Positive electrode active material, positive electrode sheet, secondary battery, power using device, and production method

Abstract

The present application provides a positive electrode active material, a positive electrode sheet, a secondary battery, an electric device, and a production method. The positive electrode active material includes polycrystal particles denoted as first active particles and single crystal or single crystal-like particles denoted as second active particles, (D v 90-D v 10) / D v 50denoted as X1, X2, respectively, and X1 / X2 satisfies 0.2 ≤ X1 / X2 ≤ 0.7.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a positive electrode active material, a positive electrode sheet, a secondary battery, an electric device and a preparation method. BACKGROUND

[0002] The statements herein are provided only to complement the background of the present application and are not necessarily prior art.

[0003] With the application popularization of lithium ion battery technology, the acceleration of life rhythm, and the development of various electronic products such as smart phones, tablet computers, smart wear, electric tools and electric vehicles, the comprehensive performance requirements of the positive electrode active material are also continuously improved to meet the comprehensive performance requirements of high energy density and long storage life of the battery. At present, the improvement of the long storage life of the battery often leads to the loss of energy density, resulting in the difficulty in balancing the two performances.

[0004] Therefore, it is urgent to develop a lithium ion battery that can balance the comprehensive requirements of energy density and long storage life. SUMMARY

[0005] In view of the above problems, the present application provides a positive electrode active material, a positive electrode sheet, a secondary battery, an electric device and a preparation method. The positive electrode active material can improve the storage life while maintaining the energy density substantially unchanged.

[0006] In a first aspect, the present application provides a positive electrode active material, which comprises first active particles and second active particles; wherein the first active particles are polycrystalline particles in the positive electrode active material, and the particle size parameter (D v 90-D v 10) / D v 50 is denoted as X1; and the second active particles are single crystal or quasi-single crystal particles in the positive electrode active material, and the particle size parameter (D v 90-D v 10) / D v 50 is denoted as X2.

[0007] X1 / X2 satisfies 0.2≤X1 / X2≤0.7.

[0008] Wherein, D v 90, D v 50 and D v 10 respectively represent the particle size corresponding to the cumulative volume distribution percentage of 90%, 50% and 10% of the multi-particle combination.

[0009] The positive electrode active material adopts the combination of polycrystalline active particles and single crystal or quasi-single crystal active particles with special particle size distribution characteristics. The (Dv 90-D v 10) / D v 50 and single crystal or single crystal-like active particles (D v 90-D v 10) / D v 50, the ratio of which is denoted as X1 / X2, is low, so that the particle size of the active particles is reasonably matched, and under the premise of maintaining the energy density basically unchanged, the storage life of the battery can be significantly improved. The inventors of the present application speculate that this is because the content of small-size polycrystalline particles is reduced, thereby reducing the active surface area, reducing the side reaction between the electrolyte and the positive material during storage, and thus improving the chemical stability of the battery and prolonging the storage life of the battery.

[0010] In some embodiments, in the particle size distribution curve of the positive active material, the first active particles and the second active particles correspond to two discontinuous independent peaks, respectively.

[0011] By controlling the particle size and distribution of the polycrystalline particles and the single crystal or single crystal-like particles, in the particle size distribution curve of the positive active material, the two kinds of particles can correspond to two discontinuous independent peaks, respectively, and at this time, the D v 90, D v 50 and D v 10 can be obtained by fitting analysis according to the respective particle size distribution peaks.

[0012] In some embodiments, the X1 / X2 satisfies 0.25≤X1 / X2≤0.55.

[0013] In some embodiments, the first active particles satisfy 0.3≤X1≤1.0. Alternatively, the first active particles satisfy 0.4≤X1≤0.8.

[0014] In some embodiments, the second active particles satisfy 0.7≤X2≤2.5. Alternatively, the second active particles satisfy 0.7≤X2≤2; further alternatively, the second active particles satisfy 0.8≤X2≤1.6.

[0015] By further adjusting the value range of X1 / X2, or by further adjusting the value of X1 of the polycrystalline active particles or selecting the value of X2 of the single crystal or single crystal-like active particles to regulate the value of X1 / X2, the matching of the active surface areas of the two size particles can be better coordinated, thereby better meeting the dual requirements of high energy density and long storage life, and the storage life of the battery can be better improved while maintaining good energy density.

[0016] In some embodiments, the D v 50 of the first active particles is less than the Dv The ratio R of 50 Dv50 Satisfying 2≤R Dv50 ≤4. Optionally, the D of the first active particle v 50 and the D of the second active particle v The ratio R of 50 Dv50 Satisfying 2.3≤R Dv50 ≤4.0.

[0017] In some embodiments, the D of the first active particle v 50 satisfies 7μm≤D v 50≤15μm. Optionally, the D of the first active particle... v 50 satisfies 7μm≤D v 50≤14μm.

[0018] In some embodiments, the D of the second active particle v 50 satisfies 1μm≤D v 50≤6μm. Further optionally, the D of the second active particle... v 50 satisfies 2μm≤D v 50≤4μm.

[0019] By separately controlling the D of polycrystalline active particles and single-crystal or near-single-crystal active particles in the positive electrode active material... v The range is 50, or through the D of both. v A 50 ratio can synergistically control the active surface area of ​​different active particles, thereby better reducing the side reactions between the electrolyte and the cathode material during storage, thus improving the chemical stability of the cell and further extending the battery's storage life.

[0020] In some embodiments, the ratio R of the weight of the first active particle to the sum of the weights of the first active particle and the second active particle is... W Satisfying 0.5≤R W ≤0.9. Optionally, the ratio R of the weight of the first active particle to the sum of the weights of the first active particle and the second active particle is... W Satisfying 0.7≤R W ≤0.9.

[0021] By adjusting the weight ratio of polycrystalline active particles in the positive electrode active particles within a certain range, for example, by controlling the ratio R of the weight of the first active particle to the sum of the weights of the first active particle (i.e., the polycrystalline active particle in the positive electrode active material) and the second active particle (i.e., the monocrystalline or near-monocrystalline active particle in the positive electrode active material). W Within a certain range, such as 0.5≤R W≤0.9, etc. can be more conducive to reducing the active surface area, reducing the side reaction between the electrolyte and the positive material during storage, and thus improving the chemical stability of the battery cell and prolonging the storage life of the battery.

[0022] In some embodiments, the first active particles and the second active particles are each independently an oxide material containing lithium and nickel elements.

[0023] Optionally, the nickel-lithium element number ratio R Ni / Li and the nickel-lithium element number ratio R Ni / Li each independently satisfies ≥0.65.

[0024] Further optionally, the nickel-lithium element number ratio R Ni / Li and the nickel-lithium element number ratio R Ni / Li each independently satisfies 0.8≤R Ni / Li ≤1.0.

[0025] In some embodiments, the first active particles and the second active particles are each independently a ternary material or a ternary material containing a doped and / or coated element.

[0026] Optionally, the first active particles and the second active particles are each independently an NCM ternary material, an NCA ternary material, an NCM ternary material containing a doped and / or coated element, or an NCA ternary material containing a doped and / or coated element.

[0027] Optionally, the first active particles and the second active particles each independently comprise a chemical composition having an element molar ratio of Li x (Ni a Co b M c M’ d )O2, wherein 0.9≤x≤1.2, 0.8≤a<1, 0

[0028] The higher the nickel content in the positive active material, the more significant the deterioration of small-size particles (i.e., small-size polycrystalline active particles) in the polycrystalline active particles to the battery storage performance, and it is more difficult to balance high energy density and long storage life. By using the positive active material provided in the present application, the battery storage life can be significantly improved without substantially losing the energy density in a high-nickel system.

[0029] In some embodiments, the first active particles have a nickel-to-lithium element number ratio R Ni / Li less than the nickel-to-lithium element number ratio R Ni / Li .

[0030] Optionally, the second active particles have a nickel-to-lithium element number ratio R Ni / Li with respect to the nickel-to-lithium element number ratio R Ni / Li of the first active particles, and a difference ΔR Ni / Li satisfies 0 < ΔR

[0031] Further optionally, 0.01 < ΔR Ni / Li ≤ 0.05.

[0032] By adjusting the relative size of the nickel-to-lithium element number ratio R Ni / Li of the polycrystalline particles and the single-crystal or single-crystal-like particles, the R Ni / Li of the polycrystalline particles is made lower than the R Ni / Li of the single-crystal or single-crystal-like particles, which can help improve the thermal stability of the positive electrode active material and improve the high-temperature storage performance of the battery while providing a higher available capacity of the positive electrode active material.

[0033] In a second aspect, the present application provides a positive electrode tab, which comprises a positive electrode active material layer, and the positive electrode active material layer comprises the positive electrode active material according to the first aspect of the present application. In this case, the use of the positive electrode tab can endow the secondary battery with superior storage performance, while maintaining good energy density.

[0034] In some embodiments, the positive electrode tab has a compacted density of 3.2-3.8 g / cm 3 ; optionally, the positive electrode tab has a compacted density of 3.4-3.7 g / cm 3 When the compacted density of the positive electrode tab is within the above range, it is beneficial to obtain higher energy density while taking into account the energy density and storage performance of the battery.

[0035] In a third aspect, the present application provides a secondary battery, which comprises the positive electrode tab according to the second aspect of the present application, and further comprises a negative electrode tab and a separator; wherein the separator is arranged between the positive electrode tab and the negative electrode tab.

[0036] The positive electrode tab of the secondary battery has a unique particle size distribution characteristic of the polycrystalline active particles and the single-crystal or single-crystal-like active particles, has superior storage performance, and can maintain good energy density at the same time.

[0037] In a fourth aspect, the present application provides an electric device, which comprises at least one of the positive electrode tab according to the second aspect of the present application and the secondary battery according to the third aspect of the present application.

[0038] In a fifth aspect, the present application provides a preparation method of the positive electrode active material, comprising the following steps:

[0039] preparing the first active particles and the second active particles respectively;

[0040] mixing the first active particles and the second active particles to obtain the positive electrode active material of the first aspect of the present application;

[0041] The first active particles are prepared by the method comprising the following steps: sintering precursor materials meeting element stoichiometric ratios, the sintering temperature is 600-900℃, and the sintering time is 8-15h.

[0042] The second active particles are prepared by the method comprising the following steps: sintering precursor materials meeting element stoichiometric ratios, the sintering temperature is 700-1000℃, and the sintering time is 8-15h.

[0043] By controlling the sintering parameters of the positive electrode active material, the unique particle size distribution characteristics of the polycrystalline active particles and the single crystal or single crystal-like active particles can be controlled.

[0044] The details of one or more embodiments of the present application are presented in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0045] For better describing and illustrating the embodiments or examples of the disclosed application, reference can be made to one or more drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and the best mode presently understood of these applications. Moreover, the same reference numbers are used throughout the drawings to represent the same components. In the drawings:

[0046] Figure 1 is a particle size distribution curve of the positive electrode active material in an embodiment of the present application;

[0047] Figure 2 is a schematic diagram of a secondary battery in an embodiment of the present application;

[0048] Figure 3 is a schematic diagram of a secondary battery in an embodiment of the present application; Figure 2 is an exploded view of the secondary battery in an embodiment of the present application shown in FIG. 2;

[0049] Figure 4 is a schematic diagram of a power-consuming device using the secondary battery in an embodiment of the present application as a power source.

[0050] BRIEF DESCRIPTION OF DRAWINGS

[0051] 5, secondary battery; 51, case; 52, electrode assembly; 53, cover plate; 6, electric device. DETAILED DESCRIPTION

[0052] Hereinafter, some embodiments of the positive electrode active material, the positive electrode sheet, the secondary battery, the electric device, and the manufacturing method according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repetitive description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0053] The numerical ranges recited in the present application are defined in terms of their lower and upper limits. The ranges are defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined by this approach can be inclusive or exclusive of the end values, either end value can be independently included or excluded, and any combination of the end values can be made, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number between the upper and lower limits of that range, wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like. For example, when a parameter is stated to be an integer selected from "2-10", it is equivalent to list the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0054] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0055] If not specified otherwise, all steps of the present application can be performed in any order, preferably in the order as specified. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in the order as specified, or the method can comprise steps (b) and (a) in the order as specified. For example, the method comprising step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or the method can comprise steps (a), (c) and (b), or the method can comprise steps (c), (a) and (b), etc.

[0056] If not specified otherwise, all terms "having", "including", "containing", and "comprising" as used herein each are meant to be open ended. For example, "including" and "comprising" can mean that other members or time characteristics not listed can also be included or comprised, or can mean that only the listed members or time characteristics are included or comprised. Members are for example materials or components, structures, elements, instruments, etc. Non-limiting examples of time characteristics are actions, conditions for actions to occur, timing, states, etc.

[0057] If not specified otherwise, the term "or" as used herein is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". Further, any of the following conditions can satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0058] In the present application, A (such as B) means that B is one non-limiting example of A, and A can be understood as not limited to B.

[0059] In the present application, "and / or" means that the corresponding feature or aspect includes any one of the two or more relevant listed items, and also includes any and all combinations of the relevant listed items. For example, "A and / or B" means that the group consisting of A, B, and the combination of A and B. Where "comprising A and / or B" means "comprising A, comprising B, and comprising A and B", and also means "comprising A, comprising B, or comprising A and B", which can be properly understood according to the sentence.

[0060] In the present application, "a plurality of", "a plurality of kinds", etc. means more than two or equal to two, if not specified otherwise. For example, "one or more" means one or more than two.

[0061] In the present document, "preferably", "more preferably", "particularly preferably" and the like are used merely for the purpose of description and do not constitute limitations on the present application. If multiple "preferably"s occur in a technical solution, each "preferably" is independent of each other unless specifically stated otherwise or there is a contradictory or restrictive relationship.

[0062] In the present document, "further", "even further", "in particular" and the like are used for the purpose of description and do not constitute limitations on the present application.

[0063] In the present document, the terms "first", "second", "third", "fourth" and the like in "first aspect", "second aspect", "third aspect", "fourth aspect" and the like are used only for the purpose of description and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the technical features indicated. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0064] In the present document, the units related to the data range, if only the right end point has a unit, it means that the units of the left end point and the right end point are the same. For example, 3-5h or 3-5h means that the units of the left end point "3" and the right end point "5" are both h (hours).

[0065] The weight of the related components mentioned in the present application embodiment specification can not only refer to the content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the present application embodiment specification is enlarged or reduced in proportion, it is within the scope disclosed in the present application embodiment specification. Further, the weight described in the present application embodiment specification can be μg, mg, g, kg and other mass units commonly known in the chemical industry.

[0066] With the popularization of the application of lithium ion battery technology, the comprehensive performance requirements of the positive active material are also continuously improved to meet the comprehensive performance requirements of high energy density and long storage life of the battery. For the positive electrode sheet in the traditional technology, in order to obtain a higher compaction density, the particle size distribution of the active particles is usually relatively wide, for example, the (D v 90-D v 10) / D v 50 is mostly above 1.2 (≥1.2). When the positive active material has such a wide particle size distribution, it often includes a large number of small-size polycrystalline particles. However, the small-size particles in the polycrystalline particles will cause the deterioration of the storage performance of the battery, and if the (D v 90-D v 10) / D v50, also leads to loss of compaction density, and thus, it is difficult to achieve both improvement of long storage life of the battery and low energy density loss.

[0067] In view of the above, in a first aspect, the present application provides a positive electrode active material, comprising first active particles and second active particles; wherein the first active particles are polycrystalline particles in the positive electrode active material, with a particle size parameter (D v 90-D v 10) / D v 50, denoted as X1; and the second active particles are single-crystal or single-crystal-like particles in the positive electrode active material, with a particle size parameter (D v 90-D v 10) / D v 50, denoted as X2.

[0068] X1 / X2 satisfies 0.2≤X1 / X2≤0.7.

[0069] wherein D v 90, D v 50, and D v 10 represent the particle sizes corresponding to the cumulative volume distribution percentages of 90%, 50%, and 10% of the multi-particle combination, respectively.

[0070] The positive electrode active material provided by the present application comprises polycrystalline particles denoted as first active particles and single-crystal or single-crystal-like particles denoted as second active particles, and the (D v 90-D v 10) / D v 50 are denoted as X1 and X2, respectively, and X1 / X2 satisfies 0.2≤X1 / X2≤0.7.

[0071] In the present application, unless otherwise specified, the electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" in the electrode sheet refers to a material capable of reversibly intercalating and deintercalating active ions. Unless otherwise specified, the "negative electrode active material" refers to a material capable of reversibly intercalating and deintercalating active ions used in the negative electrode sheet; and the "positive electrode active material" refers to a material capable of reversibly deintercalating and intercalating active ions used in the positive electrode sheet. When the secondary battery is charged, active ions are deintercalated from the positive electrode, intercalate the negative electrode through the electrolyte; and when the secondary battery is discharged, active ions are deintercalated from the negative electrode and intercalate the positive electrode. The active ion is not particularly limited, and can be a lithium ion, in which case it corresponds to a lithium ion secondary battery.

[0072] In the present application, "active material" and "active substance" have the same meaning and can be used interchangeably; "positive active material" and "positive active material" have the same meaning and can be used interchangeably; "negative active material" and "negative active material" have the same meaning and can be used interchangeably.

[0073] In the present application, unless otherwise specified, "active material layer" includes positive active material layer of positive electrode sheet and negative active material layer of negative electrode sheet, and according to the detailed circumstances, it can refer to positive active material layer or negative active material layer. It can be understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material.

[0074] In the present application, "polycrystal" is also called secondary particle, which refers to agglomerated particles formed by two or more primary particles. In the present application, the particle size of the primary particles constituting the polycrystal particles is generally controlled between 100 nm and 800 nm. If the particle size of the primary particles is too small, it may exacerbate the side reaction with the electrolyte, and if the particle size of the primary particles is too large, it may lead to deterioration of the battery dynamics.

[0075] In the present application, "single crystal" particle is also called primary particle, which refers to a single crystal grain; the micro-morphology of single crystal is a particle that is not substantially agglomerated, and the particle is dispersed. Single crystal can be an irregularly shaped particle. A single particle with a size greater than 1 μm and no obvious agglomeration is generally determined as a single crystal particle.

[0076] In the present application, "primary particle" and "secondary particle" are terms well known in the art.

[0077] In the present application, "single crystal-like" generally refers to a particle that has some agglomeration of primary particles, but has a size and properties similar to single crystal.

[0078] In the present application, the "size" or "particle size" of polycrystal particles and single crystal or single crystal-like particles, unless otherwise specified, refers to D v 50.

[0079] Polycrystal particles and single crystal or single crystal-like particles can be easily distinguished by taking SEM images using a scanning electron microscope.

[0080] In the context of the present application, the volume cumulative distribution particle size D v N (wherein N represents any numerical value selected from 0 to 100) can be used to characterize the particle size of the material, which refers to the particle size corresponding to the cumulative volume distribution percentage of N% of the material, and the particle size is less than or equal to D v N. The volume fraction of D v N can be obtained from the volume cumulative distribution curve of the material particle size, and unless otherwise specified, the volume cumulative distribution curve is cumulative from zero on the small particle size side.v 90, D v 50, D v 10, D v 90 refers to the particle size corresponding to the cumulative volume distribution percentage of 90% of the material, D v 50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50% of the material, D v 10 refers to the particle size corresponding to the cumulative volume distribution percentage of 10% of the material. For example, D v 50 indicates that 50% of the volume of the material is composed of particles with a size less than or equal to D v 50, and 50% of the volume of the material is composed of particles with a size greater than D v 50. For example, D v 90 indicates that 90% of the volume of the material is composed of particles with a size less than or equal to D v 90, and 10% of the volume of the material is composed of particles with a size greater than D v 90. For example, D v 10 indicates that 10% of the volume of the material is composed of particles with a size less than or equal to D v 10, and 90% of the volume of the material is composed of particles with a size greater than D v 10. Those skilled in the art can understand the meaning of D v 90, D v 50, D v 10, and can determine them using instruments and methods known in the art. For example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method can be referred to, and a laser particle size analyzer can be conveniently used for determination, such as Mastersizer 2000E laser particle size analyzer of Malvern Instruments Limited, UK, and LS-909 laser particle size analyzer (Eolite, USA).

[0081] For a mixed system composed of multiple particles, the particle size parameters (D v 90-D v 10) / D v 50 can reflect the distribution characteristics of the particles, and thus is also a particle size distribution parameter. Generally, the larger the value of (D v 90-D v 10) / D v 50, the wider the particle size distribution, and conversely, the smaller the value, the narrower the particle size distribution.

[0082] Small-size particles in polycrystalline particles can cause deterioration of the storage performance of the battery. This can be due to the large specific surface area of small-size polycrystalline particles, which can cause particle breakage and lead to dissolution of transition metals in the positive electrode material, thereby deteriorating the storage performance. However, if (D v 90-D v10) / D v 50, which will result in a loss of the compacted density.

[0083] The positive electrode active material provided in the present application adopts a combination of polycrystalline active particles and single-crystal or single-crystal-like active particles with special particle size distribution characteristics, the D v 90-D v 10) / D v 50 and single-crystal or single-crystal-like active particles, the D v 90-D v 10) / D v 50 ratio (denoted as X1 / X2) is low, so that the active particle size is reasonably matched, and the battery storage life can be significantly improved under the premise of basically no loss of energy density. The inventors of the present application speculate that this is because the content of small-size polycrystalline particles is reduced, thereby reducing the active surface area, reducing the side reaction between the electrolyte and the positive electrode material during storage, and thereby improving the chemical stability of the battery and prolonging the storage life of the battery.

[0084] In the positive electrode active material provided in the present application, by adjusting the value of X1 / X2, the particle size and particle size distribution between polycrystalline active particles and single-crystal or single-crystal-like active particles are finely matched, so that the balance between the content of small-size polycrystalline active particles and the compacted density of the positive electrode sheet can be better coordinated, thereby better meeting the dual requirements of battery storage performance and energy density.

[0085] In some embodiments, in the particle size distribution curve of the positive electrode active material, the first active particles and the second active particles correspond to two discontinuous independent peaks, respectively.

[0086] In the present application, if no other description is given, the particle size distribution curve can be measured by using instruments known in the art, for example, the particle size distribution curve can be tested by using a laser particle size analyzer, and further, a laser particle size analyzer such as Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK, or LS-909 laser particle size analyzer (EOLJK) can be used.

[0087] By controlling the particle size and distribution of polycrystalline particles and single-crystal or single-crystal-like particles, in the particle size distribution curve of the positive electrode active material, the two kinds of particles can correspond to two discontinuous independent peaks, respectively, at this time, the D v 90, D v 50 and D v 10 can be respectively fitted and analyzed according to the particle size distribution peaks.

[0088] Figure 1The shown particle size distribution curve is a particle size distribution curve obtained by testing the positive electrode active material in an embodiment of the present application using a laser particle size analyzer. The curve is a bimodal distribution, and has two independent peaks, respectively corresponding to the first active particles (large particles) and the second active particles (small particles) in the present application.

[0089] In the particle size distribution curve, the two peaks corresponding to the first active particles and the second active particles are discontinuous, meaning that the particle size ranges of the two active particles do not overlap, and the two particles can be easily screened out from a mixture of the two particles, and then the two active particles of different sizes can be independently tested, such as, but not limited to, composition testing, specific surface area testing, etc.

[0090] In some embodiments, the particle size distribution curve of the positive electrode active material has and only has two peaks, and the two peaks are discontinuous independent peaks, and the two peaks respectively correspond to the particle size distribution of the first active particles and the second active particles.

[0091] In some embodiments, the X1 / X2 satisfies 0.2≤X1 / X2≤0.7. The X1 / X2 can be selected from any one of the following values: 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, etc., and can also be selected from an interval formed by any two of the above values, and a non-limiting example can include 0.25≤X1 / X2≤0.55.

[0092] In some embodiments, the first active particles satisfy 0.3≤X1≤1.0. The X1 of the first active particles can be selected from any one of the following values: 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, etc., and can also be selected from an interval formed by any two of the above values, and a non-limiting example can include 0.4≤X1≤0.8.

[0093] In some embodiments, the second active particle satisfies 0.7 ≤ X2 ≤ 2.5. X2 of the second active particle can be selected from any of the following values: 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2 (e.g., 2.0), 2.1, 2.2, 2.3, 2.4, 2.45, etc., or can be selected from any range of two of the above values. Non-limiting examples may include: 1.5 ≤ X2 ≤ 2.5, 0.7 ≤ X2 ≤ 2, 0.7 ≤ X2 ≤ 1.6, 0.8 ≤ X2 ≤ 1.6, 0.7 ≤ X2 ≤ 1.5, 0.8 ≤ X2 ≤ 1.5.

[0094] By further adjusting the range of X1 / X2 values, or by further adjusting the X1 value of polycrystalline active particles or selecting the X2 value of monocrystalline or near-monocrystalline active particles to control the values ​​of X1 / X2, the matching of the active surface areas of the two particle sizes can be better coordinated, thereby better balancing the dual requirements of high energy density and long storage life, and improving battery storage life while maintaining good energy density.

[0095] In some embodiments, the D of the first active particle v 50 and the D of the second active particle v The ratio R of 50 Dv50 Satisfying 2≤R Dv50 ≤4. The D of the first active particle v 50 and the D of the second active particle v The ratio R of 50 Dv50 The value can be selected from any of the following: 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4 (e.g., 4.0), etc., or from any interval consisting of any two of the above values. A non-restrictive example could be: 2.3 ≤ R. Dv50 ≤4.0.

[0096] In some embodiments, the D of the first active particle v 50 satisfies 7μm≤D v 50≤15μm. The D of the first active particle v 50 can be selected from any of the following sizes: 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc., or it can be selected from the range formed by any two of the above sizes. Non-limiting examples may include: 7μm ≤ D v50≤ 14 μm.

[0097] In some embodiments, the second active particles have a D50 of 1 μm to 6 μm. v 50 satisfies 1 μm ≤ D v 50≤ 6 μm. The second active particles have a D50 of 1 μm to 6 μm. v 50 can be selected from any one of the following sizes: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, etc., and can also be selected from an interval formed by any two of the above sizes. Non-limiting examples can include: 2 μm ≤ D v 50≤ 6 μm, 1 μm ≤ D v 50≤ 4 μm, 2 μm ≤ D v 50≤ 4 μm, 3.5 μm ≤ D v 50≤ 6 μm.

[0098] In some embodiments, the first active particles have a specific surface area of 0.35 to 0.65 m 2 / g; the first active particles can have a specific surface area selected from any one of the following values: 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g, etc., and can also be selected from an interval formed by any two of the above values. Non-limiting examples can include: 0.35 to 0.55 m 2 / g.

[0099] In some embodiments, the second active particles have a specific surface area of 0.70 to 0.90 m 2 / g; the second active particles can have a specific surface area selected from any one of the following values: 0.7 m 2 / g, 0.72 m 2 / g, 0.74 m 2 / g, 0.75 m 2 / g, 0.76 m 2 / g, 0.78 m 2 / g, 0.8 m 2 / g, 0.82 m 2 / g, 0.84 m 2 / g, 0.85 m 2 / g, 0.86 m 2 / g, 0.88 m 2 / g, 0.9 m 2 / g, etc., and can also be selected from an interval formed by any two of the above values, and non-limiting examples can include: 0.70-0.85 m 2 / g.

[0100] In the present application, the specific surface area of the particulate matter refers to the ratio of the surface area of the particulate matter to the weight, which can be measured by using instruments and methods known in the art, for example, by using the nitrogen adsorption specific surface area analysis test method.

[0101] By respectively regulating the D v 50 of the polycrystalline active particles and the D v 50 of the single-crystal or single-crystal-like active particles in the positive electrode active material, the active surface areas of different active particles can be synergistically controlled, so as to better reduce the side reactions between the electrolyte and the positive electrode material during storage, thereby better improving the chemical stability of the battery cell and further prolonging the storage life of the battery.

[0102] In the present application, the specific surface area (BET) of the positive electrode active material can be obtained by testing using the following method: testing by using the nitrogen adsorption specific surface area analysis test method and calculating by using the BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by using the Tri Star II specific surface and pore analyzer of the American Micromeritics company, and the testing steps can refer to GB / T 19587-2004. The sample to be tested: the prepared positive electrode active material; or the positive electrode active material sampled from the positive electrode active material layer of the positive electrode sheet. The testing and analysis method is as follows: drying the sample to be tested in a vacuum drying box at 200°C for 2 hours; then using argon as the adsorption gas, measuring the adsorption / desorption curve with the relative pressure P / P0 being 0-0.99 by using the specific surface and pore analyzer, P is the equilibrium adsorption pressure, and P0 is the saturated vapor pressure, and the specific surface area of the positive electrode active material is calculated by using the BET method.

[0103] In some embodiments, the ratio R W of the weight of the first active particles to the sum of the weights of the first active particles and the second active particles satisfies 0.5≤R W ≤0.9. The ratio R Wmay be selected from any one of the following values: 0.5, 0.52, 0.54, 0.55, 0.56, 0.58, 0.6, 0.62, 0.63, 0.64, 0.65, 0.66, 0.68, 0.69, 0.7, 0.72, 0.74, 0.75, 0.76, 0.78, 0.8, 0.82, 0.84, 0.85, 0.86, 0.88, 0.9, etc., and can also be selected from an interval formed by any two of the above values, and non-limiting examples can include: 0.7≤R W ≤0.9.

[0104] By adjusting the weight ratio of the polycrystalline active particles in the positive active particles within a certain range, for example, by adjusting the weight ratio of the first active particles to the sum of the weights of the first active particles (i.e., the polycrystalline active particles in the positive active material) and the second active particles (i.e., the single-crystal or single-crystal-like active particles in the positive active material), R W within a certain range, such as 0.5≤R W ≤0.9, etc., the active surface area can be more effectively reduced, the side reaction between the electrolyte and the positive material during storage can be reduced, and thus the chemical stability of the battery cell can be improved, and the storage life of the battery can be prolonged.

[0105] In addition, the higher the nickel content in the positive active material, the more significant the deterioration of the small-size particles (i.e., small-size polycrystalline active particles) in the polycrystalline active particles on the storage performance of the battery, and it is more difficult to balance high energy density and long storage life. By using the positive active material provided in the present application, the storage life of the battery can be significantly improved without substantially sacrificing the energy density of the high-nickel system battery.

[0106] In the application, "high nickel" is a general term used by those skilled in the art for a class of substances in which the molar ratio of nickel element in lithium transition metal oxide is relatively high. Generally, the molar ratio of nickel element is above 0.8, based on 1 mole of lithium transition metal oxide. Taking NCM811 ternary positive material as an example, the molar ratio of nickel, cobalt and manganese therein is 80:10:10. Increasing the nickel content in the positive active material is beneficial to improving the energy density and can improve the battery capacity.

[0107] In the lithium ion battery system of the present application, for the positive active material and the positive electrode sheet, the element number ratio of nickel element to lithium element can be used to represent the nickel content, which can be referred to as the nickel-lithium molar ratio, which can be denoted as R Ni / Li , which can be equal to the molar ratio of nickel element to lithium element. In the present application, R Ni / Li may be independently greater than or equal to 0.65, further may be independently greater than or equal to 0.7, and more further may be independently greater than or equal to 0.8. In some embodiments of the present application, the nickel-lithium molar ratio R Ni / Limay be selected from any one of the following numerical values or interval formed by any two of the following numerical values: 0.65, 0.7, 0.75, 0.8, 0.82, 0.85, 0.9, 0.95, 1, etc. In some embodiments of the present application, the nickel-lithium molar ratio R Ni / Li may be selected from any one of the following numerical intervals (each numerical endpoint herein can be independently included or excluded): 0.65-1.0, 0.7-1.0, 0.8-1.0, 0.8-0.95, etc.

[0108] In some embodiments, the first active particles and the second active particles are each independently an oxide material containing lithium element and nickel element.

[0109] In the present application, the “oxide containing lithium element and nickel element” can be referred to as lithium nickel transition metal oxide. Non-limiting examples of the lithium nickel transition metal oxide can include, but are not limited to, one or more of lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, modified compounds thereof, etc. Among them, non-limiting examples of the lithium nickel oxide can include LiNiO2, etc. Non-limiting examples of the lithium nickel cobalt manganese oxide can include LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to as NCM 811 ) etc. Non-limiting examples of the lithium nickel cobalt aluminum oxide can include LiNi 0.85 Co 0.15 Al 0.05 O2, etc.

[0110] In some embodiments, the nickel-lithium element number ratio R Ni / Li of the first active particles and the nickel-lithium element number ratio R Ni / Li may each independently meet the definition of any one of the preceding embodiments, for example, ≥ 0.65. The R Ni / Li may each independently be selected from any one of the following numerical values: 0.65, 0.66, 2 / 3 (i.e., two-thirds), 0.67, 0.68, 0.7, 0.71, 0.75, 0.8, 0.85, 0.88, 0.89, 8 / 9 (i.e., eight-ninths), 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, etc., and can each independently be selected from an interval formed by any two of the above-mentioned numerical values. In some embodiments, the first active particles and the second active particles each independently satisfy any one of the following ranges: 0.65≤R Ni / Li≤ 1.1, 0.8≤ R Ni / Li ≤ 1.0, 0.8≤ R Ni / Li ≤ 0.95, 2 / 3≤ R Ni / Li ≤ 8 / 9, 0.66≤ R Ni / Li ≤ 0.89, 0.67≤ R Ni / Li ≤ 0.88, 0.70≤ R Ni / Li ≤ 1.07, 0.71≤ R Ni / Li ≤ 1.06, ≥ 0.7, ≥ 0.8, ≥ 0.85, ≥ 0.9, etc.

[0111] In some embodiments, the positive electrode active material of the first aspect of the present application further contains a doping element. Unless otherwise specified, the doping element in any of the positive electrode active materials in the present application (including but not limited to the positive electrode active material provided in the first aspect) can independently include one or more of transition metal elements and non-transition metal elements. Suitable doping elements and their contents can be selected according to functional requirements. The doping element can include but is not limited to one or more of Sb, K, Ca, Zr, Sr, Al, B, Ba, Nb, W, Mo, Co, P, and C, etc. For lithium-ion batteries, the doping element can include but is not limited to one or more of Na, Sb, K, Ca, Zr, Sr, Al, B, Ba, Nb, W, Mo, Co, P, and C, etc.

[0112] In some embodiments, the first active particles and the second active particles are each independently a ternary material or a ternary material containing a doping and / or coating element.

[0113] As used herein, “ternary material” has the commonly known meaning in the field of secondary battery technology, which means that in the positive electrode active material, in addition to including the corresponding element of active ions (such as lithium element), it can also include nickel (Ni) element and cobalt (Co) element, and it can also include X element, which can be but is not limited to manganese (Mn) element or aluminum (Al) element. When the X element is Mn element, the ternary material can be denoted as NCM ternary material, non-limiting examples of which can include NCM 811 , etc.; when the X element is Al element, the ternary material can be denoted as NCA ternary material, non-limiting examples of which can include LiNi 0.85 Co 0.15 Al 0.05 O2, etc.

[0114] In the present application, unless otherwise specified, “ternary material containing a doping and / or coating element” means a ternary material containing a doping original ternary material, a ternary material containing a coating element, or a ternary material containing both a doping element and a coating element.

[0115] In some embodiments, the first active particles and the second active particles are each independently NCM ternary materials, NCA ternary materials, NCM ternary materials containing doping and / or coating elements, or NCA ternary materials containing doping and / or coating elements.

[0116] In the present application, unless otherwise specified, "NCM ternary materials containing doping and / or coating elements" means NCM ternary materials containing doping original NCM ternary materials, NCM ternary materials containing coating elements, or NCM ternary materials containing both doping elements and coating elements. Unless otherwise specified, "NCA ternary materials containing doping and / or coating elements" means NCA ternary materials containing doping original NCA ternary materials, NCA ternary materials containing coating elements, or NCA ternary materials containing both doping elements and coating elements.

[0117] In the present application, when the positive electrode active material contains coating elements, it means that the positive electrode active material has a coating layer located outside the bulk structure, which is composed of coating elements.

[0118] In some embodiments, the first active particles and the second active particles are each independently composed of a chemical composition having the following molar ratio of elements: Li x (Ni a Co b M c M’ d )O2, wherein 0.9≤x≤1.2, 0.8≤a<1, 0 Ni / Li In some embodiments, R Ni / Li is selected from (2 / 3) to (8 / 9). In other embodiments, R Ni / Li is selected from 0.67 to 0.88.

[0119] In some embodiments, the first active particles and the second active particles are each independently composed of one or more of the following elements: Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, and Ta. The content of these elements can be flexibly adjusted according to the needs of improving the performance of the positive electrode active material, the positive electrode plate, or the secondary battery. For example, doping elements such as Mo, W, Zr, Nb, etc. in the positive electrode active material can control the crystal morphology and improve the interface performance of the electrolyte and the cathode material.

[0120] It should be noted that in the chemical composition formula of the first active particles and the second active particles described above, the molar equivalent of oxygen element is recorded as 2 for the sake of convenience, but there can be a certain non-integer case. In addition, x in the composition formula described above can also be the molar equivalent of the raw material at the manufacturing stage of the ternary positive electrode material. Generally, the positive electrode material in the battery appearing in the market has undergone formation aging process and can have undergone a certain number of charge and discharge cycles. Therefore, with the charge and discharge, the amount of Li in the positive electrode is sometimes lost. At this time, in the composition analysis, when discharged to the lower limit cut-off voltage of the battery, the lithium content x can be between 0.65 and 1.2.

[0121] In some embodiments, the nickel-lithium element number ratio R Ni / Li in the first active particles is less than the nickel-lithium element number ratio R Ni / Li in the second active particles. The nickel-lithium element number ratio R Ni / Li in the first active particles can be denoted as R1, and the nickel-lithium element number ratio R Ni / Li in the second active particles can be denoted as R2.

[0122] In some embodiments, the difference ΔR Ni / Li between the nickel-lithium element number ratio R Ni / Li in the second active particles relative to the nickel-lithium element number ratio R Ni / Li in the first active particles satisfies 0 < ΔR Ni / Li ≤ 0.05. Wherein, ΔR Ni / Li = R2-R1.

[0123] Non-limiting examples of ΔR Ni / Li may include 0.01, 0.02, 0.03, 0.04, 0.05, and can also be an interval composed of any two of the foregoing, such as 0.01 ≤ ΔR Ni / Li ≤ 0.05, 0.02 ≤ ΔR Ni / Li ≤ 0.05, 0.02 ≤ ΔR Ni / Li ≤ 0.04.

[0124] By adjusting the relative size of the nickel-lithium element number ratio R Ni / Li of the polycrystalline particles and the single crystal or single crystal-like particles, the R Ni / Li of the polycrystalline particles is lower than the R Ni / Li of the single crystal or single crystal-like particles, which can help to improve the thermal stability of the positive electrode active material and improve the high-temperature storage performance of the battery while providing a higher available capacity of the positive electrode active material.

[0125] In the present application, any of the positive electrode active particles (may be but not limited to the first active particle or the second active particle) at least includes a positive electrode active particle body, and can or can not include a coating layer; when including a coating layer, the coating layer is arranged on at least part of the surface of the positive electrode active particle body. By introducing a coating layer in the positive electrode active particle, the effect of reducing the cathode interface side reaction can be achieved.

[0126] In some embodiments, the first active particle includes an active particle body, and can or can not include a coating layer.

[0127] In some embodiments, the second active particle includes an active particle body, and can or can not include a coating layer.

[0128] In some embodiments, at least one of the first active particle and the second active particle includes a coating layer.

[0129] In some embodiments, the first active particle includes a coating layer, and the composition of the body and the coating layer of the first active particle can be the same or different.

[0130] In some embodiments, the second active particle includes a coating layer, and the composition of the body and the coating layer of the second active particle can be the same or different.

[0131] In some embodiments, the first active particle and the second active particle can each independently include a coating layer or not include a coating layer.

[0132] When a coating layer is arranged on the surface of the positive electrode active particle (may be but not limited to the first active particle or the second active particle), one or more of the aforementioned doping elements can be introduced in the coating layer. For example, introducing metal oxide in the coating layer can play the role of improving the stability of the electrode / electrolyte interface. For example, introducing fluoride in the coating layer can play the role of reducing electrolyte side reactions, reducing polarization, and improving the cycle stability of the positive electrode material at high current and high voltage. For example, introducing lithium in the coating layer can play the role of improving the structural stability of the positive electrode material. The thickness of the coating layer can be flexibly adjusted according to the performance improvement needs of the positive electrode active particle, the positive electrode sheet or the secondary battery. In some embodiments, the thickness of the coating layer is 1 nm to 50 nm, which can be optionally 1 nm to 10 nm. The thickness of the coating layer can be measured by a morphology observation method such as transmission electron microscopy. The mass and the composition and content of each element of the coating layer can be measured by an element analysis method such as inductively coupled plasma emission spectrometry.

[0133] In a second aspect, the present application provides a positive electrode sheet, which comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises the positive electrode active material according to the first aspect of the present application. In this case, the use of the positive electrode sheet can impart superior storage performance to the secondary battery, while maintaining good energy density.

[0134] In some embodiments, the positive electrode sheet has a compacted density of 3.2-3.8 g / cm 3 The positive electrode sheet can have a compacted density selected from any one of the following densities: 3.2 g / cm 3 , 3.25 g / cm 3 , 3.3 g / cm 3 , 3.35 g / cm 3 , 3.4 g / cm 3 , 3.45 g / cm 3 , 3.5 g / cm 3 , 3.55 g / cm 3 , 3.6 g / cm 3 , 3.65 g / cm 3 , 3.7 g / cm 3 , 3.75 g / cm 3 , 3.8 g / cm 3 , or a range formed by any two of the above values. In some embodiments, the positive electrode sheet has a compacted density of 3.4-3.7 g / cm 3 When the compacted density of the positive electrode sheet is within the above range, it is beneficial to achieve higher energy density while taking into account the energy density and storage performance of the battery.

[0135] As used herein, "compacted density" has the meaning commonly understood in the art and is one of the reference indicators of the energy density of a material. In the present application, unless otherwise specified, the compacted density of the positive electrode sheet refers to the mass of the positive electrode active material layer divided by its volume.

[0136] The positive electrode sheet comprises a positive electrode current collector and at least one positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein at least one of the positive electrode film layers comprises a positive electrode active material layer, and any one of the positive electrode active material layers independently contains a positive electrode active material. At least one of the positive electrode active material layers contains the positive electrode active material according to the first aspect of the present application.

[0137] By way of non-limiting example, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and further, the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0138] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive current collector can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive current collector can include one or more of a polypropylene (PP) base material, a polyethylene terephthalate (PET) base material, a polybutylene terephthalate (PBT) base material, a polystyrene (PS) base material, a polyethylene (PE) base material, and the like.

[0139] In some embodiments, the positive electrode film layer can further optionally include a binder. As non-limiting examples, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0140] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As non-limiting examples, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the positive electrode tab can be prepared by dispersing the components described above for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive current collector; and subjecting the positive current collector to drying, compaction (which can employ cold pressing), and the like to obtain the positive electrode tab. The type of the solvent can be selected from, but is not limited to, any of the types described in the foregoing embodiments, such as N-methyl pyrrolidone (NMP). The surface of the positive current collector to which the positive electrode slurry is coated can be a single surface of the positive current collector or both surfaces of the positive current collector.

[0142] In a third aspect, the present application provides a secondary battery including the positive electrode tab of the second aspect of the present application, and further including a negative electrode tab and a separator; wherein the separator is disposed between the positive electrode tab and the negative electrode tab.

[0143] The positive electrode tab of the secondary battery has a unique particle size distribution characteristic of the polycrystalline active particles and the single-crystal or single-crystal-like active particles, has superior storage performance, and can also maintain a good energy density.

[0144] In the present application, the secondary battery includes a positive electrode sheet (the positive electrode sheet provided in the second aspect of the present application), a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are inserted and de-inserted between the positive electrode sheet and the negative electrode sheet. The electrolyte has the function of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the short circuit of the positive and negative electrodes, and at the same time, to allow the active ions to pass through.

[0145] Positive electrode tab

[0146] The positive electrode sheet in the third aspect and the fourth aspect of the present application includes the positive electrode sheet provided in the second aspect of the present application.

[0147] In some embodiments of the present application, the secondary battery is a lithium ion secondary battery. The lithium ion secondary battery and the use of lithium ions to achieve the charging and discharging process through the insertion and de-insertion of the electrode and the transmission in the electrolyte. Generally speaking, the active ion in the lithium ion secondary battery is lithium ion, but it is not limited to this.

[0148] Negative electrode tab

[0149] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0150] As a non-limiting example, the negative electrode current collector has two opposite surfaces in the thickness direction of itself, and the negative electrode film layer is arranged on any one or both of the two opposite surfaces of the negative electrode current collector.

[0151] In some embodiments, the negative electrode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be adopted. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be obtained by forming a metal material on the polymer material base material. In the negative electrode current collector, non-limiting examples of the metal material can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. In the negative electrode current collector, non-limiting examples of the polymer material base material can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0152] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As non-limiting examples, the negative active material can include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative active materials for batteries can also be used. These negative active materials can be used alone or in combination with two or more.

[0153] In some embodiments, the negative film layer can also optionally include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0154] In some embodiments, the negative film layer can also optionally include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0155] In some embodiments, the negative film layer can also optionally include other auxiliary agents, such as thickening agents, etc. Non-limiting examples of thickening agents can include sodium carboxymethyl cellulose (CMC-Na), etc.

[0156] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (non-limiting examples of the solvent include deionized water), to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative current collector (the surface coated by the negative electrode slurry can be a single surface or both surfaces), and then drying, compacting (the compacting can employ cold pressing), etc., to obtain the negative electrode sheet.

[0157] Electrolyte

[0158] The electrolyte has the function of conducting active ions between the positive electrode sheet and the negative electrode sheet. The present application does not have a particular limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0159] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In a lithium ion secondary battery, the electrolyte salt can include an electrolyte lithium salt.

[0160] In some embodiments, the electrolyte lithium salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate, lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0161] In some embodiments, the solvent is an organic solvent.

[0162] In some embodiments, the organic solvent is an ester or an ether. In some of these embodiments, the organic solvent is an ester. Such ester solvents can include one or more of carbonates and halogenated carbonates, such as, by way of non-limiting example, one or more of 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), 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), and a fluorinated version of any of the foregoing.

[0163] In some embodiments, the solvent can include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0164] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high or low temperature performance of the battery, and the like.

[0165] In some embodiments, the additive can include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), methylene methanedisulfonate (MMDS), 1-propene-1,3-sultone (PST), ethylene sulfite (ES), propylene sulfite (PS), vinyl sulfate (DTD), succinonitrile (SN), adiponitrile (AND), sulfonate ester cyclic quaternary ammonium salt, tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)borate (TMSB), and anisole.

[0166] Separator film

[0167] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0168] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0169] Electrode assembly, electrochemical energy storage device, secondary battery, electric device

[0170] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly through a winding process or a stacking process.

[0171] In some embodiments, the electrochemical energy storage device can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0172] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0173] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0174] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, Figure 2 is a square structure secondary battery 5 as an example.

[0175] In some embodiments, referring to Figure 3 The outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be selected by those skilled in the art according to actual needs.

[0176] In a fourth aspect, the present application provides a power consuming device, which includes at least one of the positive electrode sheet of the second aspect of the present application and the secondary battery of the third aspect of the present application.

[0177] The secondary battery can be used as a power source of the power consuming device, or as an energy storage unit of the power consuming device. The power consuming device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. The mobile device can be a mobile phone, a notebook computer, etc., for example; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0178] As the power consuming device, the secondary battery can be selected according to the use requirements thereof.

[0179] Figure 4 The power consuming device 6 is an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0180] Another example of the device can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power source.

[0181] In a fifth aspect, the present application provides a preparation method of a positive electrode active material, which can be used to prepare the positive electrode active material of the first aspect of the present application.

[0182] In some embodiments, a preparation method of a positive electrode active material is provided, which includes the following steps:

[0183] Preparation of first active particles and second active particles, respectively;

[0184] The first active particles and the second active particles are mixed to obtain the positive electrode active material of the first aspect of the present application.

[0185] In some embodiments, the first active particles are prepared by a method comprising the step of sintering precursor materials in accordance with the stoichiometric ratio of elements, the sintering temperature being 600-900℃, and further, the sintering time can be 8-15h, such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc., or can be selected from an interval formed by any two of the above-mentioned time lengths. The sintering temperature for preparing the first active particles (polycrystalline particles) can be 600-900℃, or can be selected from any one of the following temperatures: 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc., or can be selected from a temperature interval formed by any two of the above-mentioned temperatures, such as 750-850℃.

[0186] In some embodiments, the second active particles are prepared by a method comprising the step of sintering precursor materials in accordance with the stoichiometric ratio of elements, the sintering temperature being 700-1000℃, and further, the sintering time can be 8-15h, such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc., or can be selected from an interval formed by any two of the above-mentioned time lengths. The sintering temperature for preparing the second active particles (single-crystalline or single-crystalline-like particles) can be 700-1000℃, or can be selected from any one of the following temperatures: 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc., or can be selected from a temperature interval formed by any two of the above-mentioned temperatures, such as 650-800℃.

[0187] For those skilled in the art, according to the component design of the target element composition and content of the positive electrode active particles, targeted adjustments can be made on the basis of the conventional method for preparing active particle precursors in the art, so as to realize the component regulation of the precursors and the active particles prepared therefrom. In addition, by adjusting the element composition in the precursor solution and controlling the sintering temperature, the size of the active particles can be regulated to a certain extent, such as the particle size distribution parameters D v 90、D v 50、D v 10, etc.

[0188] By controlling the sintering parameters of the positive electrode active material, the unique particle size distribution characteristics of the polycrystalline active particles and the single-crystalline or single-crystalline-like active particles can be regulated.

[0189] When the positive active particles are provided with the coating layer on at least a part of the surface of the active particle body, the positive active particles with the coating layer can be prepared by a step sintering method. The body precursor material can be first sintered to obtain the body of the positive active particles, and then the coating layer precursor material is coated on at least a part of the surface of the body, and then sintered for the second time, so as to obtain the positive active particles with the coating layer. It is easy for those skilled in the art to obtain or screen the positive active particles with the target structure by adjusting the preparation parameters.

[0190] In a sixth aspect, the present application provides a preparation method of a positive electrode slurry, comprising the following steps: mixing the positive active material according to the first aspect of the present application and a solvent to prepare a positive electrode slurry; wherein the positive electrode slurry is added with or without an auxiliary agent;

[0191] The first active particles can be prepared by the method described in the fifth aspect of the present application.

[0192] The second active particles can be prepared by the method described in the fifth aspect of the present application.

[0193] The auxiliary agent includes one or more of a conductive agent and a binder.

[0194] Hereinafter, some embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the technology or condition is not specified in the embodiments, it is performed according to the description above, or according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained by market purchase, or can be synthesized by market products according to the conventional method.

[0195] Preparation method of positive active material

[0196] 1. Preparation of first active particles (polycrystalline active particles)

[0197] At 50-55°C, nickel sulfate, manganese sulfate and cobalt sulfate are prepared into a 1 mol / L solution according to the molar ratio, the solvent is deionized water, and ammonia, sodium hydroxide and other hydroxides are added for co-precipitation technology to prepare polycrystalline precursors, and particle size testing is performed to confirm whether the preset requirements are met; during the preparation of the polycrystalline precursor, the particle size of the precursor can be controlled by controlling the reaction time, the pH value during co-precipitation and the ammonia concentration.

[0198] The polycrystalline precursor Ni 0.9 Co 0.02 Mn 0.08Ni(OH)2, Co(OH)2, Mn(OH)2, LiOH H2O are mixed in proper molar ratio (1:1.08), then sintered in an atmosphere furnace at 650-800°C (800°C in this case) for 8-15h, with oxygen as the gas atmosphere. After cooling, the polycrystalline active particles, i.e. the first active particles mentioned above, are obtained by mechanical grinding.

[0199] 2. Preparation of the second active particles (single-crystal active particles in this case)

[0200] At 50-55°C, NiSO4, MnSO4 and CoSO4 are prepared into 1 mol / L solutions in proper molar ratio, with deionized water as the solvent. Ammonia, sodium hydroxide and other hydroxides are added to prepare single-crystal precursors by co-precipitation technology. Particle size testing is performed to confirm whether the single-crystal precursors meet the preset requirements. During the preparation of the single-crystal precursors, the particle size of the single-crystal precursors can be controlled by controlling the reaction time, pH value and ammonia concentration during co-precipitation.

[0201] The single-crystal precursors Ni 0.9 Co 0.02 Mn 0.08 (OH)2, LiOH H2O are mixed in proper molar ratio, then sintered in an atmosphere furnace at 750-850°C (850°C in this case) for 8-15h, with oxygen as the gas atmosphere. After cooling, the single-crystal active particles, i.e. the second active particles mentioned above, are obtained by mechanical grinding.

[0202] After sintering, the particle size of the active particles formed by the conversion of the precursor particles increases slightly. Therefore, the preset particle size of the precursor is slightly smaller than the particle size of the corresponding active particles after sintering.

[0203] When at least part of the surface of the polycrystalline active particles or single-crystal active particles is provided with a coating layer, the precursor material can be first sintered in the first stage to obtain the positive electrode active particle body, then uniformly mixed with the coating layer raw material, and sintered in the second stage in a suitable gas atmosphere, so as to form the coating layer on at least part of the surface of the active particle body.

[0204] 3. Preparation of the positive electrode active material

[0205] The polycrystalline active particles (first active particles) and single-crystal active particles (second active particles) prepared as described above are mixed in a certain weight ratio to obtain the positive electrode active material.

[0206] The following Example 1 is taken as an example, in which the polycrystalline particles D v 50 are 9 μm, the polycrystalline particle (D v 90-D v 10) / D v 50 is 0.4, and the single-crystal particle D v50 is 3.3 pm, single crystal particle (D v 90-D v 10) / D v 50 is 1.6. That is, X1 / X2 can be calculated as 0.25. Please refer to Table 1.

[0207] Test analysis method

[0208] 1. Test analysis of particle size

[0209] (1) Particle size test

[0210] Sample preparation: prepared positive electrode active material; can also be the positive electrode active material sampled from the positive electrode active material layer of the positive electrode sheet. In order to avoid the influence of agglomeration in the drying process on the test of particle size, the wet sample after washing is taken for dispersion test.

[0211] Particle size type: D v 10, D v 50 and D v 90 test.

[0212] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009.

[0213] Test procedure: take an appropriate amount of sample to be tested (sample concentration to ensure 8% ~ 12% obscuration), add 20 mL of anhydrous ethanol, ultrasonic treatment for 5 min (53 KHz / 120 W), ensure that the sample is completely dispersed, and then determine the sample according to GB / T19077-2016 / ISO13320:2009 standard.

[0214] (2) X1 / X2

[0215] As known from the foregoing, in the present application, the polycrystalline active particles in the positive electrode active material are referred to as first active particles, and the single crystal or single crystal-like active particles in the positive electrode active material are referred to as second active particles. Among them, the particle size parameter (D v 90-D v 10) / D v 50 is X1, and the particle size parameter (D v 90-D v 10) / D v 50 is X2.

[0216] 2. Test method of electrode sheet compaction density

[0217] The pole piece is cut into a 1000 mm long film piece; the positive pole piece is rolled under appropriate pressure, and since the aluminum foil has ductility, the film piece length is 1006 mm (the ductility is 0.6%); a 1540.25 mm 2 small disc (area A) is punched out, the weight W and thickness d of the small disc are measured, the weight W1 and thickness d1 of the positive current collector in the small disc are deducted, the weight W2 and thickness d2 of the positive active material layer are obtained, and the compaction density of the pole piece is calculated according to the ratio W2 / (A·d2).

[0218] The test results can be seen in Table 3.

[0219] 3. Performance of the battery cell or battery

[0220] (1) Test method of battery capacity

[0221] The lithium ion battery is placed in a constant temperature environment at 25℃ for 2h, then charged at 0.33C to 4.2V at 2.8V-4.2V, then charged at 4.2V until the current is less than or equal to 0.05C, and then discharged at 0.33C to 2.8V, and the initial capacity C0 of the lithium ion battery is recorded.

[0222] The test results can be seen in Table 3.

[0223] (2) Test method of high-temperature storage performance of the battery

[0224] The battery is placed in a constant temperature oven at 60℃ for 100 days, then discharged at 0.33C to 2.8V at 25℃, then charged at 0.33C to 4.2V, then charged at 4.2V until the current is less than or equal to 0.05C, then discharged at 0.33C to 2.8V, and the capacity C1 of the lithium ion battery is recorded. The capacity retention rate of the battery (%) = C1 / C0 x 100%.

[0225] The test results can be seen in Table 3.

[0226] Example 1.

[0227] 1. Preparation of the positive active material

[0228] According to the preparation parameters shown in Tables 1 and 2, the first active particles and the second active particles are prepared in sequence by using the preparation method of the positive active material.

[0229] The first active particles and the second active particles are mixed to obtain the positive active material of this example.

[0230] 2. Preparation of the positive pole piece

[0231] The positive active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:2:1 and added to a solvent N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on both sides of a positive current collector aluminum foil, dried at 85°C, cold-pressed, and then die-cut and slitted to prepare a lithium ion battery positive electrode sheet.

[0232] 3. Preparation of a negative electrode sheet

[0233] The negative active material graphite, silicon oxide, conductive agent acetylene black, thickening agent sodium hydroxymethyl cellulose (CMC-Na), and binder styrene butadiene rubber (SBR) are added to a solvent water in a mass ratio of 72:24:2:1:1 and mixed uniformly to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on both sides of a negative current collector copper foil, dried at 85°C, and cold-pressed to prepare a lithium ion battery negative electrode sheet.

[0234] 4. Preparation of a separator

[0235] A polyethylene microporous film is used as a porous separator substrate, inorganic aluminum oxide powder, and polyvinylpyrrolidone acetone solvent are mixed in a weight ratio of 3:1.5:5.5 to prepare a slurry, which is coated on one side of the substrate and dried to obtain a separator film.

[0236] 5. Preparation of an electrolyte

[0237] Lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (volume ratio of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate is 1:2:1) to obtain a lithium ion battery electrolyte.

[0238] 6. Preparation of a battery

[0239] The positive electrode sheet, negative electrode sheet, and separator film are wound to obtain a bare cell, which is then subjected to packaging, liquid injection, formation, and exhaust processes to obtain the secondary battery of Example 1, which is a lithium ion battery.

[0240] Examples 2-10. The preparation methods of the first active particles, second active particles, positive active material, positive electrode sheet, and secondary battery are basically the same as those of Example 1, and the chemical composition, particle size and distribution, and active particle content of the active particles can be controlled according to Tables 1 and 2, and the preparation parameters of the active particles can be appropriately adjusted according to the parameters in Table 1.

[0241] Comparative Examples 1-2. The preparation methods of the first active particles, second active particles, positive active material, positive electrode sheet, and secondary battery are basically the same as those of Example 1, and the chemical composition, particle size and distribution, and active particle content of the active particles can be controlled according to Tables 1 and 2, and the preparation parameters of the active particles can be appropriately adjusted according to the parameters in Table 1.

[0242] Table 1.

[0243]

[0244] Table 2.

[0245]

[0246] Table 2:

[0247] (1) R W is the percentage of the weight of the first active particles relative to the sum of the weight of the first active particles and the second active particles;

[0248] (2) R Dv50 is the D v 50 ratio of the first active particles to the second active particles;

[0249] (3) X1 is the (D v 90-D v 10) / D v 50 of the first active particles, and X2 is the (D v 90-D v 10) / D v 50 of the second active particles.

[0250] Test results and analysis

[0251] The parameters and performance test results of the above examples and comparative examples can be referred to Table 3.

[0252] Examples 1-10 all have excellent high-temperature storage performance, with a capacity retention rate of more than 93% after 100 days of storage at 60°C, a long high-temperature storage life, and also can maintain good compaction density and battery capacity, meaning good energy density.

[0253] The X1 / X2 of Comparative Example 1 is too high, and the X1 / X2 of Comparative Example 2 is too low, both of which result in being unable to balance the high-temperature storage performance, compaction density and initial capacity, that is, being unable to balance the dual requirements of battery storage life and energy density. The high-temperature storage performance of Comparative Example 1 deteriorates; the improvement of the high-temperature storage performance of Comparative Example 2 is at the expense of a serious decline in energy density, with a serious decline in compaction density.

[0254] Table 3.

[0255]

[0256] The technical features of the above-described embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above-described embodiments are described, but it is understood that any combination of the technical features is within the scope of the present specification.

[0257] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea of the present application are included in the technical scope of the present application. The above-described embodiments merely express several embodiments of the present application, and the description is relatively detailed, but the present application is not construed as being limited to the embodiments. Furthermore, other modes constructed by applying various modifications to the embodiments or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art without departing from the spirit of the present application, are also included in the scope of the present application. It should be noted that several modifications and improvements can be made by those skilled in the art without departing from the concept of the present application, and these are included in the scope of the present application. Therefore, the scope of the present application should be determined by the appended claims, and the description and drawings are used to interpret the scope of the claims.

Claims

1. A positive electrode active material comprising first active particles and second active particles; wherein, The first active particles are polycrystalline particles in the positive electrode active material, having a particle size parameter (D v 90-D v 10) / D v 50 denoted as X1; the second active particles are single-crystal or single-crystal-like particles in the positive electrode active material, having a particle size parameter (D v 90-D v 10) / D v 50 denoted as X2; X1 / X2 satisfies 0.2≤X1 / X2≤0.65; wherein D v 90, D v 50, and D v 10 represent the particle sizes corresponding to the cumulative volume distribution percentages of 90%, 50%, and 10%, respectively, of the multi-particle combination. D50 of the first active particles v 50 satisfies 7 μm ≤ D v 50 < 10 μm.

2. The positive electrode active material according to claim 1, wherein In the particle size distribution curve of the positive electrode active material, the first active particles and the second active particles correspond to two discontinuous independent peaks respectively.

3. The positive electrode active material according to claim 1 or 2, wherein, X1 / X2 satisfies 0.25≤X1 / X2≤0.

55.

4. The positive electrode active material according to any one of claims 1 to 3, wherein, The first active particles satisfy 0.3≤X1≤1.

0.

5. The positive electrode active material according to claim 4, wherein The first active particles satisfy 0.3≤X1≤0.

45.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, The second active particles satisfy 0.7≤X2≤2.

5.

7. The positive electrode active material according to claim 6, wherein The second active particles satisfy 0.7≤X2≤1.

5.

8. The positive electrode active material according to claim 6, wherein The second active particles satisfy 0.8≤X2≤1.

0.

9. The positive electrode active material according to any one of claims 1 to 8, wherein, D50 of the first active particles v 50 of the second active particles v R, the ratio of D50 of the first active particles Dv50 satisfies 2≤R Dv50 ≤4.

10. The positive electrode active material according to claim 9, wherein The D of the first active particle v 50 and the D of the second active particle v The ratio R of 50 Dv50 Satisfying 2.3≤R Dv50 ≤3.

0.

11. The positive electrode active material according to any one of claims 1 to 10, wherein, D50 of the first active particles v 50 satisfies 8 μm ≤ D v 50 < 10 μm.

12. The positive electrode active material according to claim 11, wherein D50 of the first active particles v 50 satisfies 9 μm ≤ D v 50 < 10 μm.

13. The positive electrode active material according to any one of claims 1 to 12, wherein, D50 of the second active particles v 50 satisfies 1 μm ≤ D v 50 ≤ 6 μm.

14. The positive electrode active material according to claim 13, wherein, D50 of the second active particles v 50 satisfies 2 μm ≤ D v 50 ≤ 5 μm.

15. The positive electrode active material according to claim 13, wherein, D50 of the second active particles v 50 satisfies 2 μm ≤ D v 50 ≤ 4.5 μm.

16. The positive electrode active material according to claim 13, wherein D50 of the second active particles v 50 satisfies 2 μm ≤ D v 50 ≤ 4 μm.

17. The positive electrode active material according to any one of claims 1 to 16, wherein, the ratio R of the weight of the first active particles relative to the sum of the weights of the first active particles and the second active particles W satisfies 0.5 ≤ R W ≤ 0.

9.

18. The positive electrode active material according to claim 17, wherein, the ratio R of the weight of the first active particles relative to the sum of the weights of the first active particles and the second active particles W satisfies 0.5 ≤ R W ≤ 0.

8.

19. The positive electrode active material according to any one of claims 1 to 18, wherein, The first active particles and the second active particles are each independently an oxide material containing lithium element and nickel element.

20. The positive electrode active material according to claim 19, wherein, the nickel lithium element number ratio R in the first active particle Ni / Li and the nickel lithium element number ratio R in the second active particle Ni / Li each independently satisfies 0.65 ≤ R Ni / Li ≤ 1.

1.

21. The positive electrode active material according to claim 19, wherein, the nickel lithium element number ratio R in the first active particle Ni / Li and the nickel lithium element number ratio R in the second active particle Ni / Li each independently satisfies 0.8 ≤ R Ni / Li ≤ 1.

0.

22. The positive electrode active material according to claim 19, wherein the nickel lithium element number ratio R in the first active particle Ni / Li and the nickel lithium element number ratio R in the second active particle Ni / Li each independently satisfies 0.8 ≤ R Ni / Li ≤ 0.

95.

23. The positive electrode active material according to any one of claims 1 to 22, wherein, The first active particles and the second active particles are each independently a ternary material or a ternary material containing a doped and / or coated element.

24. The positive electrode active material according to claim 23, wherein The first active particles and the second active particles are each independently an NCM ternary material, an NCA ternary material, an NCM ternary material containing a doped and / or coated element, or an NCA ternary material containing a doped and / or coated element.

25. The positive electrode active material according to claim 23, wherein The first active particle and the second active particle each independently comprise an elemental combination Li x (Ni a Co b M c M’ d )02, wherein 0.9≤x≤1.2, 0.8≤a<1, 0<b<1, 0<c<1, a+b+c+d=1, M comprises at least one of Mn and Al, and M’ comprises one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, and Ta.

26. The positive electrode active material according to any one of claims 19 to 25, wherein, The nickel lithium element number ratio R in the first active particle Ni / Li Less than the nickel lithium element number ratio R in the second active particle Ni / Li .

27. The positive electrode active material according to claim 26, wherein the second active particle satisfies the difference AR Ni / Li between the element number ratio R Ni / Li of nickel to lithium in the first active particle. Ni / Li satisfies 0 < AR Ni / Li ≤ 0.

05.

28. The positive electrode active material according to claim 26, wherein 0.01 < ΔR Ni / Li ≤ 0.

05.

29. A positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising the positive electrode active material according to any one of claims 1-28.

30. The positive electrode sheet according to claim 29, wherein The compacted density of the positive electrode plate is 3.2-3.8 g / cm 3 .

31. The positive electrode sheet according to claim 29, wherein The compacted density of the positive electrode plate is 3.4-3.7 g / cm 3 .

32. A secondary battery comprising the positive electrode sheet according to any one of claims 29 to 31, further comprising a negative electrode sheet and a separator. The separation film is arranged between the positive electrode sheet and the negative electrode sheet.

33. An electrical device comprising at least one of the positive electrode sheet according to any one of claims 29-31 and the secondary battery according to claim 32.

34. A method for preparing a positive electrode active material, comprising the following steps: Preparation of first active particles and second active particles respectively; Mixing the first active particles and the second active particles to obtain the positive electrode active material according to any one of claims 1-28; wherein The first active particles are prepared by a method comprising the following steps: sintering precursor materials meeting element stoichiometric ratios, the sintering temperature being 600-900℃, and the sintering time being 8-15h; the second active particles are prepared by a method comprising the following steps: sintering precursor materials meeting element stoichiometric ratios, the sintering temperature being 700-1000℃, and the sintering time being 8-15h.

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