polyvinylidene fluoride, PVDF) at a mass ratio of 8:1:1 in N-methylpyrrolidone (NMP) at room temperature. The mixture was then uniformly coated onto an aluminum current collector, with an active material surface loading of 2.5-6.0 mg / cm³. -2 After drying, cutting, and rolling, the materials were transferred to a glove box for storage. CR2032 coin cells were assembled in an argon-filled glove box. The negative electrode was a lithium metal sheet, the separator was a Celgard 2400 membrane, and the electrolyte was 1.0 M LiPF6 dissolved in a mixture of EC:DMC:EMC, with a mass fraction ratio of 1:1:1 wt%. The coin cells were first activated at a current density of 0.1C (1C=200mA / g for lithium cobalt oxide / high-nickel ternary cathode material; 1C=250mA / g for lithium-rich manganese-based substrate cathode material). After activation, charge-discharge cycles were performed at a current density of 1C. The test voltage ranges were 3.0-4.5V for lithium cobalt oxide, 2.8-4.5V for high-nickel ternary cathode material, and 2.0-4.8V for lithium-rich manganese-based substrate cathode material.

[0093] Finally, the test results of initial capacity, post-cycle capacity, and capacity retention for Examples 1-2, the blank example, and Comparative Example 1 are shown in Table 1 below:

[0094] Table 1

[0095]

[0096] As shown in Table 1, compared to the blank example, Examples 1 and 2 achieve higher initial coulombic efficiency and capacity retention, but their initial discharge capacity is almost identical. This is attributed to the surface modification of the material achieved through quenching with a reducing solution (including surface oxygen vacancies, rock salt structure shell, and surface doping), which suppresses interfacial side reactions such as electrolyte decomposition under high voltage, irreversible changes in surface structure, and dissolution of transition metals. In Comparative Example 1, due to the absence of reducing substances during quenching, the degree of surface structure regulation is small, and the material surface is more susceptible to damage from water. Therefore, it has the lowest specific capacity and poorer cycle performance.

[0097] The test results of initial capacity, post-cycle capacity, and capacity retention for Examples 3-4, the blank example, and Comparative Example 2 are shown in Table 2 below:

[0098] Table 2

[0099]

[0100] As shown in Table 2, compared to the blank example, Examples 3 and 4 achieved higher initial coulombic efficiency and capacity retention, but their initial discharge capacity was almost identical. This is attributed to the surface modification of the material (including surface oxygen vacancies, rock salt structure shell, and surface doping) achieved through quenching with a reducing solution, which suppressed interfacial side reactions such as electrolyte decomposition under high voltage, irreversible changes in surface structure, and dissolution of transition metals. In Comparative Example 2, since no reducing substance was involved in the quenching, the degree of surface structure regulation was small. However, the deionized water quenching process and subsequent washing process partially removed the residual alkali on the surface and partially alleviated the interfacial side reactions. Therefore, its initial coulombic efficiency and cycle stability were better than the blank example, but still far worse than Examples 3 and 4.

[0101] The test results of initial capacity, post-cycle capacity, and capacity retention for Examples 5-7, the blank example, and Comparative Example 3 are shown in Table 3 below:

[0102] Table 3

[0103]

[0104] As can be seen from Table 3, compared with the blank example and Comparative Example 3, Examples 5-7 can achieve higher initial coulombic efficiency and discharge specific capacity. This is due to the surface modification of the material (including surface oxygen vacancies, rock salt structure shell and surface doping), which can suppress lattice oxygen release and interfacial side reactions of lithium-rich manganese-based layered cathode materials and improve the reversibility of oxygen redox process. In subsequent cycles, thanks to its stable surface structure, problems such as electrolyte decomposition, lattice oxygen release, irreversible phase transition from layered to spinel and transition metal dissolution are significantly alleviated, resulting in Examples 5-7 exhibiting the best capacity retention rate and the smallest voltage decay rate.

[0105] Based on the measurement results of Examples 1-7, Comparative Examples 1-3, and the blank example, it can be seen that adjusting the surface structure of the high-voltage layered oxide cathode using the reducing solution quenching method generates oxygen vacancies and rock salt structures on the particle surface, achieving surface doping and improving the surface stability of the high-voltage layered oxide cathode material. Specifically, the liquid-solid interface reaction in the above process ensures sufficient and uniform contact and reaction between the layered oxide cathode material and the reducing solution, resulting in complete and uniform surface structure regulation. This significantly improves the overall electrochemical performance of the lithium-ion battery (initial coulombic efficiency, high-voltage cycle stability). The entire process is simple and time-saving, and the reaction conditions are easy to control, making it suitable for continuous industrial production. This improves production efficiency and is applicable to large-scale production. It has broad applicability in solving the surface instability of battery cathode materials and can even be extended to the surface modification of high-voltage spinel and other lithium-ion battery cathode materials, as well as other sodium-ion battery layered oxide cathode materials.

[0106] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0107] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for surface modification of high-voltage layered oxide cathode materials, characterized in that, include: Step a: Take a high-pressure layered oxide cathode material sample, add it to a tube furnace, and heat it to 400-1000℃ at a heating rate of 2-8℃ / min under an oxygen atmosphere. Then add it to a pre-prepared reducing solution for quenching treatment. The mass ratio of the reducing solution to the high-pressure layered oxide cathode material sample is controlled to be 1:(0.1-1). The high-pressure layered oxide cathode material includes lithium cobalt oxide cathode material, high-nickel ternary cathode material, or lithium-rich manganese layered cathode material. Step b: After cooling the quenched high-pressure layered oxide cathode material sample, filter, wash and dry it. The sample is washed twice with deionized water and then twice with ethanol. After that, it is placed in a vacuum drying oven and dried at 80°C for 6-12 hours to obtain the surface-modified high-pressure layered oxide cathode material. Before step a, the method further includes: preparing a reducing solution consisting of an aqueous solution of organic matter with a concentration of 10~500g / L and an aqueous solution of inorganic matter with a molar concentration of 0.1~3mol / L; In this process, oxygen vacancies and rock salt structures are generated on the surface of the surface-modified high-pressure layered oxide cathode material particles, and surface doping is achieved. The organic aqueous solution includes one or more of glucose, acetaldehyde, oxalic acid, urea, and ascorbic acid; The inorganic aqueous solution includes one or more of sodium sulfite, sodium bisulfite, ammonium sulfite, ferrous sulfate, sodium nitrite, sodium sulfide, potassium sulfide, and sodium borohydride.

2. The method for surface modification of high-voltage layered oxide cathode material according to claim 1, characterized in that, The molecular formula of the lithium-rich manganese-based substrate cathode material is Li. 1+x TM 1-x O2, wherein TM is at least two of Ni, Co, and Mn, and x is 0. <x<1。

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