Positive electrode active material, method for manufacturing the same, positive electrode sheet, battery, and electric device

Abstract

The present disclosure provides a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery, and an electric device, the positive electrode active material comprising: an inner core; a carbon coating layer covering at least part of a surface of the inner core, wherein a mole ratio of sp 3 hybrid carbon atoms to sp 2 hybrid carbon atoms is not less than 0.5.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode active materials and their preparation methods, positive electrode sheets, batteries, and electrical devices. Background Technology

[0002] In recent years, with the development of lithium-ion battery technology, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, and have also found wide applications in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Currently, however, there are still many problems to be solved in the industrial production and application of lithium-ion batteries. Summary of the Invention

[0003] In one aspect of this application, a positive electrode active material is provided, comprising: a core; and a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core, wherein sp in the carbon coating layer 2 Hybridized carbon atoms and sp 3 The molar ratio of hybrid carbon atoms is not less than 0.5. This reduces the water absorption of the positive electrode active material.

[0004] According to embodiments of this application, the core material comprises a phosphate; preferably, the phosphate comprises at least one of lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate. Therefore, the conductivity of the core material can be improved and the battery performance using the core material can be optimized by surface carbon coating.

[0005] According to an embodiment of this application, the core comprises LiMPO4, and the M element includes Mn and non-Mn elements. Therefore, the conductivity of the core material can be improved and the battery performance using this core material can be optimized by surface carbon coating.

[0006] According to embodiments of this application, the non-Mn element includes one or both of a first doping element and a second doping element, wherein the first doping element is manganese site doping and the second doping element is phosphorus site doping. This improves the cycle stability of the positive electrode active material.

[0007] According to embodiments of this application, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; preferably, the first doping element includes at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. This further improves the specific capacity of the positive electrode active material.

[0008] According to embodiments of this application, the second doping element includes one or more elements selected from B (boron), S, Si, and N. This further improves the specific capacity of the positive electrode active material.

[0009] According to embodiments of this application, the kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 0.100. A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge. R includes one or more elements selected from B (boron), S, Si, and N. This improves the structural stability and capacity utilization of the positive electrode active material.

[0010] According to embodiments of this application, the kernel includes Li 1+x C m Mn 1-y A y P 1-z R z O 4-n D n x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, n is any value in the range of 0.001 to 0.1, and m is any value in the range of 0.9 to 1.1. C includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; R includes one or more elements selected from B (boron), S, Si, and N; and D includes one or more elements selected from S, F, Cl, and Br. Therefore, the specific capacity and compaction density of the positive electrode active material can be further improved.

[0011] According to embodiments of this application, the carbon coating layer contains sp 2 Hybridized carbon atoms and sp 3 The molar ratio of hybrid carbon atoms is not less than 0.8. This improves the structural order of the carbon coating layer, making the carbon coating layer more compact, reducing porosity in the carbon coating layer, and thus further reducing the water absorption of the positive electrode active material.

[0012] According to embodiments of this application, the thickness of the carbon coating layer is no greater than 10 nm; preferably, the thickness of the carbon coating layer is 4 nm-8 nm. This reduces water absorption while increasing the conductivity of the positive electrode active material.

[0013] According to embodiments of this application, the carbon content in the positive electrode active material is no more than 3 wt%, preferably, the carbon content in the positive electrode active material is 1 wt%-2.5 wt%. This allows the positive electrode active material to possess both good conductivity and low water absorption.

[0014] According to embodiments of this application, the specific surface area of ​​the positive electrode active material is no greater than 25 m². 2 / g, preferably, the specific surface area of ​​the positive electrode active material is not greater than 18m². 2 / g. This allows the positive electrode active material to possess both high conductivity, high specific capacity, and low water absorption.

[0015] According to embodiments of this application, the median particle size of the positive electrode active material is no greater than 2 μm; preferably, the median particle size of the positive electrode active material is 0.5 μm-1.5 μm. This improves the lithium-ion migration rate and specific capacity of the positive electrode active material.

[0016] According to embodiments of this application, the resistivity of the positive electrode active material powder is no greater than 200 Ω·cm; preferably, the resistivity of the positive electrode active material powder is no greater than 100 Ω·cm. Thus, the conductivity of the positive electrode active material can be further improved by the carbon coating layer, while maintaining low water absorption.

[0017] In another aspect of this application, a method for preparing a positive electrode active material is proposed, comprising providing a core and forming a carbon coating layer on at least a portion of the surface of the core. Thus, the aforementioned positive electrode active material can be obtained by a relatively simple method, which possesses all the characteristics and advantages of the aforementioned positive electrode active material, and will not be elaborated further here.

[0018] According to an embodiment of this application, forming a carbon coating layer on at least a portion of the surface of the core includes: forming a pre-carbon coating layer on the surface of the core using a carbon source to obtain a pre-coated positive electrode active material; and sintering the pre-coated positive electrode active material under an inert gas atmosphere to form the carbon coating layer, thereby obtaining the positive electrode active material, wherein the carbon source includes a first carbon source and a second carbon source. Thus, a carbon coating layer with a high degree of graphitization can be formed on the surface of the core.

[0019] According to an embodiment of this application, forming a carbon coating layer on at least a portion of the surface of the core includes: mixing the core with a first carbon source and obtaining a first coated positive electrode active material through a first sintering process; mixing the first coated positive electrode active material with a second carbon source and obtaining the positive electrode active material through a second sintering process. Thus, a carbon coating layer with a high degree of graphitization can be formed on the surface of the core.

[0020] According to embodiments of this application, the first carbon source includes at least one selected from polyvinyl alcohol, polyethylene glycol, and citric acid; the second carbon source includes at least one selected from starch, sucrose, and glucose. Thus, a carbon coating layer with a high degree of graphitization can be formed on the core surface.

[0021] According to embodiments of this application, when the first carbon source is a polymer, the molecular weight of the first carbon source is not less than 1000, preferably, the molecular weight of the first carbon source is 2000-5000. Thus, a carbon coating layer with a high degree of graphitization can be obtained.

[0022] According to an embodiment of this application, the sintering temperature is 650℃-800℃, and the sintering time is 6h-12h. This allows a carbon coating layer with a high degree of graphitization to be formed on the core surface.

[0023] According to an embodiment of this application, the temperature of the first sintering treatment is 350℃-800℃, and the time of the first sintering treatment is 6h-12h. Therefore, a carbon coating layer with a high degree of graphitization can be formed on the surface of the core.

[0024] According to an embodiment of this application, the temperature of the second sintering treatment is 650℃-850℃, and the time of the second sintering treatment is 6h-24h. This allows a carbon coating layer with a high degree of graphitization to be formed on the core surface.

[0025] In another aspect of this application, a positive electrode sheet is proposed, comprising a positive current collector and a positive active material layer, wherein the positive active material layer is located on one side of the positive current collector, and the positive active material layer comprises the aforementioned positive active material, and / or the positive active material layer comprises a positive active material prepared by the aforementioned method. Thus, this positive electrode sheet possesses all the features and advantages of the aforementioned positive active material, which will not be elaborated further here.

[0026] In another aspect of this application, a battery is proposed, comprising: a positive electrode plate, said positive electrode plate including the aforementioned positive electrode plate. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode plate, which will not be repeated here.

[0027] In another aspect of this application, an electrical device is provided, comprising a battery, said battery including the aforementioned battery. Thus, the electrical device possesses all the features and advantages of the aforementioned battery, which will not be repeated here. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 A schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application is shown;

[0031] Figure 2 This is a schematic diagram of a battery according to one embodiment of this application;

[0032] Figure 3 yes Figure 2 An exploded view of a battery according to one embodiment of this application is shown;

[0033] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0034] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0035] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0036] Figure 7 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1: Battery pack; 2: Upper casing; 3: Lower casing; 4: Battery module; 5: Battery; 10: Positive electrode sheet; 11: Positive current collector; 12: Positive active material layer; 51: Housing; 52: Electrode assembly; 53: Top cover assembly. Detailed Implementation

[0039] The embodiments of this disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0040] In one aspect of this application, a positive electrode active material is provided, comprising: a core; and a carbon coating layer, the carbon coating layer at least covering a portion of the surface of the core, wherein sp in the carbon coating layer... 2 Hybridized carbon atoms and sp 3 The molar ratio of hybridized carbon atoms is not less than 0.5. When the sp atoms in the carbon coating layer of the positive electrode active material... 2 Hybridized carbon atoms and sp 3 When the hybrid carbon atoms are within the aforementioned range, the pore structure of the carbon coating layer is relatively dense, which can significantly reduce the water absorption capacity of the carbon coating layer, thereby reducing the water absorption of the positive electrode active material and improving the safety and cycle performance of the battery.

[0041] To facilitate understanding, the principle behind the aforementioned beneficial effects of the positive electrode active material in this application is explained below:

[0042] Because the potential of lithium-ion batteries is significantly higher than the stable voltage range of water, they are extremely sensitive to moisture. Even trace amounts of moisture can severely affect their performance. Therefore, the moisture content of materials must be strictly controlled throughout the entire production process. For example, during battery production, the electrodes need to be dried after current collector coating, after cold pressing, and after cell winding. Furthermore, environmental moisture must be strictly controlled throughout the entire battery production process. The drying process and environmental moisture control in battery production consume a significant amount of energy, complicating the battery manufacturing process.

[0043] In this application, the inventors discovered that, in order to improve the conductivity of the core, a carbon coating layer can be formed on the surface of the core to improve the conductivity of the positive electrode active material. Furthermore, when the carbon coating layer of the positive electrode active material is loose and porous, this structure accelerates the absorption and storage of moisture by the material, resulting in strong water absorption and storage capabilities. Consequently, the material absorbs water during storage and processing, ultimately leading to a high water content. The presence of high water content in the battery causes the lithium salt in the electrolyte to decompose, significantly reducing the battery's cycle performance.

[0044] Furthermore, the inventors discovered that simply increasing the drying temperature and extending the drying time to remove as much moisture as possible from the positive electrode active material would lead to excessive energy consumption and a significant extension of process time. Moreover, prolonged high-temperature drying would also cause aging and failure of other components in the cell, such as the separator, resulting in a significant increase in manufacturing costs. Based on the aforementioned theoretical analysis and experimental investigation, the inventors discovered that improving the pore state of the carbon coating layer of the positive electrode active material can effectively reduce its water absorption without adding extra process steps or improving the process environment. Specifically, the inventors found that when the sp... 2 Hybridized carbon atoms and sp 3 When the molar ratio of hybrid carbon atoms is not less than 0.5, the carbon coating structure of the positive electrode active material has a high degree of order, and the pore structure of the carbon coating has a high degree of density and a small pore size distribution range. During the battery production process, it is difficult for external moisture to enter the pores of the carbon coating, thereby effectively reducing the water absorption and water storage performance of the positive electrode active material, improving the battery safety and cycle performance, effectively saving energy consumption in the drying process, and significantly reducing production costs.

[0045] According to some embodiments of this application, the type of core is not particularly limited. For example, the core may include phosphate; in some embodiments, the phosphate may include at least one of lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate. Lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate have high specific capacity and low raw material cost. Since the positive electrode active material undergoes an electrochemical reaction when used in a battery, the participation of electrons is required. Therefore, in order to increase electron transport between particles and between different positions within the particles, materials with superior conductivity can be used. By coating the surface of the phosphate core with a carbon layer, a positive electrode active material that combines low cost, high specific capacity, and high conductivity can be obtained, thus optimizing the battery performance using the positive electrode active material.

[0046] According to some embodiments of this application, the type of core is not particularly limited. For example, the core may include LiMPO4, and the M element may include Mn and non-Mn elements. In some embodiments, the non-Mn element may include one or both of a first doping element and a second doping element, wherein the first doping element is manganese doping and the second doping element is phosphorus doping. The first and second doping elements can not only effectively reduce manganese dissolution, thereby reducing the number of manganese ions migrating to the negative electrode, reducing the electrolyte consumed due to SEI film decomposition, and improving the cycle performance and safety performance of the secondary battery, but also promote Mn-O bond adjustment, lower the lithium ion migration barrier, promote lithium ion migration, and improve the rate performance of the battery.

[0047] According to some embodiments of this application, the type of the first doping element is not particularly limited. For example, the first doping element may include one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; in some embodiments, the first doping element may include at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. The first doping element can further reduce the lattice change rate of the positive electrode active material, reduce the surface activity of the material, thereby suppressing Mn dissolution and interfacial side reactions between the positive electrode material and the electrolyte. By doping with two or more metals within the above range, it is beneficial to enhance the doping effect, further reduce surface oxygen activity, and thus suppress manganese dissolution. In addition, the doping of multiple elements can increase the synergistic effect between elements, thereby increasing the battery capacity while reducing the lattice change rate of the material and enhancing the dynamic performance of the battery.

[0048] According to some embodiments of this application, the type of the second dopant is not particularly limited. For example, the second dopant may include one or more elements selected from B (boron), S, Si, and N. The second dopant can increase the rate of change of the Mn-O bond, improve the small polaron migration barrier of the positive electrode active material, and enhance the electronic conductivity. In addition, the doping of the second element can also reduce the concentration of antisite defects in the material, improve the kinetic properties and specific capacity of the material, and can also change the morphology of the material, thereby increasing the compaction density of the material.

[0049] According to some embodiments of this application, the type of kernel is not particularly limited; for example, the kernel may include Li 1+ x Mn 1-y A y P 1-z R zO4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements selected from B (boron), S, Si, and N. The manganese doping element A selected from the above elements helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improving the structural stability of the positive electrode active material, significantly reducing manganese dissolution, and lowering the oxygen activity on the particle surface. The phosphorus doping element R selected from the above elements also helps change the ease of Mn-O bond length changes, thereby improving electronic conductivity and lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the secondary battery. If the value of x is too small, it will lead to a decrease in the lithium content of the entire core, affecting the specific capacity of the positive electrode active material. The y-value limits the total amount of all dopants. If y is too small, the doping amount is too low, and the dopants will not play a role. If y exceeds 0.5, it will result in a low Mn content in the system, affecting the voltage plateau of the cathode active material. When R is doped at the P site, since the PO tetrahedron is relatively stable, an excessively large z-value will affect the stability of the cathode active material. Therefore, when x, y, and z are selected from the above ranges, the cathode active material can have superior performance.

[0050] Unless otherwise stated, in the above-described core chemical formula, when a doping site has two or more elements, the limitations on the numerical ranges of x, y, z, or m are not only limitations on the stoichiometry of each element serving as that site, but also limitations on the sum of the stoichiometry of all elements serving as that site. For example, when the core has the chemical formula Li... 1+x Mn 1- y A y P 1-z R z When A is a compound of O4, and A consists of two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the numerical range of y defined in this application, and the sum of y1, y2...yn must also fall within this numerical range. Similarly, for the case where R consists of two or more elements, the limitation on the numerical range of the stoichiometric coefficient of R in this application has the same meaning.

[0051] According to some embodiments of this application, the type of kernel is not particularly limited; for example, the kernel may include Li 1+ x C m Mn 1-y A y P 1-zR z O 4-n D n The value of x is influenced by the valence states of A and R, as well as the values ​​of y and z, to ensure the overall system is electrically neutral. If the value of x is too small, the lithium content of the entire core system will decrease, affecting the specific capacity of the material. The value of y limits the total amount of all dopants. If y is too small, i.e., the doping amount is too low, the dopants will not play a role. If y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. R is doped at the P site. Since PO tetrahedra are relatively stable, and a z value that is too large will affect the stability of the material, the z value is limited to 0.001-0.100. More specifically, x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, n is any value in the range of 0.001 to 0.1, and m is any value in the range of 0.9 to 1.1. For example, 1+x is selected from the range of 0.9 to 1.1, such as 0.97, 0.977, 0.984, 0.988, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 1.01; x is selected from the range of 0.001 to 0.1, such as 0.001, 0.005; and y is selected from the range of 0.001 to 0.5, such as 0.001. The values ​​are 0.005, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.34, 0.345, 0.349, 0.35, and 0.4, where z is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, and 0.1, and n is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, and 0.1, and the positive electrode active material is electrically neutral. C includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; R includes one or more elements selected from B (boron), S, Si, and N; and D includes one or more elements selected from S, F, Cl, and Br. By simultaneously doping specific elements at specific amounts at the Li, Mn, P, and O sites of the compound, significantly improved rate performance can be obtained, while significantly reducing the dissolution of Mn and Mn-site dopants, resulting in significantly improved cycle performance and / or high-temperature stability. Furthermore, the specific capacity and tap density of the positive electrode active material can also be improved.

[0052] According to some embodiments of this application, the carbon structure and characteristics of the carbon coating layer can be determined by Raman spectroscopy. Specifically: first, the Raman spectrum of the cathode material is measured, and then the energy spectrum of the Raman test is divided into peaks to obtain I. g / I d (where I) d For sp 3 Peak intensity of hybrid carbon atoms, I g For sp 2 The peak intensity of the hybrid carbon atom, the ratio of this peak intensity to sp. 2 The peak height of hybrid carbon atoms and sp 3 The ratio of the peak heights of hybridized carbon atoms (to obtain sp) 2 Hybridized carbon and sp 3 The molar ratio of hybrid carbon. The sp(s) content in the carbon coating layer of the positive electrode active material. 2 Hybridized carbon atoms and sp 3 The molar ratio of hybridized carbon atoms is not particularly restricted; for example, sp in the carbon coating layer. 2 Hybridized carbon atoms and sp 3 The molar ratio of hybrid carbon atoms can be not less than 0.5. In some embodiments, the sp atoms in the carbon coating layer... 2 Hybridized carbon atoms and sp 3 The molar ratio of hybridized carbon atoms can be no less than 0.8. When the sp atoms in the carbon coating layer... 2 Hybridized carbon atoms and sp 3 When the molar ratio of hybrid carbon atoms is within the above range, the carbon coating layer on the core surface has a high degree of graphitization and a more compact structure. This reduces the water absorption of the carbon coating layer while ensuring good conductivity, guaranteeing the lithium-ion pathway and improving the cycle performance and safety of the cathode active material. When sp 2 Hybridized carbon atoms and sp 3 When the molar ratio of hybrid carbon atoms is less than 0.5, the amorphous sp atoms in the carbon coating layer... 3 The carbon coating has a large number of carbon atoms, and its structure is relatively loose and porous, which is not conducive to reducing the water absorption of the carbon coating and the conductivity of the carbon coating is poor.

[0053] According to some embodiments of this application, the thickness of the carbon coating layer is not particularly limited. For example, the thickness of the carbon coating layer can be 10 nm; in some embodiments, the thickness of the carbon coating layer is 4 nm-8 nm. Forming a thinner carbon coating layer on the surface of the core is sufficient to effectively improve the conductivity of the positive electrode active material and improve the compaction performance when using the positive electrode active material to prepare battery electrodes. When the thickness of the carbon coating layer is greater than 10 nm, it is easier to form a carbon coating layer with larger pores, which increases the possibility of the carbon coating layer absorbing and storing water. An excessively thick carbon coating layer will affect the extraction and insertion of lithium ions from the core, resulting in a significant reduction in the specific capacity of the positive electrode active material. The thickness of the carbon coating layer can be tested using the following method: a thin slice of approximately 100 nm thickness is cut from the middle of a single particle of the positive electrode active material using FIB, and then the slice is subjected to TEM testing to obtain the original TEM image, which is saved in the original image format (xx.dm3). Open the original images obtained from the TEM test in Digital Micrograph software. Identify the carbon coating layer using the lattice spacing and angle information, and measure the thickness of the carbon coating layer. Measure the thickness at three locations for the selected particle and take the average value.

[0054] According to some embodiments of this application, the mass fraction of carbon in the positive electrode active material is not particularly limited. For example, the carbon content in the positive electrode active material may not exceed 3 wt% based on the sum of the mass of the core and the mass of the carbon coating layer. In some embodiments, the carbon content in the positive electrode active material may be 1 wt% to 2.5 wt%. When the mass fraction of carbon in the positive electrode active material is not greater than 3 wt%, the appropriate carbon content can improve the conductivity of the positive electrode active material, enhance electron transport between particles, and promote lithium ion migration, without causing a deterioration in the specific capacity of the positive electrode active material due to excessive carbon content. When the mass fraction of carbon in the positive electrode active material is greater than 3 wt%, it is difficult to form a carbon coating layer with a high degree of graphitization on the surface of the core, and it is easier to form a carbon coating layer with larger pores, which increases the possibility of the carbon coating layer absorbing and storing water. The mass fraction of carbon in the positive electrode active material can be determined by the following method: Turn on all power switches of the carbon-sulfur analyzer, press and hold the "zero" button, open the oxygen valve of the carbon-sulfur analyzer, and adjust the oxygen pressure to 0.02-0.04 MPa. Turn on "pre-oxygen" and "post-control," and adjust the flow meter to approximately 100 L / h. Add the following to the crucible in sequence: 0.3 g of silicon molybdenum powder, 250 mg of the weighed sample, 0.3 g of tin granules, and 1 g of pure iron. Close the crucible. Click the "test" button to start the test. The test result will be automatically displayed upon completion; record this result as the carbon content.

[0055] According to some embodiments of this application, the specific surface area of ​​the positive electrode active material is not particularly limited; for example, the specific surface area of ​​the positive electrode active material is not greater than 25 m². 2 / g, in some embodiments, the specific surface area of ​​the positive electrode active material is no greater than 18m². 2 / g. When the specific surface area of ​​the positive electrode active material is within the above range, the pore structure of the carbon coating layer is relatively dense, and its water absorption capacity is weak, which allows the positive electrode active material to have both high conductivity, high specific capacity, and low water absorption. When the specific surface area of ​​the positive electrode active material is greater than 25m², ... 2 When the specific surface area of ​​the positive electrode active material is too large, its water absorption is also stronger, which leads to a decrease in the cycle performance of the battery. The specific surface area of ​​the positive electrode active material can be tested using the following method: Using a US-made Gemini VII2390 multi-station fully automated specific surface area and porosity analyzer, take about 7g of sample and place it in a 9cc long tube with a bulb, degas at 150℃ for 15min, and then put it into the main unit for testing to obtain BET data.

[0056] According to some embodiments of this application, the particle size of the positive electrode active material is not particularly limited. For example, the median particle size of the positive electrode active material may not be greater than 2 μm; in some embodiments, the median particle size of the positive electrode active material may be 0.5 μm-1.5 μm. When the particle size of the positive electrode active material is within the above range, the particle size of the positive electrode active material is small, the lithium ion migration rate is fast, and the specific capacity of the positive electrode active material can be effectively improved. The median particle size of the positive electrode active material can be obtained by the following method: Equipment model: Malvern 3000 (MasterSizer3000) laser particle size analyzer; Reference standard procedure: GB / T19077-2016 / ISO13320:2009; Specific test procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20ml of deionized water, and simultaneously incubate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, test according to the GB / T19077-2016 / ISO13320:2009 standard.

[0057] According to some embodiments of this application, by coating at least a portion of the surface of the core with a porous carbon coating layer, such as a porous carbon layer, the conductivity of the positive electrode active material can be significantly improved. For example, the powder resistivity of a phosphate core positive electrode active material with a carbon coating layer on the surface may not exceed 200 Ω·cm; in some embodiments, the powder resistivity of the positive electrode active material may not exceed 100 Ω·cm. A lower powder resistivity can effectively reduce the interfacial impedance between positive electrode active materials, thereby reducing energy dissipation caused by the internal resistance of the positive electrode active material. The powder resistivity of the positive electrode active material can be tested using the following method: The powder resistivity is tested using a Yuaneng Technology PRCD1000 device. The device power and testing software are turned on. The required powder is weighed using a balance. The powder is pressed into a thin sheet using a fixture. The sheet is placed into the device. The test parameters are configured: test pressure 5t, holding time 5s. The test is then clicked. After the test is completed, the test result is displayed and recorded.

[0058] In this application, all figures disclosed herein, whether or not the words “approximately” or “about” are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by a person skilled in the art, such as 1%, 2%, 3%, 4%, or 5%.

[0059] In another aspect of this application, a method for preparing a positive electrode active material is proposed. This method allows for the relatively simple acquisition of the aforementioned positive electrode active material, thus possessing all the characteristics and advantages of the aforementioned positive electrode active material, which will not be elaborated further here. Specifically, the method for preparing the positive electrode active material includes the following steps:

[0060] S100: Provides kernel

[0061] According to some embodiments of this application, a core of the positive electrode active material is provided in this step. The type of positive electrode active material core is not particularly limited. For example, the core can be a positive electrode active material with a high specific capacity. For example, the core can be a phosphate positive electrode active material such as lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate. The core can also be at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based solid solution. By forming a carbon coating layer on the surface of the core, the conductivity of the positive electrode active material can be further improved, thereby obtaining a positive electrode active material with both high specific capacity and better cycle performance.

[0062] S200: A carbon coating layer is formed on at least a portion of the surface of the core.

[0063] According to some embodiments of this application, this step involves forming a carbon coating layer on at least a portion of the surface of the core. Specifically, it may include the following steps:

[0064] S211: Forming a pre-carbon coating layer on the core surface using a carbon source.

[0065] According to some embodiments of this application, a pre-carbon coating layer is formed on the core surface in this step to obtain a pre-coated positive electrode active material. The method for forming the pre-carbon coating layer on the core surface is not particularly limited. For example, the carbon source and the core can be placed in the same reaction vessel, and the carbon source can be reacted on the core surface by hydrothermal treatment to form a carbon coating layer on the core surface. Alternatively, the carbon source and the core can be placed in a ball mill, such as a sand mill, and the carbon source can be mechanically mixed to form a carbon coating layer on the core surface. According to other embodiments of this application, the carbon source includes a first carbon source and a second carbon source. The first carbon source includes at least one of polyvinyl alcohol, polyethylene glycol, and citric acid; the second carbon source includes at least one of starch, sucrose, and glucose. In some embodiments, the molecular weight of the first carbon source is not less than 1000, and in other embodiments, the molecular weight of the first carbon source can be 2000-5000. Thus, a uniformly distributed pre-carbon coating layer with a relatively consistent thickness can be formed on the core surface by ball milling, which is beneficial for forming a dense and uniform carbon coating layer pore structure after sintering.

[0066] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0067] S212: Sintering of pre-coated positive electrode active material under an inert gas atmosphere.

[0068] According to some embodiments of this application, in this step, the pre-coated positive electrode active material is sintered to obtain the positive electrode active material. The sintering process should be carried out under an inert atmosphere to avoid oxidation of the carbon source, which would prevent the formation of a carbon coating layer with a high degree of graphitization. The type of inert gas is not particularly limited; for example, the inert gas may include at least one of nitrogen and helium. The sintering conditions are not particularly limited; for example, the sintering temperature can be 650°C-800°C, and the sintering time can be 6h-12h. Thus, a carbon coating layer with a high degree of graphitization can be formed on the surface of the core. The inventors have found that as the sintering temperature increases, the degree of graphitization of carbon in the carbon coating layer also increases. By controlling the maximum sintering temperature, the degree of graphitization of the carbon coating layer can be effectively controlled, resulting in a carbon coating layer with a dense porous structure and superior conductivity.

[0069] According to other embodiments of this application, in this step, a carbon coating layer is formed on at least a portion of the surface of the core. Specifically, this step may further include the following steps:

[0070] S221: Mix the core with the first carbon source and perform the first sintering process.

[0071] According to some embodiments of this application, in this step, a first carbon coating layer is formed on the core surface using a first carbon source to obtain a first coated positive electrode active material. The type of the first carbon source is not particularly limited; for example, the first carbon source may include at least one of polyvinyl alcohol, polyethylene glycol (PEG), and citric acid. Specifically, when the first carbon source is a polymer, the molecular weight of the first carbon source may be not less than 1000. In some embodiments, the molecular weight of the first carbon source is 2000-5000. More specifically, the first carbon source may be polyethylene glycol with a molecular weight of 2000-4000.

[0072] According to some embodiments of this application, the conditions of the first sintering treatment are not particularly limited. For example, the temperature of the first sintering treatment can be 350°C-800°C, and the time of the first sintering treatment can be 6h-12h, so that a carbon coating layer with a high degree of graphitization can be finally formed on the surface of the core.

[0073] S222: The first coated positive electrode active material is mixed with the second carbon source and then subjected to a second sintering process.

[0074] According to some embodiments of this application, the positive electrode active material is obtained through a second sintering process in this step. The type of the second carbon source is not particularly limited; for example, the second carbon source may include at least one of starch, sucrose, and glucose. In some embodiments, the second carbon source may be glucose.

[0075] According to some embodiments of this application, mixing the first coated positive electrode active material with the second carbon source may include: adding the second carbon source to an optional solvent and dissolving it at 20-60°C, then adding the first coated positive electrode active material to the aforementioned solvent containing the second carbon source, and then grinding and mixing for 6-24 hours to obtain a mixed liquid, which is then dried and used for the second sintering process.

[0076] According to some embodiments of this application, the conditions for the second sintering treatment are not particularly limited. For example, the temperature of the second sintering treatment can be 650°C-850°C, and the time of the second sintering treatment can be 6 hours-24 hours, thereby forming sp on the core surface. 2 Hybridized carbon atoms and sp 3 A carbon coating layer with a hybrid carbon atom molar ratio of not less than 0.5.

[0077] In another aspect of this application, reference is made to Figure 1This application proposes a positive electrode sheet 10, including a positive current collector 11 and a positive active material layer 12. The positive active material layer 12 is located on one side of the positive current collector 11 and includes the aforementioned positive active material. Therefore, this positive electrode sheet possesses all the features and advantages of the aforementioned positive active material, which will not be repeated here. As an example, the positive current collector 11 has two surfaces opposite each other in its own thickness direction, and the positive active material layer 12 can be disposed on either or both of the two opposite surfaces of the positive current collector 11.

[0078] According to some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0079] According to some embodiments of this application, the adhesive is a polymer, whose main functions are to bond and maintain the positive electrode active material, enhance the contact between the positive electrode active material and the conductive agent, and between the positive electrode active material and the current collector, while also stabilizing the structure of the electrode sheet. According to other embodiments of this application, the type of adhesive is not particularly limited; for example, the adhesive may include at least one of polyvinylidene fluoride and polyacrylonitrile.

[0080] In another aspect, this application proposes a battery comprising: a positive electrode, the positive electrode including the aforementioned positive electrode. Thus, this battery possesses all the features and advantages of the aforementioned positive electrode, which will not be repeated here. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator is disposed between the positive and negative electrodes, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0081] According to some embodiments of this application, there are no particular limitations on the shape of the battery; it can be cylindrical, square, or other arbitrary shapes. For example, Figure 2 This is a square-structured battery 5 as an example. Specifically, refer to... Figure 3The outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0082] According to some embodiments of this application, batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module. Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple batteries 5 can be fixed in place by fasteners. Battery module 4 may also include a housing with a receiving space in which the multiple batteries 5 are received.

[0083] In the description of this application, "multiple" means two or more.

[0084] According to some embodiments of this application, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack. Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0085] In another aspect of this application, an electrical device is proposed, comprising: a battery, the battery including the aforementioned battery. Thus, the electrical device possesses all the features and advantages of the aforementioned battery, which will not be repeated here. The battery, battery module, or battery pack can be used as the power source for the electrical device, or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. The electrical device can select the battery, battery module, or battery pack according to its usage requirements.

[0086] According to some embodiments of this application, Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0087] According to some embodiments of this application, the power device can also be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and can use a battery as its power source.

[0088] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0089] Example 1:

[0090] Step S1: Add 689.6g of manganese carbonate, 455.27g of ferrous carbonate, 4.65g of cobalt sulfate, and 4.87g of vanadium dichloride to a mixer and mix thoroughly for 6 hours. Then transfer the resulting mixture to a reaction vessel, add 5L of deionized water and 1260.6g of oxalic acid dihydrate, heat to 80℃, and stir thoroughly at 500rpm for 6 hours until the mixture is homogeneous and the reaction terminates without the generation of bubbles, obtaining a Fe, Co, and V co-doped manganese oxalate suspension. Then filter the suspension, dry it at 120℃, and then mill it to obtain Fe, Co, V, and S co-doped manganese oxalate particles with a particle size of 100nm.

[0091] Step S2: Take 1793.1g of manganese oxalate, 368.3g of lithium carbonate, 1146.6g of ammonium dihydrogen phosphate, and 4.9g of dilute sulfuric acid prepared in Step S1, add them to 20L of deionized water, stir thoroughly, and react uniformly at 80℃ for 10h to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation to obtain powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700℃ for 4h to obtain the core Li of the positive electrode active material. 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4.

[0092] Step S3: Using PEG-1000 as the first carbon source, 58.2g of PEG-1000 was dissolved in 500g of deionized water, then stirred and fully dissolved to obtain an aqueous solution. 1571.9g of the above core material was added to the solution and stirred for 6 hours until homogeneous. After spray drying, a first sintering treatment was performed at a temperature of 600℃ for 9 hours, thereby obtaining the first coated positive electrode active material.

[0093] Step S4: Using glucose as the second carbon source, 37.3g of glucose was dissolved in 500g of deionized water, then stirred and fully dissolved to obtain a glucose aqueous solution. 1603.3g of the first coated positive electrode active material obtained in Step S3 was added to the aforementioned glucose solution and stirred together for 6 hours until homogeneous. After spray drying, a second sintering treatment was performed at 750℃ for 20 hours, thus obtaining the positive electrode active material.

[0094] Examples 2-20 and Comparative Examples 1-3 are the same as Example 1, except for the selection of carbon source and the sintering temperature, as detailed in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] It should be noted that PEG-1000 refers to polyethylene glycol with a molecular weight of 900-1100, PEG-1500 refers to polyethylene glycol with a molecular weight of 1350-1650, PEG-2000 refers to polyethylene glycol with a molecular weight of 1800-2200, PEG-3000 refers to polyethylene glycol with a molecular weight of 2700-3300, PEG-4000 refers to polyethylene glycol with a molecular weight of 3500-4400, PEG-6000 refers to polyethylene glycol with a molecular weight of 5500-7000, PEG-8000 refers to polyethylene glycol with a molecular weight of 7200-8800, PEG-10000 refers to polyethylene glycol with a molecular weight of 8500-11500, and PEG-20000 refers to polyethylene glycol with a molecular weight of 19000-21000.

[0099] The following tests were performed on the positive electrode active materials in Examples 1-20 and Comparative Examples 1-3, and the test results are shown in Table 2:

[0100] 1. Determination of the hybridization morphology of carbon atoms in the carbon coating layer: This test was performed using Raman spectroscopy. By fractionating the energy spectrum from the Raman test, I... g / I d , where I d For sp 3 Peak intensity of carbon speciation, I g For sp 2 The peak intensity of carbon in different forms is used to determine the molar ratio between the two.

[0101] 2. Carbon Coating Thickness Test: The thickness of the carbon coating layer was measured by cutting a thin slice of approximately 100 nm thickness from the middle of a single particle of the aforementioned positive electrode active material using FIB. The slice was then subjected to TEM testing to obtain the raw TEM image, which was saved in the raw image format (xx.dm3). The raw TEM image was opened in Digital Micrograph software, and the carbon coating layer was identified using lattice spacing and angle information. The thickness of the carbon coating layer was then measured. The thickness was measured at three locations on the selected particle, and the average value was taken.

[0102] 3. Carbon content test in positive electrode active material: Turn on all power switches of the carbon-sulfur analyzer, press and hold the "zero" button, open the oxygen valve of the carbon-sulfur analyzer, and adjust the oxygen pressure to 0.02-0.04 MPa. Turn on "pre-oxygen" and "post-control," and adjust the flow meter to approximately 100 L / h. Add silicon molybdenum powder (0.3 g), the weighed sample (250 mg), tin granules (0.3 g), and pure iron (1 g) sequentially to the crucible, then close the crucible. Click the "test" button to start the test. The test result will be automatically displayed upon completion; record this result as the carbon content.

[0103] 4. Specific surface area test of positive electrode active material: Using the American Mech GeminiVII2390 multi-station fully automatic specific surface area and porosity analyzer, about 7g of positive electrode active material sample was placed in a 9cc long tube with a bulb, degassed at 150℃ for 15min, and then placed in the main unit for testing to obtain BET data.

[0104] 5. Median particle size test of positive electrode active material: Equipment model: Malvern 3000 (MasterSizer3000) laser particle size analyzer; Reference standard procedure: GB / T19077-2016 / ISO13320:2009; Specific test procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20ml of deionized water, and simultaneously incubate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, test according to the GB / T19077-2016 / ISO13320:2009 standard.

[0105] 6. Resistivity test of positive electrode active material powder: Use Yuaneng Technology PRCD1000 equipment to test the powder resistivity. Turn on the power of the equipment and the test software. Use a balance to weigh the powder required for the test. Use a jig to press the powder into a thin sheet. Put the sheet into the equipment. Configure the test parameters: test pressure 5t, holding time 5s. Click test. After the test is completed, the test result will be displayed and recorded.

[0106] 7. Test of water absorption of positive electrode active material: Take 5g of positive electrode active material sample, heat and dry it at 110℃ for 12h, then put the sample into a vial, and put the vial containing the sample into the Karl Fischer automatic sample injection system. During the test, heat the vial containing the sample to 250℃ and pass dry gas through it. Purge the gas in the vial into the titration cup for absorption titration, and convert the result into the water content of the solid sample.

[0107] 8. Testing of the specific capacity of the positive electrode active material: (1) Preparation of coin cell: The positive electrode active material prepared above, polyvinylidene fluoride (PVDF), and acetylene black were added to N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a drying room to form a slurry. The slurry was coated on aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 A coin cell was assembled in a coin cell box using a lithium sheet as the negative electrode and a 1 mol / L LiPF6 solution in a 1:1:1 volume ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) as the electrolyte.

[0108] (2) Measurement of the initial specific capacity of the button cell: At 2.5 to 4.3V, the button cell is charged at 0.1C to 4.3V, and then charged at 4.3V at a constant voltage until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged at 0.1C to 2.0V. The discharge capacity at this time is the initial specific capacity, which is recorded as the specific capacity of the positive electrode active material.

[0109] Full cells were prepared using the positive electrode active materials from Examples 1-20 and Comparative Examples 1-3, respectively. The preparation of the full cells is as follows:

[0110] The above-mentioned positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed evenly in an N-methylpyrrolidone solvent system at a weight ratio of 92:2.5:5.5. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet. The coating amount was 0.4 g / cm³. 2 The compacted density is 2.4 g / cm³. 3 .

[0111] Artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 1.7 g / cm³. 3 .

[0112] Using a porous polyethylene (PE) polymer film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging, electrolyte is injected, and it is sealed to obtain a full battery.

[0113] Cyclic performance tests were conducted on the full batteries from Examples 1-20 and Comparative Examples 1-3. The full battery cycle performance tests were performed as follows: Under a constant temperature environment of 45°C, the full battery was charged at 1C to 4.3V at a voltage range of 2.5V-4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed by the battery at this point was recorded. The test results are shown in Table 2.

[0114] Table 2

[0115]

[0116]

[0117] Test results show that when the carbon coating layer of the positive electrode active material contains sp... 2 Hybridized carbon and sp 3 When the molar ratio of hybrid carbon is less than 0.5, the water absorption of the positive electrode active material is significantly improved, reaching more than 890 ppm. Correspondingly, the excessive water content will cause the lithium salt in the battery electrolyte to decompose, resulting in a significant reduction in the cycle performance of the battery.

[0118] It is understood that in order to control variables, the same core was used for the subsequent preparation of the positive electrode active material in the aforementioned embodiments and comparative examples. That is, the selection of the aforementioned core material is exemplary. The relevant features of the carbon coating layer of the positive electrode active material in this application can be combined with other core materials in a suitable manner. For example, the types of core materials may include at least one of lithium manganese phosphate, lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich manganese-based solid solutions. By forming the aforementioned carbon coating layer on the surface of the core, the conductivity of the positive electrode active material can be further improved, and a positive electrode active material with both high specific capacity and better cycle performance can be obtained.

[0119] Unless otherwise stated, all technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. All patents and publications referenced in this application are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this application but do not exclude other contents.

[0120] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0121] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a positive electrode active material, characterized in that, Provide a kernel, the kernel comprising phosphate; A carbon coating layer is formed on at least a portion of the surface of the core, wherein sp in the carbon coating layer 2 Hybridized carbon atoms and sp 3 The molar ratio of hybrid carbon atoms is not less than 0.8, and the thickness of the carbon coating layer is 4 nm. The cathode active material has a carbon content of 1 wt% and a wavelength of 8 nm. 2.5wt%, The median particle size of the positive electrode active material is 0.5 μm-1.5 μm. The specific surface area of ​​the positive electrode active material is no greater than 25m². 2 / g, The process of forming a carbon coating layer on at least a portion of the surface of the core includes: mixing the core with a first carbon source and obtaining a first coated positive electrode active material through a first sintering process; mixing the first coated positive electrode active material with a second carbon source and obtaining the positive electrode active material through a second sintering process. The first carbon source includes at least one of polyvinyl alcohol and polyethylene glycol; the second carbon source is selected from at least one of sucrose and glucose, and the molecular weight of the first carbon source is not less than 2000. The temperature of the first sintering treatment is 350℃-800℃, and the time of the first sintering treatment is 6h-12h; the temperature of the second sintering treatment is 650℃-850℃, and the time of the second sintering treatment is 6h-24h.

2. The method according to claim 1, characterized in that, The molecular weight of the first carbon source is 2000-5000.

3. The method according to claim 1, characterized in that, The phosphate includes at least one of lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate.

4. The method according to claim 1, characterized in that, The kernel comprises LiMPO4, and the M element includes Mn and non-Mn elements. The non-Mn element includes one or both of the first doping element and the second doping element, wherein the first doping element is manganese site doping and the second doping element is phosphorus site doping. The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; The second doping element includes one or more elements selected from boron, S, Si, and N.

5. The method according to claim 4, characterized in that, The first doping element includes at least two of Fe, Ti, V, Ni, Co and Mg.

6. The method according to claim 4 or 5, characterized in that, The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements selected from boron, S, Si, and N.

7. The method according to claim 4 or 5, characterized in that, The kernel includes Li 1+x C m Mn 1-y A y P 1-z R z O 4-n D n x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, n is any value in the range of 0.001 to 0.1, m is any value in the range of 0.9 to 1.1, C includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, R includes one or more elements selected from boron, S, Si, and N, and D includes one or more elements selected from S, F, Cl, and Br.

8. The method according to claim 1, characterized in that, The specific surface area of ​​the positive electrode active material is no greater than 18m². 2 / g.

9. The method according to claim 1, characterized in that, The resistivity of the positive electrode active material powder is no greater than 200 Ω·cm.

10. The method according to claim 9, characterized in that, The resistivity of the positive electrode active material powder is no greater than 100 Ω·cm.

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