A positive electrode material, a preparation method and application thereof

Abstract

The application relates to the technical field of positive electrode materials, and provides a positive electrode material and a preparation method and application thereof. The preparation method of the positive electrode material comprises the following steps: dispersing raw material components of a lithium-containing positive electrode material, a carbon source and a chlorine-containing additive into a solvent to obtain a mixture; grinding and spray drying the mixture, and performing sintering treatment for 1 min to 120 min to obtain the positive electrode material. The preparation method of the positive electrode material provided by the application can effectively reduce the crystallization temperature of the positive electrode material by adding the chlorine-containing additive in the preparation process, so that the positive electrode material with high crystallinity is obtained under the conditions of a lower sintering temperature and a shorter sintering time, and the positive electrode material has the characteristics of high compaction density, high specific surface area and small particle size, and the positive electrode material has the electrochemical performances of high capacity and high cycle stability.

Description

Technical Field

[0001] This application belongs to the field of cathode material technology, and in particular relates to a cathode material, its preparation method and application. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used in electronics, electric vehicles, large-scale energy storage systems and other fields. They are highly valued for their high energy density and rated voltage, strong power handling capability, long service life and low self-discharge rate.

[0003] The cathode material, a crucial component of lithium-ion batteries, plays a decisive role in their performance. For example, in lithium-ion batteries used in electric vehicles, the energy density of the cathode material determines the vehicle's driving range; this energy density is determined by the specific capacity and voltage of the cathode material. To meet the growing demand for lithium-ion batteries with higher energy density and lower cost, various cathode materials have been developed, such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, nickel-manganese-cobalt ternary layered materials, and lithium-rich layered materials. Currently, these cathode materials are mainly prepared using solid-state methods, sol-gel methods, and co-precipitation methods. However, these preparation methods all require heat treatment lasting over ten hours to produce a fine crystal structure. This means that these crystal structures are formed during a complex reaction process with a low heating rate and slow reaction kinetics, requiring a significant amount of time and heat. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode material and its preparation method, as well as a positive electrode sheet and a secondary battery, which aims to solve, to some extent, the technical problems of low synthesis efficiency and long heat treatment time of existing positive electrode materials.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0006] In a first aspect, this application provides a method for preparing a cathode material, comprising the following steps:

[0007] The raw material components, carbon source, and chlorine-containing additives of lithium-containing cathode material are dispersed in a solvent to obtain a mixture.

[0008] The mixture is ground and spray-dried, and then sintered for 1 to 120 minutes to obtain the cathode material.

[0009] Secondly, this application provides a cathode material, which includes:

[0010] The core, including lithium-containing compounds, has a porous structure;

[0011] A coating layer, covering the outer surface of the core, comprising carbon material;

[0012] The cathode material was prepared using the cathode material preparation method described in this application.

[0013] Thirdly, this application provides a positive electrode sheet, which includes a current collector and a positive active layer bonded to at least one surface of the current collector. The positive active layer includes the positive electrode material prepared by the method of preparing the positive electrode material of this application and / or the positive electrode material of this application.

[0014] Fourthly, this application provides a secondary battery, which includes the positive electrode sheet of this application.

[0015] The method for preparing the cathode material provided in the first aspect of this application firstly disperses the raw material components, carbon source, and chlorine-containing additives of the lithium-containing cathode material in a solvent. Due to the strong polarity of chlorine atoms, the interaction force between the chlorine-containing additives and the raw material components and carbon source of the lithium-containing cathode material can be effectively increased, thereby promoting the uniform dispersion of the raw material components, carbon source, and chlorine-containing additives in the solvent. After grinding, the size of the raw material components and carbon source of the lithium-containing cathode material is further reduced, while the dispersibility between the raw material components, carbon source, and chlorine-containing additives is further improved. Then, through spray drying, the chlorine-containing additives generate a solvent-solute interaction, that is, the chlorine-containing additives interact with the active ions and metal ions in the raw material components of the lithium-containing cathode material. The interaction between the chlorine-containing additives and the raw material components of the lithium-containing cathode material reduces the mutual attraction between molecules, further improving the dispersibility between the raw material components and the chlorine-containing additives. During sintering, on the one hand, the chlorine-containing additives react with the raw material components of the lithium-containing cathode material to form a multi-component eutectic, effectively promoting the melting and uniform distribution of the raw material components. This multi-component eutectic can reach its melting point and form a molten state at a lower temperature, thereby effectively reducing the crystallization temperature of the cathode material and obtaining a highly crystalline cathode material within 1 to 120 minutes. On the other hand, the chlorine-containing additives prevent lattice distortion of the raw material components, reduce the generation of impurity phases, and further improve the crystallinity of the cathode material, resulting in a uniform lattice structure. Simultaneously, the carbon source forms an adsorption layer on the surface of the multi-component eutectic, restricting particle growth and giving the cathode material a smaller particle size, thereby shortening the lithium-ion diffusion channel and promoting lithium-ion diffusion. This contributes to reducing the resistivity and increasing the compaction density of the cathode material. In addition, chlorine-containing additives also act as surfactants, which can decompose during the sintering process, thereby creating pores in the cathode material to a certain extent. This is beneficial for increasing the specific surface area of ​​the composite cathode material and giving it good electrochemical performance.

[0016] The cathode material provided in the second aspect of this application is prepared by the method for preparing the cathode material provided in the first aspect. The cathode material has excellent crystallinity and forms a core with a porous structure and a carbon coating layer covering the outer surface of the core. The presence of the porous structure gives the cathode material a high specific surface area, thereby effectively promoting the transport of lithium ions.

[0017] The positive electrode provided in the third aspect of this application contains the positive electrode material of this application, which gives the positive electrode high capacity, high cycle stability and other electrochemical properties.

[0018] The secondary battery provided in the fourth aspect of this application, because it contains the positive electrode sheet of this application, can improve the energy density, cycle stability and rate performance of the secondary battery. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 These are scanning electron microscope images of the cathode material provided in Embodiment 1 of this application;

[0021] Figure 2 These are scanning electron microscope images of the cathode material provided in Embodiment 1 of this application;

[0022] Figure 3 This is a scanning electron microscope image of the cathode material provided in Comparative Example 2 of this application;

[0023] Figure 4 This is a scanning electron microscope image of the cathode material provided in Comparative Example 3 of this application;

[0024] Figure 5 This is the X-ray diffraction pattern of the cathode material provided in this application;

[0025] Figure 6 yes Figure 5 2θ is an enlarged view of the X-ray diffraction pattern of AB;

[0026] Figure 7 These are the 0.1C voltage-to-capacity curves of Embodiment 1 and Comparative Example 1 of this application;

[0027] Figure 8 These are the 1C voltage-to-capacity curves of the cathode materials of Embodiment 1 and Comparative Example 1 of this application. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0030] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0031] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0032] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0034] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0035] The first aspect of this application provides a method for preparing a positive electrode material, including the following steps:

[0036] Step S10: Disperse the raw material components, carbon source and chlorine-containing additives of the lithium cathode material into a solvent to obtain a mixture;

[0037] Step S20: Grind and spray dry the mixture, and sinter for 1 min to 120 min to obtain the positive electrode material.

[0038] The method for preparing the cathode material provided in the first aspect of this application involves first dispersing the raw material components, carbon source, and chlorine-containing additive of the lithium-containing cathode material in a solvent. Due to the strong polarity of chlorine atoms, the interaction force between the chlorine-containing additive and the raw material components and carbon source of the lithium-containing cathode material is effectively increased, thereby promoting the uniform dispersion of the raw material components, carbon source, and chlorine-containing additive in the solvent. After grinding, the size of the raw material components and carbon source of the lithium-containing cathode material is further reduced, while the dispersibility between the raw material components, carbon source, and chlorine-containing additive is further improved. Then, through spray drying, the chlorine-containing additive generates a solvent-solute interaction, that is, the chlorine-containing additive interacts with the active ions and metals in the raw material components of the lithium-containing cathode material. Ion interactions reduce the intermolecular attraction between molecules in the raw material components of lithium-containing cathode materials, further improving the dispersibility between the raw material components and the chlorine-containing additives. During sintering, on the one hand, the chlorine-containing additives react with the raw material components of the lithium-containing cathode material to form a multi-component eutectic, effectively promoting the melting and uniform distribution of the raw material components. This multi-component eutectic can reach its melting point and form a molten state at a lower temperature, thereby effectively reducing the crystallization temperature of the cathode material and obtaining a highly crystalline cathode material within 1 to 120 minutes. On the other hand, the chlorine-containing additives prevent lattice distortion of the raw material components, reduce the generation of impurity phases, and further improve the crystallinity of the cathode material, resulting in a uniform lattice structure. Simultaneously, the carbon source forms an adsorption layer on the surface of the multi-component eutectic, restricting particle growth and giving the cathode material a smaller particle size, thereby shortening the lithium-ion diffusion channel and promoting lithium-ion diffusion. This contributes to reducing the resistivity and increasing the compaction density of the cathode material. In addition, chlorine-containing additives also act as surfactants, which can decompose during the sintering process, thereby creating pores in the cathode material to a certain extent. This is beneficial for increasing the specific surface area of ​​the composite cathode material and giving it good electrochemical performance.

[0039] It is understood that the sintering time in step S20 refers to the holding time after the sintering temperature is raised to the preset temperature. In this embodiment, a chlorine-containing additive is added during the preparation process. This chlorine-containing additive forms a multi-component eutectic with the raw material components of the lithium-containing cathode material during the sintering heating process, thereby effectively reducing the crystallization temperature of the cathode material. This multi-component eutectic can reach its melting point and form a molten state at a lower sintering temperature. Therefore, during the heating process of the sintering treatment, the multi-component eutectic gradually forms a uniform crystal structure, and thus, within a relatively short holding time, such as 1 min to 120 min, a cathode material with high crystallinity is obtained. This results in a cathode material with higher compaction density, higher specific surface area, and smaller particle size characteristics, endowing the cathode material with high capacity, high cycle stability, and other electrochemical properties.

[0040] In some specific embodiments, the sintering time can be typical but not limiting values ​​such as 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, and 120 min. The sintering time mainly affects the degree of crystallinity of the cathode material particles. If the sintering time is lower than the above range, there may be problems such as incomplete material crystallization and insufficient grain growth; if the sintering time is higher than the above range, it may cause local melting and abnormal crystal phase in the lithium-containing cathode material.

[0041] In some embodiments, the sintering time is 1 min to 60 min. During sintering, the chlorine-containing additives and the raw material components of the lithium-containing cathode material form a multi-component eutectic, thus allowing for the acquisition of a cathode material with high crystallinity within a shorter holding time. Understandably, during the heating process of sintering, the low-melting-point multi-component eutectic gradually forms a fine crystal structure. Therefore, within a shorter holding time, such as 1 min to 5 min, 1 min to 10 min, 10 min to 30 min, or 30 min to 60 min, this multi-component eutectic forms an ordered crystal structure, resulting in high crystallinity of the cathode material and endowing it with higher capacity, cycle stability, and other electrochemical properties.

[0042] In some embodiments, the solvent in step S10 includes an aqueous ethanol solution. It is understood that the amount of solvent added should be sufficient to disperse the raw material components, carbon source, and chlorine-containing additives of the lithium cathode material within the solvent.

[0043] In some embodiments, in step S10, the chlorine-containing additive accounts for 0.5 wt% to 5 wt% of the raw material components by mass fraction. Exemplarily, the mass fraction of the chlorine-containing additive can be typical but not limiting values ​​such as 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%. Controlling the content of the chlorine-containing additive within the above range has two advantages. First, it facilitates the formation of a multi-element eutectic with the raw material components of the lithium-containing cathode material during sintering, thereby lowering the crystallization temperature of the cathode material. This allows for the formation of a cathode material with a uniform lattice structure at a lower crystallization temperature and shorter crystallization time. Second, it can act as a surfactant to create pores in the cathode material during sintering, thereby increasing the specific surface area of ​​the cathode material. If the mass fraction of the chlorine-containing additive is lower than the above range, it is difficult for the raw material components to react and form a multi-element eutectic, resulting in incomplete reaction of the raw material components of the lithium cathode material during sintering, and the resulting cathode material has low crystallinity and unsatisfactory purity. If the mass fraction of the chlorine-containing additive is higher than the above range, the degree of pore formation in the cathode material during sintering is too high, which is not conducive to obtaining a cathode material with an appropriate specific surface area and has a negative impact on the structural stability of the cathode material.

[0044] In some embodiments, the chlorine-containing additive includes a chlorine-containing organic solvent containing 1 to 5 carbon atoms. By limiting the number of carbon atoms in the chlorine-containing additive to the range of 1 to 5, on the one hand, the chlorine-containing additive has an appropriate melting point, which is beneficial for the chlorine-containing additive to form a multi-component eutectic with the raw material component; on the other hand, the chlorine-containing additive has appropriate intermolecular forces, which, in conjunction with the highly polar chlorine atoms, can effectively increase the interaction force between the raw material component and the chlorine-containing additive, thereby further improving the dispersion effect between the raw material component and the chlorine-containing additive.

[0045] In some embodiments, the chlorinated organic solvent includes at least one of chloroform, dichloromethane, trichloroethylene, and 1-chloropentane. These chlorinated organic solvents can form multi-component eutectic compounds with the raw material components of the lithium-containing cathode material during sintering, thereby lowering the crystallization temperature of the cathode material and achieving the goal of obtaining a highly crystalline cathode material at a lower sintering temperature and a shorter sintering time.

[0046] In some embodiments, in step S10, the lithium-containing cathode material includes a phosphate-based cathode material. The raw material components of the phosphate-based cathode material include a lithium source, a phosphorus source, an iron source, and a metal M source. The metal M source includes at least one of manganese, chromium, cobalt, vanadium, nickel, calcium, niobium, magnesium, titanium, zirconium, indium, aluminum, cadmium, and tin. The raw materials in this phosphate-based cathode material, such as lithium, phosphorus, and iron, can form a multi-element eutectic with chlorine-containing additives during sintering. This allows for the production of cathode materials with high crystallinity, high compaction density, large specific surface area, small particle size, and high electrical conductivity at lower sintering temperatures and shorter sintering times.

[0047] Typical, but not limited, phosphate-based cathode materials in this application include lithium manganese iron phosphate, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium vanadium iron phosphate, lithium vanadium manganese phosphate, and lithium manganese iron vanadium phosphate.

[0048] In some embodiments, in step S10, the raw material components of the lithium-containing cathode material include a lithium source, an iron source, a manganese source, and a phosphorus source, and the molar ratio of lithium, iron, manganese, and phosphorus in the lithium source, iron source, manganese source, and phosphorus source is (1~1.05):x:(1-x):1, 0<x≤1.

[0049] In some specific embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium formate, lithium silicate, lithium sulfate, lithium phosphate, lithium oxalate, lithium octanoate, lithium citrate, lithium salicylate, lithium orthosilicate, lithium permanganate, lithium trifluoroacetate, lithium acetoacetate, lithium difluorophosphate, lithium hexafluorophosphate, lithium benzoate, lithium metaphosphate, lithium pyruvate, lithium acetate, lithium fluoride, lithium bromide, lithium methoxide, lithium ethanol, lithium oxide, lithium nitride, and lithium sulfide.

[0050] In some specific embodiments, the phosphorus source includes at least one of ammonium hypophosphite, ammonium polyphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hexafluorophosphate, ammonium phosphate, phosphoric acid, and pyrophosphate.

[0051] In some specific embodiments, the iron source includes at least one of ferrous oxalate, ferrous nitrate, ferrous sulfide, ferrous sulfate, ferrous phosphate, ferrous iodide, ferrous fluoride, ferrous bromide, ferrous acetylacetone, ferrous gluconate, ferrous chloride, ferrous acetate, ferric nitrate, ferric sulfate, ferric phosphate, ferric chloride, ferric oxalate, and ferric sulfide.

[0052] In some specific embodiments, the manganese source includes at least one of manganese sulfate, manganese dihydrogen phosphate, manganese oxalate, manganese carbonate, manganese dioxide, manganese oxide, manganese nitrate, manganese fluoride, manganese nitride, manganese bromide, manganese carbide, potassium permanganate, potassium manganate, manganese acetate, manganese phosphate, manganese pentacarbonyl, manganese decacarbonyl, manganese acetate, manganese acetylacetone, and manganese pyrophosphate.

[0053] In some embodiments, in step S10, the carbon source accounts for 5 wt% to 20 wt% of the raw material components by mass fraction. Exemplarily, the mass fraction of the carbon source can be typical but not limiting values ​​such as 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, and 20 wt%. During the preparation process, the carbon source can be uniformly dispersed on the outer surface of the multi-element eutectic formed from the lithium-containing cathode material, and after sintering, a carbon coating layer is formed covering the lithium-containing cathode material.

[0054] In some specific embodiments, the carbon source includes at least one selected from organic carbon sources, commercial toners, carbon nanotubes, graphene, acetylene black, and carbon aerogels. Optionally, the organic carbon source includes at least one selected from glucose, sucrose, starch, ascorbic acid, phenolic resin, and chitosan.

[0055] In some embodiments, in step S20, the particle size of the ground material is ≤300nm. Optionally, the particle size of the ground material is ≤200nm. Exemplary examples include typical but not limiting values ​​such as 20nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 250nm, 280nm, and 300nm. Controlling the particle size of the ground material within the above range is beneficial for promoting the dispersion of the raw material components, carbon source, and chlorine-containing additives in the lithium-containing cathode material, further increasing the intermolecular forces between the raw material components and the chlorine-containing additives.

[0056] In some embodiments, the grinding process is performed using wet sand milling with ethanol as the solvent.

[0057] In some embodiments, in step S20, spray drying includes freeze spray drying, wherein the pressure of freeze spray drying is 0.2 MPa to 0.5 MPa, the temperature is -60°C to -45°C, and the spray velocity is 5 m / s. 3 / min~6m 3 / min. During the freeze-spray drying process, the chlorine-containing additives interact with the lithium-containing cathode material raw material components through a solvent-solute reaction. This means the chlorine-containing additives can interact with the active ions and metal ions in the lithium-containing cathode material raw material components, reducing the intermolecular attraction between the raw material components and improving the dispersibility between them. Simultaneously, the carbon source can be uniformly dispersed on the surface of the lithium-containing cathode material raw material components during freeze-spray drying, forming a coating layer on the surface of the lithium-containing compound after sintering. Furthermore, freeze-spray drying can reduce the loss of chlorine-containing additives, ensuring that all raw material components of the lithium-containing cathode material form multi-component eutectic compounds during sintering, thereby lowering the crystallization temperature of the cathode material.

[0058] In some embodiments, the heating rate of the sintering process in step S20 is 5°C / min to 50°C / min. Exemplary examples include typical but non-limiting values ​​such as 5°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min, 30°C / min, 35°C / min, 40°C / min, 45°C / min, and 50°C / min. By optimizing and controlling the heating rate, the embodiments of this application achieve an appropriate particle size growth rate, giving the cathode material a smaller particle size characteristic. This not only effectively shortens the lithium-ion transport channels and reduces its resistivity, but also makes the cathode material particles more densely packed, allowing the cathode material to maintain a high compaction density.

[0059] In some embodiments, the sintering temperature in step S20 is 400℃ to 800℃. Typical but not limiting values ​​for the sintering temperature include 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, and 800℃. During sintering, the chlorine-containing additive and the raw material components of the lithium-containing cathode material generate a multi-component eutectic. This multi-component eutectic can form a molten state at a relatively low sintering temperature, thereby effectively reducing the crystallization temperature of the cathode material. Thus, within the aforementioned sintering temperature range, on the one hand, the various raw material components of the lithium-containing cathode material can fully react to form the multi-component eutectic; on the other hand, it promotes the formation of an ordered crystal structure in the multi-component eutectic, optimizing the morphology and size of the cathode material particles, which is beneficial for the growth of cathode material grains and the structural control of crystal faces, resulting in a cathode material with high crystallinity. If the sintering temperature is below the above range, the reaction of the raw material components of the lithium cathode material will be incomplete, resulting in low crystallinity, poor purity, and uneven composition of the synthesized cathode material. If the sintering temperature is above the above range, it may lead to problems such as local melting, abnormal crystal phase, or impurity phase formation in the cathode material.

[0060] In some embodiments, in step S20, the sintering process is carried out under an inert atmosphere, which includes at least one of nitrogen, argon, hydrogen, and helium.

[0061] A second aspect of this application provides a cathode material, the cathode material comprising:

[0062] The core, including lithium-containing compounds, has a porous structure;

[0063] A coating layer, covering the outer surface of the core, comprising carbon material;

[0064] The cathode material was prepared using the cathode material preparation method described in this application.

[0065] The cathode material provided in the second aspect of this application is prepared by the cathode material preparation method provided in the first aspect. The cathode material has excellent crystallinity and forms a core with a porous structure and a carbon coating layer covering the outer surface of the core. The presence of the porous structure makes the cathode material have a high specific surface area, thereby effectively promoting the transport of lithium ions.

[0066] The embodiments of this application have a porous structure in the core, which allows lithium ions to be extracted or inserted through the porous structure, thereby effectively improving the lithium ion extraction and insertion path and increasing the lithium ion transport rate; in addition, the presence of the porous structure gives the core a larger specific surface area, which effectively improves the lithium ion extraction and insertion efficiency of the core itself.

[0067] In some embodiments, the porous structure of the core is filled with carbon material. This application fills the porous structure with carbon material to increase the contact area between the core and the carbon material, thereby improving the lithium-ion transport efficiency and further enhancing the electronic conductivity of the cathode material. Additionally, the carbon material filling the porous structure can create a good barrier against moisture and air, preventing external moisture or carbon dioxide from entering the core and damaging it.

[0068] In some embodiments, the lithium-containing compound has the chemical formula LiFe. a M b PO4, wherein a+b=1, 0<a≤1, 0≤b<1, and M includes at least one of Mn, Cr, Co, V, Ni, Ca, Nb, Mg, Ti, Zr, In, Al, Cd, and Sn. This lithium-containing compound exhibits high capacity and structural stability, resulting in high energy density and cycle stability in secondary batteries.

[0069] In some embodiments, the specific surface area of ​​the cathode material is 6m². 2 / g~15m 2 / g. Specific surface area refers to the total surface area per unit mass of material. If the specific surface area of ​​the cathode material is lower than the above range, it affects the lithium-ion transport path and the lithium-ion insertion / extraction efficiency, thereby reducing the lithium-ion transport rate. If the specific surface area of ​​the cathode material is higher than the above range, it indicates that there are too many pores in the core, reducing its structural stability. For example, the specific surface area of ​​the cathode material can be 6m². 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g or within any of the above values.

[0070] In some embodiments, the D50 particle size of the cathode material is 1 μm to 3 μm. The D50 particle size is the particle size corresponding to a cumulative particle size distribution percentage of 50%, and can be measured using methods known in the art. Controlling the D50 particle size of the cathode material within this range results in higher lithium-ion migration efficiency and lower agglomeration effect, thus improving the rate performance of the cathode material. If the D50 particle size of the cathode material is lower than this range, the agglomeration effect is significant, which is detrimental to the capacity utilization of the cathode material; if the D50 particle size of the cathode material is higher than this range, the lithium-ion transport path is too long, thus affecting the lithium-ion transport rate.

[0071] In some embodiments, the compaction density of the cathode material is 1.5 g / cm³. 3 ~3g / cm 3 The formula for calculating compacted density can be found below:

[0072] Compacted density = powder mass / volume change after compaction.

[0073] The compaction density is related to the particle size, density, and particle size distribution of the cathode material. Generally, a higher compaction density indicates that the cathode material particles have a good normal distribution. It is understood that the higher the compaction density, the higher the mass of active material per unit volume, and the higher the volumetric capacity and energy density exhibited by the cathode material. Within the compaction density range provided in the embodiments of this application, the cathode material has high capacity and good particle size characteristics, which is beneficial to lithium-ion migration and endows the cathode material with high energy density. For example, the compaction density of the cathode material can be 1.5 g / cm³. 3 1.8g / cm 3 2.0g / cm 3 2.5g / cm 3 2.8g / cm 3 3.0g / cm 3 Or it may fall within the range of any of the above values.

[0074] In some embodiments, the resistivity of the cathode material is ≤61 Ω·cm. Exemplarily, the resistivity can be 50 Ω·cm, 30 Ω·cm, 25 Ω·cm, 20 Ω·cm, 15 Ω·cm, 10 Ω·cm, 5 Ω·cm, 2 Ω·cm, or within any range of these values. In embodiments of this application, a tightly packed carbon coating layer can be formed on the outer surface of the core, while the porous structure of the core is also filled with carbon material. This allows for a larger contact area between the core and the carbon material, preventing electron transfer obstruction, reducing the powder resistivity, and ensuring a certain degree of structural stability in the cathode material.

[0075] In some embodiments, the carbon material content in the cathode material is 0.5 wt% to 5 wt%. Some carbon material protrudes from the porous structure of the core to form a coating layer encapsulating the core. If the mass percentage of carbon material is below this range, the core is difficult to completely encapsulate by the coating layer, which is detrimental to improving the electronic conductivity of the lithium-containing compound and makes it difficult to create a good barrier against moisture and air. If the mass percentage of carbon material is above this range, the core particle size becomes too large, reducing the mass percentage of the core in the cathode material. Since the carbon material does not contribute lithium ions, this reduces the overall specific capacity of the cathode material.

[0076] A third aspect of this application provides a positive electrode sheet, which includes a current collector and a positive electrode active layer bonded to at least one surface of the current collector. The positive electrode active layer includes a positive electrode material prepared by the method of this application and / or the positive electrode material of this application. Because it contains the positive electrode material of this application, the positive electrode sheet exhibits electrochemical properties such as high capacity and high cycle stability.

[0077] In some embodiments, the mass content of the cathode material described in the above-described embodiments in the cathode active layer can be 80wt% to 95wt%. For example, the mass content of the cathode material in the cathode active layer can be typical but not limiting values ​​such as 80wt%, 82wt%, 83wt%, 85wt%, 88wt%, 90wt%, 92wt%, and 95wt%. By optimizing and controlling the mass content of the cathode material in the cathode active layer, the cathode material can fully exert its aforementioned function.

[0078] The positive electrode active layer includes, in addition to the positive electrode material, a binder and a conductive agent. The binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives. In the embodiments of this application, the conductive agent can be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0079] In some embodiments, the positive current collector includes, but is not limited to, at least one of aluminum foil, carbon-coated aluminum foil, iron foil, tin foil, zinc foil, nickel foil, titanium foil, and manganese foil.

[0080] In some embodiments, the preparation process of the positive electrode sheet can be as follows: mixing the positive active material, conductive agent and binder to obtain an electrode slurry, coating the electrode slurry on the positive current collector, and preparing the positive electrode sheet through steps such as drying, rolling and die cutting, wherein the positive active material includes the positive electrode material of the embodiments of this application.

[0081] A fourth aspect of the embodiments of this application provides a secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is the positive electrode of this application.

[0082] In the secondary battery provided in the fourth aspect of this application, the positive electrode comprises a positive electrode material prepared by the above-described positive electrode material preparation method. This positive electrode material has characteristics of high crystallinity, high compaction density, large specific surface area, and high conductivity, resulting in electrochemical properties such as high capacity, high rate performance, and high cycle stability. Therefore, it can improve the energy density, cycle stability, and rate performance of the secondary battery.

[0083] In some embodiments, the negative electrode of the secondary battery includes, but is not limited to, carbon materials such as graphite, soft carbon (such as coke), and hard carbon, or nitrides, tin-based oxides, tin alloys, and nano-anode materials.

[0084] In some embodiments, the diaphragm comprises at least one material selected from polypropylene fiber, polyacrylonitrile fiber, polyvinyl alcohol formal fiber, poly(ethylene glycol terephthalate), polyethylene terephthalate, polyamide fiber, and poly(p-phenylene terephthalamide).

[0085] In some embodiments, the electrolyte is an organic solution containing soluble lithium salt.

[0086] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to highlight the significant improvements in the performance of the cathode material and its preparation method, as well as the secondary battery, the following examples illustrate the above technical solutions.

[0087] Examples of cathode materials and their preparation methods:

[0088] Example 1

[0089] This embodiment provides a cathode material and its preparation method.

[0090] A method for preparing a positive electrode material includes the following steps:

[0091] Step S1: Weigh the raw material components containing lithium carbonate, ferric nitrate and ammonium dihydrogen phosphate according to the molar ratio of Li, Fe and P elements of 1:1:1. Weigh chloroform according to the ratio of 0.5 wt% of the total mass of the raw material components and glucose according to the ratio of 5 wt% of the total mass of the raw material components. Then add the raw material components, chloroform and glucose to the ethanol aqueous solution and mix evenly to obtain the first mixture.

[0092] Step S2: Grind the above mixture in a sand mill for 8 hours to obtain a second mixture with a particle size ≤300nm. Then, freeze-dry the second mixture to obtain a cathode material precursor.

[0093] Step S3: Under a nitrogen atmosphere, the cathode material precursor is heated to 800℃ and sintered for 1 minute at a heating rate of 5℃ / min to obtain the cathode material.

[0094] A cathode material is obtained by the above preparation method. The cathode material includes a core and a coating layer covering the outer surface of the core. The core includes lithium iron phosphate and the coating layer includes carbon material.

[0095] Example 2

[0096] This embodiment provides a cathode material and its preparation method.

[0097] A method for preparing a positive electrode material is the same as in Example 1, except that the amount of chloroform added is 1 wt%.

[0098] Example 3

[0099] This embodiment provides a cathode material and its preparation method.

[0100] A method for preparing a positive electrode material is the same as in Example 1, except that the amount of chloroform added is 5 wt%.

[0101] Example 4

[0102] This embodiment provides a cathode material and its preparation method.

[0103] A method for preparing a positive electrode material is the same as in Example 1, except that the amount of chloroform added is 7 wt%.

[0104] Example 5

[0105] This embodiment provides a cathode material and its preparation method.

[0106] A method for preparing a positive electrode material is the same as in Example 1, except that the amount of chloroform added is 0.2 wt%.

[0107] Example 6

[0108] This embodiment provides a cathode material and its preparation method.

[0109] A method for preparing a positive electrode material is the same as in Example 2, except that the sintering temperature is 550℃ and the sintering time is 30min.

[0110] Example 7

[0111] This embodiment provides a cathode material and its preparation method.

[0112] A method for preparing a positive electrode material is the same as in Example 2, except that the sintering temperature is 400℃ and the sintering time is 120min.

[0113] Example 8

[0114] This embodiment provides a cathode material and its preparation method.

[0115] A method for preparing a positive electrode material is the same as in Example 1, except that the raw material components include lithium carbonate, manganese carbonate, ferric nitrate and ammonium dihydrogen phosphate, weighed in a molar ratio of Li, Mn, Fe and P of 1:0.6:0.4:1.

[0116] Example 9

[0117] This embodiment provides a cathode material and its preparation method.

[0118] Step S1: Weigh the raw material components containing lithium oxalate, ferrous bromide and diammonium hydrogen phosphate according to the molar ratio of Li, Fe and P elements of 1:1:1. Weigh chloroform according to the proportion of 3 wt% of the total mass of the raw material components and graphene according to the proportion of 10 wt% of the total mass of the raw material components. Then add the raw material components, chloroform and graphene to the ethanol aqueous solution and mix evenly to obtain the first mixture.

[0119] Step S2: The above mixture is milled in a sand mill with ethanol as solvent for 8 hours to obtain a second mixture with a particle size ≤300nm. The second mixture is then subjected to freeze spray drying to obtain a cathode material precursor.

[0120] Step S3: Under a nitrogen atmosphere, the cathode material precursor is heated to 550°C at a heating rate of 25°C / min and sintered for 30 minutes to obtain the cathode material.

[0121] A cathode material is obtained by the above preparation method. The cathode material includes a core and a coating layer covering the outer surface of the core. The core includes lithium iron phosphate and the coating layer includes carbon material.

[0122] Example 10

[0123] This embodiment provides a cathode material and its preparation method.

[0124] Step S1: Weigh the raw material components containing lithium hydroxide, ferrous sulfate and phosphoric acid according to the molar ratio of Li, Fe and P elements of 1:1:1. Weigh dichloromethane according to 5 wt% of the total mass of the raw material components. Weigh ascorbic acid according to 20 wt% of the total mass of the raw material components. Then add the raw material components, dichloromethane and ascorbic acid to the ethanol aqueous solution and mix evenly to obtain the first mixture.

[0125] Step S2: The above mixture is milled in a sand mill with ethanol as solvent for 8 hours to obtain a second mixture with a particle size ≤300nm. The second mixture is then subjected to freeze spray drying to obtain a cathode material precursor.

[0126] Step S3: Under a nitrogen atmosphere, the cathode material precursor is heated to 400℃ and sintered for 120 minutes at a heating rate of 50℃ / min to obtain the cathode material.

[0127] A cathode material is obtained by the above preparation method. The cathode material includes a core and a coating layer covering the outer surface of the core. The core includes lithium iron phosphate and the coating layer includes carbon material.

[0128] Example 11

[0129] A method for preparing a positive electrode material is the same as in Example 2, except that the chlorine-containing additive is 1-chloropentane.

[0130] Example 12

[0131] A method for preparing a positive electrode material is the same as in Example 2, except that the chlorine-containing additive is 1-chloroheptane.

[0132] Comparative Example 1

[0133] This comparative example provides a cathode material and its preparation method.

[0134] A method for preparing a positive electrode material is the same as in Example 2, except that chloroform is not added.

[0135] Comparative Example 2

[0136] This comparative example provides a cathode material and its preparation method.

[0137] A method for preparing a positive electrode material is the same as in Example 2, except that the sintering temperature is 900℃.

[0138] Comparative Example 3

[0139] This comparative example provides a cathode material and its preparation method.

[0140] A method for preparing a positive electrode material is the same as in Example 2, except that the sintering time is 8 hours.

[0141] Example of a lithium-ion battery:

[0142] The cathode materials provided in Examples 1-12 and the cathode materials provided in Comparative Examples 1-3 were assembled into cathode electrodes and lithium-ion batteries respectively according to the following methods:

[0143] Positive electrode: Under the same conditions, the materials (main material): SuperP-Li:PVDF are mixed in a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) is used as a solvent to mix the materials evenly to form a slurry, which is then uniformly coated on the surface of aluminum foil. After being rolled to a certain thickness, it is vacuum dried at 110°C for 12 hours to form a positive electrode sheet. The main materials are the positive electrode materials provided in Examples 1 to 12 and Comparative Examples 1 to 3, respectively.

[0144] Counter electrode: Lithium metal sheet.

[0145] Electrolyte: The electrolyte is a 1 mol / L LiPF6 / ethylene carbonate: methyl ethyl carbonate (volume ratio) solution of 1:1.

[0146] Diaphragm: Polypropylene microporous membrane.

[0147] Lithium-ion battery assembly: The lithium metal sheet, separator, electrolyte, and positive electrode are assembled into a button-type lithium-ion battery in an inert atmosphere glove box. Batteries containing the positive electrode materials provided in Examples 1 to 12 are respectively designated as Examples S1 to S12, and batteries containing the positive electrode materials provided in Comparative Examples 1 to 3 are designated as Comparative Examples DS1 to DS3.

[0148] Performance testing

[0149] (1) Physical property characterization

[0150] The cathode material prepared in Example 1 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figures 1-2 As shown. Figure 1 This is a SEM image of the cathode material magnified 20,000 times. Figure 1 It can be seen that the lithium iron phosphate cathode material is granular with a clear outline and uniform particle size. Figure 2 This is a SEM image of the cathode material magnified 5000 times, combined with... Figure 1 and Figure 2 The lithium iron phosphate prepared in this embodiment has a particle size between 50 nm and 800 nm.

[0151] The cathode material prepared in Comparative Example 2 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 3 As shown, from Figure 3 It is evident that excessively high sintering temperatures result in larger and more irregular particle sizes in the cathode material.

[0152] The cathode material prepared in Comparative Example 3 was analyzed by scanning electron microscopy (SEM), and the results are as follows: Figure 4 As shown, it is clear that the extended sintering time results in larger and more irregular particle sizes in the material.

[0153] The cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 3 were subjected to X-ray diffraction (XRD), and the results are as follows: Figure 5-6 As shown, where Figure 6 yes Figure 5 2θ is an enlarged view of the X-ray diffraction pattern of AB (without impurities), where A is 14.38° and B is 34.96°.

[0154] Yes, that's understandable. Crystallinity refers to the percentage of crystalline phases in a material, and it can be obtained by fitting diffraction peaks in an X-ray diffraction (XRD) pattern. In the XRD results, higher crystallinity results in sharper diffraction peaks. Naturally, higher crystallinity in a cathode material indicates higher electrochemical performance, such as capacity and cycle capacity retention. Figure 5-6 It is evident that the addition of chlorine-containing additives enables the raw material components to rapidly synthesize a cathode material with high crystallinity at a lower sintering temperature and shorter sintering time. This cathode material exhibits good crystallinity without obvious impurity peaks. In Comparative Example 1, due to the absence of chlorine-containing additives, the synthesized cathode material has lower crystallinity. In Comparative Example 3, due to the excessively long sintering time, local melting occurs, resulting in a lower level of crystallinity for the synthesized cathode material.

[0155] The cathode materials prepared in Examples 1-12 and Comparative Examples 1-3 were subjected to physical property characterization tests. The results of the physical property characterization tests of the cathode materials are shown in Table 1 below. As can be seen from Table 1, by adding chlorine-containing additives, the D50 particle size and resistivity of the cathode materials in this application are lower than those of the comparative examples, while the compaction density and carbon content are significantly lower. Specifically analyzing Examples 1-5, the carbon content and specific surface area of ​​the cathode materials are positively correlated with the amount of chlorine-containing additives added, while the D50 particle size, resistivity, and compaction density of the cathode materials all show a trend of first decreasing and then increasing with the increase of the amount of chlorine-containing additives added.

[0156] Table 1. Physical property characterization results of the cathode material

[0157]

[0158] (2) Electrochemical performance testing

[0159] The electrochemical performance of the lithium secondary batteries composed of Examples S1-S12 and Comparative Examples DS1-DS3 was tested.

[0160] The relevant electrochemical performance test results of the lithium secondary battery are shown in Table 2 below, where the voltage-to-capacity curves of Example 1 and Comparative Example 1 are shown in Table 2 below. Figure 7-8 As shown in the figure, it can be clearly seen that the cathode material prepared in Example 1 of this application has higher 0.1C and 1C discharge capacity, which indicates that the cathode material prepared in this application has higher crystallinity.

[0161] As shown in Table 2, the secondary battery containing the cathode material prepared in this embodiment exhibits higher discharge capacity and cycle performance than the comparative example, specifically showing increased initial discharge capacity and increased capacity retention after 100 cycles. Example S1 demonstrates the best performance, with an initial discharge capacity of 160.83 mAh / g at 0.1C, an initial discharge capacity of 150.19 mAh / g at 1C, and a capacity retention of 99.58% after 100 cycles. Although Examples 2 and 3 have lower D50 particle size and resistivity, their excessively high carbon content and low compaction density result in an initial discharge capacity of only 158.64 mAh / g at 0.1C for Example S2 and only 156.64 mAh / g for Example S3. In summary, the control of the amount of chlorine-containing additives in Example S3 leads to optimal overall battery performance.

[0162] Table 2 Electrochemical performance test results of lithium secondary batteries

[0163]

[0164] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a positive electrode material, characterized in that, Includes the following steps: The raw material components, carbon source, and chlorine-containing additives of the lithium-containing cathode material are dispersed in a solvent to obtain a mixture; the chlorine-containing additives include at least one of chloroform, dichloromethane, trichloroethylene, and 1-chloropentane. The mixture is ground and spray-dried, and then sintered for 1 min to 120 min to obtain the positive electrode material. The chlorine-containing additive accounts for 0.5 wt% to 5 wt% of the raw material components by mass fraction. The particle size of the ground material is ≤300nm; In the sintering process, the chlorine-containing additive reacts with the raw material components to form a multi-component eutectic compound, which is then sintered for 1 min to 120 min to obtain the cathode material. The cathode material includes a core and a coating layer. The core includes a lithium-containing compound and has a porous structure. The coating layer covers the outer surface of the core. The spray drying includes freeze spray drying.

2. The method for preparing the cathode material as described in claim 1, characterized in that, The sintering time is 1 min to 60 min.

3. The method for preparing the cathode material according to any one of claims 1 to 2, characterized in that, The heating rate of the sintering process is 5℃ / min to 50℃ / min; and / or The sintering temperature is 400℃~800℃.

4. The method for preparing the cathode material according to any one of claims 1 to 2, characterized in that, The cryo-spray drying process involves a pressure of 0.2 MPa to 0.5 MPa, a temperature of -60°C to -45°C, and a spray velocity of 5 m / s. 3 / min~6m 3 / min.

5. The method for preparing the cathode material according to any one of claims 1 to 2, characterized in that, The lithium-containing cathode material includes a phosphate-based cathode material. The raw material components of the phosphate-based cathode material include a lithium source, a phosphorus source, an iron source, and a metal M source. The metal M source includes at least one of the following: manganese source, chromium source, cobalt source, vanadium source, nickel source, calcium source, niobium source, magnesium source, titanium source, zirconium source, indium source, aluminum source, cadmium source, and tin source; and / or The carbon source accounts for 5 wt% to 20 wt% of the raw material components by mass.

6. The method for preparing the cathode material as described in claim 5, characterized in that, The raw material components of the lithium-containing cathode material include lithium source, iron source, manganese source and phosphorus source, and the molar ratio of lithium, iron, manganese and phosphorus in the lithium source, iron source, manganese source and phosphorus source is (1~1.05):x:(1-x):1, 0<x≤1.

7. A positive electrode material, characterized in that, The cathode material includes: The core, comprising a lithium-containing compound, has a porous structure; A coating layer covering the outer surface of the core, the coating layer comprising a carbon material; The cathode material is prepared using the cathode material preparation method according to any one of claims 1 to 6.

8. The cathode material as described in claim 7, characterized in that, The porous structure of the core is filled with carbon material; and / or The specific surface area of ​​the cathode material is 6m². 2 / g~15m 2 / g; and / or The D50 particle size of the positive electrode material is 1μm~3μm; and / or The compaction density of the positive electrode material is 1.5 g / cm³. 3 ~3g / cm 3 ; and / or The resistivity of the positive electrode material is ≤61Ω·cm; and / or The carbon material in the cathode material has a mass content of 0.5wt% to 5wt%.

9. A positive electrode sheet, characterized in that, The positive electrode sheet includes a current collector and a positive active layer bonded to at least one surface of the current collector, wherein the positive active layer includes a positive electrode material prepared by the method of preparing a positive electrode material as described in any one of claims 1 to 6 and / or a positive electrode material as described in any one of claims 7 to 8.

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

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