Positive electrode material, positive electrode pole piece thereof, and secondary battery

Abstract

Provided in the present application are a positive electrode material, a positive electrode pole piece thereof, and a secondary battery. The positive electrode material comprises a plurality of particles. At least some of the particles have micro-cracks. The size of the micro-cracks is 0.5 nm to 30 nm. The proportion of the number of the particles having micro-cracks in the total number of particles of the positive electrode material is 1.5% to 13%. The method for measuring the proportion comprises: performing a scanning electron microscope test on the positive electrode material to obtain a scanning electron microscope image, selecting 300 positive electrode material particles from the scanning electron microscope image, and counting the number of positive electrode material particles having micro-cracks to obtain the proportion. The positive electrode material or a positive electrode pole piece using the positive electrode material is applied to a secondary battery, which has significantly reduced gas generation behavior and a relatively high capacity, which can facilitate the improvement of the cycle stability and safety of the secondary battery.

Description

Cathode material, cathode sheet and secondary battery thereof

[0001] The present application claims priority to the Chinese patent application No. 202411940321.X filed on December 26, 2024, and entitled "Cathode material, cathode sheet and secondary battery thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of electrochemical energy storage, in particular to a cathode material, a cathode sheet and a secondary battery. BACKGROUND

[0003] In a conventional preparation process, the cathode material precursor is mixed and sintered, nucleated and grown, then dispersed and crushed to form a powder, and the crushed material is coated and processed to form a cathode material. However, the cathode material prepared by such conventional preparation method has poor structural stability, and the conventional coating and processing cannot solve the problem of structural instability during sintering and dispersion. At high voltage, the structure of the cathode material is easily damaged, which causes gas production and affects the stability and safety of the cathode material. SUMMARY

[0004] Therefore, the present application provides a cathode material to solve at least one of the above problems.

[0005] To achieve the above-mentioned purpose, the present application provides a cathode material, which includes a plurality of particles, at least part of the particles having micro-cracks, the size of the micro-cracks being 0.5 nm to 30 nm, and the number ratio of the particles having micro-cracks in the total number of particles of the cathode material being 1.5% to 13%. The test method of the number ratio includes: performing scanning electron microscope test on the cathode material to obtain a scanning electron microscope image, randomly selecting 300 cathode material particles in the scanning electron microscope image, and counting the number of cathode material particles having micro-cracks to obtain the number ratio.

[0006] The present application also provides a cathode sheet, which includes a cathode current collector and a cathode active material layer arranged on the cathode current collector, and the cathode material layer includes the above-mentioned cathode material.

[0007] The present application also provides a secondary battery, which includes the above-mentioned cathode sheet.

[0008] In the cathode material of the present application, based on the total number of cathode material particles, when the number ratio of the cathode material particles having micro-cracks is 1.5% to 13%, the continuous infiltration of the electrolyte into the cathode material particles can be effectively reduced, thereby the gas production behavior of the cathode material in the secondary battery can be more effectively reduced, and the cycle stability and safety of the secondary battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG. 1 is a structural schematic diagram of micro-cracks of a positive electrode material particle according to the present application.

[0010] FIG. 2 is a structural schematic diagram of a secondary battery according to an embodiment of the present application when charging.

[0011] FIG. 3 is a structural schematic diagram of a secondary battery according to an embodiment of the present application when discharging.

[0012] FIG. 4 is an SEM image of a positive electrode material before rolling according to Example 1 of the present application.

[0013] FIG. 5 is an SEM image of a positive electrode material after rolling according to Example 1 of the present application.

[0014] FIG. 6 is an SEM image of a positive electrode material after charge-discharge cycling according to Example 1 of the present application.

[0015] FIG. 7 is an SEM image of a positive electrode material before rolling according to Example 2 of the present application.

[0016] FIG. 8 is an SEM image of a positive electrode material after rolling according to Example 2 of the present application.

[0017] FIG. 9 is an SEM image of a positive electrode material after charge-discharge cycling according to Example 2 of the present application.

[0018] FIG. 10 is an SEM image of a positive electrode material before rolling according to Comparative Example 1 of the present application.

[0019] FIG. 11 is an SEM image of a positive electrode material after rolling according to Comparative Example 1 of the present application.

[0020] FIG. 12 is an SEM image of a positive electrode material after charge-discharge cycling according to Comparative Example 1 of the present application.

[0021] FIG. 13 is an SEM image of a positive electrode material before rolling according to Comparative Example 4 of the present application.

[0022] FIG. 14 is an SEM image of a positive electrode material after rolling according to Comparative Example 4 of the present application.

[0023] FIG. 15 is an SEM image of a positive electrode material after charge-discharge cycling according to Comparative Example 4 of the present application.

[0024] Main element symbol explanation Positive electrode material particle 10 Cracks 11, 12, 13 Electrode assembly 100 Positive electrode sheet 101 Negative electrode sheet 102 Separation film 103. DETAILED DESCRIPTION

[0025] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only, and are not intended to be limiting of the present application unless otherwise specified. It should be noted that, as used in this specification, all technical and scientific terms have the meaning commonly understood by one with ordinary skill in the art to which the present application belongs unless otherwise defined. In case of conflict, the present specification, including explanations of terms, will control. In the description of the present application, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application, however, can be practiced without all or with only a portion of these specific details. In other instances, well known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the present application.

[0026] After the sintering growth of the positive electrode material, the nucleation is formed into a powder (micropowder particles) by rolling. It is generally believed that the powder (micropowder particles) is the source of gas generation of the positive electrode material. In order to solve the problem of gas generation of the positive electrode material under high voltage, the related art maintains the interface stability of the positive electrode material by surface treatment, such as coating treatment, to improve the problem of gas generation of the positive electrode material under high voltage. However, the surface coating generally forms island-shaped coating, and it is difficult to form uniform protection, which cannot effectively improve the problem of gas generation, and too much coating material will also affect the capacity of the positive electrode material and increase the manufacturing cost. In the related art, the strength of the positive electrode material is increased to reduce the micro-powder generated by rolling to reduce the gas generation behavior of the material. However, improving the generation of micro-powder can only slightly reduce the initial gas generation of the positive electrode material, and still cannot effectively solve the problem of gas generation of the positive electrode material under long-term high temperature conditions. Moreover, this method also reduces the compaction of the electrode sheet, and puts forward strict requirements on the crushing and sintering process of the material, which is not conducive to the commercial application of the material.

[0027] The present application finds that the gas generation behavior of the positive electrode material is affected by the content of micro-cracks in the positive electrode material particles. Referring to FIG. 1, the sources of micro-cracks in the positive electrode material particles 10 mainly include three cases. One is the first type of cracks 11 generated due to the anisotropy of the unit cell during the growth of the positive electrode material particles 10. One is the second type of cracks 12 generated during the crushing or rolling of the positive electrode material particles 10. The other is the third type of cracks 13 generated due to intergranular displacement after the positive electrode material particles 10 participate in the charge and discharge cycle. Due to the existence of the above-mentioned first type of cracks 11 and second type of cracks 12, when the positive electrode material is immersed in the electrolyte environment, the electrolyte continuously erodes from the outside of the positive electrode material particles to the inside of the positive electrode material particles 10 through the first type of cracks 11 and the second type of cracks 12, thereby causing a large number of side reactions to occur, and further causing the gas generation to deteriorate. Moreover, since the micro-cracks are intrinsic defects of the positive electrode material particles, simply improving the mechanical strength of the positive electrode material particles or controlling the generation of micro-powder cannot avoid the generation of micro-cracks, nor can it avoid the continuous gas generation problem caused by micro-cracks.

[0028] In view of the gas generation mechanism of the positive electrode material at high voltage discovered by the inventors of the present application, one embodiment of the present application provides a secondary battery including a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located in the housing.

[0029] The housing can be a packaging bag obtained by packaging with a packaging film (e.g., an aluminum plastic film), for example, the secondary battery can be a soft package battery. In other embodiments, the secondary battery can also be a steel can battery, an aluminum can battery, or the like.

[0030] Referring to FIGS. 2 and 3, the electrode assembly 100 includes a positive electrode sheet 101, a negative electrode sheet 102, and a separator 103 disposed between the positive electrode sheet 101 and the negative electrode sheet 102. When an electrolyte (not shown) is provided, upon charging, referring to FIG. 2, active ions (e.g., lithium ions) are deintercalated from the crystal lattice of the positive electrode material of the positive electrode sheet 101, pass through the separator 103 via the electrolyte, reach the negative electrode sheet 102, and are intercalated into the crystal lattice of the negative electrode material. Upon discharging, referring to FIG. 3, active ions (e.g., lithium ions) are deintercalated from the crystal lattice of the negative electrode material of the negative electrode sheet 102, pass through the separator 103 via the electrolyte, reach the positive electrode sheet 101, and are intercalated into the crystal lattice of the positive electrode material. The movement of electrons from the negative electrode sheet 102 to the positive electrode sheet 101 via an external circuit forms an electric current, and the reverse movement of the electrons forms an electric current, which can be used by an electrical device.

[0031] In some embodiments, the electrode assembly 100 can have a jelly-roll structure formed by alternately stacking the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102. In other embodiments, the electrode assembly 100 can also have a wound structure formed by winding the positive electrode sheet 101, the separator 103, and the negative electrode sheet 102.

[0032] Positive electrode sheet

[0033] The positive electrode sheet 101 includes a positive electrode current collector and a positive electrode material active layer including a positive electrode material, a binder, and a conductive agent. The positive electrode material, the binder, and the conductive agent are prepared into a slurry, and the slurry is coated and rolled on the positive electrode current collector to form the positive electrode sheet.

[0034] The positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be an aluminum foil or a nickel foil, and the composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy) on a polymer substrate.

[0035] The positive electrode material layer comprises a positive electrode material, the positive electrode material comprises a plurality of particles, at least part of the particles have micro-cracks, the size of the micro-cracks is 0.5 nm to 30 nm, and the number ratio of the particles having the micro-cracks in the total number of the particles of the positive electrode material is 1.5% to 13%. The number ratio is tested by the following method: scanning electron microscope testing is performed on the positive electrode material to obtain a scanning electron microscope image, 300 particles of the positive electrode material are randomly selected from the scanning electron microscope image, and the number of the positive electrode material particles having the micro-cracks is counted to obtain the number ratio.

[0036] It should be noted that in the present application, the positive electrode material includes the positive electrode material in the powder state and the positive electrode material in the positive electrode sheet. The size of the micro-crack is 0.5 nm to 30 nm, and the size of the micro-crack refers to the width of the micro-crack. The micro-crack extends along the length direction, and the width of the micro-crack is perpendicular to the length direction.

[0037] The applicant finds that when the micro-crack of the positive electrode material particle in the present application is less than 0.5 nm, the size of the micro-crack is too small, which is not conducive to the infiltration of the electrolyte. The negative impact of the physical indicators and chemical properties of the positive electrode material particles themselves and the subsequent battery application on the performance of the battery can be ignored. When the crack is greater than 30 nm, the crack with such a large size may have caused the positive electrode material particles to break or break. Therefore, the applicant believes that it does not belong to the category of micro-cracks in the present application. Therefore, the present application exists 0.5 nm to 30 nm of the micro-crack particles in the positive electrode material particles, and the micro-crack is mainly generated by the anisotropy of the unit cell or the crushing process. Further research shows that based on the total number of the particles of the positive electrode material, when the number ratio of the positive electrode material particles having the above-mentioned micro-cracks is 1.5% to 13%, the continuous infiltration of the electrolyte to the positive electrode material particles can be effectively reduced, thereby effectively reducing the gas generation behavior of the positive electrode material in the secondary battery, thereby facilitating the improvement of the cycle stability and safety of the secondary battery, and also controlling the intergranular displacement generated after the positive electrode material particles participate in the charge and discharge cycle in the actual application until the crack is generated. At the same time, it also enables the positive electrode material to maintain a high compaction density based on the above-mentioned positive electrode material, increases the contact area between the positive electrode material particles, and increases the active area that can participate in the reaction, thereby facilitating the improvement of the specific capacity of the secondary battery. When the number ratio of the positive electrode material particles having the above-mentioned micro-cracks in the total number of the positive electrode material particles is too low (i.e. lower than 1.5%), the positive electrode material particles are too round, which will cause the compaction density of the positive electrode material powder to be low, thereby causing the compaction density of the positive electrode sheet to be low, affecting the electronic conductivity and the specific capacity of the secondary battery. When the number ratio of the positive electrode material particles having the above-mentioned micro-cracks in the total number of the positive electrode material particles is too high (i.e. higher than 13%), the secondary battery produced by the positive electrode material will significantly deteriorate and be difficult to control.

[0038] In some embodiments, the number of particles having micro-cracks accounts for 4% to 8% of the total number of particles of the positive electrode material. When the number of particles of the positive electrode material having the above-mentioned micro-cracks is further controlled to account for 4% to 8% of the total number of particles of the positive electrode material, the gas generation behavior of the positive electrode material when used as a secondary battery can be further reduced, especially the probability of intercrystalline displacement and crack generation after the positive electrode material participates in the charge-discharge cycle, while the electrode sheet based on the positive electrode material has a relatively high compaction density, which is beneficial to improving the stability, safety and specific capacity of the secondary battery.

[0039] In some embodiments, the micro-cracks extend from the surface of the particles and communicate with the interior of the particles, or extend from the interior of the particles to the surface of the particles and communicate with the surface of the particles. The above-mentioned micro-cracks will cause the electrolyte to continuously erode from the outside of the material to the interior of the positive electrode material particles, and in practical application, will continuously aggravate the infiltration of the electrolyte into the positive electrode material particles, thereby causing a large number of side reactions and deteriorating gas generation. It should be noted that if there are micro-cracks in the positive electrode material particles that do not communicate between the surface and the interior, the electrolyte cannot be infiltrated, and therefore the extension direction of the micro-cracks needs to be specifically controlled to avoid counting the micro-cracks that do not communicate between the surface and the interior of the particles. Therefore, controlling the morphology of the above-mentioned micro-cracks and the content of the micro-cracks in the positive electrode material particles is beneficial to controlling the gas generation behavior of the positive electrode material when used as an electrode sheet or a secondary battery. Specifically, the content of the above-mentioned micro-cracks is represented by the number of positive electrode material particles having the micro-cracks.

[0040] In some embodiments, the positive electrode material has a 7-day gas generation amount of 0.1 mL / g to 1 mL / g at 60°C. For example, the above-mentioned gas generation amount of the positive electrode material can be 0.1 mL / g, 0.25 mL / g, 0.30 mL / g, 0.40 mL / g, 0.45 mL / g, 0.50 mL / g, 0.55 mL / g, 0.60 mL / g, 0.65 mL / g, 0.85 mL / g, 1 mL / g or any value within the range formed by any two of the above-mentioned values. The gas generation amount obtained by using the positive electrode material in a secondary battery (such as a soft package battery) within the above-mentioned range indicates that the positive electrode material has a relatively low gas generation amount, especially the gas generation caused by the anisotropy of the unit cell and the cracks generated during the crushing or rolling process of the positive electrode material particles, which is beneficial to improving the cycle stability and safety of the secondary battery.

[0041] In some embodiments, the strain rate of the positive electrode material is 0.035% to 0.13%. For example, the strain rate of the positive electrode material can be 0.035%, 0.040%, 0.046%, 0.051%, 0.054%, 0.062%, 0.075%, 0.081%, 0.094%, 0.103%, 0.13%, or any value within the range between any two of the above-mentioned values. The strain rate in the present application refers to the change of the lattice cell parameter, which means the change of the micro-strain calculated by the cell volume. Therefore, when the strain rate is within the above-mentioned range, the change of the lattice cell parameter is low, which not only indicates that the crystal structure of the positive electrode material itself is more stable, but also can effectively prevent the stress concentration of the positive electrode material particles from causing cracks, which is beneficial to improve the cycle stability of the obtained secondary battery.

[0042] In some embodiments, the positive electrode material is a single-crystal positive electrode material. Compared with polycrystalline positive electrode materials, single-crystal positive electrode materials have better structural stability, longer cycle life, higher safety, and better compaction performance. The difference between single-crystal positive electrode materials and polycrystalline positive electrode materials (i.e., polycrystalline secondary particles) is that the smallest particles of the polycrystalline secondary particles are secondary particles formed by agglomeration of nanoscale primary particles. The smallest particles of the single-crystal positive electrode material are usually micrometer-scale single primary particles. The obtained positive electrode material can be characterized and judged to be a single-crystal material by electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and the like. For example, in SEM analysis, the shape of the single-crystal positive electrode material particles generally exhibits a regular or irregular polyhedral shape, and obvious particle agglomeration is less common. In TEM analysis, the crystal face orientation of the single-crystal positive electrode material is similar or the same. For the convenience of understanding, the single-crystal positive electrode material in the present application can be understood as containing single grains with the same orientation. That is, a plurality of primary particles can be included in one grain, and the orientations of all the primary particles in one grain are the same.

[0043] It should be specifically pointed out that the single-crystal positive electrode material known to those skilled in the art is not a single crystal in the strict sense of crystallography. In crystallography, an ideal single crystal refers to a crystal with the same arrangement and direction. However, due to impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal positive electrode material known in the art is actually a positive electrode material with a "single-crystal-like morphology", which exhibits a single-crystal-like large particle size in size, and is different from a polycrystal composed of numerous small primary particles.

[0044] In some embodiments, the particles comprise one or more primary particles, all the primary particles in at least one particle have the same orientation, and the average particle size of the primary particles is 1-5 μm. In this way, the positive electrode material can stably achieve a high degree of filling, while reducing the risk of cracks caused by extrusion and the like after the particles reach their maximum density. Because the grains have the same orientation, the stress and strain of the positive electrode material particles during the charge and discharge cycle can be relieved, reducing the risk of cracking of the positive electrode material particles during the cycle, thereby improving the structural stability of the positive electrode material. It should be noted that the grain orientation of the positive electrode material can also be tested by electron backscatter diffraction (EBSD), and 100 single grains with the same orientation are randomly selected, the particle size of each grain is measured, and the arithmetic mean is taken as the average particle size of the single grains.

[0045] In some embodiments, the specific surface area of the positive electrode material is 0.5 m 2 / g to 1 m 2 / g. For example, the specific surface area of the positive electrode material can be 0.5 m 2 / g, 0.6 m 2 / g, 0.66 m 2 / g, 0.72 m 2 / g, 0.78 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1 m 2 / g, or any value within a range defined by any two of the above values. Controlling the specific surface area of the positive electrode material within the above range is beneficial for reducing the contact between the electrolyte and the material, reducing the side reactions between the material and the electrolyte, and thus reducing the gas generation behavior of the positive electrode material in the battery.

[0046] In some embodiments, the particle size D10, D50 and D90 of the positive electrode material satisfy (D90-D10) / D50 (volume particle size distribution width L) is greater than or equal to 1.0. For example, (D90-D10) / D50 can be 1.0, 1.1, 1.15, 1.18, 1.20, 1.22, 1.23, 1.24, 1.30, 1.31, or any value within a range defined by any two of the above values. Among them, the measured volume-based cumulative particle size distribution D10 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 10%, D50 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 50%, and D90 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 90%. When the above particle size distribution of the positive electrode material is within the above range, the large particles with a larger particle size and the small particles with a smaller particle size of the positive electrode material can cooperate with each other, and the small particles fill the pores between the large particles, which is beneficial for improving the tap density and the powder compaction density of the positive electrode material.

[0047] In some embodiments, the tap density of the positive electrode material is greater than or equal to 1.8 g / cm 3 . For example, the tap density of the positive electrode material can be 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , or any value within a range defined by any two of the above values. The above higher tap density is conducive to improving the tightness between the positive electrode material particles, thereby improving the transport of active particles and the conduction of electrons, increasing the energy density of the battery, prolonging the cycle life, and improving the safety performance.

[0048] In some embodiments, the powder compaction density of the positive electrode material at 3T tonnage is greater than or equal to 3.0 g / cm 3 . For example, the powder compaction density of the positive electrode material can be 3.0 g / cm 3 , 3.1 g / cm 3 , 3.12 g / cm 3 , 3.13 g / cm 3 , 3.14 g / cm 3 , 3.15 g / cm 3 , 3.16 g / cm 3 , 3.17 g / cm 3 , 3.18 g / cm 3 , 3.19 g / cm 3 , or any value within a range defined by any two of the above values. The above higher powder compaction density is conducive to reducing the distance between the positive electrode material particles, increasing the contact area, increasing the conductive channels and bridges, and increasing the active area that can participate in the reaction, thereby improving the specific capacity of the battery.

[0049] In some embodiments, the powder electrical conductivity of the positive electrode material is greater than or equal to 1 x 10 -4 S / cm. For example, the powder electrical conductivity of the positive electrode material can be 1 x 10 -4 S / cm, 1.2 x 10 -4 S / cm, 1.6 x 10 -4 S / cm, 1.7 x 10 -4 S / cm, 1.8 x 10 -4 S / cm, 1.9 x 10 -4 S / cm, 2.0 x 10 -4 S / cm, 2.1 x 10 -4 S / cm, 2.3 x 10 -4S / cm or any value within a range between any two of the above values. Controlling the powder conductivity of the positive electrode material within the above range is beneficial to make the material have lower impedance, thereby improving the conductivity of the obtained electrode sheet or secondary battery.

[0050] In some embodiments, the positive electrode material has a unit cell size (Dp) of 80 nm to 110 nm. For example, the positive electrode material can have a unit cell size of 80 nm, 85 nm, 88 nm, 89 nm, 90 nm, 92 nm, 93 nm, 95 nm, 96 nm, 110 nm, or any value within a range between any two of the above values. The material having the above unit cell size has a more stable crystal structure, a larger unit cell volume, and is easier to deintercalate lithium during the charging and discharging process, and has a shorter lithium ion transport channel. Therefore, controlling the unit cell size of the positive electrode material within the above range is beneficial to improve the capacity of the obtained secondary battery.

[0051] In some embodiments, the positive electrode material has a general formula of Li a Ni b Co c M (1-b-c) O2, wherein 0.95≤a≤1.2, 0

[0052] In some embodiments, the positive electrode material has a general formula of Li a Ni b Co c M (1-b-c) O2, wherein 0.95≤a≤1.2, 0

[0053] In some embodiments, the M2 element includes at least one of W, Sr, and B.

[0054] In some other embodiments, the positive electrode material has a core-shell structure, which includes an inner core and a cladding layer, and the cladding layer is arranged on at least part of the surface of the inner core. The inner core has a general formula of Li a Ni b Co c M (1-b-c)O2, wherein 0.95≤a≤1.2, 0 x N y O2, wherein 0≤x≤5, N is one or more of Zr, Ti, Al, W, Nb, La, Mo, and Y. The coating layer including the above material is beneficial to maintaining the interface stability of the positive electrode material, and further improving the gas generation problem of the material in a high voltage environment.

[0055] In some embodiments, the difference between the percentage of micro-crack particles after rolling of the positive electrode material and the percentage of micro-crack particles before rolling of the positive electrode material is 0.8% to 3.6%, and specifically can be 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.9%, 2.1%, 2.3%, 2.6%, 2.9%, 3.1%, 3.3%, 3.6%. Thus, it is shown that the positive electrode material in the present application has good crack propagation resistance during rolling, which can reduce the diffusion of the positive electrode material during the rolling of the pole piece, so that the positive electrode material has a lower gas generation performance.

[0056] In some embodiments, the difference between the percentage of micro-crack particles after rolling of the positive electrode material and the percentage of micro-crack particles after cycling is 0.2% to 3.0%, and specifically can be 0.2%, 0.5%, 0.6%, 0.9%, 1.3%, 1.4%, 1.5%, 1.6%, 1.9%, 2.1%, 2.3%, 2.6%, 2.9%, 3.0%. Thus, it is shown that the positive electrode material in the present application has good crack propagation resistance during cycling, and the number of micro-cracks increases less during the cycling, so that the positive electrode material has a lower gas generation performance. The binder in the positive electrode material layer is used to bond the positive electrode material particles to facilitate the formation of a film layer, and also can improve the bonding force between the positive electrode material layer and the positive electrode current collector. In some embodiments, the binder can include but is not limited to at least one of adhesive polymers such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefin, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0057] The conductive agent in the positive electrode material layer is used to form a conductive network, to provide a channel for electron transport, thereby improving the conductivity of the positive electrode material. In some embodiments, the conductive agent includes a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. Among them, the carbon-based material is, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, or carbon fiber; the metal-based material is, for example, metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; the conductive polymer is, for example, polyphenylene derivative.

[0058] Negative electrode sheet

[0059] The negative electrode sheet 102 is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the negative electrode sheet 102 includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. For example, the negative electrode material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or can be provided on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the negative electrode current collector, or can be a partial area of the negative electrode current collector, and the present application is not particularly limited as long as the purpose of the present application can be achieved.

[0060] The negative electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, it can include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collector (such as carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc.), etc.

[0061] In the present application, the thickness of the negative electrode current collector, the negative electrode material layer, and the negative electrode sheet is not particularly limited as long as the purpose of the present application can be achieved.

[0062] The negative electrode material layer of the present application includes a negative electrode material, which includes but is not limited to at least one of graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate with spinel structure, Li4Ti5O12, Li-Al alloy, and metallic lithium. 12

[0063] ​The negative electrode material layer in the present application further includes a negative electrode binder and a negative electrode conductive agent, or the negative electrode material layer further includes a negative electrode binder, a negative electrode conductive agent, and a thickening agent. The kind of the negative electrode binder and the negative electrode conductive agent in the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the negative electrode binder includes but is not limited to at least one of the binders of the positive electrode material layer described above, and the negative electrode conductive agent can include but is not limited to at least one of the conductive agents of the positive electrode material layer described above. The kind of the thickening agent in the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickening agent can include but is not limited to at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose.

[0064] In some embodiments, the binder includes but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0065] In some embodiments, the conductive agent includes but is not limited to carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0066] Separating film

[0067] The material and shape of the separating film 103 used in the electrochemical device of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separating film 103 includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0068] For example, the separating film 103 can include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0069] A surface treatment layer is provided on at least one surface of the substrate layer, which can be a polymer layer or an inorganic layer, or a mixed layer of polymer and inorganic material. The inorganic layer includes inorganic particles selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate, and a binder selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0070] Electrolyte

[0071] The electrolyte has a function of conducting active ions between the positive electrode sheet and the negative electrode sheet. The state of the electrolyte can be one or more of a gel state, a solid state, and a liquid state. In some embodiments, the electrolyte employs an electrolyte solution. In some embodiments, the electrolyte solution includes one of a lithium salt and an organic solvent, or further includes an additive. The lithium salt, the organic solvent, or the additive are not particularly limited in the present application, and can be any of the techniques disclosed in the prior art as long as the purpose of the present application can be achieved. For example, the lithium salt includes but is not limited to lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis-trifluoromethanesulfonimide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2), LiFSI), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), or lithium difluoro(oxalato)borate (LiBF2(C2O4), LiDFOB). The organic solvent includes but is not limited to a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, or a combination thereof, for example, the carbonate compound includes but is not limited to diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.

[0072] The present application also provides a preparation method of the positive electrode material, comprising:

[0073] The first step is to mix the positive electrode material precursor, the lithium salt, and the additive, wherein the additive includes a low-melting-point transition metal compound, to obtain a mixture, and then to perform a first sintering on the mixture to obtain a first sintered product.

[0074] The additive is a low-melting-point transition metal compound, and such oxides help to promote the growth of the positive electrode material and to fill the cracks generated in the growth process of the positive electrode material. In the sintering process of the present step, the additive accelerates the growth of the positive electrode material in the early sintering stage and helps to fill the cracks of the positive electrode material in the late sintering stage, thereby controlling the content of micro-cracks in the first sintered product and making the first sintered product have a certain roundness and dispersity.

[0075] In some embodiments, the low melting point transition metal compound includes one or more of WO3, B2O3, Sr(OH)2, SrCO3, and SrO.

[0076] In some embodiments, the positive electrode material precursor includes a precursor containing excessive metal elements such as Ni, Co, Mn, etc., which can be hydroxide, oxide, carbonate, or phosphate, etc. For example, in some embodiments, the positive electrode material precursor can be Ni 0.65 Co 0.1 Mn 0.25 (OH)2, Ni 0.75 Co 0.05 Mn 0.2 O, Ni 0.7 Co 0.1 Mn 0.2 O.

[0077] In some embodiments, the lithium salt includes one or more of lithium hydroxide, lithium carbonate, lithium oxide, and lithium phosphate.

[0078] In some embodiments, the first sintering is performed in an oxygen atmosphere.

[0079] In some embodiments, the first sintering is performed in stages, with a minimum temperature of no less than 500°C and a maximum temperature of no more than 950°C.

[0080] In some embodiments, the first sintering is performed in three stages, including a first stage, a second stage, and a third stage, the temperature of the first stage being 400°C-600°C, the temperature of the second stage being 600°C-850°C, and the temperature of the third stage being 840°C-950°C. In some embodiments, the temperatures of the first stage, the second stage, and the third stage can be 500°C, 800°C, and 920°C, respectively; 500°C, 800°C, and 910°C, respectively; 500°C, 800°C, and 940°C, respectively; 500°C, 600°C, and 820°C, respectively; or 500°C, 800°C, and 880°C, respectively. In this way, the precursor material is processed by three-stage sintering, which can promote slow growth of the crystal grains. Slow and stable growth of the crystal grains can release the lattice stress during the growth process, reducing stress accumulation and generating a large number of single-crystal cracks.

[0081] In some embodiments, the first sintering is further followed by a rapid annealing process, with a cooling rate of 6°C-10°C. Specifically, the cooling rate can be 6°C, 7°C, 8°C, 9°C, or 10°C. During the rapid annealing process, the single-crystal particles can be inhibited from continuing to grow and forming adhesion between the crystal grains, which can be more easily dispersed during subsequent crushing, reducing single-crystal cracks.

[0082] Second step: The first sintering product is subjected to airflow crushing to obtain a crushed product.

[0083] In some embodiments, the amount of the grinding bodies for the jet milling is 200g to 600g. Specifically, the amount of the grinding bodies for the jet milling is 200g, 300g, 400g, 500g or 600g.

[0084] In some embodiments, the gas pressure for the jet milling is 0.35MPa to 0.65MPa. Specifically, the gas pressure for the jet milling is 0.35MPa, 0.45MPa, 0.55MPa or 0.65MPa.

[0085] In some embodiments, the specific surface area of the pulverized product is less than or equal to 0.8m2 / g. Specifically, the specific surface area of the pulverized product is 0.8m2 / g, 0.75m2 / g, 0.70m2 / g, 0.65m2 / g, 0.6m2 / g, 0.5m2 / g, 0.4m2 / g or 0.3m2 / g. 2 2 2 2 2 2 2 2

[0086] Step 3: mixing the pulverized product with a coating material, and performing secondary sintering to obtain the positive electrode material.

[0087] In some embodiments, the coating material comprises a metal oxide containing one or more elements of Zr, Ti, Al, W, Nb, La, Mo and Y. Specifically, it can be Al2O3, ZrO2, La2O3 or WO3.

[0088] In some embodiments, the sintering atmosphere for the secondary sintering is an oxygen atmosphere.

[0089] In some embodiments, the sintering temperature for the secondary sintering is 450℃ to 700℃. Specifically, it can be 450℃, 480℃, 500℃, 550℃, 600℃, 650℃ or 700℃.

[0090] The preparation method of the positive electrode material, by combining the above-mentioned additive and controlling the jet milling parameters, is conducive to controlling the generation of micro-cracks in the positive electrode material, thereby facilitating the control of the number of positive electrode materials with micro-cracks to fall within the expected range, thereby reducing the storage and cycle gas generation behavior of the obtained positive electrode material at high voltage when used as a battery, and improving the stability and safety of the battery.

[0091] The scheme of the present application will be explained below in conjunction with examples. Those skilled in the art will understand that the following examples are only used to explain the present application, and cannot be understood as a limitation of the present application. Unless otherwise stated, the reagents, software and instruments involved in the following examples which are not specifically stated are all conventional commercially available products or open source.​​​​​​​​

[0092] Example 1:

[0093] A positive electrode material, a preparation method thereof comprises:

[0094] S1, 500g of Ni 0.65 Co 0.1 Mn 0.25 (OH)2, 232g of LiOH H2O and 1.8g of WO3 are uniformly mixed to obtain a mixture, and the mixture is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 800℃ and 920℃ respectively, and rapid annealing cooling is performed at a cooling rate of 8℃ / min to obtain a primary sintered product.

[0095] S2, the primary sintered product is subjected to air flow crushing, the amount of grinding body for air flow crushing is controlled to be 200g (20% of the upper limit of grinding body), the air pressure for air flow crushing is controlled to be 0.55Mpa, and a crushed material is obtained, and the specific surface area of the final crushed material is 0.6m 2 / g.

[0096] S3, 100g of the crushed material is mixed with 0.2g of TiO2, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature of the secondary sintering is 550℃, and a secondary sintered product is obtained.

[0097] S4, after the secondary sintered product is cooled, a positive electrode material is obtained by screening.

[0098] Example 2:

[0099] A positive electrode material, a preparation method thereof comprises:

[0100] S1, 300g of Ni 0.75 Co 0.05 Mn 0.2 O, 227g of Li2CO3 and 1.3g of B2O3 are uniformly mixed to obtain a mixture, and the mixture is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 800℃ and 910℃ respectively, and rapid annealing cooling is performed at a cooling rate of 8℃ / min to obtain a primary sintered product.

[0101] S2, the primary sintered product is subjected to air flow crushing, the amount of grinding body for air flow crushing is controlled to be 240g (24% of the upper limit of grinding body), the air pressure for air flow crushing is controlled to be 0.65MPa, and a crushed material is obtained, and the specific surface area of the obtained crushed material is 0.75m 2 / g.

[0102] S3, 100g of the crushed material is mixed with 0.2g of Al2O3, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature of the secondary sintering is 500℃, and a secondary sintered product is obtained.

[0103] S4, after the cooling of the second sintering product, screening to obtain the positive electrode material.

[0104] Example 3:

[0105] A positive electrode material, the preparation method comprising:

[0106] S1, 500g of Ni 0.6 Co 0.1 Mn 0.3 CO3, 220g of Li2CO3 and 2.4g of WO3 are uniformly mixed to obtain a mixture, and the mixture is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 800℃ and 940℃ respectively, and rapid annealing is performed for cooling, the cooling speed is 10℃ / min, to obtain a primary sintering product.

[0107] S2, the primary sintering product is subjected to air flow crushing, the amount of grinding body of the air flow crushing is controlled to be 350g (35% of the upper limit of the grinding body), and the air pressure of the air flow crushing is controlled to be 0.40MPa, to obtain a crushed material, the specific surface area of the obtained crushed material is 0.6m 2 / g.

[0108] S3, 200g of the crushed material is mixed with 0.3g of ZrO2, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature of the secondary sintering is 700℃, to obtain a secondary sintering product.

[0109] S4, after the cooling of the secondary sintering product, screening to obtain the positive electrode material.

[0110] Example 4:

[0111] The difference from example 3 is that, in S2, the amount of grinding body of the air flow crushing is controlled to be 600g (60% of the upper limit of the grinding body), and the specific surface area of the crushed material is 0.7m 2 / g.

[0112] Example 5:

[0113] The difference from example 3 is that, in S2, the amount of grinding body of the air flow crushing is controlled to be 200g (20% of the upper limit of the grinding body), and the specific surface area of the crushed material is 0.5m 2 / g.

[0114] Example 6:

[0115] The difference from example 3 is that, in S2, the air pressure of the air flow crushing is controlled to be 0.3Mpa.

[0116] Example 7:

[0117] The difference from Example 3 is that in S2, the air pressure of the air flow pulverization is controlled at 0.65 Mpa, and the specific surface area of the pulverized material is 0.8 m 2 / g.

[0118] Example 8:

[0119] The difference from Example 3 is that in S2, the air pressure of the air flow pulverization is controlled at 0.50 Mpa, and the specific surface area of the pulverized material is 0.7 m 2 / g.

[0120] Example 9:

[0121] A positive electrode material, a preparation method thereof comprises:

[0122] S1, uniformly mix 500 g of Ni 0.9 Co 0.05 Mn 0.05 CO3, 230 g of LiOH and 3.7 g of SrO to obtain a mixed material, and place the mixed material in an oxygen atmosphere furnace to perform primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 600℃ and 820℃ respectively, and rapid annealing cooling is performed, the cooling speed is 8℃ / min, to obtain a primary sintered product.

[0123] S2, perform air flow pulverization on the primary sintered product, control the amount of the grinding body of the air flow pulverization at 300 g (30% of the upper limit of the grinding body), control the air pressure of the air flow pulverization at 0.40 MPa, to obtain a pulverized material, and the specific surface area of the obtained pulverized material is 0.8 m 2 / g.

[0124] S3, mix 400 g of the pulverized material with 0.8 g of La2O3, and perform secondary sintering in a compressed air atmosphere furnace, the temperature of the secondary sintering is 650℃, to obtain a secondary sintered product.

[0125] S4, after cooling the secondary sintered product, screen to obtain a positive electrode material.

[0126] Example 10:

[0127] A positive electrode material, a preparation method thereof comprises:

[0128] S1, uniformly mix 500 g of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, 230 g of LiOH and 2.8 g of SrO to obtain a mixed material, and place the mixed material in an oxygen atmosphere furnace to perform primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 600℃ and 840℃ respectively, and rapid annealing cooling is performed, the cooling speed is 8℃ / min, to obtain a primary sintered product.

[0129] S2, the one-burn product is subjected to air flow crushing, the amount of grinding body for air flow crushing is controlled to be 500 g (50% of the upper limit of grinding body), the air pressure for air flow crushing is controlled to be 0.3 MPa, to obtain a crushed material, and the specific surface area of the obtained crushed material is 0.75 m 2 / g.

[0130] S3, 200 g of the crushed material is mixed with 0.6 g of TiO2, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature for secondary sintering is 450℃, to obtain a two-burn product.

[0131] S4, after the two-burn product is cooled, screening is performed to obtain a positive electrode material.

[0132] Example 11:

[0133] A positive electrode material, a preparation method thereof comprises:

[0134] S1, 500 g of Ni 0.72 Co 0.12 Mn 0.16 O, 240 g of Li2CO3 and 3.1 g of B2O3 are uniformly mixed to obtain a mixed material, the mixed material is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 800℃ and 880℃ respectively, and rapid annealing cooling is performed, the cooling speed is 6℃ / min, to obtain a one-burn product.

[0135] S2, the one-burn product is subjected to air flow crushing, the amount of grinding body for air flow crushing is controlled to be 400 g (40% of the upper limit of grinding body), the air pressure for air flow crushing is controlled to be 0.55 MPa, to obtain a crushed material, and the specific surface area of the obtained crushed material is 0.7 m 2 / g.

[0136] S3, 200 g of the crushed material is mixed with 0.3 g of ZrO2, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature for secondary sintering is 650℃, to obtain a two-burn product.

[0137] S4, after the two-burn product is cooled, screening is performed to obtain a positive electrode material.

[0138] Example 12:

[0139] A positive electrode material, a preparation method thereof comprises:

[0140] S1, 300 g of Ni 0.55 Co 0.15 Mn 0.30O, 141g of Li2CO3 and 1.6g of WO3 are uniformly mixed to obtain a mixture, the mixture is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 800℃ and 950℃ respectively, and rapid annealing cooling is performed at a cooling rate of 10℃ / min, to obtain a primary sintered product.

[0141] S2, the primary sintered product is subjected to jet milling, the amount of grinding bodies for jet milling is controlled to be 300g (30% of the upper limit of the grinding bodies), and the gas pressure for jet milling is controlled to be 0.6MPa, to obtain a milled product, the specific surface area of the obtained milled product is 0.6m 2 / g.

[0142] S3, 100g of the milled product is mixed with 0.2g of Al2O3, and secondary sintering is performed in an oxygen atmosphere furnace, the temperature for secondary sintering is 550℃, to obtain a secondary sintered product.

[0143] S4, after the secondary sintered product is cooled, sieving is performed to obtain a positive electrode material.

[0144] Example 13:

[0145] A positive electrode material, a preparation method thereof comprises:

[0146] S1, 500g of Ni 0.65 Co 0.07 Mn 0.23 (OH)2, 220g of Li2CO3 and 3.5g of SrCO3 are uniformly mixed to obtain a mixture, the mixture is placed in an oxygen atmosphere furnace for primary sintering, the primary sintering is three-stage sintering, the temperatures are 500℃, 850℃ and 920℃ respectively, and rapid annealing cooling is performed at a cooling rate of 7℃ / min, to obtain a primary sintered product.

[0147] S2, the primary sintered product is subjected to jet milling, the amount of grinding bodies for jet milling is controlled to be 450g (45% of the upper limit of the grinding bodies), and the gas pressure for jet milling is controlled to be 0.45MPa, to obtain a milled product, the specific surface area of the obtained milled product is 0.65m 2 / g.

[0148] S3, 200g of the milled product is mixed with 0.6g of Y2O3, and secondary sintering is performed in a compressed air atmosphere furnace, the temperature for secondary sintering is 700℃, to obtain a secondary sintered product.

[0149] S4, after the secondary sintered product is cooled, sieving is performed to obtain a positive electrode material.

[0150] Example 14:

[0151] A positive electrode material, a preparation method thereof comprises:

[0152] S1, 400g of Ni0.7 Co 0.1 Mn 0.2 O, 170g of Li2CO3 and 2.1g of Sr(OH)2 are uniformly mixed to obtain a mixture, and the mixture is placed in an oxygen atmosphere furnace for primary sintering, which is three-stage sintering at 550℃, 800℃ and 930℃, and then is rapidly annealed and cooled at a cooling rate of 8℃ / min to obtain a primary sintered product.

[0153] S2, the primary sintered product is subjected to air flow crushing, the amount of grinding bodies for air flow crushing is controlled to be 200g (20% of the upper limit of the grinding bodies), and the air pressure for air flow crushing is controlled to be 0.3MPa to obtain a crushed product, and the specific surface area of the obtained crushed product is 0.7m 2 / g.

[0154] S3, 200g of the crushed product is mixed with 0.4g of Al2O3, and secondary sintering is performed in oxygen at a temperature of 650℃ to obtain a secondary sintered product.

[0155] S4, after the secondary sintered product is cooled, a positive electrode material is obtained by sieving.

[0156] Example 15:

[0157] A positive electrode material, a preparation method thereof comprises:

[0158] S1, 600g of Ni 0.67 Co 0.05 Mn 0.28 (OH)2, 285g of LiOH and 2.1g of WO3 are uniformly mixed to obtain a mixture, and the mixture is placed in an oxygen atmosphere furnace for primary sintering, which is three-stage sintering at 500℃, 850℃ and 920℃, and then is rapidly annealed and cooled at a cooling rate of 8℃ / min to obtain a primary sintered product.

[0159] S2, the primary sintered product is subjected to air flow crushing, the amount of grinding bodies for air flow crushing is controlled to be 600g (60% of the upper limit of the grinding bodies), and the air pressure for air flow crushing is controlled to be 0.65MPa to obtain a crushed product, and the specific surface area of the obtained crushed product is 0.8m 2 / g.

[0160] S3, 200g of the crushed product is mixed with 0.3g of ZrO2, and secondary sintering is performed in an oxygen atmosphere furnace at a temperature of 700℃ to obtain a secondary sintered product.

[0161] S4, after the secondary sintered product is cooled, a positive electrode material is obtained by sieving.

[0162] Example 16:

[0163] The difference from Example 3 is that in S1, the amount of WO3 is 3.0 g; in S2, the amount of grinding bodies for jet milling is controlled to 600 g (60% of the upper limit of grinding bodies), and the air pressure for jet milling is controlled to 0.65 MPa.

[0164] Example 17:

[0165] The difference from Example 3 is that in S1, the amount of WO3 is 1.5 g; in S2, the amount of grinding bodies for jet milling is controlled to 200 g (20% of the upper limit of grinding bodies).

[0166] Example 18:

[0167] The difference from Example 3 is that in S1, the amount of WO3 is 5.4 g; in S2, the amount of grinding bodies for jet milling is controlled to 200 g (20% of the upper limit of grinding bodies), and the air pressure for jet milling is controlled to 0.30 MPa.

[0168] Comparative Example 1:

[0169] The difference from Example 1 is that in S1, 1.8 g of WO3 is not added.

[0170] Comparative Example 2:

[0171] The difference from Example 2 is that in S1, 1.3 g of B2O3 is not added.

[0172] Comparative Example 3:

[0173] The difference from Example 3 is that in S1, 2.4 g of WO3 is not added.

[0174] Comparative Example 4:

[0175] The difference from Example 3 is that in S1, 2.4 g of WO3 is not added; in S2, the temperature for secondary sintering is 600℃.

[0176] Comparative Example 5:

[0177] A positive electrode material, a preparation method thereof comprises:

[0178] S1, 200 g of Ni 0.90 Co 0.05 Al 0.05 O, 86 g of LiOH·H2O with a D50 of 10.4 μm is added to a mixing container, 3 g of H3BO3 and 1.2 g of LiF are added at the same time, and they are uniformly mixed to obtain a mixture, the mixture is placed in an oxygen atmosphere furnace for primary sintering, the temperature for primary sintering is 550℃, the time for primary sintering is 6 h, and the heating rate is 5℃ / h, to obtain a primary sintering product.

[0179] S2, after cooling, the primary sintering product is crushed to obtain a crushed product.

[0180] S3, 100 g of the crushed material and 14.8 g of Li2CO3 with a D50 of 4.2 μm were added to a mixing container, 1.7 g of niobium pentoxide was added, and they were uniformly mixed to obtain a mixture, and the mixture was placed in an oxygen atmosphere furnace for secondary sintering, the temperature of the secondary sintering was 900 ℃, the time of the primary sintering was 8 h, and the heating rate was 5 ℃ / h, to obtain a secondary sintering product.

[0181] S4, after cooling, the secondary sintering product was crushed to obtain a positive electrode material.

[0182] Comparative Example 6:

[0183] A positive electrode material, the preparation method comprising:

[0184] S1, 200 g of Ni 0.90 Co 0.08 Al 0.02 O, 73 g of LiOH·H2O with a D50 of 6.5 μm was added to a mixing container, 2 g of SrCO3 and 1.4 g of NH4F were added, and they were uniformly mixed to obtain a mixture, and the mixture was placed in an oxygen atmosphere furnace for primary sintering, the temperature of the primary sintering was 650 ℃, the time of the primary sintering was 4 h, and the heating rate was 5 ℃ / h, to obtain a primary sintering product.

[0185] S2, after cooling, the primary sintering product was crushed to obtain a crushed material.

[0186] S3, 100 g of the crushed material and 19.5 g of Li2CO3 with a D50 of 5 μm were added to a mixing container, 3.4 g of niobium pentoxide was added, and they were uniformly mixed to obtain a mixture, and the mixture was placed in an oxygen atmosphere furnace for secondary sintering, the temperature of the secondary sintering was 950 ℃, the time of the primary sintering was 10 h, and the heating rate was 5 ℃ / h, to obtain a secondary sintering product.

[0187] S4, after cooling, the secondary sintering product was crushed to obtain a positive electrode material.

[0188] Examples 1-15 and Comparative Examples 1-6 also provide a positive electrode sheet, the preparation method comprising: the obtained positive electrode material, conductive carbon black, and binder PVDF (polyvinylidene fluoride) were mixed in a mass ratio of 80:10:10, NMP (N-methyl pyrrolidone) was added to make a uniform slurry, which was coated on a copper foil, dried in an oven, and then rolled under a pressure of 10 MPa, and then cut into a circular electrode sheet with a diameter of 14 mm.

[0189] The positive electrode material or the positive electrode sheet of Examples 1-15 and Comparative Examples 1-6 were tested for performance by the following method.

[0190] The number ratio test of particles with micro-cracks in the positive electrode material: first, take the powder positive electrode material, mix the powder positive electrode material with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 80:10:10, then add NMP (N-methyl pyrrolidone) to make a uniform slurry, coat it on an aluminum foil, dry it in an oven, make a pole piece, take the pole piece as a sample, according to the standardization process of section sample preparation, use electron microscope to focus ion beam into small size ion beam to bombard the surface of the sample, realize the peeling of the sample. After peeling, the sample is tested by scanning electron microscope (SEM), under the field of view of 3k or 5k, the field of view of different areas is counted, the number ratio of positive electrode material particles with micro-cracks to the total number of positive electrode material particles is counted, and the number ratio is used to represent the number of micro-cracks. The test results of the present application are the statistical results obtained by randomly selecting the cross sections of about 300 positive electrode material particles in the SEM image as samples. The SEM test requires random sampling of the positive electrode material, random selection of the area, and the SEM image obtained by the test can represent the average level of the measured positive electrode material. Since there is no rolling of the pole piece in the process of making the pole piece in the present test method, the number ratio of the micro-cracks obtained by the test can be regarded as the number ratio of the micro-crack particles of the positive electrode material in the powder state.

[0191] The number ratio test of particles with micro-cracks in the positive electrode material in the positive electrode sheet (the number ratio of particles with micro-cracks in the positive electrode material after 10Mpa rolling): first, take the powder positive electrode material, mix the powder material with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 80:10:10, then add NMP (N-methyl pyrrolidone) to make a uniform slurry, coat it on an aluminum foil, dry it in an oven, roll it under the pressure of 10Mpa, make a pole piece, take the pole piece as a sample, according to the standardization process of section sample preparation, use electron microscope to focus ion beam into small size ion beam to bombard the surface of the sample, realize the peeling of the sample. After peeling, the sample is tested by scanning electron microscope (SEM), under the field of view of 3k or 5k, the field of view of different areas is counted, the number ratio of positive electrode material particles with micro-cracks to the total number of positive electrode material particles is counted, and the number ratio is used to represent the number of micro-cracks. The test results of the present application are the statistical results obtained by randomly selecting the cross sections of about 300 positive electrode material particles in the SEM image as samples. The SEM test requires random sampling of the positive electrode material, random selection of the area, and the SEM image obtained by the test can represent the average level of the measured positive electrode material.

[0192] Particle micro-crack particle number ratio test after 100 cycles of the positive electrode material: the electrode sheet in the button cell after 100 cycles is taken out, and the ion beam is focused into a small size ion beam to hit the surface of the sample, so as to realize the peeling of the sample. The peeled sample is tested by scanning electron microscope (SEM), and the field of view of different regions is counted under the field of view of 3k or 5k, the proportion of the positive electrode material particles with micro-cracks in the total number of positive electrode material particles is counted, and the proportion is used to represent the number of micro-cracks. The test results of the present application are the statistical results obtained by randomly selecting about 300 cross sections of positive electrode material particles in the SEM image as samples. The proportion of the number of positive electrode material particles with micro-cracks in the total number of positive electrode material particles obtained by the test is the particle micro-crack particle number ratio of the positive electrode material after 100 cycles. According to different causes, the above micro-cracks can be divided into three types: (1) growth micro-crack, that is, the crack extending from the surface of the material to the interior of the material during the growth of the positive electrode material particle, or the crack in the interior of the particle; (2) crushing micro-crack: the crack extending from the surface of the particle to the interior of the material, or the crack in the interior of the particle, which is generated during the crushing process of the positive electrode material particle; (3) cycle crack: the crack observed by scanning electron microscope after disassembly and testing after the button cell is assembled and cycled, which is mainly caused by intergranular displacement.

[0193] Strain rate test of the positive electrode material: the XRD diffractometer is used to test the positive electrode material, the scanning speed is 1° / min, the step size is 0.005°, the scanning range is 10° to 70°, the diffraction peak of the material is obtained, and the strain value of the positive electrode material is calculated and output by XRD refinement diffraction peak. In the XRD refinement process, the calculation of micro-strain and grain size is one of the key steps. First, according to Bragg equation and Scherrer formula, the calculation formula is changed to: By analyzing βs and βp, the widening degree of FWHM caused by strain can be obtained. In the Rietveld refinement process, the pseudo-Voigt function is used to represent the half-width (FWHM) of the diffraction peak shape function, which is divided into Gaussian and Lorentzian two parts, which respectively contain the parameters related to micro-strain and grain size. The specific formula is: Gaussian part: Lorentzian part: Where, U, Y are parameters related to micro-strain, X, P are parameters related to grain size, and these parameters correspond to the peak shape correction parameters GU, LY, LX and GP in the refinement process. Therefore, the four parameters can be derived by refining the peak shape of the measured XRD data, and then substituted into the corresponding calculation formula, so as to obtain the micro-strain parameter.

[0194] Gas production test of the positive electrode material: the positive electrode material is assembled into a soft pack battery of 2 Ah, stored in a 60°C high temperature oven for 7 days, and the gas production is tested by the drainage method. The obtained gas production is the 7-day gas production of the soft pack battery per unit mass, and the unit is mL / g. Specifically, the primitive soft pack battery is used to evaluate the storage gas production performance of the positive electrode material, and the specific method is as follows: the positive electrode material, PVDF, SP and CNT are weighed according to the mass ratio of 97.0:1.0:1.5:0.5, NMP is added according to the solid content of 50%, and a thick slurry is prepared. The slurry is uniformly coated on an aluminum foil using a doctor blade, dried in an 80°C oven, and then rolled, cut into a positive electrode sheet of 4 cm x 8 cm. The graphite negative electrode, SP, CMC and SBR are weighed according to the mass ratio of 96:1.0:1.2:1.8, dispersed into a slurry, coated on a copper foil, and cut into a negative electrode sheet of 4 cm x 8 cm. The positive electrode sheet and the negative electrode sheet are assembled into a primitive soft pack battery, and the capacity of the soft pack battery is controlled to be 2 Ah. After formation, it is charged to 50 SOC%, and then stored in a 60°C oven for 7 days. The volume difference before and after storage is tested by the drainage method, and the volume change rate is calculated, which is the gas production index.

[0195] Specific surface area test of the positive electrode material: the specific surface area is tested by using a U.S. Micromeritics instrument (equipment model: Tristar3020). The sample is degassed at 300°C for 1 h under vacuum before testing. For example, the specific surface area of the positive electrode material can be tested by the following steps: the total mass of the empty sample tube and rubber plug is weighed as m1; 3 g of sample is taken and added to the sample tube through a long neck funnel; the sample tube is degassed at 300°C for 1 h under vacuum, and then the total mass of the sample tube + rubber plug + sample is weighed as m2 after cooling; the sample mass m = m2-m1; the sample is placed in liquid nitrogen, and the nitrogen adsorption amount V of the sample is measured at 6 relative pressures P / P0 to obtain the adsorption isotherm. Among them, P / P0 is set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30; the specific surface area is obtained according to the adsorption isotherm.

[0196] Tap density test of the positive electrode material: the tap density of the positive electrode material is tested by using a Dandong Betatech instrument (equipment model BT-303), the vibration frequency is 3000 times / min, the vibration time is 1 min, and the vibration amplitude is 3 mm±0.1 mm.

[0197] Powder compaction density test of the positive electrode material: the powder compaction density of the positive electrode material is tested by using a compaction density instrument (equipment model: U.S. carver 4350). 1 g of sample is placed in the mold, and the compaction density is obtained under a pressure of 3T tons for 30 s.

[0198] The powder conductivity test method is: under the pressure of 20KN, the test is carried out by the probe method of powder conductivity instrument. For example, the powder conductivity of the positive electrode material can be tested by the following steps: using resistivity tester (Suzhou crystal lattice electron ST-2255A), taking 5g powder sample, using electronic press to constant pressure to 20KN, maintaining 15-25s. The sample is placed between the electrodes of the tester, the sample height h (cm), the voltage at both ends U, the current I, the area S of the powder after pressing =3.14cm 2 , the powder electronic conductivity is calculated according to the formula σ = h / (S * R) / 1000.

[0199] Particle size test of positive electrode material: the particle size D10, D50 and D90 of positive electrode material based on volume distribution are tested by Malvern laser particle size tester MS 3000, and the particle size distribution width L = (D90-D10) / D50 is calculated. For example, the particle size of the positive electrode material can be characterized by the following steps: take an appropriate amount of sample, pour into pure water for ultrasonic dispersion, ultrasonic time is 30s, ultrasonic power is 240w, then drop an appropriate amount of sodium hexametaphosphate into the dispersed sample and stir uniformly, then pour into the sample cell of the detection equipment, wait for 10S, then click start to test the sample.

[0200] Cell size test of positive electrode material: XRD diffractometer is used to test the positive electrode material, the peak intensity of 003 and 104 diffraction peak is obtained, I003 / I104 is calculated, 003 and 104 related half peak width is obtained, and Dp is calculated by Bragg formula.

[0201] Orientation test of primary particles of grain: equipment: backscattered electron diffractometer (EBSD) equipped on scanning electron microscope, model Gemini SEM300. Method: observing and measuring the color of single primary particle in the grain can determine whether it is a single grain containing all primary particles with the same orientation in the grain. When the color of all primary particles in the grain is the same, it is determined that the orientation of all primary particles in the grain is the same.

[0202] Secondary battery electrochemical cycle performance test: the positive electrode material is mixed with conductive carbon black and binder PVDF (polyvinylidene fluoride) at a mass ratio of 80:10:10, then NMP (N-methyl pyrrolidone) is added to make a uniform slurry, which is coated on an aluminum foil, dried in an oven, and rolled under a pressure of 10 MPa. The lithium ion battery is assembled according to the CR2025 type button cell in the industry, the separator is Cellgard separator, the electrolyte is 1 mol / L LiPF6 solution with EC / PC / DEC as solvent, and the anode is lithium sheet. The entire assembly process is assembled in an argon-filled glove box, and the oxygen content and moisture content in the glove box are controlled to be below 0.5 ppm. The temperature is 25℃±1℃, the voltage range of charge and discharge cycle is 3.0V to 4.4V, the first charge and discharge current is 0.1C (20mAh / g), and the cycle charge and discharge rate is 0.5C charge / 1C discharge under the condition of 100 week cycle test.

[0203] The test results of the above test methods are shown in Figures 4 to 15 and Table 1.

[0204] Referring to Figures 4, 5 and 6, taking Example 1 as an example, the SEM analysis in the above test method is taken as an example, and the observed field is taken as an example. The positive electrode material with cracks is shown by arrows in the figure. Overall, the crack content caused by grain growth before crushing and rolling and the crack content generated after crushing and rolling are both less.

[0205] Referring to Figures 7, 8 and 9, taking Example 2 as an example, the SEM analysis in the above test method is taken as an example, and the observed field is taken as an example. The positive electrode material with cracks is shown by arrows in the figure. Overall, the crack content caused by grain growth before crushing and rolling and the crack content generated after crushing and rolling are both less.

[0206] Referring to Figures 10, 11 and 12, taking Comparative Example 1 as an example, and taking the observed field as an example, the positive electrode material with cracks is shown by arrows in the figure. Overall, the crack content is more.

[0207] Referring to Figures 13, 14 and 15, taking Comparative Example 4 as an example, and taking the observed field as an example, the crack content is more overall, and more cracks can be observed on a single positive electrode material.

[0208] Table 1. Performance test results of positive electrode materials of Examples 1-18 and Comparative Examples 1-6 of the present application

[0209] In the positive electrode materials prepared in embodiments 1-18, the number percentage of positive electrode material particles with micro-cracks is in the range of 1.5% to 13%. After being made into electrode sheets or secondary batteries and participating in charge and discharge cycles, due to the stable particle structure of the positive electrode material, the micro-cracks are few, and the structural change during the cycle is small, so the number percentage of newly added micro-crack particles after the cycle is also relatively small. At the same time, from the gas production, it can be seen that the positive electrode materials prepared in embodiments 1-18 have better high-temperature cycle stability, and the gas production is obviously lower and the capacity is higher, which shows that controlling the number percentage of positive electrode materials with micro-cracks in the positive electrode material in the above range can reduce the gas production behavior of the material in actual application, thereby helping to improve the storage gas and cycle gas problems of the positive electrode material under high pressure conditions.

[0210] Compared with embodiments 1-3, comparative examples 1-3 do not add corresponding additives (low-melting-point transition metal compounds) during preparation, which causes the positive electrode materials obtained in comparative examples 1-3 to have significantly more micro-cracks before rolling (i.e., during growth) and after rolling. The number percentage of positive electrode material particles with micro-cracks exceeds the preset range, and too many micro-cracks will continuously intensify the infiltration of the electrolyte into the positive electrode material particles, and even cause the electrolyte to continuously erode from the outside of the material to the inside of the particles, thereby causing a large number of side reactions to occur, resulting in difficult-to-control gas production deterioration and other adverse effects, thereby making these positive electrode materials have significantly higher gas production and lower capacity when used in batteries, which is not conducive to the cycle stability and safety of the secondary battery.

[0211] Based on comparative example 3, comparative example 4 further reduces the temperature of the primary sintering, which causes the growth of the positive electrode material to be further limited, resulting in more cracks or holes in the positive electrode material particles during growth, and the number of positive electrode material particles with micro-cracks further increases, and its gas production behavior is also significantly more deteriorated, which is not conducive to the cycle stability and safety of the secondary battery.

[0212] Comparative examples 5 and 6 both use high-nickel positive electrode materials, so they have relatively high capacity. However, comparative examples 5 and 6 only perform surface treatment (coating and doping) on the material, do not add corresponding additives (low-melting-point transition metal compounds), and do not perform multi-stage sintering and rapid annealing treatment. The number percentage of positive electrode material particles with micro-cracks in the positive electrode material obtained is still high, and the gas production in the battery has not been improved well, which shows that micro-cracks are intrinsic defects of positive electrode material particles, and methods such as surface treatment that do not directly intervene in the formation of micro-cracks cannot effectively solve the continuous gas production problem caused by micro-cracks.

[0213] The above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application, and although the present application is explained in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or equivalent replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises a plurality of particles, at least part of the particles have micro-cracks, the size of the micro-cracks is 0.5nm to 30nm, the number ratio of the particles with the micro-cracks in the total number of particles of the positive electrode material is 1.5% to 13%, and the testing method of the number ratio is as follows: The positive electrode material is subjected to scanning electron microscope test to obtain a scanning electron microscope image, 300 positive electrode material particles are randomly selected in the scanning electron microscope image, the number of positive electrode material particles with the micro-cracks is counted, and the number ratio is obtained.

2. The positive electrode material of claim 1, wherein, The positive electrode material satisfies any one of the following conditions: (1) the number ratio of the particles with the micro-cracks in the total number of particles of the positive electrode material is 1.5%, 2%, 4%, 5%, 8%, 10%, 13% or within a range formed by any two of the above values; (2) the number ratio of the particles with the micro-cracks in the total number of particles of the positive electrode material is 3% to 8%; (3) the number ratio of the particles with the micro-cracks in the total number of particles of the positive electrode material is 4% to 8%.

3. The positive electrode material of claim 1, wherein, The positive electrode material comprises at least one of W, B and Sr.

4. The positive electrode material of claim 1, wherein, The micro-cracks are located in the interior of the particles and communicate with the surface of the particles.

5. The cathode material of claim 1, wherein, The strain rate of the positive electrode material is 0.035% to 0.13%.

6. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the positive electrode material is a single-crystal positive electrode material; (2) the particles comprise one or more primary particles, the orientations of all the primary particles in at least one of the particles are the same, and the average particle size of the primary particles is 1μm to 5μm.

7. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the specific surface area of the positive electrode material is 0.5 m 2 / g to 1 m 2 / g; (2) the volume particle size distribution width L of the positive electrode material is greater than or equal to 1.

0.

8. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the tap density of the positive electrode material is greater than or equal to 1.8 g / cm3 3 ; (2) the powder compaction density of the positive electrode material at 3T tonnage is greater than or equal to 3.0 g / cm 3 .

9. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the powder electrical conductivity of the positive electrode material is greater than or equal to 1 x 10 -4 S / cm; (2) the unit cell size of the positive electrode material is 80nm to 110nm.

10. The cathode material of claim 1, wherein The positive electrode material satisfies at least one of the following conditions: (1) the positive electrode material has a general formula of Li a Ni b Co c M (1-b-c) O2, wherein 0.95≤a≤1.2, 0 (2) the general formula of the positive electrode material is Li a Ni b Co c M (1-b-c) O2, wherein 0.95≤a≤1.2, 0 b+c≤1, M includes M1 elements and M2 elements, the M1 elements are Mn, and the M2 elements include at least one of W, Sr, and B.

11. The cathode material of claim 1, wherein, The positive electrode material comprises an inner core and a coating layer, the coating layer is arranged on at least part of the surface of the inner core, and the coating layer comprises Li x N y O2, wherein 0≤x≤5, N is one or more of Zr, Ti, Al, W, Nb, La, Mo and Y.

12. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the difference between the number ratio of the particles with the micro-cracks after the positive electrode material is rolled at 10Mpa and the number ratio of the particles with the micro-cracks before rolling is 0.8% to 3.6%. (2) the difference between the number ratio of the particles with the micro-cracks after the positive electrode material is rolled at 10Mpa and the number ratio of the particles with the micro-cracks after cycling is 0.2% to 3.0%.

13. The cathode material of claim 1, wherein, The positive electrode material satisfies at least one of the following conditions: (1) the number ratio of the particles with the micro-cracks after the positive electrode material is rolled at 10Mpa is 1.6% to 13%; (2) the number ratio of the particles with the micro-cracks after the positive electrode material is cycled for 100 times is 4.2% to 15.4%.

14. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, characterized by The positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 13.

15. A secondary battery characterized by comprising: The positive electrode sheet according to claim 14 or the positive electrode material according to any one of claims 1 to 13.

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