Lithium-containing nickel-manganese composite oxide, method for preparing the same, and positive electrode sheet, secondary battery, and electric device comprising the same

Abstract

The application provides a lithium-containing nickel-manganese composite oxide, a preparation method thereof, a positive electrode sheet containing the lithium-containing nickel-manganese composite oxide, a secondary battery and an electric device. The lithium-containing nickel-manganese composite oxide is a single crystal or a single crystal-like particle, and the grain shape of the lithium-containing nickel-manganese composite oxide is spherical or spherical-like. The general formula of the lithium-containing nickel-manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5‑x‑y‑z‑a A a O 4‑k , -0.2≤x≤0.5, -0.2≤y≤0.2, 0≤z≤0.2, 0 The lithium-containing nickel-manganese composite oxide provided by the application can improve the capacity performance, energy density and cycle life of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a lithium-containing nickel-manganese composite oxide, a preparation method thereof, a positive electrode sheet comprising the lithium-containing nickel-manganese composite oxide, a secondary battery, and an electric device. BACKGROUND

[0002] In recent years, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and promotion of secondary batteries, people's demand for secondary batteries with high energy density, safety and reliability, and low cost is growing. The cobalt-free spinel LiNi 0.5 Mn 1.5 O4 has become one of the most concerned positive active materials due to its high energy density, good thermal stability and low cost, etc. However, its high working voltage hinders its compatibility with conventional electrolyte, and causes serious side reactions and deterioration of the positive electrode-electrolyte interface, thereby hindering its practical application. SUMMARY

[0003] The purpose of the present application is to provide a lithium-containing nickel-manganese composite oxide, a preparation method thereof, a positive electrode sheet comprising the lithium-containing nickel-manganese composite oxide, a secondary battery, and an electric device, which can improve the capacity performance, energy density and cycle life of the secondary battery.

[0004] The first aspect of the present application provides a lithium-containing nickel-manganese composite oxide, which is a single crystal or a single crystal-like morphology particle and the grain shape of the lithium-containing nickel-manganese composite oxide is spherical or spherical-like, and the general formula of the lithium-containing nickel-manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z-a A a O 4-k , -0.2≤x≤0.5, -0.2≤y≤0.2, 0≤z≤0.2, 0

[0005] The lithium-containing nickel-manganese composite oxide provided by the present application can achieve the maximum reduction of electrolyte corrosion, reduce the positive electrode-electrolyte interface side reaction, and reduce the positive electrode-electrolyte interface impedance, so that the lithium-containing nickel-manganese composite oxide provided by the present application can have good comprehensive performance, such as higher specific capacity and cycle stability, thereby improving the capacity performance, energy density and cycle life of the secondary battery.

[0006] In any embodiment of the present application, the ratio of the length L to the short diameter S of the crystal grain of the lithium-containing nickel-manganese composite oxide satisfies 1.0≤L / S≤1.25, and optionally, 1.0≤L / S≤1.15. Thus, the lithium-containing nickel-manganese composite oxide can have a smaller stress corrosion rate.

[0007] In any embodiment of the present application, M comprises one or more selected from Mo, Nb, Ru, Te, Ta, Ce and Yb, and optionally comprises two or more selected from Mo, Nb, Ru, Te, Ta, Ce and Yb. These doping elements M, in addition to promoting the roundness of the crystal grain shape of the lithium-containing nickel-manganese composite oxide, can themselves form strong bonds with oxygen, thereby further enhancing the structural stability of the lithium-containing nickel-manganese composite oxide, reducing oxygen defects, and thus enabling the lithium-containing nickel-manganese composite oxide and the secondary battery to have better electrochemical performance.

[0008] In any embodiment of the present application, 0.01≤a≤0.2, and optionally, 0.01≤a≤0.1. When the content of the doping element A is within a suitable range, it helps the secondary battery to better balance good kinetic performance and long service life.

[0009] In any embodiment of the present application, 0<z≤0.2, and optionally, 0.005≤z≤0.1. When the content of the doping element M is within a suitable range, it helps the secondary battery to better balance good kinetic performance and long service life.

[0010] In any embodiment of the present application, 0.01≤z+a≤0.2, and optionally, 0.01≤z+a≤0.15. When the total amount of the doping elements A and M is within a suitable range, it is beneficial for the lithium-containing nickel-manganese composite oxide and the secondary battery to have better electrochemical performance.

[0011] In any embodiment of the present application, 0<z≤0.2 and 1≤a / z≤5, and optionally, 0<z≤0.2 and 2≤a / z≤4. When the ratio of the doping element A to the doping element M is within a suitable range, it can achieve the maximum reduction of electrolyte corrosion, thereby enabling the lithium-containing nickel-manganese composite oxide and the secondary battery to have better electrochemical performance.

[0012] In any embodiment of this application, the 4V platform charging capacity ratio R of the lithium nickel manganese composite oxide satisfies 0 < R ≤ 0.125, and optionally, 0.03 ≤ R ≤ 0.105. The 4V platform charging capacity ratio R of the lithium nickel manganese composite oxide is tested as follows: a coin cell is assembled using an electrode containing the lithium nickel manganese composite oxide as the positive electrode and a lithium sheet as the negative electrode; it is charged to 4.95V with a current of 0.1 times the battery capacity, and then charged at a constant voltage to a current of 0.05 times the battery capacity; the ratio of the charging capacity in the range of 3.5V-4.4V to the total charging capacity of the coin cell is taken as the 4V platform charging capacity ratio R of the lithium nickel manganese composite oxide. The lithium nickel manganese composite oxide provided in this application is applicable to high-voltage systems above 4.5V, and its charging capacity ratio is relatively low at low voltages (e.g., 3.5V-4.4V) and relatively high at high voltages, thereby fully leveraging its advantage of high voltage capacity and enabling the secondary battery to have high energy density.

[0013] In any embodiment of this application, the volumetric particle size Dv50 of the lithium-containing nickel-manganese composite oxide satisfies 3μm≤Dv50≤16μm, and optionally, 5μm≤Dv50≤13μm. This helps the secondary battery to better balance good kinetic performance and long service life.

[0014] In any embodiment of this application, the BET specific surface area S0 of the lithium-containing nickel-manganese composite oxide is ≤0.8m². 2 / g, optionally, 0.1m 2 / g≤S0≤0.5m 2 / g. This helps secondary batteries better balance good kinetic performance and long service life.

[0015] In any embodiment of this application, the tap density TD of the lithium-containing nickel-manganese composite oxide satisfies 1.5 g / cm³. 3 ≤TD≤3.0g / cm 3 1.7g / cm³ is an optional value. 3 ≤TD≤2.3g / cm 3 This helps secondary batteries achieve higher energy density.

[0016] In any embodiment of this application, the lithium-containing nickel-manganese composite oxide also has a coating layer on its surface. This further improves the structural stability of the lithium-containing nickel-manganese composite oxide and reduces direct contact between the lithium-containing nickel-manganese composite oxide and the electrolyte, reducing manganese ion dissolution, thereby contributing to a longer service life of the secondary battery.

[0017] In any embodiment of the present application, the coating layer comprises one or more selected from conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials. Optionally, the conductive carbon materials include one or more selected from soft carbon, hard carbon, graphene, and graphene oxide. Optionally, the metal oxides include one or more selected from Al2O3, B2O3, TiO2, ZrO2, WO3, MoO3, Y2O3, Ta2O5, TeO2, Nb2O5. Optionally, the metal fluorides include one or more selected from LiF, AlF3, GaF3. Optionally, the polyanionic materials include one or more selected from orthophosphates and fluorinated orthophosphates containing at least one element selected from Li, Ni, Co, Mn, Fe, Nb, Mo, W, Ta, and Te, and more optionally include one or more selected from LiNiPO4, LiPO2F2, and Li2PO3F.

[0018] The second aspect of the present application provides a method for preparing a lithium nickel manganese composite oxide, comprising the following steps: S1, providing raw materials, which are obtained by mixing a source of Li element, a source of Ni element, a source of Mn element, a source of A element, and an optional source of M element in a predetermined ratio; S2, heating the raw materials obtained in S1 to a first temperature T1 in an oxygen-containing atmosphere and holding at the first temperature T1 for a first time t1, and then cooling to room temperature after completion to obtain an intermediate product, and 850 °C ≤ T1 ≤ 1100 °C; S3, heating the intermediate product obtained in S2 to a second temperature T2 in an oxygen-containing atmosphere and holding at the second temperature T2 for a second time t2, and then obtaining a lithium nickel manganese composite oxide after completion, 0 °C ≤ T1 - T2 ≤ 200 °C, and T2 ≥ 800 °C, wherein the lithium nickel manganese composite oxide is in the form of single crystal or quasi-single crystal particles and the grain shape of the lithium nickel manganese composite oxide is spherical or quasi-spherical, and the general formula of the lithium nickel manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z-a A a O 4-k , -0.2 ≤ x ≤ 0.5, -0.2 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 < a ≤ 0.2, 0 ≤ k ≤ 0.2, A includes one or more selected from Si, P, and S, M includes one or more selected from metal doping elements, and is optionally selected from one or more selected from Ti, Cr, Mo, Nb, Ru, Te, Ta, W, Ce, Y, and Yb.

[0019] In the preparation method of the present application, the first temperature T1 during the first sintering satisfies 850 °C ≤ T1 ≤ 1100 °C,

[0020] This can ensure that the grains grow to the target size and the grain structure is complete. By controlling the temperature T2 during the second sintering to be less than or equal to the temperature T1 during the first sintering, the fine powder in the intermediate product obtained after the first sintering can be promoted to recrystallize, and at the same time, large grains can be prevented from recrystallizing again. Thus, it can be ensured that the grains of the lithium nickel manganese composite oxide obtained have a round spherical or quasi-spherical shape.

[0021] In any embodiment of the present application, 900°C ≤ T1 ≤ 1100°C, optionally, 950°C ≤ T1 ≤ 1100°C. This is beneficial for the grains of the lithium nickel manganese composite oxide to grow to the target size, have appropriate particle size and specific surface area, and at the same time is beneficial for maintaining the integrity of the grain structure of the lithium nickel manganese composite oxide, so that the secondary battery can have better cycling performance.

[0022] In any embodiment of the present application, 0°C ≤ T1 - T2 ≤ 100°C, and 850°C ≤ T2 ≤ 1000°C, optionally, 0°C < T1 - T2 ≤ 100°C, and 850°C ≤ T2 ≤ 1000°C. This is beneficial for the grains of the lithium nickel manganese composite oxide to have a higher degree of roundness and sphericity, and further makes it more resistant to strong acid corrosion in the electrolyte and stress corrosion under high voltage.

[0023] In any embodiment of the present application, t2 ≤ t1, optionally, t2 < t1. This is beneficial for the grains of the lithium nickel manganese composite oxide to have a higher degree of roundness and sphericity, and further makes it more resistant to strong acid corrosion in the electrolyte and stress corrosion under high voltage, and at the same time can prevent large grains in the intermediate product obtained after the first sintering from recrystallizing again.

[0024] In any embodiment of the present application, 2h ≤ t1 ≤ 50h.

[0025] In any embodiment of the present application, 0.5h ≤ t2 ≤ 20h.

[0026] In any embodiment of the present application, 10h ≤ t1 + t2 ≤ 40h.

[0027] In any embodiment of the present application, the method further includes the step: S4, annealing the product obtained in S3 to obtain a lithium nickel manganese composite oxide, which can further reduce oxygen defects. Optionally, the annealing temperature is 500°C - 800°C. Optionally, the annealing time is 5h - 50h.

[0028] In any embodiment of this application, the method further includes the step of: mixing the lithium-containing nickel-manganese composite oxide obtained in S4 with a coating agent, and then sintering it under a protective gas atmosphere to obtain a lithium-containing nickel-manganese composite oxide with a coating layer. Optionally, the coating agent is one or more precursor compounds used to form conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials.

[0029] In any embodiment of this application, the method further includes the step of: mixing the lithium-containing nickel-manganese composite oxide obtained in S3 with a coating agent, and then sintering it under a protective gas atmosphere to obtain a lithium-containing nickel-manganese composite oxide with a coating layer. Optionally, the coating agent is one or more precursor compounds used to form conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials.

[0030] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer comprises a lithium-containing nickel-manganese composite oxide of the first aspect of this application or a lithium-containing nickel-manganese composite oxide prepared by the preparation method described in the second aspect of this application, wherein the content of the lithium-containing nickel-manganese composite oxide in the positive electrode film layer is 1 wt% to 99 wt%, optionally 85 wt% to 99 wt%, based on the total weight of the positive electrode film layer.

[0031] The fourth aspect of this application provides a secondary battery, including the positive electrode sheet of the third aspect of this application.

[0032] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0033] The lithium-containing nickel-manganese composite oxide provided in this application can minimize electrolyte corrosion, thereby exhibiting excellent overall performance and improving the capacity utilization, energy density, and cycle life of the secondary battery. The electrical device of this application includes the secondary battery provided in this application, and therefore possesses at least the same advantages as the aforementioned secondary battery. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0035] FIG. 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0036] FIG. 2yes FIG. 1 An exploded view of the implementation method of the secondary battery.

[0037] FIG. 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0038] FIG. 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0039] FIG. 5 yes FIG. 4 An exploded view of an embodiment of the battery pack shown.

[0040] FIG. 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0041] FIG. 7 This is a scanning electron microscope image of the lithium-containing nickel-manganese composite oxide prepared in Example 1.

[0042] FIG. 8 This is a scanning electron microscope image of the lithium-containing nickel-manganese composite oxide prepared in Comparative Example 1.

[0043] FIG. 9 This is a scanning electron microscope image of the lithium-containing nickel-manganese composite oxide prepared in Comparative Example 5.

[0044] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0045] The following detailed description, with appropriate reference to the accompanying drawings, discloses the lithium-containing nickel-manganese composite oxide, its preparation method, and embodiments thereof, including a positive electrode, a secondary battery, and an electrical device. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for a thorough understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0046] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0048] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0049] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0050] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0051] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0052] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0053] Spinel-type LiMn₂O₄ is a positive electrode active material with three-dimensional lithium-ion transport channels, and it has advantages such as low cost and good safety performance. However, its operating voltage is relatively low (approximately 4.0V), resulting in poor capacity utilization in secondary batteries. Spinel-type LiMn₂O₄ also exhibits a severe Jahn-Teller effect during charge and discharge, causing the crystal structure of the positive electrode active material to transform from a cubic to a tetrahedral structure, leading to rapid capacity decay and poor cycle stability in secondary batteries. In contrast, spinel-type LiNi… 0.5 Mn 1.5 In O4, the manganese ion is in principle at a +4 oxidation state, which makes it less affected by lattice distortion compared to LiMn2O4. Therefore, Li + Mn is almost non-existent during de-embedding. 3+ / Mn 4+ The redox reaction does not occur, but rather Ni exists. 2+ / Ni 4+ Ni 2+ / Ni 3+ Because of its redox properties, it hardly produces the Jahn-Teller effect or crystal structure transformation, and it has a voltage plateau of 4.7V, thus significantly improving its energy density.

[0054] However, spinel-type LiNi 0.5 Mn 1.5 O4's high operating voltage and the catalytic properties of transition metal ions easily oxidize and decompose organic solvents in the electrolyte, forming a carbonized film on the surface of the positive electrode active material. This leads to thickening of the positive electrode-electrolyte interface, increased interfacial impedance, and also hinders the oxidation of Li. + The insertion and extraction of spinel-type LiNi; 0.5 Mn 1.5 The high operating voltage of O4 also leads to a stronger acidity in the electrolyte, resulting in the production of a large amount of strong acid, including HF, which severely corrodes the surface of the positive electrode active material, causing a large amount of transition metal ions (especially manganese ions) to dissolve, thus seriously deteriorating the electrochemical performance of the secondary battery.

[0055] In addition, the currently prepared spinel LiNi0.5 Mn 1.5 The shape of MnO4 grains is mostly octahedron or truncated octahedron. Due to many sharp edges and corners on its surface, these edges and corners are prone to stress corrosion, which will further deteriorate the overall performance of the secondary battery.

[0056] In view of the above problems, the inventors of the present application have provided a lithium-containing nickel manganese composite oxide with a rounded spherical or spherical-like grain shape through a large amount of research.

[0057] Lithium-containing nickel-manganese composite oxide

[0058] In the first aspect of the embodiment of the present application, a lithium-containing nickel manganese composite oxide is provided. The lithium-containing nickel manganese composite oxide is a single crystal or single crystal-like morphology particle, and the grain shape of the lithium-containing nickel manganese composite oxide is spherical or spherical-like. The general formula of the lithium-containing nickel manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z-a A a O 4-k , -0.2 ≤ x ≤ 0.5, -0.2 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 < a ≤ 0.2, 0 ≤ k ≤ 0.2, A includes one or more selected from Si, P and S, and M includes one or more selected from metal doping elements.

[0059] The grain shape of the lithium-containing nickel manganese composite oxide provided by the present application is a rounded spherical or spherical-like shape. Rounded means that when observed microscopically, in a micron-level field of view, there are no sharp edges or vertices where the planes of the grains directly intersect, the flat sides on the surface are connected by curved surfaces, or the entire surface is a curved surface. Thus, when the grain shape of the lithium-containing nickel manganese composite oxide is a rounded spherical or spherical-like shape, the stress corrosion rate under high voltage can be significantly reduced, and the overall performance of the secondary battery can be improved.

[0060] The inventors of the present application surprisingly found through a large number of experiments that the above doping element A can promote the roundness of the grain shape of the lithium-containing nickel manganese composite oxide, making its grain shape a rounded spherical or spherical-like shape, and also helps to obtain single crystal or single crystal-like morphology particles. Therefore, the stress corrosion rate of the lithium-containing nickel manganese composite oxide under high voltage can be significantly reduced, and the electrochemical performance of the secondary battery can be improved.

[0061] The inventors of the present application also found through a large number of experiments that the above doping element A can also be applied to a high voltage system above 4.5V, can capture strong acids in the electrolyte, such as HF, and form a composite oxide containing elements such as Li, A, O, F, etc. on the surface of the lithium-containing nickel manganese composite oxide. This composite oxide can further reduce the corrosion effect of strong acids in the electrolyte, thereby reducing the dissolution of manganese ions.

[0062] Therefore, the lithium-containing nickel-manganese composite oxide provided in this application can minimize electrolyte corrosion, reduce side reactions at the cathode-electrolyte interface, and lower the cathode-electrolyte interface impedance. As a result, the lithium-containing nickel-manganese composite oxide provided in this application can have good comprehensive performance, such as higher specific capacity and cycle stability, thereby improving the capacity utilization, energy density, and cycle life of the secondary battery.

[0063] In this application, "grain" and "particle" are two completely different concepts. A grain is a region of a crystalline material that is internally completely ordered, with regular atomic arrangement at its boundaries (grain boundaries), and exhibits overall variation. In this application, a particle refers to an aggregate that cannot be further dispersed by methods such as ultrasonic dispersion, and can be composed of one or more grains. When a particle consists of a single grain, it is a monocrystalline particle; when a particle consists of multiple aggregates of grains, it is a polycrystalline particle.

[0064] In this application, the term "quasi-single crystal" refers to a particle composed of an aggregate of several or a dozen crystal grains.

[0065] The lithium-containing nickel-manganese composite oxide provided in this application consists of single-crystal or near-single-crystal particles, preferably single-crystal particles. Polycrystalline particles contain numerous grain boundaries, which are prone to cracking under stress during the fabrication and use of secondary batteries, exposing unstable surfaces and reducing grain roundness. In contrast, single-crystal particles do not contain grain boundaries, and near-single-crystal particles consist of aggregates of several or a dozen grains with very few grain boundaries. Therefore, during the fabrication and use of secondary batteries, the probability of unstable surfaces being exposed in the lithium-containing nickel-manganese composite oxide provided in this application is relatively low, thus better maintaining grain roundness. Consequently, the lithium-containing nickel-manganese composite oxide provided in this application exhibits high resistance to electrolyte corrosion, resulting in better capacity utilization, higher energy density, and longer cycle life in the secondary battery.

[0066] The lithium-containing nickel-manganese composite oxide provided in this application has a spherical or near-spherical grain shape. In this application, the term "near-spherical" means that the shape is basically spherical or the aspect ratio is close to 1, for example, the aspect ratio is not greater than 1.3, and optionally not greater than 1.2.

[0067] In some embodiments, the ratio of the major axis L to the minor axis S of the lithium-containing nickel-manganese composite oxide grains satisfies 1.0 ≤ L / S ≤ 1.25, and optionally, 1.0 ≤ L / S ≤ 1.15. The lithium-containing nickel-manganese composite oxide grains of this application have a rounded spherical or near-spherical shape with high roundness and sphericity, thereby achieving a lower stress corrosion rate.

[0068] In some embodiments, 0.01 ≤ a ≤ 0.2, and optionally, 0.01 ≤ a ≤ 0.1. When the content of the doping element A is within a suitable range, it helps the secondary battery to better balance good kinetic performance and long service life.

[0069] In some embodiments, M is a transition metal element, and may be selected from one or more of Ti, Cr, Mo, Nb, Ru, Te, Ta, W, Ce, Y, and Yb. The above doping element M can also promote the roundness of the grain shape of the lithium nickel manganese composite oxide, making its grain shape a round spherical or quasi-spherical shape, and helping to obtain particles with a single crystal or quasi-single crystal morphology. Thereby, the stress corrosion rate of the lithium nickel manganese composite oxide at high voltage can be further reduced, and the electrochemical performance of the secondary battery can be improved.

[0070] In some embodiments, M includes one or more of Mo, Nb, Ru, Te, Ta, Ce, and Yb. Optionally, M includes two or more of Mo, Nb, Ru, Te, Ta, Ce, and Yb. Optionally, M includes two or more of Nb, Te, Ta, and Ce. For example, M is a combination of Te and Ta, a combination of Nb and Te, a combination of Nb and Ce, etc. In addition to promoting the roundness of the grain shape of the lithium nickel manganese composite oxide, these doping elements M can also form strong bonds with oxygen by themselves, thereby further enhancing the structural stability of the lithium nickel manganese composite oxide, reducing oxygen defects, and further enabling the lithium nickel manganese composite oxide and the secondary battery to have better electrochemical performance.

[0071] In some embodiments, z is 0.

[0072] In some embodiments, 0 < z ≤ 0.2, and optionally, 0.005 ≤ z ≤ 0.1, 0.005 ≤ z ≤ 0.09, 0.005 ≤ z ≤ 0.08, 0.005 ≤ z ≤ 0.07, 0.005 ≤ z ≤ 0.06, 0.005 ≤ z ≤ 0.05. When the content of the doping element M is within a suitable range, it helps the secondary battery to better balance good kinetic performance and long service life.

[0073] In some embodiments, 0.01 ≤ z + a ≤ 0.2, and optionally, 0.01 ≤ z + a ≤ 0.175, 0.01 ≤ z + a ≤ 0.15, 0.01 ≤ z + a ≤ 0.125, 0.01 ≤ z + a ≤ 0.1. When the total doping amount of the doping element A and the doping element M is within a suitable range, it is beneficial for the lithium nickel manganese composite oxide and the secondary battery to have better electrochemical performance. And it can effectively avoid the following situation: when the total doping amount of the doping element A and the doping element M is too high, it may significantly reduce the specific capacity of the lithium nickel manganese composite oxide and reduce the energy density of the secondary battery.

[0074] In some embodiments, 0 < z ≤ 0.2 and 1 ≤ a / z ≤ 5, optionally, 0 < z ≤ 0.2 and 2 ≤ a / z ≤ 4. The doping element A is more suitable for a high-voltage system above 4.5V, can capture strong acids in the electrolyte and reduce the corrosion effect of strong acids in the electrolyte, and reduce the dissolution of manganese ions. The doping element M helps to enhance the structural stability of the lithium-containing nickel manganese composite oxide. Thus, when the ratio of the doping element A to the doping element M is within a suitable range, the corrosion of the electrolyte can be minimized, so that the lithium-containing nickel manganese composite oxide and the secondary battery have better electrochemical performance.

[0075] In some embodiments, the ratio R of the charging capacity of the 4V plateau of the lithium-containing nickel manganese composite oxide satisfies 0 < R ≤ 0.125, optionally, 0.03 ≤ R ≤ 0.115, 0.03 ≤ R ≤ 0.105, 0.03 ≤ R ≤ 0.95, 0.03 ≤ R ≤ 0.85.

[0076] The ratio R of the charging capacity of the 4V plateau of the lithium-containing nickel manganese composite oxide is tested by the following method: An electrode sheet containing the lithium-containing nickel manganese composite oxide is used as the positive electrode, and a lithium sheet is used as the negative electrode to assemble a button cell. The cell is charged to 4.95V at a current of 0.1 times the cell capacity, and then charged at a constant voltage until the current is 0.05 times the cell capacity. The ratio of the charging capacity within the range of 3.5V - 4.4V to the total charging capacity of the button cell is used as the ratio R of the charging capacity of the 4V plateau of the lithium-containing nickel manganese composite oxide.

[0077] The lithium-containing nickel manganese composite oxide provided by the present application is applicable to a high-voltage system above 4.5V, and its charging capacity ratio at a low voltage (such as 3.5V - 4.4V) is relatively low, and its charging capacity ratio at a high voltage is relatively high. Thus, the advantage of its large high-voltage capacity can be fully utilized, and the secondary battery has a high energy density.

[0078] In some embodiments, the volume particle size Dv50 of the lithium-containing nickel manganese composite oxide satisfies 3μm ≤ Dv50 ≤ 16μm, optionally, 5μm ≤ Dv50 ≤ 13μm. When the volume particle size Dv50 of the lithium-containing nickel manganese composite oxide is within a suitable range, it can have good ion transport ability and high tap density, which helps the secondary battery to better balance good kinetic performance and long service life.

[0079] In some embodiments, the BET specific surface area S0 of the lithium-containing nickel manganese composite oxide is ≤ 0.8m 2 / g, optionally, 0.1m 2 / g ≤ S0 ≤ 0.5m 2 / g. When the BET specific surface area of ​​lithium nickel manganese composite oxide is within a suitable range, it can reduce the side reactions of the electrolyte on its surface and reduce the dissolution of manganese ions, thereby helping the secondary battery to better balance good kinetic performance and long service life.

[0080] In some embodiments, the tap density TD of the lithium-containing nickel-manganese composite oxide satisfies 1.5 g / cm³. 3 ≤TD≤3.0g / cm 3 1.7g / cm³ is an optional value. 3 ≤TD≤2.3g / cm 3 When the tap density of lithium-containing nickel-manganese composite oxides is within a suitable range, it helps secondary batteries to have higher energy density.

[0081] In some embodiments, the lithium-containing nickel-manganese composite oxide has a coating layer on its surface, which can further improve the structural stability of the lithium-containing nickel-manganese composite oxide and reduce the direct contact between the lithium-containing nickel-manganese composite oxide and the electrolyte, thereby reducing the dissolution of manganese ions and thus helping the secondary battery to have a longer service life.

[0082] In some embodiments, the coating layer comprises one or more selected from conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials. Optionally, the conductive carbon material comprises one or more selected from soft carbon, hard carbon, graphene, and graphene oxide. Optionally, the metal oxide comprises one or more selected from Al₂O₃, B₂O₃, TiO₂, ZrO₂, WO₃, MoO₃, Y₂O₃, Ta₂O₅, TeO₂, and Nb₂O₅. Optionally, the metal fluoride comprises one or more selected from LiF, AlF₃, and GaF₃. Optionally, the polyanionic material comprises one or more selected from orthophosphates and fluorinated orthophosphates containing at least one element selected from Li, Ni, Co, Mn, Fe, Nb, Mo, W, Ta, and Te, and more preferably comprises one or more selected from LiNiPO₄, LiPO₂F₂, and Li₂PO₃F.

[0083] Preparation method

[0084] The second aspect of this application provides a method for preparing a lithium-containing nickel-manganese composite oxide, which can prepare the lithium-containing nickel-manganese composite oxide of the first aspect of this application.

[0085] The preparation method includes the following steps: S1, providing raw materials, which are obtained by mixing sources of Li element, Ni element, Mn element, A element and optionally M element in a predetermined ratio; S2, heating the raw materials obtained in S1 to a first temperature T1 in an oxygen-containing atmosphere and holding at the first temperature T1 for a first time t1, and then cooling to room temperature after completion to obtain an intermediate product, and 850°C ≤ T1 ≤ 1100°C; S3, heating the intermediate product obtained in S2 to a second temperature T2 in an oxygen-containing atmosphere and holding at the second temperature T2 for a second time t2, and then obtaining a lithium nickel manganese composite oxide after completion, 0°C ≤ T1 - T2 ≤ 200°C, and T2 ≥ 800°C, wherein the lithium nickel manganese composite oxide is in the form of single crystal or quasi-single crystal particles and the grain shape of the lithium nickel manganese composite oxide is spherical or quasi-spherical, and the general formula of the lithium nickel manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z-a A a O 4-k , -0.2 ≤ x ≤ 0.5, -0.2 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 < a ≤ 0.2, 0 ≤ k ≤ 0.2, A includes one or more selected from Si, P and S, M includes one or more selected from metal doping elements, and optionally includes one or more selected from Ti, Cr, Mo, Nb, Ru, Te, Ta, W, Ce, Y and Yb.

[0086] When preparing the lithium nickel manganese composite oxide in the present application, at least two discontinuous sintering processes are adopted. The discontinuous sintering process means that after the previous sintering process is completed, it is necessary to first undergo a cooling treatment and then heat up for the next sintering process.

[0087] In the preparation method of the present application, the first temperature T1 during the first sintering satisfies 850°C ≤ T1 ≤ 1100°C, which can ensure that the grains grow to the target size and the grain structure is complete.

[0088] In some embodiments, optionally, 900°C ≤ T1 ≤ 1100°C, 950°C ≤ T1 ≤ 1100°C. This is beneficial for the grains of the lithium nickel manganese composite oxide to grow to the target size, have a suitable particle size and specific surface area, and at the same time is beneficial for maintaining the integrity of the grain structure of the lithium nickel manganese composite oxide, so that the secondary battery can have better cycle performance.

[0089] In the preparation method of the present application, the second temperature T2 during the second sintering satisfies 0°C ≤ T1 - T2 ≤ 200°C, and T2 ≥ 800°C.

[0090] By controlling the temperature T2 during the second sintering to be less than or equal to the temperature T1 during the first sintering, it is possible to promote the recrystallization of the fine powder in the intermediate product obtained after the first sintering and simultaneously avoid the recrystallization of large grains. Thereby, it can be ensured that the grain shape of the lithium-containing nickel manganese composite oxide obtained is a round spherical or quasi-spherical shape. When the temperature T2 during the second sintering is greater than the temperature T1 during the first sintering, the large grains in the intermediate product obtained after the first sintering will also recrystallize, resulting in a poor sphericity of the grains of the lithium-containing nickel manganese composite oxide obtained, and at the same time, it is not conducive to controlling its particle size and specific surface area.

[0091] When T1 - T2 is greater than 200 °C or T2 is less than 800 °C, the temperature T2 during the second sintering is too low. At this time, the grain shape of the lithium-containing nickel manganese composite oxide obtained is an octahedron (or truncated octahedron) or a round octahedron (or truncated octahedron), and its stress corrosion at high voltage is still relatively high, and the dissolution amount of manganese ions is also relatively high, thereby shortening the service life of the secondary battery.

[0092] In some embodiments, optionally, 0 °C ≤ T1 - T2 ≤ 100 °C, 0 °C < T1 - T2 ≤ 100 °C. This is beneficial for the grain shape of the lithium-containing nickel manganese composite oxide to have a higher degree of roundness and sphericity, and further makes it more resistant to strong acid corrosion in the electrolyte and stress corrosion under high voltage.

[0093] In some embodiments, optionally, 850 °C ≤ T2 ≤ 1000 °C. This is beneficial for the grain shape of the lithium-containing nickel manganese composite oxide to have a higher degree of roundness and sphericity, and further makes it more resistant to strong acid corrosion in the electrolyte and stress corrosion under high voltage.

[0094] In some embodiments, 0 °C ≤ T1 - T2 ≤ 100 °C, and 850 °C ≤ T2 ≤ 1000 °C, optionally, 0 °C < T1 - T2 ≤ 100 °C, and 850 °C ≤ T2 ≤ 1000 °C.

[0095] In some embodiments, the heating rate in S2 and S3 is independently 1 °C / min to 10 °C / min, and can be optionally 1 °C / min to 5 °C / min.

[0096] In some embodiments, the first time t1 and the second time t2 satisfy t2 ≤ t1, optionally, t2 < t1. This is beneficial for the grain shape of the lithium-containing nickel manganese composite oxide to have a higher degree of roundness and sphericity, and further makes it more resistant to strong acid corrosion in the electrolyte and stress corrosion under high voltage, and at the same time can avoid the recrystallization of large grains in the intermediate product obtained after the first sintering.

[0097] In some embodiments, optionally, 2 h ≤ t1 ≤ 50 h.

[0098] In some embodiments, optionally, 0.5h ≤ t2 ≤ 20h.

[0099] In some embodiments, optionally, 10h ≤ t1 + t2 ≤ 40h.

[0100] In the preparation method of this application, the sintering atmosphere in S2 and S3 is an oxygen-containing atmosphere. In some embodiments, the oxygen partial pressure in the oxygen-containing atmosphere may be 20% to 100%, and the oxygen-containing atmosphere may also contain one or more inert gases, such as nitrogen, helium, and argon.

[0101] In some embodiments, the oxygen-containing atmosphere in S2 and S3 may optionally be an air atmosphere. This is beneficial for reducing production costs.

[0102] In the preparation method of this application, the sintering pressure in S2 and S3 is a slightly positive pressure, for example, a positive pressure of 0.03 ± 0.03 MPa relative to atmospheric pressure.

[0103] In the preparation method of this application, the source of each element can be a compound known in the art that can be used to prepare lithium-containing nickel-manganese composite oxides. For example, the source of Li element may include one or a combination of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, etc.; the source of Ni element may include one or a combination of elemental nickel, nickel oxide, nickel phosphate, nickel oxalate, nickel carbonate, and nickel sulfate; the source of Mn element may include one or a combination of elemental manganese, manganese oxide, manganese phosphate, manganese oxalate, manganese carbonate, and manganese sulfate; the source of A element may include one or a combination of elemental A, oxide, silicate, phosphate, and sulfate; and the source of M element may include one or a combination of elemental M, oxide, phosphate, oxalate, carbonate, and sulfate.

[0104] In the preparation method of this application, the amount of each element source added conforms to the stoichiometric ratio. In some embodiments, the amount of Li element source added may be slightly excessive, for example, it may be 100% to 110% of the theoretical mass. The theoretical mass refers to the mass of Li element source calculated based on the stoichiometric ratio of the lithium-containing nickel-manganese composite oxide.

[0105] In some embodiments, the preparation method further includes the step of: S4, annealing the product obtained in S3 to obtain a lithium-containing nickel-manganese composite oxide, thereby further reducing oxygen defects. Optionally, the annealing temperature is 500℃-800℃. Optionally, the annealing time is 5h-50h.

[0106] In some embodiments, the preparation method further includes the step of: mixing the lithium-containing nickel-manganese composite oxide obtained in S3 with a coating agent, and then sintering it under a protective gas atmosphere to obtain a lithium-containing nickel-manganese composite oxide with a coating layer. Optionally, the coating agent is one or more precursor compounds selected from conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials.

[0107] In some embodiments, the preparation method further includes the step of: mixing the lithium-containing nickel-manganese composite oxide obtained in S4 with a coating agent, and then sintering it under a protective gas atmosphere to obtain a lithium-containing nickel-manganese composite oxide with a coating layer. Optionally, the coating agent is one or more precursor compounds selected from conductive carbon materials, metal oxides, metal fluorides, and polyanionic materials.

[0108] In this application, the protective gas may be nitrogen, helium, argon, or a combination thereof.

[0109] In the second aspect of this application, some parameters of the lithium-containing nickel-manganese composite oxide (such as the types and contents of doping elements) involved in the preparation of lithium-containing nickel-manganese composite oxides can be referred to the lithium-containing nickel-manganese composite oxides of the first aspect of this application, and will not be repeated here.

[0110] Unless otherwise specified, all raw materials used in the preparation method of the second aspect of this application can be obtained commercially.

[0111] Positive electrode sheet

[0112] A third aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer comprises a lithium-containing nickel-manganese composite oxide according to the first aspect of this application or a lithium-containing nickel-manganese composite oxide prepared by the preparation method of the second aspect of this application. The content of the lithium-containing nickel-manganese composite oxide in the positive electrode film layer is 1 wt% to 99 wt%, optionally 85 wt% to 99 wt%, based on the total weight of the positive electrode film layer. The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0113] The positive electrode film layer may also include other positive electrode active materials known in the art for use in secondary batteries. For example, these other positive electrode active materials may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. In this application, the modified compounds of the above-mentioned positive electrode active materials may be those obtained by doping and / or surface coating modification of the positive electrode active materials.

[0114] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0116] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0117] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0118] Secondary battery

[0119] A fourth aspect of this application provides a secondary battery, which includes the positive electrode sheet of the third aspect of this application. A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to activate its active materials and continue to be used. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrode sheets. The separator is disposed between the positive and negative electrode sheets, primarily serving to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through. The electrolyte, located between the positive and negative electrode sheets, conducts lithium ions.

[0120] [Positive electrode plate]

[0121] The positive electrode used in the secondary battery of this application is the positive electrode described in any embodiment of the third aspect of this application.

[0122] [Negative electrode plate]

[0123] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0124] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy materials. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0125] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0127] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0128] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0129] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0130] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0131] [Electrolytes]

[0132] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte may include at least one selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0133] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0134] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0135] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0136] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0137] [Isolation membrane]

[0138] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0139] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0140] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0141] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0142] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0143] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. FIG. 1 This is an example of a square-structured secondary battery 5.

[0144] In some embodiments, such as FIG. 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0145] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0146] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0147] FIG. 3 This is a schematic diagram of battery module 4 as an example. FIG. 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0149] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0150] FIG. 4 and FIG. 5 This is a schematic diagram of battery pack 1 as an example. FIG. 4 and FIG. 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] Electric device

[0152] A fifth aspect of this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0153] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0154] FIG. 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0155] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0156] Embodiment

[0157] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0158] Example 1

[0159] (1) Preparation of lithium-containing nickel-manganese composite oxides

[0160] According to the target component LiNi 0.5 Mn 1.35 Te 0.05 P 0.1 Weigh out the stoichiometric amounts of Li₂CO₃ (as the source of Li) and Ni. 0.5 Mn 1.35 (OH) 3.7 The raw material mixture powder was obtained by uniformly mixing NH4H2PO4 (as the source of Ni and Mn elements), NH4H2PO4 (as the source of A element), and TeO2 (as the source of M element). The raw material mixture powder was heated to 950℃ (as the first temperature T1) at 5℃ / min in air and held for 20 hours (as the first time t1), then cooled to room temperature to obtain an intermediate product. The intermediate product was then heated to 850℃ (as the second temperature T2) at a positive pressure of 0.03 MPa relative to atmospheric pressure in air and held for 10 hours (as the second time t2) to obtain a lithium-containing nickel-manganese composite oxide. The elemental content was determined by inductively coupled plasma atomic emission spectrometry (ICP) according to EPA 6010D-2014.

[0161] (2) Preparation of button cell (half-cell)

[0162] The lithium-containing nickel-manganese composite oxide (as the positive electrode active material) prepared above was mixed with conductive carbon black and polyvinylidene fluoride at a weight ratio of 90:5:5. An appropriate amount of NMP solvent was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto a positive electrode current collector aluminum foil, and after drying, a positive electrode sheet was obtained. The loading of the lithium-containing nickel-manganese composite oxide on the positive electrode sheet was 0.015 g / cm³.2 .

[0163] A lithium sheet was used as the counter electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. A 12 μm thick polypropylene film (Φ16 mm) was used as the separator. Together with the positive electrode sheet prepared above, they were assembled into a CR2030 coin cell in a coin cell box and left to stand for 24 hours to obtain a half cell.

[0164] (3) Preparation of secondary batteries (full cells)

[0165] The lithium-containing nickel-manganese composite oxide (as the positive electrode active material) prepared above was mixed with conductive carbon black and polyvinylidene fluoride at a weight ratio of 96:2.5:1.5. An appropriate amount of NMP solvent was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto both surfaces of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained. The loading of the lithium-containing nickel-manganese composite oxide on one side of the positive electrode current collector was 0.02 g / cm³. 2 .

[0166] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96:1:1:2 to form a negative electrode slurry. The negative electrode slurry was coated onto both surfaces of the copper foil used as the negative electrode current collector. After drying and cold pressing, the negative electrode sheet was obtained. The loading of the negative electrode active material on one side of the negative electrode current collector was 0.008 g / cm³. 2 .

[0167] A 12μm thick polypropylene film (Φ16mm) was used as a separator and placed in sequence with the positive and negative electrode sheets prepared above, so that the separator was placed between the positive and negative electrode sheets to provide isolation. Then, the electrode assembly was wound to obtain the electrode assembly. The electrode assembly was placed in an outer packaging aluminum-plastic bag, dried, and then injected with the same electrolyte as the button cell prepared above. After vacuum sealing, standing, formation, capacity testing and other processes, a secondary battery was obtained.

[0168] Examples 2-30 and Comparative Examples 1-7

[0169] Except for the preparation of the lithium-containing nickel-manganese composite oxide, the preparation of the coin cell and the secondary cell were the same as in Example 1. The differences in the preparation process of the lithium-containing nickel-manganese composite oxide are detailed in Table 1. Furthermore, Example 30 added an annealing step, with an annealing temperature of 680°C and an annealing time of 10 hours.

[0170] Test section

[0171] (1) Morphology test of lithium-containing nickel-manganese composite oxide

[0172] The lithium-containing nickel-manganese composite oxide prepared above was tested using a scanning electron microscope, and then tested according to JY / T010-1996, and the morphology of the sample was observed. The testing instrument can be a ZEISS Sigma 300.

[0173] (2) Measurement of the aspect ratio of lithium-containing nickel-manganese composite oxide grains

[0174] The lithium-containing nickel-manganese composite oxide prepared above was tested using a scanning electron microscope. The average ratio of the major axis L of the circumscribed ellipse to the minor axis S of the inscribed ellipse in any field of view of 5×Dv50 to 10×Dv50 containing at least 50 visible grains was counted. This average ratio is the L / S of the lithium-containing nickel-manganese composite oxide grain. A ZEISS sigma 300 microscope can be used for testing.

[0175] (3) Volume particle size Dv50 test of lithium nickel manganese composite oxide

[0176] In this application, the volumetric particle size Dv50 of the lithium nickel manganese composite oxide has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer in accordance with GB / T 19077-2016. The testing instrument can be the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0177] (4) BET specific surface area test of lithium nickel manganese composite oxide

[0178] In this application, the BET specific surface area of ​​lithium nickel manganese composite oxides has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0179] (5) Tap density test of lithium-containing nickel-manganese composite oxide

[0180] In this application, the tap density of lithium-containing nickel-manganese composite oxides has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester in accordance with GB / T 5162-2006. The testing instrument can be Dandong Baite BT-301.

[0181] (6) Testing of the percentage of charging capacity on a 4V platform containing lithium nickel manganese composite oxide

[0182] At 25°C, the prepared coin cells were charged at a constant current of 0.1C to a voltage of 4.95V, and then charged at a constant voltage of 4.95V to a current of 0.05C. The charging capacity within the voltage range of 3.5V-4.4V (denoted as C1) and the total charging capacity within the voltage range of 3.5V-4.95V (3.5V being the lower cutoff voltage) (denoted as C2) were extracted from the obtained raw charging data. The percentage of the charging capacity at the 4V plateau containing lithium nickel manganese composite oxide is R = C1 / C2.

[0183] (7) Initial discharge capacity test of secondary battery

[0184] At 25°C, the secondary battery prepared above is charged at a constant current of 0.3C to a voltage of 4.9V, and then charged at a constant voltage of 4.9V to a current of 0.05C. After standing for 5 minutes, the secondary battery is discharged at a constant current of 0.33C to a voltage of 3.5V. The discharge capacity obtained at this time is the initial discharge capacity of the secondary battery.

[0185] (8) Secondary battery cycle performance test

[0186] At 45°C, the prepared secondary battery was charged at a constant current of 0.3C to a voltage of 4.9V, then charged at a constant voltage of 4.9V to a current of 0.05C. After standing for 5 minutes, the secondary battery was discharged at a constant current of 0.33C to a voltage of 3.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the secondary battery after the first cycle. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of the discharge capacity after the first cycle, and the number of cycles completed by the secondary battery at this point was recorded.

[0187] As can be seen from the test results in Table 2, the lithium nickel manganese composite oxide obtained by the preparation method of this application has a rounded spherical or near-spherical grain shape and a single crystal or near-single crystal morphology. This can minimize the corrosion of the electrolyte, such as strong acid corrosion and stress corrosion under high voltage, thereby improving the capacity utilization, energy density and cycle life of the secondary battery.

[0188] Based on the test results of Examples 1-7 and Comparative Examples 1-5, it can be seen that in the preparation of lithium-containing nickel-manganese composite oxides, using a two-stage discontinuous sintering process, and controlling the first sintering temperature between 850℃ and 1100℃ (selectively between 950℃ and 1100℃), and the second sintering temperature greater than or equal to 800℃ with the difference between the first and second sintering temperatures between 0℃ and 200℃ (selectably between 0℃ and 100℃), can yield lithium-containing nickel-manganese composite oxides with rounded spherical or near-spherical grain shapes and single-crystal or near-single-crystal particle morphology. The grain shape is as follows... FIG. 7 As shown.

[0189] Comparative Examples 1 and 2 used only a single sintering process to prepare lithium-containing nickel-manganese composite oxides. The resulting lithium-containing nickel-manganese composite oxide particles had a near-single-crystal morphology and an octahedral grain shape. FIG. 8 As shown, its grains have sharp edges, which makes it susceptible to severe stress corrosion under high voltage and it is not resistant to strong acid corrosion in the electrolyte. At this time, manganese ions dissolve severely, which leads to a short cycle life of the secondary battery.

[0190] Comparative Example 3 used two discontinuous sintering processes to prepare lithium-containing nickel-manganese composite oxides, but the temperature of the second sintering was less than 800℃. The resulting lithium-containing nickel-manganese composite oxide particles had a single-crystal morphology and an octahedral grain shape. Comparative Example 4 used two discontinuous sintering processes to prepare lithium-containing nickel-manganese composite oxides, but the temperature of the second sintering was higher than the temperature of the first sintering. The resulting lithium-containing nickel-manganese composite oxide particles had a single-crystal morphology and an octahedral grain shape. Comparative Example 5 used two discontinuous sintering processes to prepare lithium-containing nickel-manganese composite oxides, but the temperature difference between the first and second sintering processes was greater than 200℃. FIG. 9 As shown, the lithium-containing nickel-manganese composite oxide particles prepared in this way have a single crystal morphology and a rounded octahedral grain shape.

[0191] Compared with Comparative Example 1, the cycling performance of the lithium-containing nickel-manganese composite oxides prepared in Comparative Examples 3 to 5 was slightly improved, but the improvement effect was not significant.

[0192] In Comparative Examples 6 and 7, excessive amounts of doping element M and doping element A were added during the preparation of lithium-containing nickel-manganese composite oxides, respectively, which resulted in a significant decrease in the initial discharge capacity of the secondary batteries.

[0193] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0194]

[0195]

[0196] Table 2

[0197]

[0198]

Claims

1. A lithium-containing nickel-manganese complex oxide, wherein, The lithium-containing nickel-manganese composite oxide is a single crystal or a single crystal-like morphology particle and a grain shape of the lithium-containing nickel-manganese composite oxide is spherical or spherical-like, a general formula of the lithium-containing nickel-manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z-a A a O 4-k , -0.2 ≤ x ≤ 0.5, -0.2 ≤ y ≤ 0.2, 0 ≤ z ≤0.2, 0 < a ≤ 0.2, 0 ≤ k ≤ 0.2, A includes one or more selected from Si, P and S, M includes one or more selected from metal doping elements, The 4V platform charging capacity ratio R of the lithium-containing nickel-manganese composite oxide satisfies 0 < R ≤ 0.125, and the 4V platform charging capacity ratio R of the lithium-containing nickel-manganese composite oxide is tested according to the following method: a coin cell is assembled with a pole piece containing the lithium-containing nickel-manganese composite oxide as a positive electrode and a lithium sheet as a negative electrode, charged to 4.95V at a current of 0.1 times the battery capacity, and then charged to a current of 0.05 times the battery capacity at a constant voltage, and the ratio of the charging capacity in the range of 3.5V-4.4V to the total charging capacity of the coin cell is taken as the 4V platform charging capacity ratio R of the lithium-containing nickel-manganese composite oxide.

2. The lithium-containing nickel manganese complex oxide according to claim 1, wherein The ratio of the long diameter L to the short diameter S of the crystal grain of the lithium-containing nickel-manganese composite oxide satisfies 1.0 ≤ L / S ≤ 1.

25.

3. The lithium-containing nickel manganese complex oxide according to claim 2, wherein 1.0 ≤ L / S ≤ 1.

15.

4. The lithium-containing nickel manganese complex oxide according to claim 1, wherein M includes one or more selected from Ti, Cr, Mo, Nb, Ru, Te, Ta, W, Ce, Y and Yb.

5. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 4, wherein M includes one or more selected from Mo, Nb, Ru, Te, Ta, Ce and Yb.

6. The lithium-containing nickel manganese complex oxide according to claim 5, wherein M includes two or more selected from Mo, Nb, Ru, Te, Ta, Ce and Yb.

7. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 6, wherein 0.01 ≤ a ≤ 0.2; and / or, 0 < z ≤ 0.

2.

8. The lithium-containing nickel manganese complex oxide according to claim 7, wherein 0.01 ≤ a ≤ 0.1。 9. The lithium-containing nickel manganese complex oxide according to claim 7, wherein 0.005 ≤ z ≤ 0.1。 10. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 9, wherein 0.01 ≤ z+a ≤ 0.2; and / or, 0 < z ≤ 0.2 and 1 ≤ a / z ≤ 5.

11. The lithium-containing nickel manganese complex oxide according to claim 10, wherein 0.01 ≤ z+a ≤ 0.

15.

12. The lithium-containing nickel manganese complex oxide according to claim 10, wherein 0 < z ≤ 0.2 and 2 ≤ a / z ≤ 4.

13. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 12, wherein 0.03≤R≤0.105。 14. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 13, wherein The lithium-containing nickel-manganese composite oxide satisfies at least one of the following conditions (1) to (3): (1) the volume particle size Dv50 of the lithium-containing nickel-manganese composite oxide satisfies 3μm ≤ Dv50 ≤ 16μm; (2) the BET specific surface area S0of the lithium-containing nickel-manganese complex oxide is ≤ 0.8 m2 / g 2 / g; (3) the tap density TD of the lithium-containing nickel-manganese complex oxide satisfies 1.5 g / cm 3 ≤ TD ≤ 3.0 g / cm 3 .

15. The lithium-containing nickel manganese complex oxide according to claim 14, wherein 5μm ≤ Dv50 ≤ 13μm.

16. The lithium-containing nickel manganese complex oxide according to claim 14, wherein 0.1 m 2 / g ≤ S0 ≤ 0.5 m 2 / g.

17. The lithium-containing nickel manganese complex oxide according to claim 14, wherein 1.7 g / cm 3 ≤ TD ≤ 2.3 g / cm 3 .

18. The lithium-containing nickel manganese complex oxide according to any one of claims 1 to 17, wherein The lithium-containing nickel-manganese composite oxide further has a coating layer on the surface, and the coating layer includes one or more selected from conductive carbon materials, metal oxides, metal fluorides and polyanion materials.

19. The lithium-containing nickel manganese complex oxide according to claim 18, wherein The conductive carbon material includes one or more selected from soft carbon, hard carbon, graphene and graphene oxide.

20. The lithium-containing nickel manganese complex oxide according to claim 18, wherein The metal oxide includes one or more selected from Al2O3, B2O3, TiO2, ZrO2, WO3, MoO3, Y2O3, Ta2O5, TeO2, Nb2O5.

21. The lithium-containing nickel manganese complex oxide according to claim 18, wherein The metal fluoride includes one or more selected from LiF, AlF3, GaF3.

22. The lithium-containing nickel manganese complex oxide according to claim 18, wherein The polyanion material includes one or more selected from orthophosphates and fluorinated orthophosphates containing at least one element selected from Li, Ni, Co, Mn, Fe, Nb, Mo, W, Ta and Te.

23. The lithium-containing nickel manganese complex oxide according to claim 18, wherein The polyanion material includes one or more of LiNiPO4, LiPO2F2 and Li2PO3F.

24. A preparation method of a lithium-containing nickel-manganese composite oxide, comprising the following steps: S1, providing raw materials, the raw materials are obtained by mixing a source of Li element, a source of Ni element, a source of Mn element, a source of A element and an optional source of M element according to a predetermined ratio; S2, the raw material obtained in S1 is heated to a first temperature T1 under an oxygen-containing atmosphere and is kept at the first temperature T1 for a first time t1, and after the end of the keeping, is cooled to room temperature to obtain an intermediate product, and 850℃ ≤ T1 ≤ 1100℃; S3, the intermediate product obtained in S2 is heated to a second temperature T2 under an oxygen-containing atmosphere and held at the second temperature T2 for a second time t2, and after the end, a lithium-nickel-manganese composite oxide is obtained, 0°C ≤ T1-T2 ≤ 200°C, and T2 ≥ 800°C, wherein, The lithium-containing nickel-manganese composite oxide is a single crystal or a single crystal-like morphology particle and the grain shape of the lithium-containing nickel-manganese composite oxide is spherical or spherical-like, the general formula of the lithium-containing nickel-manganese composite oxide is Li 1+x Ni 0.5+y M z Mn 1.5-x-y-z- a A a O 4-k , -0.2 ≤ x ≤ 0.5, -0.2 ≤ y ≤ 0.2, 0 ≤ z ≤ 0.2, 0 < a ≤ 0.2, 0 ≤ k ≤ 0.2, A includes one or more selected from Si, P and S, M includes one or more selected from metal doping elements, The 4V platform charge capacity ratio R of the lithium-containing nickel-manganese composite oxide satisfies 0 < R ≤ 0.125, and the 4V platform charge capacity ratio R of the lithium-containing nickel-manganese composite oxide is tested according to the following method: a coin cell is assembled with a pole piece containing the lithium-containing nickel-manganese composite oxide as a positive electrode and a lithium sheet as a negative electrode, is charged to 4.95V at a current of 0.1 times the battery capacity, and is then charged at a constant voltage until the current is 0.05 times the battery capacity, and the ratio of the charge capacity in the range of 3.5V-4.4V to the total charge capacity of the coin cell is taken as the 4V platform charge capacity ratio R of the lithium-containing nickel-manganese composite oxide.

25. The method of manufacturing according to claim 24, wherein, M comprises one or more selected from Ti, Cr, Mo, Nb, Ru, Te, Ta, W, Ce, Y and Yb.

26. The method of manufacturing according to claim 24, wherein, 900℃ ≤ T1 ≤ 1100℃; and / or, 0℃ ≤ T1-T2 ≤ 100℃, and 850℃ ≤ T2 ≤ 1000℃.

27. The method of manufacturing according to claim 26, wherein, 950℃ ≤ T1 ≤ 1100℃。 28. The method of making according to claim 26, wherein, 0℃ < T1-T2 ≤ 100℃, and 850℃ ≤ T2 ≤ 1000℃.

29. The method of making according to any one of claims 24-28, wherein, t2 ≤ t1.

30. The method of manufacturing according to claim 29, wherein, t2 < t1.

31. The method of making according to any one of claims 24-30, wherein, 2h ≤ t1 ≤ 50h; and / or, 0.5h ≤ t2 ≤ 20h; and / or, 10h ≤ t1 + t2 ≤ 40h.

32. The preparation method according to any one of claims 24-31, further comprising a step S4 of annealing the product obtained in S3 to obtain the lithium-containing nickel-manganese composite oxide.

33. The method of manufacturing according to claim 32, wherein, The annealing temperature is 500℃-800℃.

34. The method of manufacturing according to claim 32, wherein, The annealing time is 5h-50h.

35. The preparation method according to claim 32, further comprising a step of mixing the lithium-containing nickel-manganese composite oxide obtained in S4 with a coating agent, and then sintering under a protective gas atmosphere to obtain the lithium-containing nickel-manganese composite oxide with a coating layer.

36. The preparation method according to claim 35, wherein the coating agent is a precursor compound for forming one or more of conductive carbon material, metal oxide, metal fluoride and polyanion-based material.

37. The preparation method according to any one of claims 24-36, further comprising a step of mixing the lithium-containing nickel-manganese composite oxide obtained in S3 with a coating agent, and then sintering under a protective gas atmosphere to obtain the lithium-containing nickel-manganese composite oxide with a coating layer.

38. The method of manufacturing according to claim 37, wherein, The coating agent is a precursor compound for forming one or more of conductive carbon material, metal oxide, metal fluoride and polyanion-based material.

39. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein, The positive electrode film layer comprises the lithium-containing nickel-manganese composite oxide according to any one of claims 1-23 or prepared by the preparation method according to any one of claims 24-38, and the content of the lithium-containing nickel-manganese composite oxide in the positive electrode film layer is 1 wt% to 99 wt% based on the total weight of the positive electrode film layer.

40. The cathode sheet of Claim 39, wherein, The content of the lithium-containing nickel-manganese composite oxide in the positive electrode film layer is 85 wt% to 99 wt% based on the total weight of the positive electrode film layer.

41. A secondary battery comprising the positive electrode sheet of claim 39 or 40.

42. An electric device comprising the secondary battery of claim 41.

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