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 of the present application comprises cobalt-containing particles, wherein the cobalt-containing particles comprise titanium. As characterized by X-ray photoelectron spectroscopy, in a region on the surface of the cobalt-containing particle, the average mass content of titanium is W1%; in a region 80-100 nm away from the surface of the cobalt-containing particle, the average mass content of titanium is W2%; and W1>W2. The secondary battery of the present application still has a good capacity retention rate at low temperatures, and also has relatively good safety performance under overcharge conditions.

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. Among the cathode materials used in lithium-ion batteries, cobalt-containing cathode materials have attracted attention due to their excellent electrochemical performance and energy density.

[0003] However, cobalt-containing cathode materials have low chemical stability and poor structural integrity, which can adversely affect the capacity retention rate of secondary batteries at low temperatures and their safety under overcharge conditions. Summary of the Invention

[0004] This application provides a positive electrode material, a positive electrode sheet, and a secondary battery. The positive electrode material of this application has high chemical stability and its structure is not easily changed during charge-discharge cycles. Therefore, the positive electrode sheet of this application has good integrity, and the secondary battery has good capacity retention at low temperatures and good safety performance under overcharge conditions.

[0005] In a first aspect, this application provides a cathode material comprising cobalt-containing particles, wherein the cobalt-containing particles include titanium; based on X-ray photoelectron spectroscopy characterization, the average mass content of titanium is W1% in the region on the surface of the cobalt-containing particles, and the average mass content of titanium is W2% in the region 80nm to 100nm away from the surface of the cobalt-containing particles, wherein W1 > W2.

[0006] In the above technical solution, the inventors discovered that when the cathode material satisfies the gradient distribution of titanium (i.e., W1>W2), the titanium in the cobalt-containing particles can form a spinel-stabilized passivation layer mainly composed of LiTi2O4 on the cobalt-containing particles. The spinel phase has a high oxygen vacancy concentration, which inhibits electrolyte decomposition and Co 3+ The titanium gradient distribution reduces the occurrence of side reactions and inhibits the H2→H3 phase transition during charge-discharge cycles, which is beneficial to improving the chemical stability of the cathode material. In addition, titanium can also effectively enhance the structural integrity of the surface of cobalt-containing particles, which can reduce the structural changes of the cathode material during charge-discharge cycles. Therefore, when the cathode material of this application is used in cathode sheets and secondary batteries, it can improve the integrity of the cathode sheets, so that the secondary battery has good low-temperature capacity retention and safety performance under overcharge.

[0007] 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 average mass content of titanium is W. a% and W b %, 1≤(W) b -W a ) / (D a -D b )≤2, 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 average mass content of titanium is W. c % and W d %, 0.1≤(W c -W d ) / (D d -D c )≤1, and 20≤D c <D d ≤100.

[0008] Among the above technical solutions, cobalt-containing particles have higher chemical stability, and their electrochemical reaction uniformity, conductivity, internal stress, and thermal conductivity are all superior. When used in secondary batteries, they can further improve the low-temperature capacity retention rate and safety performance under overcharge.

[0009] In one possible implementation, the cobalt-containing particles also include aluminum, and the mass ratio of aluminum to titanium is (0.25:1) to (5:1).

[0010] In the above technical solution, on the one hand, aluminum and titanium have different electrochemical properties, which can improve the reaction consistency in the cathode material; on the other hand, they can also work synergistically to improve the mechanical and thermal stability of the cathode material, reduce ion migration barriers, and improve the rate performance of the secondary battery.

[0011] In one possible implementation, a portion of the surface of the cobalt-containing particles is recessed inward to form a crack, with a crack depth of 10 nm to 10,000 nm and a crack width of 1 nm to 500 nm. The outer surface of the crack contains aluminum and titanium.

[0012] In the above technical solutions, the stability of the cathode material remains relatively high, and it is not likely to have an adverse effect on the low-temperature capacity retention rate and safety performance under overcharge of the secondary battery.

[0013] In one possible implementation, the mass content of aluminum is 0.3% to 5% based on the mass of the cobalt-containing particles.

[0014] In one possible implementation, the mass content of titanium is 0.05% to 1%, based on the mass of the cobalt-containing particles.

[0015] In one possible implementation, the angle of repose of the cobalt-containing particles is no greater than 35°.

[0016] In the above technical solution, the positive electrode material has good fluidity, which is beneficial to improving the uniformity and compaction density of the positive electrode sheet during preparation.

[0017] In one possible implementation, the cobalt-containing particles are characterized by atomic force microscopy, and the surface roughness of the cobalt-containing particles is 0.5 nm to 1.5 nm.

[0018] In the above technical solutions, the surface area of ​​the positive electrode material is relatively large, which can further improve the low-temperature capacity retention rate and safety performance under overcharge conditions when used in secondary batteries.

[0019] 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.

[0020] Thirdly, this application provides a secondary battery comprising the aforementioned positive electrode. Therefore, the secondary battery provided by this application exhibits excellent rate performance and cycle performance.

[0021] The beneficial effects of this application are:

[0022] This application provides a positive electrode material, a positive electrode sheet, and a secondary battery. The positive electrode material includes cobalt-containing particles doped with titanium. X-ray photoelectron spectroscopy (XPS) analysis shows that the average mass content of titanium on the surface of the cobalt-containing particles is W1%, and the average mass content of titanium in the region 80 nm to 120 nm from the surface of the cobalt-containing particles is W2%, where W1 > W2. By setting different concentrations of titanium in different regions, this application can improve the chemical stability of the positive electrode material, making its structure less prone to change during charge-discharge cycles. Attached Figure Description

[0023] 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.

[0024] Figure 1 is a graph showing the relationship between the titanium content and the distance from the surface of the cobalt-containing particles in the cathode material provided in Example 1-1 of this application.

[0025] Figure 2 is a SEM image of the cobalt-containing particles in Example 1-1 of this application. Detailed Implementation

[0026] 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.

[0027] While existing cobalt-containing cathode materials such as LiCoO2 possess excellent electrochemical performance and energy density, their chemical stability is low and their structural integrity is poor, which can negatively impact the capacity retention of secondary batteries at low temperatures and their safety under overcharge conditions. Although there are technical solutions for doping cobalt-containing materials with titanium, these solutions still cannot effectively solve or improve the aforementioned problems.

[0028] Based on the above-mentioned technical problems, this application provides a positive electrode material with high chemical stability and whose structure is not easily changed during charge-discharge cycles. When the positive electrode material of this application is used in the positive electrode sheet, it can improve the integrity of the positive electrode sheet. When used in a secondary battery, it can enable the secondary battery to not only have good low-temperature capacity retention rate, but also good safety performance under overcharge conditions.

[0029] The positive electrode material, positive electrode sheet, and secondary battery of the present application embodiments are described in detail below.

[0030] In a first aspect, this application provides a cathode material comprising cobalt-containing particles, wherein the cobalt-containing particles include titanium; based on X-ray photoelectron spectroscopy characterization, the average mass content of titanium is W1% in the region on the surface of the cobalt-containing particles, and the average mass content of titanium is W2% in the region 80nm to 100nm away from the surface of the cobalt-containing particles, wherein W1 > W2.

[0031] 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 called 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, in this application, the equivalent particle size of the cobalt-containing particles is generally at the micrometer level; therefore, the region 0–100 nm from the cobalt-containing particles can be considered the "surface layer" of the cobalt-containing particles. Additionally, for ease of explanation, as an example, the cobalt-containing particles in this application are based on lithium cobalt oxide particles and can be called "modified lithium cobalt oxide particles."

[0032] Furthermore, it should be noted that although this application only specifies that the average mass content of titanium in the region "80nm to 100nm from the surface of the cobalt-containing particles" is less than the average mass content of titanium on the surface, in actual products, in order to reduce the difficulty of preparation, cobalt-containing particles generally also have the following properties: in the region 0 to 100nm from the surface of the cobalt-containing particles, the greater the distance to the surface of the cobalt-containing particles, the smaller the average mass content of titanium.

[0033] In the cathode material of this application, the inventors discovered that because the surface layer of cobalt-containing particles contains a large amount of titanium, titanium can form a stable passivation layer on the surface of the cobalt-containing particles. When the cathode material of this application is used in cathode plates or secondary batteries, the passivation layer can reduce the occurrence of side reactions such as electrolyte decomposition, which is beneficial to improving the chemical stability of the cathode material. In addition, since the average mass content of titanium in the 80nm-100nm region of the surface layer is less than the average mass content of titanium in the surface region, titanium can also effectively enhance the structural integrity of the surface layer of cobalt-containing particles, making the structure of the cathode material less prone to change during charge-discharge cycles. When the cathode material of this application is used in cathode plates, the cathode plate not only has high structural integrity, but its surface is also less prone to side reactions such as electrolyte decomposition, which can enable the secondary battery to have good low-temperature capacity retention and overcharge pass rate.

[0034] In some embodiments of this application, to improve the low-temperature capacity retention and safety performance under overcharge conditions of the secondary battery, the average mass content change rate of titanium varies in different regions within the 0-100 nm range from the cobalt-containing particles. Preferably, the absolute value of the average mass content change rate of titanium is larger in the 0-20 nm region and smaller in the 20 nm-100 nm region, as detailed below:

[0035] D at a distance from the surface of the cobalt-containing particles a nm and D b In the region of nm, the average mass content of titanium is W. a % and W b %, 1≤(W) b -W a ) / (D a -D b )≤2, 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 average mass content of titanium is W. c % and W d%, 0.1≤(W c -W d ) / (D d -D c )≤1, and 20≤D c <D d ≤100.

[0036] In the 0–20 nm region, titanium can form both a conductive network and a LiTiO compound with lithium. The conductive network enhances the electronic conductivity of the cathode material, while the LiTiO compound facilitates rapid lithium-ion insertion and extraction, further improving the cathode's electronic conductivity. Therefore, the ion diffusion path of the entire cathode material can be optimized, resulting in good conductivity and ion conductance even at low temperatures, which is beneficial for further improving the capacity retention of the secondary battery at low temperatures. Furthermore, the gradient distribution of titanium in the 0–20 nm region helps to uniform the electrochemical reaction of the cathode material, preventing localized overheating and overcharging, and further improving the safety performance of the secondary battery under overcharge conditions. In the 20 nm–100 nm region, titanium can maintain the crystal structure of cobalt-containing particles, reducing structural shrinkage or expansion caused by temperature decreases, which also helps to further improve the capacity retention of the secondary battery at low temperatures. In addition, the titanium element in this region helps to optimize the internal stress distribution of cobalt-containing particles, reduce stress concentration under high voltage, and also improve the thermal conductivity of cobalt-containing particles. This helps to further reduce the overcharge risk of secondary batteries and improve the safety performance of secondary batteries under overcharge conditions.

[0037] In some embodiments of this application, the cobalt-containing particles also include aluminum, with a mass ratio of aluminum to titanium of (0.25:1) to (5:1). Typically, the mass content of aluminum in the cobalt-containing particles is 0.3% to 5%, and the mass content of titanium is 0.05% to 1%. Due to the different electrochemical properties of aluminum and titanium, uniform ion migration paths can be created on the surface and inside the cathode material and cathode sheet, thereby slowing down the accumulation of the passivation layer and improving the consistency of the reaction. Furthermore, the synergistic effect of aluminum and titanium can form Li-Al-Ti oxides at the grain boundaries. These oxides can enhance interfacial bonding, improve the mechanical stability of the cathode material, act as a thermal runaway barrier to suppress unstable reactions of the cathode material at high temperatures, and reduce ion migration barriers, making the movement of Li+ during charging and discharging smoother. Therefore, cathode materials containing a specific amount of aluminum can improve the rate performance of secondary batteries.

[0038] Furthermore, due to factors such as mechanical stress, manufacturing process, and thermal expansion and contraction, some areas on the surface of cobalt-containing particles often develop inward depressions, forming cracks with a depth of 10 nm to 10,000 nm and a width of 1 nm to 500 nm. These cracks lead to insufficient durability and decreased electrochemical stability of the cobalt-containing particles, thus affecting the performance of the secondary battery. However, in some embodiments of this application, since the cracks in the cobalt-containing particles also contain titanium and aluminum elements, the overall stability of the cathode material at the cracks and defects is relatively high, making it less likely to adversely affect the low-temperature capacity retention rate and overcharge safety performance of the secondary battery.

[0039] In some embodiments of this application, the angle of repose of the cobalt-containing particles is no greater than 35°. This gives the cathode material good flowability, which is beneficial for improving the uniformity and compaction density of the cathode sheet during preparation.

[0040] In addition, in some embodiments of this application, the cobalt-containing particles, characterized by atomic force microscopy (AFM), have a surface roughness Ra of 0.5 nm to 1.5 nm. This results in a relatively large surface area for the cathode material, offering the following advantages: (1) increased actual contact area with the electrolyte during operation, which is beneficial for enhancing electrochemical reaction activity; (2) reduced stress concentration at the joints of large particles, lowering the risk of crack formation and propagation in the cathode material during electrochemical cycling, and enhancing the mechanical stability of the cathode material; (3) better heat dissipation performance; and (4) more uniform current distribution, reducing the risk of localized overcharging. Therefore, when the Ra of the cobalt-containing particles in the cathode material is 0.5 nm to 1.5 nm, the low-temperature capacity retention rate and safety performance under overcharging conditions of the secondary battery are better.

[0041] 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:

[0042] S100: Preparation of precursors: Titanium tetrachloride (TiCl4), 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.

[0043] During the formation of the mixed solution, a magnetic stirrer is usually used to stir thoroughly to dissolve the components. If necessary, filtration can also be used to remove insoluble particles.

[0044] In spray pyrolysis, spray drying equipment is typically used to atomize the solution into fine droplets (i.e., solution atomization). Then, in a high-temperature pyrolysis chamber, these droplets rapidly evaporate and decompose, generating a powdery precursor (i.e., pyrolysis reaction). During precursor preparation, droplet size can be controlled by adjusting the atomization pressure, and the titanium content on the surface of the precursor powder can be controlled by adjusting the pyrolysis temperature and time. The atomization pressure can range from 0.4 MPa to 1.8 MPa, resulting in precursor particles with a Dv50 of 5–30 μm. The pyrolysis reaction sequentially progresses through three stages: a drying zone, a decomposition zone, and a crystallization zone. The drying zone rapidly evaporates moisture. The decomposition zone rapidly decomposes nitrates and titanium salts; the decomposition rate of titanium salts can be controlled by adjusting the temperature and time in the decomposition zone, thereby controlling the enrichment and content of titanium on the precursor surface. The crystallization zone reacts the decomposed salts to form the precursor of this step. The temperature and time of each of the three stages can be adjusted according to actual needs. The following sections will use Example 1-1 as an example for detailed explanation. The preparation process of the cathode material in the other examples will not be repeated. Those skilled in the art can make conventional adjustments as needed.

[0045] In addition, aluminum nitrate can be added in this step to dope the cobalt particles with aluminum.

[0046] S200, High-temperature sintering: In an inert gas environment (such as nitrogen or argon), the powdered precursor is placed in a high-temperature furnace for sintering to form a positive electrode material.

[0047] During the sintering process, the lithium cobalt oxide crystal structure can be formed by controlling the sintering temperature and time, and the oxidation of titanium can be suppressed, maintaining the concentration gradient distribution of titanium on the surface of the cobalt-containing particles. Moreover, the high-temperature sintering temperature and time can be adaptively adjusted when the mass content of titanium is different, which will not be elaborated here.

[0048] Furthermore, in some embodiments of this application, other elements such as fluorine, lanthanum, and zirconium can be doped onto the surface of the cathode material to improve other aspects of its performance. The specific preparation steps are as follows:

[0049] S300, doping with other elements: The cathode material is placed in the nitrates corresponding to other elements and stirred continuously, and then cured and dried.

[0050] S400, Secondary Sintering: The solidified and dried particles are sintered a second time.

[0051] Secondly, this application provides a positive electrode sheet, which includes the above-mentioned positive electrode material, and its specific structure is as follows:

[0052] 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.

[0053] 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.

[0054] 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 z At 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.

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] Thirdly, this application provides a secondary battery comprising the aforementioned positive electrode sheet. Because the positive electrode material in the secondary battery of this application has high chemical stability and its structure is not easily altered during charge-discharge cycles, the secondary battery of this application exhibits good capacity retention even at low temperatures and good safety performance under overcharge conditions.

[0060] In the secondary battery of this application, the positive electrode is as shown above, and the other structures are as follows:

[0061] Negative electrode sheet

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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).

[0067] 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.

[0068] 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.

[0069] electrolyte

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Additives include, but are not limited to, nitriles, sulfones, sulfoxides, fluoronitriles, and fluoroesters.

[0074] Separating membrane

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 5 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.

[0080] 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.

[0081] 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).

[0082] 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.

[0083] 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.

[0084] Example

[0085] 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.

[0086] Test methods and equipment:

[0087] Low-temperature capacity retention test

[0088] (1) Pre-treatment of secondary batteries:

[0089] Charge the capacitor at 0.1C constant current to 4.5V at 25℃, then switch to constant voltage charging until the current is ≤0.05C; let it stand for 30 minutes, then discharge it at 0.1C to 3.0V, and record the initial capacity C0.

[0090] (2) Then, perform low-temperature cycling tests:

[0091] Place the battery in a 0℃ constant temperature chamber and let it stand for 2 hours;

[0092] Charging: Charge at a constant current of 0.5C to 4.5V, then switch to constant voltage charging until the current is ≤0.05C;

[0093] Discharge: 0.5C constant current discharge to 3.0V;

[0094] The capacity C was recorded after every 50 charge-discharge cycles. n The cycle repeats a total of 500 times.

[0095] Capacity retention calculation:

[0096] Capacity retention rate (%) = C n / C0*100%

[0097] (3) The key parameters during the testing process are as follows:

[0098] Number of loops: 500;

[0099] Charge / discharge rate: 0.5C;

[0100] Temperature stability: Temperature fluctuation of the constant temperature chamber ≤ ±0.5℃.

[0101] Safety performance test under overcharge

[0102] (1) Pre-treatment of secondary batteries:

[0103] Charge the battery at 0.1C to 4.5V at 25℃ (overcharge limit is 5.2V); let it stand for 1 hour to ensure the battery is fully charged.

[0104] (2) Then perform an overcharge test:

[0105] Charging conditions: Charge at a constant current of 0.1C to the rated voltage (5.2V, which is 1.3 times the conventional upper limit voltage);

[0106] Termination conditions: After the voltage reaches 5.2V, maintain a constant voltage until the current drops to 0.05C; or continue charging until the battery experiences thermal runaway (temperature ≥150℃ or fire / explosion).

[0107] Safety performance assessment:

[0108] Thermal runaway time: the time from the start of overcharging to a sudden temperature rise (≥80℃); the longer the time, the better the safety performance under overcharging.

[0109] Determination of Ti element content in cobalt-containing particles

[0110] X-ray photoelectron spectroscopy (XPS) was used to characterize the cobalt content at different depths of cobalt-containing particles. XPS depth profiling analysis was employed.

[0111] Equipment: Thermo Scientific K-Alpha+XPS system, Ar + Sputtering gun (sputtering rate: 0.5 nm / s, calibrated with SiO2 standard)

[0112] method:

[0113] Ti 2p3 / 2 spectra were collected at 5 nm intervals from the particle surface to a depth of 100 nm.

[0114] Quantitatively calculate the Ti mass content (W%) at each depth point and fit the gradient variation curve;

[0115] Gradient slope calculation:

[0116] 0nm~20nm region: a1=(W b-W a ) / (D a -D b ), the unit is % / nm.

[0117] 20nm~100nm region: a2=(W c -W d ) / (D d -D c ), the unit is % / nm.

[0118] Methods for testing surface roughness

[0119] The lithium cobalt oxide particle sample to be tested was uniformly coated onto a smooth substrate, ensuring the sample was stable and free of impurities. The AFM instrument was then started, and the probe was ensured to be in good working order and suitable for measuring surface roughness. The instrument was calibrated to ensure accurate measurements.

[0120] Select the contact mode, then set the scanning area and resolution to measure the sample surface. Next, start AFM to scan the surface of the cobalt-containing particles, recording the height changes and the three-dimensional profile data. Then, use AFM software to analyze the scan data and extract surface roughness parameters. The surface roughness is then calculated, which is the average absolute height difference between each point in the measured area and the mean line. The calculation formula is as follows: [\text{Ra}=\frac{1}{n}\sum_{i=1}^n|y_i|].

[0121] Where (|y_i|) is the absolute height difference of each data point, and (n) is the total number of data points.

[0122] The inventors discovered that the surface roughness of the cobalt-containing particles in the embodiments of this application is all in the range of 0.5nm to 1.5nm, while that of the comparative examples is not in this range.

[0123] Surface crack observation of cobalt-containing particles

[0124] The surface cracks of the cobalt-containing particles were observed using SEM (Scanning Electron Microscope), and the crack width was measured. A cross-sectional image of the crack was then created to determine its depth. Finally, EDS (Energy Dispersive Spectrometer) was used to detect the elemental composition of the outer surface of the crack.

[0125] The SEM image of the cobalt-containing particles is shown in Figure 2.

[0126] Angle of repose measurement

[0127] Test method for angle of repose of lithium cobalt oxide battery cell electrode powder

[0128] Step 1: Sample Pretreatment

[0129] • Place the disassembled electrode in an argon glove box (O2 < 0.1 ppm, H2O < 0.1 ppm).

[0130] • Use a ceramic scraper to scrape off ≥5g of active substance powder.

[0131] Vacuum drying: 60℃ / 10 -3 Treated under Pa conditions for 12 hours

[0132] Step 2: Dedicated testing equipment

[0133] • Antistatic stacking platform: Surface resistivity 10 6 -10 8 Ω, diameter D = 100.0 ± 0.1 mm

[0134] • Adjustable slit funnel: outlet diameter d = 5.00 ± 0.05 mm, height from platform H = 50.0 ± 0.2 mm

[0135] • Laser scanning system: Equipped with a 635nm line laser and a 10μm resolution CCD sensor

[0136] Step 3: Test the program

[0137] 1. Inside the glove box, align the funnel with the center of the platform (x).

[0138] 2. Inject the powder uniformly at a rate of 0.5 g / s ± 0.05 g / s.

[0139] 3. After naturally piling up to form a cone shape, let it stand for 30 seconds.

[0140] 4. Start the laser scanning system and acquire contour curves along four orthogonal directions.

[0141] Step 4: Data Processing

[0142] • Fit the conical surface using the least squares method:

[0143] ·thanθ=2H cone / D base

[0144] ·(θ: angle of repose, H) cone Cone height, D base (Base diameter)

[0145] • Take the arithmetic mean of the four measurements and round it to 0.1°.

[0146] Example 1-1

[0147] <Preparation of Electrolyte>

[0148] In an argon-atmospheric glove box with a water content of less than 10 ppm, methyl ethyl carbonate and ethyl acetate were mixed in a 1:1 mass ratio to prepare a base solvent. Then, lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate, 1,3-propanesulfonate lactone, and adiponitrile were added. Based on the total mass of the electrolyte, the mass content of LiPF6 was 12.5%, fluoroethylene carbonate was 3%, 1,3-propanesulfonate lactone was 2%, adiponitrile was 0.5%, and the remainder was the base solvent.

[0149] <Preparation of the positive electrode>

[0150] Cobalt particles (containing the positive electrode material), conductive carbon black (a conductive agent), 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 onto 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 specified sizes to obtain the positive electrode sheet.

[0151] The specific preparation method of the cathode material is as follows:

[0152] (1) Preparation of precursors: 0.028 mol titanium tetrachloride (TiCl4), 1 mol cobalt nitrate (Co(NO3)2), and 1.05 mol lithium nitrate (LiNO3) were added to deionized water and magnetically stirred at 600 rpm for 3 h to fully dissolve them in the deionized water to form a 1.25 L mixed solution, which was then subjected to spray pyrolysis. During the spray pyrolysis process, a dual-fluid nozzle was used for solution atomization at a pressure of 1.0 MPa. During the pyrolysis reaction, the atomized droplets successively passed through three stages: the drying zone, the decomposition zone, and the crystallization zone. The temperature of the drying zone was 250 °C for 5 s; the temperature of the decomposition zone was 600 °C for 15 s; and the temperature of the crystallization zone was 850 °C for 25 s.

[0153] (2) High-temperature sintering: In a high-purity argon environment (oxygen content ≤1ppm), the powdered precursor is placed in a high-temperature furnace, and then the high-temperature furnace is heated from room temperature to 900℃ at a rate of 5℃ / min. After holding at 900℃ for 12h, the furnace is cooled to room temperature for sintering to form the positive electrode material.

[0154] <Preparation of Negative Electrode Sheets>

[0155] 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.

[0156] <Isolation membrane>

[0157] A porous polyethylene film with a thickness of 15μm was used as the separator.

[0158] <Preparation of Lithium-ion Batteries>

[0159] 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.

[0160] Examples 1-2 to Examples 1-10

[0161] Compared to Example 1-1, in <Preparation of Positive Electrode Sheet>, the atomization pressure, the temperature and time of the decomposition zone, and the temperature and time of high-temperature sintering were changed to form the positive electrode material shown in Table 1. The rest is the same as in Example 1-1.

[0162] Comparative Example 1

[0163] Compared to Example 1-1, in <Preparation of Positive Electrode>, when preparing the positive electrode material, 1 mol Co3O4, 1.02 mol Li2CO3 and 0.028 mol TiO2 were mixed by solid-state ball milling, and then sintered in air at 900°C for 12 h to ensure uniform distribution of titanium elements on the surface of the positive electrode material. Otherwise, it was the same as Example 1-1.

[0164] Comparative Example 2

[0165] Compared to Example 1-1, in <Preparation of Positive Electrode>, the atomization pressure and the temperature and time of the decomposition zone were changed during the preparation of the positive electrode material to form the positive electrode material shown in Table 1. The rest is the same as in Example 1-1.

[0166] Table 1

[0167] Example 2-1

[0168] Except for the preparation of the positive electrode sheet in the following manner, the rest is the same as in Examples 1-2:

[0169] <Preparation of the positive electrode>

[0170] (1) Preparation of precursors: Al(NO3)3, TiCl4, Co(NO3)2, and LiNO3 were added to deionized water and magnetically stirred at 600 rpm for 3 hours to fully dissolve them in the deionized water to form a 1.25 L mixed solution, which was then subjected to spray pyrolysis. During the spray pyrolysis process, a dual-fluid nozzle was used for solution atomization, and the atomization pressure was 0.9 MPa. During the pyrolysis reaction, the atomized droplets successively passed through three stages: the drying zone, the decomposition zone, and the crystallization zone. The temperature of the drying zone was 250℃ for 5 s; the temperature of the decomposition zone was 580℃ for 14 s; and the temperature of the crystallization zone was 850℃ for 25 s.

[0171] (2) High-temperature sintering: In a high-purity argon environment (oxygen content ≤1ppm), the powdered precursor is placed in a high-temperature furnace, and then the high-temperature furnace is heated from room temperature to 880℃ at a rate of 5℃ / min. After holding at 880℃ for 13h, the furnace is cooled to room temperature for sintering to form the positive electrode material.

[0172] Examples 2-2 to 2-7

[0173] Except for the adaptive adjustment of the amount of Al(NO3)3 in the <Preparation of Positive Electrode Sheet>, as well as the temperature and time during the decomposition zone and high-temperature sintering to form the positive electrode material in Table 2, the rest is the same as in Example 2-1.

[0174] Comparative Example 3

[0175] Compared to Comparative Example 1's <Preparation of Positive Electrode Sheet>, Li2CO3 was added to prepare the positive electrode material, and the rest was the same as Comparative Example 1.

[0176] Table 2

[0177] Example 3-1

[0178] Except for the preparation of the positive electrode sheet in the following manner, the rest is the same as in Examples 1-2:

[0179] <Preparation of the positive electrode>

[0180] (1) Preparation of precursors: 0.028 mol titanium tetrachloride (TiCl4), 1 mol cobalt nitrate (Co(NO3)2), and 1.05 mol lithium nitrate (LiNO3) were added to deionized water and magnetically stirred at 600 rpm for 3 h to fully dissolve them in the deionized water to form a 1.25 L mixed solution, which was then subjected to spray pyrolysis. During the spray pyrolysis process, a dual-fluid nozzle was used for solution atomization, and the atomization pressure was 0.95 MPa. During the pyrolysis reaction, the atomized droplets successively passed through three stages: the drying zone, the decomposition zone, and the crystallization zone. The temperature of the drying zone was 250℃ for 5 s; the temperature of the decomposition zone was 600℃ for 15 s; and the temperature of the crystallization zone was 850℃ for 25 s.

[0181] (2) High-temperature sintering: In a high-purity argon environment (oxygen content ≤1ppm), the powdered precursor is placed in a high-temperature furnace, and then the high-temperature furnace is heated from room temperature to 880℃ at a rate of 5℃ / min. After holding at 880℃ for 13h, the furnace is cooled to room temperature for sintering to form the positive electrode material.

[0182] Examples 3-2 to 3-8

[0183] Except for adaptively adjusting the atomization pressure to adjust the angle of repose of the cathode material according to Table 3, the rest is the same as in Example 3-1.

[0184] Table 3

[0185] As shown in Table 1, the cathode material of this application exhibits high chemical stability and its structure is not easily altered during charge-discharge cycles. In particular, when a1 is in the range of 1 to 2 and a2 is in the range of 0.1 to 0.1, the performance of the cathode material can be further improved, which is more conducive to enhancing the low-temperature capacity retention rate and overcharge safety performance of the secondary battery.

[0186] In particular, as shown in Tables 1 and 2, aluminum and titanium elements in the cathode material can work synergistically to further improve the low-temperature capacity retention rate and safety performance under overcharge of the secondary battery; moreover, the improvement effect is more obvious when the aluminum content is between 0.3% and 5%.

[0187] In particular, as shown in Table 3, when the angle of repose of the cobalt-containing particles in the cathode material is no greater than 35°, the uniformity and compaction density of the cathode sheet can be improved. Therefore, the low-temperature capacity retention rate and safety performance under overcharge of the secondary battery can also be improved.

[0188] 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 titanium. Based on X-ray photoelectron spectroscopy characterization, the average mass content of titanium in the region on the surface of the cobalt-containing particles is W1%, and the average mass content of titanium in the region 80 nm to 100 nm away from the surface of the cobalt-containing particles is W2%, where W1 > W2.

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

3. The cathode material according to claim 1, characterized in that, The cobalt-containing particles also include aluminum, and the mass ratio of aluminum to titanium is (0.25:1) to (5:1).

4. The cathode material according to claim 3, characterized in that, The surface of the cobalt-containing particles is partially recessed to form cracks, the depth of which is 10 nm to 10000 nm and the width of which is 1 nm to 500 nm. The outer surface of the cracks contains the aluminum and titanium elements.

5. The cathode material according to claim 3 or 4, characterized in that, Based on the mass of the cobalt-containing particles, the mass content of the aluminum element is 0.3% to 5%.

6. The cathode material according to any one of claims 1 to 4, characterized in that, Based on the mass of the cobalt-containing particles, the mass content of the titanium element is 0.05% to 1%.

7. The cathode material according to claim 1, characterized in that, The angle of repose of the cobalt-containing particles is no greater than 35°.

8. The positive electrode material according to claim 1, characterized in that, The cobalt-containing particles were characterized by atomic force microscopy, and the surface roughness of the cobalt-containing particles was 0.5 nm to 1.5 nm.

9. A positive electrode sheet, characterized in that, It includes the cathode material as described in any one of claims 1 to 8.

10. A secondary battery, characterized in that, It includes the positive electrode sheet as described in claim 9.

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