Positive electrode material, positive electrode sheet and secondary battery

Abstract

Provided in the present application are a positive electrode material, a positive electrode sheet and a secondary battery. The positive electrode material comprises cobalt-containing particles, which contain a fluorine element, wherein on the basis of characterization by X-ray photoelectron spectroscopy, the content of the fluorine element on the surfaces of the cobalt-containing particles is W1％, the content of the fluorine element in a region 100 nm from the surfaces of the cobalt-containing particles is W2％, and W1>W2. The positive electrode material of the present application has good thermal stability and electrochemical stability and relatively high electrical conductivity under high-temperature conditions, such that when used in a secondary battery, the positive electrode material can improve the high-temperature cycling stability and charge-discharge efficiency of the secondary battery.

Description

A positive electrode material, a positive electrode sheet, and a secondary battery Technical Field

[0001] This application relates to the field of energy storage materials, specifically to a cathode material, a cathode sheet, and a secondary battery. Background Technology

[0002] Lithium-ion batteries, as high-efficiency power sources, are widely used in various devices and energy storage systems. With the increasing demand for commercial applications such as electronic products and electric vehicles, lithium-ion batteries are receiving more attention, and their performance urgently needs further improvement. Among the cathode materials for lithium-ion batteries, lithium cobalt oxide (LiCoO2) has attracted attention due to its excellent electrochemical performance and energy density. However, current lithium-ion batteries using lithium cobalt oxide cathodes exhibit insufficient cycle stability at high temperatures. Summary of the Invention

[0003] This application can provide a positive electrode material, a positive electrode sheet, and a secondary battery. The positive electrode material of this application has good thermal stability, electrochemical stability, and high conductivity under high temperature conditions. When used in a secondary battery, it can improve the high-temperature cycle stability and charge-discharge efficiency of the secondary battery.

[0004] In a first aspect, this application provides a cathode material, characterized in that it comprises cobalt-containing particles, the cobalt-containing particles containing fluorine, and based on X-ray photoelectron spectroscopy characterization, the fluorine content on the surface of the cobalt-containing particles is W1%, and the fluorine content in a region 100 nm from the surface of the cobalt-containing particles is W2%, where W1 > W2.

[0005] In the aforementioned technical solution, the inventors discovered that under high-temperature conditions, a higher fluorine content on the surface of cobalt-containing particles facilitates the formation of a stable fluoride protective layer. This protective layer acts as a barrier to thermal stability, reducing the dissolution and structural breakdown of the cathode material, thereby improving its thermal stability. Furthermore, because the fluorine content is low in the region 100 nm from the surface of the cobalt-containing particles, it not only ensures that the electron and ion transport paths remain effective even at high temperatures, thus improving the conductivity of the cathode material, but also reduces potential structural distortions, maintains the integrity of the material, and has a positive impact on the cycle life of the battery. Additionally, when the cathode material of this application is used in a secondary battery, the fluoride layer on the surface of the cathode material can effectively block the decomposition reaction of the electrolyte, preventing the electrolyte in the secondary battery from decomposing rapidly at high temperatures, which is crucial for the interface stability of the secondary battery.

[0006] In one possible implementation, at a distance D from the surface of the cobalt-containing particles a nm and D b In the region of nm, the fluorine content is W.a % and W b %, 0.2% ≤ (W a -W b ) / (D b -D a )≤1%, and 0≤D a <D b ≤20; at a distance D from the surface of the cobalt-containing particles c nm and D d In the region of nm, the fluorine content is W. c % and W d %, 0.01% ≤ (W c -W d ) / (D d -D c )≤0.1%, and 20≤D c <D d ≤100.

[0007] In the above technical solution, the above-mentioned cathode material can make the cathode material have better electrical conductivity and thermal stability.

[0008] In one possible implementation, 0.4% ≤ (W a -W b ) / (D b -D a )≤0.6%, and / or, 0.03%≤(W c -W d ) / (D d -D c ≤0.05%.

[0009] In one possible implementation, the fluorine content is 0.1% to 1% by mass, based on the mass of the cobalt-containing particles.

[0010] In the above technical solution, the fluorine content allows sufficient fluoride to form on the surface of cobalt particles as a protective layer, thereby improving the high-temperature stability and electrochemical stability of the cathode material. At the same time, it can also avoid the significant negative impact of fluorine on the internal conductivity of the cathode material. The fluorine content within the above range helps the cathode material achieve a good balance between improving thermal stability and maintaining conductivity.

[0011] In one possible implementation, the cobalt-containing particles also include aluminum, and the mass ratio of fluorine to aluminum is 0.1 to 5.

[0012] In the above technical solution, aluminum can enhance the structure of cobalt-containing particles and improve the stability of the cathode material. Furthermore, fluorine and aluminum can form AlF3 on the surface of the cobalt-containing particles. This compound exhibits excellent thermal stability and chemical inertness at high temperatures, effectively improving the cycle stability of the cathode material. Additionally, when the cathode material is used in a secondary battery, AlF3 can form a robust protective layer on the surface of the cathode material, effectively mitigating reactions with the electrolyte and other external environments, and reducing the probability of side reactions. Moreover, the distribution of AlF3 at grain boundaries enhances the structural strength of the grain boundaries, reducing performance degradation caused by internal structural changes, especially during repeated charge-discharge cycles. Furthermore, through the formation of the AlF3 compound, the cathode material is well protected during high-temperature operation, improving the battery's high-temperature cycle performance and capacity retention.

[0013] In one possible implementation, the mass ratio of fluorine to aluminum is (0.5:1) to (2:1).

[0014] In one possible implementation, the cobalt-containing particles also include at least one of magnesium, zirconium, titanium, yttrium, calcium, lanthanum, cerium, or lithium.

[0015] In the above technical solution, the aforementioned elements can react with fluorine to form corresponding fluorides, thereby improving the relevant performance of the cathode material.

[0016] In one possible implementation, based on the mass of the cobalt-containing particles, it satisfies at least one of the following conditions: (1) the magnesium content is 0.01% to 2%, and the mass ratio of fluorine to magnesium is 0.1 to 10; (2) the zirconium content is 0.05% to 1%, and the mass ratio of fluorine to zirconium is 0.1 to 20; (3) the titanium content is 0.02% to 2%, and the mass ratio of fluorine to titanium is 0.1 to 10; (4) the yttrium content is 0.01% to 0.5%, and (5) The content of calcium is 0.01% to 0.5%, and the mass ratio of fluorine to calcium is 1 to 50; (6) The content of lanthanum is 0.01% to 0.5%, and the mass ratio of fluorine to lanthanum is 1 to 50; (7) The content of cerium is 0.01% to 0.5%, and the mass ratio of fluorine to cerium is 1 to 50; (8) The content of lithium is 4% to 8%, and the mass ratio of fluorine to lithium is 0.01 to 2.

[0017] In one possible implementation, the cathode material satisfies at least one of the following conditions: (1) the mass ratio of fluorine to magnesium is 1 to 5; (2) the mass ratio of fluorine to zirconium is 1 to 2; (3) the mass ratio of fluorine to calcium is 20 to 30; and (4) the mass ratio of fluorine to lanthanum is 4 to 6.

[0018] Secondly, this application provides a positive electrode sheet comprising the aforementioned positive electrode material. Therefore, the positive electrode sheet of this application also has good performance in use.

[0019] Thirdly, this application provides a secondary battery including the aforementioned positive electrode. Therefore, the secondary battery provided by this application exhibits good high-temperature cycle stability and charge-discharge efficiency. Furthermore, the fluoride layer on the surface of the positive electrode material of the secondary battery in this application can effectively block the decomposition reaction of the electrolyte, preventing the electrolyte in the secondary battery from decomposing rapidly at high temperatures, which is crucial for the interface stability of the secondary battery.

[0020] The beneficial effects of this application are:

[0021] This application provides a positive electrode material, a positive electrode sheet, and a secondary battery. The positive electrode material includes cobalt-containing particles containing fluorine. Based on X-ray photoelectron spectroscopy characterization, the fluorine content on the surface of the cobalt-containing particles is W1%, and the fluorine content in a region 100 nm from the surface of the cobalt-containing particles is W2%, where W1 > W2. By setting the surface fluorine content to be lower than the bulk fluorine content, this application can significantly improve the thermal stability, electrochemical stability, and conductivity of the positive electrode material. When used in a secondary battery, it also prevents the electrolyte in the secondary battery from decomposing rapidly at high temperatures, thereby improving the high-temperature cycle stability and charge-discharge efficiency of the secondary battery. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 is a graph showing the relationship between the fluorine content of the cathode material provided in Examples 1-10 of this application and the distance from the surface of the cobalt-containing particles. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] In existing technologies, taking lithium-ion batteries as an example, the cathode material often contains cobalt-containing particles such as lithium cobalt oxide, which can improve the electrochemical performance and energy density of the electrochemical device. However, secondary batteries using the above-mentioned cathode material have insufficient cycle stability at high temperatures. Although there are technologies to dope cobalt-containing particles such as lithium cobalt oxide with fluorine, the added fluorine will affect the charge and discharge efficiency of the secondary battery.

[0026] Based on the aforementioned technical problems, the cathode material provided in this application possesses excellent thermal and electrochemical stability, resulting in good high-temperature cycle performance of the secondary battery and also improving the charge-discharge efficiency of the secondary battery. The cathode material, cathode sheet, and secondary battery of this application are described in detail below.

[0027] In a first aspect, this application provides a cathode material comprising cobalt-containing particles containing fluorine. Based on X-ray photoelectron spectroscopy characterization, the fluorine content on the surface of the cobalt-containing particles is W1%, and the fluorine content in a region 100 nm from the surface of the cobalt-containing particles is W2%, where W1 > W2.

[0028] It should be noted that the terms "surface of cobalt-containing particles" and "distance to the surface of cobalt-containing particles" mentioned in this application are calculated using the following standard: The lowest point of the surface of the cobalt-containing particle is located exactly on the outer surface of the inscribed sphere. In this case, "surface of cobalt-containing particles" refers to the region of the cobalt-containing particle located outside the inscribed sphere; this region can be referred to as the "surface of cobalt-containing particles," and the distance from this region to the surface of the cobalt-containing particle is 0 nm. The "distance to the surface of cobalt-containing particles" is also defined with the surface of the inscribed sphere as the reference frame; "distance to the surface of cobalt-containing particles of D nm" means that the distance from the interior of the cobalt-containing particle to the surface of the inscribed sphere is D nm. Furthermore, for ease of explanation, as an example, the cobalt-containing particles in this application are based on lithium cobalt oxide particles and can be referred to as "modified lithium cobalt oxide particles."

[0029] In the cathode material of this application, the inventors discovered that under high-temperature conditions, a higher fluorine content on the surface of cobalt-containing particles facilitates the formation of a stable fluoride protective layer. For example, LiF forms on the surface of modified lithium cobalt oxide particles. This protective layer acts as a barrier to thermal stability, reducing the dissolution and structural disintegration of the cathode material, thereby improving its thermal stability. Furthermore, because the fluorine content is low in the region 100 nm from the surface of the cobalt-containing particles, this not only ensures that the electron and ion transport paths remain effective even at high temperatures, thus improving the conductivity of the cathode material, but also reduces potential structural distortions, maintains the integrity of the material, and has a positive impact on the cycle life of the battery.

[0030] It should also be noted that although this application only specifies that the fluorine content in the region "100 nm from the surface of the cobalt-containing particles" is less than the fluorine content on the surface, in actual products, to reduce manufacturing difficulty, the cobalt-containing particles generally also have the following properties: in the region of 0–100 nm from the surface of the cobalt-containing particles, the greater the distance to the surface, the smaller the fluorine content. Preferably, in the region of 0–100 nm from the cobalt-containing particles, the rate of change of fluorine content is also different in different regions. In the region of 0–20 nm, the absolute value of the rate of change of fluorine content is larger, and in the region of 20 nm–100 nm, the absolute value of the rate of change of fluorine content is smaller. This allows the cathode material to have better electrical conductivity and thermal stability, as detailed below:

[0031] D at a distance from the surface of the cobalt-containing particles a nm and D b The region nm (0≤D) a <D b ≤20), the fluorine content is W a % and W b %, 0.2% ≤ (W a -W b ) / (D b -D a )≤1%, preferably 0.4%≤(W a -W b ) / (D b -D a )≤0.6%; at a distance D from the surface of cobalt-containing particles c nm and D d The region nm (20≤D) c <D d ≤100), the fluorine content is W c % and W d %, 0.01% ≤ (W c -W d ) / (Dd -D c )≤0.1%, preferably 0.03%≤(W c -W d ) / (D d -D c ≤0.05%.

[0032] In some embodiments of this application, the mass content of fluorine in the cathode material is 0.1% to 1% based on the mass of the cobalt-containing particles. This ensures that there is enough fluorine in the cobalt-containing particles to form a fluoride protective layer, thereby improving the high-temperature stability and electrochemical stability of the cathode material. In addition, an appropriate amount of fluorine will not have a significant negative impact on the internal conductivity of the cathode material. Thus, the cathode material can balance thermal stability, electrochemical performance, and conductivity.

[0033] In addition, in some embodiments of this application, the cobalt-containing particles also include aluminum, and the mass ratio of fluorine to aluminum is 0.1 to 5; preferably 0.5 to 2. Aluminum can enhance the structure of the cobalt-containing particles and improve the stability of the cathode material. Furthermore, aluminum and fluorine can form AlF3 on the surface of the cobalt-containing particles, which has the following effects:

[0034] AlF3 exhibits excellent thermal stability and chemical inertness at high temperatures, effectively improving the cycle stability of cathode materials. Furthermore, in secondary batteries, AlF3 can form a robust protective layer on the surface of the cathode material, effectively mitigating reactions with the electrolyte and other external environments, and reducing the probability of side reactions. In addition, the distribution of AlF3 at grain boundaries enhances the structural strength of the grain boundaries, reducing performance degradation caused by internal structural changes, especially during repeated charge-discharge cycles. Moreover, the formation of AlF3 compounds provides excellent protection for the cathode material during high-temperature operation, improving the battery's high-temperature cycle performance and capacity retention.

[0035] Furthermore, in some embodiments of this application, the cobalt-containing particles also include at least one of magnesium, zirconium, titanium, yttrium, calcium, lanthanum, cerium, or lithium. These elements can react with fluorine to generate corresponding fluorides, thereby improving the performance of the cathode material. Based on the mass of the cobalt-containing particles, the specific content of the aforementioned elements is as follows:

[0036] The magnesium content is 0.01% to 2%, preferably 0.05% to 0.2%, and the mass ratio of fluorine to magnesium is 0.1 to 10, preferably 0.5 to 5. The MgF2 formed by the combination of magnesium and fluorine can protect the surface of the cathode material, reducing the occurrence of side reactions; moreover, the addition of magnesium increases the structural stability of the cathode material, reduces phase decomposition, and is beneficial to improving the stability of the cathode material.

[0037] The zirconium content is 0.05% to 1%, preferably 0.07% to 0.2%, and the mass ratio of fluorine to zirconium is 0.1 to 20, preferably 1 to 10. ZrF4 formed by the combination of zirconium and fluorine can provide excellent corrosion resistance, and zirconium also helps to improve the stability of the crystal structure, which can increase the performance of the cathode material in high temperature and electrochemical cycling.

[0038] The titanium content is 0.02% to 2%, preferably 0.1% to 0.5%, and the mass ratio of fluorine to titanium is 0.1 to 10, preferably 0.5 to 5. The TiF4 formed by the combination of titanium and fluorine can improve the conductivity and stability of the cathode material; in addition, the presence of titanium helps to modify the lattice parameters of the material, reducing stress concentration and the generation of microcracks.

[0039] The yttrium content is 0.01% to 0.5%, preferably 0.05% to 0.2%, and the mass ratio of fluorine to yttrium is 1 to 50, preferably 5 to 30. The YF3 formed by the combination of yttrium and fluorine at the grain boundaries can improve interfacial stability; moreover, yttrium can also prevent cation mixing to maintain the structural integrity of the cathode material, thereby improving the high-temperature performance of the cathode material.

[0040] The calcium content is 0.01% to 0.5%, preferably 0.05% to 0.2%, and the mass ratio of fluorine to calcium is 1 to 50, preferably 5 to 30. The CaF2 formed by the combination of calcium and fluorine can provide a buffering effect and reduce the structural stress of the cathode material. In addition, calcium can improve the electrical conductivity of the cathode material while maintaining its mechanical properties.

[0041] The lanthanum content is 0.01%–0.5%, preferably 0.05%–0.2%, and the mass ratio of fluorine to lanthanum is 1–50, preferably 5–30. The cerium content is 0.01%–0.5%, preferably 0.05%–0.2%, and the mass ratio of fluorine to cerium is 1–50, preferably 5–30. The lanthanum, and the LaF3 and CeF3 formed by the combination of cerium and fluorine, are beneficial for enhancing the ionic conductivity of the cathode material and promoting charge balance. In addition, lanthanum and cerium can also enhance the thermal stability and electrochemical durability of the cathode material.

[0042] The lithium content is 4%–8%, preferably 6%–7%, and the mass ratio of fluorine to lithium is 0.01–2, preferably 0.05–1. The LiF formed by the combination of lithium and fluorine can enhance the electrochemical stability of the cathode material and protect it from electrolyte corrosion. Furthermore, the inventors have found that the composite protective layer formed by the combination of multiple elemental fluorides can further reduce the reactivity between the cathode surface and the electrolyte, providing long-term protection against side reactions.

[0043] In addition, in some embodiments of this application, the particle size of the cobalt-containing particles is also optimized; specifically, the Dv90, Dv50, and Dv10 particle sizes of the cobalt-containing particles are R1μm, R2μm, and R3μm, respectively, with 0.3≤(R1-R3) / R2≤0.6, preferably 0.4≤(R1-R3) / R2≤0.5. This is beneficial for increasing the compact packing density of the cathode material and allows for more uniform mixing of the cathode material, which can improve the rate performance and discharge capacity of the prepared cathode electrode. Furthermore, the values ​​of R1, R2, and R3 can be controlled separately, especially the Dv50 particle size (i.e., the median particle size), which can optimize the energy density and reaction uniformity of the prepared secondary battery. Specifically, in some embodiments of this application, the values ​​of R1, R2, and R3 can be: (1) 8 ≤ R1 ≤ 20, for example, 8, 10, 13, 16, 18, 20, etc., or within the range of any two of the above values; (2) 2 ≤ R2 ≤ 20, for example, 2, 5, 8, 10, 12, 15, 18, 20, etc., or within the range of any two of the above values; (3) 1 ≤ R3 ≤ 3, for example, 1, 1.5, 1.8, 2, 2.4, 2.6, 2.8, 3, etc., or within the range of any two of the above values. When the Dv90, Dv50, and Dv10 of the cobalt-containing particles are within the above ranges, the particle size distribution of the cobalt-containing particles is narrower, which can significantly improve the stability of the cathode material in the electrochemical process. Moreover, the highly consistent particle size distribution makes the slurry more dispersed and the coating more uniform during the preparation of the cathode sheet, resulting in a more uniform thickness and cathode material distribution in the cathode sheet. Such improved uniformity can reduce local hot spots during battery operation, thereby further improving the overall thermal management performance and cycle life of the battery.

[0044] Furthermore, in some embodiments of this application, the energy density and reaction uniformity of the corresponding secondary battery can be optimized by controlling the specific surface area of ​​the cobalt-containing particles in the cathode material. Specifically, the specific surface area of ​​the cobalt-containing particles can be 0.05 m². 2 / g~2m 2 / g, preferably 0.1m 2 / g~0.3m 2 / g, for example, could be 0.05m 2 / g, 0.08m 2 / g, 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.8m 2 / g, 1.5m 2 / g、2m 2 / g or the range consisting of any two of the above values.

[0045] As an example, this application also provides a method for preparing a cathode material, taking a lithium cobalt oxide-based cathode material as an example, the steps of which are as follows:

[0046] S100. Preparation of precursors: Cobalt nitrate (Co(NO3)2) and lithium nitrate (LiNO3) are dissolved in deionized water to form a mixed solution, and then spray pyrolysis is performed.

[0047] During the formation of the mixed solution, a magnetic stirrer is typically used to thoroughly stir the solution until it is homogeneous and free of impurities. Filtration may also be performed if necessary to remove insoluble particles.

[0048] Spray pyrolysis typically involves solution atomization and a pyrolysis reaction, specifically:

[0049] Solution atomization: using spray drying equipment to atomize a mixed solution into fine droplets.

[0050] Pyrolysis reaction: The droplets are rapidly evaporated and decomposed in a high-temperature pyrolysis reaction chamber to generate precursor powder.

[0051] During the preparation of the precursor, the fluorine content on the surface of the precursor powder can be controlled by adjusting the atomization pressure during solution atomization and the temperature and time during the pyrolysis reaction. The atomization pressure can be between 0.3 MPa and 1.3 MPa. The pyrolysis reaction proceeds through three stages: a drying zone, a decomposition zone, and a crystallization zone. The drying zone is used for rapid evaporation of moisture, the decomposition zone for rapid decomposition of nitrates, and the crystallization zone for the formation of the precursor from the decomposed nitrates. The temperature and time of these three stages can be adjusted according to actual needs; the crystallization zone time can be between 20 s and 70 s. This paper will subsequently use Example 1-1 as an example for detailed explanation; the preparation process of the cathode material in other examples will not be repeated, and those skilled in the art can make conventional adjustments as needed.

[0052] S200, First sintering: Under the protection of an inert gas (such as nitrogen or argon), the precursor powder is placed in a high-temperature furnace to form lithium cobalt oxide powder.

[0053] During the first sintering process, the temperature and time can be adjusted to promote the formation of lithium cobalt oxide crystal structure in the precursor powder, optimize the crystallinity of the surface layer, and maintain the rate of change of fluorine concentration in the surface layer.

[0054] S300, Fluorine Doping: Lithium cobalt oxide powder is added to a fluorine-containing solution and stirred, then cured and dried to coat the surface of the lithium cobalt oxide powder with fluorine salts from the fluorine-containing solution, forming a modified powder.

[0055] In this step, the fluoride salt in the fluoride-containing solution includes, but is not limited to, at least one of LiF, NH4F, NaF, KF, MgF2, ZnF2, etc.

[0056] S400, Second sintering: The modified powder is sintered again.

[0057] The second sintering process can ensure that the cobalt-containing particle structure of the cathode material is more stable, which can improve the durability of the cathode material.

[0058] In some embodiments of this application, the product obtained in S400—lithium cobalt oxide substrate—can be directly used as a cathode material. Alternatively, at least one element selected from magnesium, aluminum, lanthanum, zirconium, titanium, calcium, and cerium can be doped onto the surface of the lithium cobalt oxide substrate obtained in S400 before it can be used as a cathode material. These elements are generally provided by their corresponding precursors, which can be oxides or salts, such as:

[0059] Magnesium: Magnesium oxide (MgO) or magnesium nitrate (Mg(NO3)2).

[0060] Aluminum: aluminum oxide (Al2O3) or aluminum nitrate (Al(NO3)3).

[0061] Lanthanum: Lanthanum oxide (La2O3) or Lanthanum nitrate (La(NO3)3).

[0062] Zirconium: Zirconium oxide (ZrO2) or Zirconium nitrate (Zr(NO3)4).

[0063] Titanium element: titanium oxide (TiO2) or titanium isopropoxide (TTIP).

[0064] Calcium element: calcium oxide (CaO) or calcium nitrate (Ca(NO3)2).

[0065] Cerium element: cerium oxide (CeO2) or cerium nitrate (Ce(NO3)3).

[0066] The specific steps for doping the above-mentioned elements onto the surface of a lithium cobalt oxide substrate are as follows:

[0067] S500, doping with other elements: The precursors of the above-mentioned doping elements are mixed with the lithium cobalt oxide substrate and then calcined at high temperature.

[0068] When mixing the precursor and lithium cobalt oxide substrate, a ball mill or mortar can be used to mix the powder evenly. In order to improve the uniformity, a small amount of alcohol solvent (such as ethanol) can be added to make a slurry before mixing. If a solvent is added, the mixed slurry needs to be dried at a low temperature (such as 60℃~80℃) until the solvent is completely removed.

[0069] In this step, high-temperature calcination is typically carried out in a high-temperature furnace at a temperature of 700-900℃. The calcination time depends on the specific material properties and generally lasts for several hours. The calcination process can be conducted under an atmosphere of air, oxygen, or an inert gas (such as argon) to control the redox reaction.

[0070] Secondly, this application provides a positive electrode sheet, which includes the above-mentioned positive electrode material, and its specific structure is as follows:

[0071] The positive electrode includes 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 contains the positive electrode material of this application. The positive electrode material of this application is generally used as a positive active material, and the positive active material can be any material capable of reversibly inserting and de-intercalating Li. + Na + Substances containing alkali metal ions are used to ensure that the positive electrode and secondary battery can be charged and discharged normally.

[0072] It should be noted that, in this application, "a positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the positive electrode current collector. Moreover, in this application, "the surface of the positive electrode current collector" can be the entire area of ​​the positive electrode current collector or a part of the positive electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0073] Furthermore, in this application, the positive electrode active material may include not only lithium cobalt oxide (LiCoO2), but also at least one of lithium iron phosphate (LiFePO4), lithium manganese oxide, lithium nickel oxide, and ternary materials, including but not limited to LiNi. x Co y Mn z O2, LiNi x Co y Al zAt least one of O2, etc., and the contents of Ni, Co, Mn, Al, etc., can be adjusted to ensure that x+y+z=1. For example, the ternary material can be LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.88 Co 0.1 Al 0.02 O2, etc.

[0074] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent; this application does not limit the type of positive electrode conductive agent, and any known conductive material can be used. Specifically, the positive electrode conductive agent includes, but is not limited to, at least one of the following: acetylene black, Super-P carbon black, or amorphous carbon such as needle coke, or carbon nanotubes, or graphene.

[0075] In some embodiments, the positive electrode active material layer generally also contains a positive electrode binder. There are no particular restrictions on the type of positive electrode binder used in the manufacture of the positive electrode active material layer. In the case of the coating method, any material that can be dissolved or dispersed in the liquid medium used in the electrode manufacturing process is acceptable. Positive electrode binders include, but are not limited to, any one or at least two of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions).

[0076] In the positive electrode sheet, there are no particular restrictions on the type of positive current collector; it can be any known material suitable for use as a positive current collector. Materials for the positive current collector include, but are not limited to, metals such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Furthermore, to reduce the electronic contact resistance between the positive current collector and the positive active material layer, conductive additives or conductive coatings can be applied to the surface of the positive current collector. Conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. The conductive coating can be a mixture of inorganic oxides, conductive agents, and positive electrode binders.

[0077] In preparing the positive electrode sheet, the components of the aforementioned positive electrode active material layer can be dissolved or dispersed in a liquid solvent to form a positive electrode slurry. This slurry is then coated onto a positive electrode current collector and dried, thereby forming the positive electrode active material layer on the current collector, thus obtaining the positive electrode sheet. When preparing the positive electrode sheet using this method, there are no particular limitations on the solvent in the positive electrode slurry, as long as it can dissolve or disperse the aforementioned components. Specifically, the solvent in the positive electrode slurry includes, but is not limited to, N-methylpyrrolidone (NMP) and ethylene carbonate (EC). Alternatively, in preparing the positive electrode sheet, the various components of the positive electrode active material layer can be dry-mixed to form a sheet, which is then pressed onto the positive electrode current collector.

[0078] Thirdly, this application provides a secondary battery comprising the aforementioned positive electrode sheet. Because the positive electrode material contained in the positive electrode sheet of this application possesses good conductivity, interfacial stability, and structural stability, the secondary battery of this application not only has excellent energy density but also good cycle performance and thermal safety performance. Furthermore, since a fluoride layer can be formed on the surface of the positive electrode material in the secondary battery of this application, this fluoride layer can effectively block the decomposition reaction of the electrolyte, preventing the electrolyte in the secondary battery from decomposing rapidly at high temperatures, which is crucial to the interfacial stability of the secondary battery.

[0079] In the secondary battery of this application, the positive electrode is as shown above, and the other structures are as follows:

[0080] Negative electrode sheet

[0081] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The composition of the negative electrode active material layer includes the negative electrode sheet active material. That is, in this application, the negative electrode active material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. Moreover, in this application, the "surface of the negative electrode current collector" can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0082] The negative electrode active material layer generally contains a negative electrode active material, and this application does not impose any particular limitation on the negative electrode active material. Specifically, the negative electrode active material may include at least one of carbon materials or silicon-based materials. More specifically, carbon materials include, but are not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, or soft carbon; silicon-based materials include, but are not limited to, at least one of silicon, silicon-oxygen composite materials, or silicon-carbon composite materials.

[0083] In some embodiments, the negative electrode active material layer typically also contains a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it achieves the purpose of this application. For example, negative electrode conductive agents include, but are not limited to, at least one of acetylene black, Ketjen black, carbon nanotubes, carbon fibers, carbon dots, or graphene.

[0084] In some embodiments, the negative electrode active material layer may also contain a negative electrode binder and a thickener. This application does not impose any particular limitation on the types of negative electrode binders and thickeners, as long as they can achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener in the negative electrode slurry may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0085] In the negative electrode sheet, the material of the negative electrode current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with a conductive metal, etc., and this application does not have any particular limitations. Among them, the conductive metal includes, but is not limited to, copper, nickel, or titanium, and the material of the polymer substrate includes, but is not limited to, at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate, or poly(p-phenylene terephthalamide).

[0086] Furthermore, this application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 160 μm.

[0087] Furthermore, similar to the preparation of the positive electrode sheet, the preparation of the negative electrode sheet can be achieved either by preparing a negative electrode slurry, coating the slurry onto a negative electrode current collector, and drying it to form a negative electrode active material layer on the current collector, thus obtaining the negative electrode sheet; or by dry mixing the components of the negative electrode active material layer to form a sheet, which is then pressed onto the negative electrode current collector to form the negative electrode active material layer, thereby obtaining the negative electrode sheet. The solvent in the negative electrode slurry includes any one of aqueous solvents and organic solvents. Aqueous solvents include, but are not limited to, mixtures of alcohol and water or water itself. Organic solvents include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide. In some other embodiments, when using aqueous solvents, the negative electrode slurry composition may also include a thickener and styrene-butadiene rubber (SBR) emulsion to slurry the negative electrode slurry, thereby adjusting its viscosity. The types of thickeners in the positive electrode slurry include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0088] electrolyte

[0089] Electrolytes play a role in transporting lithium ions and electrons, ensuring the formation of internal pathways in secondary batteries. Electrolytes typically contain lithium salts, solvents, and additives. It should be noted that this application does not impose specific restrictions on the amount of each component in the electrolyte, as long as the purpose of this application can be achieved.

[0090] Specifically, lithium salts can dissolve in solvents to form ionic conductors and be used as conductive media and lithium-ion transport media; lithium salts include, but are not limited to, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorooxalate-borate), and lithium bis(fluorosulfonyl)imide.

[0091] Solvents can dissolve lithium salts and additives. Solvents can be at least one of carbonates, carboxylic esters, ethers, and alcohols. Carbonates can be classified as cyclic carbonates and linear carbonates. Cyclic carbonates specifically include, but are not limited to, at least one of ethylene carbonate and propylene carbonate; linear carbonates specifically include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; carboxylic esters include, but are not limited to, at least one of methyl formate, methyl acetate, methyl butyrate, ethyl propionate, propyl propionate, and propyl acetate; ethers include, but are not limited to, at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane; and alcohols include, but are not limited to, at least one of ethanol, ethylene glycol, and glycerol.

[0092] Additives include, but are not limited to, nitriles, sulfones, sulfoxides, fluoronitriles, and fluoroesters.

[0093] Separating membrane

[0094] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0095] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator material can be resin, glass fiber, inorganic materials, etc., formed from materials stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of resin or glass fiber separator materials include, but are not limited to, polyolefins, aromatic polyamides, polyimide (PI), polyamide (PA), polytetrafluoroethylene, polyethersulfone, spandex, or aramid. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0096] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0097] Inorganic materials include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The forms of inorganic materials include, but are not limited to, particulate or fibrous forms.

[0098] The separator can be in the form of a thin film, including but not limited to non-woven fabric, woven fabric, and microporous membranes. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 50 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0099] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0100] In this application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the aforementioned inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the aforementioned binders, and may include at least one of the aforementioned binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0101] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0102] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0103] Example

[0104] The following uses lithium-ion batteries as an example to illustrate this application in more detail with examples and comparative examples. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0105] Test methods and equipment:

[0106] High temperature cycling stability test

[0107] The cycle stability of lithium-ion batteries is evaluated by the capacity retention rate after 400 cycles at 45°C. A higher capacity retention rate after 400 cycles at 45°C indicates better cycle stability of the lithium-ion battery.

[0108] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at 45°C with a constant current of 0.2C to 4.5V, followed by constant voltage charging at 4.5V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 3.0V, and left to stand for 5 minutes. The initial discharge capacity C0 of the lithium-ion battery was then tested. Next, the battery was charged at a constant current of 1.8C to 4.15V, followed by constant voltage charging at 4.15V to 1C. It was then charged at a constant current of 1C to 4.25V, followed by constant voltage charging at 4.25V to 0.8C. It was then charged at a constant current of 0.8C to 4.5V, followed by constant voltage charging at 4.5V to 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 3.0V and left to stand for 5 minutes. This completes one charge-discharge cycle. The discharge capacity C1 of the lithium-ion battery after 400 cycles was measured by following the above charge / discharge cycle steps.

[0109] The capacity retention rate after 400 cycles at 45°C is calculated as C1 / C0 × 100%. The higher the capacity retention rate after 400 cycles at 45°C, the better the high-temperature cycle stability of the lithium-ion battery. The specific data on the high-temperature cycle stability of the lithium-ion batteries in each embodiment and comparative example are shown in the table.

[0110] Charge and discharge efficiency

[0111] Test procedure (taking full battery as an example, based on GB / T 31484-2015):

[0112] Constant current charge-discharge cycle (3 times, electrode activation):

[0113] Charging: After constant current charging to 4.5V at 1C, constant voltage charging is performed until the current is ≤0.05C;

[0114] Discharge: 1C constant current discharge to 3.0V;

[0115] Record the charging capacity (C) of the 3rd cycle. charge ) and discharge capacity (C discharge ).

[0116] The formula for calculating Coulomb efficiency is as follows:

[0117] CE (%) = C discharge / C charge *100%.

[0118] Determination of fluorine content and its rate of change in cobalt-containing particles

[0119] X-ray photoelectron spectroscopy (XPS) was used to characterize the cobalt content at different depths of cobalt-containing particles.

[0120] XPS depth profile analysis

[0121] Equipment: Thermo Scientific K-Alpha+ XPS system, Ar+ sputtering gun (sputtering rate: 0.5 nm / s, calibrated with SiO2 standard)

[0122] method:

[0123] F1s spectra were collected at 5nm intervals from the particle surface to a depth of 100nm.

[0124] Quantitatively calculate the mass content (W%) of F at each depth point and fit the gradient change curve;

[0125] Gradient slope calculation:

[0126] 0nm~20nm region: a1=(W a -Wb ) / (D b -D a (%), the unit is "% / nm".

[0127] 20nm~100nm region: a2=(W c -W d ) / (D d -D c (%), the unit is "% / nm".

[0128] Example 1-1

[0129] <Preparation of Electrolyte>

[0130] In an argon-atmospheric glove box with a water content of less than 10 ppm, methyl ethyl carbonate and ethyl acetate were mixed at a mass ratio of 1:1 to prepare a base solvent, and then lithium hexafluorophosphate (LiPF6) was added. Based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, with the remainder being the base solvent.

[0131] <Preparation of the positive electrode>

[0132] The positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated on the upper and lower surfaces of a 9 μm thick aluminum foil for the positive electrode current collector. After drying and pressure treatment, the foil was cut into the specified size to obtain the positive electrode sheet.

[0133] The preparation method of the cathode material is as follows:

[0134] Step 1: Preparation of precursors.

[0135] Cobalt nitrate (Co(NO3)2·6H2O) and lithium nitrate (LiNO3) were dissolved in deionized water at a molar ratio of Co:Li = 1:1.05 to prepare a solution with a total metal concentration of 0.8 mol / L. The solution was magnetically stirred for 2 hours, filtered to remove impurities, and then spray pyrolysis was performed.

[0136] The spray pyrolysis parameters are:

[0137] When the solution is atomized: atomization pressure 0.5MPa, droplet Dv50 = 20μm.

[0138] During the pyrolysis reaction: drying zone 250℃ / 5s → decomposition zone 550℃ / 10s → crystallization zone 800℃ / 30s, to obtain precursor powder (Dv50=5μm).

[0139] Step 2: First sintering.

[0140] The precursor powder was sintered at 900°C for 12 hours under an argon atmosphere to obtain a lithium cobalt oxide substrate (LiCoO2, XRD shows a layered structure with space group R-3m).

[0141] Step 3: Doping with fluorine.

[0142] The lithium cobalt oxide substrate was immersed in a 5% NH4F ethanol solution (solid-liquid ratio 1:10), stirred for 4 hours, and then centrifuged.

[0143] The powder was vacuum dried at 80℃ for 12 hours to obtain fluorine-modified powder (surface fluorine content W1 = 57%, fluorine content at a depth of 100 nm W2 = 63.5%, verified by XPS).

[0144] Step 4: Second sintering.

[0145] Fluorine-modified powder was annealed in argon at 750°C for 2 hours to obtain the final cathode material (particle Dv50 = 6 μm, BET specific surface area 0.8 m²). 2 / g).

[0146] <Preparation of Negative Electrode Sheets>

[0147] Artificial graphite, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carbon nanotubes (CNTs): carboxymethyl cellulose (CMC) were mixed in a mass ratio of 95.8:2.4:0.5:0.5:0.8. Deionized water was then added as a solvent and the mixture was stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto the upper and lower surfaces of a 6 μm thick copper foil used as a negative electrode current collector. After drying and pressure treatment, the foil was cut into specified sizes to obtain the negative electrode sheet.

[0148] <Isolation membrane>

[0149] A porous polyethylene film with a thickness of 15μm was used as the separator.

[0150] <Preparation of Lithium-ion Batteries>

[0151] The prepared positive electrode, separator, negative electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, shaping, and capacity testing.

[0152] Examples 1-2

[0153] Compared to Example 1-1, the fluorine content in step 3 of the <Preparation of Positive Electrode> was adjusted, and the preparation of the positive electrode material also includes the following steps:

[0154] Step 5: Doping with other elements

[0155] The above material was mixed with aluminum nitrate (Al(NO3)3) and ball-milled for 6 hours (ethanol medium); then calcined at 800℃ for 5 hours to obtain Al-F co-doped lithium cobalt oxide (AlF3 coating thickness was about 8 nm, verified by TEM (transmission electron microscopy)).

[0156] Examples 1-3 to Examples 1-20

[0157] Compared to Examples 1-2, the preparation parameters of the positive electrode material in the <Preparation of Positive Electrode Sheet> were adaptively adjusted to obtain the positive electrode material shown in Table 1.

[0158] Comparative Example 1

[0159] In the preparation of the positive electrode sheet, the positive electrode material was prepared using conventional solid-state sintering (i.e., without spray pyrolysis). The concentration of fluorine in the surface layer of the obtained positive electrode material remained unchanged. The rest was basically the same as in Examples 1-1.

[0160] Comparative Example 2

[0161] Compared to Examples 1-2, the preparation parameters of the positive electrode material in the <Preparation of Positive Electrode Sheet> were adaptively adjusted to obtain the positive electrode material shown in Table 1.

[0162] Table 1

[0163] Examples 2-1 to 2-9

[0164] Compared to Examples 1-4, the preparation parameters of the positive electrode material in <Preparation of Positive Electrode Sheet> were adaptively adjusted to obtain the positive electrode material shown in Table 2.

[0165] Comparative Example 3

[0166] Compared to Example 2-1, the preparation parameters of the positive electrode material in <Preparation of Positive Electrode Sheet> were adaptively adjusted to obtain the positive electrode material shown in Table 2.

[0167] Table 2

[0168] As shown in Table 1, the cathode material of this application exhibits good thermal stability, electrochemical stability, and high conductivity under high-temperature conditions. When used in secondary batteries, it can improve the high-temperature cycle stability and charge-discharge efficiency of the secondary battery. In particular, when a1 is in the range of 0.2% to 1% and a2 is in the range of 0.01% to 0.1%, the performance of the cathode material can be further improved, which is more conducive to improving the high-temperature cycle stability and charge-discharge efficiency of the secondary battery.

[0169] In particular, as shown in Tables 1 and 2, when fluorine is combined with aluminum, magnesium, lanthanum, zirconium, and calcium in the cathode material, the high-temperature cycle stability and charge-discharge efficiency of the secondary battery can be further improved.

[0170] The above are merely embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A positive electrode material, characterized in that, It includes cobalt-containing particles, which contain fluorine. Based on X-ray photoelectron spectroscopy, the fluorine content on the surface of the cobalt-containing particles is W1%, and the fluorine content in a region 100 nm from the surface of the cobalt-containing particles is W2%, where W1 > W2.

2. The cathode material according to claim 1, characterized in that, D at a distance from the surface of the cobalt-containing particles a nm and D b The fluorine content in the nm region is W. a % and W b %, 0.2% ≤ (W a -W b ) / (D b -D a )≤1%, and 0≤D a <D b ≤20; D at a distance from the surface of the cobalt-containing particles c nm and D d The fluorine content in the nm region is W. c % and W d %, 0.01% ≤ (W c -W d ) / (D d -D c )≤0.1%, and 20≤D c <D d ≤100.

3. The cathode material according to claim 2, characterized in that, 0.4% ≤ (W a -W b ) / (D b -D a ≤0.6%, and / or, 0.03%≤(W c -W d ) / (D d -D c )≤0.05%。 4. The cathode material according to claim 1, characterized in that, Based on the mass of the cobalt-containing particles, the mass content of the fluorine element is 0.1% to 1%.

5. The positive electrode material according to claim 1, characterized in that, The cobalt-containing particles also include aluminum, and the mass ratio of fluorine to aluminum is 0.1 to 5.

6. The cathode material according to claim 5, characterized in that, The mass ratio of fluorine to aluminum is (0.5:1) to (2:1).

7. The cathode material according to any one of claims 1 to 5, characterized in that, The cobalt-containing particles also include at least one of the following elements: magnesium, zirconium, titanium, yttrium, calcium, lanthanum, cerium, or lithium.

8. The cathode material according to claim 7, characterized in that, Based on the mass of the cobalt-containing particles, at least one of the following conditions is satisfied: (1) The content of magnesium element is 0.01% to 2%, and the mass ratio of fluorine element to magnesium element is 0.1 to 10; (2) The content of zirconium is 0.05% to 1%, and the mass ratio of fluorine to zirconium is 0.1 to 20; (3) The content of titanium element is 0.02% to 2%, and the mass ratio of fluorine element to titanium element is 0.1 to 10; (4) The content of yttrium is 0.01% to 0.5%, and the mass ratio of fluorine to yttrium is 1 to 50; (5) The content of calcium element is 0.01% to 0.5%, and the mass ratio of fluorine element to calcium element is 1 to 50; (6) The content of the lanthanum element is 0.01% to 0.5%, and the mass ratio of the fluorine element to the lanthanum element is 1 to 50; (7) The content of the cerium element is 0.01% to 0.5%, and the mass ratio of the fluorine element to the cerium element is 1 to 50; (8) The lithium content is 4% to 8%, and the mass ratio of the fluorine to the lithium is 0.01 to 2.

9. The cathode material according to any one of claims 1 to 5, characterized in that, The cobalt-containing particles also include at least one of magnesium, zirconium, calcium, and lanthanum, and satisfy at least one of the following conditions: (1) The mass ratio of the fluorine element to the magnesium element is 1 to 5; (2) The mass ratio of the fluorine element to the zirconium element is 1 to 2; (3) The mass ratio of the fluorine element to the calcium element is 20 to 30; (4) The mass ratio of the fluorine element to the lanthanum element is 4 to 6.

10. A positive electrode plate, characterized in that, It includes the cathode material as described in any one of claims 1 to 9.

11. A secondary battery, characterized in that, It includes the positive electrode sheet as described in claim 10.

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