Positive electrode material and preparation method thereof, positive electrode plate and secondary battery

Abstract

The invention discloses a positive electrode material and a preparation method thereof, a positive electrode plate and a secondary battery. The positive electrode material comprises a base body and a coating layer coating the surface of the base body, the coating layer comprises Li and W, analysis is carried out in the depth direction of particles of the positive electrode material through XPS, and the sum of atomic weight ratios of Li and W measured after the surface of the positive electrode material is etched for 0 second, 4 seconds and 8 seconds through XPS is 80% or above. The surface of the positive electrode material is provided with a complete and uniform coating layer, so that the cycle life and the thermal stability of the positive electrode material are improved.

Description

Technical Field

[0001] This application relates to the field of battery cathode material technology, specifically to a cathode material and its preparation method, a cathode sheet, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles; however, their energy density is insufficient, resulting in short driving range on a single charge, failing to meet the needs of most car consumers. Therefore, there is an urgent need to further improve the energy density of lithium-ion batteries, and developing cathode materials with higher specific capacity is key to this improvement. Increasing the Ni content in the cathode material can improve its discharge specific capacity and energy density. However, increasing the Ni content causes severe phase transitions and oxygen release during charging and discharging, and the surface is prone to side reactions with the electrolyte, leading to poor cycle performance and thermal stability, thus limiting its widespread application. Therefore, there is an urgent need to develop a novel cathode material to address these issues. Summary of the Invention

[0003] In view of this, in order to solve at least one of the above defects, this application provides a cathode material.

[0004] In addition, this application also provides a method for preparing the aforementioned positive electrode material, a positive electrode sheet using the aforementioned positive electrode material, and a secondary battery.

[0005] In a first aspect, embodiments of this application provide a cathode material, the cathode material comprising a substrate and a coating layer, the coating layer being coated on the surface of the substrate, the coating layer comprising Li and W elements, and the cathode material satisfying: Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) All are greater than 80%. Specifically, X-ray photoelectron spectroscopy (XPS) analysis was performed on the cathode material particles along their depth direction. The sum of the atomic percentages of Li and W atoms measured after 0 seconds of XPS etching on the surface of the cathode material was the Z value. (Li+W)-XPS(0秒) The sum of the atomic weight ratios of Li and W atoms obtained after etching the surface of the cathode material using XPS for 4 seconds is the Z. (Li+W)-XPS(4秒) The sum of the atomic weight ratios of Li and W atoms obtained by etching the surface of the cathode material using XPS for 8 seconds is the Z. (Li+W)-XPS(8秒) .

[0006] In some possible embodiments, Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) With Z (Li+W)-XPS(8秒) The relation satisfies: 0 ≤ |Z (Li+W)-XPS(0秒) -Z (Li+W)-XPS(4秒) |≤0.1,0≤|Z(Li+W)-XPS(0秒) -Z (Li+W)-XPS(8秒) |≤0.1

[0007] In some possible embodiments, the positive electrode material satisfies: Z (Li+W)-XPS(0秒) is above 90%, Z (Li+W)-XPS(4秒) is above 80%, Z (W)-XPS(8秒) is above 80%

[0008] In some possible embodiments, the chemical formula of the coating layer is Li d W e O f , where 0 < d < 0.5, 0 < e < 0.002, 0 < f ≤ 2

[0009] In some possible embodiments, the mass proportion of W element in the positive electrode material is 500 ppm to 2000 ppm

[0010] In some possible embodiments, the chemical formula of the positive electrode material is: Li b Ni x Co y F z W h M m O2, where 0.95 ≤ b ≤ 1.05, 0.8 ≤ x < 1, 0 < y + z ≤ 0.2, x + y + z + h = 1, 0.0001 ≤ h ≤ 0.003, 0 ≤ m < 1, the F element is selected from at least one of Mn and Al; the M element is selected from at least one of Ca, Ti, Zr, Sr, Mg, Sb, Y, and La

[0011] In some possible embodiments, the thickness of the coating layer is 2 - 5 nm

[0012] In some possible embodiments, the matrix includes secondary particles, the secondary particles include a plurality of primary particles, and the secondary particles are spherical or quasi-spherical

[0013] In some possible embodiments, the specific surface area of the positive electrode material is 0.5 m 2 / g - 2.0 m 2 / g

[0014] In some possible embodiments, the tap density of the positive electrode material is 1.0 g / m 3 - 3.0 g / m 3

[0015] In some possible embodiments, the powder conductivity of the positive electrode material under a pressure of 4 kN / cm 2 is greater than 0.02 S / cm

[0016] Secondly, embodiments of this application provide a method for preparing the aforementioned cathode material, comprising: mixing an oxide or hydroxide precursor with a lithium source and sintering the mixture to obtain a primary sintering product; crushing and dispersing the primary sintering product, and then re-sintering the dispersed primary sintering product with added lithium to obtain a re-sintered product; washing the re-sintered product with water, and then filtering the washed re-sintered product by pressure to obtain a filter cake; and spraying a suspension containing a coating material onto the surface of the filter cake, continuously stirring, so that the coating elements in the coating material react with the lithium in the re-sintered product through intermittent gradient temperature to form a coating layer, thereby obtaining the cathode material.

[0017] Thirdly, embodiments of this application also provide a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive electrode material as described above.

[0018] Fourthly, embodiments of this application also provide a secondary battery, including a casing, an electrode assembly, and an electrolyte or electrolyte solution, wherein the electrode assembly and the electrolyte or electrolyte solution are both located within the casing, the electrode assembly includes a separator and a negative electrode plate, characterized in that the electrode assembly further includes a positive electrode plate as described above, and the separator is disposed between the positive electrode plate and the negative electrode plate.

[0019] The cathode material provided in this embodiment has a complete coating layer on its surface, and by controlling Z... (Li+W)-XPS(0秒 Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) The percentages are all greater than 80%, indicating that the sum of the atomic weights of Li and W atoms at multiple detection points at different depths in different layers within the 0-2nm depth range is all above 80%. This indicates that the coating layer formed on the surface of the cathode material is complete, uniform, and has no obvious voids, which is beneficial to improving the structural stability of the particles. At the same time, the complete coating layer can effectively isolate the cathode material from direct contact with the electrolyte, reducing interfacial side reactions. While suppressing battery polarization and buffering the volume expansion of the cathode material, the coating layer also has lithium-ion transport capacity, thereby improving the cycle life and thermal stability of the cathode material. Attached Figure Description

[0020] Figure 1 This is a cross-sectional schematic diagram of a secondary battery charging using the cathode material of an embodiment of this application.

[0021] Figure 2 This is a cross-sectional schematic diagram of a secondary battery discharging using the cathode material of this application embodiment.

[0022] Figure 3This is a scanning electron microscope (SEM) image of the cathode material of Example 1 of this application.

[0023] Figure 4 This is a SEM image of the cathode material in Comparative Example 1. Detailed Implementation

[0024] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0025] Existing high-nickel cathode materials have poor cycle performance and structural stability. They are usually improved by coating the material surface. However, the resulting coating layer has many voids and is uneven, resulting in poor coating effect.

[0026] Therefore, this application provides a cathode material comprising a matrix and a coating layer covering the surface of the matrix, the coating layer comprising Li and W elements, and the cathode material satisfying: Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) All are greater than 80%. Among them, the sum of the atomic weight ratios of Li atoms and W atoms measured by X-ray photoelectron spectroscopy (XPS) at the depth direction of the cathode material particles, after 0 seconds of XPS etching on the surface of the cathode material, is the Z. (Li+W)-XPS(0秒) The sum of the atomic weights of Li and W atoms measured after 4 seconds of XPS etching on the surface of the cathode material is the Z. (Li+W)-XPS(4秒) The sum of the atomic weight ratios of Li and W atoms measured after etching the surface of the cathode material using XPS for 8 seconds is the Z. (Li+W)-XPS(8秒) .

[0027] It should be noted that the sum of the atomic weights of Li and W atoms at a certain etching time, Z, is... (Li+W)-XPS(x秒) Z is calculated using the following formula (1): (Li+W)-XPS(x秒)=M(Li+W) / M(A)×100%——(1), where M(Li+W) in equation (1) is the sum of the atomic masses of Li and W atoms at the corresponding XPS etching time x seconds, and M(A) is the sum of the atomic masses of Li, Ni, Co, F, W, and M measured at the corresponding XPS etching time. F is selected from at least one of Mn and Al, and M is selected from at least one of Ca, Ti, Zr, Sr, Mg, Sb, Y, and La. It can be understood that Z... (Li+W)-XPS(x秒) This represents the average percentage of Li and W atoms at n locations at an etching time of X seconds. Testing at these n locations reflects the coating at the etching depth. n is a natural number greater than 10.

[0028] The coating layer includes Li and W elements, and the distribution of Li and W elements in the coating layer directly reflects the coating effect. The position at 0 seconds of XPS etching corresponds to the surface of the cathode material; the position at 4 seconds represents the cathode material extending radially inward from the surface to a depth of 1 nm; and the position at 8 seconds represents the cathode material extending radially inward from the surface to a depth of 2 nm. In other words, by controlling Z... (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) The percentages are all greater than 80%, indicating that the sum of the atomic weights of Li and W atoms at different depths within the 0-2nm depth range is all above 80%. This suggests that the coating layer on the surface of the cathode material is complete, has good uniformity, and has no obvious voids, which is beneficial to improving the structural stability of the particles. At the same time, this complete coating layer can effectively isolate the cathode material from direct contact with the electrolyte, reduce interfacial side reactions, and thus improve the cycle life and thermal stability of the cathode material.

[0029] It should be noted that, in the embodiments of this application, the area etched by the X-ray photoelectron spectrometer at 0 seconds is the surface of the positive electrode material, and the area etched by the X-ray photoelectron spectrometer from 0 to 8 seconds (excluding 0 seconds) is the surface layer of the positive electrode material.

[0030] Furthermore, the sum of the atomic weights Z of Li and W atoms obtained from the surface of the cathode material after 0 seconds of XPS etching was determined. (Li+W)-XPS(0秒) The sum of the atomic weights of Li and W atoms obtained from the surface of the cathode material after XPS etching for 4 seconds is over 90%. (Li+W)-XPS(4秒) The sum of the atomic percentages of Li and W atoms at the surface of the cathode material, obtained by XPS etching for 8 seconds, is over 80%. (Li+W)-XPS(8秒)The percentage is above 80%. This indicates that the surface of the cathode material is uniformly coated with a Li and W-containing layer, especially at XPS etching 0 seconds, where the sum of the atomic weights of Li and W atoms exceeds 90%. This high Li+W content indicates that a complete coating layer has been formed on the surface of the cathode material. Furthermore, the difference in the sum of the atomic weights of Li and W atoms at XPS etching 0 seconds, 4 seconds, and 8 seconds is small, indicating that the difference in the sum of the atomic weights of Li and W atoms at different depths on the surface of the cathode material is small. This suggests that the coating layer on the surface of the cathode material is uniform and complete, which is beneficial to improving the structural stability of the particles, thereby improving the cycle life and thermal stability of the cathode material.

[0031] Preferably, Z (Li+W)-XPS(0秒) Further above 95%; Z (Li+W)-XPS(4秒) Further above 85%, further above 90%; Z (Li+W)-XPS(8秒) Furthermore, it exceeds 85%.

[0032] Furthermore, Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) With Z (Li+W)-XPS(8秒) The following relationship must be satisfied: 0 ≤ |Z (Li+W)-XPS(0秒) -Z (Li+W)-XPS(4秒) |≤0.1,0≤|Z (Li+W)-XPS(0秒) -Z (Li+W)-XPS(8秒) |≤0.1. This formula shows that the difference in the sum of the atomic weights of Li and W at different depths on the surface of the cathode material is small, below 10%, indicating that the coating layer on the surface of the cathode material is uniform and complete.

[0033] In some embodiments, the chemical formula of the coating layer is Li d W e O f Where 0 < d < 0.5, 0 < e < 0.002, and 0 < f ≤ 2. The coating element W in the coating layer formed on the surface of the cathode material reacts with the Li element on the surface of the cathode material to form a more stable lithium tungstate composite compound, which can improve the stability of the coating layer, thereby reducing the risk of Li atom dissolution, and further improving the cycle life and thermal stability of the cathode material.

[0034] In some embodiments, the thickness of the coating layer can be 2–5 nm. This application embodiment effectively isolates negative reactions such as those caused by the electrolyte by forming a 2–5 nm coating layer on the surface of the positive electrode material. Exemplarily, the thickness of the coating layer can be any value within the range of 2 nm, 3 nm, 4 nm, 5 nm, or any two of these values.

[0035] In some embodiments, the general chemical formula of the positive electrode material is: Li b Ni x Coy F z N h M m O2, where 0.95 ≤ b ≤ 1.05, 0.8 ≤ x < 1, 0 < y + z ≤ 0.2, x + y + z + h + m = 1, 0.0001 ≤ h ≤ 0.003, 0 ≤ m < 1. The F element is selected from at least one of Mn and Al; the N element is selected from at least one of tungsten, molybdenum, antimony, zirconium, etc.; the M element is selected from at least one of Ca, Ti, Zr, Sr, Mg, Sb, Y, La.

[0036] In some embodiments, the mass ratio of the W element in the cathode material is 500 ppm to 2000 ppm. By controlling the content of the coating element W, the active Li on the surface layer of the cathode material can be fully neutralized to transform into a more stable composite compound, and at the same time, a dense and uniform complete coating layer is formed. Exemplarily, the mass ratio of the W element in the cathode material can be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm or any value within the range composed of any two of the above values.

[0037] In some embodiments, the matrix is secondary particles formed by the aggregation of primary particles, and the shape of the secondary particles is spherical or quasi-spherical. In the field of cathode materials, primary particles are usually single fine grains, and secondary particles are formed by the stacking and agglomeration of primary particles. By controlling that there are multiple primary particles in the secondary particles, grain boundaries are formed between the multiple primary particles, and the grain boundaries can provide a large number of migration channels for the migration of Li ions, thereby further improving the lithium ion migration rate.

[0038] In some embodiments, the specific surface area of the cathode material is 0.5 m 2 / g to 2.0 m 2 / g. Controlling the specific surface area of the cathode material within the above suitable range effectively reduces the side reactions between the particles and the electrolyte to optimize the cycling performance and storage performance of the cathode material. Exemplarily, the specific surface area of the cathode material can be 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g or any value within the range of any two of the above values.

[0039] In some embodiments, the loose packing density of the positive electrode material is 1.0 g / m³. 3 ~3.0g / m 3 The cathode material has a suitable loose packing density, thereby improving the battery's energy density, capacity, and cycle performance. For example, the loose packing density of the cathode material can be 1.0 g / m³. 3 2.0g / m 3 3.0g / m 3 Or any value within the range formed by any two of the above values.

[0040] In some embodiments, the positive electrode material is at 4 kN / cm 2 The electrical conductivity of the powder under pressure is greater than 0.02 S / cm. The cathode material exhibits excellent powder conductivity and low resistance.

[0041] The cathode material provided in this application embodiment has a coating layer containing Li and W on its surface, and by controlling Z... (Li+W)-XPS(0秒 Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) The percentages of Li and W atoms at multiple detection points at different depths and layers within the 0–2 nm depth range are all greater than 80%, indicating that the surface coating of the cathode material is complete, uniform, and free of significant voids. This is beneficial for improving the structural stability of the particles. Furthermore, this complete coating effectively isolates the cathode material from direct contact with the electrolyte, reducing interfacial side reactions. In addition to suppressing battery polarization and buffering the volume expansion of the cathode material, this coating also possesses lithium-ion transport capabilities, thereby improving the cycle life and thermal stability of the cathode material.

[0042] The aforementioned method for preparing the cathode material specifically includes the following steps:

[0043] Step S1: Mix the oxide precursor or hydroxide precursor with the lithium source and sinter the mixture to obtain a primary sintering product.

[0044] Specifically, Ni x Co y F z oxides or Ni x Coy F z The hydroxide is mixed with a lithium source to obtain a mixture, which is then sintered to obtain a primary sintering product, wherein x+y+z=1 and M is selected from at least one of Mn or Al.

[0045] In some embodiments, the amount of lithium source added is such that the ratio of the total molar content of Ni, Co and M to the molar content of Li is 1:(0.95 to 1.2).

[0046] In some embodiments, the lithium source may include at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, and lithium oxalate.

[0047] In some embodiments, a dopant containing element M may be added during the sintering process to improve the structural stability and electrical properties of the cathode material, wherein element M is selected from at least one of Ca, Ti, Zr, Sr, Mg, Sb, Y, and La.

[0048] In some embodiments, the primary sintering temperature of the mixture can be 710°C to 730°C. Controlling the sintering temperature within this range can promote the diffusion of ions and vacancies, promote particle rearrangement, and improve crystallization performance and sintering rate. In addition, the primary particle size of the sintered product formed at the above sintering temperatures is suitable and the density is compact, which is beneficial to improving the tap density and also facilitates the extraction and insertion of lithium ions. The primary sintering temperature can be, by example, any value within the range of 710°C, 720°C, 730°C, or any two of the above values.

[0049] In some embodiments, the sintering time of the mixture at one stage can be 5 h to 13 h. The above sintering time can control the single crystal particle size of the sintered product within a suitable particle size range.

[0050] Step S2: The above-mentioned primary sintering product is crushed and dispersed, and the dispersed primary sintering product is re-sintered with lithium to obtain the re-sintered product.

[0051] The process of crushing and dispersing the first sintering product can effectively improve its dispersibility. Then, the dispersed first sintering product is re-sintered with lithium to re-incorporate lithium into the crystal nucleus, which can improve the crystal structure of the cathode material, increase the lithium content in the crystal nucleus, and control the low lithium content on the surface and high lithium content inside the re-sintered product. This results in a gradient diffusion distribution of lithium concentration between the crystal nucleus and the surface of the re-sintered product, creating a certain concentration difference between the inner and outer Li components.

[0052] In some embodiments, the re-firing temperature can be 600℃ to 740℃, and the re-firing time can be 2h to 10h. By controlling the re-firing temperature and time, the lithium salt and precursor can be fully dissolved and mixed, increasing the contact and reaction area and the degree of mixing. This effectively replenishes lithium within the crystal nucleus of the primary sintering product, improves the crystal structure, and increases the capacity of the cathode material. Furthermore, the distribution pattern of lithium in the re-firing product can be controlled, allowing lithium to fully penetrate the crystal nucleus, reducing the surface lithium content, and ensuring that the concentrations of lithium in the crystal nucleus and on the surface of the re-firing product exhibit a gradient diffusion distribution as described above. For example, the reheating temperature can be any value within the range of any two values ​​of 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, or above; the reheating time can be any value within the range of any two values ​​of 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, or above.

[0053] In some embodiments, a lithium source of 0.1 wt% to 0.5 wt% based on the mass of the first sintered product is added for re-sintering.

[0054] In some embodiments, the lithium source for re-firing may include at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, and lithium oxalate. During the re-firing process, the lithium source added may be the same as or different from that in step S1.

[0055] Step S3: Wash the re-fired product with water, and then filter the washed re-fired product by pressure to obtain a filter cake.

[0056] The re-fired product is placed in a reactor, pure water is added and stirred for washing. By washing the re-fired product, some of the Li on the surface can be washed away, which can control the content of residual Li on the material surface and further control the content of lithium on the material surface and the lithium in the crystal core.

[0057] In some embodiments, the amount of pure water added is 30% to 100% of the weight of the sintered product, and the water washing temperature can be 10°C to 25°C. By controlling the amount of pure water added and the water washing temperature, the content of residual Li on the material surface can be further adjusted to further control the content of lithium on the material surface and lithium in the crystal nucleus. The amount of pure water added can further be 50% to 80% of the weight of the sintered product. For example, the amount of pure water added can further be any value within the range of any two values ​​of 30%, 40%, 50%, 60%, 70%, 80% or more of the weight of the sintered product.

[0058] In some embodiments, the stirring speed during water washing is 200 rpm to 2000 rpm. By controlling the stirring speed during water washing, the thoroughness of Li removal from the material surface can be controlled. Controlling the stirring speed within this range allows the Li element content on the surface of the cathode material to be within a suitable range, facilitating further regulation of the Li gradient concentration difference on the surface. The stirring speed during water washing can further be 200 rpm to 1000 rpm, or further 500 rpm to 800 rpm. Exemplarily, the stirring speed during water washing can be any value within the range of 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, or any two of the above values.

[0059] Step S4: Spray a suspension containing the coating material onto the surface of the filter cake and stir continuously. Through intermittent gradient temperature reaction, the coating elements in the coating material react with the lithium elements in the reburning product to form a coating layer, thereby obtaining the cathode material.

[0060] The filter cake is returned to the reactor, and a suspension of coating material is sprayed onto the filter cake to allow it to penetrate. Simultaneously, by controlling the stirring speed and reaction temperature, the coating elements react fully with the lithium in the refired product to form a coating layer. Using a spray method improves the dispersibility of the suspension on the surface of the refired product, increases the contact probability between the suspension and the product, and thus improves the uniformity and integrity of the coating. Furthermore, the spray method allows for more effective control of the coating layer thickness. Specifically, the suspension of coating material can be uniformly sprayed onto the surface of the filter cake using an atomizing nozzle.

[0061] The coating material can be an oxide, hydroxide, or other form of the coating element. Specifically, the coating element can be W, which reacts with Li in the remelting product to form Li. d W e O f Where 0 < d < 0.5, 0 < e < 0.002, and 0 < f ≤ 2. During the spraying of W, W can not only react with Li on the surface of the reburned product, but also penetrate to a certain depth inside the reburned product, and then react with the Li inside, thereby forming a coating layer with a certain thickness. Since Li with a concentration gradient distribution is formed in the reburned product in the aforementioned step S3, lithium tungstate with a concentration gradient distribution is formed in the coating layer, realizing a coating layer with low Li on the surface and high Li inside.

[0062] Furthermore, by using intermittent gradient temperature reactions, each layer in the formed coating layer can have sufficient time and temperature to react, achieving coating layer recombination. This results in a more complete and uniform coating layer, reducing the formation of gaps. Specifically, the intermittent gradient temperature reaction includes a first reaction stage, a second reaction stage, and a third reaction stage that proceed continuously.

[0063] In some embodiments, the reaction temperature of the first reaction stage can be 100°C to 140°C, and the reaction time can be 1 hour to 6 hours. This stage is a low-temperature reaction stage, under short-term low-temperature conditions, which can remove moisture from the coated reheated product. Exemplarily, the reaction temperature can be any value within the range of any two values ​​of 100°C, 110°C, 120°C, 130°C, 140°C, or above; the reaction time can be any value within the range of any two values ​​of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or above.

[0064] In some embodiments, the reaction temperature of the second reaction stage can be 150°C to 170°C, and the reaction time can be 5 h to 13 h. At a relatively low temperature and over a longer time, W element can penetrate uniformly and sufficiently into the re-fired product, facilitating subsequent reaction with Li to form a lithium tungstate coating layer. Exemplarily, the reaction temperature can be any value within the range of 150°C, 160°C, 170°C, or any two of these values; the reaction time can be any value within the range of 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, or any two of these values.

[0065] In some embodiments, the reaction temperature of the third reaction stage can be 180°C to 220°C, and the reaction time can be 11h to 18h. This stage is a high-temperature reaction stage. Under relatively high temperature and long reaction time conditions, Li and W can react fully to form a uniform and complete lithium tungstate coating layer. Exemplarily, the reaction temperature can be any value within the range of 180°C, 190°C, 200°C, 210°C, 220°C, or any two of the above values; the reaction time can be any value within the range of 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, or any two of the above values.

[0066] In some embodiments, the thickness of the coating layer can be 2–5 nm. During the reaction process, by controlling the amount of sprayed coating material and process parameters, a thin and uniform coating layer with a thickness of less than 5 nm can be formed on the surface of the re-fired product. This effectively isolates negative reactions such as those caused by the electrolyte, and the coating layer with a thickness of less than 5 nm can also modify active substances, resulting in better material properties.

[0067] In some embodiments, the stirring speed of the reaction can be from 100 rpm to 500 rpm. By controlling the stirring speed, the contact opportunity between the suspension and the surface of the reheated product can be increased, thereby ensuring sufficient contact between W and the surface of the reheated product, and improving the uniformity and integrity of the formed coating layer.

[0068] In some embodiments, the solid content in the suspension of the coating material is 1% to 100%. During the coating process, the coating material forms a suspension by mixing with water. By controlling the solid content of the suspension, it is possible to adapt to different spraying conditions and achieve uniform spraying of the coating material. In some embodiments, the moisture content of the filter cake is 0% to 10%. By controlling the moisture content of the filter cake within the above range, it is possible to suppress the slurry formation of the filter cake, which leads to an increase in viscosity. This is beneficial for the diffusion of W element into the interior of the refired product and the reaction between W element and Li element. At the same time, it can also shorten the drying time and improve production efficiency. In addition, it can further suppress lithium dissolution, reduce residual alkali on the material surface, and improve the cycle life of the cathode material. The moisture content of the filter cake can further be 0% to 5%, or further, 0% to 3%. Exemplarily, the moisture content can be any value within the range of 0%, 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of the above values.

[0069] This application also provides a positive electrode sheet using the aforementioned positive electrode material, including a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the aforementioned positive electrode material.

[0070] The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, the current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0071] This application also provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing. The electrode assembly includes a separator, a negative electrode, and the aforementioned positive electrode, with the separator disposed between the positive and negative electrode.

[0072] like Figure 1 and Figure 2 The figures shown are schematic diagrams illustrating the lithium delithiation and lithium insertion processes during charging and discharging of lithium-ion batteries prepared using the aforementioned cathode materials. Figure 1 As shown, when a lithium-ion battery is charged, lithium ions are released from the positive electrode and embedded in the negative electrode; as... Figure 2 As shown, when a lithium-ion battery discharges, lithium ions are released from the negative electrode and inserted back into the positive electrode.

[0073] In some embodiments, the outer casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), for example, the secondary battery is a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0074] In some embodiments, the electrode assembly may be a stacked structure, which is formed by alternating layers of a positive electrode, a separator, and a negative electrode. In other embodiments, the electrode assembly may also be a wound structure, which is formed by winding a positive electrode, a separator, and a negative electrode after they are stacked in sequence.

[0075] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this 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. The battery provided in this application embodiment has advantages such as high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and there is no limitation here.

[0076] The cathode material in this embodiment has a Li and W-containing coating layer on its surface. This coating layer is complete and uniform, with no obvious voids, which improves the structural stability of the cathode material. Simultaneously, it effectively isolates the cathode material from direct contact with the electrolyte, reducing interfacial side reactions and gas generation. Furthermore, it suppresses volume strain during the charging and discharging process of the active material, improving safety. In addition to suppressing battery polarization and buffering the volume expansion of the cathode material, this coating layer also possesses lithium-ion transport capabilities, thereby improving the cycle life and thermal stability of the cathode material. This is beneficial for enhancing the cycle life and thermal stability of the battery, thus promoting the development and application of lithium-ion batteries.

[0077] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0078] Example 1

[0079] Step S1: Weigh 3 kg of the hydroxide precursor Ni 0.905 Co 0.042 Al 0.053 (HO)2 and 1.725 kg of lithium hydroxide pulverized to a particle size of 18 μm were placed in a high-speed mixer and mixed at a speed of 800 rpm. The mixed material was then placed in a box furnace at 720°C for a first sintering to obtain a first sintered product.

[0080] Step S2: After crushing the above-mentioned primary sintering product, it is sieved, and the sieved primary sintering product is then subjected to lithium replenishment and re-sintering.

[0081] Among them, the lithium supplementation sintering stage: 0.1 wt% of lithium hydroxide based on the mass of the primary sintering product is added and the primary sintering material is re-sintered at 650°C for 3 hours to obtain the re-sintered product;

[0082] Step S3: Take 3 kg of the above recalcined product and put it into the reactor. Add 2.4 kg of pure water for washing. Set the washing time to 30 min, the washing temperature to 20℃, and the stirring speed to 800 rpm. Pour the washed slurry into a filter press for filtration to obtain a filter cake with a moisture content of 5% by mass.

[0083] Step S4: Return the filter cake to the reactor; weigh 5g of tungsten oxide powder, place it in a graduated cylinder, add pure water, and ultrasonically disperse to prepare a suspension with a solid content of 5%. Spray the suspension evenly onto the filter cake in the reactor using an atomizing nozzle. Set three sets of gradient temperature stirring: the reaction temperature for the first stage is 120℃, and the reaction time is 5h; the reaction temperature for the second stage is 160℃, and the reaction time is 7h; the reaction temperature for the third stage is 200℃, and the reaction time is 12h. The stirring speed for all three stages is 100rpm. After the reaction is complete, a high-capacity cathode material is obtained.

[0084] Example 2

[0085] The difference from Example 1 is that the 3 kg hydroxide precursor in step S1 is replaced with 3 kg of oxide precursor Ni. 0.905 Co 0.042 Al 0.053 O2, the other steps are basically the same as in Example 1, please refer to Example 1 for details.

[0086] Example 3

[0087] The difference from Example 1 is that 1.725 kg of lithium hydroxide pulverized to a particle size of 18 μm in step S1 is replaced with 1.725 kg of lithium carbonate pulverized to a particle size of 18 μm. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0088] Example 4

[0089] The difference from Example 1 is that 1.725 kg of lithium hydroxide pulverized to a particle size of 18 μm in step S1 is replaced with 1.725 kg of lithium acetate pulverized to a particle size of 18 μm. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0090] Example 5

[0091] The difference from Example 1 is that 1.725 kg of lithium hydroxide pulverized to a particle size of 18 μm in step S1 is replaced with 1.725 kg of lithium nitrate pulverized to a particle size of 18 μm. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0092] Example 6

[0093] The difference from Example 1 is that 1.725 kg of lithium hydroxide pulverized to a particle size of 18 μm in step S1 is replaced with 1.725 kg of lithium oxalate pulverized to a particle size of 18 μm. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0094] Example 7

[0095] The difference from Example 1 is that the sintering temperature in step S1 is 710°C. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0096] Example 8

[0097] The difference from Example 1 is that the sintering temperature in step S1 is 730°C. The other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0098] Example 9

[0099] The difference from Example 1 is that in step S3, the amount of pure water added is 1.8 kg. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0100] Example 10

[0101] The difference from Example 1 is that in step S3, the amount of pure water added is 3 kg. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0102] Example 11

[0103] The difference from Example 1 is that the water washing temperature in step S3 is 10°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0104] Example 12

[0105] The difference from Example 1 is that the water washing temperature in step S3 is 15°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0106] Example 13

[0107] The difference from Example 1 is that in step S3, the water washing temperature is 25°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0108] Example 14

[0109] The difference from Example 1 is that in step S3, the stirring speed for water washing is 200 rpm. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0110] Example 15

[0111] The difference from Example 1 is that in step S3, the stirring speed for water washing is 1000 rpm. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0112] Example 16

[0113] The difference from Example 1 is that in step S3, the stirring speed for water washing is 2000 rpm. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0114] Example 17

[0115] The difference from Example 1 is that in step S3, the water content of the filter cake is 0% by mass. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0116] Example 18

[0117] The difference from Example 1 is that in step S3, the water content of the filter cake is 10% by mass. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0118] Example 19

[0119] The difference from Example 1 is that in step S4, the reaction temperature of the first reaction stage is 140°C and the reaction time is 6 hours; the reaction temperature of the second reaction stage is 170°C and the reaction time is 5 hours; the reaction temperature of the third reaction stage is 190°C and the reaction time is 13 hours. Other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0120] Example 20

[0121] The difference from Example 1 is that in step S4, the reaction temperature of the first reaction stage is 140°C and the reaction time is 2 hours; the reaction temperature of the second reaction stage is 1500°C and the reaction time is 13 hours; the reaction temperature of the third reaction stage is 210°C and the reaction time is 7 hours. Other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0122] Example 21

[0123] The difference from Example 1 is that in step S4, the reaction temperature of the first reaction stage is 120°C and the reaction time is 1 hour; the reaction temperature of the second reaction stage is 160°C and the reaction time is 5 hours; the reaction temperature of the third reaction stage is 200°C and the reaction time is 18 hours. Other steps are basically the same as in Example 1. Please refer to Example 1 for details.

[0124] Example 22

[0125] The difference from Example 1 is that in step S4, the solid content of the suspension is 100%. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0126] Example 23

[0127] The difference from Example 1 is that the 3 kg hydroxide precursor in step S1 is replaced with 3 kg of oxide precursor Ni. 0.8 Co 0.1 Al 0.1 O2, the other steps are basically the same as in Example 1, please refer to Example 1 for details.

[0128] Example 24

[0129] The difference from Example 1 is that the 3 kg hydroxide precursor in step S1 is replaced with 3 kg of oxide precursor Ni. 0.88 Co 0.062 Al 0.058 O2, the other steps are basically the same as in Example 1, please refer to Example 1 for details.

[0130] Example 25

[0131] The difference from Example 1 is that the 3 kg hydroxide precursor in step S1 is replaced with 3 kg of oxide precursor Ni. 0.93 Co 0.032 Al 0.038 O2, the other steps are basically the same as in Example 1, please refer to Example 1 for details.

[0132] Comparative Example 1

[0133] The difference from Example 1 is that the sintering temperature in step S1 is 650°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0134] Comparative Example 2

[0135] The difference from Example 1 is that the sintering temperature in step S1 is 750°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0136] Comparative Example 3

[0137] The difference from Example 1 is that in step S3, the amount of pure water added is 0.5 kg. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0138] Comparative Example 4

[0139] The difference from Example 1 is that in step S3, the amount of pure water added is 0.8 kg. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0140] Comparative Example 5

[0141] The difference from Example 1 is that in step S3, the amount of pure water added is 4 kg. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0142] Comparative Example 6

[0143] The difference from Example 1 is that the water washing temperature in step S3 is 0°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0144] Comparative Example 7

[0145] The difference from Example 1 is that the water washing temperature in step S3 is 30°C. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0146] Comparative Example 8

[0147] The difference from Example 1 is that in step S3, the stirring and washing speed is 3000 rpm. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0148] Comparative Example 9

[0149] The difference from Example 1 is that in step S3, the water content of the filter cake is 20% by mass. The other steps are basically the same as in Example 1; please refer to Example 1 for details.

[0150] Test methods

[0151] The following methods were used to test the performance of the cathode materials obtained in Examples 1-22 and Comparative Examples 1-8.

[0152] (1) The electrochemical performance of the positive electrode materials prepared in Examples 1-22 and Comparative Examples 1-8 was evaluated using coin cell half-cells. The specific method is as follows: The positive electrode active material, SP and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1:1. N-methylpyrrolidone was added at a solid content of 50%. The mixture was prepared into a viscous slurry using a high-speed disperser. The slurry was then uniformly coated onto aluminum foil with a scraper. After drying in an oven at 80°C, the slurry was rolled and cut into circular positive electrode sheets with a diameter of 14 mm. A lithium sheet with a diameter of 16 mm was used as the negative electrode sheet. A Celgard (PP / PE / PP) membrane was used as the separator. A 1 mol / L LiPF6 carbonate (DEC / EC volume ratio 1:1) solution was used as the electrolyte. The assembly was carried out in an argon-filled glove box.

[0153] The LAND battery testing system was used, and the test conditions were as follows: discharge capacity and first charge-discharge efficiency performance were tested at 25℃±1℃ and 2.5V~4.3V. The reference capacity was set to 200mA / g, and the current density corresponding to 1C was 200mA / g.

[0154] (2) Initial efficiency test: The test battery was installed on the Blue Electric instrument and placed in a test environment of (25±1)℃. The following program was set: stand for 10 min; charge at a constant current of 0.1C to 4.3V, then charge at a constant voltage until the current drops to 0.05C, and then stop charging; stand for 5 min; then discharge at a constant current of 0.1C to 2.5V to obtain the initial efficiency. The test results are shown in Table 2 below.

[0155] (3) Cyclic performance test: The test battery was installed on the Blue Electric instrument and placed in a test environment of (25±1)℃. The following program was set: stand for 10 min; charge at a constant current of 1.0C to 4.3V, then charge at a constant voltage until the current drops to 0.05C, and then stop charging; stand for 5 min; then discharge at a constant current of 1.0C to 2.5V; repeat this charge-discharge program 55 times, and the capacity retention rate after 55 cycles is the cycle performance. The test results are shown in Table 2 below.

[0156] (4) Scanning electron microscopy test: The cathode material was tested using a Hitachi S4800 scanning electron microscope to observe the micro-particle state.

[0157] (5) XPS testing: The PHI5800ESCA SYSTEM manufactured by Vlvac-Phi was used. The analysis area was φ800μm, the X-ray source was an Al tube, the output power of the X-ray source was 150W, the analysis angle was 45°, and the spectral types were 2p orbitals for Co and Al. In addition, the spectral types for Mn, Ni, Li and W were also 2p orbitals. The background processing was done using the Shirley method. The default XPS etching rate was 0.25nm / s. XPS etching was performed from the outermost surface of the sample to the inside. Eleven points were measured at different depths at different etching times (i.e., 11 points were tested at each depth). The average atomic weight of each element at different corresponding depths on the sample surface was obtained, and the ratio of each element at each depth was obtained. Then, the atomic weight ratio of Li+W was calculated using the above formula (1). For example, after 0 seconds of XPS etching, 11 points are measured to obtain the atomic weights of Li, Ni, Co, F, W, and M at each of the 11 points. The average atomic weights of Li, Ni, Co, F, W, and M are obtained by summing and averaging these values ​​at each point. Then, M(A) is obtained by adding the average atomic weights of Li, Ni, Co, F, W, and M. Finally, the atomic weight percentage of Li+W is calculated using the above formula (1). Where Z... (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) With Z (Li+W)-XPS(8秒) Perform the test using the method described above.

[0158] (6) Specific surface area test: The dynamic specific surface area rapid analyzer JW-DX from Beijing Jingwei Gaobo Science and Technology Co., Ltd. was used for testing. A standard sample with a known specific surface area was used as a reference to determine the adsorption amount of the unknown sample relative to the standard sample. The specific surface area of ​​the sample was then calculated by proportional calculation, with the unit being m². 2 / g.

[0159] (7) Loose packing density test: Using the BT-303 equipment, a certain mass of powder sample is placed in the sample tube and a certain pressure is generated by vibrating it up and down. After the sample tube is vibrated for a period of time, the bulk density measured after the powder freely fills the standard container under specified conditions is the loose packing density.

[0160] (8) Powder conductivity test: The conductivity of the positive electrode material powder is tested using the FT-8100 series four-probe powder conductivity tester. This parameter describes the ease of charge flow in the material. The product of its value and the electric field strength in the medium is the current density, which is the powder conductivity.

[0161] The test results of the cathode materials of Examples 1-25 and Comparative Examples 1-9 are shown in Tables 1 and 2 below.

[0162] Table 1

[0163]

[0164]

[0165] Table 2

[0166]

[0167]

[0168] Combining the results in Tables 1 and 2, and comparing Example 1 and Comparative Example 1, it can be seen that the cathode material of Example 1, with its lithium tungstate coating layer, exhibits a high W+Li atomic ratio at the three etching times of 0s, 4s, and 8s using XPS etching. Furthermore, the W+Li atomic ratio at all 11 points at the 0-second etching position is above 99.2%, indicating a relatively complete coating layer on the cathode material of Example 1. In contrast, the W+Li atomic ratio at 4 and 8 seconds of etching in Comparative Example 1 is below 80%, indicating that a complete coating layer cannot be formed within the 0-2nm range on the cathode material's surface, resulting in poor coating uniformity.

[0169] Combination Figure 3 and Figure 4 As can be seen from the SEM images, the cathode material prepared in Example 1 of this application has good particle dispersion and no obvious agglomeration, while the cathode material of Comparative Example 1 has obvious particle agglomeration and poor dispersion.

[0170] As can be seen from the results of Examples 1-25 above, the cathode material of this application has good particle dispersion and no obvious agglomeration. The elemental content of Li+W at the surface layer of the cathode material is relatively high, indicating that the surface coating of the cathode material is good. The measured Z of the cathode material is... (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) The proportion of Li+W in the total atomic mass is over 90%, and Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒)The differences between the samples are small (below 10%), indicating that the coating layer on the surface of the cathode material is uniform and complete, which can improve the structural stability of the cathode material, reduce the volume expansion of the material, and thus improve the cycle life and thermal stability of the cathode material. In contrast, the cathode materials in Comparative Examples 1-9 show significant particle agglomeration and poor dispersion, and the content of Li and tungsten elements in the surface layer is low. They do not meet the requirement that the proportion of total Li+W atomic mass is above 80% at XPS etching times of 0 seconds, 4 seconds, and 8 seconds, and that the proportion of total Li+W atomic mass fluctuates significantly at different depths. (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) The significant differences (above 10%) indicate poor uniformity and integrity of the cathode material coating, resulting in poor structural stability and cycle life of the cathode material.

[0171] Based on the above test data, the cathode materials provided in Examples 1-25 of this application have a complete and uniform lithium tungstate coating layer on their surface, which can improve the structural stability of the cathode material, effectively isolate the cathode material from direct contact with the electrolyte, reduce interfacial side reactions, reduce gas generation, and suppress volume strain of the active material during charging and discharging, thereby improving safety. In addition, while suppressing battery polarization and buffering the volume expansion of the cathode material, this coating layer also has lithium-ion transport capacity, thus improving the cycle life and thermal stability of the cathode material. This characteristic is specific to cathode materials that have undergone water washing to remove lithium, and helps maintain the cycle performance and thermal stability of the cathode material.

[0172] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a substrate and a coating layer, wherein the coating layer covers the surface of the substrate, and the coating layer includes Li and W elements. The positive electrode material satisfies: Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) and Z (Li+W)-XPS(8秒) All are greater than 80%, among which, X-ray photoelectron spectroscopy (XPS) was used to analyze the cathode material particles along their depth direction. The sum of the atomic weights of Li and W atoms measured after 0 seconds of XPS etching on the surface of the cathode material was defined as Z. (Li+W)-XPS(0秒) The sum of the atomic weights of Li and W atoms measured after 4 seconds of XPS etching on the surface of the cathode material is Z. (Li+W)-XPS(4秒) The sum of the atomic weight ratios of Li and W atoms obtained by etching the surface of the cathode material using XPS for 8 seconds is the Z. (Li+W)-XPS(8秒) .

2. The cathode material as described in claim 1, characterized in that, Z (Li+W)-XPS(0秒) Z (Li+W)-XPS(4秒) With Z (Li+W)-XPS(8秒) The relation satisfies: 0 ≤ |Z (Li+W)-XPS(0秒) -Z (Li+W)-XPS(4秒) |≤0.1,0≤|Z (Li+W)-XPS(0秒) -Z (Li+W)-XPS(8秒) |≤0.

1.

3. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies: Z (Li+W)-XPS(0秒) In over 90%, Z (Li+W)-XPS(4秒) In over 80%, Z (W)-XPS(8秒) More than 80%.

4. The positive electrode material as described in claim 1, characterized in that, The coating layer has the general chemical formula Li. d W e O f , where 0 < d < 0.5, 0 < e < 0.002, and 0 < f ≤ 2.

5. The positive electrode material as described in claim 4, characterized in that, The mass percentage of W in the cathode material is 500 ppm to 2000 ppm.

6. The positive electrode material as described in claim 1, characterized in that, The chemical general formula of the positive electrode material is: Li b Ni x Co y F z W h M m O2, where 0.95 ≤ b ≤ 1.05, 0.8 ≤ x < 1, 0 < y + z ≤ 0.2, x + y + z + h = 1, 0.0001 ≤ h ≤ 0.003, 0 ≤ m < 1, the F element is selected from at least one of Mn and Al; the M element is selected from at least one of Ca, Ti, Zr, Sr, Mg, Sb, Y, and La.

7. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The thickness of the coating layer is 2-5 nm; (2) The matrix includes secondary particles, which include a plurality of primary particles, and the secondary particles are spherical or near-spherical. (3) The specific surface area of ​​the positive electrode material is 0.5 m². 2 / g~2.0m 2 / g; (4) The loose packing density of the positive electrode material is 1.0 g / m³. 3 ~3.0g / m 3 ; (5) The positive electrode material has a strength of 4 kN / cm 2 The electrical conductivity of the powder under pressure is greater than 0.02 S / cm.

8. A method for preparing a positive electrode material as described in any one of claims 1 to 7, characterized in that, include: An oxide or hydroxide precursor is mixed with a lithium source, and the mixture is sintered to obtain a primary sintering product. The primary sintering product is crushed and dispersed, and the dispersed primary sintering product is then re-sintered with lithium to obtain the re-sintered product. The re-fired product is washed with water, and the washed re-fired product is then filtered by pressure to obtain a filter cake. as well as A suspension containing a coating material is sprayed onto the surface of the filter cake and continuously stirred. Through intermittent gradient temperature reaction, the coating elements in the coating material react with the lithium in the recalcined product to form a coating layer, thereby obtaining the cathode material.

9. A positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, characterized in that, The positive electrode active material layer includes the positive electrode material as described in any one of claims 1 to 7.

10. A secondary battery, comprising a casing, an electrode assembly, and an electrolyte or electrolyte solution, wherein the electrode assembly and the electrolyte or electrolyte solution are both located within the casing, and the electrode assembly includes a separator and a negative electrode plate, characterized in that, The electrode assembly further includes the positive electrode as described in claim 9, wherein the separator is disposed between the positive electrode and the negative electrode.

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