Positive electrode active material, positive electrode sheet, battery, and electric device

Abstract

The application relates to a positive electrode active material, a positive electrode sheet, a battery and an electric device. The positive electrode active material comprises a lithium-containing phosphate in components, and comprises secondary particles in morphology, the volume average particle size Dv50 of the secondary particles is 0.5-25 mu m; the average particle size of primary particles forming the secondary particles is 0.2-2 mu m; in the positive electrode active material, the particle size distribution of particles with a particle size of more than 3 mu m accounts for X>=10%, and the particle size distribution of particles with a particle size of more than 5 mu m accounts for Y>=5%.

Description

TECHNICAL FIELD

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

[0002] The positive electrode active material can be used as a positive electrode active material of a battery. Since the crystal structure of lithium iron phosphate is stable, it can maintain a relatively high capacity retention rate during multiple lithium ion intercalation and deintercalation processes. Therefore, the positive electrode active material can be applied to scenarios that require a long service life.

[0003] With the continuous deepening of research on positive electrode active materials and the continuous improvement of market requirements, higher demands are currently placed on the cycle capacity retention rate of batteries using positive electrode active materials. How to maintain the long cycle life characteristics of the battery while further reducing the decay of the cycle capacity retention rate of the battery and improving the cycle capacity retention rate of the battery has become a key point that needs to be broken through. SUMMARY

[0004] Therefore, it is necessary to provide a positive electrode active material, a positive electrode sheet, a battery and an electric device that can maintain the long cycle life characteristics of the battery while reducing the decay of the cycle capacity retention rate of the battery and improving the cycle capacity retention rate of the battery.

[0005] The present application is achieved by the following technical solutions.

[0006] In a first aspect, the present application provides a positive electrode sheet, comprising: the positive electrode active material comprising lithium-containing phosphate in composition, the positive electrode active material comprising secondary particles in morphology, the volume average particle size Dv50 of the secondary particles being 0.5 μm to 25 μm; primary particles forming the secondary particles, the average particle size of the primary particles being 0.2 μm to 2 μm; in the positive electrode active material, the number fraction X of particles with a particle size of 3 μm or more is ≥10%, and the number fraction Y of particles with a particle size of 5 μm or more is ≥5%.

[0007] In some embodiments, the positive electrode active material further comprises primary particles mixed with the secondary particles and having an average particle size of 0.2 μm to 2 μm in morphology; optionally, the average particle size of the primary particles is 0.2 μm to 1 μm.

[0008] In some embodiments, the primary particles mixed with the secondary particles have a spherical or spherical-like shape.

[0009] In some embodiments, the positive electrode active material satisfies at least one of the following conditions (1-1) to (1-2):

[0010] (1-1) primary particles forming the secondary particles, having an average particle diameter of 0.2 μm to 1 μm;

[0011] (1-2) primary particles forming the secondary particles, having a spherical or spheroid shape.

[0012] In some embodiments, the positive electrode active material satisfies at least one of the following conditions (2-1) to (2-5):

[0013] (2-1) 100% > X ≥ 10%; optionally, 30% ≥ X ≥ 10%;

[0014] (2-2) 100% > Y ≥ 5%; optionally, 10% ≥ Y ≥ 5%;

[0015] (2-3) 95% ≥ X - Y ≥ 0; optionally, 25% ≥ X - Y ≥ 0; more optionally, 25% ≥ X - Y > 0;

[0016] (2-4) the secondary particles have a volume average particle diameter Dv50 of 1 μm to 15 μm;

[0017] (2-5) the secondary particles have a spherical or spheroid shape.

[0018] In some embodiments, the positive electrode active material satisfies at least one of the following conditions (3-1) to (3-2):

[0019] (3-1) the positive electrode active material further includes a carbon material in terms of components, the carbon material being complexed with the lithium-containing phosphate;

[0020] (3-2) the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and lithium vanadium phosphate.

[0021] In some embodiments, the positive electrode active material includes an inner core and a coating layer formed on a surface of the inner core, the inner core including the lithium-containing phosphate, and the coating layer including a carbon material.

[0022] Optionally, the coating layer has a mass content of 0.9% to 2.5% relative to the total mass of the positive electrode active material.

[0023] In some embodiments, the positive electrode active material has a powder compaction density of 2.25 to 2.65 g / cm 3 .

[0024] In a second aspect, the present application provides a positive electrode tab, including:

[0025] a positive electrode current collector; and

[0026] a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material.

[0027] In some embodiments, the positive electrode tab satisfies at least one of the following conditions (4-1) to (4-4):

[0028] (4-1) the thickness of the positive electrode film layer is 150 μm to 180 μm;

[0029] (4-2) the coating area density of the positive electrode film layer is 0.1 mg / mm 2 to 0.3 mg / mm 2 ;

[0030] (4-3) the compaction density of the positive electrode film layer is 2.0 g / cm 3 to 2.7 g / cm 3 ;

[0031] (4-4) in the positive electrode film layer, the mass fraction of the positive electrode active material is 85% to 100%.

[0032] In some embodiments, the positive electrode tab satisfies at least one of the following conditions (5-1) to (5-2):

[0033] (5-1) the positive electrode current collector is an aluminum foil;

[0034] (5-2) the thickness of the positive electrode current collector is 7 μm to 20 μm.

[0035] In a third aspect, the present application provides a battery comprising the positive electrode tab provided in the second aspect.

[0036] In a fourth aspect, the present application provides an electric device comprising the battery provided in the third aspect.

[0037] The positive electrode active material of the present application is applied to a battery. In the initial stage of charge and discharge cycle, due to the volume average particle size Dv50 of the secondary particles being in the above specific range, the particle size is large, the lithium ion transmission channel between the particles is long, and the electrolyte cannot infiltrate the inside of the secondary particles, so the ion polarization degree of the battery positive electrode plate in the initial stage of cycle is large. At the same time, the specific particle size distribution in the secondary particles is controlled to ensure that the particle size of the secondary particles is distributed in a specific content of more than 3 μm and more than 5 μm. With the continuous intercalation and deintercalation of lithium ions in the positive electrode in the cycle process, the secondary particles formed by the agglomeration of primary particles in the above specific particle size range will crack, and with the progress of the cycle, a larger secondary particle will crack into multiple smaller secondary particles, thereby increasing the contact area of the lithium iron phosphate particles and the electrolyte, shortening the lithium ion transmission path, and further reducing the ion polarization degree. Make the battery maintain the long cycle life characteristics of the battery, further slow down the capacity retention rate in the cycle process, especially in the early and middle stages, so that the capacity retention rate will have a phased increase, thereby increasing the capacity retention rate of the battery cycle compared with the same cycle number. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 SEM image of the positive electrode active material powder in some embodiments of the present application;

[0039] Figure 2 SEM image of the positive electrode active material powder in some embodiments of the present application;

[0040] Figure 3 Ion polishing section topography of the positive electrode active material in some embodiments of the present application;

[0041] Figure 4 Identification diagram of the ion polishing section topography shown in Figure 3

[0042] Figure 5 Particle size distribution statistical diagram obtained according to the identification diagram shown in Figure 4

[0043] Figure 6 Schematic diagram of a secondary battery according to an embodiment of the present application;

[0044] Figure 7 Exploded view of the secondary battery according to an embodiment of the present application shown in Figure 6

[0045] Schematic diagram of a use device using the secondary battery according to an embodiment of the present application as a power supply. Figure 8 BRIEF DESCRIPTION OF DRAWINGS

[0046]

[0047] ​​​1 secondary battery; 11 case; 12 electrode assembly; 13 cover plate; 2 electric device. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed description is omitted. For example, there are cases where detailed description of matters known to those skilled in the art, repeated 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.

[0049] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be arbitrarily combined, 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 minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, 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 specified, a numerical range "a-b" indicates a shorthand for any real combination of integers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand for these numerical combinations. In addition, when it is stated that a parameter is 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, etc.

[0050] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0051] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0052] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0053] If not specifically stated, the present application refers to "comprising" and "including" as open terms, which can also be closed terms. For example, "comprising" and "including" can mean that other components not listed can also be included or comprised, or can mean that only the listed components are included or comprised.

[0054] If not specifically stated, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0056] Battery

[0057] A battery is a device that converts chemical energy into electrical energy. Generally, a battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. A secondary battery refers to a battery that can be used continuously by activating active materials through charging after discharging. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. Further, the secondary battery can further include a separator.

[0058] In some examples, the above-mentioned secondary battery is a lithium ion battery.

[0059] An embodiment of the present application provides a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector.

[0060] As an example, the positive current collector has two surfaces opposite in the thickness direction thereof, and the positive film layer is disposed on any one or both of the two opposite surfaces of the positive current collector.

[0061] The positive electrode film layer includes a positive electrode active material. An embodiment of the present application provides a positive electrode active material. The positive electrode active material includes a lithium-containing phosphate in composition and includes secondary particles in morphology. The volume average particle size Dv50 of the secondary particles is 0.5 μm to 25 μm; the primary particles forming the secondary particles have an average particle size of 0.2 μm to 2 μm. In the secondary particles, the number ratio of particles with a particle size of 3 μm or more is X≥10%, and the number ratio of particles with a particle size of 5 μm or more is Y≥5%.

[0062] It can be understood that the secondary particles and the primary particles are the same in composition, and mainly differ in morphology.

[0063] It should be noted that the secondary particles have a meaning known in the art. The secondary particles refer to agglomerated particles formed by two or more primary particles. As an example, the positive electrode active material can be tested by a scanning electron microscope such as ZEISS sigma 300 to obtain the morphology. Specifically, the morphology of the positive electrode active material can be observed according to the standard JY / T010-1996.

[0064] The volume average particle size Dv50 is a meaning known in the art, which can be tested by a method known in the art. Among them, Dv50 represents the particle size corresponding to the cumulative volume distribution percentage of 50%. For example, in this paper, a laser particle size analyzer is used, specifically a MasterSizer 3000, and the standard process is referred to: GB / T19077-2016 / ISO13320:2009. Since the primary particles in the positive electrode active material are small, the particle size corresponding to the cumulative volume distribution percentage of 50% measured is basically the particle size corresponding to the cumulative volume distribution percentage of 50% of the secondary particles.

[0065] The specific test process can be as follows: take an appropriate amount of sample to be tested, and the sample concentration can be ensured to be 8% to 12% optical density, add 20 mL of deionized water, and simultaneously ultrasonic for 5 min, the ultrasonic frequency is 53 KHz, and the ultrasonic power is 120 W, to ensure that the sample is completely dispersed, and then the sample is measured according to the standard GB / T19077-2016 / ISO 13320:2009.

[0066] The particle size distribution of the secondary particles is a meaning known in the art, which can be tested by a method known in the art. As an example, in this paper, an IB-19500CP ion polisher is used to analyze the cross-sectional micro-morphology of the active material powder or the corresponding electrode sheet according to the standard GB / T 17359-2012, and Avizo2D software is used to analyze the graphics, and the particle size and distribution of the secondary particles are counted.

[0067] Without wishing to be bound by any theory, the positive electrode active material of the present application is applied to a secondary battery. At the initial stage of charge-discharge cycle, due to the volume average particle size Dv50 of the secondary particles being in the above-mentioned specific range, the particle size is large, the lithium ion transmission channel between the particles is long, and the electrolyte cannot infiltrate the inside of the secondary particles, so the degree of ion polarization of the positive electrode plate of the battery at the initial stage of cycle is large. At the same time, the specific particle size distribution in the secondary particles is controlled to ensure that the distribution of the particle size of the secondary particles above 3 pm and above 5 pm is at a specific content. With the continuous intercalation and deintercalation of lithium ions in the positive electrode during the cycle process, the secondary particles formed by the agglomeration of primary particles in the above-mentioned specific particle size range will crack, and with the progress of the cycle, a larger secondary particle will crack into multiple smaller secondary particles, thereby increasing the contact area of the lithium iron phosphate particles and the electrolyte, shortening the lithium ion transmission path, and further reducing the degree of ion polarization, so that the battery can maintain the long cycle life characteristics of the battery, further slow down the capacity retention rate during the cycle process, especially in the early and middle stages, and the capacity retention rate will have a phased increase, so the capacity retention rate of the battery cycle is improved compared to the same cycle number.

[0068] Optionally, in the secondary particles, the proportion of the number of particles with a particle size of 3 pm or more X can be 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc. In some optional embodiments, 100% > X > 10%. In some optional embodiments, 30% > X > 10%.

[0069] Optionally, in the secondary particles, the proportion of the number of particles with a particle size of 5 pm or more Y can be 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc. In some optional embodiments, 100% > Y > 5%. In some optional embodiments, 10% > Y > 5%.

[0070] In some embodiments, 95% > X-Y > 0. As an example, X-Y can be 0, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%. In some optional embodiments, 25% > X-Y > 0. More optionally, 25% > X-Y > 0, 10% > X-Y > 5%. In this way, by adjusting the proportion of the number of particles with a particle size of 3 pm to 5 pm and 5 pm or more in the secondary particles, the powder compaction density can be further improved.

[0071] As an example, the volume average particle size Dv50 of the secondary particles can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 23 μm, 25 μm. In some alternative embodiments, the volume average particle size Dv50 of the secondary particles can be 1 μm to 15 μm. Alternatively, the volume average particle size Dv50 of the secondary particles can be 2 μm to 10 μm.

[0072] As an example, the morphology of the secondary particles can be spherical or spheroid. Further, the secondary particles are polycrystalline.

[0073] The primary particles forming the secondary particles have an average particle size distribution within the range of 0.2 μm to 2 μm. Lithium phosphate-containing materials such as lithium iron phosphate powder can achieve long cycle and high energy density. The secondary particles formed by the primary particles having the particle size distribution can crack into a plurality of secondary particles with smaller particle sizes during the cycling process, further increasing the contact area of lithium iron phosphate particles with electrolyte, shortening the lithium ion transport path, and thus reducing the degree of ion polarization. Alternatively, the primary particles forming the secondary particles have an average particle size of 0.2 μm to 1 μm, 0.2 μm to 0.5 μm.

[0074] As an example, the morphology of the primary particles forming the secondary particles can be spherical or spheroid. Further, the primary particles are single crystals.

[0075] In some embodiments, the above-mentioned positive electrode active material further includes primary particles having an average particle size of 0.2 μm to 2 μm mixed with the above-mentioned secondary particles. Mixing the primary particles having the particle size distribution with the above-mentioned secondary particles can improve the packing density of the particles of the positive electrode active material to some extent, increase the compaction density of the prepared positive electrode sheet, and provide higher energy density.

[0076] Alternatively, the primary particles mixed with the above-mentioned secondary particles have an average particle size of 0.2 μm to 1 μm, 0.2 μm to 0.5 μm.

[0077] As an example, the morphology of the primary particles mixed with the secondary particles is spherical or spheroid. Further, the primary particles are single crystals.

[0078] In some embodiments, the powder compaction density of the positive electrode active material under a pressure of 3 t can be 2.25 to 2.65 g / cm 3 .

[0079] The powder compaction density is the meaning known in the art, which can be tested by methods known in the art. During the compression of the powder under external force, the larger voids are filled, the contact area between particles is increased, the interatomic attractive force is generated and the mechanical wedge effect between particles is enhanced, so that a green compact with certain strength is formed. At this time, the density of the green compact is the powder compaction density.

[0080] As an example, in this paper, the test method of powder compaction density can include the following steps: a certain amount of powder is placed on a compaction special mold with a known diameter, a metal sheet is placed on the upper and lower parts of the mold, the powder is placed in the middle, the corresponding powder thickness is tested by applying pressure, and the corresponding powder volume at this time is obtained. The compaction density p is calculated by the formula p = m / v. The specific operation can be carried out according to the standard GB / T24533-2009.

[0081] In some embodiments, the positive electrode active material further includes a carbon material in composition, and the carbon material is compounded with the lithium-containing phosphate.

[0082] As an example, the positive electrode active material can be a coating material prepared by surface coating modification of the lithium-containing phosphate with the carbon material. In some alternative embodiments, the positive electrode active material includes a core and a coating layer formed on the surface of the core, the core includes the lithium-containing phosphate, and the coating layer includes the carbon material. It can be understood that when the positive electrode active material is the coating material, the primary particles mixed with the secondary particles and the primary particles forming the secondary particles also have the structure of the core and the coating layer.

[0083] Alternatively, the coating layer partially or completely coats the surface of the core. Alternatively, the material of the core can be the lithium-containing phosphate. Alternatively, the material of the coating layer can be the carbon material.

[0084] In some embodiments, the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate and lithium vanadium phosphate. Further, the lithium iron phosphate can be olivine-structured lithium iron phosphate (LiFePO4, referred to as LFP).

[0085] In some specific examples, the positive electrode active material includes a lithium iron phosphate core and a carbon coating layer formed on the surface of the lithium iron phosphate core.

[0086] In some embodiments, the mass content of the coating layer relative to the total mass of the positive electrode active material (i.e. the mass content of the coating layer in the positive electrode active material) is 0.9% to 2.5%. As an example, the mass content of the coating layer relative to the total mass of the positive electrode active material can be 0.9%, 1.0%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.1%, 2.2%, 2.4%, 2.5%.

[0087] It is understood that in other embodiments, the positive electrode active material of the above-described positive electrode film may also contain other positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may also include at least one of the following materials: lithium transition metal oxides and modified compounds thereof. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0088] Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds.

[0089] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0090] like Figures 1-2 The images shown are scanning electron microscope (SEM) images of a specific example of a positive electrode active material, which is carbon-coated lithium iron phosphate. It can be seen that it mainly consists of secondary particles with a small amount of primary particles.

[0091] Figure 1The positive electrode active material shown is a spheroid and spherical primary particle, and large particles are more. Specifically, in the specific example shown, the active material is mainly composed of single-crystal primary particles and polycrystal secondary particles, and large particles are more. Figure 2 The positive electrode active material shown is a spheroid and spherical primary particle, and large particles are more. Specifically, in the specific example shown, the active material is mainly composed of single-crystal primary particles and polycrystal secondary particles, and large particles are more.

[0092] The present application also provides a preparation method of the positive electrode active material. The preparation method can include the following steps S1-S2:

[0093] S1, mixing a precursor for preparing a lithium-containing phosphate with a solvent to prepare a slurry, and controlling the Dv50 particle size of the slurry to be 100-700 nm.

[0094] It can be understood that the Dv50 particle size of the solid in the slurry can be controlled by grinding and the like.

[0095] S2, after spray drying the slurry, sintering in a non-oxidizing atmosphere, and then performing jet milling, so that the Dv50 distribution of the milled positive electrode active material is 0.5-25 μm.

[0096] In some embodiments, the classification machine frequency of the jet milling is controlled to be 50-100 Hz and the frequency of the air blower is controlled to be 20-50 Hz, so that the Dv50 distribution of the milled positive electrode active material is 0.5-25 μm.

[0097] The preparation method controls the Dv50 particle size of the slurry and the classification machine frequency and the frequency of the air blower of the jet milling, so as to control the particle size and the particle size distribution of the secondary particles formed.

[0098] It can be understood that the precursor can be selected according to the type of the positive electrode active material. In some embodiments, the positive electrode active material is carbon-coated lithium iron phosphate, and the precursor can include iron phosphate, lithium carbonate, and a carbon source. Further, the carbon source can be at least one of glucose, sucrose, and polyethylene glycol.

[0099] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector.

[0100] For example, as the metal foil, an aluminum foil can be used. Alternatively, the thickness of the positive electrode current collector is 7-20 μm. For example, an aluminum foil with a thickness of 7-20 μm is used.

[0101] For example, 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 formed by forming a metal material on a polymer material base layer. Herein, the metal material includes, but is not limited to, at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like; and the polymer material base layer includes, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0102] In some embodiments, the mass ratio of the positive electrode active material in the positive electrode film layer is 85% to 100%. For example, the mass ratio of the positive electrode active material in the positive electrode film layer can be 85%, 90%, 92%, 94%, 96%, or 98%.

[0103] In some embodiments, the positive electrode film layer can optionally further include a binder. For example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a fluorine-containing acrylate resin, styrene butadiene rubber (SBR), a water-based acrylic resin, ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0104] In some embodiments, the positive electrode film layer can optionally further include a conductive agent. For example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the positive electrode tab can be prepared by preparing a positive electrode slurry containing the positive electrode active material described above; and coating the positive electrode slurry on a positive electrode current collector to form a positive electrode film layer.

[0106] In some embodiments, the positive electrode tab can be prepared by dispersing the components used to prepare the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, followed by drying, cold pressing, and the like to obtain the positive electrode tab.

[0107] In some embodiments, the thickness of the positive electrode film layer is 150 μm to 180 μm. For example, the thickness of the positive electrode film layer can be 150 μm, 160 μm, 170 μm, or 180 μm.

[0108] In some embodiments, the areal density of the positive electrode film layer is 0.1 mg / mm 2 ~ 0.3 mg / mm 2 .

[0109] In some embodiments, the compaction density of the positive electrode tab is 2.0 g / cm 3 ~ 2.7 g / cm 3 . For example, the compaction density of the positive electrode tab can be 2.0 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.6 g / cm 3 , or 2.7 g / cm 3 .

[0110] The compaction density of the positive electrode tab is a meaning known in the art, which can be tested by methods known in the art. The compaction density of the positive electrode tab refers to the ratio of the areal density of the tab to the coating thickness, and is one of the reference indicators of the energy density of the material. In other words, the compaction density of the positive electrode tab refers to the compaction density of the positive electrode film layer of the positive electrode tab.

[0111] For example, in this paper, the test method of the compaction density of the positive electrode tab includes the following steps: 1) according to the energy density design requirement, the areal density of the tab can be determined. 2) After the tab is dried and cold-pressed, the total thickness of the tab is measured using a vernier caliper, and the coating thickness can be calculated by deducting the thickness of the current collector. 3) According to the two parameters of the areal density and the coating thickness, the compaction density of the tab can be calculated.

[0112] Specifically, the positive electrode tab is cut into a film piece with a length of 1000 mm; the positive electrode tab is rolled by a certain pressure, and due to the ductility of the aluminum foil, the length of the film piece is 1006 mm, and a small round piece with a diameter of 1540.25 mm 2 is punched out. According to the areal density and the coating thickness of the small round piece, the compaction density of the positive electrode tab can be obtained. As shown in Figure 3 , it is the ion polishing cross-sectional morphology (CP map) of the positive active material in some embodiments of the present application, which refers to the standard GB / T 17359-2012. The ion polishing cross-sectional morphology shown in Figure 3 is identified by using Avizo2D software, and Figure 4 is obtained; according to the particle size distribution statistical diagram obtained from the identification map shown in Figure 4 , as shown in Figure 5 .

[0113] From Figure 5It can be seen that the particle size distribution of the positive active material in the positive electrode film layer, wherein the abscissa is the particle size size, the unit is nm, and the first column chart is taken as an example, the corresponding abscissa is [668.834, 3068.834], which represents the particle size size in the range of 668.834 nm to 3068.834 nm; the left side of the ordinate represents the number of particles with a particle size distribution in the range of [668.834, 3068.834], and the right side of the ordinate represents the percentage of the number of particles in the range of [668.834, 3068.834] to the total number of particles; the number on the column chart represents the number of particles with a particle size distribution in the range, and the curve represents the percentage curve of the number of particles in the corresponding particle size range from 668.834 nm to the point to the total number of particles. From the Figure 6 It can be seen from the CP chart of the positive active material that a total of 834 particles are counted, of which 735 particles have a particle size distribution in the range of (668.834 nm, 3068.834 nm), accounting for 88.13%, and 50 particles have a particle size distribution in the range of (3068.834 nm, 5468.834 nm), accounting for 6.0%. The total number of particles in the first two intervals accounts for 94.13% of the total number of particles, and the remaining particle distribution information is similar.

[0114] Negative electrode sheet

[0115] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative active material.

[0116] As an example, the negative electrode current collector has two opposite surfaces in the thickness direction thereof, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0117] 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 layer. The composite current collector can be formed by forming a metal material on a polymer material base layer. The metal material includes, but is not limited to, at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy; and the polymer material base layer includes, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0118] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0119] In some embodiments, the negative film layer can further optionally include a binder. The binder can be selected from at least one 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).

[0120] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0121] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent, for example, sodium carboxymethyl cellulose (CMC-Na), etc.

[0122] 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 such as deionized water, to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0123] Electrolyte

[0124] The electrolyte functions to conduct ions between the electrode sheet and the negative electrode sheet. The present application does not have a specific limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0125] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0127] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0128] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0129] Separator film

[0130] In some embodiments, a separator film is further included in the battery. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be used.

[0131] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0132] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0133] In some embodiments, the battery can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte.

[0134] In some embodiments, the outer package of the 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-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0135] The shape of the battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example,Figure 6 is a square structure secondary battery 1 as an example.

[0136] In some embodiments, referring to Figure 7 , the outer package can include a housing 11 and a cover plate 13. The housing 11 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 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can form an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and the person skilled in the art can select according to the specific actual needs.

[0137] In addition, the application also provides a power utilization device, which includes at least one of the secondary battery, the battery module or the battery pack provided by the application. The secondary battery, the battery module or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization 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. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; 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.

[0138] As the power utilization device, the secondary battery, the battery module or the battery pack can be selected according to the use requirements thereof.

[0139] Figure 8 is a power utilization device 2 as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0140] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc.

[0141] In order to make the purpose, technical scheme and advantages of the application more concise and clear, the application is described by the following specific embodiments, but the application is not limited to these embodiments. The embodiments described below are only better embodiments of the application, which can be used to describe the application, and should not be understood as limiting the scope of the application. It should be pointed out that any modification, equivalent replacement and improvement made within the spirit and principle of the application should be included in the protection scope of the application.

[0142] In order to better illustrate the application, the content of the application is further described below in combination with the embodiments. The following are specific embodiments.

[0143] Example 1

[0144] 1) Provide positive electrode active material powder LFP: specifically carbon-coated lithium iron phosphate, which contains a lithium iron phosphate core and a carbon coating layer covering its surface. The preparation method is as follows: using iron phosphate and lithium carbonate as raw materials, glucose and polyethylene glycol are added in a mass ratio of 7:3 as carbon sources, with the carbon source accounting for 17% of the total mass of the raw materials. The above iron phosphate:lithium carbonate:carbon source are mixed in a mass ratio of 3.85:1:1 and wet-milled with water as a solvent. The Dv50 of the slurry after milling is 300nm. The obtained slurry is spray-dried and then sintered in a roller furnace at 760℃ for 24h, with nitrogen gas introduced during the sintering process. Then, it is naturally cooled to a material temperature <80℃ and discharged to obtain calcined material. The calcined material is subjected to air-jet crushing, sieving, demagnetization, and vacuum packaging. The frequency of the air-jet crusher is controlled at 80Hz and the frequency of the induced draft fan is controlled at 40Hz to obtain lithium iron phosphate positive electrode material with secondary particle Dv50 of 4μm. The carbon coating layer accounts for 1.2% of the mass of carbon-coated lithium iron phosphate, and the surface morphology, particle size distribution and compaction density of the active material powder are measured.

[0145] a. Surface morphology test:

[0146] The positive electrode active material was tested using a ZEISS Sigma 300 scanning electron microscope, and then tested according to standard JY / T010-1996. The morphology of the sample was observed, and the scanning electron microscope images were obtained, as shown below. Figure 1 As shown in the figure, it contains both secondary and primary particles.

[0147] b. Particle size statistics of primary particles:

[0148] The morphology of primary particles was observed by selecting particles of the same size and shape from 10 regions within the same scanning electron microscope (SEM) image at 10kV and 30kV magnification. Each of these 10 regions was further subdivided into five positions: the four corners and the center. The Feret diameter of any primary particle at each position was selected at this magnification, and the average of the Feret diameters from the five positions (corners and center) was taken to obtain the particle diameter for that region. This average of the particle diameters from all 10 regions was then taken to obtain the final primary particle diameter. Specifically, the Feret diameter of the particle was defined as the average of four dimensions: the dimension along the direction of the two adjacent sides of the rectangle circumscribed in the image, and the dimension along the direction of the 45-degree inclination of the two adjacent sides of the rectangle circumscribed in the image.

[0149] c. Volume average particle size Dv50 test of positive electrode active material:

[0150] Determination was made using a Malvern 3000 (MasterSizer 3000) laser particle size analyzer, referring to the standard procedure: GB / T19077-2016 / ISO 13320:2009. The specific test procedure is as follows: take an appropriate amount of sample to be tested, and the sample concentration is guaranteed to be 8%~12% optical density, add 20 mL of deionized water, and simultaneously externally ultrasonic for 5 min, ultrasonic frequency 53 KHz, ultrasonic power 120 W, to ensure that the sample is completely dispersed, and then the sample is determined according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0151] d, particle size distribution and statistics of secondary particles:

[0152] The IB-19500CP ion polisher is used to analyze the cross-section micro-morphology of the active material powder according to the standard GB / T 17359-2012, and the Avizo2D software is used to analyze the graphics, and the secondary particle size and distribution are counted, as shown in Figure 3

[0153] e, powder compaction density:

[0154] A certain amount of powder is used on a compaction special mold with a known diameter, and a metal sheet is placed on the upper and lower molds, and the powder is placed between the two metal sheets. By applying a pressure of 3t and simultaneously testing the corresponding powder thickness, the corresponding powder volume at this time is obtained. The formula ρ=m / v is used to calculate the compaction density ρ. The specific operation can refer to the standard: GB / T24533-2009.

[0155] The average particle size of the primary particles is 300 nm. The volume average particle size Dv50 of the secondary particles is 4 μm, wherein the proportion of the secondary particles with a particle size of 3 μm or more is X=11%, the proportion of the secondary particles with a particle size of 5 μm or more is Y=6%, and the powder compaction density is 2.55 g / cm 3 .

[0156] f, carbon content analysis

[0157] A certain amount of sample is heated at high temperature under oxygen-rich conditions to burn completely, so that carbon is oxidized to carbon dioxide, and the generated gas is introduced into the corresponding absorption cell for absorption. The corresponding infrared radiation is reabsorbed, and then converted into a corresponding signal by a detector. The signal is sampled and converted into a value positively related to the concentration of carbon dioxide by a computer. After processing, the percentage of carbon in the sample can be obtained, and the mass content of the carbon coating layer can be obtained.

[0158] 2) Preparation of positive electrode sheet

[0159] ​The positive active material powder LFP, the adhesive polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a mass ratio of 97.3:2:0.7, an appropriate amount of N-methyl pyrrolidone (NMP) solvent is added, and the mixture is stirred thoroughly to form a uniform positive electrode slurry with a viscosity of 3000 mPa·s at room temperature.

[0160] The positive electrode slurry is coated on a 13-μm-thick aluminum foil, followed by drying to form an active material layer with a coating density of 350 mg / 1540.25 cm 2 After coating, the positive electrode sheet is prepared by drying, cold pressing, and slitting, and the compaction density of the film is calculated and tested.

[0161] f. Compaction density of the electrode sheet:

[0162] The electrode sheet is cut into a film with a length of 1000 mm, and the positive electrode sheet is rolled under a certain pressure. Since the aluminum foil is ductile, the film length is 1006 mm, and a small disc with a diameter of 1540.25 mm 2 is punched out. The coating thickness is obtained by measuring the thickness of the small disc after removing the electrode sheet. According to the coating density and the coating thickness of the small disc, the compaction density can be obtained.

[0163] 3) Preparation of the negative electrode sheet

[0164] The negative active material graphite, the thickening agent sodium carboxymethyl cellulose, the adhesive styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum stirrer. The negative electrode slurry is uniformly coated on a copper foil with a thickness of 8 μm. Subsequently, drying, cold pressing, and slitting are performed to obtain the negative electrode sheet.

[0165] 4) Preparation of the electrolyte

[0166] Vinyl carbonate, methyl ethyl carbonate, and diethyl carbonate are configured into a mixed solution in a volume ratio of 20:20:60, and then a fully dried lithium salt is dissolved in the mixed solution. Then, 10 wt% of fluoroethylene carbonate additive is added and mixed uniformly to obtain an electrolyte. The concentration of the lithium salt is 1 mol / L. The entire operation process is carried out in an argon glove box with a water content of <10 ppm.

[0167] 5) Separating film

[0168] A polyethylene film with a thickness of 12 μm is used as the separating film.

[0169] 6) Preparation of the battery

[0170] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is positioned in the middle of the positive and negative electrodes to play a role of separation, and a bare battery cell is obtained by winding. The bare battery cell is placed in an outer package, electrolyte solution prepared in advance is injected, and processes such as sealing, liquid injection, formation, and degassing are performed to obtain a lithium ion battery.

[0171] Example 2

[0172] The example 1 is basically the same, the difference is only in adjusting the wet grinding slurry Dv50 of the positive active material to about 500 nm, and adjusting the classifier frequency and the frequency of the air blower of the jet mill to make the Dv50 of the powder after jet milling to be 6 μm, the average particle size of the primary particles of the obtained positive active material is 500 nm, the Dv50 of the secondary particles is 6 μm, and the powder compaction density is 2.6 g / cm 3 .

[0173] Example 3

[0174] The example 1 is basically the same, the difference is only in adjusting the wet grinding slurry Dv50 of the positive active material to about 200 nm, and adjusting the classifier frequency and the frequency of the air blower of the jet mill to make the Dv50 of the powder after jet milling to be 2 μm, the average particle size of the primary particles of the obtained positive active material is 200 nm, the Dv50 of the secondary particles is 2 μm, and the powder compaction density is 2.48 g / cm 3 .

[0175] Example 4

[0176] The example 1 is basically the same, the difference is only in adjusting the wet grinding slurry Dv50 of the positive active material to about 300 nm, and adjusting the classifier frequency and the frequency of the air blower of the jet mill to make the Dv50 of the powder after jet milling to be 2 μm, the average particle size of the primary particles of the obtained positive active material is 300 nm, the Dv50 of the secondary particles is 2 μm, and the powder compaction density is 2.52 g / cm 3 .

[0177] Examples 5-15

[0178] The example 1 is basically the same, the difference is only in adjusting the wet grinding slurry Dv50 of the positive active material to about 300 nm, and adjusting the classifier frequency and the frequency of the air blower of the jet mill to make the Dv50 of the powder after jet milling to be 2 μm, the average particle size of the primary particles of the obtained positive active material is 300 nm, the Dv50 of the secondary particles is 2 μm, and the powder compaction density is 2.52 g / cm

[0179] Example 16

[0180] The same as Example 1, except that manganese source manganese dioxide is used to replace 50% of the amount of substance of the iron source (iron phosphate), and the remaining preparation conditions are the same as those of Example 1, to prepare lithium manganese iron phosphate.

[0181] Comparative Example 1

[0182] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has an average particle size of primary particles of 150 nm, a Dv50 of secondary particles of 1 μm, and a powder compaction density of 2.1 g / cm 3 .

[0183] Comparative Example 2

[0184] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has an average particle size of primary particles of 3.5 μm, a Dv50 of secondary particles of 7 μm, and a powder compaction density of 2.5 g / cm 3 .

[0185] Comparative Example 3

[0186] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has an average particle size of primary particles of 2 μm, a Dv50 of secondary particles of 27 μm, and a powder compaction density of 2.3 g / cm 3 .

[0187] Comparative Example 4

[0188] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has a ratio X of secondary particles with a particle size of 3 μm or more of 9%.

[0189] Comparative Example 5

[0190] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has a ratio Y of secondary particles with a particle size of 5 μm or more of 3%.

[0191] Comparative Example 6

[0192] The difference from Example 1 is only that the preparation parameters of the positive electrode active material are adjusted, and the obtained positive electrode active material has a ratio X of secondary particles with a particle size of 3 μm or more of 9%, and a ratio Y of secondary particles with a particle size of 5 μm or more of 3%.

[0193] The following is the performance test of the battery of each example and comparative example

[0194] (I) Energy density test

[0195] Charged at 0.33C to 3.65V at 25℃, constant voltage charged to 3.65V at 0.05C, rested for 10 min, discharged at 0.33C to 2.5V, record the discharge capacity, then calculate the energy density at discharge.

[0196] Energy density (Wh / L) = Discharge capacity (Wh) / Lithium ion secondary battery mass (kg).

[0197] (ii) Cycle life test

[0198] Before the start of the cycle, the capacity and power need to be tested as the initial cycle capacity value and power value of the cell, the process is as follows: 1) the battery is rested for 120 min at 25℃; 2) the battery is discharged to 2.5V at 0.5P; 3) the battery is discharged to 2.0V at 0.1P; 4) the battery is rested for 30 min at 25℃; 5) 0.5C constant current charged to 3.8V; 6) 0.04C constant current charged to 3.8V; 7) the battery is rested for 30 min at 25℃; 8) 0.5C cross current discharged to 2.5V, and the discharge power of this step is recorded as P; 9) 0.04C constant current discharged to 2.0V, and the capacity of steps 8, 9 is recorded as the initial discharge capacity C of the cycle; 10) the battery is rested for 30 min at 25℃.

[0199] The cycle test process is as follows: 1) the battery is rested for 120 min at 25℃; 2) the battery is discharged to 2.5V at 0.5P; 3) the battery is rested for 30 min at 25℃; 4) the battery is charged to 3.8V at 0.5P constant power; 5) rested for 1 min at 25℃; 6) charged to 3.8V at 0.05P constant power; 7) the battery is rested for 30 min at 25℃; 8) the battery is discharged to 2.5V at 0.5P; 9) the battery is rested for 5 min at 25℃; 10) steps 4)~8) above are one charge-discharge cycle of the battery, which is constantly repeated until the battery capacity decays to 80% of the initial value, and the cycle number at this time is recorded, which is the cycle life, unit: cls, as shown in Table 1.

[0200] Cycle capacity retention rate at the n th cycle = (discharge capacity at the n th cycle / initial discharge capacity of the cycle) x 100%.

[0201] Cycle capacity retention rate at the 300 th cycle; cycle capacity retention rate at the 300 th cycle = (discharge capacity at the 300 th cycle / initial discharge capacity of the cycle) x 100%.

[0202] Cycle climbing degree:

[0203] The cycle number at which the capacity retention rate is continuously higher than 100% in the first 3000 cycles is recorded. If the cycle number at which the capacity retention rate is continuously higher than 100% is ≥ 10, it is determined that the cycle process has a cycle climbing degree, and the maximum capacity retention rate when the capacity retention rate is higher than 100% in the cycle process is recorded. If the cycle number at which the capacity retention rate is continuously higher than 100% is < 10, it is determined that the cycle process does not have a cycle climbing degree, and is recorded as “-” in Table 1.

[0204] Table 1

[0205]

[0206]

[0207] In Table 1,

[0208] X: the proportion of secondary particles with a size of 3 μm or more;

[0209] Y: the proportion of secondary particles with a size of 5 μm or more.

[0210] From Table 1 above,

[0211] The average particle size of the primary particles of the positive electrode active material of Comparative Example 1 is relatively small, the powder compaction density is relatively low, the capacity retention rate in the early and middle stages decays relatively fast, the capacity retention rate in the 300th cycle is relatively low, and no capacity retention rate climbing phenomenon occurs in the entire cycle process.

[0212] The average particle size of the primary particles of the positive electrode active material of Comparative Example 2 is relatively large, the powder compaction density is improved, and the corresponding cycle retention rate is improved compared with Comparative Example 1, and no cycle climbing phenomenon occurs.

[0213] The Dv50 particle size of the secondary particles of the positive electrode active material of Comparative Example 3 is too large, and the powder compaction density is also relatively low, the cycle capacity retention rate is relatively low, and the capacity decay degree is relatively high.

[0214] The particle size distribution X and Y of the positive electrode active materials in Comparative Examples 4-6 are not within the appropriate parameters, and no cycle climbing phenomenon occurs in the first 3000 cycles.

[0215] Each of Examples 1-16 of the positive electrode active material of the present application is used, the Dv50 particle size and the particle size distribution of the secondary particles of the positive electrode active material are adjusted, and the positive electrode active material is used as the positive electrode active material of a lithium ion battery. The positive electrode for preparing a lithium ion battery is coated according to the coating weight requirement, and the obtained battery sample has a long cycle life, a good cycle capacity retention rate, and a cycle climbing performance.

[0216] It can be seen from the comparison of Example 3 and Examples 5-7 that, when the average particle size of the primary particles is equivalent, the Dv50 of the secondary particles in Example 3 and Example 6 is within 1-15 μm, and the cycle life, cycle capacity retention rate and cycle climbing performance are more excellent.

[0217] It can be seen from the comparison of Example 6 and Examples 8-9 that, when the Dv50 of the secondary particles is equivalent, the average particle size of the primary particles in Example 6 and Examples 8-9 is 210 nm, 1 μm and 2 μm respectively, and it can be seen that the average particle size of the primary particles in Example 6 and Example 8 is within 0.2-1 μm, and the cycle life, cycle capacity retention rate and cycle climbing performance are more excellent.

[0218] It can be seen from the comparison of Example 1, 10, 12, 14-15 that, when the Dv50 of the secondary particles and the average particle size of the primary particles are equivalent, compared with Example 12, 30% ≥ X ≥ 10% in Example 1, 10, 14-15, and the cycle life, cycle capacity retention rate and cycle climbing performance are more excellent. Among them, both Example 10 and Example 15 meet Y is the same, and 30% ≥ X ≥ 10%, but X-Y = 0 in Example 10, and it can be seen that the cycle climbing performance of Example 10 is slightly inferior to that of Example 15.

[0219] It can be seen from the comparison of Example 1 and Example 16 that the positive electrode active materials formed by different lithium-containing phosphates in the application all have good cycle capacity retention rate and cycle climbing performance. Compared with lithium manganese iron phosphate, the cycle capacity retention rate and cycle climbing performance of lithium iron phosphate are more excellent.

[0220] The technical features of the above-described embodiments can be combined arbitrarily, and in order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, it should be considered as the scope of the description.

[0221] The above-described embodiments only express several implementation manners of the application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are all within the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material comprises lithium phosphate in its composition and secondary particles in its morphology, wherein the volume average particle size Dv50 of the secondary particles is 0.5 μm to 25 μm; the primary particles forming the secondary particles have an average particle size of 0.2 μm to 2 μm; in the positive electrode active material, the proportion of particles with a particle size distribution of 3 μm or more is X≥10%, and the proportion of particles with a particle size distribution of 5 μm or more is Y≥5%.

2. The positive electrode active material as described in claim 1, characterized in that, The positive electrode active material also includes primary particles that are mixed with the secondary particles and have an average particle size of 0.2 μm to 2 μm.

3. The positive electrode active material as described in claim 2, characterized in that, The average particle size of the primary particles mixed with the secondary particles is 0.2 μm to 1 μm.

4. The positive electrode active material as described in claim 2, characterized in that, The primary particles mixed with the secondary particles are spherical or near-spherical in shape.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The positive electrode active material satisfies at least one of the following conditions (1-1) to (1-2): (1-1) The primary particles that form the secondary particles have an average particle size of 0.2 μm to 1 μm; (1-2) The primary particles that form the secondary particles are spherical or near-spherical in shape.

6. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The positive electrode active material satisfies at least one of the following conditions (2-1) to (2-5): （2-1）、100%＞X≥10%； （2-2）、100%＞Y≥5%； (2-3) 95% ≥ XY ≥ 0; (2-4) The volume average particle size Dv50 of the secondary particles is 1μm~15μm; (2-5) The secondary particles are spherical or near-spherical in shape.

7. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The positive electrode active material satisfies at least one of the following conditions: （1）30%≥X≥10%； （2）10%≥Y≥5%； (3) 25% ≥ XY ≥ 0.

8. The positive electrode active material according to any one of claims 1 to 4, characterized in that, The positive electrode active material satisfies at least one of the following conditions (3-1) to (3-2): (3-1) The positive electrode active material also includes carbon material in its composition, and the carbon material is composited with the lithium phosphate; (3-2) The lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate and lithium vanadium phosphate.

9. The positive electrode active material as described in claim 8, characterized in that, The positive electrode active material includes a core and a coating layer formed on the surface of the core. The core includes the lithium phosphate, and the coating layer includes a carbon material.

10. The positive electrode active material as described in claim 9, characterized in that, The coating layer accounts for 0.9% to 2.5% of the total mass of the positive electrode active material.

11. The positive electrode active material according to any one of claims 1 to 4, 9 to 10, characterized in that, The compacted density of the positive electrode active material under a pressure of 3t is 2.25~2.65 g / cm³. 3 .

12. A positive electrode plate, characterized in that, include: Positive current collector; and A positive electrode film layer is disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material as described in any one of claims 1 to 11.

13. The positive electrode sheet as described in claim 12, characterized in that, The positive electrode sheet satisfies at least one of the following conditions (4-1) to (4-4): (4-1) The thickness of the positive electrode film is 150μm~180μm; (4-2) The surface density of the positive electrode film is 0.1 mg / mm². 2 ~0.3mg / mm 2 ; (4-3) The compaction density of the positive electrode film is 2.0 g / cm³. 3 ~2.7g / cm 3 ; (4-4) In the positive electrode film layer, the mass percentage of the positive electrode active material is 85%~100%.

14. The positive electrode sheet as described in claim 12 or 13, characterized in that, The positive electrode sheet satisfies at least one of the following conditions (5-1) to (5-2): (5-1) The positive current collector is aluminum foil; (5-2) The thickness of the positive current collector is 7μm~20μm.

15. A battery, characterized in that, It includes the positive electrode sheet as described in any one of claims 12 to 14.

16. An electrical appliance, characterized in that, Includes the battery as described in claim 15.

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