Positive electrode material, surface-reconstructed material and lithium-ion battery

Abstract

A positive electrode material, a surface-reconstructed material and a lithium-ion battery. In an XPS spectrum of the positive electrode material, after peak fitting processing, a surface oxygen O1s characteristic peak of the positive electrode material can yield at least two characteristic peaks, including: a first characteristic peak within the range of 529.0±0.5 eV and a second characteristic peak within the range of 531.2±0.5 eV. The positive electrode material satisfies at least one of the following conditions: (1) the degree of separation between the first characteristic peak and the second characteristic peak is less than or equal to 1.0; and (2) the distance between the peak positions of the first characteristic peak and the second characteristic peak is less than or equal to 2.4 eV. The positive electrode material in the embodiments of the present application has a more stable structure, thereby helping to improve performance in terms of the cycling life, safety, etc. of a battery.

Description

Cathode materials, surface reconstruction materials and lithium-ion batteries Cross-references to related applications

[0001] This application claims priority to Chinese patent application filed on January 20, 2025, with application number 202510093164.1 and entitled "Cathode Material, Surface Reconstruction Material and Lithium-ion Battery". Technical Field

[0002] This application generally relates to the field of battery cathode materials technology. More specifically, this application relates to a cathode material, a surface reconstruction material, and a lithium-ion battery. Background Technology

[0003] In recent years, lithium-ion batteries (LIBs) have been widely used in various fields such as consumer electronics, power tools, electric vehicles, and energy storage, and are gradually expanding into areas such as electric ships and electric aircraft. As related technologies mature and the application market becomes more sophisticated, consumers are placing increasingly stringent demands on lithium-ion batteries regarding energy density, cycle life, and safety. The cathode material, as one of the core components, plays a crucial role in the various performance indicators of lithium-ion batteries.

[0004] Currently, with the increase in cathode material capacity, the number of active oxygen sites on the cathode material surface increases, exacerbating the side reactions with the electrolyte. These side reactions oxidize the electrolyte, generating some gas, causing the battery to swell and affecting safety performance. Simultaneously, the gas generation leads to poorer contact between the electrode and the electrolyte, resulting in reduced cycle life. Regarding improving the battery's charge / discharge voltage window, as the charge / discharge depth increases, the expansion / contraction of cathode material grains and internal stress intensify, making cathode material particles prone to cracking and pulverization, thus affecting the battery's cycle life and safety.

[0005] In view of this, there is an urgent need to provide a cathode material solution in order to improve the cycle life and safety performance of batteries. Summary of the Invention

[0006] In order to at least solve one or more of the technical problems mentioned above, this application proposes cathode materials, surface reconstruction materials for cathode materials, preparation methods of cathode materials, and lithium-ion battery solutions in several aspects.

[0007] In a first aspect, this application provides a cathode material in which, after peak splitting, the surface oxygen element O1s characteristic peak of the cathode material can be divided into at least two characteristic peaks, including: a first characteristic peak in the range of 529.0±0.5eV and a second characteristic peak in the range of 531.2±0.5eV; and the cathode material also satisfies at least one of the following conditions: (1) the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0; (2) the peak position spacing between the first characteristic peak and the second characteristic peak is ≤2.4eV.

[0008] In a second aspect, this application provides a surface reconstruction material, the surface reconstruction material comprising Ni x Co y M z M” 1-x-y-z OOH, Ni x Co y M z M” 1-x-y-z (OH)2、(Ni x Co y M z M” 1-x-y-z )O d At least one of the following, wherein 0≤x≤0.6, 0.4≤y≤1, 0≤z≤0.6, 0≤1-xyz≤0.15, 1≤d≤2, M includes Mn and / or Al, and M" includes at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy; the Na content in the surface reconstruction material ranges from 50ppm to 300ppm.

[0009] In a third aspect, this application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode material made of the positive electrode material described in the first aspect or the surface reconstruction material described in the second aspect.

[0010] In a fourth aspect, this application provides a lithium-ion battery comprising a positive electrode material made of the positive electrode material described in any one of the first aspects or the surface reconstruction material described in the second aspect.

[0011] As can be seen from the cathode material scheme provided above, the cathode material of the embodiments of this application satisfies at least one of the following conditions in its XPS spectrum: the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0, and the peak spacing between the first characteristic peak and the second characteristic peak is ≤2.4 eV. On the one hand, the peak spacing between the first characteristic peak and the second characteristic peak is ≤2.4 eV, indicating that the binding energy of the active oxygen characteristic peak on the surface of the cathode material is large and the bond energy is strong, making it more difficult for active oxygen to be oxidized. Alternatively, the binding energy of the adsorbed oxygen vacancy is small and the bond energy is weak, making it easier to capture active oxygen and avoid the overflow of active oxygen, thereby suppressing the side reaction between the cathode material surface and the electrolyte, and improving the cell safety and cycle life. On the other hand, the separation degree between the first and second characteristic peaks is ≤1.0, indicating that the peak spacing between the first and second characteristic peaks in the cathode material is small and the half-peak width is large. Thus, on the one hand, the small peak spacing between the first and second characteristic peaks indicates that the binding energy of the active oxygen characteristic peaks is large and the bond energy is strong, making it more difficult for active oxygen to be oxidized, or the binding energy of the adsorbed oxygen vacancies is small and the bond energy is weak, making it easier to capture active oxygen and avoid its leakage, thereby reducing the side reactions between the cathode material surface and the electrolyte. On the other hand, the large half-peak width of the first and second characteristic peaks indicates that active oxygen and adsorbed oxygen vacancies have a wide bond energy range, which allows the cathode material to withstand a wider range of voltage changes, further improving the cycle stability of the cathode material. Attached Figure Description

[0012] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0013] Figure 1 shows a schematic diagram of a battery in a discharged state, i.e., during operation.

[0014] Figure 2 shows the XPS spectrum of O1s obtained from the test of Comparative Example 1;

[0015] Figure 3 shows the XPS spectrum of O1s obtained from the cathode material test of Example 1 of this application;

[0016] Figure 4 shows a flowchart of a method for preparing a cathode material according to some embodiments of this application;

[0017] Figure 5 shows a flowchart of the preparation method of the cathode material in some other embodiments of this application;

[0018] Figure 6 shows a comparison of the cycle retention rates of Example 1 and Comparative Example 1. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0022] As used in this specification and claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [described condition or event] is detected," or "in response to detection of [described condition or event]."

[0023] The specific embodiments of this application are described in detail below with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the embodiments of this application are obtained through conventional commercial channels.

[0024] Figure 1 shows a schematic diagram of a battery in a discharged state, i.e., during operation. As shown in Figure 1, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator 130 disposed between the positive electrode 110 and the negative electrode 120. The electrode assembly can be a stacked structure, formed by alternately stacking the separator 130, the positive electrode 110, the separator 130, and the negative electrode 120. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the separator, the positive electrode, the separator, and the negative electrode.

[0025] Positive electrode sheet: The positive electrode sheet 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining a conductive foil (aluminum foil or nickel foil, etc.) and a polymer substrate. The positive active layer 112 contains the positive electrode material described below.

[0026] Negative electrode sheet: The negative electrode sheet 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer includes a negative electrode material. The negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc.

[0027] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, and are embedded in the lattice of the positive electrode material.

[0028] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, and the metal ions are embedded in the lattice of the negative electrode material.

[0029] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0030] In some embodiments, the silicon-based material in the negative electrode material may include at least one of elemental silicon, amorphous silicon, crystalline silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, silicate, and silicon alloy.

[0031] In some embodiments, the silicon-based material includes silicon oxide, which includes silicon and oxygen elements, with an atomic ratio of oxygen to silicon of 0 to 2, excluding 0.

[0032] In some embodiments, the silicon-based material includes silicon oxide, which has the general chemical formula SiOx, where 0 < x ≤ 2. Specifically, SiOx can be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5SiO 1.8 SiO 1.9 etc. are not specified here.

[0033] Silicon oxides can be represented by the general formula SiOx (0 < x ≤ 2). They can be materials formed by silicon dispersed in SiO2; or they can be materials with tetrahedral structural units, where silicon atoms are located at the center of the tetrahedral structural units, and oxygen atoms and / or silicon atoms are located at the four vertices of the tetrahedral structural units.

[0034] In some embodiments, the graphite material in the negative electrode material may include at least one of natural graphite, artificial graphite, expanded graphite, and graphite oxide.

[0035] In some embodiments, the negative electrode material includes a carbon material, which includes at least one of amorphous carbon and graphitized carbon.

[0036] In some embodiments, the tin-based material in the negative electrode material may include at least one of elemental tin, tin oxide, and tin alloy.

[0037] This application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0038] Because the charge-discharge reaction process of cathode materials always proceeds from the particle surface to the core, the charge-discharge depth of the particle surface is always higher than that of the particle core. Furthermore, the failure process of cathode materials is also based on this reason: the continuous deep charge-discharge reaction causes the particle surface to fail first. Without the protection of the surface layer, the failure reaction rapidly spreads to the particle core, ultimately leading to the failure of the entire material. Therefore, the stability of the surface structure of cathode materials is crucial, and improving the stability of the surface structure can significantly improve the overall performance of the cathode material.

[0039] The inventors increased the stability of the surface structure of the cathode material by optimizing the process. Their research revealed that changes in the performance of the cathode material can be reflected in the distribution of oxygen types (active oxygen and vacancy-adsorbed oxygen) on the particle surface. Specifically, this application obtained at least two characteristic peaks after peak-splitting of the O1s characteristic peak: a first characteristic peak (splitting 1) and a second characteristic peak (splitting 2). On the one hand, the peak spacing between the first and second characteristic peaks is ≤2.4 eV, indicating that the binding energy of the active oxygen characteristic peak on the cathode material surface is relatively large, the bond energy is strong, and the active oxygen is more difficult to oxidize. On the other hand, the binding energy of the adsorbed oxygen vacancies is relatively small, the bond energy is weak, and it is easier to capture active oxygen, preventing its leakage. This suppresses side reactions between the cathode material surface and the electrolyte, improving cell safety and cycle life. On the other hand, the separation degree between the first and second characteristic peaks is ≤1.0, indicating that the peak spacing between the first and second characteristic peaks in the cathode material is small and the half-peak width is large. Thus, on the one hand, the small peak spacing between the first and second characteristic peaks indicates that the binding energy of the active oxygen characteristic peaks is large and the bond energy is strong, making it more difficult for active oxygen to be oxidized, or the binding energy of the adsorbed oxygen vacancies is small and the bond energy is weak, making it easier to capture active oxygen and avoid its leakage, thereby reducing the side reactions between the cathode material surface and the electrolyte. On the other hand, the large half-peak width of the first and second characteristic peaks indicates that active oxygen and adsorbed oxygen vacancies have a wide bond energy range, which allows the cathode material to withstand a wider range of voltage changes, further improving the cycle stability of the cathode material.

[0040] In some embodiments of this application, in the XPS spectrum of the cathode material, the oxygen element O1s characteristic peak on the surface of the cathode material can be divided into at least two characteristic peaks after peak separation processing, including: a first characteristic peak in the range of 529.0±0.5eV and a second characteristic peak in the range of 531.2±0.5eV, wherein the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0.

[0041] It should be noted that the O1s characteristic peak of oxygen on the surface of the cathode material refers to the fine spectrum of the O1s orbital (i.e., the 1s orbital of oxygen) obtained by XPS (X-ray photoelectron spectroscopy) characterization of the cathode material surface. In the XPS spectrum of the cathode material, after separating the O1s characteristic peak, the first and second characteristic peaks can be obtained. The peak position (binding energy) of the first characteristic peak is located at 529.0 ± 0.5 eV. This first characteristic peak is the characteristic peak of active oxygen, which refers to the active chemical form of oxygen. The peak position (binding energy) of the second characteristic peak is located at 531.2 ± 0.5 eV. This second characteristic peak is the characteristic peak of adsorbed oxygen vacancies. Oxygen vacancies can accommodate some of the overflowing active oxygen under high-voltage charging conditions, reducing side reactions between the cathode material surface and the electrolyte.

[0042] The separation degree between the first characteristic peak and the second characteristic peak can be calculated using formula (1):

[0043]

[0044] In formula (1), α represents the separation degree between the first and second characteristic peaks on the surface of the cathode material; P3 represents the peak position of the second characteristic peak, P1 represents the peak position of the first characteristic peak, and P3-P1 represents the peak position spacing between the first and second characteristic peaks; FWHM1 represents the full width at half maximum (FWHM1) of the first characteristic peak, and FWHM3 represents the full width at half maximum (FWHM3) of the second characteristic peak. The FWHM1 refers to the peak width at half the peak height of the characteristic peak, which is mainly affected by the bond energy range formed by oxygen and the transition metal. An increase in the bond energy range corresponds to an increase in the FWHM1, while a decrease in the bond energy range corresponds to a relative decrease in the FWHM1.

[0045] Based on the above formula (1), it can be seen that the resolution is mainly affected by the peak spacing and full width at half maximum (FWHM) between the first and second characteristic peaks. The smaller the peak spacing between the first and second characteristic peaks, the smaller the resolution. The larger the peak spacing between the first and second characteristic peaks, the greater the resolution. The larger the FWHM between the first and second characteristic peaks, the smaller the resolution. The smaller the FWHM between the first and second characteristic peaks, the greater the resolution.

[0046] In the embodiments of this application, the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0, indicating that the peak spacing between the first and second characteristic peaks in the cathode material is small and the half-peak width is large. Thus, on the one hand, the small peak spacing between the first and second characteristic peaks indicates that the binding energy of the active oxygen characteristic peak is large and the bond energy is strong, making it more difficult for active oxygen to be oxidized, or the binding energy of the adsorbed oxygen vacancy is small and the bond energy is weak, making it easier to capture active oxygen and avoid its leakage, thereby reducing the side reactions between the cathode material surface and the electrolyte. On the other hand, the large half-peak width of the first and second characteristic peaks indicates that active oxygen and adsorbed oxygen vacancy have a wide bond energy range, thus enabling the cathode material to withstand a wider range of voltage changes and further improving the cycle stability of the cathode material.

[0047] Specifically, the separation degree between the first characteristic peak and the second characteristic peak can be within the range of 1.0, 0.98, 0.97, 0.96, 0.95, 0.94, 0.92, 0.9, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, 0.82, 0.81, 0.8, 0.79, 0.78, 0.77, 0.76, 0.75, 0.74, 0.73, 0.72, 0.71, 0.7, 0.68, 0.66, 0.65, 0.64, 0.62, 0.6, 0.58, 0.56, 0.55, 0.54, 0.52, 0.5, or any combination thereof. Preferably, the separation degree between the first characteristic peak and the second characteristic peak is ≤0.9.

[0048] In some implementations, the peak spacing between the first characteristic peak and the second characteristic peak is ≤2.4eV, indicating that the binding energy of the active oxygen characteristic peak on the surface of the cathode material is large and the bond energy is strong, making it more difficult for active oxygen to be oxidized. Alternatively, the binding energy of the adsorbed oxygen vacancy is small and the bond energy is weak, making it easier to capture active oxygen and prevent its leakage. This suppresses the side reactions between the cathode material surface and the electrolyte, thereby improving the safety and cycle life of the battery cell. Specifically, the peak spacing between the first characteristic peak and the second characteristic peak can be within the range of 2.4 eV, 2.35 eV, 2.32 eV, 2.31 eV, 2.3 eV, 2.2 eV, 2.17 eV, 2.1 eV, 2.09 eV, 2.02 eV, 2.0 eV, 1.96 eV, 1.94 eV, 1.93 eV, 1.92 eV, 1.91 eV, 1.9 eV, 1.89 eV, 1.88 eV, 1.87 eV, 1.85 eV, 1.84 eV, 1.8 eV, 1.79 eV, 1.76 eV, 1.75 eV, 1.72 eV, 1.7 eV, 1.6 eV, 1.57 eV, 1.5 eV, or any combination thereof.

[0049] Preferably, the peak spacing between the first and second characteristic peaks is ≤2.3 eV. It should be noted that the peak position of the second characteristic peak (i.e., the bond energy of vacancy-adsorbed oxygen) is closely related to the material's crystal lattice structure and is relatively stable, usually a fixed value. The peak position of the first characteristic peak (i.e., the bond energy of active oxygen) is easily affected by the surface state of the cathode material and the state of surrounding ions, and is prone to shift fluctuations. Therefore, a smaller peak spacing between the first and second characteristic peaks usually indicates an increase in the bond energy of active oxygen, a larger peak position (binding energy) of the first characteristic peak, meaning a larger binding energy and stronger bond energy for the active oxygen characteristic peak, making it more difficult for active oxygen to be oxidized, thereby suppressing side reactions between the cathode material surface and the electrolyte.

[0050] In some embodiments, the full width at half maximum (FWHM) of the second characteristic peak is ≥2.9 eV, indicating that the bond energy range of the vacant adsorbed oxygen on the surface of the cathode material is relatively wide, and the tolerance of the adsorbed oxygen bonds on the surface of the cathode material is enhanced (that is, it can tolerate the changes in valence state of the transition metal ions (such as Ni, Co, Mn / Al, etc.) bonded to it) in a wider range). This allows the oxygen bonds on the surface of the cathode material to balance the charge distribution in a wider range without breaking, thereby significantly enhancing the structural stability of the material and improving its high voltage withstand capability, cycle stability, safety and other performance characteristics. Specifically, the full width at half maximum (FWHM) of the second characteristic peak can be, for example, 2.9 eV, 2.95 eV, 2.98 eV, 2.99 eV, 3.0 eV, 3.02 eV, 3.06 eV, 3.09 eV, 3.1 eV, 3.12 eV, 3.14 eV, 3.17 eV, 3.2 eV, 3.25 eV, 3.26 eV, 3.27 eV, 3.3 eV, 3.31 eV, 3.35 eV, 3.37 eV, 3.38 eV, 3.4 eV, 3.41 eV, 3.42 eV, 3.44 eV, 3.45 eV, 3.48 eV, 3.5 eV, 3.51 eV, 3.6 eV, 3.7 eV, 3.8 eV, 3.82 eV, 3.9 eV, or any combination thereof. Preferably, the full width at half maximum (FWHM) of the second characteristic peak is ≥2.95 eV.

[0051] In some embodiments, the O1s characteristic peak of oxygen on the surface of the cathode material can be divided into three characteristic peaks after peak-splitting: the first characteristic peak, the third characteristic peak, and the second characteristic peak. This embodiment uses Figure 3 as an example. In Figure 3, the first characteristic peak is peak-splitting 1, the third characteristic peak is peak-splitting 3, and the second characteristic peak is peak-splitting 2. As shown in Figure 3, the horizontal axis of the XPS spectrum represents the electron binding energy (eV), and the vertical axis represents the intensity. "XPS test - O1s" indicates the surface oxygen O1s characteristic peak obtained by XPS testing of the material. O1s refers to the energy spectrum of the 1s orbital electrons of oxygen in X-ray photoelectron spectroscopy (XPS). In the XPS spectrum, the O1s characteristic peak can characterize the valence electron state of oxygen on the material surface. By analyzing the position, shape, and area of ​​the O1s characteristic peak, the chemical state and environmental information of oxygen in the material can be characterized. Specifically, by dividing the O1s characteristic peak, different types of oxygen can be distinguished, such as vacancy-adsorbed oxygen, active oxygen, and oxygen in residual alkali. Based on the positions of each peak (i.e., peak positions), it can be determined that "peak 1" in the figure represents the first characteristic peak of active oxygen, "peak 2" represents the second characteristic peak of vacancy-adsorbed oxygen, and "peak 3" represents the third characteristic peak of residual alkali oxygen on the material surface. Here, the third characteristic peak of residual alkali oxygen refers to the characteristic peak of oxygen in the residual alkali (such as LiOH, Li2CO3, Li2O, etc.) formed on the material surface. The "peak summary" in the figure represents the spectrum after summarizing the peaks, which is used to compare with the original O1s characteristic peak before peaking to verify the accuracy of the peaking results.

[0052] Furthermore, the oxygen content corresponding to the residual alkali formed by the bonding of Li with the cathode material surface also affects the processing performance of the cathode material slurry. A higher oxygen content corresponds to a higher residual alkali content, leading to a greater degree of reaction between the cathode material and NMP ("N-methylpyrrolidone") solvent. This results in increased slurry viscosity during electrode fabrication, leading to increased NMP solvent usage, which not only increases costs but also negatively impacts electrode coating effectiveness. Additionally, a higher residual alkali content can cause electrochemical oxidation decomposition reactions during battery charging, resulting in cell gas generation and reduced initial coulombic efficiency (i.e., first-time efficiency). To improve the processing performance of the cathode material, in some embodiments, the area of ​​the third characteristic peak of residual alkali oxygen on the cathode material surface accounts for ≤8.5% of the total area of ​​the O1s characteristic peak. This indicates a lower oxygen content corresponding to the residual alkali formed by the bonding of Li with the cathode material surface, which reduces the degree of reaction between the material and NMP solvent, lowers the slurry viscosity during electrode fabrication, and improves the material's processing performance. It also reduces the electrochemical oxidation reaction of residual alkali during charging, lowers cell gas generation, and improves the first-time efficiency.

[0053] In some embodiments, the cathode material includes a lithium transition metal oxide. Specifically, the lithium transition metal oxide can be one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, or lithium nickel oxide. Specifically, the cathode material can be characterized by inductively coupled plasma optical emission spectrometry (ICP-OES) or intramolecular plasma mass spectrometry (ICP-MS) to determine the presence of lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn) / aluminum (Al) and their elemental ratios to characterize the cathode material as a lithium transition metal oxide. The cathode material can also be characterized by X-ray diffraction (XRD). The XRD pattern showing that the cathode material includes a layered α-NaFeO2 structure, a rock salt phase structure, a spinel phase structure, or a combination thereof characterizes the cathode material as a lithium transition metal oxide.

[0054] In some implementations, the cathode material has the general formula: Li λ Ni a Co b M c M' e M” 1-a-b-c-e O2, wherein 0.95≤λ≤1.3, 0.3≤a<1.0, 0.01≤b≤0.33, 0≤c≤0.5, 0≤e≤0.01, 0≤1-abce≤0.01, M includes Mn and / or Al, M' includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy, and M” includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy.

[0055] For example, λ can be 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, etc.; a can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc.; b can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, etc.; c can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.; and e can be 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, etc. The M' element and the M” element in the above cathode material can be the same or different.

[0056] In other embodiments, the free lithium content per unit area of ​​the surface of the cathode material is 200 μg / m². 2 ~800μg / m 2 For example, the free lithium content is 200 μg / m³. 2 250μg / m 2300μg / m 2 350μg / m 2 400μg / m 2 450μg / m 2 500μg / m 2 550μg / m 2 600μg / m 2 650μg / m 2 700μg / m 2 750μg / m 2 800μg / m 2 .

[0057] Free lithium on the surface of the cathode material can react with NMP, the solvent used in electrode processing. Excessive free lithium content can lead to gel-like or jelly-like defects in the slurry. The conventional free lithium content refers to the free lithium contained per unit mass of the material. This numerical value alone cannot determine whether it affects the slurry's processing performance. This is because the solvent NMP reacts with the Li within the surface area of ​​the material particles it contacts. Therefore, the processing performance of the slurry is related to the free Li concentration per unit area of ​​the cathode material, not the free lithium concentration per unit weight. For example, some materials may have a relatively low free lithium content per unit mass, but if the specific surface area of ​​the material particles is even lower, the free lithium concentration per unit surface area will be high, easily leading to high slurry viscosity and a jelly-like consistency. Therefore, the free lithium content per unit surface area of ​​the cathode material should be 200 μg / m². 2 ~800μg / m 2 This indicates that the cathode material has good processing performance.

[0058] It should be noted that the free lithium content per unit area of ​​the cathode material in this article refers to the ratio of the free lithium content per unit mass of the cathode material to the specific surface area of ​​the cathode material.

[0059] In some embodiments, the cathode material is a single-crystal cathode material, and the average particle size of the cathode material is 1 μm to 10 μm. The cathode material contains at least one particle with the same orientation. For example, the average particle size of the cathode material can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or other values ​​within the range of 1 μm to 10 μm. It should be noted that the average particle size of the cathode material can be determined by taking five electron microscope images at 3K magnification using a Hitachi S4800 scanning electron microscope at different positions, or by taking five cross-sectional electron microscope images at different positions at 3K magnification after preparing the sample. These electron microscope images should be imported into Nano Measure software, and random measurements should be performed using Nano Measure software. The diameter of the circumcircle of the particle completely exposed in the field of view is the particle size. At least 200 particles should be counted, and the average value should be taken as the average value for one set of measurements. A single-crystal particle completely appearing in the electron microscope image's field of view means that the outline of the single-crystal particle is completely displayed in the electron microscope image, and the outline of the single-crystal particle is not covered by other single-crystal particles in the field of view or divided by the boundaries of the electron microscope image.

[0060] It is important to clarify that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., secondary particles composed of primary particles) lies in the fact that the smallest particles in polycrystalline secondary particles are formed by the aggregation of nanoscale particles. In contrast, the smallest particles in single-crystal cathode materials are typically micrometer-sized individual particles. Generally, in addition to backscattered electron diffraction (EBSD) testing, scanning electron microscopy (SEM) and other characterization methods can be used to determine whether the obtained cathode product is a single-crystal material. For example, for single-crystal cathode materials, SEM can characterize the morphology of single-crystal particles, showing that they are generally regular or irregular spherical in shape, with no significant particle aggregation. EBSD can also characterize the orientation of single-crystal cathode materials; by observing that at least one grain has the same color, it can be determined that at least one grain has the same orientation, and grains with the same orientation are single crystals. It is important to note that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal is a crystal with completely identical arrangement and orientation. However, due to limitations caused by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in this field are actually more often "single-crystal morphology" cathode materials, which only differ from polycrystalline materials composed of numerous small primary particles in size due to their large particle size resembling single crystals.

[0061] It should be noted that the aforementioned single-crystal cathode material may also contain a small number of "quasi-secondary particles" formed by the adhesion of up to 10 primary particles. "Primary particles" refer to the smallest particle unit identified when observing cathode active materials using a scanning electron microscope.

[0062] It is important to clarify that the "single-crystal material" known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations imposed by impurities, strain, and crystal defects, ideal single crystals are extremely rare and difficult to produce in reality. Therefore, the single-crystal materials known in the art are actually more accurately described as "single-crystal-like" cathode materials, which differ from polycrystalline particles composed of numerous small particles only in size due to their large, single-crystal-like particle size.

[0063] In some embodiments, the cathode material includes a matrix material and a surface structure, wherein the surface structure is located on at least a portion of the surface of the matrix material, and the surface structure includes at least one element selected from Ni, Co, and Na. It should be noted that the Ni, Co, and Na elements in the surface structure can be obtained by characterizing the surface of the cathode material using X-ray photoelectron spectroscopy (XPS). In a second aspect, this application provides a surface reconstruction material for a cathode material, which can be used to form the surface structure of the cathode material described in any of the first aspects, and the surface reconstruction material includes Ni. x Co y M z M” 1-x-y-z OOH, Ni x Co y M z M” 1-x-y-z (OH)2、(Ni x Co y M z M” 1-x-y-z )O d At least one of the following, wherein 0≤x≤0.6, 0.4≤y≤1, 0≤z≤0.6, 0≤1-xyz≤0.15, 1≤d≤2, M includes Mn and / or Al, and M" includes at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy; the Na content in the surface reconstruction material ranges from 50ppm to 300ppm.

[0064] For example, x can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, etc.; y can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, etc.; z can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, etc.; and d can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc. The Na content in the surface reconstruction material can be 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 110ppm, 120ppm, 130ppm, 140ppm, 150ppm, 160ppm, 170ppm, 180ppm, 190ppm, 200ppm, 210ppm, 220ppm, 230ppm, 240ppm, 250ppm, 260ppm, 270ppm, 280ppm, 290ppm, 300ppm, etc.

[0065] In some implementations, the median particle size D50 of the surface reconstruction material satisfies: 10nm ≤ D50 ≤ 1000nm. For example, the median particle size D50 of the surface reconstruction material can be 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, etc. During the surface reconstruction of micron-sized matrix materials (e.g., median particle size of 3–20µm), the nanoscale surface reconstruction material can effectively and uniformly coat the surface of the matrix material, rather than simply mixing it. This results in a uniform surface thickness of the reconstructed cathode material, providing more effective and durable protection for the matrix material within the cathode material. It should be noted that the median particle size D50 represents the particle size of the material when the cumulative particle size distribution percentage reaches 50% by volume.

[0066] In other embodiments, the loose bulk density (AD) of the surface reconstruction material is ≤0.6 g / cm³. 3 For example, the loose bulk density AD can be 0.1 g / cm³. 3 0.15g / cm 3 0.2g / cm 3 0.25g / cm 3 0.3g / cm 30.35g / cm 3 0.4g / cm 3 0.45g / cm 3 0.5g / cm 3 0.55g / cm 3 0.6g / cm 3 The median particle size of the surface reconstruction material is in the nanometer range, resulting in a lower loose packing density. For the micrometer-sized matrix material, the loose packing density is higher than that of the surface reconstruction material. This difference in loose packing density between the matrix and surface reconstruction materials leads to inconsistent particle movement rates under the force of the stirring blades during mixing, resulting in relative motion. This allows the surface reconstruction material to be dispersed more effectively and uniformly, achieving a better coating effect on the matrix material.

[0067] In some other embodiments, the specific surface area (BET) of the surface reconstruction material is ≥20 m². 2 / g. For example, the specific surface area BET can be 20m². 2 / g、30m 2 / g, 50m 2 / g、80m 2 / g, 120m 2 / g, 140m 2 / g、160m 2 / g、180m 2 / g etc. The higher the BET of the surface reconstruction material, the higher its reactivity in the second sintering process, and the easier it is to generate the structure with surface oxygen element O1s characteristics described in the embodiments of this application.

[0068] In some embodiments, this application employs nanoscale hydroxyl oxides, hydroxides, and / or oxides composed of multiple elements such as Ni, Co, M, and M' as surface reconstruction materials. The elemental composition of these materials is essentially the same as that of the NCM material's core, resulting in minimal difference in lattice parameters. This allows for chemical bonding and strong adhesion, significantly improving the cycle life and DCIR amplification of the cathode material. Conventional oxide coatings or lithium cobalt oxide coatings, on the other hand, have significantly different lattice parameters from the NCM material's core. They are mostly physically attached rather than chemically bonded to the NCM material's surface, resulting in weak adhesion. Consequently, during long-term charge-discharge cycles, as the lattice parameters of the NCM material's core continuously change, conventional coatings are prone to detaching from the NCM substrate, leading to coating failure and impacting material performance.

[0069] Furthermore, in some embodiments, the surface reconstruction material coats at least a portion of the surface of the matrix material. The Ni content in the surface reconstruction material is lower than the Ni content in the matrix material, and the Co content in the surface reconstruction material is higher than the Co content in the matrix material. During the preparation of cathode materials using the surface reconstruction material and the matrix material, when the Ni content in the surface reconstruction material is lower than that in the matrix material (i.e., x in the chemical formula of the surface reconstruction material is less than f in the chemical formula of the matrix material below), and the Co content is higher than that in the matrix material (i.e., y in the chemical formula of the surface reconstruction material is greater than g in the chemical formula of the matrix material), the binding ability of Ni to surface active oxygen is weaker, while the binding ability of Co to surface active oxygen is stronger. Simultaneously, the surface reconstruction material also contains 50 ppm to 300 ppm of sodium. + With a small difference in ionic radius compared to transition metals, Na can locally embed itself in surface lattice interstices or substitute for trace metal sites. + The surface-reconstructed material carries less charge than transition metal elements, weakening the polarization of oxygen in the metal-oxygen bond structure and increasing the bond energy range of the metal-oxygen bond. Therefore, this surface-reconstructed material can bond with active oxygen on the surface of the matrix material, converting some active oxygen into vacant adsorbed oxygen, while simultaneously increasing the bond energy of the remaining active oxygen, reducing the peak spacing between the first characteristic peak of active oxygen and the second characteristic peak of vacant adsorbed oxygen, increasing the full width at half maximum (FWHM) of the second characteristic peak, and decreasing the separation between the first and second characteristic peaks, thus obtaining the cathode material after surface reconstruction in the embodiments of this application. To facilitate understanding of the process of preparing cathode materials through surface-reconstructed material and matrix material in the embodiments of this application, a detailed description will be provided below with reference to Figures 4 and 5.

[0070] In a third aspect, this application also provides a method for preparing a cathode material, which will be described exemplarily below with reference to FIG4.

[0071] Figure 4 shows a flowchart of a method for preparing a cathode material according to some embodiments of this application. As shown in Figure 4, preparation method 400 may include: in step S402, a matrix material and a surface reconstruction material according to any one of the second aspects of this application may be mixed a second time to obtain a second mixture, wherein the matrix material is a lithium nickel cobalt composite oxide. The matrix material may be a conventional NCM material or other existing lithium nickel cobalt composite oxides rich in lithium.

[0072] In other embodiments, the matrix material may have the general chemical formula: Li k Ni f Co g M h M' 1-f-g-hO2, wherein 1.0≤k≤1.3, 0.3≤f<1.0, 0.01≤g≤0.33, 0≤h≤0.5, 0≤1-fgh≤0.01, M includes Mn and / or Al, and M' includes one or more of Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy. For example, k can be 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, etc., f can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., g can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.33, etc., and h can be 0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, etc.

[0073] The matrix material and the aforementioned surface reconstruction material may contain the same or different M element. The M” element in the surface reconstruction material and the M' element in the aforementioned matrix material may contain the same or different M element. In some preferred embodiments, the M element in the surface reconstruction material is the same as the M element in the matrix material, and / or the M” element in the surface reconstruction material is the same as the M' element in the matrix material, making the composition of the surface reconstruction material and the matrix material more similar or completely identical, facilitating bonding between the surface reconstruction material and the matrix material, thereby further improving the stability of the cathode material's surface structure.

[0074] This application's embodiments achieve the reconstruction of the substrate material's surface structure by using a surface reconstruction material with the same or similar composition as the substrate material to coat the substrate material. Chemical bonding occurs between the reconstructed surface layer and the substrate material, and the reconstructed surface layer maintains the same crystal structure and lattice parameters as the substrate material. This results in a more stable structure for the cathode material, continuously protecting the substrate material from electrolyte corrosion and mitigating cracking and pulverization of cathode material particles under high-voltage conditions. Consequently, it improves the cathode material's cycle life and safety performance.

[0075] In the embodiments of this application, k ≥ 1.0 indicates that the lithium content in the matrix material used to prepare the cathode material is excessive. With this setting, during the reaction between the matrix material and the surface reconstruction material, some lithium elements in the matrix material can be transferred to the surface reconstruction material to form a lithium-containing compound (i.e., to form the surface structure in the cathode material).

[0076] In other embodiments, during the second mixing, the molar ratio of the matrix material to the surface reconstruction material can be controlled to be 1:(0.005 to 0.1). Exemplary examples include molar ratios of 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, and 1:0.1. In some preferred embodiments, during the second mixing, the molar ratio of the matrix material to the surface reconstruction material can be controlled to be 1:(0.01 to 0.05).

[0077] When the amount of surface reconstruction material is too small, the reconstructed surface structure cannot adequately protect the surface of the substrate material, and the concentration of surface active oxygen remains high in some locations, limiting its improvement on the battery's electrical performance, such as gas generation and cycle performance. When the amount of surface reconstruction material is too large, the thickness of the surface structure increases, preventing Li ions in the substrate material from fully transferring to the surface of the cathode material to form lithium-containing compounds with the surface reconstruction material. This weakens the bonding between the reconstructed surface structure and the substrate, making the surface structure prone to detachment and affecting the cycle performance and DCIR performance of the cathode material.

[0078] Within the aforementioned molar ratio of matrix material to surface reconstruction material, the surface reconstruction material can completely and uniformly cover the entire surface of the matrix material without affecting the conversion process of the surface reconstruction material to lithium-containing compounds. This provides better protection for the matrix material, continuously protecting it from electrolyte erosion. Simultaneously, it allows some of the active oxygen on the original surface of the matrix material to be converted into vacant adsorbed oxygen, significantly improving the surface structure stability of the cathode material. This results in the XPS spectrum of the prepared cathode material exhibiting the characteristics described above, further enhancing the cycle life, DCIR, and other performance characteristics of the cathode material.

[0079] Furthermore, it is understood that since the surface reconstruction material in the embodiments of this application has the same or similar composition as the matrix material, the amount of surface reconstruction material added in the embodiments of this application can be much higher than the amount of conventional oxide coating in the prior art (the molar ratio of conventional oxide coating to matrix material is usually less than 0.005:1). This not only increases the thickness of the surface structure to better protect the matrix material, but also helps to improve the structural stability, cycle life, DCIR and other performance of the cathode material.

[0080] In other embodiments, the Ni content in the matrix material is higher than that in the surface reconstruction material, and the Co content in the matrix material is lower than that in the surface reconstruction material. Since Ni has a weaker binding affinity to surface reactive oxygen species, while Co has a stronger binding affinity, this facilitates the surface reconstruction material's ability to bond with reactive oxygen species on the matrix material surface. This converts some of the reactive oxygen species into vacancy-adsorbed oxygen, while simultaneously increasing the bond energy of the remaining reactive oxygen species. This reduces the peak-to-peak distance between the first characteristic peak of the reactive oxygen species and the second characteristic peak of the vacancy-adsorbed oxygen, increases the full width at half maximum (FWHM) of the second characteristic peak, and decreases the separation between the first and second characteristic peaks.

[0081] In other embodiments, the surface reconstruction material also contains 50 ppm to 300 ppm of sodium. + With a small difference in ionic radius compared to transition metals, Na can locally embed itself in surface lattice interstices or substitute for trace metal sites. + The amount of charge carried is less than that of transition metal elements, which weakens the polarization of oxygen in the metal-oxygen bond structure and increases the bond energy range of the metal-oxygen bond, thereby helping to increase the full width at half maximum (FWHM) of the first and second characteristic peaks.

[0082] In other embodiments, in step S402, a second mixing can be performed in a CO2 atmosphere with a CO2 volume concentration ≥80%, such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc. Unlike conventional mixing and coating conditions that use dry air, the preparation method of this application uses a CO2 atmosphere for the second mixing. This is because CO2 readily reacts with Li2O or LiOH on the surface of the matrix material to form Li2CO3, which adheres to the surface of the matrix material particles. This makes it easier for the surface reconstruction material used in this application to react with the matrix material, forming a Li-containing compound (i.e., the surface material) with the same composition as the matrix material, thereby achieving the reconstruction of the matrix material surface and forming the positive electrode material of this application.

[0083] In some other embodiments, during step S402, when performing the second mixing in the CO2 atmosphere, the CO2 atmosphere may contain a water concentration of 0.05% to 10% by volume, for example, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10%, etc. The presence of water in the CO2 atmosphere will help to further improve the reaction rate and degree of reaction between Li2O or LiOH on the substrate material surface and CO2, as well as the reaction rate and degree of reaction between Li2CO3 and the surface reconstruction material. When the water volume concentration is too low, the improvement effect on the reaction rate and degree of reaction is not significant, and the difference from that under a pure CO2 atmosphere is not significant. When the volume concentration of water is too high, water is prone to condense and precipitate into a liquid state, causing material particles to agglomerate and making it difficult for the surface reconstruction material to coat evenly.

[0084] In some embodiments, during the second mixing in step S402, an M” element additive may be added, controlling the molar ratio of the matrix material, the surface reconstruction material, and the M” element additive to be 1:(0.005~0.1):(0.0001~0.01), for example 1:0.005:0.0001, 1:0.005:0.0005, 1:0.005:0.001, 1:0.005:0.002, 1:0.005:0.005, 1:0.01:0.0001, 1:0.01:0.0005, 1:0.01:0.001, 1:0.01:0.002, 1:0.01:0.002, 1:0.01:0.005, 1: 0.01:0.01, 1:0.02:0.0001, 1:0.02:0.0005, 1:0.02:0.001, 1:0.02:0.002, 1:0.02:0.005, 1:0.02:0.01, 1:0.05:0.0001, 1:0.05:0.005, 1:0.05:0.001, 1:0.05:0.002, 1:0.05:0.005, 1:0.05:0.01, 1:0.1:0.0001, 1:0.1:0.0005, 1:0.1:0.001, 1:0.1:0.002, 1:0.1:0.005, 1:0.1:0.01, etc.

[0085] In some embodiments, when the surface reconstruction material does not contain the M" element, an M" element additive can be added during the second mixing. In other embodiments, when the M" element content in the surface reconstruction material is too low, an M" element additive can be added during the second mixing. The addition of the M" element helps to increase lattice defects in the formed surface material, thereby further improving the conductivity of the cathode material. When the amount of M" element additive added is too low, the improvement effect on the conductivity of the cathode material is not significant. However, since the conductivity of the M" element additive itself is usually worse than that of the matrix material, excessive addition of the M" element additive will affect the formation of the layered structure of the cathode material and the overall conductivity of the cathode material.

[0086] In some embodiments, the "M" element additive may include at least one of the following: oxides, hydroxides, hydrochlorides, basic carbonates, fluorides, and borides of the "M" element. The "M" element includes one or more of the following elements: Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

[0087] In other embodiments, during the second mixing in step S402, the second mixing speed is ≥300 rpm and the second mixing time is ≥15 min. A second mixing speed that is too low or a second mixing time that is too short is detrimental to the uniform mixing of the second mixture. A sufficiently high second mixing speed and a sufficiently long second mixing time facilitate thorough mixing of the second mixture, allowing the surface reconstruction material to uniformly and completely coat the surface of the matrix material, thereby promoting the formation of cathode material particles with more uniform composition, structure, and particle size.

[0088] As further shown in Figure 4, the preparation method also includes step S404, in which the second mixture is subjected to a second sintering at a temperature of 600℃ to 900℃ to obtain the cathode material. Exemplarily, the second sintering temperature can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc. When the second sintering temperature is <600℃, it is difficult to form stable chemical bonds between the surface reconstruction material and the matrix material. The formed surface material can only be physically attached to the surface of the matrix material, making it difficult to form a stable surface structure on the matrix material surface. When the second sintering temperature is >900℃, due to the increased atomic diffusion and rearrangement rates at high temperatures, the surface reconstruction material will fully diffuse into the matrix material, forming a uniform material composition. It is impossible to obtain a cathode material with a core-shell structure, and thus the improvement effect on the distribution and relative content of active oxygen and vacancy adsorbed oxygen types on the surface of the cathode material cannot be achieved. Therefore, a second sintering temperature in the range of 600℃ to 900℃ is beneficial for forming a stable surface structure on the base material.

[0089] In other embodiments, the second sintering time can be 4 to 10 hours, and the second sintering atmosphere is air and / or oxygen. Exemplarily, the second sintering time can be, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, etc. Since it takes time for lithium ions in the matrix material to diffuse into the surface reconstructed material, if the second sintering time is too short, the surface reconstructed material and the matrix material cannot be guaranteed to react sufficiently. If the second sintering time is too long, it does not significantly improve the performance of the prepared cathode material, but it will increase the production cost of the cathode material, which is not conducive to the industrialization and commercial value of the product. Therefore, controlling the second sintering time to 4 to 10 hours is beneficial to ensuring the full progress of the second sintering reaction and is also more suitable for industrial applications.

[0090] In some other embodiments, the heating rate of the second sintering process can be ≤5℃ / min. For example, the heating rate of the second sintering process can be, for example, 0.5℃ / min, 1.0℃ / min, 2.0℃ / min, 2.5℃ / min, 3.0℃ / min, 4.0℃ / min, 5.0℃ / min, etc. Since the amount of surface reconstruction material used is relatively large, a completely new surface layer will be generated on the surface of the base material during the second sintering process, achieving the effect of surface reconstruction. However, if the heating rate is too fast, the stress between the surface reconstruction layer and the base material will not be effectively released, resulting in insufficient bonding and failing to achieve the desired improvement in the material's cycle performance.

[0091] Furthermore, Figure 5 shows a flowchart of a method for preparing a cathode material according to other embodiments of this application. As shown in Figure 5, the preparation method 500 may include: in step S501, a matrix precursor and a lithium source may be first mixed to obtain a first mixture. In some embodiments, the matrix precursor includes at least one of nickel-cobalt metal oxides, hydroxides, carbonates, and basic carbonates. In other embodiments, the lithium source includes at least one of Li₂CO₃, LiOH·H₂O, LiOH, Li₂O, Li₂O₂, and LiF.

[0092] In some other embodiments, during the first mixing in step S501, the molar ratio of the matrix precursor to the lithium source can be controlled to be 1:(1.0 to 1.3), for example, 1:1, 1:1.01, 1:1.06, 1:1.3, etc. This molar ratio range ensures that the lithium source is sufficient during the preparation of the matrix material, so as to obtain a matrix material with an excess of lithium content. This setting is beneficial for the subsequent reaction between the matrix material and the surface reconstruction material, allowing sufficient lithium ions in the matrix material to be transferred to the surface reconstruction material to form a surface material with a composition more similar to the matrix material.

[0093] In some other embodiments, during the first mixing in step S501, an M' element additive may be added, controlling the molar ratio of the matrix precursor, the lithium source, and the M' element additive to be 1:(1.0~1.3):(0.0001~0.01), for example 1:1:0.0001, 1:1:0.0005, 1:1:0.001, 1:1:0.002, 1:1:0.005, 1:1:0.01, 1:1.01:0.0001, 1:1.01:0.0005, 1:1.01:0.0005. .001, 1:1.01:0.002, 1:1.01:0.005, 1:1.01:0.01, 1:1.06:0.0001, 1:1.06:0.0005, 1:1.06:0.001, 1:1.06:0.002, 1:1.06:0.005, 1:1.06:0.01, 1:1.3:0.0001, 1:1.3:0.0005, 1:1.3:0.001, 1:1.3:0.002, 1:1.3:0.005, 1:1.3:0.01, etc.

[0094] In some embodiments, the M' element additive may include at least one of the following: oxides, hydroxides, hydrochlorides, basic carbonates, fluorides, and borides of the M' element. The M' element includes one or more of the following elements: Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

[0095] In some embodiments, when the matrix precursor does not contain M' element, M' element additive can be added during the first mixing. In other embodiments, when the M' element content in the matrix precursor is too low, M' element additive can be added during the first mixing. The addition of M' element is beneficial for increasing lattice defects in the formed matrix material, thereby improving the conductivity of the cathode material. When the amount of M' element additive added is too low, the improvement effect on the conductivity of the cathode material is not significant. However, since the conductivity of M' element additive itself is usually worse than that of the matrix material, excessive addition of M' element additive will affect the capacity of the cathode material, the formation of the layered structure of the cathode material, and the overall conductivity of the cathode material.

[0096] In other embodiments, during the first mixing in step S501, the first mixing speed is ≥300 rpm and the first mixing time is ≥15 min. A first mixing speed that is too low or a first mixing time that is too short is detrimental to the uniform mixing of the first mixture. A sufficiently high first mixing speed and a sufficiently long first mixing time are beneficial for the thorough mixing of the first mixture, thereby promoting the formation of matrix material particles with more uniform composition, structure, and particle size.

[0097] As further shown in Figure 5, the preparation method 500 also includes step S502, in which the first mixture is subjected to a first sintering to obtain a matrix material. In some embodiments, the first sintering temperature can be 700℃~1000℃, the first sintering time can be 4h~10h, and the first sintering atmosphere is air and / or oxygen. For example, the first sintering temperature can be 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc. The first sintering time can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, etc.

[0098] As further shown in Figure 5, after obtaining the matrix material, the preparation method 500 also includes steps S503 and S504. Steps S503 and S504 are the same as or similar to steps S402 and S404 described in conjunction with the preparation method 400 above, and will not be repeated here.

[0099] The cathode material and its preparation method according to embodiments of this application have been described in detail above with reference to several accompanying drawings. In another aspect, this application provides a lithium-ion battery, which includes the cathode material described in any one of the first aspects of this application or the cathode material prepared according to the preparation method described above with reference to FIG4 or FIG5.

[0100] One embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing.

[0101] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0102] The lithium-ion battery of this application embodiment also includes electrode components such as the positive current collector, negative electrode sheet, and separator shown in FIG1, which will not be described in detail here.

[0103] Example:

[0104] To better understand the performance of the cathode material and its preparation method according to the embodiments of this application, specific examples will be described below. Several comparative examples are also provided below to further illustrate the advantages of the cathode material according to the embodiments of this application.

[0105] Example 1:

[0106] Step 1) Use a high-speed mixer to mix the matrix precursor Ni0.6 Co 0.1 Mn 0.298 (OH)2, lithium source Li2CO3, and ZrO2 were mixed in a molar ratio of 1:1.06:0.002 for a first mixing at a speed of 1000 rpm for a time of 30 min to obtain a homogeneous first mixture.

[0107] Step 2) The first mixture obtained in Step 1) is subjected to a first sintering at a temperature of 970°C for 8 hours in a pure oxygen atmosphere. Then, it is cooled, crushed by rollers and airflow pulverization, sieved through a 400-mesh sieve, and demagnetized from the sieve material to obtain the matrix material.

[0108] Step 3) Use a high-speed mixer to mix the matrix material obtained in step 2) with the surface reconstruction material Ni. 0.08 Co 0.8 Mn 0.08 Al 0.04 OOH and additive WO3 were mixed in a second mixture at a molar ratio of 1:0.03:0.001, wherein the Na content in the surface reconstruction material was 135 ppm; the second mixing speed was 1000 rpm, the second mixing time was 30 min, and the atmosphere during the second mixing was 95% CO2 and 5% H2O (gaseous) by volume concentration, to obtain the second mixture.

[0109] Step 4) The second mixture obtained in Step 3) is subjected to a second sintering. The second sintering heating rate is 1.5℃ / min, the temperature is 800℃, the second sintering time is 8h, and the second sintering atmosphere is pure oxygen. Then, after cooling, roller crushing, 400-mesh sieving, and demagnetization of the sieve material, the positive electrode material of this embodiment is obtained.

[0110] This application also provides Examples 2 to 27 and Comparative Examples 1 to 4, the different process conditions of which are different from those of Example 1 are shown in Tables 1 and 2. This application also tested the cathode material samples prepared in the above examples and comparative examples.

[0111] (1) Element content test

[0112] The elemental content in the cathode material and surface reconstruction material can be determined using instruments such as ICP, ICP-MS (inductively coupled plasma mass spectrometry), and ICP-OES (inductively coupled plasma optical emission spectrometry) for qualitative and / or quantitative analysis. The test method follows GB / T 24194-2009. For example, in the test example of this application, an Agilent 5110 ICP-OES instrument was used. Specifically, 0.3g of the sample to be tested was dissolved in aqua regia, cooled, and brought to a final volume of 100mL to prepare the stock solution. 1mL of the stock solution was diluted 100 times to obtain the diluted solution. The diluted solution was tested using an Agilent 5110 ICP-OES instrument to characterize the content of the main elements Li / Ni / Co / Mn, and the stock solution was tested using the Agilent 5110 ICP-OES instrument to characterize the content of other elements.

[0113] (2) XPS test

[0114] XPS testing procedure: After pressing the sample powder into a pellet, fix it to the sample stage with double-sided tape or conductive adhesive. After sample preparation, place it in the sample injection chamber and evacuate it until the vacuum degree reaches 1×10⁻⁶. -2 Below Pa, the sample was introduced into the analysis chamber to begin detection. XPS testing was performed using an X-ray photoelectron spectroscopy (ThermoFischer, ESCALAB 250Xi) instrument. The vacuum level in the analysis chamber was 8 × 10⁻⁶. -10 The excitation source was Al ka rays (hv = 1486.6 eV), the operating voltage was 12.5 kV, the filament current was 16 mA, and the signal was accumulated in approximately 3 to 10 cycles. The work function of the XPS test instrument was selected as 4.85 eV, the passing energy was 30 eV, and the step size was 0.1 eV.

[0115] Peak splitting method: Using Origin 8.5 software, select XPS test data → Line mode plotting → Baseline removal (Analysis window Peaks and baseline → Peak Analyzer → Opening Dialog → Recalculate, select Manual option, Goal option, select Fit Peaks (Pro) → Click Next → Baseline Mode, select Constant, Constant = Minimum → Click Next) → Peak splitting (Click Next → Uncheck Enable Auto Find, check Smoothing Window Size option in Peak Finding Settings, select Positive in Direction option, select 2nd Derivative (Search Hidden peaks) in Method, select None in Smooth Derivative Method, select By Number in Peak Filtration Method, uncheck the Auto option for Number of Peaks, and change the number of peaks to 3 → Click Find → Click Next) → Fit correction (Select No Weighting in Weight Method, select Max. Number of in Fit Control) Set Iterations to 20 and Tolerance to 1E-6 → Click Fit → Click Finish. Once completed, you can obtain the relevant results for each peak in the peak division report: peak positions P1, P2, P3; full width at half maximum (FWHM1, FWHM2, FWHM3); and peak areas Area1, Area2, Area3.

[0116] (3) Test of free lithium content per unit area of ​​surface

[0117] The residual alkali of the material was tested according to GB / T 5211.6-2020 "General Test Methods for Pigments and Extenders - Part 6: Determination of pH Value of Aqueous Suspensions". 5g of the positive electrode material sample was dispersed in 100ml of deionized water and magnetically stirred for 10min (450r / min) while maintaining the water temperature at 25℃ to obtain a solid-liquid mixture. This mixture was then filtered to obtain a filtrate, which was placed on an automatic potentiometric titrator. Hydrochloric acid solution was added dropwise to the filtrate, and titration was performed using an equivalence point titration method. Based on the tipping point during titration and the degree of hydrochloric acid consumption, the lithium content in lithium carbonate and lithium hydroxide in the positive electrode material sample was calculated. A Mettler G20S potentiometric titrator was used for this test.

[0118] (5) Particle size

[0119] The particle size distribution of the surface reconstructed material is characterized according to GB / T 19077-2016. A laser particle size analyzer, such as the Mastersizer 3000 from Malvern Instruments Ltd., UK, can be used for convenient measurement. Specifically, the particle size is tested according to GB / T 19077.1-2016 "Particle Size Distribution - Laser Diffraction Method": A suitable amount of sample is taken, poured into pure water, and ultrasonically dispersed until uniform. Then, surfactant is added dropwise at a ratio of 1 g:1 drop, stirred until homogeneous, and then tested.

[0120] (6) Loose packing density AD

[0121] The Scott volumetric meter method was used for testing. The specific testing process was as follows: The powder was placed on the sieve in the upper combined funnel of the BT101 testing equipment and flowed naturally into the feeding box. It alternately passed through four glass plates with an inclination angle of 25° and a square funnel in the feeding box, and flowed into a cylindrical cup with a known weight m0 and volume V0. Finally, the material on the top of the cylindrical cup was gently scraped off with a flat plate to make its surface flush with the cylindrical cup. Finally, the total mass m1 of the powder in the cylindrical cup was weighed, and the loose density of the material AD = (m1-m0) / V0 was calculated.

[0122] (7) Specific surface area BET

[0123] The specific surface area test method refers to GB / T 19587-2017. The nitrogen adsorption specific surface area analysis method is used, and the result is calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri Star II specific surface area and porosity analyzer from Micromeritics, USA. Specifically, the specific surface area was tested using a Tristar 3020 micrometer from the USA. A dry specific surface area tube was used, and material was weighed to fill 1 / 2 to 2 / 3 of the tube's volume. Before testing, degassing (removing moisture or impurities) was required using a vacuum heating method. The degassing temperature was set to 300℃, and the degassing time was 1 hour. After degassing, the tube was placed in a cooling tank or an external specific surface area tube holder for 20 minutes, followed by backfilling with gas for 5-10 seconds (depending on the situation, to avoid sample ejection and adhesion to the sample tube sidewall). The sample tube was then disassembled, quickly sealed with a rubber stopper, and the subsequent tests were performed. The P / P0 ratio was set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. An isothermal adsorption curve was fitted, and the monolayer saturated adsorption capacity Vm was calculated based on the slope and intercept. Then, the specific surface area and pore size information were calculated based on Vm.

[0124] (8) The battery preparation and testing methods are as follows:

[0125] Battery manufacturing

[0126] Preparation of the positive electrode sheet:

[0127] The positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black prepared in the examples or comparative examples were dissolved in solvent N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2. After thorough stirring and mixing, a positive electrode slurry was obtained. The positive electrode slurry was then uniformly coated onto a positive electrode current collector with a primer coating. After drying, cold pressing, and slitting, a positive electrode sheet was obtained with an areal density of 350 g / m³. 2 Compacted density 3.5 g / cm³ 3 .

[0128] Negative electrode preparation:

[0129] Active material graphite, binder (styrene-butadiene rubber SBR), and conductive agent acetylene black were dissolved in deionized water at a weight ratio of 96:2:2. After uniform mixing, a negative electrode slurry was prepared. The slurry was coated onto copper foil, dried, and then cold-pressed and slit to obtain the negative electrode sheet. The areal density of the negative electrode sheet was 210 g / m³. 2 Compacted density 1.6 g / cm³ 3 .

[0130] Diaphragm:

[0131] The diaphragm is a PE diaphragm with a PVDF and alumina coating on the surface to improve adhesion and heat resistance.

[0132] Electrolyte:

[0133] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte. The electrolyte contained 1.1 mol / L of lithium salt and also contained 2% (by mass) vinylene carbonate and 1% (by mass) polysulfone.

[0134] Battery manufacturing:

[0135] The ratio of negative electrode capacity to positive electrode charging capacity (N / P) is controlled at 1.05, and the electrolyte injection amount is 3.2 g / Ah. The positive electrode, separator, negative electrode, and separator are stacked sequentially, with the separator acting as a separator between the positive and negative electrodes. They are then wound to obtain a bare cell. Tabs are welded to the bare cell, and it is placed in an aluminum-plastic bag and baked at 80°C to remove water. Electrolyte is then injected and the bag is sealed, resulting in a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, secondary sealing, shaping, and capacity testing to obtain the lithium-ion battery product.

[0136] Gram capacity test

[0137] Battery capacity testing procedure: Take the formed and capacity-graded batteries, charge them to 4.45 / 4.40 / 4.30V in CCCV mode at 25℃ (charging current 0.33C, constant voltage cutoff current 0.01C), let them stand for 10 minutes, and then discharge them to 3.0V in CC mode (discharge current 0.33C). Calculate the discharge capacity C mAh / g based on the discharge capacity. The selected equipment model is Xinweier CT-4008T-5V1A battery testing cabinet.

[0138] (6) (25℃) 500-cycle capacity retention test

[0139] Cyclic testing procedure: After formation and capacity grading, the batteries are charged to 4.45 / 4.40 / 4.30V in CCCV mode at 25℃ (charging current 1.0C, constant voltage cutoff current 0.01C), left to stand for 10 minutes, and then discharged in CC mode to 3.0V (discharge current 1.0C) to obtain the initial specific capacity as C1 mAh / g. After standing for 10 minutes, the CCCV charging and CC discharging are repeated until 500 cycles are completed. The specific capacity of the last discharge is recorded as C2 mAh / g. The capacity retention rate after 500 cycles is calculated as C2 / C1*100%.

[0140] (7) Test of bulging rate

[0141] Swelling rate test procedure: Take the formed and capacity-graded batteries, charge them to 4.45 / 4.40 / 4.30V in CCCV mode at 25℃ (charging current 1.0C, constant voltage cutoff current 0.01C), let them stand for 10 minutes, seal the tabs, and use the water displacement method to test the battery volume V1 cm⁻¹. 3 Then, place it in a 60℃ constant temperature chamber for 30 days, remove it and let it stand until the temperature drops to 25℃, reseal the tabs, and use the water displacement method to test the battery volume as V² cm⁻¹. 3 The bulging rate is calculated as (V2-V1) / V1*100%.

[0142] (8) DCIR growth rate test

[0143] DCIR growth rate test procedure: After formation and capacity grading, the battery is charged to 4.45 / 4.40 / 4.30V in CCCV mode at 25℃ (charging current 1.0C, constant voltage cutoff current 0.01C), left to stand for 10 minutes, then discharged in CC mode to 3.70V (discharge current 1.0C), left to stand for 10 minutes, and then discharged at a high rate of 5C for 60 seconds. The battery voltage U1 before the 5C high-rate discharge, the voltage U2 after 60 seconds of discharge, and the discharge current I5 are recorded. The initial DCIR0 of the battery is then calculated as (U1-U2) / I5. After testing the initial DCIR0, the battery is discharged in CC mode to 3.0V (discharge current 1.0C), and then cycled 500 times according to the cycle test procedure. After the cycle is completed, the battery is tested using the same method as the DCIR0 test to obtain the DCIR after 500 cycles. 500 Calculate DCIR growth rate = (DCIR) 500 -DCIR0) / DCIR0*100%.

[0144]

[0145] To facilitate the description of the differences between the above embodiments and comparative examples, as well as the test results of each embodiment and comparative example, further explanation will be provided below with reference to Tables 1 to 5. Table 1 shows the corresponding preparation conditions and composition of the matrix materials in each embodiment and comparative example; Table 2 shows the corresponding preparation conditions for the cathode materials in each embodiment and comparative example; Table 3 shows the parameter test results of some of the surface reconstruction materials used in each embodiment and comparative example; Table 4 shows the XPS test results of the cathode materials obtained in each embodiment and comparative example; and Table 5 shows the electrical performance test results of the cathode materials obtained in each embodiment and comparative example.

[0146] Table 1:

[0147] Table 2:

[0148] Table 3:

[0149] Table 4:

[0150] Table 5:

[0151] The data in Tables 1 to 5 above show that:

[0152] (1) Examples 1 to 4 used surface reconstruction materials with different molar ratios to treat the matrix materials. The results showed that as the amount of surface reconstruction material increased, the separation α gradually decreased, the peak spacing between peak 1 (first characteristic peak) and peak 2 (second characteristic peak) gradually decreased, the half-width at half maximum (FWHM) of peak 2 gradually increased, and the area ratio of peak 3 (third characteristic peak) gradually decreased. This indicates that increasing the amount of surface reconstruction material is beneficial for converting active oxygen on the surface of the cathode material into vacancy-adsorbed oxygen, thereby increasing the bond energy of active oxygen and the bond energy range of vacancy-adsorbed oxygen. As can be seen from the results in Table 5, the cathode materials of Examples 1 to 4 have high specific capacity and cycle retention, and low swelling rate and DCIR increase, indicating that the cathode materials of Examples 1 to 4 all have good electrical properties such as specific capacity, cycle life, safety, and DCIR performance. Among them, the cathode material obtained in Example 1 with a molar ratio of 0.03 has the best overall performance. In Example 4, the amount of surface reconstruction material was relatively large, which has begun to have a certain impact on the capacity and DCIR growth rate of the cathode material.

[0153] (2) Examples 5 to 27 used different compositions of matrix precursors, surface reconstruction materials, lithium sources, M' element additives, M” element additives, molar ratios, first and second sintering temperatures, first and second sintering times, and second mixed atmospheres, among other process parameters. It can be seen that the XPS test results of the cathode materials in Examples 5 to 27 all met the following requirements: resolution α ≤ 1.0, peak spacing between the first and second characteristic peaks ≤ 2.4 eV, full width at half maximum (FWHM) of the second characteristic peak ≥ 2.9 eV, and area ratio of the third characteristic peak ≤ 8.5%. Furthermore, the corresponding electrical properties, such as specific capacity, cycle retention, swelling rate, and DCIR increase, remained at relatively good levels. Among these, improving the swelling rate helps ensure battery safety, improving the DCIR increase helps improve the material's conductivity, and specific capacity reflects the battery's capacity utilization performance.

[0154] (3) In Comparative Example 1, no surface reconstruction material was used for coating, and its product composition consisted only of the matrix material itself (i.e., equivalent to conventional NCM material). Compared with Examples 1 to 27, Comparative Example 1 showed a resolution α > 1, peak spacing > 2.4 eV, half-width at half-maximum (FWHM) of the second characteristic peak < 2.9 eV, and area ratio of the third characteristic peak > 8.5%, indicating that the surface of the cathode material in Comparative Example 1 had a higher content of active oxygen, a lower bond energy of active oxygen, and a narrower bond energy range of vacancy-adsorbed oxygen, which was detrimental to the stability and electrical performance of the cathode material structure. Furthermore, referring to the cycle retention rate comparison chart of Example 1 and Comparative Example 1 shown in Figure 6, and combining the data shown in Table 5, it can be seen that all electrical performance indicators in Comparative Example 1 were significantly inferior to those in Examples 1 to 27. In addition, in Comparative Example 1, a second sintering treatment was also performed without the use of surface reconstruction material for coating, which further proves that the above-mentioned effect was brought about by the reconstructed surface structure, rather than by the second sintering process.

[0155] (4) Comparative Example 2 used a conventional coating material to conventionally coat the substrate material. Compared with Examples 1 to 27, Comparative Example 1 showed a resolution α > 1, peak spacing > 2.4 eV, half-width at half-maximum (FWHM) of the second characteristic peak < 2.9 eV, and area ratio of the third characteristic peak > 8.5%. This indicates that the cathode material in Comparative Example 1 had a higher content of active oxygen on its surface, lower bond energy of active oxygen, and a narrower bond energy range for vacancy-adsorbed oxygen, which is detrimental to the stability and electrical performance of the cathode material structure. As shown in Table 4, all electrical performance indicators in Comparative Example 1 were significantly inferior to those in Examples 1 to 27.

[0156] (5) Although Comparative Example 3 used the same surface reconstruction material as Example 1 to coat the substrate material, the second sintering temperature of Comparative Example 3 was too low, which made it impossible for the surface reconstruction material to form a stable surface reconstruction layer on the surface of the substrate material. Instead, it simply formed a physical coating and failed to convert some active oxygen into vacancy adsorbed oxygen by forming an effective chemical bond with the surface of the substrate material. As a result, the XPS parameters of the obtained cathode material were not within the range of parameters described in this application, and the corresponding electrical performance indicators were significantly worse than those of Examples 1 to 27.

[0157] (6) As can be seen from Examples 19 and 4, the molar ratio of the surface reconstruction material to the matrix material in Comparative Example 4 is only 0.002, which is lower than 0.005 in Example 19. From the test results in Table 4, the resolution α > 1, peak spacing > 2.4 eV, full width at half maximum (FWHM) of the second characteristic peak < 2.9 eV, and area ratio of the third characteristic peak > 8.5% in Comparative Example 4 indicate that the surface of the cathode material in Comparative Example 4 has a high content of active oxygen, low bond energy of active oxygen, and a narrow bond energy range for vacancy-adsorbed oxygen, which is detrimental to the stability and electrical performance of the cathode material structure. From the test results in Table 5, although the various properties of the cathode material prepared in Comparative Example 4 are improved compared to Comparative Examples 1 to 3, they do not reach the level of Examples 1 to 27. This is because the surface reconstruction material used in Comparative Example 4 is too small, failing to fully cover the entire matrix surface, resulting in the original matrix being exposed and unable to form effective chemical bonds with the surface reconstruction material for protection.

[0158] Furthermore, Figure 2 shows the XPS spectrum of O1s obtained from Comparative Example 1. Figure 3 shows the XPS spectrum of O1s obtained from the cathode material of Example 1 of this application. As shown in Figure 2, peak 1 has a larger area, peak spacing between peak 1 and peak 2 is larger, and the full width at half maximum (FWHM) of peak 2 is narrower. This indicates that the cathode material of Comparative Example 1 has a higher content of active oxygen and a lower bond energy on the particle surface, a narrower bond energy range for vacancy-adsorbed oxygen, and a clear separation between the first characteristic peak of active oxygen and the second characteristic peak of vacancy-adsorbed oxygen. As shown in Figure 3, the cathode material of Example 1 has a smaller peak spacing between peak 1 and peak 2, a wider FWHM of peak 2, and no clear separation between peak 1 and peak 2.

[0159] As can be seen from Figures 2 and 3, compared with the prior art, the cathode material particles provided in this application have higher active oxygen bond energies and a wider range of vacancy-adsorbed oxygen bond energies on their surface. This allows them to withstand changes in the valence states of the transition metal ions bonded to them over a wider range, balancing charge distribution over a broader range without breakage. This improves the overcharge and over-discharge tolerance of the particle surface structure, preventing particle cracking and pulverization, and consequently improving the cycle life and impedance increase of the lithium-ion battery. Furthermore, the cathode material particles in this embodiment have higher vacancy-adsorbed oxygen content and lower active oxygen content on their surface, effectively mitigating the occurrence of side reactions between the cathode material surface and the electrolyte, reducing gas production in the lithium-ion battery, and ultimately improving the cycle life, impedance increase, and safety of the lithium-ion battery.

[0160] In summary, the embodiments of this application provide a cathode material whose surface material and matrix material have the same or similar composition, making the cathode material structure more stable. This effectively avoids problems such as easy peeling of the coating layer and easy cracking or pulverization of material particles under high voltage windows, thereby improving the operating voltage of the cathode material and its electrical performance in terms of cycle life, swelling rate, conductivity, and capacity utilization. Furthermore, the cathode material of the embodiments of this application has the characteristics of low surface active oxygen content, high active oxygen bond energy, wide range of vacancy adsorption oxygen bond energy, and low oxygen content corresponding to the residual alkali formed by combining with Li, thereby improving the electrical performance of the cathode material in terms of cycle life, swelling rate, conductivity, and capacity utilization.

[0161] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A positive electrode material, characterized in that, In the XPS spectrum of the cathode material, the surface oxygen element O1s characteristic peak of the cathode material can be split into at least two characteristic peaks after peak splitting, including: a first characteristic peak in the range of 529.0±0.5eV and a second characteristic peak in the range of 531.2±0.5eV. The cathode material also satisfies at least one of the following conditions: (1) The separation degree between the first characteristic peak and the second characteristic peak is ≤1.0; (2) The peak spacing between the first characteristic peak and the second characteristic peak is ≤2.4eV.

2. The cathode material according to claim 1, characterized in that, After peak splitting, a third characteristic peak can be obtained from the surface oxygen element O1s characteristic peak of the cathode material. The third characteristic peak is in the range of 530.0±0.5eV, and the area of ​​the third characteristic peak accounts for ≤8.5% of the total area of ​​the O1s characteristic peak.

3. The cathode material according to claim 1, characterized in that, The full width at half maximum (FWHM) of the second characteristic peak is ≥2.9 eV.

4. The cathode material according to claim 1, characterized in that, The separation degree between the first characteristic peak and the second characteristic peak is ≤1.

0.

5. The positive electrode material according to claim 1, characterized in that, The peak spacing between the first characteristic peak and the second characteristic peak is ≤2.4eV.

6. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The cathode material has the general chemical formula: Li λ Ni a Co b M c M' e M” 1-a-b-c-e O2, where 0.95≤λ≤1.3, 0.3≤a<1.0, 0.01≤b≤0.33, 0≤c≤0.5, 0≤e≤0.01, 0≤1-abce≤0.01, M includes Mn and / or Al, M' includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy, and M” includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy; (2) The cathode material includes lithium transition metal oxide.

7. The cathode material according to claim 1, characterized in that, The free lithium content per unit area on the surface of the cathode material is 200 μg / m². 2 ~800μg / m 2 .

8. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The cathode material includes a single-crystal cathode material, and the average particle size of the cathode material is 1μm to 10μm; (2) The cathode material includes a single-crystal cathode material, wherein the cathode material contains at least one particle with the same orientation.

9. The positive electrode material according to claim 1, characterized in that, The cathode material includes a matrix material and a surface structure, wherein the surface structure is located on at least a portion of the surface of the matrix material, and the surface structure includes at least one element selected from Ni, Co, and Na.

10. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The separation degree between the first characteristic peak and the second characteristic peak can be within the range of 1.0, 0.98, 0.97, 0.96, 0.95, 0.94, 0.92, 0.9, 0.89, 0.88, 0.87, 0.86, 0.85, 0.84, 0.83, 0.82, 0.81, 0.8, 0.79, 0.78, 0.77, 0.76, 0.75, 0.74, 0.73, 0.72, 0.71, 0.7, 0.68, 0.66, 0.65, 0.64, 0.62, 0.6, 0.58, 0.56, 0.55, 0.54, 0.52, 0.5 or any combination thereof; (2) The separation degree between the first characteristic peak and the second characteristic peak is ≤0.9; (3) The separation degree between the first characteristic peak and the second characteristic peak is ≤0.

8.

11. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) The peak spacing between the first characteristic peak and the second characteristic peak can be within the range of 2.4 eV, 2.35 eV, 2.32 eV, 2.31 eV, 2.3 eV, 2.2 eV, 2.17 eV, 2.1 eV, 2.09 eV, 2.02 eV, 2.0 eV, 1.96 eV, 1.94 eV, 1.93 eV, 1.92 eV, 1.91 eV, 1.9 eV, 1.89 eV, 1.88 eV, 1.87 eV, 1.85 eV, 1.84 eV, 1.8 eV, 1.79 eV, 1.76 eV, 1.75 eV, 1.72 eV, 1.7 eV, 1.6 eV, 1.57 eV, 1.5 eV or any combination thereof; (2) The peak spacing between the first characteristic peak and the second characteristic peak is ≤2.3eV; (3) The peak spacing between the first characteristic peak and the second characteristic peak is ≤2.0eV.

12. A surface reconstruction material, characterized in that, The surface reconstruction material includes Ni. x Co y M z M” 1-x-y-z OOH, Ni x Co y M z M” 1-x-y-z (OH)2、(Ni x Co y M z M” 1-x-y-z )O d At least one of the following, wherein 0≤x≤0.6, 0.4≤y≤1, 0≤z≤0.6, 0≤1-xyz≤0.15, 1≤d≤2, M includes Mn and / or Al, and M" includes at least one of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy; the Na content in the surface reconstruction material ranges from 50ppm to 300ppm.

13. The surface reconstruction material according to claim 10, characterized in that, The surface reconstruction material also satisfies at least one of the following conditions: (1) The median particle size D50 of the surface reconstruction material satisfies: 10nm≤D50≤1000nm; (2) The loose density AD of the surface reconstruction material is ≤0.6 g / cm³. 3 ; (3) The specific surface area BET of the surface reconstruction material is ≥20m². 2 / g.

14. A positive electrode plate, characterized in that, The positive electrode sheet comprises a positive electrode material made of any one of the positive electrode materials as described in claims 1 to 11 or a positive electrode material made of any one of the surface reconstruction materials as described in claims 12 to 13.

15. A lithium-ion battery, characterized in that, The lithium-ion battery comprises a positive electrode material made of any one of claims 1-11 or a surface reconstruction material made of any one of claims 12-13.

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