Positive electrode material and preparation method therefor, and secondary battery

Abstract

A positive electrode material and a preparation method therefor, and a secondary battery. The positive electrode material is a lithium-nickel-cobalt-oxide-based composite oxide. In an XRD pattern of the positive electrode material, the characteristic peak of the (104) crystal plane comprises, after peak separation, a (104)-Kα1 diffraction peak and a (104)-Kα2 diffraction peak, wherein the separation degree of the (104)-Kα1 diffraction peak and the (104)-Kα2 diffraction peak is α, and 0.7≤α≤2.0. The positive electrode material has a proper particle size, good particle strength and a sufficient number of internal defects, which is beneficial for reducing the polarization phenomenon of the positive electrode material, allowing a secondary battery based on the positive electrode material to have relatively good cycling stability and rate capability.

Description

Positive electrode material and preparation method thereof, and secondary battery Technical Field

[0001] The present application relates to the technical field of positive electrode materials, and in particular to a positive electrode material, a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium-ion batteries are widely used in laptops, mobile phones, digital products, and other fields due to their high energy density, good safety, long cycle life, and environmental friendliness. The development of high-capacity and high-voltage cathode materials will help increase the energy density of lithium-ion batteries and meet more market demands.

[0003] It's generally believed that increasing the nickel content in ternary cathode materials can improve their capacity. However, this increase in nickel content can lead to increased side reactions between the material and the electrolyte. Furthermore, as charge and discharge cycles increase, the expansion and contraction of the cathode material's grains and internal stress increase, leading to cracking and pulverization of the cathode material particles, which in turn affects the battery's cycle life and safety. Furthermore, existing cathode materials have relatively few internal defects, and larger particle sizes hinder the diffusion of lithium ions during charge and discharge, leading to severe electrochemical and concentration polarization phenomena and compromising the battery's electrical performance.

[0004] Summary of the Invention

[0005] In order to solve at least one of the above problems, it is necessary to provide a positive electrode material.

[0006] In addition, it is also necessary to provide a secondary battery having the above-mentioned positive electrode material.

[0007] In a first aspect, the present application provides a positive electrode material, wherein the positive electrode material is a lithium nickel cobalt oxide composite oxide. In an XRD pattern of the positive electrode material, a characteristic peak of the (104) crystal plane, after peak separation, includes a (104)-Kα1 diffraction peak and a (104)-Kα2 diffraction peak, and the separation degree of the (104)-Kα1 diffraction peak and the (104)-Kα2 diffraction peak is α, 0.7≤α≤2.0.

[0008] In a second aspect, the present application provides a method for preparing a positive electrode material, the preparation method comprising: mixing nickel cobalt hydroxide and a lithium source to obtain a mixture; and sintering the mixture once and crushing it to obtain the positive electrode material. The primary sintering comprises N stepped temperature rise sections and M constant temperature sections, where N is greater than or equal to 3 and M is greater than or equal to 1. The stepped temperature rise section comprises n temperature rise sub-stages, where n is greater than or equal to 2, the temperature rise rate of the nth temperature rise sub-stage is greater than the temperature rise rate of the first temperature rise sub-stage of the same stepped temperature rise section, and the temperature rise rate of the nth temperature rise sub-stage is non-negative.

[0009] In a third aspect, the present application provides a secondary battery, which includes the positive electrode material according to the first aspect or the positive electrode material prepared by the preparation method according to the second aspect.

[0010] In the present application, the separation α of the above two diffraction peaks of the positive electrode material is within a preset range, which is beneficial to controlling the particle size of the positive electrode material, shortening the diffusion distance of lithium ions, and reducing the risk of deterioration of capacity or rate performance in secondary batteries. At the same time, the positive electrode material maintains good particle strength, thereby improving the positive electrode material's resistance to cracking and pulverization under high rolling pressure or high voltage window conditions, thereby improving the cycle performance of the positive electrode material. On the other hand, the separation α of the above two diffraction peaks of the positive electrode material is within a preset range, which is also beneficial to increase the internal defects of the positive electrode material particles, enrich the diffusion path of lithium ions and increase the diffusion rate of lithium ions, so that the degree of lithium intercalation and deintercalation inside and on the surface of the positive electrode material particles is closer, thereby improving the polarization phenomenon between the surface and inside of the positive electrode material particles. Therefore, the present application controls the particle size of the positive electrode material by controlling the separation α of the above two diffraction peaks within a preset range, while improving the particle strength of the positive electrode material and increasing the internal defects of the material, so that the positive electrode material has better cycle stability and rate performance.

[0011] In the present application, in the preparation method of the positive electrode material: by setting the above-mentioned stepped heating section and constant temperature section during a single sintering process, in the stepped heating section, the heating rate of the first sub-stage is relatively low, which is conducive to maintaining a stable growth rate of the particles, thereby making the size of the particles more uniform, and the heating rate of the last sub-stage is relatively high, which is conducive to increasing the particle growth rate and increasing the internal defects of the particles; and in the constant temperature section, some of the internal defects of the particles can be repaired as the single crystal particles grow, and the intergranular stress inside the particles is gradually released, which is conducive to improving the particles' ability to resist cracking and pulverization. Therefore, the preparation method of the positive electrode material provided in the present application can control the particle size, particle strength and internal defects of the positive electrode material, thereby helping to improve the cycle stability and rate performance of the positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG1 is a schematic structural diagram of a secondary battery provided in the present application during discharge.

[0013] FIG2 is a schematic structural diagram of the secondary battery provided in this application during charging.

[0014] FIG3 is a temperature curve diagram of a primary sintering in the method for preparing the positive electrode material provided in Example 1 of the present application.

[0015] FIG4 is a schematic diagram of the peak separation of the characteristic peaks of the (104) crystal plane of the positive electrode material provided in Example 1 of the present application.

[0016] Description of Main Component Symbols Positive electrode sheet 110 Positive electrode current collector 111 Positive electrode active material layer 112 Negative electrode sheet 120 Negative electrode current collector 121 Negative electrode active material layer 122 Separator 130 Lithium ion 140 DETAILED DESCRIPTION

[0017] In order to better understand the technical solution of the present application, the present application is further described in detail below. It should be clear that the following embodiments are only embodiments of a part of the present application, rather than all embodiments. The following embodiments are only simple examples of the present application and do not represent or limit the scope of protection of the present application. The scope of protection of the present application is subject to the claims. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0018] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0019] In order to easily understand the present invention, specific terms are appropriately defined in this application. Unless otherwise defined herein, scientific terms and technical terms used in the present invention have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0020] The present application provides a positive electrode material, which is a lithium nickel cobalt oxide composite oxide. In the X-ray diffraction (XRD) pattern of the positive electrode material, the characteristic peak of the (104) crystal plane includes a (104)-Kα1 diffraction peak and a (104)-Kα2 diffraction peak after peak separation, and the separation degree of the (104)-Kα1 diffraction peak and the (104)-Kα2 diffraction peak is α, 0.7≤α≤2.0. For example, α can be 0.7, 0.75, 0.8, 0.82, 0.85, 0.88, 0.90, 0.95, 0.98, 1.0, 1.05, 1.08, 1.1, 1.15, 1.2, 1.3, 1.4, 1.58, 1.6, 1.8, 2.0, or any value within the range of any two of the above values.

[0021] In the present application, the separation α of the above two diffraction peaks of the positive electrode material is within a preset range, which is beneficial to controlling the particle size of the positive electrode material, shortening the diffusion distance of lithium ions, increasing the diffusion coefficient of lithium ions, and improving the electrochemical polarization and concentration polarization of the positive electrode material. This can improve the phenomenon that the charging internal resistance (DCR) of the secondary battery increases at a high state of charge (SOC) or the discharge internal resistance increases at a low state of charge. The lower internal resistance is conducive to maintaining a higher capacity of the secondary battery. Therefore, the above scheme can reduce the risk of deterioration of the capacity or rate performance of the secondary battery by setting the separation α within a preset range. At the same time, the positive electrode material maintains good particle strength, thereby improving the anti-cracking and anti-powdering ability of the positive electrode material under high rolling pressure or high voltage window conditions, thereby improving the cycle performance of the positive electrode material. On the other hand, the separation α of the above two diffraction peaks of the positive electrode material is within a preset range, which is also beneficial to increase the internal defects of the positive electrode material particles, enrich the diffusion path of lithium ions and increase the diffusion rate of lithium ions, so that the degree of lithium intercalation and deintercalation inside and on the surface of the positive electrode material particles is closer, thereby improving the polarization phenomenon between the surface and inside of the positive electrode material particles. Therefore, the positive electrode material provided in the present application has better cycle stability and rate performance by controlling particle size, improving particle strength and increasing internal defects of the material.

[0022] In this field, the separation degree α of the (104)-Kα1 diffraction peak and the (104)-Kα2 diffraction peak after peak separation is related to the peak position Q and the half-maximum width FWHM of (104)-Kα1 and (104)-Kα2:

[0023] Therefore, when the separation α between the two diffraction peaks is too small, for example, less than 0.7, it means that the half-width at half maximum of the two diffraction peaks is too large while the peak positions are basically constant. According to the Scherrer equation of the XRD mechanism, the particle size of the positive electrode material is too small, which further means that the number of primary particles constituting the secondary particles increases, that is, the number of grain boundaries increases. This phenomenon can lead to a decrease in particle strength, making the secondary particles more susceptible to breakage and pulverization during the electrode rolling and particle charging and discharging processes, ultimately affecting the material's cycling performance. This phenomenon can also lead to an increase in the number of internal voids and pore structures in the positive electrode material particles, resulting in a decrease in the material's tap density. In addition, when the primary particle size of the material is smaller, the lattice ordered structure is also shorter, and defects such as dislocations and stacking faults inside the lattice are more easily improved through atomic rearrangement in high-temperature solid-phase reactions and are more easily discharged to the outside of the grains; at the same time, the smaller primary particle size is generally caused by the lower temperature of the high-temperature solid-phase reaction. The grain production is slower at low temperatures and is less likely to introduce internal defects; therefore, when the primary particle size of the material is smaller, the number of defects inside the grains will also decrease, resulting in a reduction in the lithium ion diffusion path, resulting in an increase in the difference in the degree of lithium insertion and extraction between the surface and interior of the positive electrode material particles, resulting in an aggravated polarization phenomenon of the positive electrode material and a decrease in the cycle life of the positive electrode material.

[0024] On the other hand, when the separation α of the two diffraction peaks is too large, for example, greater than 2.0, the particle size of the positive electrode material is too large, the lithium ion diffusion path is extended, and it is not conducive to the migration of lithium ions within the particles. This leads to increased concentration polarization and electrochemical polarization of the positive electrode material, resulting in a deterioration of the capacity and rate performance of the secondary battery. Therefore, when the separation α of the two diffraction peaks is controlled within the above range, the positive electrode material can have an appropriate particle size, good particle strength, and more internal defects, thereby having better cycle performance and capacity rate performance.

[0025] In some embodiments, the lithium nickel cobalt oxide-based composite oxide includes lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide.

[0026] In some embodiments, the tap density of the cathode material is T g / cm 3 , the median particle size D of the positive electrode material 50 Pμm, 1≤T-(1.04α-0.25α 2 +0.004P 2 -0.02P)≤1.5.

[0027] In the related art, the tap density T and particle size D are generally controlled. 50 The relationship between the cycle stability and rate performance of the positive electrode material is not considered, and the influence of the separation degree α on the electrochemical performance of the positive electrode material is not considered, which makes it difficult to balance the electrical performance indicators. For example, in order to obtain a higher energy density, a higher tap density and a lower particle size D are selected.50 When the positive electrode material is used, the rate performance of the positive electrode material is low; and in order to obtain higher rate performance, a lower tap density and a higher D 50 When the positive electrode material is used, the energy density and cycle stability of the positive electrode material are low.

[0028] On the basis of proposing that the separation degree α is controlled within a preset range, the present application further proposes the tap density T and particle size D of the positive electrode material. 50 When the relationship between the three is within the above range, a higher tap density and a lower D 50 When the positive electrode material is used, the separation degree α is controlled to be appropriately increased within its preset range (not higher than 2.0), so that the number of internal defects of the positive electrode material particles is large and the lithium ion diffusion path is increased, thereby compensating for or improving the rate performance of the positive electrode material; and in order to obtain higher rate performance, a lower tap density and a larger D 50 When the positive electrode material is used, the separation degree α is controlled to be appropriately reduced within its preset range (not less than 0.7). In this way, the particle size of the positive electrode material is reduced while still maintaining good particle strength, which can reduce the risk of cracking or pulverization of the positive electrode material under high roller pressure or high voltage window, thereby compensating for or improving the cycle stability of the positive electrode material. Therefore, in the above scheme, by controlling the tap density T and particle size D of the positive electrode material, the positive electrode material can be further improved. 50 When the relationship between the three is within the above preset range, the energy density, particle strength and defect level of the material can be balanced, so that the positive electrode material has both better cycle stability and rate performance.

[0029] In some embodiments, the gram capacity of the positive electrode material is C mAh / g, and the molar ratio of Ni element in all metal elements except Li element in the positive electrode material is n Ni ,125≤C-(100n Ni -α 2 P)≤135. Controlling the positive electrode material to satisfy the above relationship can improve the particle strength of the positive electrode material and reduce the polarization phenomenon of the positive electrode material, so that the positive electrode material has both better specific capacity and cycle stability.

[0030] In the related art, the positive electrode material products with different gram capacities are generally obtained by controlling the Ni element content nNi, but the separation degree α and particle size D are not fully realized. 50 The impact on other electrochemical properties of the positive electrode material. For example, in order to obtain higher energy density, a higher Ni content and lower D 50 When the positive electrode material is used, the cycle performance and high temperature gas production performance of the positive electrode material are reduced. This application uses Ni content nNi, separation degree α, particle size D 50Based on the solution of this application, a higher Ni content is selected to obtain a multi-element material with higher energy density. In order to control the value of the relationship within the preset range, it is necessary to increase the separation degree α. 2 and particle size D 50 The product of separation degree α and particle size D 50 The increase of separation degree α (not higher than 2.0) means the decrease of half-height width, that is, the increase of primary particle size of the material and the decrease of the number of grain boundaries. The stress caused by the expansion / contraction of multi-material grains during the charge and discharge cycle is reduced, the particle strength is enhanced, and the cyclic performance of the material is guaranteed; the particle size D 50 When the particle size increases, the specific surface area of ​​the material is greatly reduced, the side reaction with the electrolyte is reduced, and the cycle stability is improved, which helps to overcome the shortcomings of the related technology. In addition, it should be noted that the separation degree α is closely related to the particle size D 50 You can also increase one and decrease the other, just need to ensure α 2 The value of P is increased, and it can be seen that the separation degree α is a square relationship. While ensuring the improvement of gram capacity, it is more critical to ensure the performance of circulation and storage. Therefore, in the above scheme, by controlling the gram capacity C and particle size D of the positive electrode material 50 The relationship between the three, namely, the separation degree α, is within the above-mentioned preset range, which can balance the material's gram capacity, primary particle size, particle strength, specific surface area, etc., so that the positive electrode material has both better gram capacity and cycle stability.

[0031] In some embodiments, the cycle life of the positive electrode material is L, 1800≤L-(2245α-5000n Ni +100P)≤2400. Controlling the positive electrode material to satisfy the above relationship can improve the particle strength of the positive electrode material and reduce the polarization phenomenon of the positive electrode material, so that the positive electrode material has both excellent cycle stability and gram capacity.

[0032] In the related art, generally by controlling D 50 The size and Ni content of the cathode materials are used to obtain cathode materials with different cycle life, but the effect of separation degree α on the electrochemical properties such as cycle life of the cathode materials is not fully realized. For example, in order to obtain a longer cycle life, a lower Ni content and a higher D 50 When the positive electrode material is used, the capacity and rate performance of the positive electrode material are reduced. In the present invention, the Ni content nNi, separation degree α, particle size D 50 The above relationship is constructed and the above preset range is set to balance the electrochemical performance in various aspects. Based on the solution of this application, in order to obtain a longer cycle life, a lower Ni content and a higher D50 When the positive electrode material is used, in order to control the value of the relationship within the preset range, it is necessary to reduce the value of the separation degree α. A reduction in the separation degree α (not less than 0.7) means an increase in the half-height width, that is, a reduction in the primary particles of the material, a shortening of the diffusion path of lithium ions, and at the same time, the defects inside the material particles are not too few, and the capacity and rate performance of the material are guaranteed, thereby helping to overcome the shortcomings of the relevant technology. Therefore, in the above scheme, by controlling the cycle life L of the positive electrode material and the Ni content n Ni , particle size D 50 The relationship between the separation degree α is within the above preset range, which can balance the internal defects of the material, the primary particle size, etc., so that the positive electrode material has better gram capacity, rate and cycle stability.

[0033] In some embodiments, the tap density of the cathode material is T g / cm 3 , 1.7≤T≤2.5. For example, T can be 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or any value within the range formed by any two of the above values. The tap density of the positive electrode material is one of the indicators to measure the energy density of the material. If the tap density of the positive electrode material is too large, the positive electrode sheet will be too dense, which is not conducive to the infiltration of the electrolyte into the positive electrode sheet, resulting in the obstruction of lithium ion embedding and the reduction of the battery's rate performance. If the tap density of the positive electrode material is too low, the energy density of the material will decrease. Controlling the tap density of the positive electrode material within the above range is beneficial for the positive electrode material to have both high energy density and excellent rate performance.

[0034] In some embodiments, the median particle size D of the positive electrode material 50 P is P μm, 3≤P≤16. For example, P can be 3, 4, 5, 8, 10, 12, 15, 16 or any value within the range of any two of the above values. Median particle size D 50 Indicates the particle size of the material corresponding to the cumulative particle size distribution percentage reaching 50% by volume. 50 When the D of the positive electrode material is too small, the particle size is small, the tap density is low, and the specific surface area is large, which easily leads to serious side reactions between the particle surface and the electrolyte, and reduces the safety and cycle life. 50 When the particle size is larger, the internal stress of the particle increases, and the electrochemical polarization and concentration polarization of lithium ions inside and outside the particle intensify, resulting in a decrease in the capacity and rate performance of the positive electrode material. 50 Within the above range, it is beneficial for the positive electrode material to maintain better compaction density, gram capacity and cycle life.

[0035] In some embodiments, the gram capacity of the positive electrode material is C mAh / g, 140≤C≤230. For example, C can be 140, 160, 170, 180, 190, 200, 210, 220, 230, or any value within the range formed by any two of the above values. It should be noted that the gram capacity of the positive electrode material is the discharge capacity of a full battery made of the positive electrode material under the conditions of 0.33C / 0.33C@3.0V~4.3V, 25°C. Controlling the gram capacity within the above range is beneficial for maintaining a better energy density and cycle life of the positive electrode material. Preferably, 170≤C≤220.

[0036] In some embodiments, the molar ratio of Ni element in all metal elements except Li element in the positive electrode material is n Ni , 0.33≤n Ni ≤1. For example, n Ni It can be 0.33, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.8, 0.9, 1 or any value within the range of any two of the above values. Ni Within the above range, it is beneficial to control the gram capacity of the positive electrode material within a suitable range and improve the energy density of the lithium-ion battery; at the same time, it can reduce n Ni Reducing the amount of cobalt will increase the cobalt content, which is beneficial to controlling production costs and improving the cost-effectiveness of unit energy density.

[0037] In some embodiments, the cycle life of the positive electrode material is L, 300≤L≤6000. For example, L can be 300, 500, 600, 800, 1100, 1200, 1500, 1600, 1700, 1800, 2100, 2200, 2400, 2500, 2900, 3000, 3500, 3900, 4000, 4500, 6000 or any value within the range formed by any two of the above values. It should be noted that when the full battery made of the positive electrode material is charged and discharged under the conditions of 1C / 1C@3.0V~4.3V and 25°C until the capacity retention rate reaches 80%, the number of cycles recorded is the cycle life number L. Controlling L within the above range is beneficial for the positive electrode material to have better energy density and cycle life. L is the measured value of the corresponding lithium-ion battery cycle life, which is affected by n Ni The influence is greater and is related to the particle size D 50 There is also a close relationship between the particle size D 50 The fluctuation of the separation degree α causes the L value to deviate from the above range, resulting in a too low cycle life of the battery, which will affect practicality. In order to achieve both energy density and practicality of the positive electrode material, preferably, 1000≤L≤4000.

[0038] In some embodiments, the chemical general formula of the positive electrode material is Li a Ni x Co y M1 z M2 k O2, where M1 includes one or both of Mn and Al, M2 includes one or more of Ni, Co, Mn, Na, K, Mg, Ca, Sr, Al, Ti, Y, Zr, W, Nb, Ce, La, and Dy, 0.9 < a ≤ 1.1, 0.33 ≤ x ≤ 1, 0 ≤ y ≤ 0.33, 0 < z < 0.33, 0 ≤ k < 0.1, and x + y + z + k = 1. It should be noted that based on the chemical general formula of the positive electrode material, the molar ratio of the Ni element among all metal elements except the Li element is n Ni = N Ni / N Ni + N Co + N M1 + N M2 . Among them, N Ni is the molar mass of the Ni element, N Co is the molar mass of the Co element, N M1 is the molar mass of the M1 element, and N M2 is the molar mass of the M2 element. For example, a can be 0.9, 0.95, 0.98, 1.0, 1.01, 1.02, 1.03, 1.05, 1.1 or any value within the range formed by any two of the above values. x can be 0.33, 0.45, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 1 or any value within the range formed by any two of the above values. y can be 0, 0.02, 0.05, 0.07, 0.08, 0.1, 0.15, 0.2, 0.25, 0.28, 0.30, 0.33 or any value within the range formed by any two of the above values. z can be 0.01, 0.06, 0.1, 0.15, 0.2, 0.25, 0.3 or any value within the range formed by any two of the above values. k can be 0, 0.001, 0.005, 0.01, 0.02, 0.05, 0.099 or any value within the range formed by any two of the above values. It should be noted that the content of each element in the positive electrode material can be determined by well-known instruments for qualitative analysis and / or quantitative analysis of each element such as ICP and ICP-MS.

[0039] When M2 includes the above elements, these elements are doped in the surface lattice of the positive electrode material, which is beneficial to changing the lattice constant of the positive electrode material or the valence state of the elements in the material itself, reducing cation mixing, improving the electronic conductivity and ionic conductivity of the material, improving the stability of the material structure, and reducing the risk of structural collapse, thereby improving the cycle stability performance of the positive electrode material.

[0040] In some embodiments, the positive electrode material is analyzed using a scanning electron microscope. The resulting scanning electron microscope image shows that the positive electrode material is a single crystal positive electrode material. The single crystal positive electrode material has a more stable structure, a more uniform distribution of bulk components, and better particle strength than the polycrystalline positive electrode material, which is beneficial for providing better cycle stability and safety for lithium-ion batteries. It can also reduce particle cracking during the electrode pressing process and improve the electrode compaction density and volume energy density. It should be noted that the difference between single crystal positive electrode materials and polycrystalline positive electrode materials (i.e., polycrystalline secondary particles) is that the smallest particles of polycrystalline secondary particles are secondary particles formed by the agglomeration of primary particles. For single crystal positive electrode materials, the smallest particles are usually single primary particles of micron size. In general, in addition to EBSD testing methods, characterization methods such as scanning electron microscopy (SEM) can also be used to determine whether the obtained positive electrode product is a single crystal material. For example, for single crystal positive electrode materials, the morphology of single crystal particles can be characterized by SEM, and it can be seen that the shape of single crystal particles generally appears as regular or irregular polyhedrons, and there is no significant particle agglomeration. The orientation of the single crystal positive electrode material can also be characterized by EBSD. Through EBSD, it can be observed that the orientation within the grains is the same, and the grains with the same orientation are single crystals. It should be specially noted that the "single crystal positive electrode material" known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely the same arrangement and orientation. 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 materials known in the art are actually more of a "single crystal morphology" positive electrode material, which only shows a large particle size similar to a single crystal in size, which is different from a polycrystal composed of many small primary particles.

[0041] In a second aspect, the present application provides a method for preparing a positive electrode material, the preparation method comprising:

[0042] A precursor and a lithium source are mixed to obtain a mixture; the mixture is subjected to a primary sintering and pulverized to obtain a positive electrode material. The primary sintering includes N step-by-step temperature increase sections and M constant temperature sections, where N is greater than or equal to 3 and M is greater than or equal to 1. The step-by-step temperature increase section includes n temperature increase sub-stages, where n is greater than or equal to 2. When n>1, the temperature increase rate of the nth temperature increase sub-stage is greater than the temperature increase rate of the first temperature increase sub-stage of the same step-by-step temperature increase section, and the temperature increase rate of the nth temperature increase sub-stage is non-negative.

[0043] The present application study found that by setting multiple step heating sections and setting a difference between the heating rate of the first sub-stage and the heating rate of the last sub-stage, the separation degree α of the positive electrode material can be better controlled to fall within the preset range. It can be understood that when the heating rate is faster, the particle growth rate changes faster, the particle size is uneven, and the number of internal defects of the particles increases; when the heating rate is slower, the particles tend to grow stably, the particle size is uniform, and some of the internal defects of the particles are repaired as the single crystal grows. In the fast and slow alternating changes in the heating rate, the stress and the number of defects inside the grains can be taken into account, so that the positive electrode material will not cause insufficient particle strength and easy cracking due to excessive internal stress, nor will it cause Li due to insufficient internal defects. + The diffusion path is reduced and the polarization is aggravated.

[0044] Therefore, in the present application, the preparation method of the positive electrode material is to set the above-mentioned stepped heating section and constant temperature section during the primary sintering process. In the stepped heating section, the heating rate of the first sub-stage is relatively low, which is conducive to maintaining a stable growth rate of the particles, thereby making the size of the particles more uniform, and the heating rate of the last sub-stage is relatively high, which is conducive to increasing the particle growth rate and increasing the internal defects of the particles; and in the constant temperature section, some of the internal defects of the particles can be repaired as the particles grow, and the intergranular stress inside the particles is gradually released, which is conducive to improving the particles' ability to resist cracking and pulverization. Therefore, the preparation method of the positive electrode material provided in the present application can control the particle size, particle strength and internal defects of the positive electrode material, thereby helping to improve the cycle stability and rate performance of the positive electrode material.

[0045] In some embodiments, the maximum temperature of the step-temperature increasing section is 700° C. to 1000° C. For example, the maximum temperature of the step-temperature increasing section can be 700° C., 800° C., 850° C., 900° C., 950° C., 980° C., 1000° C., or any value within a range formed by any two of the above values.

[0046] In some embodiments, the time of the step-by-step heating section is 6 hours to 14 hours. For example, the time of the step-by-step heating section can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 14 hours, or any value within the range formed by any two of the above values.

[0047] In some embodiments, the sintering temperature of the constant temperature section is (1150-500n Ni )℃ to (1150-280n Ni )℃,n Ni Indicates the molar ratio of Ni element in all metal elements except Li in the positive electrode material, 0.33≤n Ni≤1. It should be noted that, based on the chemical formula of the above-mentioned positive electrode material, the molar proportion of Ni element in all metal elements except Li element is n Ni =N Ni / N Ni +N Co +N M1 +N M2 Among them, N Ni is the molar mass of Ni element, N Co is the molar mass of Co element, N M1 is the molar mass of element M1, N M2 is the molar mass of element M2.

[0048] The constant temperature section may be a period of time during which the temperature remains constant, or may be composed of multiple temperature sections that alternate. In some embodiments, the constant temperature section includes alternating cooling sub-stages and heating sub-stages, wherein the temperature of the cooling sub-stage in the constant temperature section is lower than the temperature of the adjacent heating sub-stage.

[0049] In some embodiments, the mixture further includes a dopant, and the dopant element includes one or more of Ni, Co, Mn, Na, K, Mg, Ca, Sr, Al, Ti, Y, Zr, W, Nb, Ce, La, and Dy. For example, the dopant can be a salt or oxide of the above elements.

[0050] In some embodiments, after the pulverization in the above preparation method, the process further comprises: mixing the primary sintered product with a coating agent and performing a secondary sintering to obtain a positive electrode material. The coating agent comprises one or more elements selected from the group consisting of Ni, Co, Mn, Na, K, Mg, Ca, Sr, Al, Ti, Y, Zr, W, Nb, Ce, La, and Dy. For example, the coating agent may be a salt or oxide of the above elements. Alternatively, the coating agent may comprise a Co compound or a W compound.

[0051] The preparation method of the present application is described in detail below with reference to the examples:

[0052] In some embodiments, the chemical formula of the cathode material precursor is Ni a1 Co b1 M1 c1 O d , wherein 0.33≤a1≤1, 0≤b1≤0.33, 0≤c1<0.33, 4 / 3≤d≤3 / 2, and a1+b1+c1=1, and M1 includes one or both of Mn and Al.

[0053] In some embodiments, the chemical formula of the cathode material precursor is Ni a2 Co b2 M1 c2(OH)2, wherein 0.33≤a2≤1, 0≤b2≤0.33, 0≤c2<0.33, and a2+b2+c2=1, and M1 includes one or both of Mn and Al.

[0054] In some embodiments, the median particle size of the cathode material precursor is 3 μm to 18 μm. For example, the median particle size of the cathode material precursor can be 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or any value within a range formed by any two of the above values.

[0055] In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium nitrate, lithium acetate, lithium sulfate, and lithium oxalate.

[0056] In some embodiments, the amount of lithium source and cathode material precursor added satisfies the following conditions: the ratio of the molar amount of Li to the total molar amount of all metals in the cathode material precursor is (0.9-1.1):1. For example, the above ratio can be 0.9:1, 0.95:1, 0.98:1, 1:1, 1.02:1, 1.05:1, 1.1:1, or any value within the range formed by any two of the above values. Within this range, the degree of Li / Ni cation mixing can be reduced, and the excessive residual lithium on the surface of the sintered material can be reduced to affect the processing performance and safety performance.

[0057] In some embodiments, the amount of dopant added is controlled so that the ratio of the molar amount of M2 to the total molar amount of transition metal in the prepared positive electrode material is (0-0.1):1. For example, the above ratio can be 0.01:1, 0.02:1, 0.05:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, or any value within the range formed by any two of the above values.

[0058] In some embodiments, mixing includes solid-phase mixing, and the solid-phase mixing method can be dry grinding or ball milling, etc., which is not limited here, as long as the components are mixed evenly.

[0059] In some embodiments, the mixing equipment can be one or more of a ball mill, a three-dimensional mixer, a high-speed mixer, a coating machine, and a VC mixer.

[0060] In some embodiments, the primary sintering is performed in an oxygen-containing atmosphere, wherein the oxygen content in the oxygen-containing atmosphere is greater than or equal to 20% by volume. For example, the oxygen content in the oxygen-containing atmosphere can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 100%, or any value within a range between any two of the foregoing values. To ensure sufficient reaction, the oxygen content in the oxygen-containing atmosphere is preferably greater than or equal to 90% by volume.

[0061] In some embodiments, the pulverization method includes one or more of a double roller, a plowshare mixer, a plowshare crusher, a jet mill, and a mechanical mill.

[0062] In some embodiments, the mass ratio of the coating agent to the primary sintered product is (0-0.1):1. For example, the mass ratio can be 0:1, 0.002:1, 0.005:1, 0.01:1, 0.03:1, 0.05:1, 0.1:1, or any value within the range formed by any two of the above values.

[0063] In some embodiments, the secondary sintering is performed in an oxygen-containing atmosphere, wherein the volume content of oxygen in the oxygen-containing atmosphere is greater than or equal to 20%. For example, the volume content of oxygen in the oxygen-containing atmosphere can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, 100%, or any value within a range formed by any two of the foregoing values.

[0064] In some embodiments, the secondary sintering temperature is 300° C. to 900° C. For example, the secondary sintering temperature can be 300° C., 380° C., 450° C., 550° C., 600° C., 700° C., 750° C., 800° C., 840° C., 900° C., or any value within a range formed by any two of the foregoing values.

[0065] In some embodiments, the holding time of the secondary sintering is 6 hours to 24 hours. For example, the holding time of the secondary sintering can be 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 24 hours, or any value within the range formed by any two of the above values.

[0066] In some embodiments, the preparation method further comprises cooling, shaping and screening the secondary sintered product. The shaping comprises one or more of pulverizing, grinding, ball milling and gas crushing.

[0067] In some embodiments, the sieve used has a mesh size of 300 to 400 mesh.

[0068] In a third aspect, the present application provides a secondary battery, which comprises the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0069] The secondary battery comprises a housing, an electrode assembly, and an electrolyte. The electrode assembly and electrolyte are both located within the housing. The housing may be a packaging bag encapsulated with an encapsulating film (e.g., aluminum-plastic film), such as a soft-pack battery. In other embodiments, the secondary battery may also be a steel-cased battery, an aluminum-cased battery, or the like.

[0070] Referring to Figures 1 and 2 , the electrode assembly of the secondary battery includes a positive electrode sheet 110, a negative electrode sheet 120, and a separator 130, with the separator 130 disposed between the positive electrode sheet 110 and the negative electrode sheet 120. The electrode assembly may be a laminated structure, in which the positive electrode sheet 110, the separator 130, the negative electrode sheet 120, and the separator 130 are alternately stacked in sequence. In other embodiments, the electrode assembly may also be a wound structure, in which the positive electrode sheet 110, the separator 130, the negative electrode sheet 120, and the separator 130 are stacked in sequence and then wound.

[0071] Positive electrode

[0072] The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active material layer 112 disposed on at least one surface of the positive electrode current collector 111. The positive electrode current collector 111 can be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active material layer 112 includes the aforementioned positive electrode material.

[0073] The positive electrode active material layer 112 also includes a binder to bind the positive electrode active material particles to facilitate film formation and improve the bonding strength between the positive electrode material active layer and the positive electrode current collector 111. In some embodiments, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0074] The positive electrode active material layer 112 may further include a conductive material, including but not limited to a carbon-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0075] Negative electrode

[0076] The negative electrode sheet 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 provided on at least one surface of the negative electrode current collector 121. The negative electrode current collector 121 can use at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, etc., or it can be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer 122 includes a negative electrode material, and the negative electrode material includes but is not limited to graphite, mesophase microcarbon beads (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, spinel structured lithium titanate, lithiated TiO2-Li4Ti5O 12 , Li-Al alloy and at least one of metallic lithium.

[0077] The negative electrode active material layer 122 also includes a binder to bind the negative electrode active material particles to facilitate film formation and improve the bonding strength between the negative electrode material active layer and the negative electrode current collector 121. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0078] The negative electrode active material layer 122 may further include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, the carbon-based material may include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0079] Isolation film

[0080] The isolation membrane 130 comprises a porous membrane layer, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the isolation membrane 130 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0081] electrolytes

[0082] The electrolyte conducts ions between the positive electrode 110 and the negative electrode 120. The electrolyte can be in one or more of a gel, solid, and liquid state. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution conducts active ions between the positive electrode 110 and the negative electrode 120. In some embodiments, the electrolyte solution includes a lithium salt and an organic solvent. The lithium salt can be selected from but is not limited to one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bisoxalatoborate (LiBOB) and lithium difluorophosphate (LiPO2F2). For example, the lithium salt is selected from LiPF6 because it can give high ionic conductivity and improve cycle characteristics. The organic solvent can be a carbonate compound, a carboxylate compound, an ether compound, Compounds, nitrile compounds, other organic solvents or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl 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-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or combinations thereof.

[0083] Referring to Figure 1, when the battery is discharged, lithium ions 140 are released from the lattice of the negative electrode material, pass through the electrolyte or electrolyte solution through the separator 130, and embed into the lattice of the positive electrode material. Electrons generated at the negative electrode move through an external circuit to the positive electrode. This reverse flow of electrons forms an electric current, which can power electrical appliances. Conversely, referring to Figure 2, when the battery is charged by applying an external circuit, lithium ions 140 are released from the lattice of the positive electrode material, pass through the electrolyte or electrolyte solution through the separator 130, and migrate to the negative electrode material, where they are embedded into the lattice of the negative electrode material. As lithium ions 140 move back and forth between the positive and negative electrodes, the battery can achieve discharge and charge processes over multiple cycles.

[0084] The present invention is described in detail below through specific examples and comparative examples. It should be understood by those skilled in the art that the preparation methods described in this application are only examples, and any other suitable preparation methods are within the scope of this application.

[0085] Example 1

[0086] A method for preparing a positive electrode material comprises the following steps:

[0087] S1: D 50 The precursor Ni is 4.0 μm 0.6 Co 0.1 Mn 0.3 (OH)2, Li2CO3 and ZrO2 are uniformly mixed in a ratio of 1:1.05:0.0025 to obtain a mixture.

[0088] S2: The mixture obtained in S1 is sintered once in a dry air atmosphere according to the following temperature settings, wherein the temperature settings include the following steps in sequence:

[0089] Step heating stage 1: 0℃→0.2h, 50℃→0.5h, 250℃;

[0090] Step heating section 2: 250℃→0.5h, 270℃→0.5h, 400℃;

[0091] Step heating section 3: 400℃→0.5h, 420℃→0.5h, 550℃;

[0092] Step heating stage 4: 550℃→0.5h, 570℃→0.5h, 700℃;

[0093] Step heating section 5: 700℃→0.5h, 720℃→0.5h, 850℃;

[0094] Step heating section 6: 850℃→0.5h, 830℃→0.8h, 920℃;

[0095] Step heating section 7: 920℃→1h, 900℃→1h, 970℃;

[0096] And, constant temperature section: 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 970℃→1h, 950℃→1h, 970℃.

[0097] S3: The material sintered in S2 is crushed and sieved to obtain a matrix material.

[0098] S4: The matrix material obtained in S3 is evenly mixed with Al2O3 and Co(OH)2 in a weight ratio of 1:0.002:0.04, and calcined at 850°C for 8 hours, and then cooled, crushed, sieved, and demagnetized to obtain a positive electrode material.

[0099] FIG3 shows a temperature change curve of the primary sintering process in the method for preparing the positive electrode material provided in Example 1 of the present application. In conjunction with FIG3 , it can be understood that the aforementioned “step heating section 1: 0°C → 0.2h, 50°C → 0.5h, 250°C” indicates that within the current step heating section, the temperature is raised from 0°C to 50°C within 0.2h, i.e., the heating rate is approximately 250°C / h; then, the temperature is raised from 50°C to 250°C within 0.5h, i.e., the heating rate is approximately 400°C / h. The aforementioned “step heating section 6: 850°C → 0.5h, 830°C → 0.8h, 920°C” indicates that within the current step heating section, the temperature is lowered from 850°C to 830°C within 0.5h, i.e., the heating rate is negative; then, the temperature is raised from 830°C to 920°C within 0.8h, i.e., the heating rate is non-negative. By analogy, the specific heating or cooling method of the temperature setting described in this application can be understood.

[0100] Example 2

[0101] The difference from Example 1 is that in S2, the temperature setting for the primary sintering is:

[0102] The step temperature rise section 6 was adjusted to: 850℃→1h, 830℃→0.8h, 920℃;

[0103] The step temperature rise section 7 is adjusted to: 920℃→0.7h, 900℃→1h, 970℃;

[0104] The constant temperature section is adjusted to: 970℃→8h, 970℃.

[0105] Example 3

[0106] The difference from Example 1 is that in S2, the temperature setting of the primary sintering includes the following steps performed in sequence:

[0107] Step heating stage 1: 0℃→0.2h, 50℃→0.5h, 250℃;

[0108] Step heating section 2: 250℃→0.5h, 270℃→0.3h, 400℃;

[0109] Step heating stage 3: 400℃→0.6h, 420℃→0.4h, 550℃;

[0110] Step heating stage 4: 550℃→0.5h, 570℃→0.4h, 700℃;

[0111] Step heating section 5: 700℃→0.5h, 720℃→0.3h, 850℃;

[0112] Step heating section 6: 850℃→0.5h, 870℃→0.5h, 970℃;

[0113] And, constant temperature section: 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 950℃→1h, 970℃→1h, 970℃→1h, 950℃→1h, 970℃.

[0114] Example 4

[0115] The difference from Example 1 is that in S2, the temperature setting for the primary sintering is:

[0116] The step temperature rise section 6 was adjusted to: 850℃→1h, 830℃→0.8h, 920℃;

[0117] The step temperature rise section 7 is adjusted to: 920℃→1h, 900℃→1h, 950℃;

[0118] The constant temperature section is adjusted to: 950℃→1h, 930℃→1h, 950℃→1h, 930℃→1h, 950℃→1h, 930℃→1h, 950℃→1h, 930℃→1h, 950℃→1h, 930℃→1h, 950℃.

[0119] Example 5

[0120] The difference from Example 4 is that in S1, the D of the precursor is adjusted 50 10μm.

[0121] Example 6

[0122] The difference from Example 4 is that in S1, the D of the precursor is adjusted 50 It is 16μm.

[0123] Example 7

[0124] The difference from Example 1 is that in S1, the precursor is replaced by D 50 4.0μm Ni 0.5 Co 0.2 Mn 0.3 (OH)2; In S2, the temperature setting for the first sintering is:

[0125] The step temperature rise section 6 was adjusted to: 850℃→1h, 830℃→0.8h, 920℃;

[0126] The step temperature rise section 7 is adjusted to: 920℃→0.7h, 900℃→1h, 990℃;

[0127] The constant temperature section is adjusted to: 990℃→1h, 970℃→1h, 990℃→1h, 970℃→1h, 990℃→1h, 970℃→1h, 990℃→1h, 970℃→1h, 990℃→1h, 990℃→1h, 970℃→1h, 990℃.

[0128] Example 8

[0129] The difference from Example 1 is that in S1, the precursor is replaced by D 50 4.0μm Ni 0.7 Co 0.1 Mn 0.2 (OH)2, Li2CO3 is replaced by LiOH·H2O; in S2, the temperature setting of the first sintering is:

[0130] The step temperature rise section 6 was adjusted to: 850℃→1h, 830℃→0.8h, 920℃;

[0131] The step temperature rise section 7 is adjusted to: 920℃→0.7h, 900℃→1h, 930℃;

[0132] The constant temperature section is adjusted to: 930℃→1h, 910℃→1h, 930℃→1h, 910℃→1h, 930℃→1h, 910℃→1h, 930℃→1h, 910℃→1h, 930℃→1h, 930℃→1h, 930℃→1h.

[0133] Example 9

[0134] The difference from Example 1 is that in S1, the precursor is replaced by D 50 4.0μm Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Li2CO3 is replaced by LiOH·H2O; in S2, the temperature setting of the first sintering is:

[0135] The step temperature rise section 6 was adjusted to: 850℃→1h, 830℃→0.8h, 860℃;

[0136] The step temperature rise section 7 was adjusted to: 860℃→0.7h, 840℃→1h, 870℃;

[0137] The constant temperature section is adjusted to: 870℃→1h, 890℃→1h, 870℃→1h, 890℃→1h, 870℃→1h, 890℃→1h, 870℃→1h, 890℃→1h, 870℃→1h, 890℃→1h, 870℃→1h, 890℃.

[0138] Example 10

[0139] The difference from Example 1 is that in S1, the precursor is replaced by D 50 4.0μm Ni0.9 Co 0.05 Mn 0.05 (OH)2, Li2CO3 is replaced by LiOH·H2O; in S2, in the temperature setting of the first sintering: remove the step temperature rising section 6 and the step temperature rising section 7, and adjust the constant temperature section to: 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 830℃→1h.

[0140] Example 11

[0141] The difference from Example 1 is that in S1, the precursor is replaced by D 50 4.0μm Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Li2CO3 is replaced by LiOH·H2O; in S2, in the temperature setting of the first sintering: remove the step temperature rising section 6 and the step temperature rising section 7, and adjust the constant temperature section to: 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h, 830℃→1h, 850℃→1h.

[0142] Comparative Example 1

[0143] The difference from Example 1 is that in S2, the temperature setting of the first sintering is adjusted to: 0°C → 8h, 950°C → 8h, 950°C, that is, the first sintering is performed according to a uniform temperature increase and a constant temperature section.

[0144] Comparative Example 2

[0145] The difference from Example 1 is that in S2, the temperature setting of the first sintering is adjusted to: 0°C → 2h, 960°C → 8h, 960°C, that is, the first sintering is performed according to a uniform temperature increase and a constant temperature section.

[0146] Comparative Example 3

[0147] The difference from Example 1 is that in S2, the temperature setting of the primary sintering is adjusted to: 0°C→4h, 850°C→3h, 850°C→1h, 950°C→8h, 950°C.

[0148] Comparative Example 4

[0149] The difference from Example 5 is that in S2, the temperature setting of the first sintering is adjusted to: 0°C → 8h, 950°C → 8h, 950°C, that is, the first sintering is performed according to a uniform temperature increase and a constant temperature section.

[0150] Comparative Example 5

[0151] The difference from Example 6 is that in S2, the temperature setting of the first sintering is adjusted to: 0°C → 8h, 950°C → 8h, 950°C, that is, the first sintering is performed according to a uniform temperature increase and a constant temperature section.

[0152] The present application also prepares lithium-ion batteries using the positive electrode materials of Examples 1-11 and Comparative Examples 1-5, respectively. The preparation method includes:

[0153] S1, the positive electrode material, polyvinylidene fluoride (PVDF) (as a binder), acetylene black (as a conductive agent) and polyaniline (PANI) (as a conductive liquid) are dissolved in a solvent N-methylpyrrolidone (NMP) in a weight ratio of 96:2:1.5:0.5, and the mixture is fully stirred and mixed to obtain a positive electrode slurry. The obtained positive electrode slurry is evenly coated on the positive electrode current collector with the primer slurry, and the positive electrode sheet is obtained after drying, cold pressing and slitting. The surface density of the obtained positive electrode sheet is measured to be about 350g / m 2 , compacted density is about 3.5g / cm 3 .

[0154] S2, graphite (as active material), styrene-butadiene rubber (SBR) (as binder), and acetylene black (as conductive agent) were dissolved in deionized water at a weight ratio of 96:2:2, and the mixture was uniformly mixed to prepare a negative electrode slurry. The obtained negative electrode slurry was coated on copper foil, dried, and cold-pressed to obtain a negative electrode sheet. The surface density of the obtained negative electrode sheet was determined to be approximately 210 g / m 2 , compacted density is about 1.6g / cm 3 .

[0155] S3, the isolation membrane adopts polyethylene film, and polyvinylidene fluoride and aluminum oxide coating are coated on the surface of the polyethylene film to improve adhesion and heat resistance.

[0156] S4, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is added and dissolved to obtain an electrolyte solution with a lithium salt concentration of 1.1 mol / L. The electrolyte solution also contains 2% by weight of vinylene carbonate and 1% by weight of polysulfone as additives.

[0157] S5, control the ratio of the negative electrode capacity to the positive electrode discharge capacity of the battery (N / P) to 1.16, and the injection amount of electrolyte is 3.2g / Ah; stack the positive electrode sheet, separator, negative electrode sheet, and separator in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wind to obtain a bare battery cell, weld the tabs to the bare battery cell, and place the bare battery cell in an aluminum shell, and bake it at 80℃ to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery then undergoes static standing, hot and cold pressing, formation, shaping, capacity testing and other processes in sequence to obtain a lithium-ion battery.

[0158] Performance Testing

[0159] 1. Battery capacity test method: At 25°C, charge to 4.3V in CCCV mode (charging current 0.33C, constant voltage cutoff current 0.01C), let stand for 10 minutes, and discharge to 3.0V in CC mode (discharge current 0.33C). The discharge capacity (C mAh / g) is calculated based on the discharge capacity.

[0160] 2. Battery rate test method: After the battery capacity test is completed, at 25°C, let it stand for 10 minutes, charge it in CCCV mode to 4.3V (charging current 0.33C, constant voltage cut-off current 0.01C), let it stand for 10 minutes, and discharge it in CC mode to 3.0V (discharge current 2.0C). The discharge capacity is recorded as C R mAh / g, the rate performance R=C is obtained by calculation R / C×100%.

[0161] 3. Battery cycle life test method: Take the battery after formation and capacity separation, charge it to 4.3V in CCCV mode (charging current 1.0C, constant voltage cut-off current 0.1C) at 25°C, let it stand for 10 minutes, and discharge it to 3.0V in CC mode (discharge current 1.0C) to obtain the initial gram capacity C1mAh / g, let it stand for 10 minutes; then repeat CCCV mode charging and CC mode discharging until the discharge gram capacity is less than 0.8*C1mAh / g; record the cumulative number of discharges, which is the cycle life L.

[0162] 4. Test method for tap density of positive electrode material: GB / T5162-1985 Metal powder - Determination of tap density is used, and the test result is recorded as T g·cm -3 .

[0163] 5. Particle size D of positive electrode material 50 Test method: Refer to GB / T 19077-2016. It can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The test result is recorded as Pμm.

[0164] 6. Test method for nNi of positive electrode material: refer to GB / T 24194-2009. It can be conveniently measured by inductively coupled plasma optical emission spectrometer (ICP-OES), such as Agilent 5110 ICP-OES. The molar mass of Ni element tested by ICP is N Ni , the molar mass of Co element is N Co , the molar mass of element M1 is N M1 , the molar mass of element M2 is N M2 The molar ratio of Ni in all metal elements except Li is nNi=N Ni / N Ni +N Co +N M1 +N M2 .

[0165] 7. XRD test of positive electrode material: XRD ray was used to measure the positive electrode material to obtain the characteristic peak corresponding to the (104) crystal plane of the positive electrode material. The characteristic peak was separated to obtain two diffraction peaks, namely (104)-Kα1 and (104)-Kα2. Among them, the peak positions of the (104)-Kα1 and (104)-Kα2 diffraction peaks were Q1 and Q2, respectively, and the half-maximum widths were FWHM1 and FWHM2, respectively. The separation degree α can be calculated by the following formula:

[0166] The XRD test conditions include: Cu target, voltage 40 kV, current 40 mA, scanning range 43.5° to 45°, step size 0.02°, and scanning speed 2° / min. Peak separation methods include: Origin8.5 software, select XRD test data → Line mode drawing → baseline removal (Analysis window Peaks and baseline → Peak Analyzer → Opening Dialog → Recalculate option select Manual option, Goal option select Fit Peaks (Pro) → Click Next → Baseline Mode option select Constant, Constant = Minimum → Click Next) → Peak separation (uncheck Auto Subtract Baseline option and Auto Rescale option, check Fix baseline Parameters option, click Next → uncheck Enable Auto Find, check Smoothing Window Size option as Auto in Peak Finding Settings, select Positive in Direction option, select Local Maximum in Method, set Local Points parameter to 2, select By Number in Peak Filtreing Method, change Number of Peaks to 2 → Click Find → Click Next) → Fit correction (Select NoWeightin in Weight Method, select Max.Number of Set Iterations to 50 and Tolerance to 0.05 → Click Fit → Click Finish. Once completed, the values ​​for Q1, Q2, FWHM1, and FWHM2 are displayed in the Peak Analysis Report.

[0167] Taking Example 1 as an example, please refer to Figure 4. The characteristic peak of the (104) crystal plane of the positive electrode material is a non-left-right symmetrical structure, and the two diffraction peaks after peak separation are left-right symmetrical structures, that is, the diffraction peak curve is normally distributed.

[0168] In this application, T-(1.04α-0.25α 2 +0.004P 2 -0.02P) is recorded as E, and C-(100n Ni -α 2 The value of P) is recorded as H, and L-(2245α-5000n Ni The value of (+100P) is recorded as F. Please refer to Table 1 for the above test or calculation results.

[0169] Table 1. Test results of positive electrode material parameters and lithium-ion battery performance of Examples 1-11 and Comparative Examples 1-5 of the present application

[0170] Please refer to Table 1. Examples 1-11 sinter the positive electrode material precursor and the lithium source through a specific temperature setting. The temperature changes of the multiple step-by-step temperature rising sections and the constant temperature section in the temperature setting are used to control the particle size of the obtained positive electrode material and appropriately increase the internal defects of the particles, thereby obtaining a positive electrode material with a separation degree α that meets the preset range. The interior of the particles of these positive electrode materials is suitable for the diffusion of lithium ions and has good particle strength, which is conducive to reducing the polarization phenomenon of the positive electrode material and improving the ability to resist cracking or pulverization, thereby maintaining good capacity, rate performance and cycle stability. In addition, the E, H, and F values ​​of these positive electrode materials are also in line with the preset range, so that they have both excellent cycle stability and rate performance.

[0171] Examples 1-4 further illustrate the specific effects of the aforementioned temperature settings on the particle size and internal defects of the positive electrode material. Compared to Example 1, the temperature fluctuations in the constant temperature section of Example 2 were relatively small, and the growth of the positive electrode material particles was relatively stable during this treatment stage, resulting in a slight increase in the particle size of the positive electrode material and an increase in the separation degree α. This indicates that within a certain range of primary particle numbers, increasing the size of the primary particles can improve the cycle life of the positive electrode material. Compared to Example 1, the stepped temperature section of Example 3 had a relatively faster heating rate, which promoted the formation of more internal defects in the positive electrode material particles during this treatment stage, thereby increasing the separation degree α. This indicates that within a certain range of primary particle numbers, increasing the internal defects of the positive electrode material can further improve the cycle life of the positive electrode material. Compared to Example 1, the temperature in the constant temperature section of Example 4 was relatively low, and the growth rate of the positive electrode material particles during this treatment stage was relatively slow. As a result, the particle size of the positive electrode material was reduced, thereby reducing the separation degree α. This indicates that within a certain range of primary particle numbers, reducing the primary particle size can reduce the cycle life of the positive electrode material.

[0172] It can also be seen from Examples 1-4 that as the separation degree α increases, the tap density T of the positive electrode material increases, the gram capacity C decreases, and the cycle life L increases. The tap density T, gram capacity C and cycle life L of the positive electrode material each have a good correlation with the separation degree α. Therefore, controlling the separation degree α can help improve the particle strength of the positive electrode material, reduce the polarization phenomenon of the positive electrode material, and enable the positive electrode material to have both better cycle stability and rate performance.

[0173] Compared with Example 1, Comparative Example 4 compared with Example 5, and Comparative Example 5 compared with Example 6, none of the above-mentioned multiple step-by-step temperature increase sections and constant temperature sections were used for sintering. The temperature fluctuation during the sintering process was significantly lower, resulting in a significant lack of internal defects in the positive electrode material particles. Among them, although the P values ​​of the positive electrode materials obtained in Comparative Examples 1, 3, 4, and 5 were close to those of the corresponding examples, due to the significant lack of internal defects in the positive electrode material particles, their separation α was too small. Comparative Example 2, due to the short low-temperature time it experienced, did not fully form a sufficient number of crystal nuclei before entering the high-temperature stage, resulting in the final positive electrode material having an excessively large grain size. The corresponding P value was significantly greater than that of Example 1. Therefore, even though the internal defects of its positive electrode material particles were relatively few, its separation α was too large due to the influence of the excessively large grain size. Therefore, the separation α of the positive electrode materials of the above-mentioned Comparative Examples 1-5 all deviated from the preset range of the present application, and these positive electrode materials were difficult to achieve both excellent cycle stability and rate performance.

[0174] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application should not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode material, wherein: The positive electrode material is a nickel-cobalt-lithium oxide composite oxide; In the XRD pattern of the positive electrode material, the characteristic peak of the (104) crystal plane includes a (104)-Kα1 diffraction peak and a (104)-Kα2 diffraction peak after peak separation, and the separation degree of the (104)-Kα1 diffraction peak and the (104)-Kα2 diffraction peak is α. 0.7≤α≤2.0。 2. The positive electrode material according to claim 1, wherein The tap density of the positive electrode material is T g / cm 3 , the median particle size D of the positive electrode material 50 Pμm, 1≤T-(1.04α-0.25α 2 +0.004P 2 -0.02P)≤1.

5.

3. The positive electrode material according to claim 1, wherein The gram capacity of the positive electrode material is C mAh / g, and the median particle size of the positive electrode material is D 50 is P μm, and the molar proportion of Ni element in all metal elements except Li element in the positive electrode material is n Ni , 125≤C-(100n Ni -α 2 P)≤135.

4. The positive electrode material according to claim 1, wherein The cycle life of the positive electrode material under the conditions of charging to 4.3V at 1.0C current and discharging to 3.0V at 1.0C current is L, and the median particle size D of the positive electrode material is 50 is P μm, and the molar proportion of Ni element in all metal elements except Li element in the positive electrode material is n Ni , 1800≤L-(2245α-5000n Ni +100P)≤2400.

5. The positive electrode material according to claim 1, wherein The tap density of the positive electrode material is T g / cm 3 , 1.7≤T≤2.

5.

6. The positive electrode material according to claim 1, wherein The gram capacity of the positive electrode material is C mAh / g, 140≤C≤230.

7. The positive electrode material according to claim 1, wherein The positive electrode material has a cycle life of L under the conditions of being charged to 4.3V at a current of 1.0C and being discharged to 3.0V at a current of 1.0C, 300≤L≤6000.

8. The positive electrode material according to claim 1, wherein The median particle size D of the positive electrode material 50 is Pμm, 3≤P≤16.

9. The positive electrode material according to claim 1, wherein The molar proportion of Ni element in all metal elements except Li element in the positive electrode material is n Ni , 0.33≤n Ni ≤1.

10. The positive electrode material according to claim 1, wherein The positive electrode material is a single crystal positive electrode material.

11. The positive electrode material according to claim 1, wherein The chemical formula of the positive electrode material is Li a Ni x Co y M1 z M2 k O2, M1 includes one or two of Mn and Al, M2 includes one or more of Ni, Co, Mn, Na, K, Mg, Ca, Sr, Al, Ti, Y, Zr, W, Nb, Ce, La and Dy, 0.9 <a≤1.1 0.33≤x≤1 0≤y≤0.33 0<z<0.33 0≤k<0.1 x+y+z+k=1。 12. A method for preparing a positive electrode material, wherein: The preparation method comprises: mixing a precursor and a lithium source to obtain a mixture; The mixture is sintered and crushed to obtain the positive electrode material; The primary sintering includes N step temperature rising sections and M constant temperature sections performed in sequence, N is greater than or equal to 3, and M is greater than or equal to 1; The step heating section includes n heating sub-stages, n is greater than or equal to 2, when n is greater than 1, the heating rate of the nth heating sub-stage is greater than the heating rate of the first heating sub-stage of the same step heating section, and the heating rate of the nth heating sub-stage is a non-negative value.

13. The preparation method according to claim 12, wherein: The preparation method satisfies at least one of the following conditions: (1) The maximum temperature of the step-temperature rising section is 700° C. to 1000° C.; (2) The time of the step-by-step heating stage is 6 hours to 14 hours; (3) The temperature of the constant temperature section is (1150-500n Ni )℃ to (1150-280n Ni )℃,n Ni It indicates the molar ratio of Ni element in all metal elements except Li element in the positive electrode material; (4) The constant temperature section includes a temperature reduction sub-stage and a temperature increase sub-stage that are performed alternately, and the temperature of the temperature reduction sub-stage in the constant temperature section is lower than the temperature of the adjacent temperature increase sub-stage.

14. The preparation method according to claim 12, wherein: After the pulverization, the method further comprises: The product of the primary sintering is mixed with a coating agent and subjected to secondary sintering, wherein the elements of the coating agent include one or more of Ni, Co, Mn, Na, K, Mg, Ca, Sr, Al, Ti, Y, Zr, W, Nb, Ce, La and Dy.

15. A secondary battery, wherein: The secondary battery comprises the positive electrode material according to any one of claims 1 to 11 or comprises the positive electrode material prepared by the preparation method according to any one of claims 12 to 14.

Images