Secondary battery and electrical equipment

Abstract

This application discloses a secondary battery and an electrical device. The secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing compound having a layered structure; the positive electrode plate satisfies: 4000≤U≤14560, and U = C 003 / {[2Thea(110) - 2Theta(018)]×FWHM[(110)+(018)]}. By reasonably controlling the U value of the positive electrode plate in this application, the layer order degree of the layered compound in the positive electrode plate can be improved and the orientation degree of the 003 crystal plane in the layered compound can be reduced, creating a good crystal structure basis for realizing the rapid deintercalation and intercalation of lithium ions, ensuring that there is a high transmission performance between the positive electrode material particles for lithium ions, and enabling the secondary battery to have good kinetic performance.

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and particularly relates to a secondary battery and an electrical device using the same. Background Art

[0002] The performance of secondary batteries depends to a large extent on the positive active material on the positive electrode sheet. Among them, when nickel-cobalt-manganese ternary material is used as the positive active material, due to its poor structural stability during long-term cycling, the disordered arrangement of cations will hinder the transport of lithium ions, resulting in a continuous decline in the power performance of the battery; at the same time, the layered structure of the nickel-cobalt-manganese ternary positive electrode material is severely damaged under high current, and the decline of the structure also leads to a rapid decline in the cycle life of the battery. Existing technologies often improve the fast charge and discharge ability of lithium-ion batteries by reducing the loading of active substances on the electrode sheet or increasing the proportion of conductive agents, but these methods usually result in a decrease in the energy density of the battery; in addition, designing primary particles with small particle sizes is also a common strategy to improve fast charging performance, but when the particle size is too small, side reactions on the surface increase, leading to a rapid decline in cycle performance, and small particles are prone to agglomeration, affecting the processing performance of the electrode sheet, resulting in a decrease in the compaction density of the electrode sheet and particle fragmentation problems caused by high compaction density. Summary of the Invention

[0003] Object of the Invention: This application provides a secondary battery for improving the layer order degree of the layered compound in the positive electrode sheet and reducing the orientation degree of the crystal plane of the layered compound; another object of this application is to provide an electrical device including the above secondary battery.

[0004] Technical Solution: A secondary battery of this application includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive electrode mixture layer disposed on the positive current collector, the positive electrode mixture layer includes a positive active material, and the positive active material includes a lithium-containing compound with a layered structure;

[0005] The positive electrode sheet satisfies: 4000≤U≤14560,

[0006] And

[0007] Wherein, C 003 is the peak area of the 003 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of AU·min; [2Theta(110)-2Theta(018)] is the relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of min; FWHM[(110)+(018)] is the sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of min.

[0008] In some embodiments, the positive electrode sheet satisfies: 5500 ≤ U ≤ 12500, preferably 6500 ≤ U ≤ 10500.

[0009] In some embodiments, the range of the U value is related to the peak area of the 003 characteristic diffraction peak obtained by X-ray diffraction test, the relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak, and the sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak; wherein, the sum of the peak area and the full width at half maximum can be directly obtained through pattern analysis, and the relative distance can be calculated by obtaining the 2θ angular positions of the 110 and 018 diffraction peaks from the XRD diffraction pattern and then subtracting the two.

[0010] In some embodiments, the peak area of the 003 characteristic diffraction peak satisfies: 2200 ≤ C 003 ≤ 3500;

[0011] The relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.40 ≤ [2Theta(110) - 2Theta(018)] ≤ 0.70;

[0012] The sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.55 ≤ FWHM[(110) + (018)] ≤ 0.80.

[0013] In some embodiments, the positive electrode sheet satisfies: 1050 ≤ U / P ≤ 4500, where P g / cm 3 is the tap density of the positive electrode sheet, and 3.0 ≤ P ≤ 3.8.

[0014] In some embodiments, the lithium-containing compound is a lithium nickel cobalt oxide, the lithium nickel cobalt oxide further contains an M element, the lithium nickel cobalt oxide further contains an A element, and the A element is at least one of Mn, Al, Ti, Mg, and Zr.

[0015] In some embodiments, the lithium nickel cobalt oxide further contains an M element, and the M element contains one or more of Al, B, Ca, W, Nb, Mg, Zr, Sr, Si, Y, and Ti.

[0016] In some embodiments, the lithium-containing compound contains Li x Ni a Co b A c O2, where 0.95 ≤ x ≤ 1.05, 0.5 ≤ a ≤ 0.9, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and a + b + c = 1.

[0017] In some embodiments, M is a doping element and / or a coating element;

[0018] Wherein, the doping element includes one or more of Al, B, Ca, W, Nb, Mg, Zr, Sr; the coating element includes one or more of Al, B, Zr, Sr, Si, Y, Ti, Sn;

[0019] When M is a combination of the doping element and the coating element, the doping element and the coating element are different elements.

[0020] In some embodiments, the median particle size D of the positive electrode active material v 50 is 2 μm to 20 μm.

[0021] In some embodiments, the present application further provides an electrical device, including the secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0022] Beneficial effects: Compared with the prior art, the secondary battery of the present application includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer includes a positive electrode active material, the positive electrode active material includes a layered lithium-containing compound, and the positive electrode plate satisfies: 4000 ≤ U ≤ 14560, and U = C 003 / {[2Thea(110)-2Theta(018)]×FWHM[(110)+(018)]}. By reasonably controlling the U value of the positive electrode mixture layer in the positive electrode plate of the present application, the layer order degree of the layered compound in the positive electrode plate can be improved and the orientation degree of the 003 crystal plane in the layered compound can be reduced, creating a good crystal structure basis for realizing the rapid deintercalation and intercalation of lithium ions, ensuring that there is a high transmission performance of lithium ions between the positive electrode material particles, and enabling the positive electrode plate to have good kinetic performance. The positive electrode plate of the present application also satisfies: 1050 ≤ U / P ≤ 4500, where P is the compaction density of the positive electrode plate. By controlling the relationship between the U value and the compaction density of the positive electrode plate, the high structural stability of the positive electrode material is ensured, the structural damage degree of the layered structure compound during cycling is small, and the adverse impact of the structural damage of the positive electrode material on the cycling performance is avoided. Therefore, the lithium ion battery can have the advantages of high energy density, excellent kinetic performance, and long cycling life. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following will make the technical solutions and other beneficial effects of the present application obvious by describing the specific embodiments of the present application in detail in conjunction with the drawings.

[0024] Figure 1 It is a comparative diagram of the rate performance curves of Example 1 and Comparative Example 1 provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0026] In the description of the present application, "a plurality of" means two or more, unless otherwise specifically defined. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0027] In the description of the present application, the term "process" not only includes independent processes, but also includes those that can achieve the purpose of the process even when they cannot be clearly distinguished from other processes. In addition, in this specification, the numerical range indicated by "~" means a range including the values described before and after "~" as the minimum value and the maximum value respectively. In addition, in this specification, regarding the term "layer", when observed in a plan view, it includes not only the configuration of the shape formed over the entire surface, but also the configuration of the shape formed on a part.

[0028] The following disclosure provides many different embodiments or examples for implementing different structures of the present application. To simplify the disclosure of the present application, components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present application.

[0029] Benefiting from the advantages of high energy density, low self-discharge, long cycle life, and low price, in recent years, lithium-ion batteries have been widely used in the electric vehicle market. With the booming development of the electric vehicle market, higher requirements have been put forward for the cycle life and power density of lithium-ion batteries. Lithium-ion batteries with fast charge and discharge capabilities and long cycle life can greatly shorten the charging time of electric vehicles and increase the driving range, playing a crucial role in accelerating the global demand for electric vehicles. The performance of lithium-ion batteries depends to a large extent on the cathode material. Selecting a high-quality cathode material system is decisive for achieving the fast charge and discharge performance and long cycle life of lithium-ion batteries. Therefore, it is particularly important to develop a high-energy density lithium-ion battery cathode material system with both good fast charging ability and excellent cycle life. Among them, nickel-cobalt-manganese ternary materials are a type of cathode material that has been widely studied in recent years due to their more prominent energy density advantage compared to the existing commercial lithium iron phosphate cathode materials. However, there are still relatively major challenges in the structural stability and cycle life of the materials. When nickel-cobalt-manganese ternary layered materials are used as cathode materials, the structural stability during long-term cycling is poor. The disordered arrangement of cations will hinder the transport of lithium ions, resulting in a continuous decline in power performance. The layered structure of the cathode material is severely damaged under high current, and the decline of the structure leads to a rapid decrease in cycle life. Improving the structural stability of layered ternary materials and ensuring fast charging ability and cycle performance under high current have always been the focus of research and improvement. Existing technologies often achieve the improvement of the fast charge and discharge ability of lithium-ion batteries by reducing the loading of active substances in the electrode or increasing the proportion of conductive agents. However, these methods usually lead to a decrease in the energy density of lithium-ion batteries, which does not meet the high energy density requirements put forward by the power battery market, and their practical applications are limited. Designing primary particles with small particle sizes can shorten the diffusion distance of Li + ions, which is also a commonly used strategy to improve fast charging performance. However, when the particle size is too small, side reactions on the surface increase, resulting in a rapid decline in cycle performance. Moreover, small particles are prone to agglomeration, affecting the processing performance of the electrode, leading to a decrease in the compaction density of the electrode and the problem of particle breakage easily occurring under high compaction density, which in turn affects the cycle, gas generation, and other performances of lithium-ion batteries.

[0030] Based on this, the present application proposes a secondary battery and an electrical device using the same, such that the layered lithium-containing compound of the positive electrode has a highly ordered layered structure and a low degree of crystal plane preferred orientation, which can greatly improve the speed of lithium ion extraction and insertion and has excellent kinetic performance.

[0031] In some embodiments, the present application provides a secondary battery, which includes the following positive electrode, negative electrode, electrolyte, and separator.

[0032] Positive electrode

[0033] The positive electrode plate includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector. The positive electrode mixture layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing compound with a layered structure; the positive electrode plate satisfies: 4000 ≤ U ≤ 14560,

[0034] and

[0035] wherein, C 003 is the peak area of the 003 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode plate, with the unit of AU·min; [2Theta(110) - 2Theta(018)] is the relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode plate, with the unit of min; FWHM[(110)+(018)] is the sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode plate, with the unit of min.

[0036] In some embodiments, the U value of the positive electrode plate can be obtained by the following method. The positive electrode plate is subjected to XRD testing according to the X-ray diffraction method to obtain an XRD pattern. By analyzing the 2θ positions and the full width at half maximum of the diffraction peaks corresponding to the 018 and 110 crystal planes, and the peak area of the diffraction peak corresponding to the 003 crystal plane in the XRD pattern, it is obtained after calculation. The test conditions for the specific XRD pattern are conventional conditions. For example, the power is 1.6 kW, the test scanning speed is 5° / min, and the kα2 is subtracted from the test pattern. After research, it is found that the U value of the positive electrode plate is closely related to the orderliness of the layered structure and the orientation degree of the 003 crystal plane.

[0037] In some embodiments, the peak area is directly obtained by analyzing the X-ray diffraction pattern. The peak area refers to the integral value of the peak height and the retention time, representing the relative content. The peak area is not determined by a single value and is related to the number of corresponding crystal planes, the unit cell volume, the grain volume, etc. of the sample itself; the relative distance specifically represents the difference in the 2θ angles corresponding to the diffraction peaks. By the X-ray diffraction analysis method, the XRD diffraction pattern of the positive electrode plate can be obtained, and the 2θ angles of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak are subtracted to calculate the relative distance between the 110 and 018 diffraction peaks; the full width at half maximum (FWHM) is a conventional means for characterizing the peak width. The peak width is affected by many factors, such as the wavelength distribution of X-rays, the grain size, etc., and can be calculated by the Scherrer Equation.

[0038] In some embodiments, the peak area of the 003 characteristic diffraction peak satisfies: 2200 ≤ C 003≤3500. For example, the peak area can be any one or any range of two values among 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, or 3500. The unit of the peak area is AU·min. The relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.40 ≤ [2Theta(110) - 2Theta(018)] ≤ 0.70. For example, the relative distance can be any one or any range of two values among 0.40, 0.50, 0.60, or 0.70. The sum of the full-width at half-maximum (FWHM) of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.55 ≤ FWHM[(110) + (018)] ≤ 0.80. For example, the sum of the full-width at half-maximum can be any one or any range of two values among 0.55, 0.60, 0.65, 0.70, 0.75, or 0.80.

[0039] In some embodiments, cation mixing in the layered structure ternary cathode material easily leads to a disordered layered phenomenon. The disordered arrangement of cations in the layered structure hinders the transport of lithium ions, resulting in a continuous decline in power performance. Under high current, the layered structure of the cathode material is severely damaged, and the decline of the structure leads to a rapid decrease in cycle life. In the layered structure ternary cathode material, there is a phenomenon of double-peak splitting in the XRD characteristic diffraction peaks corresponding to the 018 and 110 crystal planes. The degree of double-peak splitting can reflect the layered characteristics of the ternary cathode material. The greater the degree of double-peak splitting, the stronger the layered structure characteristics and the higher the layered order. Furthermore, the Li / Ni mixing degree can be obtained by refining the XRD pattern, which can also reflect the order of the ternary layered structure. The degree of splitting of the XRD characteristic diffraction peaks can be reflected by their relative positions and full-width at half-maximum. Therefore, {[2Thea(110) - 2Theta(018)] × FWHM[(110) + (018)]} can be used to reflect the layered order characteristics in the ternary cathode material.

[0040] In some embodiments, there is generally a preferred orientation in the 003 crystal plane of the layered structure ternary cathode material, which is manifested as a larger integrated area corresponding to this diffraction peak in the XRD diffraction pattern. The preferred orientation of the 003 crystal plane has an important impact on the lithium ion deintercalation rate. The larger the area of the diffraction peak corresponding to the 003 crystal plane, the greater the probability that the layered plane of the lithium-containing compound is parallel to the positive electrode current collector, and the slower the lithium ion deintercalation rate from the positive electrode plate. Conversely, the smaller the area of the diffraction peak corresponding to the 003 crystal plane, the greater the probability that the layered plane of the lithium-containing compound is perpendicular to the positive electrode current collector, and the faster the lithium ion deintercalation rate from the positive electrode plate, and the better the kinetic performance of the positive electrode plate. Therefore, the degree of orientation is characterized by analyzing the peak area of the 003 characteristic diffraction peak to further characterize the lithium ion deintercalation rate.

[0041] In some embodiments, the U value of the positive electrode sheet is controlled within a certain range. The positive active material in such a positive electrode sheet has a high degree of orderliness, creating a good crystal structure basis for the rapid transmission of lithium ions. During the cycling process, the structural stability of the positive electrode material is high, which can effectively inhibit the collapse of the structure, and the degree of 003 crystal plane orientation is small, enabling lithium ions to quickly escape from and embed into the positive electrode sheet, thereby ensuring that the lithium-ion battery has both excellent kinetic performance and long cycle life. When the U value of the positive electrode sheet is greater than 14560 or less than 4000, the layered orderliness of the lithium-containing compound in the positive electrode sheet is low, the degree of structural damage of the positive electrode material during cycling is large, and the degree of 003 crystal plane orientation is large, resulting in a slower speed of lithium ions escaping from and embedding into the positive electrode sheet, and further deterioration of the rate and cycle performance of the battery.

[0042] In some embodiments, the typical but non-limiting values of U are any one or the range of any two of 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 10500, 11000, 11500, 12000, 12500, 13000, 13500, 14000, 14500, 14560. It should be noted that the specific values of U are only given exemplarily, and any value within the range of 4000 to 14560 is within the protection scope of the present application.

[0043] In some embodiments, the U value is 5500 ≤ U ≤ 12500.

[0044] In some embodiments, the U value is 6500 ≤ U ≤ 10500.

[0045] In some embodiments, the compaction density of the positive electrode sheet also has a certain impact on the performance of the lithium-ion battery. The positive electrode sheet further satisfies: 1050 ≤ U / P ≤ 4500, where P g / cm 3 is the compaction density of the positive electrode sheet. When the positive electrode sheet satisfies the above relationship, the kinetic performance and cycle life of the battery can be further improved.

[0046] In some embodiments, the compaction density = areal density / thickness of the active material layer. During the production process of lithium-ion power batteries, the compaction density has a great impact on the battery performance. Experiments have proved that the compaction density is closely related to the specific capacity per unit area, efficiency, internal resistance, and battery cycle performance.

[0047] It can be understood that when the lower limit value of U / P is less than 1050, the lithium-containing compound in the positive electrode sheet has a relatively high degree of layered order, and the degree of 003 crystal plane orientation is small, which is beneficial to the insertion and extraction of lithium ions. However, at the same time, the active material particles in the positive electrode sheet are prone to breakage during the electrode sheet processing, which will exacerbate the occurrence of side reactions during the cycle, and the interfacial impedance between the positive electrode active material and the electrolyte is relatively large, which is not conducive to the improvement of the fast charging and cycle performance of the lithium-ion battery. When the upper limit value of U / P is greater than 4500, the layered order of the lithium-containing compound in the positive electrode sheet is relatively low, and the disorder of the structure will hinder the transmission of lithium ions. At the same time, it will lead to a large degree of structural damage during the cycle, resulting in a rapid decline in the cycle performance, and the degree of 003 crystal plane orientation is large, which will further hinder the speed of lithium ion insertion and extraction, affecting the improvement of the fast charging performance of the lithium-ion battery.

[0048] In some embodiments, 1150 ≤ U / P ≤ 4500. By further controlling the relationship between the U value of the positive electrode sheet and the compaction density value of the positive electrode sheet, and keeping the product of the two within a reasonable range, that is, 1150 ≤ U / P ≤ 4500, the charging ability and cycle life of the lithium-ion battery can be better improved.

[0049] In some embodiments, the compaction density is tested by a compaction density meter, and the test process can refer to the national standard GB / T24533-2019. The compaction density is 3.0 g / cm 3 ~3.8 g / cm 3 , preferably 3.2 g / cm 3 ~3.6 g / cm 3 ; for example, the compaction density can be 3.0 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 , 3.3 g / cm 3 , 3.4 g / cm 3 , 3.5 g / cm 3 , 3.6 g / cm 3 , 3.7 g / cm 3 , 3.8 g / cm 3 or any range between any two of them. It should be noted that the specific values of the compaction density are only given exemplarily. As long as it is within the range of 3.0 g / cm 3 ~3.8 g / cm 3Any value within the range is within the protection scope of this application. When the compaction density meets the above range, it can ensure that the battery cell has both high energy density and long cycle life. Generally speaking, the larger the compaction density, the higher the capacity of the battery. Therefore, the compaction density is also used as one of the reference indicators for the energy density of the material. However, if the compaction density is too large, the porosity of the electrode sheet will decrease, the wetting performance of the electrode sheet for the electrolyte will weaken, the migration rate of lithium ions in the electrode sheet will decrease, the internal resistance of the battery will increase, polarization will occur, and the cycle stability and rate performance of the battery will decrease.

[0050] In some embodiments, the smaller the compaction density of the positive electrode sheet, the faster the lithium ions are deintercalated from the positive electrode sheet, the better the kinetic performance of the positive electrode sheet, and the more conducive to improving the fast charging performance of the battery. However, reducing the compaction density of the positive electrode sheet will result in a decrease in the energy density of the battery. When the compaction density of the positive electrode sheet is too large, although the overall energy density of the battery can be increased, it will lead to an increase in the interfacial charge impedance between the positive active material and the electrolyte, and further reduce the rate of lithium ions deintercalated from the positive electrode sheet. Therefore, by further reasonably controlling the compaction density of the positive electrode sheet within a reasonable range, the lithium ion battery can have both high energy density and long cycle life.

[0051] In some embodiments, 1250 ≤ U / P ≤ 3500. The typical but non-limiting values of U / P are any one or any range between any two of 1250, 1300, 1350, 1400, 1450, 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450, 2500, 2550, 2600, 2650, 2700, 2750, 2800, 2850, 2900, 2950, 3000, 3050, 3100, 3150, 3200, 3250, 3300, 3350, 3400, 3450, 3500; It should be noted that the specific values of U / P are only given exemplarily, and any value within the range of 1250 to 3500 is within the protection scope of this application.

[0052] In some embodiments, the positive electrode sheet satisfies the relational expression 1250 ≤ U / P ≤ 3300.

[0053] In some embodiments, the positive electrode sheet satisfies the relational expression 1800 ≤ U / P ≤ 2500.

[0054] In some embodiments, the positive electrode sheet further satisfies: the sheet resistance of the positive electrode sheet is 0.2 to 0.5 Ω; when the sheet resistance of the positive electrode sheet satisfies this range, the transport ability of lithium ions in the solid phase can be significantly improved, the initial DCR value and the DCR growth rate of the battery can be reduced, and the power performance of the battery can be effectively improved.

[0055] In some embodiments, the porosity of the positive electrode sheet is 20% to 35%. When the porosity satisfies this range, the number of pores in the positive electrode sheet can be controlled to be moderate, ensuring that the electrolyte can infiltrate into the active particles of the electrode sheet, thereby conducting the ion path, ensuring that the positive active material has good ion conduction performance, and at the same time ensuring that the positive active material has a certain compressive strength, and ensuring that lithium ions are uniformly deintercalated and intercalated during charge and discharge, reducing the concentration of stress, alleviating the occurrence of phase change, and being able to improve the cracking problem of the particles during cycling, thereby ensuring that the lithium ion battery using the positive electrode sheet of the present invention has good cycle performance and kinetic performance.

[0056] In some embodiments, the peel force of the positive electrode sheet is 15 to 50 N / m. When the peel force satisfies this range, the bonding strength between the positive active material and the aluminum foil can be improved, the stability of the current collector can be ensured, and the peeling and falling off of the active material from the surface of the foil during long-term cycling can be prevented, thereby improving the cycle life of the lithium ion battery.

[0057] In some embodiments, the positive active material includes a layered lithium-containing compound, the lithium-containing compound is a lithium nickel cobalt oxide, the lithium nickel cobalt oxide further includes element A, and the element includes at least one of Mn, Al, Ti, Mg, and Zr; wherein, based on the sum of the molar amounts of nickel element, cobalt element, and manganese element being 1, the content of nickel element is greater than or equal to 0.5; or based on the sum of the molar amounts of nickel element, cobalt element, and aluminum element being 1, the content of nickel element is greater than or equal to 0.5. While the U value satisfies the above range, when the nickel element is within this range, the side reactions of the secondary battery are reduced and the comprehensive performance is better.

[0058] In some embodiments, the lithium nickel cobalt oxide further contains element M, and element M includes one or more of Al, B, Ca, W, Nb, Mg, Zr, Sr, Si, Y, Ti, and Sn. The above elements can improve the stability and specific capacity of the lithium nickel cobalt oxide.

[0059] In some embodiments, element M can be a doping element and / or a coating element, that is, the lithium nickel cobalt oxide can contain only a doping element, only a coating element, or both a doping element and a coating element at the same time.

[0060] In some embodiments, when the M element is a doping element, the M element is embedded in the lithium nickel cobalt oxide, and the doping element is selected from one or more of Al, B, Ca, W, Nb, Mg, Zr, Sr; when the M element is a coating element, the M element coats at least part of the surface of the lithium nickel cobalt oxide, and the coating element is selected from one or more of Al, B, Zr, Sr, Si, Y, Ti, Sn; when the positive electrode active material contains both a doping element and a coating element, the doping element and the coating element can be different elements or the same element.

[0061] The composition of the coating element can be characterized by TEM (Transmission Electron Microscope) for phase identification to distinguish the specific composition; the doping element can be determined by X-ray photoelectron spectroscopy (XPS) valence state analysis or EDS (Energy Dispersive Spectroscopy) scanning to determine the presence of the doping element.

[0062] The introduction of the doping element can make the order of the layered structure higher, the probability of cation disordered arrangement lower, and the structural stability during cycling higher, which is more beneficial to improving the cycling performance of the lithium-ion battery. The introduction of the coating element can play a role in isolating the electrolyte, can largely reduce the interfacial side reaction between the electrolyte and the layered structure compound, can inhibit the irreversible phase change of the material and the dissolution of transition metal ions during charge and discharge, and improve the structural stability of the layered structure compound. In this embodiment, the substance used for doping or coating is the oxide or hydroxide of the above doping element or coating element. Introducing these substances during the sintering process to achieve doping or coating can effectively improve the structural order and stability of the layered material, thereby improving the long-term cycling performance of the battery cell.

[0063] In some embodiments, the lithium-containing compound contains Li x Ni a Co b A c O2, where 0.95 ≤ x ≤ 1.05, 0.5 ≤ a ≤ 0.9, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and a + b + c = 1.

[0064] In some embodiments, the median particle size D v 50 of the positive electrode active material is 2 μm to 20 μm, and the preferred median particle size D v 50 is 6 μm to 15 μm. For example, the median particle size D v50 is in the range of any one or any two of 2μm, 3μm, 4μm, 56μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm and 20μm. D v 50 has the meaning well-known in the art, also known as the median particle size, which represents the particle size corresponding to 50% of the volume distribution of the positive electrode active material particles. The average particle size D of the positive electrode active material v 50 can be measured by a laser particle size analyzer.

[0065] In some embodiments, the average pore size of the positive electrode active material is 30nm to 200nm; preferably, the average pore size of the positive electrode active material is 50nm to 150nm, and more preferably 60nm to 100nm. For example, the average pore size of the positive electrode active material is 80nm. The average pore size of the positive electrode active material reflects the state of the primary particle packing. An appropriate pore size can not only provide a transport channel for the coating material but also ensure the density of the secondary particles, enabling the mechanical strength of the material to meet the requirements of cycle stability.

[0066] In some embodiments, the specific surface area of the positive electrode active material is 0.3m 2 / g to 0.9m 2 / g; preferably, the specific surface area of the positive electrode active material is 0.4m 2 / g to 0.8m 2 / g, and more preferably 0.5m 2 / g to 0.7m 2 / g. For example, the specific surface area of the positive electrode active material is 0.6m 2 / g. When the specific surface area of the positive electrode active material is within an appropriate range, the contact area between the positive electrode active material and the electrolyte is in a better range, enabling the positive electrode sheet to have a better wetting effect while having a smaller ohmic impedance and the battery having better comprehensive performance. The specific surface area of the positive electrode active material has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, it can be tested by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method.

[0067] In some embodiments, the preparation of the positive electrode active material includes: dispersing a nickel source, a cobalt source, and a manganese source in deionized water by a coprecipitation method to obtain a mixed solution; in a continuous co-current reaction mode, simultaneously pumping the mixed solution, a strong base solution, and a complexing agent solution into a stirred reaction kettle, controlling the pH value of the reaction solution to be 10-13 and the temperature in the reaction kettle to be 25°C-90°C, and protecting with an inert gas during the reaction process; after the reaction is completed, through processes such as washing, filtering, vacuum drying, and sieving to remove iron, a transition metal hydroxide precursor is obtained; then, the relatively loose and porous nickel-cobalt-manganese hydroxide precursor prepared by the coprecipitation method is mixed with a lithium source and a compound containing a doping element in a high-speed mixer, and then the uniformly mixed material is placed in an atmosphere tube furnace, and calcined by introducing a certain content of oxygen, and at the same time, gas flow crushing treatment is carried out to prepare a layered structure oxide positive electrode material; finally, the prepared layered structure oxide positive electrode material is mixed with a compound containing a coating element in a high-speed mixer, and then transferred to an atmosphere tube furnace and calcined by introducing a certain content of oxygen to obtain the positive electrode active material.

[0068] In some embodiments, the nickel source, cobalt source, and manganese source are one or more of oxides, hydroxides, or carbonates containing Ni, Co, and Mn selected according to the stoichiometric ratio. In some embodiments, the structure of the precursor can be regulated by adjusting the selection of reaction raw materials, the pH value of the reaction solution, the concentration of the mixed solution, the concentration of the complexing agent, the reaction temperature, and the reaction time in the preparation of the nickel-cobalt-manganese hydroxide precursor. In some embodiments, the nickel source can include one or more of nickel acetate, nickel nitrate, nickel sulfate, nickel hydroxide, nickel chloride, or nickel carbonate. In some embodiments, the cobalt source can include one or more of cobalt sulfate, cobalt hydroxide, cobalt nitrate, cobalt fluoride, cobalt chloride, or cobalt carbonate. In some embodiments, the manganese source can include one or more of manganese sulfate, manganese chloride, manganese nitrate, or manganese hydroxide.

[0069] In some embodiments, the strong base solution can include one or more of LiOH, NaOH, and KOH; the complexing agent can be one or more of ammonia water, ammonium sulfate, ammonium nitrate, and ammonium chloride. In some embodiments, there are no special restrictions on the solvents of the mixed solution, the strong base solution, and the complexing agent solution. For example, the solvents of the mixed solution, the strong base solution, and the complexing agent solution are each independently one or more of deionized water, methanol, ethanol, acetone, isopropanol, and n-hexanol.

[0070] In some embodiments, the inert gas is one or more of nitrogen, argon, and helium.

[0071] In some embodiments, the lithium source can include one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, or lithium chloride.

[0072] In some embodiments, the compound containing a doping element and the compound containing a coating element may each be one or more of oxides, chlorides, sulfates, nitrates, hydroxides, fluorides, carbonates, bicarbonates, acetates, phosphates, dihydrogen phosphates, and organic compounds of their respective elements.

[0073] In some embodiments, the intermediate product can also be crushed and screened to obtain a cathode active material with an optimized particle size distribution and specific surface area. There are no particular limitations on the crushing method, which can be selected according to actual needs, such as using a particle crusher. The preparation method of the cathode active material of the present application is not limited to the above preparation method, as long as the formed cathode active material has the characteristics shown in the present application.

[0074] In some embodiments, the preparation process of the cathode electrode sheet may include steps such as stirring, coating, drying, cold pressing, slitting, and cutting. During the preparation of the cathode electrode sheet, there are various feasible ways to regulate the structural characteristics of the lithium-containing compound in the cathode electrode sheet, thereby affecting the U value of the cathode electrode sheet. For example, the synthesis process parameters of the selected cathode active material, such as the calcination temperature and calcination time, the doping and coating type of the cathode active material, and the median particle size D v 50 physical properties will all affect the U value of the cathode electrode sheet. The desired U value of the cathode electrode sheet can be controlled by controlling the synthesis process parameters of the synthesized cathode active material, selecting different doping and coating types, or cathode materials with different physical properties. In addition, during the cold pressing process in the production of the cathode electrode sheet, by changing parameters such as the cold pressing pressure to adjust the compaction density of the cathode electrode sheet, the arrangement of the cathode active material in the cathode electrode sheet can also be changed, thereby changing the U value of the cathode electrode sheet.

[0075] In some embodiments, the cathode electrode sheet further includes a conductive agent and a binder. The types and contents of the conductive agent and the binder are not specifically limited and can be selected according to actual needs. In some embodiments, the conductive agent may include conductive carbon black, carbon nanotubes, graphene, etc., and the binder may include polyvinylidene fluoride.

[0076] In some embodiments, the preparation of the cathode electrode sheet includes: dispersing the above-mentioned cathode active material, conductive agent, and binder in N-methylpyrrolidone (NMP) in a certain proportion, coating the obtained slurry on an aluminum foil, drying it, and then obtaining the cathode electrode sheet through cold pressing and slitting.

[0077] Negative electrode sheet

[0078] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material, a binder, and a conductive agent covering the negative electrode current collector. The types and contents of the negative electrode active material, the binder, and the conductive agent are not particularly limited and can be selected according to actual needs. In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, mesocarbon microbeads, amorphous carbon, lithium titanate, or silicon-carbon alloy. The negative electrode active material also needs to have characteristics such as high tap density, relatively high mass specific capacity and volume specific capacity.

[0079] Electrolyte

[0080] In some embodiments, the main components of the electrolyte include a lithium salt and an organic solvent, and may also include additive components. The types and compositions of the lithium salt and the organic solvent are not particularly limited and can be selected according to actual needs. Among them, the lithium salt can include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, etc., the solvent can include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate, etc., and the additive can include lithium difluorophosphate, lithium bis(oxalato)borate, and succinonitrile, etc.

[0081] Separator

[0082] In some embodiments, the type of the separator is not particularly limited and can be selected according to actual needs. The separator can be a polypropylene film, a polyethylene film, a polyvinylidene fluoride, a spandex film, an aramid film, or a multilayer composite film after coating modification.

[0083] In some embodiments, the preparation of the secondary battery includes: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator between the positive and negative electrode sheets to play a role in isolation, then winding it into a square bare battery cell, installing it in a battery case, then baking to remove water at 65 - 95 °C, injecting the electrolyte, sealing, and after processes such as standing, hot and cold pressing, formation, clamping, and grading, the secondary battery is obtained.

[0084] In some embodiments, the secondary battery includes a lithium-ion battery. Taking the soft-pack lithium-ion battery as an example only, this application is not limited to the application of soft-pack batteries, but also includes the application of common lithium-ion battery forms such as aluminum-shell batteries and cylindrical batteries.

[0085] Electrical equipment

[0086] In some embodiments, the present application provides an electrical equipment, and the electrical equipment of the present application includes the above-mentioned secondary battery. The electrical equipment can be used for but is not limited to backup power supplies, motors, electric vehicles, electric motorcycles, assisted bicycles, bicycles, power tools, large household storage batteries, etc.

[0087] Example 1

[0088] Step 1: Prepare the cathode material precursor by coprecipitation method. Mix nickel sulfate, cobalt sulfate, and manganese sulfate evenly according to the molar ratio of 83:12:5 to prepare a mixed transition metal salt solution with a concentration of 1 mol / L. Use sodium hydroxide and ammonia water solutions as the strong base solution and complexing agent respectively. Under the conditions of a water bath temperature of 55 °C and a titration end point pH = 11, stir and react for 6 h. After standing and aging for 12 h, filter and wash to prepare the precursor of transition metal hydroxide.

[0089] Step 2: Place the transition metal hydroxide precursor prepared in Step 1, lithium hydroxide, and the doping raw material zirconia into a high-speed mixer according to the molar ratio of 0.995:1.05:0.0025 and mix evenly. Then place the evenly mixed material into an atmosphere tube furnace, introduce a certain content of oxygen, and calcine at 730 °C for 10 h while performing gas flow crushing treatment to prepare the layered structure oxide cathode material.

[0090] Step 3: Mix the layered structure oxide cathode material prepared in Step 2 with 0.3 wt% of the coating raw material alumina in a high-speed mixer, then transfer it to an atmosphere tube furnace, introduce a certain content of oxygen, and calcine at 450 °C for 6 h to form an oxide coating layer on the surface of the cathode material to obtain the cathode active material Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2.

[0091] Step 4: Mix the cathode active material Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2, conductive agent conductive carbon black, and binder PVDF to make a cathode slurry. The proportion of the cathode active material in the slurry is 97%, the proportion of conductive carbon black is 2%, and the proportion of binder PVDF is 1%. Add NMP as a solvent for mixing. After stirring for a certain time, obtain a uniform cathode slurry with a certain fluidity; evenly coat the cathode slurry on the cathode current collector aluminum foil, then transfer it to an oven at 110 °C for drying, and then obtain the cathode pole piece after rolling, slitting, and cutting. During the preparation process of the cathode pole piece, different cathode pole piece U values can be obtained by selecting different types of cathode active materials and adjusting the rolling process parameters.

[0092] Preparation of the negative electrode sheet: The negative electrode active material graphite, the conductive agent Super P, the thickening agent CMC, and the binder SBR are mixed to form a negative electrode slurry. In the slurry, the proportion of graphite is 96.1%, the proportion of the conductive agent Super P is 1%, the proportion of the thickening agent CMC is 1%, and the binder SBR is 1.9%. Deionized water is added as a solvent for mixing. After stirring for a certain time, a uniform negative electrode slurry with certain fluidity is obtained; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, then transferred to an oven at 120 °C for drying, and then obtained the negative electrode sheet through rolling, slitting, and cutting.

[0093] Preparation of the electrolyte: The organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 2:2:6. In an argon atmosphere glove box with a water content < 10 ppm, the thoroughly dried LiPF6 lithium salt is dissolved in the above organic solvents and mixed evenly to obtain the electrolyte. Among them, the concentration of LiPF6 in the electrolyte is 1 mol / L.

[0094] A 16-μm polypropylene film is selected as the separator.

[0095] The above positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, then wound into a square bare battery cell and placed in an aluminum-plastic film. Then, after baking at 85 °C to remove moisture, a certain amount of organic electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, secondary packaging, and grading, the finished secondary battery is obtained.

[0096] Example 2

[0097] The specific preparation process is the same as that of Example 1. The differences from Example 1 are that in Step 1, the titration end point pH = 11.5 and the stirring reaction time is 8 h. In Step 2, the doping raw material added is niobium pentoxide, and the calcination parameters are calcination at 750 °C for 10 h. In Step 3, the coating raw material added is 0.3 wt% boron oxide.

[0098] The prepared positive electrode active material is Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2.

[0099] Example 3

[0100] The specific preparation process is the same as that of Example 1. The differences from Example 1 are that in Step 1, the titration end point pH = 12. In Step 2, the calcination parameters are calcination at 750 °C for 10 h. In Step 3, the coating raw material added is 0.3 wt% titanium dioxide.

[0101] The prepared positive electrode active material is Li 1.02 Ni0.83 Co 0.12 Mn 0.05 O2。

[0102] Example 4

[0103] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in Step 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate is 60:20:20, and the pH at the titration end point is 12.

[0104] The prepared cathode active material is Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2。

[0105] Example 5

[0106] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in Step 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate is 50:20:30, the pH at the titration end point is 12, and the stirring reaction time is 8 h.

[0107] The prepared cathode active material is Li 1.02 Ni 0.5 Co 0.2 Mn 0.3 O2。

[0108] Example 6

[0109] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in Step 2, no doping raw material is added. The transition metal oxide precursor prepared in Step 1 is directly mixed with lithium hydroxide and then calcined. The calcination parameters are calcination at 750 °C for 12 h.

[0110] The prepared cathode active material is Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2。

[0111] Example 7

[0112] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in Step 3, no coating raw material is added. The cathode active material prepared in Step 2 is transferred to a tube furnace with oxygen introduced and calcined at 500 °C for 8 h.

[0113] The prepared cathode active material is Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2。

[0114] Example 8

[0115] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in step one, nickel sulfate, cobalt sulfate, and aluminum sulfate are mixed evenly according to a molar ratio of 83:12:5.

[0116] The prepared cathode active material is Li 1.02 Ni 0.83 Co 0.12 Al 0.05 O2.

[0117] Example 9

[0118] The specific preparation process is the same as that of Example 4. The difference from Example 4 is that nickel sulfate, cobalt sulfate, and aluminum sulfate are used with a molar ratio of 60:20:20.

[0119] The prepared cathode active material is Li 1.02 Ni 0.6 Co 0.2 Al 0.2 O2.

[0120] Example 10

[0121] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in step one, nickel sulfate, cobalt sulfate, and aluminum sulfate are mixed evenly according to a molar ratio of 50:30:20.

[0122] The prepared cathode active material is Li 1.02 Ni 0.50 Co 0.3 Al 0.2 O2.

[0123] Example 11

[0124] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that in step one, nickel sulfate, cobalt sulfate, and aluminum sulfate are mixed evenly according to a molar ratio of 80:10:10.

[0125] The prepared cathode active material is Li 1.02 Ni 0.8 Co 0.1 Al 0.1 O2.

[0126] Example 12

[0127] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that the doping raw material in step two is magnesium oxide; the coating raw material in step three is strontium oxide.

[0128] Example 13

[0129] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that the doping raw material in Step 2 is strontium oxide; the coating raw material in Step 3 is zirconium oxide.

[0130] Example 14

[0131] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that the doping raw material in Step 2 is calcium oxide; the coating raw material in Step 3 is zirconium oxide.

[0132] Comparative Example 1

[0133] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that the pH at the titration end point in Step 1 is 11.5, and the stirring reaction time is 8 h; no doping raw material is added in Step 2. The transition metal oxide precursor prepared in Step 1 is directly mixed evenly with lithium hydroxide and then subjected to calcination treatment. The calcination parameters are calcination at 770 °C for 12 h; no coating raw material is added in Step 3. The positive electrode active material prepared in Step 2 is transferred to a tube furnace with oxygen introduced and calcined at 550 °C for 8 h.

[0134] The finally prepared positive electrode active material is Li 1.02 Ni 0.83 Co 0.12 Mn 0.05 O2.

[0135] Comparative Example 2

[0136] The specific preparation process is the same as that of Example 1. The difference from Example 1 is that the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate in Step 1 is 60:20:20, the pH at the titration end point is 12, and the stirring reaction time is 8 h; no doping raw material is added in Step 2. The transition metal oxide precursor prepared in Step 1 is directly mixed evenly with lithium hydroxide and then subjected to calcination treatment. The calcination parameters are calcination at 770 °C for 12 h; no coating raw material is added in Step 3. The positive electrode active material prepared in Step 2 is transferred to a tube furnace with oxygen introduced and calcined at 550 °C for 8 h.

[0137] The finally prepared positive electrode active material is Li 1.02 Ni 0.6 Co 0.2 Mn 0.2 O2.

[0138] Comparative Example 3

[0139] The specific preparation process is the same as that of Example 1. The differences from Example 1 are as follows: in Step 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate is 50:20:30, the pH at the titration end point is 12, and the stirring reaction time is 8 h; in Step 2, no doping raw material is added. The transition metal oxide precursor prepared in Step 1 is directly mixed evenly with lithium hydroxide and then subjected to calcination treatment. The calcination parameters are calcination at 770 °C for 12 h; in Step 3, no coating raw material is added. The positive electrode active material prepared in Step 2 is transferred to a tube furnace filled with oxygen and calcined at 550 °C for 8 h.

[0140] The finally prepared positive electrode active material is Li 1.02 Ni 0.5 Co 0.2 Mn 0.3 O2.

[0141] Testing methods

[0142] (1) U value testing method

[0143] Slowly scan the 10-80° interval of the XRD pattern of the sample to be tested at a scanning speed of 5° / min, and subtract kα2 from the test pattern. After analysis and calculation, obtain the positions, half-peak widths of the diffraction peaks corresponding to the 018 and 110 crystal planes, and the area of the diffraction peak corresponding to the 003 crystal plane, and substitute them into the formula U = C 003 / {[2Thea(110)-2Theta(018)]×FWHM[(110)+(018)]} and further calculate the U value of the sample.

[0144] (2) Cycling performance test of the battery

[0145] Under room temperature conditions, charge the batteries prepared in Examples 1-7 and Comparative Examples 1-3 at a 1C rate and discharge at a 1C rate, and perform a full charge and discharge cycle test until the capacity of the battery decays to 80% of the initial capacity, and record the number of cycles.

[0146] (3) Rate performance test of the battery

[0147] Under room temperature conditions, discharge the batteries prepared in Examples 1-7 and Comparative Examples 1-3 to the lower voltage limit at a 1C rate, and then sequentially complete charging to the upper voltage limit (without CV charging) at rates of 1 / 3C, 0.5C, 1C, 1.5C, and 2C, and record the capacity and capacity retention rate to obtain the rate performance curve of the battery.

[0148] Table 1 shows the test results of the parameters of the positive electrode active materials and positive electrode plates corresponding to Examples 1-7 and Comparative Examples 1-3; Table 2 shows the test results of the battery parameters corresponding to Examples 1-7 and Comparative Examples 1-3.

[0149] Table 1

[0150]

[0151]

[0152] Table 2

[0153]

[0154] From the analysis of the test results in Table 1 and Table 2, it can be seen that in Examples 1-7 of this application, the U values of the prepared positive electrode sheets are all within the defined range. The positive active materials in the positive electrode sheets have a high degree of order, creating a good crystal structure basis for the rapid transmission of lithium ions. During the cycling process, the structural stability of the positive electrode material is high, which can effectively inhibit the collapse of the structure, and the degree of 003 crystal plane orientation is small, enabling lithium ions to quickly escape from and embed into the positive electrode sheet. Thus, it is ensured that the lithium-ion battery has both excellent kinetic performance and long cycle life, can effectively shorten the charging time of electric vehicles and increase the cruising range of electric vehicles, and greatly improve the usage experience of new energy vehicles.

[0155] In Comparative Example 1, the U value of the prepared positive electrode sheet is too large, and the layered order degree of the lithium-containing compound in the positive electrode sheet is low. The disorder of the structure will hinder the transmission of lithium ions, and at the same time, it will cause a large degree of structural damage during cycling, resulting in a rapid decline in the cycling performance. In addition, the degree of 003 crystal plane orientation is large, which will further hinder the speed of lithium ion deintercalation / insertion, and is not conducive to the improvement of the fast charging performance of the lithium-ion battery. It cannot meet the design requirements of the battery for fast charging, nor can it meet the usage requirements of the battery for long cycle life. It can also be found from the test results of the rate performance and cycling performance in Table 2 that the rate performance and cycling performance of Comparative Example 1 are significantly inferior to those of Example 1.

[0156] When the compaction density of the positive electrode sheet is further reasonably controlled so that U / P also satisfies the range between 1150 and 4500, the kinetic performance and cycle life of the battery can be further improved. In Example 6, the U value of the positive electrode sheet is relatively larger than that in Examples 1-3, and the compaction density P is smaller. The upper limit value of U / P is greater than 4500. At this time, the layered order degree of the lithium-containing compound in the positive electrode sheet is lower than that in the other examples, the degree of disorder of the structure increases, and the orientation degree of the 003 crystal plane is larger, which will further hinder the speed of lithium-ion insertion and extraction, and is not conducive to the improvement of the fast charging and cycle performance of the lithium-ion battery. The smaller compaction density P also results in a decrease in the overall energy density of the battery. In Example 7, the U value of the positive electrode sheet is smaller. At this time, although the lithium-containing compound in the positive electrode sheet has a high layered order degree and a low orientation degree of the 003 crystal plane, the compaction density of the sheet is too high at this time, resulting in insufficient infiltration of the electrolyte into the positive active material. The interfacial impedance between the positive active material and the electrolyte is higher, and particle breakage is likely to occur during the processing of the sheet, leading to an increase in harmful side reactions, which is not conducive to the improvement of the fast charging and cycle performance of the battery. Therefore, preferably, the positive electrode sheet also satisfies 1150≤U / P≤4500, so that the lithium-ion battery has the advantages of high energy density, fast charging ability and long cycle life at the same time.

[0157] The secondary battery and the electrical device provided by the embodiments of the present application have been introduced in detail above. Specific examples are used in the present application to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the technical solution and its core idea of the present application; those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A secondary battery, characterized in that, comprising a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector, the positive electrode mixture layer including a positive electrode active material, and the positive electrode active material including a lithium-containing compound having a layered structure; the positive electrode plate satisfies: 4000 ≤ U ≤ 14560, and In the formula, C 003 is the peak area of the 003 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of AU·min; [2Theta(110)-2Theta(018)] is the relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of min; FWHM[(110)+(018)] is the sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak in the X-ray diffraction pattern of the positive electrode sheet, with the unit of min; The peak area of the characteristic diffraction peak described satisfies: 2200 ≤ C 003 ≤ 3500; the relative distance between the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.40 ≤ [2Theta(110) - 2Theta(018)] ≤ 0.70; the sum of the full width at half maximum of the 110 characteristic diffraction peak and the 018 characteristic diffraction peak satisfies: 0.55 ≤ FWHM[(110) + (018)] ≤ 0.80; The chemical formula of the lithium-containing compound includes Li x Ni a Co b A c O2, where 0.95 ≤ x ≤ 1.05, 0.5 ≤ a ≤ 0.9, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and a + b + c = 1, and A includes at least one of Mn, Al, Ti, Mg, and Zr.

2. The secondary battery according to claim 1, characterized in that, the positive electrode plate satisfies: 5500 ≤ U ≤ 12500.

3. The secondary battery according to claim 1, wherein 6500≤U≤10500。 4. The secondary battery according to claim 1, wherein, The positive electrode sheet satisfies: 1050 ≤ U / P ≤ 4500, where P is the tap density of the positive electrode sheet, and 3.0 ≤ P ≤ 3.8 g / cm 3 3.

5. A secondary battery according to claim 1, characterized in that, the lithium nickel cobalt oxide further contains an M element, and the M element includes one or more of Al, B, Ca, W, Nb, Mg, Zr, Sr, Si, Y, Ti, and Sn.

6. The secondary battery according to claim 5, wherein, the M is a doping element and / or a coating element; wherein, the doping element includes one or more of Al, B, Ca, W, Nb, Mg, Zr, and Sr; the coating element includes one or more of Al, B, Zr, Sr, Si, Y, Ti, and Sn; when M is a combination of the doping element and the coating element, the doping element and the coating element are different elements.

7. A secondary battery according to claim 1, characterized in that, The median particle size D of the positive electrode active material v 50 is 2 μm to 20 μm.

8. An electrical device, characterized in that, comprising the secondary battery according to any one of claims 1-7, and the secondary battery serves as a power supply for the electrical device.

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