Positive electrode material, surface reconstruction material and lithium ion battery

Abstract

The invention discloses a positive electrode material, a surface layer reconstruction material and a lithium ion battery, in an XPS spectrogram of the positive electrode material, after a surface oxygen element O1s characteristic peak of the positive electrode material is subjected to peak division treatment, at least two characteristic peaks can be obtained, including a first characteristic peak in a range of 529.0 + / -0.5 eV and a second characteristic peak in a range of 531.2 + / -0.5 eV; the positive electrode material meets at least one of the following conditions: (1) the separation degree of the first characteristic peak and the second characteristic peak is less than or equal to 1.0; and (2) the peak position distance between the first characteristic peak and the second characteristic peak is less than or equal to 2.4 eV. The positive electrode material disclosed by the embodiment of the invention has a more stable structure, so that the cycle life of the battery is prolonged, and the performance of the battery in the aspects of safety and the like is improved.

Description

Technical Field

[0001] The present application generally relates to the technical field of battery positive electrode materials. More specifically, the present application relates to a positive electrode material, a surface reconstruction material and a lithium-ion battery. Background Art

[0002] In recent years, lithium-ion batteries (LIB) have been widely used in various fields such as 3C consumption, power tools, electric vehicles, energy storage, etc., and have gradually expanded to electric ships, electric aircraft and other fields. As related technologies are gradually improved and the application market becomes more mature, consumers have put forward more stringent requirements on the energy density, cycle life, safety and other aspects of lithium-ion batteries. As one of the core components, the positive electrode material plays a vital role in the various performance indicators of lithium-ion batteries.

[0003] At present, with the increase of positive electrode material capacity, the number of active oxygen sites on the surface of positive electrode materials increases, and the degree of side reaction with electrolyte intensifies. This side reaction oxidizes the electrolyte to produce some gas, causing the battery to swell and affect safety performance; at the same time, the generation of gas leads to poor contact between the electrode and the electrolyte, resulting in a decrease in cycle life. In terms of improving the battery charge and discharge voltage window, as the degree of charge and discharge deepens, the degree of expansion / contraction of the positive electrode material grains and the internal stress intensify, causing the positive electrode material particles to crack and pulverize, which in turn affects the battery's cycle life and safety.

[0004] In view of this, there is an urgent need to provide a positive electrode material solution to improve battery performance such as cycle life and safety. Summary of the invention

[0005] In order to at least solve one or more of the technical problems mentioned above, the present application proposes a positive electrode material, a surface reconstruction material for a positive electrode material, a method for preparing a positive electrode material, and a lithium-ion battery solution in multiple aspects.

[0006] In a first aspect, the present application provides a positive electrode material, in which in the XPS spectrum of the positive electrode material, the surface oxygen element O1s characteristic peak of the positive electrode material can obtain at least two characteristic peaks after peak separation treatment, 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 positive electrode 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 distance between the first characteristic peak and the second characteristic peak is ≤2.4eV.

[0007] In some embodiments, the surface oxygen element O1s characteristic peak of the positive electrode material can also obtain a third characteristic peak after peak separation processing. 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.

[0008] In other embodiments, the half-width of the second characteristic peak is ≥2.9 eV.

[0009] In some other embodiments, the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0.

[0010] In some embodiments, the peak distance between the first characteristic peak and the second characteristic peak is ≤2.4 eV.

[0011] In some embodiments, the cathode material has a chemical 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.

[0012] In other embodiments, the positive electrode material satisfies at least one of the following conditions: (1) the free lithium content per unit area of ​​the surface of the positive electrode material is 200 μg / m 2 ~800 μg / m 2 ; (2) the positive electrode material is a single crystal positive electrode material, and the average particle size of the positive electrode material is: 1 μm to 10 μm; (3) the positive electrode material is a single crystal positive electrode material, and the positive electrode material contains at least one particle with the same orientation; (4) the surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the Ni content of the surface reconstruction material is lower than the Ni content of the matrix material; (5) the surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the Co content of the surface reconstruction material is higher than the Co content of the matrix material; (6) the surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the matrix material has a chemical formula: Li k Ni f Co g M hM' 1-f-g-h O2, 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 Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy.

[0013] In a second aspect, the present application provides a surface reconstruction material, wherein the surface reconstruction material is used to form a surface structure of a positive electrode material as described in any one of the first aspects of the present application, 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 ) 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; and the content of Na in the surface reconstruction material is in the range of 50ppm to 300ppm.

[0014] In some embodiments, the median particle size D50 of the surface reconstruction material satisfies: 10 nm≤D50≤1000 nm.

[0015] In other embodiments, the bulk density AD of the surface reconstruction material is ≤ 0.6 g / cm 3 .

[0016] In some other embodiments, the specific surface area of ​​the surface reconstruction material is BET ≥ 20 m 2 / g.

[0017] In a third aspect, the present application provides a lithium-ion battery, comprising the positive electrode material described in any one of the first aspects of the present application.

[0018] It can be seen from the positive electrode material scheme provided above that the positive electrode material of the embodiment of the present application satisfies at least one of the conditions such as the separation degree of the first characteristic peak and the second characteristic peak ≤1.0, the peak distance between the first characteristic peak and the second characteristic peak ≤2.4eV in its XPS spectrum, thereby having the characteristics of low surface active oxygen content, large active oxygen bond energy, and a wide range of vacancy adsorption oxygen bond energy. It has a more stable surface structure, which can continuously protect the matrix material from being corroded by the electrolyte, and is beneficial to improving the cracking and pulverization of the positive electrode material particles under the high voltage window, thereby improving the cycle life and safety of the positive electrode material. Performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] By reading the detailed description below with reference to the accompanying drawings, the above and other purposes, features and advantages of the exemplary embodiments of the present application will become easy to understand. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0020] Figure 1 A schematic diagram of a battery in a discharge state, i.e., during operation, is shown;

[0021] Figure 2 The XPS spectrum of O1s obtained by the test of Comparative Example 1 is shown;

[0022] Figure 3 The XPS spectrum of O1s obtained by testing the positive electrode material of Example 1 of the present application is shown;

[0023] Figure 4 A flow chart of a method for preparing a positive electrode material according to some embodiments of the present application is shown;

[0024] Figure 5 A flow chart showing a method for preparing a positive electrode material according to other embodiments of the present application is shown;

[0025] Figure 6 A comparison chart of the cycle retention rates of Example 1 and Comparative Example 1 is shown. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0027] It should be understood that the terms "include" and "comprising" used in the specification and claims of the present application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0028] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in this application specification and claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms. It should also be further understood that the term "and / or" used in this application specification and claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0029] As used in this specification and claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0030] The specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the examples of the present application are all obtained from conventional commercial channels.

[0031] Figure 1 FIG. 1 shows a schematic diagram of a battery in a discharge state, that is, during operation. Figure 1 As shown, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120 and a separator 130, and the separator 130 is disposed between the positive electrode sheet 110 and the negative electrode sheet 120. The electrode assembly can be a laminated structure, which is formed by alternately stacking the separator 130, the positive electrode sheet 110, the separator 130 and the negative electrode sheet 120. In other embodiments, the electrode assembly can also be a winding structure, which is formed by stacking the separator, the positive electrode sheet, the separator and the negative electrode sheet in sequence and then winding them.

[0032] Positive electrode sheet: The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may be aluminum foil or nickel foil, or may be 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 electrode active layer 112 includes the positive electrode material described below.

[0033] 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 may use at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, etc., or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector 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 material, tin-based material, lithium titanate, etc.

[0034] During battery operation, that is, when the battery is in a discharge state, the metal ions 140 (eg, lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the isolation membrane 130 through the electrolyte / electrolyte, and are embedded in the lattice of the positive electrode material.

[0035] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes the metal ions (such as lithium ions) in the positive electrode to escape from the lattice of the positive electrode material, pass through the isolation membrane through the electrolyte / electrolyte, 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.

[0036] As metal ions move back and forth between the positive and negative electrodes, the battery can be discharged and charged thousands of times.

[0037] 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.

[0038] In some embodiments, the silicon-based material includes silicon oxide, the silicon oxide includes silicon element and oxygen element, and the atomic ratio of oxygen element to silicon element is 0 to 2, and does not include zero.

[0039] In some embodiments, the silicon-based material includes silicon oxide, and the chemical formula of silicon oxide is SiOx, where 0<x≤2. Specifically, SiOx can be SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 Etc., no limitation is made here.

[0040] Silicon oxide can be represented by a general formula of SiOx (0<x≤2). It can be a material formed by silicon dispersed in SiO2; it can also be a material with a tetrahedral structural unit, in which the silicon atom is located at the center of the tetrahedral structural unit and the oxygen atoms and / or silicon atoms are located at the four vertices of the tetrahedral structural unit.

[0041] In some embodiments, the graphite-based material in the negative electrode material may include at least one of natural graphite, artificial graphite, expanded graphite, and graphite oxide.

[0042] In some embodiments, the negative electrode material includes a carbon material, and the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0043] In some embodiments, the tin-based material in the negative electrode material may include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0044] The present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0045] Since the charge and discharge reaction process of the positive electrode material always proceeds from the surface of the material particles to the inner core, the charge and discharge depth of the particle surface is always higher than that of the particle inner core. In addition, the failure process of the positive electrode material is also based on this reason. The continuous deep charge and discharge reaction causes the surface of the particles to fail first. After losing the protection of the surface layer, the failure reaction will quickly spread to the inner core of the particles, eventually leading to the failure of the entire material. Therefore, the stability of the surface structure of the positive electrode material is crucial, and improving the stability of the surface structure can greatly improve the overall performance of the positive electrode material.

[0046] The inventors have increased the stability of the surface structure of the positive electrode material by optimizing the process. After research, the inventors found that the performance changes of the positive electrode material can be reflected in the distribution of oxygen element types (active oxygen, vacancy adsorbed oxygen) on the surface of the material particles and their relative content. Specifically, the present application obtains at least two characteristic peaks after peak separation of the O1s characteristic peak, namely the first characteristic peak (peak 1) and the second characteristic peak (peak 2). On the one hand, the peak spacing between peak 1 and peak 2 is ≤2.4eV, indicating that the bond energy of the active oxygen on the surface of the positive electrode material is strong. At this time, the degree of energy band overlap between the transition metal element and the O element is increased, the bond length of the formed chemical bond is shortened, the bond energy is enhanced, the stability of the active oxygen is improved, the oxygen evolution side reaction and the oxidation-reduction side reactions between the transition metal and the electrolyte are more difficult to occur, and the safety and cycle life of the battery cell are improved. On the other hand, the separation degree between the first characteristic peak and the second characteristic peak is ≤1.0. At this time, it shows that the active oxygen content on the surface of the positive electrode material is low, the vacancy adsorbed oxygen content is high, the degree of side reaction between the surface of the positive electrode material and the electrolyte is slowed down, and the safety of the battery cell is improved; the active oxygen bond energy is high and the vacancy adsorbed oxygen bond energy range is wide, which enables the positive electrode material to withstand a wider voltage change range and improves the cycle stability of the positive electrode material.

[0047] In some embodiments of the present application, in the XPS spectrum of the positive electrode material, the characteristic peak of the oxygen element O1s on the surface of the positive electrode material can obtain 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.

[0048] It should be noted that in the XPS spectrum of the positive electrode material, the separation degree of the first characteristic peak of active oxygen on the surface of the positive electrode material and the second characteristic peak of vacancy adsorbed oxygen can be calculated by the following formula:

[0049]

[0050] In formula (1), α represents the separation degree between the first characteristic peak and the second characteristic peak on the surface of the positive electrode 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 distance between the first characteristic peak and the second characteristic peak; FWHM1 represents the half-height width of the first characteristic peak, and FWHM3 represents the half-height width of the second characteristic peak. The half-height width 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 the oxygen element and the transition metal. The increase in the bond energy range corresponds to an increase in the half-height width, and the decrease in the bond energy range corresponds to a decrease in the half-height width.

[0051] Based on the above formula (1), it can be known that the separation is mainly affected by the peak spacing between peak 1 and peak 2 and the half-height width of the two. The smaller the peak spacing between peak 1 and peak 2, the smaller the separation. The larger the half-height width of peak 1 and peak 2, the smaller the separation.

[0052] The increase in the bond energy range of vacancy adsorbed oxygen (corresponding to the half-height width of the second characteristic peak) can lead to a decrease in the separation degree α. The decrease in the peak spacing between the first characteristic peak and the second characteristic peak can lead to a decrease in the separation degree α. Under the combined effect of the increase in the half-height width of the second characteristic peak and the decrease in the above-mentioned peak spacing, the separation degree of the first characteristic peak and the second characteristic peak in the embodiment of the present application is ≤1.0. At this point, it shows that the active oxygen content on the surface of the positive electrode material is low, the vacancy adsorbed oxygen content is high, the degree of side reaction between the surface of the positive electrode material and the electrolyte is slowed down, and the safety of the battery cell is improved; the active oxygen bond energy is high and the vacancy adsorbed oxygen bond energy range is wide, so that the positive electrode material can withstand a wider voltage variation range, which improves the cycle stability of the positive electrode material. Specifically, the separation degree between the first characteristic peak and the second characteristic peak can be 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, etc. Preferably, the separation degree between the first characteristic peak and the second characteristic peak is ≤0.9.

[0053] In some embodiments, the peak distance between peak 1 and peak 2 is ≤2.4 eV, indicating that the bond energy of the active oxygen on the surface of the positive electrode material is relatively strong. At this time, the energy band overlap between the transition metal element and the O element is increased, the bond length of the formed chemical bond is shortened, the bond energy is enhanced, the stability of the active oxygen is improved, the oxygen evolution side reaction and the redox side reaction between the transition metal and the electrolyte are more difficult to occur, and the safety and cycle life of the battery cell are improved. Specifically, the peak distance between peak 1 and peak 2 can be, for example, 2.4eV, 2.35eV, 2.32eV, 2.31eV, 2.3eV, 2.2eV, 2.17eV, 2.1eV, 2.09eV, 2.02eV, 2.0eV, 1.96eV, 1.94eV, 1.93eV, 1.92eV, 1.91eV, 1.9eV, 1.89eV, 1.88eV, 1.87eV, 1.85eV, 1.84eV, 1.8eV, 1.79eV, 1.76eV, 1.75eV, 1.72eV, 1.7eV, 1.6eV, 1.57eV, 1.5eV, etc.

[0054] Preferably, the distance between the peak positions of sub-peak 1 and sub-peak 2 is ≤2.3eV. It should be noted that in the XPS spectrum, the peak position of the oxygen bond is mainly affected by the bond energy formed by the oxygen element and the transition metal. The greater the bond energy of oxygen, the more the peak position shifts to the right. The bond energy of vacancy adsorbed oxygen (corresponding to the peak position of sub-peak 2) is closely related to the lattice structure of the material, the peak position is relatively stable, the offset fluctuation range is extremely small, and it can usually be considered as a fixed value. The active oxygen bond energy (corresponding to the peak position of sub-peak 1) is greatly affected by the surface state of the material and the surrounding ionic state, and the offset fluctuation is more obvious. Therefore, with the increase of the bond energy of active oxygen, the peak position of sub-peak 1 will gradually shift to the right, that is, the distance between the peak positions of sub-peak 1 and sub-peak 2 will decrease.

[0055] In some embodiments, the half-width of peak 2 is ≥2.9 eV, indicating that the vacant oxygen adsorption bond energy range on the surface of the positive electrode material is relatively wide, and the tolerance of the vacant oxygen adsorption bonds on the surface of the positive electrode material is enhanced (that is, it can tolerate the transition metal ions (such as Ni, Co, Mn / Al, etc.) bonded thereto to change in a wider valence range), so that the oxygen bonds on the surface of the positive electrode material can balance the charge distribution within a wider range without breaking, thereby significantly enhancing the structural stability of the material, thereby improving the high voltage tolerance, cycle stability, safety and other performance of the material. Specifically, the half-width of peak 2 can be, for example, 2.9eV, 2.95eV, 2.98eV, 2.99eV, 3.0eV, 3.02eV, 3.06eV, 3.09eV, 3.1eV, 3.12eV, 3.14eV, 3.17eV, 3.2eV, 3.25eV, 3.26eV, 3.27eV, 3.3eV, 3.31eV, 3.35eV, 3.37eV, 3.38eV, 3.4eV, 3.41eV, 3.42eV, 3.44eV, 3.45eV, 3.48eV, 3.5eV, 3.51eV, 3.6eV, 3.7eV, 3.8eV, 3.82eV, 3.9eV, etc. Preferably, the half-width of the peak 2 is ≥2.95 eV.

[0056] In some embodiments, the characteristic peak of oxygen element O1s on the surface of the positive electrode material can be subjected to peak separation to obtain three characteristic peaks, namely, the first characteristic peak, the third characteristic peak and the second characteristic peak. Figure 3 Take this as an example to illustrate: Figure 3 In the figure, the first characteristic peak is peak 1, the third characteristic peak is peak 3, and the second characteristic peak is peak 2. Figure 3As shown in the figure, the abscissa of the XPS spectrum represents the electron binding energy (eV), the ordinate represents the intensity, and "XPS test--O1s" represents the surface oxygen element O1s characteristic peak obtained by the XPS test of the material. O1s refers to the energy spectrum of the 1s orbital electron of the oxygen element in the X-ray photoelectron spectroscopy (XPS). In the XPS spectrum, the O1s characteristic peak can characterize the valence electron state of the oxygen element on the surface of the material. By analyzing the position, shape and area of ​​the O1s characteristic peak, the chemical state and environmental information of the oxygen element in the material can be characterized. Specifically, by performing peak separation on the O1s characteristic peak, different types of oxygen elements can be distinguished, such as vacancy adsorbed oxygen, active oxygen, oxygen in residual alkali, etc. According to the location of each peak (i.e., peak position), 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 surface of the material. Here, the third characteristic peak of residual alkali oxygen refers to the characteristic peak of oxygen element in residual alkali (such as LiOH, Li2CO3, Li2O, etc.) formed on the surface of the material. The "peak summary" in the figure represents the spectrum after the peaks are summarized, which is used to compare with the original O1s characteristic peak before the peak separation process to verify the accuracy of the peak separation results.

[0057] In addition, the oxygen content corresponding to the residual alkali formed by the surface of the positive electrode material combined with Li also affects the processing performance of the positive electrode material slurry. The higher the oxygen content of this part, the higher the residual alkali content corresponding to the material, resulting in a higher degree of reaction between the positive electrode material and the NMP ("N-methylpyrrolidone") solvent, which increases the viscosity of the slurry during the production of the pole piece, and then increases the amount of NMP solvent used, which not only increases the cost, but also is not conducive to the effect of pole piece coating. In addition, the higher the residual alkali content, the electrochemical oxidation decomposition reaction will occur during the battery charging process, causing the battery cell to produce gas and reduce the first coulomb efficiency (referred to as the first efficiency). In order to improve the processing performance of the positive electrode material, in some embodiments, the area of ​​the third characteristic peak of the residual alkali oxygen on the surface of the positive electrode material accounts for ≤8.5% of the total area of ​​the O1s characteristic peak. Based on this, the oxygen content corresponding to the residual alkali formed by the surface of the positive electrode material combined with Li in the embodiment of the present application is low, which can reduce the degree of reaction between the material and the NMP solvent, reduce the viscosity of the slurry during the production of the pole piece, and improve the processing performance of the material; it can also reduce the electrochemical oxidation reaction of the residual alkali during the charging process, reduce the gas production of the battery cell and improve the first efficiency.

[0058] In some embodiments, the cathode material has the general formula: Li λ Ni a Co b M c M' e M” 1-a-b-c-eO2, 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.

[0059] 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., 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-mentioned positive electrode material can be the same or different.

[0060] In other embodiments, the free lithium content per unit area of ​​the surface of the positive electrode material is 200 μg / m 2 ~800 μg / m 2 For example, the free lithium content is 200 μg / m 2 , 250 μg / m 2 , 300 μg / m 2 , 350μg / m 2 400 μg / m 2 450 μg / m 2 , 500 μg / m 2 , 550μg / m 2 , 600 μg / m 2 , 650μg / m 2 , 700 μg / m 2 , 750 μg / m 2 , 800 μg / m 2 .

[0061] The free lithium on the surface of the positive electrode material can react with the solvent NMP used in the processing of the electrode. Excessive free lithium content will cause the slurry to appear gel-like or jelly-like, and other failure consequences. The conventional free lithium content refers to the free lithium contained in the unit mass of the material. The free lithium content cannot be judged based on its numerical value to determine whether it will affect the processing performance of the slurry. This is because the solvent NMP reacts with the Li within the surface area of ​​the material particles it contacts, so the processing performance of the slurry is related to the free Li concentration per unit area, not the free lithium concentration per unit weight. For example, some materials have a relatively low free lithium content per unit mass, but the specific surface area of ​​the material particles is even lower, then the free lithium concentration per unit area of ​​the surface is high, which can easily lead to high slurry viscosity and jelly-like conditions.

[0062] In comparison, the free lithium content per unit area of ​​the surface of the positive electrode material in this article is obtained by testing and calculating the ratio of the free lithium content per unit mass of the positive electrode material to its specific surface area. The free lithium content can be used to accurately determine the impact of the positive electrode material on the slurry processing performance during the slurry coating process.

[0063] In some embodiments, the positive electrode material is a single crystal positive electrode material, and the average particle size of the positive electrode material is: 1 μm to 10 μm. The positive electrode material contains at least one particle with the same orientation. For example, the average particle size of the positive electrode 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, etc., or other values ​​within the range of 1 μm to 10 μm.

[0064] It should be noted that the difference between single crystal positive electrode materials and polycrystalline positive electrode materials (i.e., secondary particles composed of primary particles) is that the smallest particle of polycrystalline secondary particles is a secondary particle formed by the agglomeration of nano-scale particles. For single crystal positive electrode materials, the smallest particle is usually a single particle of micrometer size. Generally speaking, in addition to the electron backscatter diffraction (EBSD) test method, it is also possible to determine whether the obtained positive electrode product is a single crystal material by characterization methods such as scanning electron microscopy (SEM). For example, for single crystal positive electrode materials, the morphology of single crystal particles can be characterized by SEM, and it can be seen that the shape of single crystal particles is generally regular or irregular spherical, and there is no significant particle agglomeration. The orientation of single crystal positive electrode materials can also be characterized by EBSD. It can be observed by EBSD that the color in at least one grain is the same, so as to judge that the orientation in at least one grain is the same, and the grains with the same orientation are single crystals. It should be specifically noted that the "single crystal positive electrode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely the same arrangement and orientation. However, due to impurities, strains and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single crystal cathode materials known in the art are actually more "single crystal morphology" cathode materials, which only show a single crystal-like large particle size in size, which is different from the polycrystal composed of many small primary particles.

[0065] It should be noted that the above-mentioned single crystal positive electrode material may also contain a small amount of "quasi-secondary particles" formed by the adhesion of less than 10 primary particles. "Primary particles" refer to the smallest particle unit identified when observing the positive electrode active material through a scanning electron microscope.

[0066] It should be specifically pointed out 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 exactly the same arrangement and direction. However, due to impurities, strain and crystal defects, ideal single crystals are very rare and difficult to produce in reality. Therefore, the single crystal materials known in the art are actually more of "single crystal-like morphology" positive electrode materials, which only show a single crystal-like large particle size in size, which is different from the polycrystalline particles composed of many small particles.

[0067] During the charge and discharge process of lithium-ion batteries, the removal and embedding of lithium ions are carried out from the surface of the particles to the inside. For single-crystal positive electrode materials, since the particles of single-crystal positive electrode materials are dense inside and lack grain boundaries formed by primary particle agglomeration, the electrolyte cannot directly enter the particles. Li ions can only slowly transfer from the surface of the particles to the inside of the particles (by means of electromigration and diffusion, etc.). Therefore, the surface of the positive electrode material particles is always in an overcharged or over-discharged state compared to the inside.

[0068] However, in the state of overcharge or overdischarge, the higher active oxygen content and lower bond energy on the surface of conventional NCM materials make the bond between active oxygen and the transition metal of the positive electrode material very easy to break, thereby aggravating the oxygen evolution side reaction of the material. Therefore, by satisfying the above range through the peak separation of the characteristic peak of O1s of the single crystal positive electrode material in the present application, the active oxygen bond energy on the surface of the single crystal positive electrode material particles is higher and the vacancy adsorption oxygen bond energy range is wider, which can tolerate the transition metal ions bonded to it to change in a wider valence range, and can balance the charge distribution in a wider range without breaking, thereby improving the tolerance of the surface structure of the particles to overcharge and overdischarge, avoiding particle cracking and pulverization, and then improving the cycle life and impedance increase of the lithium ion battery. At the same time, the vacancy adsorption oxygen content of the surface layer of the positive electrode material particles of the embodiment of the present application is higher, and the active oxygen content is lower, which can effectively alleviate the occurrence of side reactions between the surface layer of the positive electrode material and the electrolyte, reduce the gas production of the lithium ion battery, and finally achieve the effects of improving the cycle life, impedance increase, safety, etc. of the lithium ion battery.

[0069] In a second aspect, the present application provides a surface reconstruction material for a positive electrode material, the surface reconstruction material is used to form the surface structure of the positive electrode material described in any one of the first aspects, 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 ) d At least one of, 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 content of Na element in the surface reconstruction material is in the range of 50ppm to 300ppm.

[0070] Illustratively, 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., 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 and the like.

[0071] In some embodiments, the median particle size D50 of the surface reconstruction material satisfies: 10nm≤D50≤1000nm. Exemplarily, 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. In the process of surface reconstruction of micron-scale base materials (e.g., median particle size of 3 to 20um), the nano-scale surface reconstruction material can be effectively and evenly coated on the surface of the base material, rather than simply mixed, so that the surface thickness of the reconstructed positive electrode material is uniform, and the protective effect of the base material in the positive electrode material is more effective and lasting. It should be noted that the median particle size D50 represents the particle size of the material particles corresponding to the cumulative particle size distribution percentage reaching 50% by volume.

[0072] In other embodiments, the bulk density AD of the surface reconstruction material is ≤ 0.6 g / cm 3 For example, the bulk density AD may be 0.1 g / cm 3 , 0.15g / cm 3 , 0.2g / cm 3 , 0.25g / cm 3 , 0.3g / cm 3, 0.35g / cm 3 , 0.4g / cm 3 , 0.45g / cm 3 , 0.5g / cm 3 , 0.55g / cm 3 , 0.6g / cm 3 etc. Since the median particle size of the surface reconstruction material is nanometer-scale, its bulk density is relatively low. For the base material at the micrometer level, its bulk density is higher than that of the surface reconstruction material. Due to the difference in bulk density between the base material and the surface reconstruction material, the particle movement rates of the two are inconsistent under the force of the stirring blade when they are mixed, resulting in relative movement, so that the surface reconstruction material can be dispersed more effectively and evenly to achieve a better coating effect on the base material.

[0073] In some other embodiments, the specific surface area of ​​the surface reconstruction material is BET ≥ 20 m 2 / g. For example, the specific surface area BET can be 20m 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 the surface oxygen element O1s characteristics described in the embodiment of this application.

[0074] The lattice parameters of conventional oxide coatings or lithium cobalt oxide coatings are quite different from those of the NCM material core, and they are mostly physically attached rather than chemically bonded to the surface of the NCM material, and their bonding ability is not strong. As a result, during long-term charging and discharging, when the lattice parameters of the NCM material core continue to change, the conventional coating is very easy to fall off from the NCM substrate, thereby causing the coating to fail and affecting the material performance. The implementation method of the present application adopts nano-scale hydroxyl oxides, hydroxides and / or oxides of a multi-element combination of Ni, Co, M, M” as surface reconstruction materials, and the elemental composition types are basically the same as those of the core of the NCM material. Therefore, the lattice parameter difference between the two is small, chemical bonding can occur, and the bonding ability is strong, thereby greatly improving the cycle life, DCIR amplification and other properties of the positive electrode material.

[0075] Furthermore, in the process of preparing positive electrode materials using surface reconstruction materials and matrix materials, 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), since the Ni element has a weaker binding ability with the active oxygen on the surface of the material, and the Co element has a stronger binding ability with the active oxygen on the surface of the material, the surface reconstruction material can bond with the active oxygen on the surface of the matrix material, convert part of the active oxygen into vacant adsorbed oxygen, and at the same time increase the bond energy of the remaining active oxygen, reduce the peak distance between the first characteristic peak of the active oxygen and the second characteristic peak of the vacant adsorbed oxygen, increase the half-height width of the second characteristic peak, and reduce the separation degree between the first characteristic peak and the second characteristic peak, so as to obtain the positive electrode material after the surface is reconstructed in the embodiment of the present application. In order to facilitate the understanding of the process of preparing the positive electrode material by using the surface reconstruction material and the matrix material in the embodiment of the present application, the following will be combined with Figure 4 and Figure 5 Provide a detailed description.

[0076] In the third aspect, the present application also provides a method for preparing a positive electrode material. Figure 4 An exemplary description is given.

[0077] Figure 4 A flow chart of a method for preparing a positive electrode material according to some embodiments of the present application is shown. Figure 4 As shown in , the preparation method 400 may include: in step S402, the base material may be secondly mixed with the surface reconstruction material according to any one of the second aspects of the present application to obtain a second mixture, wherein the base material is a lithium nickel cobalt composite oxide, and the Ni content of the base material is higher than the Ni content of the surface reconstruction material. The base material may be an existing conventional NCM material, or other existing lithium-rich lithium nickel cobalt composite oxides.

[0078] In other embodiments, the matrix material may have a 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 Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy. Exemplarily, 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.

[0079] The matrix material may be the same as or different from the M element in the aforementioned surface reconstruction material. The M" element in the surface reconstruction material may be the same as or different from the M' element in the aforementioned matrix material. 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, so that the composition of the surface reconstruction material and the matrix material are more similar or completely the same, and it is easier to bond between the surface reconstruction material and the matrix material, so as to further improve the stability of the surface structure of the positive electrode material.

[0080] The embodiment of the present application realizes the reconstruction of the surface structure of the base material by coating the base material with a surface reconstruction material having the same or similar composition as the base material. Chemical bonding occurs between the reconstructed surface layer and the base material, and the crystal structure and lattice parameters of the reconstructed surface layer and the base material are consistent, so that the positive electrode material has a more stable structure, which can continuously protect the base material from being corroded by the electrolyte, and is conducive to improving the cracking and pulverization of the positive electrode material particles under the high voltage window, thereby improving the cycle life and safety of the positive electrode material.

[0081] In the embodiment of the present application, k≥1.0, indicating that the lithium content in the base material used to prepare the positive electrode material is excessive. According to such a setting, during the reaction between the base material and the surface reconstruction material, part of the lithium element in the base material can be transferred to the surface reconstruction material to form a lithium-containing compound (i.e., forming a surface structure in the positive electrode material).

[0082] In other embodiments, during the second mixing, the molar ratio of the base material to the surface reconstruction material can be controlled to be 1:(0.005-0.1). For example, the molar ratio can be 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, 1:0.1, etc. In some preferred embodiments, during the second mixing, the molar ratio of the base material to the surface reconstruction material can be controlled to be 1:(0.01-0.05).

[0083] When the amount of surface reconstruction material is too small, the reconstructed surface structure is difficult to fully protect the surface of the base material, and the surface active oxygen concentration at some locations is still high, which has limited effect on improving the battery's electrical properties such as gas production and cycle performance. When the amount of surface reconstruction material is too large, the thickness of the formed surface structure increases, resulting in the inability of Li ions in the base material to fully transfer to the surface of the positive electrode material to form lithium-containing compounds with the surface reconstruction material, which in turn leads to a weakened bonding ability between the reconstructed surface structure and the base material, and the surface structure is easy to fall off, affecting the cycle performance and DCIR performance of the positive electrode material.

[0084] The molar ratio of the base material to the surface reconstruction material is within the above range, so that the surface reconstruction material can completely and evenly cover the surface of the entire base material without affecting the conversion process of the surface reconstruction material into a lithium-containing compound, thereby providing better protection for the base material and continuously protecting the base material from corrosion by the electrolyte; at the same time, part of the active oxygen on the original surface of the base material can be converted into vacancy adsorbed oxygen, greatly improving the surface structural stability of the positive electrode material, so that the XPS spectrum of the prepared positive electrode material has the characteristics described above, further improving the cycle life, DCIR and other properties of the positive electrode material.

[0085] In addition, it can be understood that since the surface reconstruction material of the embodiment of the present application has the same or similar composition as the base material, the amount of surface reconstruction material added in the embodiment of the present application can be much higher than the amount of conventional oxide coating added in the prior art (the molar ratio of conventional oxide coating to base material is usually less than 0.005:1), thereby not only increasing the thickness of the surface structure to better protect the base material, but also being beneficial to improving the structural stability and cycle life, DCIR and other properties of the positive electrode material.

[0086] In other embodiments, in step S402, the second mixing can be performed in a CO2 atmosphere, and the volume concentration of CO2 in the CO2 atmosphere is ≥80%, such as 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc. Different from the dry air used in conventional mixing and coating conditions, the second mixing is performed in a CO2 atmosphere in the preparation method of the embodiment of the present application. This is because CO2 easily reacts with Li2O or LiOH on the surface of the matrix material to form Li2CO3 attached to the surface of the matrix material particles, making it easier for the surface reconstruction material used in the embodiment of the present application to react with it to form a Li-containing compound (i.e., surface material) with the same composition as the matrix material, thereby realizing the reconstruction of the surface of the matrix material to form the positive electrode material of the embodiment of the present application.

[0087] In some other embodiments, in step S402, when the second mixing is performed in the CO2 atmosphere, the CO2 atmosphere is controlled to contain water with a volume concentration of 0.05% to 10%, such as 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 surface of the matrix material and CO2, as well as the reaction rate and degree of reaction between Li2CO3 and the surface reconstruction material. When the volume concentration of water is too low, the improvement effect on the reaction rate and reaction degree is not obvious, and the difference is not much with that in the pure CO2 atmosphere. When the volume concentration of water is too high, the water will easily condense and precipitate into liquid, causing the material particles to agglomerate and making it difficult to evenly coat the surface reconstruction material.

[0088] In some embodiments, during the second mixing in step S402, an M" element additive may be further added to control 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, 1:0.01:005, 1:0.01:0.002. 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, 1:0.05:0.0005, 1:0.05:0.001, 1:0.05:0.002, 1:0.05:0.005, 1:0.05:0.01, 1:0.1:0001, 1:0.1:0.0005, 1:0.1:0.001, 1:0.1:0.002, 1:0.1:005, 1:0.1:01, etc.

[0089] In some embodiments, when the surface reconstruction material does not contain the M" element, the 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 little, the M" element additive can be added during the second mixing. The addition of the M" element is beneficial to increase the lattice defects in the formed surface material, which helps to further improve the conductivity of the positive electrode material. When the amount of the M" element additive added is too small, the improvement effect on the conductivity of the positive electrode material is not obvious. However, since the conductivity of the M" element additive itself is usually worse than that of the matrix material, when the amount of the M" element additive added is too much, it will affect the formation of the layered structure of the positive electrode material and affect the overall conductivity of the positive electrode material.

[0090] In some embodiments, the M" element additive may include at least one of the oxide, hydroxide, hydrochloride, basic carbonate, fluoride, and boride of the M" element. The M" element includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

[0091] In other embodiments, when the second mixing is performed in step S402, the second mixing speed is ≥300 rpm, and the second mixing time is ≥15 min. If the second mixing speed is too low and the second mixing time is too short, it is not conducive to uniform mixing of the second mixture. A sufficiently large second mixing speed and a sufficiently long second mixing time can be conducive to the full mixing of the second mixture, so that the surface reconstruction material can be evenly and completely coated on the surface of the base material, thereby facilitating the formation of positive electrode material particles with more uniform composition, structure, and particle size.

[0092] like Figure 4 As further shown in , the preparation method also includes step S404, in which the second mixture can be subjected to a second sintering, and the second sintering temperature is 600°C to 900°C to obtain a positive electrode material. Exemplarily, the second sintering temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, etc. When the second sintering temperature is less than 600°C, it is difficult to form a stable chemical bond between the surface reconstruction material and the matrix material, and the formed surface material can only be simply physically attached to the surface of the matrix material, making it difficult to form a stable surface structure on the surface of the matrix material. When the second sintering temperature is greater than 900°C, due to the increased atomic diffusion and rearrangement rate at high temperature, the surface reconstruction material will fully diffuse into the matrix material to form a uniform material composition, and a positive electrode material with a core-shell structure cannot be obtained, and the distribution and relative content of active oxygen and vacancy adsorbed oxygen types on the surface of the positive electrode material cannot be improved. Therefore, the second sintering temperature is in the range of 600° C. to 900° C., which is conducive to forming a stable surface structure on the surface of the base material.

[0093] In other embodiments, the second sintering time may be 4h to 10h, and the second sintering atmosphere may be air and / or oxygen. Exemplarily, the second sintering time may be, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, etc. Since it takes a certain amount of time for the lithium ions in the matrix material to diffuse into the surface reconstruction material, if the second sintering time is too short, the full reaction of the surface reconstruction material and the matrix material cannot be guaranteed. If the second sintering time is too long, there will be no significant improvement in the performance of the prepared positive electrode material, but the production cost of the positive electrode material will be increased, which is not conducive to the industrialization of the product and the embodiment of its commercial value. Therefore, the second sintering time is controlled at 4h to 10h, which is conducive to ensuring the full progress of the second sintering reaction and can also be more suitable for industrial applications.

[0094] In some other embodiments, the heating rate of the second sintering process may be ≤5°C / min. For example, the heating rate of the second sintering process may be, for example, 0.5°C / min, 1.0°C / min, 2.0°C / min, 2.5°C / min, 3.0°C / min, 4.0°C / min, 5.0°C / min, etc. Since the amount of surface reconstruction material used is relatively large, a new surface layer will be generated on the surface of the base material during the second sintering process to achieve the effect of surface reconstruction. If the heating rate is too fast, the stress between the surface reconstruction layer and the base material cannot be effectively released, the bonding is not strong enough, and the expected ideal effect of improving the cyclic performance of the material cannot be achieved.

[0095] Further, Figure 5 The flowchart of the preparation method of the positive electrode material of other embodiments of the present application is shown. Figure 5 As shown in , 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 an oxide, a hydroxide, a carbonate, and a basic carbonate of a nickel-cobalt series metal. In other embodiments, the lithium source includes at least one of Li2CO3, LiOH·H2O, LiOH, Li2O, Li2O2, and LiF.

[0096] In some other embodiments, when the first mixing is performed in step S501, the molar ratio of the matrix precursor to the lithium source can be controlled to be 1:(1.0-1.3), such as 1:1, 1:1.01, 1:1.06, 1:1.3, etc. This molar ratio range allows the lithium source to be sufficient in the preparation of the matrix material so as to obtain a matrix material with an excessive lithium content. This arrangement is beneficial to the subsequent reaction between the matrix material and the surface reconstruction material, so that sufficient lithium ions in the matrix material can be transferred to the surface reconstruction material to form a surface material that is closer to the composition of the matrix material.

[0097] In some other embodiments, during the first mixing in step S501, an M' element additive may be added to control 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, 1:1.01:0.0006. .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.

[0098] In some embodiments, the M' element additive may include at least one of an oxide, hydroxide, hydrochloride, basic carbonate, fluoride, and boride of the M' element. The M' element includes one or more of Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo, and Dy.

[0099] In some embodiments, when the matrix precursor does not contain the M' element, the M' element additive can be added during the first mixing. In other embodiments, when the M' element content in the matrix precursor is too little, the M' element additive can be added during the first mixing. The addition of the M' element is beneficial to increase the lattice defects in the formed matrix material, thereby helping to improve the conductivity of the positive electrode material. When the amount of the M' element additive added is too little, the effect of improving the conductivity of the positive electrode material is not obvious. However, since the conductivity of the M' element additive itself is usually worse than that of the matrix material, when the amount of the M' element additive added is too much, it will affect the capacity of the positive electrode material, affect the formation of the layered structure of the positive electrode material, and affect the overall conductivity of the positive electrode material.

[0100] In other embodiments, when performing the first mixing in step S501, the first mixing speed is ≥300 rpm, and the first mixing time is ≥15 min. If the first mixing speed is too low and the first mixing time is too short, it is not conducive to uniform mixing of the first mixture. A sufficiently large first mixing speed and a sufficiently long first mixing time can be conducive to sufficient mixing of the first mixture, thereby facilitating the formation of matrix material particles with more uniform composition, structure, and particle size.

[0101] like Figure 5 As further shown in , the preparation method 500 also includes step S502, in which the first mixture can be subjected to a first sintering to obtain a matrix material. In some embodiments, the first sintering temperature of the first sintering can be 700°C to 1000°C, the first sintering time can be 4h to 10h, and the first sintering atmosphere can be air and / or oxygen. Exemplarily, the first sintering temperature can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 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.

[0102] like Figure 5 As further shown in the figure, after obtaining the base material, the preparation method 500 further includes step S503 and step S504. Step S503 and step S504 are the same or similar to step S402 and step S404 described in the above text in conjunction with the preparation method 400, and will not be repeated here.

[0103] The above describes in detail the positive electrode material and the preparation method thereof according to the embodiments of the present application in combination with multiple drawings. In another aspect, the present application provides a lithium ion battery, which includes the positive electrode material described in any one of the first aspects of the present application or the positive electrode material described in the first aspect of the present application. Figure 4 or Figure 5 The preparation method described herein is used to prepare the positive electrode material.

[0104] An embodiment of the present application provides a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), comprising a housing, an electrode assembly, and an electrolyte / electrolyte. The electrode assembly and the electrolyte / electrolyte are both located in the housing.

[0105] The outer shell can be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery can also be a steel shell battery, an aluminum shell battery, etc.

[0106] The lithium-ion battery of the present application embodiment also includes, for example Figure 1 The electrode components such as the positive electrode current collector, negative electrode sheet, and separator shown in the figure will not be described in detail here.

[0107] Example:

[0108] In order to facilitate understanding of the performance of the positive electrode material and its preparation method according to the embodiment of the present application, the following will be described in conjunction with specific examples. At the same time, a number of comparative examples are also provided below to further understand the advantages of the positive electrode material according to the embodiment of the present application.

[0109] Embodiment 1:

[0110] Step 1), using a high-speed mixer to mix the matrix precursor Ni 0.6 Co 0.1 Mn 0.298 (OH)2, lithium source Li2CO3, and ZrO2 are first mixed in a molar ratio of 1:1.06:0.002, the first mixing speed is 1000 rpm, the first mixing time is 30 min, and a uniform first mixture is obtained.

[0111] Step 2), the first mixture obtained in step 1) is subjected to a first sintering, the first sintering temperature is 970°C, the first sintering time is 8 hours, the first sintering atmosphere is pure oxygen, and then cooled, roller crushed and air flow crushed, 400 mesh sieving, and demagnetizing the undersize to obtain a matrix material.

[0112] Step 3), using 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 are mixed for the second time in a molar ratio of 1:0.03:0.001, wherein the content of Na element in the surface reconstruction material is 135 ppm; the second mixing speed is 1000 rpm, the second mixing time is 30 min, and the atmosphere during the second mixing is 95% CO2 and 5% H2O (gaseous) by volume concentration to obtain a second mixture.

[0113] Step 4), the second mixture obtained in step 3) is subjected to a second sintering, the second sintering heating rate is 1.5°C / min, the temperature is 800°C, the second sintering time is 8h, the second sintering atmosphere is pure oxygen, and then cooled, roller crushed, 400 mesh sieved, and the sieved material is demagnetized to obtain the positive electrode material of this embodiment.

[0114] The present application also provides Examples 2 to 27 and Comparative Examples 1 to 4. The process conditions different from those of Example 1 are shown in Tables 1 and 2. The present application also tests the positive electrode material samples prepared in the above Examples and Comparative Examples. The battery preparation and testing methods are as follows:

[0115] (1) Preparation of batteries

[0116] Preparation of positive electrode :

[0117] The positive electrode material prepared in the embodiment or comparative example, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 96:2:2, and the mixture is stirred and mixed to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on the positive electrode current collector with the primer, and then dried, cold pressed, and cut to obtain a positive electrode sheet, the surface density of which is 350 g / m 2 , compacted density 3.5g / cm 3 .

[0118] Negative electrode sheet preparation:

[0119] The active material graphite, binder (styrene butadiene rubber SBR), and conductive agent acetylene black were dissolved in solvent deionized water at a weight ratio of 96:2:2, and evenly mixed to prepare negative electrode slurry. The slurry was coated on copper foil, dried, and cold pressed to obtain negative electrode sheets. The surface density of the negative electrode sheet was 210g / m 2 , compacted density 1.6g / cm 3 .

[0120] Diaphragm:

[0121] The diaphragm is a PE diaphragm with PVDF and alumina coating on the surface to improve adhesion and heat resistance.

[0122] Electrolyte:

[0123] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of lithium salt is 1.1 mol / L, and the electrolyte also contains 2% by weight of vinylene carbonate and 1% by weight of polysulfone.

[0124] Preparation of the battery:

[0125] The ratio of the negative electrode capacity to the positive electrode charge capacity of the battery (N / P) is controlled to be 1.05, and the injection amount of the electrolyte is 3.2g / Ah. The positive electrode sheet, the separator, the negative electrode sheet, and the separator are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare battery cell, the bare battery cell is welded with a pole ear, and the bare battery cell is placed in an aluminum-plastic bag and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes the processes of static, hot and cold pressing, formation, secondary sealing, shaping, capacity testing, etc. to obtain a lithium-ion battery product.

[0126] (2) Detecting the composition of the base material obtained in the preparation process and the prepared positive electrode material, the detection method comprising:

[0127] The content of each element in the material can be determined by instruments for qualitative analysis and / or quantitative analysis such as ICP, ICP-MS (inductively coupled plasma mass spectrometer), ICP-OES (inductively coupled plasma emission spectrometer), etc. The test method refers to GB / T24194-2009. For example, in the test example of the present application, an Agilent 5110 ICP-OES is used.

[0128] (3)XPS test

[0129] XPS test steps: After the sample powder is pressed into a tablet, it is fixed on the sample table with double-sided tape or conductive tape. After the sample is prepared, it is placed in the sample chamber and evacuated. When the vacuum degree reaches 1×10 -2 Pa, the sample was pushed into the analysis chamber for testing. X-ray photoelectron spectrometer (ESCALAB 250Xi, ThermoFischer, USA) was used for XPS testing. The vacuum degree of the analysis chamber was 8×10 -10 Pa, Al ka ray (hv=1486.6eV) was used as the excitation source, the operating voltage was 12.5kV, the filament current was 16mA, and the signal accumulation was performed for about 3 to 10 cycles. The work function of the XPS test instrument was selected to be 4.85eV, the passing energy was 30eV, and the step size was 0.1eV.

[0130] Peak separation method: Use Origin8.5 software, select XPS test data → Line mode drawing → remove baseline (Analysis window Peaks and baseline → Peak Analyzer → Opening Dialog → Recalculate select Manual option, select Fit Peaks (Pro) in Goal option → Click Next → Select Constant in Baseline Mode option, Constant = Minimum → Click Next) → Peak separation (Click Next → Uncheck Enable AutoFind, 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 Filtreing Method, cancel the Auto option in Number of Peaks, and change the number of peaks to 3 → Click Find → Click Next) → Fit correction (Select NoWeighting in Method in Weight, and select Max.Number of in Fit Control Iterations is 20, Tolerance is 1E-6 → click Fit) → click Finish. After completion, you can get the relevant results of each peak in the peak report: peak position P1, P2, P3, half-height width FWHM1, FWHM2, FWHM3, peak area Area1, Area2, Area3 values.

[0131] (4) Test of free lithium content per unit surface area

[0132] Take 5g of the positive electrode material sample and disperse it in 100ml of deionized water. Stir it magnetically for 10min and keep the water temperature at 25°C to obtain a solid-liquid mixture of dissolved residual lithium carbonate and lithium hydroxide. The solid-liquid mixture is filtered to obtain a filtrate, which is then placed on an automatic potentiometric titrator, and hydrochloric acid solution is dripped into the filtrate for titration by equivalence point titration. Based on the situation of the breakthrough point in the titration and the degree of consumption of the hydrochloric acid solution, the lithium content in the lithium carbonate and lithium hydroxide in the positive electrode material sample is calculated. In this test, a Mettler G20S potentiometric titrator was used for the above titration operation.

[0133] (5) Gram capacity test

[0134] Battery capacity test system: Take the formed and divided batteries, charge them to 4.45 / 4.40 / 4.30V in CCCV mode at 25°C (charging current 0.33C, constant voltage cut-off current 0.01C), let them stand for 10 minutes, discharge them to 3.0V in CC mode (discharge current 0.33C), and calculate the discharge capacity C mAh / g based on the discharge capacity; the equipment model is Xinweier CT-4008T-5V1A battery test cabinet.

[0135] (6) Capacity retention rate test after 500 cycles (25°C)

[0136] Cycle test system: Take the formed and capacity-divided battery, charge it to 4.45 / 4.40 / 4.30V (charging current 1.0C, constant voltage cut-off current 0.01C) in CCCV mode at 25°C, let it stand for 10 minutes, discharge it to 3.0V (discharge current 1.0C) in CC mode, and get the initial gram capacity of C1mAh / g, let it stand for 10 minutes; then repeat CCCV mode charging and CC mode discharging until 500 cycles, the last discharge gram capacity is recorded as C2mAh / g; calculate C2 / C1*100%, which is the 500-cycle capacity retention rate.

[0137] (7) Test of swelling rate

[0138] Swelling rate test system: Take the formed and divided batteries, charge them to 4.45 / 4.40 / 4.30V (charging current 1.0C, constant voltage cut-off current 0.01C) in CCCV mode at 25℃, let them stand for 10 minutes, seal the tabs and test the battery volume using the drainage method to V1cm 3 Then put it in a 60℃ constant temperature box for 30 days, take it out and let it stand until the temperature drops to 25℃, seal the tabs again and use the drainage method to test the battery volume V2cm 3 ; Calculate (V2-V1) / V1*100% to get the expansion rate.

[0139] (8) Test of DCIR growth rate

[0140] DCIR growth rate test system: Take the battery after formation and capacity division, charge it to 4.45 / 4.40 / 4.30V (charging current 1.0C, constant voltage cut-off current 0.01C) in CCCV mode at 25°C, let it stand for 10 minutes, discharge it to 3.70V (discharge current 1.0C) in CC mode, let it stand for 10 minutes, discharge it for 60 seconds using a high-rate 5C current, record the battery voltage U1 before 5C high-rate discharge, the voltage U2 after 60 seconds of discharge, and the discharge current I5; then calculate the initial DCIR0 of the battery = (U1-U2) / I5. After testing the initial DCIR0, the battery is discharged to 3.0V (discharge current 1.0C) in CC mode, and then cycled for 500 cycles according to the cycle test system. After the cycle is completed, the battery is tested using the same test method as DCIR0 to obtain the DCIR after 500 cycles. 500 Calculate the DCIR growth rate = (DCIR 500 -DCIR0) / DCIR0*100%.

[0141] (9) Median particle size D50

[0142] The particle size test method refers to GB / T 19077-2016 to characterize the particle size volume distribution of the surface reconstruction material. It can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer produced by Malvern Instruments Ltd., UK.

[0143] (10) Bulk density AD

[0144] The Scott volumetric method was used for testing. The specific testing process was as follows: the powder was placed on the screen in the upper combined funnel of the BT101 test equipment, and naturally flowed into the material distribution box, alternately passing through the four glass plates with an inclination angle of 25° and the square funnel in the material distribution box, and then flowed into the 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 keep 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 AD of the material was calculated as (m1-m 0) / V0.

[0145] (11) Specific surface area BET

[0146] The specific surface area test method refers to GB / T 19587-2017. The specific surface area analysis test method of nitrogen adsorption is used for testing, and the specific surface area analysis test is calculated by the BET (BrunauerEmmettTeller) method, wherein the specific surface area analysis test of nitrogen adsorption can be carried out by the TriStarⅡ specific surface and pore analyzer of Micromeritics Company of the United States.

[0147] In order to facilitate the description of the differences between the above-mentioned embodiments and comparative examples, as well as the test results of each embodiment and each comparative example, further description will be given below in conjunction with Tables 1 to 5. Among them, Table 1 shows the corresponding preparation conditions for preparing the base material and the composition of the base material in each embodiment and comparative example, Table 2 shows the corresponding preparation conditions for preparing the positive electrode material in each embodiment and comparative example, Table 3 shows the parameter test results of the surface reconstruction material used in each embodiment and comparative example, Table 4 shows the XPS test results of the positive electrode material prepared in each embodiment and comparative example, and Table 5 shows the electrical property test results of the positive electrode material prepared in each embodiment and comparative example.

[0148] Table 1:

[0149]

[0150]

[0151]

[0152] Table 2:

[0153]

[0154]

[0155] Table 3

[0156] Surface reconstruction materials D50 / nm <![CDATA[AD / gcm -3 ]]> <![CDATA[BET / g m 2 ]]> <![CDATA[Ni 0.08 What 0.8 Mn 0.079 Al 0.04 OOH]]> 170 0.32 72 <![CDATA[Ni 0.08 What 0.8 Mn 0.079 Al 0.04 (OH)2]]> 360 0.42 35 <![CDATA[Ni 0.08 What 0.8 Mn 0.079 Al 0.04 ABOUT 1.50 ]]> 820 0.54 23 <![CDATA[Ni 0.5 What 0.4 Mn 0.059 Al 0.04 OOH]]> 280 0.37 56 <![CDATA[Ni 0.3 What 0.4 Mn 0.259 Al 0.04 OOH]]> 523 0.41 38 <![CDATA[Ni 0.1 What 0.459 Mn 0.5 Al 0.04 OOH]]> 270 0.35 52

[0157] Table 4:

[0158]

[0159]

[0160]

[0161] Table 5:

[0162]

[0163]

[0164] From the data in Tables 1 to 5 above, we can see that:

[0165] (1) Examples 1 to 4 used surface reconstruction materials with different molar ratios to treat the base material. The results showed that as the amount of surface reconstruction material increased, the separation degree α gradually decreased, the peak spacing between peak 1 (first characteristic peak) and peak 2 (second characteristic peak) gradually decreased, the half-height width of peak 2 gradually increased, and the area proportion of peak 3 (third characteristic peak) gradually decreased. This shows that as the amount of surface reconstruction material increased, it was beneficial to convert the active oxygen on the surface of the positive electrode material into vacant adsorbed oxygen, increase the bond energy of active oxygen and the bond energy range of vacant adsorbed oxygen. From the results in Table 5, it can be seen that the gram capacity and cycle retention rate of the positive electrode materials of Examples 1 to 4 are relatively high, and the swelling rate and DCIR increase rate are relatively low, indicating that the positive electrode materials of Examples 1 to 4 have good electrical properties such as gram capacity, cycle life, safety and DCIR performance. Among them, the overall performance of the positive electrode material obtained when the molar ratio is 0.03 in Example 1 is the best. In Example 4, the amount of surface reconstruction material used is relatively large, which has begun to have a certain impact on the capacity and DCIR growth rate of the positive electrode material.

[0166] (2) Examples 5 to 27 respectively used different compositions of substrate precursor, surface reconstruction material, lithium source, M' element additive, M" element additive, molar ratio, first sintering temperature and second sintering temperature, first sintering time and second sintering temperature time, second mixed atmosphere and other process parameters. It can be seen that the XPS test results of the positive electrode materials of Examples 5 to 27 all meet the following requirements: separation α≤1.0, peak spacing between the first characteristic peak and the second characteristic peak≤2.4eV, half-height width of the second characteristic peak≥2.9eV, and area ratio of the third characteristic peak≤8.5%; and the corresponding electrical properties such as gram capacity, cycle retention rate, swelling rate, and DCIR increase are also maintained at a relatively good level. Among them, the improvement of swelling rate is conducive to ensuring the safety performance of the battery, the improvement of DCIR increase is conducive to improving the conductivity of the material, and the gram capacity reflects the capacity performance of the battery.

[0167] (3) In Comparative Example 1, no surface reconstruction material is used for coating, and its product composition is only the base material itself (i.e., equivalent to conventional NCM material). Compared with Examples 1 to 27, the separation degree α in Comparative Example 1 is greater than 1, the peak spacing is greater than 2.4 eV, the half-height width of the second characteristic peak is less than 2.9 eV, and the third characteristic peak area accounts for more than 8.5%, indicating that the active oxygen content on the surface of the positive electrode material in Comparative Example 1 is high, the bond energy of the active oxygen is low, and the bond energy range of vacancy adsorbed oxygen is narrow, which is not conducive to the stability of the positive electrode material structure and the electrical performance. For further information, see Figure 6From the cycle retention comparison chart of Example 1 and Comparative Example 1 shown in FIG, and the data shown in Table 5, it can be seen that the various electrical performance indicators in Comparative Example 1 are significantly inferior to those of Examples 1 to 27. In addition, in Comparative Example 1, without using the surface reconstruction material for coating, the second sintering treatment was also performed at the same time, which further proves that the above effect is brought about by the reconstructed surface structure, rather than the process of the second sintering treatment.

[0168] (4) Comparative Example 2 uses conventional coating layer materials to conventionally coat the base material. Compared with Examples 1 to 27, the separation α in Comparative Example 1 is greater than 1, the peak spacing is greater than 2.4 eV, the half-height width of the second characteristic peak is less than 2.9 eV, and the third characteristic peak area accounts for more than 8.5%, indicating that the active oxygen content on the surface of the positive electrode material in Comparative Example 1 is high, the bond energy of the active oxygen is low, and the bond energy range of the vacancy adsorbed oxygen is narrow, which is not conducive to the stability of the positive electrode material structure and electrical properties. As shown in Table 4, the electrical performance indicators in Comparative Example 1 are significantly inferior to those in Examples 1 to 27.

[0169] (5) Although Comparative Example 3 uses the same surface reconstruction material as Example 1 to coat the base material, the second sintering temperature of Comparative Example 3 is too low, and the surface reconstruction material cannot form a stable surface reconstruction layer on the surface of the base material, but only forms a simple physical coating. It fails to form an effective chemical bond with the surface of the base material to convert part of the active oxygen into vacant adsorbed oxygen. The XPS parameters of the finally obtained positive electrode material are not within the parameter range described in the present application, and the corresponding electrical performance indicators are significantly inferior to those of Examples 1 to 27.

[0170] (6) It can be seen from Example 19 and Comparative Example 4 that 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 separation degree α in Comparative Example 4 is greater than 1, the peak spacing is greater than 2.4 eV, the half-height width of the second characteristic peak is less than 2.9 eV, and the third characteristic peak area ratio is greater than 8.5%, indicating that the active oxygen content on the surface of the positive electrode material in Comparative Example 4 is high, the bond energy of the active oxygen is low, and the bond energy range of the vacancy adsorbed oxygen is narrow, which is not conducive to the stability of the positive electrode material structure and electrical properties. From the test results in Table 5, although the various properties of the positive electrode material prepared in Comparative Example 4 are improved compared with 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 little and fails to fully cover the entire substrate surface, resulting in the original substrate being exposed and unable to form an effective chemical bond with the surface reconstruction material and be protected.

[0171] also, Figure 2The XPS spectrum of O1s obtained by testing Comparative Example 1 is shown. Figure 3 The XPS spectrum of O1s obtained by testing the positive electrode material of Example 1 of the present application is shown. Figure 2 As shown in , the area of ​​peak 1 is larger, the peak spacing between peak 1 and peak 2 is larger, and the half-height width of peak 2 is narrower, indicating that the active oxygen content on the surface of the positive electrode material particles of comparative example 1 is higher and the bond energy is lower, the bond energy range of vacancy adsorption oxygen is narrower, and the first characteristic peak of active oxygen and the second characteristic peak of vacancy adsorption oxygen are obviously separated. Figure 3 As shown in the figure, the peak distance between peak 1 and peak 2 of the positive electrode material of Example 1 is small, the half-height width of peak 2 is wide, and there is no obvious separation between peak 1 and peak 2.

[0172] Combination Figure 2 and Figure 3 It can be seen that compared with the prior art, the active oxygen bond energy on the surface of the positive electrode material particles provided by the present application is higher, and the vacancy adsorption oxygen bond energy range is wider, which can tolerate the transition metal ions bonded thereto to change in a wider valence range, and can balance the charge distribution in a wider range without breaking, thereby improving the tolerance of the particle surface structure to overcharge and overdischarge, avoiding particle cracking and pulverization, and further improving the cycle life and impedance increase of the lithium-ion battery. At the same time, the vacancy adsorption oxygen content of the surface layer of the positive electrode material particles of the embodiment of the present application is higher, and the active oxygen content is lower, which can effectively alleviate the occurrence of side reactions between the surface layer of the positive electrode material and the electrolyte, reduce the gas production of the lithium-ion battery, and ultimately achieve the effects of improving the cycle life, impedance increase, safety, etc. of the lithium-ion battery.

[0173] In summary, the embodiments of the present application provide a positive electrode material having the same or similar composition as the base material of the surface material, so that the structure of the positive electrode material is more stable, so as to effectively avoid the problem that the coating layer is easy to fall off, and the material particles are easy to crack or pulverize under the high voltage window, thereby helping to increase the use voltage of the positive electrode material, and improving the electrical properties of the positive electrode material in terms of cycle life, swelling rate, conductivity and capacity. Further, the positive electrode material of the embodiments of the present application has the characteristics of low surface active oxygen content, large active oxygen bond energy, wide range of vacancy adsorption oxygen bond energy, low content of oxygen element corresponding to the residual base formed by combining with Li, thereby improving the electrical properties of the positive electrode material in terms of cycle life, swelling rate, conductivity and capacity.

[0174] Although multiple embodiments of the present application have been shown and described herein, it is obvious to those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art can think of many changes, modifications and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The attached claims are intended to limit the scope of protection of the present 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 positive electrode material, the surface oxygen element O1s characteristic peak of the positive electrode material can obtain at least two characteristic peaks after peak separation, 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 positive electrode 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 distance between the first characteristic peak and the second characteristic peak is ≤2.4 eV.

2. The positive electrode material according to claim 1, characterized in that The surface oxygen element O1s characteristic peak of the positive electrode material can also obtain a third characteristic peak after peak separation. The third characteristic peak is within 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 positive electrode material according to claim 1, characterized in that The half-width of the second characteristic peak is ≥2.9 eV.

4. The positive electrode 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 distance between the first characteristic peak and the second characteristic peak is ≤2.4 eV.

6. The positive electrode material according to any one of claims 1 to 5, characterized in that The positive electrode material has the general chemical 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.

7. The positive electrode material according to any one of claims 1 to 5, characterized in that The positive electrode material satisfies at least one of the following conditions: (1) The free lithium content per unit area of ​​the surface of the positive electrode material is 200 μg / m 2 ~800 μg / m 2 ; (2) The positive electrode material is a single crystal positive electrode material, and the average particle size of the positive electrode material is 1 μm to 10 μm; (3) The positive electrode material is a single crystal positive electrode material, and the positive electrode material contains at least one particle with the same orientation.

8. A surface reconstruction material, characterized in that: The surface reconstruction material is used to form the surface structure of the positive electrode material according to any one of claims 1 to 7, 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 ) 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; and the content of Na in the surface reconstruction material is in the range of 50ppm to 300ppm.

9. The surface reconstruction material according to claim 8, 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: 10 nm ≤ D50 ≤ 1000 nm; (2) The bulk density AD of the surface reconstruction material is ≤ 0.6 g / cm 3 ; (3) The specific surface area of ​​the surface reconstruction material is BET ≥ 20 m 2 / g; (4) The surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the Ni content of the surface reconstruction material is lower than the Ni content of the matrix material; (5) The surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the Co content of the surface reconstruction material is higher than the Co content of the matrix material; (6) The surface reconstruction material is used to react with the matrix material to form the positive electrode material, wherein the matrix material has a chemical formula: Li k Ni f Co g M h M' 1-f-g-h O2, 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 Al, Ti, Y, Zr, Mg, Sr, W, Nb, Ce, La, Mo and Dy.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to any one of claims 1 to 7.

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