Battery cell, battery device, electric device, and positive electrode active material

Abstract

The present application discloses a battery cell, a battery device, an electric device, and a positive electrode active material. The battery cell comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer bonded to at least one surface of the positive electrode current collector; the positive electrode film layer comprises a positive electrode active material; and the positive electrode active material comprises a lithium-containing phosphate material, wherein based on the total number of primary particles of the lithium-containing phosphate material being 100%, the proportion of the number of primary particles having a primary particle size greater than 0.8 µm is greater than or equal to 7%. In the battery cell provided in the present application, the positive electrode active material having a primary particle size greater than 0.8 µm generates stress due to a volume change, and the stress causes particles of the positive electrode active material to gradually form cracks, thereby forming more pathways through which lithium ions can pass, effectively shortening transport pathways of lithium ions, exerting a sustained-release effect, and thus effectively improving the cycle capacity of batteries.

Description

A battery cell, a battery device, an electrical device, and a positive electrode active material.

[0001] This application claims priority to Chinese Patent Application No. 202510111797.0, filed on January 23, 2025, with the Chinese Patent Office, entitled "A Battery Cell, Battery Device, Electrical Device and Positive Electrode Active Material", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a battery cell, a battery device, an electrical device, and a positive electrode active material. Background Technology

[0003] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0004] Currently, judging from market trends, the application scope of lithium-ion batteries is becoming increasingly widespread. Lithium-ion batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as power tools, electric bicycles, electric motorcycles, and electric cars. In these application scenarios, the performance of lithium-ion batteries is directly related to the operating efficiency and lifespan of the related equipment; therefore, higher requirements are placed on the cycle performance of lithium-ion batteries.

[0005] Application content

[0006] The purpose of this application is to provide a battery cell, a battery device, an electrical device, and a positive electrode active material, including but not limited to solving the problem of unsatisfactory battery cycle performance.

[0007] The technical solution adopted in the embodiments of this application is:

[0008] In a first aspect, a battery cell is provided, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer bonded to at least one surface of the positive current collector, the positive electrode film layer containing a positive electrode active material; the positive electrode active material includes a lithium phosphate material, wherein, based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%.

[0009] The battery cell provided in this application uses a composite of particles with different primary particle sizes to form the positive electrode active material. Specifically, the proportion of primary particles with a primary particle size greater than 0.8 μm is controlled to be greater than or equal to 7%. During battery cycling, due to the repeated insertion and extraction of lithium ions, the positive electrode active material with a primary particle size greater than 0.8 μm experiences stress due to volume changes. This stress causes the positive electrode active material particles to gradually crack, and the grain boundaries separate, thus forming more pathways for lithium ions to pass through and effectively shortening the lithium ion transport path. In this way, more lithium ions can participate in the reaction during battery cycling, allowing lithium ions to be inserted and extracted more uniformly and quickly within the particles. Therefore, by combining primary particles with a primary particle size greater than 0.8 μm and primary particles with a primary particle size less than or equal to 0.8 μm in the aforementioned proportion, lithium ions in the positive electrode active material can be inserted and extracted at a faster rate. In this way, the positive electrode active material can effectively exert a slow-release effect, thereby significantly improving the cycle capacity of the battery.

[0010] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is 7%-30%.

[0011] By controlling the proportion of primary particles with a primary particle size greater than 0.8 μm in the positive electrode active material within the above range, the particles with a primary particle size greater than 0.80 μm can fully exert their slow-release performance, thereby improving the cycle performance of the battery.

[0012] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; and the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%.

[0013] By controlling the primary particle size range and the proportion of primary particles in the positive electrode active material within the above range, positive electrode active material particles with a primary particle size greater than 0.8 μm can fully exert their slow-release effect, while positive electrode active material particles with a primary particle size less than or equal to 0.8 μm can effectively improve the battery capacity. The synergistic effect of the two results in the battery exhibiting high cycle performance.

[0014] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%.

[0015] By controlling the content of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm, and primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm within the above range, the positive electrode active material not only has an appropriate initial capacity, but also can generate cracks or even break due to stress due to its larger particle size. This allows it to fully exert its capacity release effect during cycling, effectively slowing down capacity decay. In this way, the battery can still maintain a high capacity output after multiple cycles, extending the battery's cycle life.

[0016] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-12%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-5%.

[0017] By adjusting the proportion of primary particles with a particle size greater than 0.8 μm and less than or equal to 1.2 μm and greater than 1.2 μm and less than or equal to 2.5 μm, and maintaining their content within the aforementioned range, the positive electrode active material is endowed with an appropriate initial capacity. It can also fully exert its capacity-releasing function during cycling, thereby effectively improving the cycle capacity of the battery.

[0018] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; and the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%.

[0019] By controlling the primary particle size range and the proportion of primary particles in the positive electrode active material within the above range, multi-level lithium-ion diffusion channels can be constructed, enabling lithium ions to be rapidly inserted and extracted in these positive electrode active materials, thereby effectively improving the overall efficiency of lithium-ion diffusion. As a result, the battery can still maintain a high capacity retention rate after multiple cycles.

[0020] In some embodiments, taking the total number of primary particles of lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%.

[0021] By combining positive electrode active materials with different primary particle sizes in a certain proportion, it is possible to achieve high capacity by utilizing positive electrode active materials with smaller primary particle sizes, and to rely on positive electrode active materials with larger primary particle sizes to play a gradual release role. This multi-combination synergistically improves the cycle performance of the battery.

[0022] In some embodiments, the volumetric particle size distribution curve of the positive electrode active material is a single-peak curve.

[0023] The positive electrode active material includes secondary particles, which are composed of multiple primary particles. The particle size distribution curve is mainly used to characterize the particle size distribution of the secondary particles. A single peak in the particle size distribution curve of the positive electrode active material indicates that the diffusion path of lithium ions in the positive electrode material is relatively uniform and stable. This can improve the diffusion efficiency of lithium ions in the positive electrode material, reduce local concentration polarization, and thus enable lithium ions to quickly insert and extract during charging and discharging, improving the rate performance of the battery.

[0024] In some embodiments, the molecular formula of the lithium phosphate material is Li a Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in,

[0025] M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr;

[0026] Q includes at least one element selected from B, S, Si, and N;

[0027] R includes one or more elements selected from S, F, Cl, and Br;

[0028] Q and R are not both elements of S;

[0029] 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1.

[0030] Examples of lithium phosphate-containing materials include, but are not limited to, LiFePO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, LiMnPO4, and LiMn. 0.2 Fe 0.8 PO4 and LiFe 0.5 Mn 0.5 One or more of PO4.

[0031] In some embodiments, after compaction under a pressure of 3T, the compacted density of the positive electrode active material powder is 2.4-2.6 g / cm³.3 Within this range, it means that more positive electrode active material can be accommodated in the same volume of positive electrode sheet, thereby increasing the energy density of the battery.

[0032] In some embodiments, the specific surface area of ​​the positive electrode active material is 9-13 m². 2 / g. Within this range, it means that the positive electrode active material has an appropriate number of active sites, which can provide more channels and sites for the adsorption and desorption of lithium ions, thereby accelerating the transport speed of lithium ions and improving the rate performance of the battery.

[0033] In some embodiments, the compaction density of the positive electrode sheet is 2.5-2.7 g / cm³. 3 Within this range, it means that more active material can be accommodated per unit volume of the positive electrode, which helps to improve the energy density of the battery.

[0034] In some embodiments, the porosity of the positive electrode is 15%-30%. Within this range, the electrolyte can fully wet the positive electrode, promoting smoother transport of lithium ions between the electrolyte and the positive electrode active material.

[0035] Secondly, a battery device is provided, comprising a plurality of battery cells according to the above embodiments.

[0036] Thirdly, an electrical device is provided, comprising a plurality of battery cells or battery devices according to the above embodiments.

[0037] Fourthly, this application provides a positive electrode active material, which includes a lithium phosphate material, wherein, based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%.

[0038] The positive electrode active material of this application is composed of a composite of particles with different primary particle sizes, and the proportion of primary particles with a primary particle size greater than 0.8 μm is controlled within the above-mentioned range. During battery cycling, due to the repeated insertion and extraction of lithium ions, the positive electrode active material with a primary particle size greater than 0.8 μm generates stress due to volume changes. This stress causes the positive electrode active material particles to gradually crack and form cracks, and the grain boundaries are separated, thereby forming more pathways for lithium ions to pass through and effectively shortening the lithium ion transport path. In this way, more lithium ions can participate in the reaction during battery cycling, allowing lithium ions to be inserted and extracted more uniformly and quickly inside the particles. Thus, the positive electrode active material can effectively exert a slow-release effect, thereby significantly improving the cycle capacity of the battery.

[0039] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; and the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%.

[0040] By controlling the primary particle size range and the proportion of primary particles in the positive electrode active material within the above range, positive electrode active material particles with a primary particle size greater than 0.8 μm can fully exert their slow-release effect, while positive electrode active material particles with a primary particle size less than or equal to 0.8 μm can effectively improve the battery capacity. The synergistic effect of the two results in the battery exhibiting high cycle performance.

[0041] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%.

[0042] By controlling the content of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm, and primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm within the above range, the positive electrode active material not only has an appropriate initial capacity, but also can generate cracks or even break due to stress due to its larger particle size. This allows it to fully exert its capacity release effect during cycling, effectively slowing down capacity decay. In this way, the battery can still maintain a high capacity output after multiple cycles, extending the battery's cycle life.

[0043] In some embodiments, taking the total number of primary particles of lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%.

[0044] By combining positive electrode active materials with different primary particle sizes in a certain proportion, it is possible to achieve high capacity by utilizing positive electrode active materials with smaller primary particle sizes, and to rely on positive electrode active materials with larger primary particle sizes to play a gradual release role. This multi-combination synergistically improves the cycle performance of the battery.

[0045] In some embodiments, the molecular formula of the lithium phosphate material is Li aFe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in,

[0046] M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr;

[0047] Q includes at least one element selected from B, S, Si, and N;

[0048] R includes one or more elements from S, F, Cl, and Br; Q is not simultaneously an element S with R;

[0049] 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or exemplary technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 is an exploded view of the battery device provided in an embodiment of this application;

[0052] Figure 2 is an exploded view of a single battery cell provided in an embodiment of this application;

[0053] Figure 3 is a schematic diagram of one embodiment of an electrical device that uses a battery cell as a power source according to an embodiment of this application.

[0054] Figure 4 is a cycle test diagram of the battery cells provided in Example 1 and Comparative Example 1.

[0055] In the figure, the following reference numerals are used: 100, battery device; 10, housing; 11, first housing; 12, second housing; 20, battery cell assembly; 30, battery cell; 31, casing; 32, electrode assembly; 33, cover plate. Detailed Implementation

[0056] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0058] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0060] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0061] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0063] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0064] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0065] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0066] In the embodiments of this application, SEI film is short for "solid electrolyte interface", which refers to a solid electrolyte interface film with the characteristics of a solid electrolyte. That is, during the first charge and discharge process of a liquid lithium-ion battery, a passivation layer formed by the reaction between the electrode material and the electrolyte at the solid-liquid interface is formed and covers the surface of the negative electrode material.

[0067] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0068] In this application, a primary particle refers to the smallest unit of a particle within a certain observation range. A primary particle may contain defects of any form, but it is impossible to further define smaller particles within a primary particle. Primary particles may aggregate under physical forces such as van der Waals forces, but such aggregation is easily deaggregated under external forces such as ultrasound, stirring, and rolling, so that the main constituent morphology of the active material in the film layer is still primary particles.

[0069] In this application, the secondary particles are formed by the agglomeration of primary particles. The agglomeration here is a hard agglomeration caused by the chemical bonding of primary particles, which makes the secondary particles have a clear surface and boundary and are not easy to disperse under external forces such as ultrasound. However, after cutting the cross-section of the secondary particles, it can be seen that the secondary particles are formed by the agglomeration of many primary particles.

[0070] In this article, the term "primary particle size" refers to the particle size of a primary particle.

[0071] Secondary particles and primary particles are identical in composition, differing mainly in morphology. It should be noted that "secondary particles" has a commonly known meaning in the art. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles. As an example, the morphology of positive electrode active materials can be obtained by testing with a scanning electron microscope such as the ZEISS Sigma 300. Specifically, the morphology of positive electrode active materials can be observed by referring to standard JY / T010-1996.

[0072] In this paper, the primary particle size of the primary particles of the positive electrode active material in the positive electrode sheet of a battery cell can be determined using the following method:

[0073] The battery was disassembled to obtain the positive electrode sheet. The positive electrode film layer of the positive electrode sheet was peeled off, and the positive electrode film layer was thoroughly washed with acetone, filtered, and dried to obtain powder. An appropriate amount of powder was subjected to scanning electron microscopy (SEM) testing to obtain an SEM image. Understandably, the positive electrode active material of the positive electrode sheet in this application can be one or more of primary and secondary particles.

[0074] The statistical analysis of the particle size and quantity ratio of primary particles in the positive electrode active material can be performed as follows. As an example, disassemble the battery to obtain the positive electrode sheet. Peel off the positive electrode film layer, thoroughly wash the film layer with acetone, filter, and dry to obtain powder. Dissolve 0.05g of the uniformly mixed powder in 40mL of anhydrous ethanol, then add an appropriate amount of dispersant and stir until a suspension is obtained. Mix 2mL of the suspension with 2mL of anhydrous ethanol and sonicate at a power of 480W for 5 minutes to obtain a uniformly dispersed suspension. Take an appropriate amount of the middle layer suspension for transmission electron microscopy (TEM) testing to obtain TEM images. Select 5-10 TEM images containing 50 to 100 particles as sampling areas, ensuring at least 500 particles are tested. Then, using Avizo 3D software image processing software, the projected area of ​​each primary particle in each sampling area can be statistically calculated, which is the cross-sectional area S of the primary particle. During primary particle identification, for particles with obvious adhesion, a combination of manual and software identification can be used to determine whether the particle is a single primary particle or two secondary particles. The equivalent circle diameter of the primary particle is obtained using the equivalent circle method, which is the primary particle diameter d. In the above statistical process of primary particles and their primary particle diameters, primary particles with a primary particle diameter less than 50 nm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50 nm are considered valid particles).

[0075] In this article, the compaction density of the positive electrode sheet refers to the mass contained per unit volume, which is usually calculated by dividing the areal density by the thickness of the material, and the unit is g / cm³. 3 The following methods can be used for testing:

[0076] For online testing, the thickness of the positive electrode sheet is measured online using laser or X-ray (this thickness does not include the thickness of the positive current collector). In this case, the compaction density of the positive electrode sheet is the areal density of the positive electrode sheet divided by the thickness of the positive electrode sheet. For offline testing, the thickness of the positive electrode sheet is measured using a micrometer or ten-thousand-meter (this thickness does not include the thickness of the positive current collector). In this case, the compaction density of the positive electrode sheet is the areal density of the positive electrode sheet divided by the thickness of the positive electrode sheet.

[0077] In this paper, porosity refers to the ratio of the volume of pores in the positive electrode to the total volume of the positive electrode, usually expressed as a percentage. It can be tested using the mercury intrusion porosimetry method. Specifically, mercury does not wet solids, and external pressure must be applied to allow mercury to enter the pores. The greater the external pressure, the smaller the radius of the pore that mercury can enter. By measuring the amount of mercury entering the pores under different external pressures, the pore volume of the corresponding pore size can be determined.

[0078] In this paper, specific surface area refers to the total surface area per unit mass of a substance. It can be determined using instruments and methods known in the art, based on principles such as low-temperature nitrogen adsorption and / or static volumetric methods. For example, the specific surface area of ​​solid substances can be determined using the gas adsorption BET method (GB / T+19587-2004), conveniently measured using a pore size analyzer. As an example, a JW-BK122F analyzer is used for testing.

[0079] In this paper, the particle size distribution curve of the positive electrode active material can be determined using a laser particle size analyzer in accordance with GB / T 19077-2016. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0080] In this paper, powder compaction density refers to the compaction density of the positive electrode active material after compaction under a pressure of 3T. This compaction density can be measured by any known method. As an example, referring to GB / T 24533-2009 Powder Compaction Density Method: A certain amount of powder is placed in a special compaction mold, and then the mold is placed on a compaction density instrument. The pressure is set to 3T. After compaction, the pressure is released, and the thickness of the compacted powder in the mold is read on the instrument. The result is calculated using the following formula (I): pC=m / V=m / (S*H)

[0081] In the formula: pC - compacted density of the powder, in g / cm³ 3 m - Sample mass, in g; S - Mold bottom area, in cm² 2 H - Compacted thickness, in cm.

[0082] With the continued strength of the new energy vehicle market, the demand for power batteries is growing, and people are placing higher demands on the lifespan of new energy vehicles. This demand translates into requirements for battery cycle performance.

[0083] Lithium iron phosphate (LFP) batteries dominate the current power battery field due to their advantages such as high safety, excellent high-temperature performance, no memory effect, and wide availability, low price, and no environmental pollution. However, LFP batteries experience significant degradation in the early stages of cycling, drastically reducing the effective number of cycles and severely weakening the overall cycle performance. Furthermore, this early degradation can cause imbalances in the battery's internal structure and reactions, further accelerating capacity decay in subsequent cycles and greatly hindering its cycle performance.

[0084] Typically, lithium iron phosphate (LFP) is modified by doping to improve its conductivity, reduce internal resistance, and thus increase energy density. Furthermore, appropriate low-concentration doping does not disrupt the olivine structure of LFP, maintaining its high stability and improving cycle performance. However, doping offers limited improvement in cycle performance and is not suitable for current LFP operating conditions.

[0085] Based on this, the first aspect of the present application provides a battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer bonded to at least one surface of the positive current collector, the positive electrode film layer containing a positive electrode active material, the positive electrode active material including a lithium phosphate material; wherein, based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%.

[0086] During battery cycling, the repeated insertion and extraction of lithium ions causes stress in the positive electrode active material with a primary particle size greater than 0.8 μm due to volume changes. This stress causes the positive electrode active material particles to gradually crack, and the grain boundaries separate. This effectively shortens the lithium ion transport path. Moreover, the formation of cracks and the separation of grain boundaries create more pathways for lithium ions to pass through within the positive electrode active material. This change allows more lithium ions to continuously participate in the reaction, meaning that more lithium ions can be inserted and extracted more uniformly and rapidly within the positive electrode active material particles. In this way, the positive electrode active material can effectively exert a slow-release effect, thereby effectively improving the battery's cycle capacity. Furthermore, in subsequent cycles, the cracked particles become more stable due to the release of stress to a certain extent, reducing the impact of stress on the positive electrode active material and further reducing the occurrence of adverse phenomena such as particle pulverization, thus extending the battery's cycle life.

[0087] Controlling the proportion of primary particles with a diameter greater than 0.8 μm to be greater than or equal to 7% means that there are enough primary particles in the positive electrode active material to play a role in capacity slow release. Thus, during cycling, the capacity increase generated by these particles through their capacity slow release will exceed the capacity loss due to thermodynamic losses in the positive electrode active material. Therefore, in the initial stage of cycling, the capacity of the positive electrode active material not only does not decrease but also shows a capacity increase trend. This additional capacity increase provides more buffer space for capacity decay in subsequent cycles. In particular, with a larger capacity base, even if capacity decay occurs later, a high residual capacity can still be maintained after multiple cycles, thereby effectively improving the battery's cycle capacity retention rate and extending battery life.

[0088] Therefore, this application controls the number of particles with a primary diameter greater than 0.8 μm within a suitable range, so that the positive electrode active material can fully exert its slow-release effect, thereby effectively improving the cycle capacity retention rate of the battery.

[0089] In some embodiments, the above-mentioned "positive electrode film layer bonded to at least one surface of the positive electrode current collector" means that the positive electrode film layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction.

[0090] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0091] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0092] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry, coating the positive electrode slurry on the surface of the positive current collector, drying it and then cold pressing it through a cold rolling mill to form the positive electrode sheet.

[0094] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is 7%-30%.

[0095] For example, the percentage of primary particles with a primary diameter greater than 0.8 μm can be typical but not limiting values ​​such as 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%.

[0096] Primary particles with a primary particle size of less than or equal to 0.8 μm have shorter ion diffusion paths, which allows lithium ions to migrate more quickly within the electrode material during charging and discharging. They also have a larger surface area, which provides more active sites, allowing the small particles of positive electrode active material to fully contact the electrolyte. Therefore, primary particles with a primary particle size of less than or equal to 0.8 μm have a higher initial capacity.

[0097] Primary particles with a primary diameter greater than 0.8 μm have a long internal diffusion path for lithium ions due to their large size, resulting in a relatively small specific surface area and limited contact area with the electrolyte. This leads to insufficient electrochemical reaction active sites and thus a lower initial capacity. However, during continuous battery cycling, these large-diameter primary particles can play a role in slowing down capacity release. Primary particles with a primary diameter less than or equal to 0.8 μm have a shorter ion diffusion path, allowing lithium ions to migrate more quickly within the electrode material during charge and discharge. Therefore, primary particles with a primary diameter less than or equal to 0.8 μm have a higher initial capacity.

[0098] Therefore, this application controls the proportion of primary particles with a primary particle size less than or equal to 0.8 μm within the above-mentioned range. On the one hand, the small-diameter particles contained in the positive electrode active material play a full role, giving the battery a higher initial capacity; on the other hand, the large-diameter particles contained in the positive electrode active material fully exert their capacity release capability during cycling, reducing the rate of capacity decay of the battery. In this way, the capacity retention rate of the battery after multiple cycles can be significantly improved, enhancing the overall cycle performance of the battery.

[0099] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; and the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%.

[0100] For example, the percentage of primary particles with a primary diameter greater than 0.8 μm and less than or equal to 2.5 μm can be typical but not limiting values ​​such as 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and 30%. The primary particle diameter can be typical but not limiting values ​​such as 0.81 μm, 0.9 μm, 1 μm, 1.2 μm, 1.5 μm, 2 μm, 2.2 μm, and 2.5 μm.

[0101] For example, the percentage of primary particles with a primary diameter greater than or equal to 0.05 μm and less than or equal to 0.8 μm can be typical but not limiting values ​​such as 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, and 93%. The primary particle diameter can be typical but not limiting values ​​such as 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, and 0.8 μm.

[0102] Because primary particles with a diameter greater than 0.8 μm have a long ion diffusion path and a small specific surface area, resulting in a lower initial capacity, the particle size range of these primary particles is limited to greater than 0.8 μm and less than or equal to 2.5 μm. Within this range, these primary particles can retain an appropriate amount of initial capacity, and at the same time, during battery cycling, these primary particles can fully exert their capacity release function, effectively slowing down the capacity decay rate, so that the battery has a higher cycle capacity, thereby significantly improving the battery's cycle performance.

[0103] Because primary particles with excessively small primary diameters have a large surface area, they are more prone to side reactions, thus affecting the battery's cycle life. Therefore, the particle size range of these primary particles is limited to greater than or equal to 0.05 μm and less than or equal to 0.8 μm. This results in a shorter diffusion path for lithium ions within the positive electrode active material particles, significantly improving the lithium ion transport rate. This facilitates lithium ion insertion and extraction, thereby improving the battery's capacity output efficiency and ultimately increasing the overall battery capacity. Simultaneously, the smaller primary particle size reduces the stress experienced by the positive electrode active material particles during cycling, effectively mitigating stress concentration, reducing the likelihood of particle pulverization, and thus improving the battery's cycle stability.

[0104] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%.

[0105] For example, the percentage of primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm can be typical but not limiting values ​​such as 5%, 7%, 10%, 12%, and 15%. The primary particle diameter can be typical but not limiting values ​​such as 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.1 μm, 1.15 μm, and 1.2 μm.

[0106] For example, the percentage of primary particles with a primary diameter greater than 1.2 μm and less than or equal to 2.5 μm can be typical but not limiting values ​​such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. The primary particle diameter can be typical but not limiting values ​​such as 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, and 2.5 μm.

[0107] During battery cycling, primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm gradually develop cracks due to stress, effectively reducing the lithium-ion transport path and thus contributing to capacity control. Primary particles with a diameter greater than 1.2 μm and less than or equal to 2.5 μm, due to their larger size, experience more significant stress during cycling. This high-intensity stress leads to more pronounced particle breakage, resulting in a significant increase in cracks and even grain boundary separation. Therefore, compared to primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm, primary particles with a primary diameter greater than 1.2 μm and less than or equal to 2.5 μm, due to their greater degree of breakage, generate more channels and active sites for lithium-ion transport, thus more fully realizing the capacity control effect. During battery charge-discharge cycles, primary particles with a diameter greater than 1.2 μm and less than or equal to 2.5 μm can effectively slow down the rate of battery capacity decay, and have a more prominent effect on maintaining the overall battery performance and reducing the degree of performance degradation.

[0108] Primary particles with a primary diameter greater than 0.8 μm have a lower lithium ion diffusion rate due to their long ion diffusion path and small specific surface area, resulting in a limited contact area with the electrolyte and thus a lower initial capacity. Moreover, this limitation on initial capacity becomes more pronounced as the particle size increases. Therefore, compared to primary particles with a primary diameter greater than 1.2 μm and less than or equal to 2.5 μm, primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm have a relatively higher initial capacity.

[0109] Based on this, by controlling the content of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm and primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm within the above range, the positive electrode active material not only has an appropriate initial capacity, but also can generate cracks or even break due to stress due to its larger particle size. This allows it to fully exert its capacity release effect during cycling, effectively slowing down capacity decay. In this way, the battery can still maintain a high capacity output after multiple cycles, extending the battery's cycle life.

[0110] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-12%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-5%.

[0111] For example, the percentage of primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm can be typical but not limiting values ​​such as 7%, 8%, 9%, 10%, 11%, 12%, etc.

[0112] For example, the percentage of primary particles with a primary diameter greater than 1.2 μm and less than or equal to 2.5 μm can be typical but not limiting values ​​such as 2%, 3%, 4%, 5%.

[0113] By adjusting the proportion of primary particles with a particle size greater than 0.8 μm and less than or equal to 1.2 μm and greater than 1.2 μm and less than or equal to 2.5 μm, and maintaining their content within the aforementioned range, the positive electrode active material is endowed with an appropriate initial capacity. It can also fully exert its capacity-releasing function during cycling. This synergistic allocation of particles with different particle sizes can effectively reduce the rate of battery capacity decay, so that the battery can still maintain a high capacity output after multiple cycles, thus extending the battery's cycle life.

[0114] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; and the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%.

[0115] For example, the percentage of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm can be typical but not limiting values ​​such as 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, and 60%.

[0116] For example, the percentage of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm can be typical but not limiting values ​​such as 30%, 32%, 35%, 38%, 40%, 42%, and 45%.

[0117] The proportion of primary particles within the two ranges of 0.05 μm to 0.4 μm and 0.4 μm to 0.8 μm is within the above range. The positive electrode active material in these two ranges can form a good gradation with the primary particles with a primary particle size greater than 0.8 μm, so that the small-diameter positive electrode material particles can fill the gaps between the large-diameter positive electrode active material particles, thereby effectively improving the energy density of the positive electrode active material.

[0118] Positive electrode active material particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm have shorter diffusion paths, allowing lithium ions to rapidly intercalate and deintercalate within these particles. Therefore, by adjusting the primary particle size and its proportion in the positive electrode active material, not only can multi-level lithium-ion diffusion channels be effectively constructed, but also the pulverization and shedding of the positive electrode active material can be reduced. This helps improve the structural integrity of the positive electrode active material, thereby increasing the cycle life of the battery.

[0119] In some embodiments, taking the total number of primary particles of lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%.

[0120] For example, the percentage of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm can be typical but not limiting values ​​such as 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, and 60%.

[0121] For example, the percentage of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm can be typical but not limiting values ​​such as 30%, 32%, 35%, 38%, 40%, 42%, and 45%.

[0122] For example, the percentage of primary particles with a primary diameter greater than 0.8 μm and less than or equal to 1.2 μm can be typical but not limiting values ​​such as 7%, 8%, 9%, 10%.

[0123] For example, the percentage of primary particles with a primary diameter greater than 1.2 μm and less than or equal to 2.5 μm can be typical but not limiting values ​​such as 2%, 3%, or 4%.

[0124] The positive electrode active material is composed of a composite of primary particles with various primary particle sizes. Among them, the positive electrode active material particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm have shorter diffusion paths, allowing lithium ions to quickly intercalate and deintercalate, thus giving the positive electrode active material a high capacity. During cycling, the positive electrode active material particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm gradually develop cracks under stress, which accelerates the release of lithium ions. As the cracks further expand and the grain boundaries separate, the lithium ion transport rate also gradually increases significantly, thereby playing a capacity-slowing role and reducing the degradation of battery performance. In this way, the battery's cycle capacity remains at a high level, and the cycle performance is stable and reliable.

[0125] In addition, the positive electrode active material particles with different primary particle sizes form a gradation, with smaller positive electrode active material particles filling the gaps between larger positive electrode active material particles, thereby effectively increasing the compaction density of the positive electrode active material and thus significantly improving the discharge capacity of the positive electrode active material.

[0126] In some embodiments, the volumetric particle size distribution curve of the positive electrode active material is a single-peak curve.

[0127] The positive electrode active material includes secondary particles, which are composed of multiple primary particles. The particle size distribution curve is mainly used to characterize the particle size distribution of the secondary particles. A single peak in the particle size distribution curve of the positive electrode active material indicates that the positive electrode active material exhibits more consistent performance in the battery, thus providing more stable electrochemical performance.

[0128] In some embodiments, the molecular formula of the lithium phosphate material is Li a Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in,

[0129] M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr;

[0130] Q includes at least one element selected from B, S, Si, and N;

[0131] R includes one or more elements selected from S, F, Cl, and Br;

[0132] Q and R are not both elements of S;

[0133] 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1.

[0134] Examples of lithium phosphate-containing materials include, but are not limited to, LiFePO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, LiMnPO4, and LiMn. 0.2 Fe 0.8 PO4 and LiFe 0.5 Mn 0.5 One or more of PO4.

[0135] Lithium phosphate materials have good chemical stability and are difficult to decompose. Therefore, by adjusting the particle size of the primary particles they contain, the lithium phosphate material can fully exert its slow-release function, and this stability is not easily compromised. This helps to improve the structural stability of the positive electrode active material and reduce phenomena such as particle pulverization. In this way, the battery can still maintain a high capacity retention rate after multiple cycles.

[0136] In some embodiments, after compaction under a pressure of 3T, the compacted density of the positive electrode active material powder is 2.4-2.6 g / cm³. 3 For example, under 3T pressure, the compaction density of the positive electrode active material powder can be 2.4 g / cm³. 3 2.45g / cm 3 2.5g / cm 3 2.55g / cm 3 2.6g / cm 3 Typical but not restrictive values.

[0137] Within this range, it means that more positive electrode active material can be accommodated in the same volume of positive electrode sheet, thereby increasing the energy density of the battery.

[0138] In some embodiments, the specific surface area of ​​the positive electrode active material is 9-13 m². 2 / g. For example, the specific surface area of ​​the positive electrode active material can be 9m². 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g and other typical but non-restrictive values.

[0139] Within this range, it means that the positive electrode active material has an appropriate number of active sites, which can provide more channels and sites for the adsorption and desorption of lithium ions, thereby accelerating the transport speed of lithium ions and improving the rate performance of the battery.

[0140] In some embodiments, the compaction density of the positive electrode sheet is 2.5-2.7 g / cm³. 3 For example, the compaction density of the positive electrode sheet can be 2.5 g / cm³. 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 Typical but not restrictive values.

[0141] Within this range, it means that more active material can be accommodated per unit volume of the positive electrode sheet, which helps to improve the energy density of the battery.

[0142] In some embodiments, the porosity of the positive electrode is 15%-30%. Exemplary examples show that the porosity of the positive electrode can be typical but not limiting values ​​such as 15%, 18%, 20%, 22%, 25%, 27%, and 30%.

[0143] Within this range, the electrolyte can fully wet the positive electrode, promoting smoother transport of lithium ions between the electrolyte and the positive electrode active material.

[0144] In some embodiments, a single battery cell includes a negative electrode and a separator disposed between the positive and negative electrodes, in addition to a positive electrode. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0145] [Negative electrode plate]

[0146] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0147] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0148] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0149] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include, but is not limited to, one or more of carbon materials (e.g., carbon materials include at least one of natural graphite, artificial graphite, soft carbon, and hard carbon), silicon-based materials, tin-based materials, and lithium titanate.

[0150] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0151] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose).

[0153] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0154] [Electrolytes]

[0155] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0156] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0157] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium fluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluorooxalate phosphate, N-dialkylpyrrolidine onium lithium salt, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and N-ethylpyrrolidine onium lithium tetrafluoroborate.

[0158] In some embodiments, the solvent may 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, butyl 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.

[0159] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0160] [Isolation membrane]

[0161] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0162] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0163] In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer package, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. The shape of the battery cell is not particularly limited; it can be cylindrical, square, or any other arbitrary shape.

[0164] A second aspect of this application provides a battery device including a plurality of battery cells as described in the above embodiments.

[0165] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0166] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0167] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0168] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cell assemblies housed within the housing.

[0169] As an example, the battery cell assembly can be a battery module, and the battery cell assembly can be housed in the housing by fixing the battery module in the housing.

[0170] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0171] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0172] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0173] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0174] A third aspect of this application provides an electrical device, including a battery cell or a battery device as described in the above embodiments, wherein the battery cell or battery device is used to store or provide electrical energy.

[0175] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0176] The following description, with appropriate reference to the accompanying drawings, describes the battery cell, battery device, and power consumption device provided in the embodiments of this application.

[0177] Figure 1 is an exploded view of a battery device 100 as an example. The battery device 100 includes a housing 10 and battery cell assemblies 20, the battery cell assemblies 20 being housed within the housing 10. The housing 10 provides a space for housing the battery cell assemblies 20, and the housing 10 can have various structures. In some embodiments, the housing 10 may include a first housing 11 and a second housing 12, which overlap each other, collectively defining a closed space for housing the battery cell assemblies 20. Of course, the housing 10 formed by the first housing 11 and the second housing 12 can have various shapes, such as a cylinder, a cuboid, etc. Multiple battery cell assemblies 20 can be arranged in any manner within the battery housing.

[0178] In the battery device 100, there can be one or more battery cell components 20. Multiple battery cell components 20 can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cell components 20 are connected in both series and parallel. Multiple battery cell components 20 can be directly connected in series, parallel, or in a mixed manner, and then the whole formed by multiple battery cell components 20 is housed in the housing 10. Of course, the battery device 100 can also be formed by first connecting multiple battery cell components 20 in series, parallel, or in a mixed manner to form a battery module, such as a battery module or battery pack. Multiple battery modules are then connected in series, parallel, or in a mixed manner to form a whole and housed in the housing 10.

[0179] The battery cell assembly 20 includes multiple battery cells 30. Figure 2 is an exploded view of a battery cell 30 as an example. The battery cell 30 includes a housing 31, a cover plate 33, a wound electrode assembly 32, and other functional components.

[0180] The housing 31 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 31 is a hollow structure with an opening at one end, and the housing 31 is used to cooperate with the cover plate 33 to form an internal environment for accommodating the wound electrode assembly 32, electrolyte, and other functional components. The housing 31 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 31 can be determined according to the specific shape and size of the wound electrode assembly 32. The material of the housing 31 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited here. The cover plate 33 is a component that covers the opening of the housing 31 to isolate the internal environment of the battery cell 30 from the external environment. The material of the cover plate 33 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and is not limited here.

[0181] Figure 3 is a schematic diagram of an example electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0182] The fourth aspect of this application provides a positive electrode active material, which includes a lithium phosphate material, wherein, based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%.

[0183] The positive electrode active material of this application is composed of a composite of particles with different primary particle sizes, and the proportion of primary particles with a primary particle size greater than 0.8 μm is controlled within the above-mentioned range. During battery cycling, due to the repeated insertion and extraction of lithium ions, the positive electrode active material with a primary particle size greater than 0.8 μm generates stress due to volume changes. This stress causes the positive electrode active material particles to gradually crack and form cracks, and the grain boundaries are separated, thereby forming more pathways for lithium ions to pass through and effectively shortening the lithium ion transport path. In this way, more lithium ions can participate in the reaction during battery cycling, allowing lithium ions to be inserted and extracted more uniformly and quickly inside the particles. Thus, the positive electrode active material can effectively exert a slow-release effect, thereby significantly improving the cycle capacity of the battery.

[0184] Controlling the proportion of primary particles with a diameter greater than 0.8 μm to be greater than or equal to 7% means that there are enough primary particles in the positive electrode active material to play a role in capacity slow release. Thus, during cycling, the capacity increase generated by these particles through their capacity slow release will exceed the capacity loss due to thermodynamic losses in the positive electrode active material. Therefore, in the initial stage of cycling, the capacity of the positive electrode active material not only does not decrease but also shows a capacity increase trend. This additional capacity increase provides more buffer space for capacity decay in subsequent cycles. In particular, with a larger capacity base, even if capacity decay occurs later, a high residual capacity can still be maintained after multiple cycles, thereby effectively improving the battery's cycle capacity retention rate and extending battery life.

[0185] Therefore, this application uses a combination of particles with different primary particle sizes to form the positive electrode active material, and controls the number of primary particles with different particle sizes, so that the positive electrode active material can fully exert its slow-release effect, thereby effectively improving the cycle capacity retention rate of the battery.

[0186] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; and the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%.

[0187] Because primary particles with a diameter greater than 0.8 μm have a long ion diffusion path and a small specific surface area, resulting in a lower initial capacity, the particle size range of these primary particles is limited to greater than 0.8 μm and less than or equal to 2.5 μm. Within this range, these primary particles can retain an appropriate amount of initial capacity, and at the same time, during battery cycling, these primary particles can fully exert their capacity-releasing effect, effectively slowing down the capacity decay rate, so that the battery has a higher cycle capacity, thereby significantly improving the battery's cycle performance.

[0188] Because primary particles with excessively small primary diameters have a large surface area, they are more prone to side reactions, thus affecting the battery's cycle life. Therefore, the particle size range of these primary particles is limited to greater than or equal to 0.05 μm and less than or equal to 0.8 μm. This results in a shorter diffusion path for lithium ions within the positive electrode active material particles, significantly improving the lithium ion transport rate. This facilitates lithium ion insertion and extraction, thereby improving the battery's capacity output efficiency and ultimately increasing the overall battery capacity. Simultaneously, the smaller primary particle size reduces the stress experienced by the positive electrode active material particles during cycling, effectively mitigating stress concentration, reducing the likelihood of particle pulverization, and thus improving the battery's cycle stability.

[0189] In some embodiments, with the total number of primary particles of lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%.

[0190] By controlling the content of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm, and primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm within the above range, the positive electrode active material not only has an appropriate initial capacity, but also can generate cracks or even break due to stress due to its larger particle size. This allows it to fully exert its capacity release effect during cycling, effectively slowing down capacity decay. In this way, the battery can still maintain a high capacity output after multiple cycles, extending the battery's cycle life.

[0191] In some embodiments, taking the total number of primary particles of lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%.

[0192] By combining positive electrode active materials with different primary particle sizes in a certain proportion, it is possible to achieve high capacity by utilizing positive electrode active materials with smaller primary particle sizes, and to rely on positive electrode active materials with larger primary particle sizes to play a gradual release role. This multi-combination synergistically improves the cycle performance of the battery.

[0193] In some embodiments, the molecular formula of the lithium phosphate material is Li a Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in,

[0194] M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr;

[0195] Q includes at least one element selected from B, S, Si, and N;

[0196] R includes one or more elements selected from S, F, Cl, and Br;

[0197] Q and R are not both elements of S;

[0198] 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1.

[0199] Lithium phosphate materials have good chemical stability and are difficult to decompose. Therefore, by adjusting the particle size of the primary particles they contain, the lithium phosphate material can fully exert its slow-release function, and this stability is not easily compromised. This helps to improve the structural stability of the positive electrode active material and reduce phenomena such as particle pulverization. In this way, the battery can still maintain a high capacity retention rate after multiple cycles.

[0200] Example

[0201] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0202] Example 1

[0203] This embodiment provides a positive electrode active material and a battery cell.

[0204] Positive electrode active material

[0205] This embodiment provides a positive electrode active material, lithium iron phosphate. In this positive electrode active material, taking the total number of primary particles as 100%, the proportion of primary particles with a diameter greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 53%; the proportion of primary particles with a diameter greater than 0.4 μm and less than or equal to 0.8 μm is 38%; the proportion of primary particles with a diameter greater than 0.8 μm and less than or equal to 1.2 μm is 7%; and the proportion of primary particles with a diameter greater than 1.2 μm and less than or equal to 2.5 μm is 2%. The powder compaction density of this positive electrode active material under 3T pressure is 2.53 g / cm³. 3 Its specific surface area is 10.6 m². 2 / g.

[0206] The preparation process of the above-mentioned lithium iron phosphate is as follows:

[0207] S1. Provide raw materials: ferric phosphate, lithium carbonate, and glucose, wherein the D50 of ferric phosphate is 7-10 μm. The molar ratio of iron atoms in ferric phosphate to lithium atoms in lithium carbonate is 1:1.05, and the amount of glucose added is 2% of the total weight of raw materials. Mix ferric phosphate, lithium carbonate, and glucose in the above proportions and pump them into a coarse grinding system. Use zirconia balls with a diameter of 5 mm for coarse grinding for 30 minutes; then transfer to a fine grinding system for sand grinding, using zirconia balls with a diameter of 0.5 mm as the grinding media for 2 hours. The D50 particle size of the material after fine grinding is 258 nm.

[0208] S2. The finely ground slurry is transported to the iron removal transfer tank for iron removal for 30 minutes.

[0209] S3. The slurry after iron removal is spray-dried. At a temperature of 240℃, the material is atomized into micron-sized droplets through a spray drying tower. The particle size of the spray-dried powder is D50 < 20μm and D100 < 100μm.

[0210] S4. The spray-dried powder is subjected to high-temperature sintering treatment at 720℃ for 6 hours. The sintering process is an oxygen-free process and is carried out in a high-purity nitrogen atmosphere (N2≥99.99%). The particle size of the sintered material is D50<10μm and D100<50μm.

[0211] S5. The material after high-temperature sintering is pulverized. Air jet milling can be used for this process. The particle size of the pulverized material is D50 < 2μm and D100 < 20μm.

[0212] S6. The crushed material is conveyed to the iron removal machine for magnetic separation to remove iron. The magnetic impurities in the material are adsorbed and removed by a strong magnetic field to obtain lithium iron phosphate.

[0213] battery cell

[0214] [Positive electrode plate]

[0215] The positive electrode active material, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) provided in Example 1 were mixed in a weight ratio of 94:4:2. N-methylpyrrolidone solvent was added, and the mixture was thoroughly stirred to obtain a uniform positive electrode slurry. The positive electrode slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil, with a coating weight of 0.224 g / 1540.25 mm. 2 (Based on weight excluding solvent), then dried and cold-pressed to obtain the positive electrode sheet (compacted density of 2.65 g / cm³). 3 ).

[0216] [Negative electrode plate]

[0217] Artificial graphite (negative electrode active material), acetylene black (conductive agent), SBR (styrene-butadiene rubber) (binder), and CMC (carboxymethyl cellulose) (thickener) were mixed in a weight ratio of 95:1.5:3.1:0.4. Deionized water was added as a solvent, and the mixture was stirred thoroughly to obtain a uniform negative electrode slurry. The negative electrode slurry was then coated onto both surfaces of the copper foil used as the negative electrode current collector, with a coating weight of 0.136 g / 1540.25 mm. 2 (Based on weight excluding solvent), the negative electrode sheet is obtained after drying and cold pressing.

[0218] Electrolyte

[0219] In an argon atmosphere glove box with a water content of <10ppm, EC (ethylene carbonate), PC (propylene carbonate), and DMC (dimethyl carbonate) were mixed in a weight ratio of EC:PC:DMC = 3:3:3. Then, LiPF6 (lithium hexafluorophosphate) was added to the mixed organic solvent and stirred until homogeneous to obtain an electrolyte, wherein the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0220] [Isolation membrane]

[0221] Polyethylene porous membrane is used as the separation membrane.

[0222] [Rechargeable Battery]

[0223] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. These are then wound to obtain a bare cell. The bare cell is placed in an outer package, infused with a prepared electrolyte, and sealed for formation to obtain a lithium-ion battery cell.

[0224] Example 2

[0225] This embodiment provides a positive electrode active material and a battery cell.

[0226] A positive electrode active material, lithium iron phosphate, comprises the following: 55% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 36% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 7% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 2% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.49 g / cm³. 3 Its specific surface area is 10.2 m². 2 / g.

[0227] The difference between this method for preparing lithium iron phosphate and Example 1 is that the conditions for high-temperature sintering in step 4 are: temperature 715℃ and time 6h.

[0228] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 2 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.65 g / cm³. 3 .

[0229] Example 3

[0230] This embodiment provides a positive electrode active material and a battery cell.

[0231] A positive electrode active material, lithium iron phosphate, comprises the following: 55% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 32% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 9% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 4% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.58 g / cm³. 3 Its specific surface area is 11.1 m². 2 / g.

[0232] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 223 nm.

[0233] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 3 to prepare the positive electrode sheet, which has a compaction density of 2.68 g / cm³. 3 .

[0234] Example 4

[0235] This embodiment provides a positive electrode active material and a battery cell.

[0236] A positive electrode active material, lithium iron phosphate, comprises the following: 48% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 38% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 10% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 4% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.55 g / cm³. 3 Its specific surface area is 11.5 m². 2 / g.

[0237] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 223 nm; and the conditions for high-temperature sintering in step 4 are: temperature 725 °C and time 6 h.

[0238] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 4 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.66 g / cm³. 3 .

[0239] Example 5

[0240] This embodiment provides a positive electrode active material and a battery cell.

[0241] A positive electrode active material, lithium iron phosphate, comprises the following: 43% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 40% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 12% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 5% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.6 g / cm³. 3 Its specific surface area is 10.3 m². 2 / g.

[0242] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 223 nm; and the conditions for high-temperature sintering in step 4 are: temperature 730 °C and time 6 h.

[0243] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 5 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.7 g / cm³. 3 .

[0244] Example 6

[0245] This embodiment provides a positive electrode active material and a battery cell.

[0246] A positive electrode active material, lithium iron phosphate, comprises the following: 55% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 38% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 5% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 2% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.58 g / cm³. 3 Its specific surface area is 11.3 m². 2 / g.

[0247] The difference between this method for preparing lithium iron phosphate and Example 1 is that the conditions for high-temperature sintering in step 4 are: temperature 725℃ and time 6h.

[0248] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 6 to prepare the positive electrode sheet, which has a compaction density of 2.68 g / cm³. 3 .

[0249] Example 7

[0250] This embodiment provides a positive electrode active material and a battery cell.

[0251] A positive electrode active material, lithium iron phosphate, comprises the following: 40% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 40% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 13% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 7% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.42 g / cm³. 3 Its specific surface area is 10.6 m². 2 / g.

[0252] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 282 nm.

[0253] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 7 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.55 g / cm³. 3 .

[0254] Example 8

[0255] This embodiment provides a positive electrode active material and a battery cell.

[0256] A positive electrode active material, lithium iron phosphate, comprises the following: 40% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 35% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 15% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 10% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.48 g / cm³. 3 Its specific surface area is 11.2 m². 2 / g.

[0257] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 282 nm; and the conditions for high-temperature sintering in step 4 are: temperature 725 °C and time 6 h.

[0258] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 8, and the compaction density of this positive electrode sheet is 2.63 g / cm³. 3 .

[0259] Example 9

[0260] This embodiment provides a positive electrode active material and a battery cell.

[0261] A positive electrode active material, lithium iron phosphate, comprises the following: 40% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 30% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 15% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 15% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.58 g / cm³. 3 Its specific surface area is 10.2 m². 2 / g.

[0262] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 282 nm; and the conditions for high-temperature sintering in step 4 are: temperature 740 °C and time 6 h.

[0263] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 9 to prepare the positive electrode sheet, which has a compaction density of 2.7 g / cm³. 3 .

[0264] Example 10

[0265] This embodiment provides a positive electrode active material and a battery cell.

[0266] A positive electrode active material, lithium iron phosphate, comprises the following: 35% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 30% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 20% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 15% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.6 g / cm³. 3 Its specific surface area is 10.1 m². 2 / g.

[0267] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 282 nm; and the conditions for high-temperature sintering in step 4 are: temperature 745 °C and time 6 h.

[0268] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Example 10 to prepare the positive electrode sheet, which has a compaction density of 2.72 g / cm³. 3 .

[0269] Example 11

[0270] This embodiment provides a positive electrode active material and a battery cell.

[0271] A positive electrode active material, lithium iron phosphate, comprises the following: 34% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 27% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 25% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 14% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.69 g / cm³. 3 Its specific surface area is 9.2 m². 2 / g.

[0272] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 205 nm; and the conditions for high-temperature sintering in step 4 are: temperature 745 °C and time 6 h.

[0273] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 11, and the compaction density of this positive electrode sheet is 2.82 g / cm³. 3 .

[0274] Example 12

[0275] This embodiment provides a positive electrode active material and a battery cell.

[0276] A positive electrode active material, lithium iron phosphate, comprises the following: primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm account for 53%; primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm account for 38%; and primary particles with a primary particle size greater than 2.5 μm and less than or equal to 3.0 μm account for 9%. The powder compaction density of this positive electrode active material under 3T pressure is 2.73 g / cm³. 3 Its specific surface area is 9.7 m². 2 / g.

[0277] The difference between this method for preparing lithium iron phosphate and Example 1 is that: in step 1, after fine grinding, materials with a D50 particle size of 180 nm and materials with a D50 particle size of 282 nm are obtained respectively; in step 2, the materials with a D50 particle size of 180 nm and materials with a D50 particle size of 282 nm are mixed at a mass ratio of 2:8; in step 4, the conditions for high-temperature sintering are: temperature of 745℃ and time of 6 h.

[0278] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 12, and the compaction density of this positive electrode sheet is 2.85 g / cm³. 3 .

[0279] Example 13

[0280] This embodiment provides a positive electrode active material and a battery cell.

[0281] A positive electrode active material, lithium iron phosphate, comprises the following: 53% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 38% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; and 9% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.62 g / cm³. 3 Its specific surface area is 10.3 m². 2 / g.

[0282] The difference between this method for preparing lithium iron phosphate and Example 1 is that: in step 1, after fine grinding, materials with a D50 particle size of 205 nm and materials with a D50 particle size of 282 nm are obtained respectively; in step 2, the materials with a D50 particle size of 205 nm and materials with a D50 particle size of 282 nm are mixed at a mass ratio of 2:8; in step 4, the conditions for high-temperature sintering are: temperature of 745℃ and time of 6 h.

[0283] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 13, and the compaction density of this positive electrode sheet is 2.73 g / cm³. 3 .

[0284] Example 14

[0285] This embodiment provides a positive electrode active material and a battery cell.

[0286] A positive electrode active material, lithium iron phosphate, comprises the following: 53% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 38% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; and 9% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.65 g / cm³. 3 Its specific surface area is 10.1 m². 2 / g.

[0287] The difference between this method for preparing lithium iron phosphate and Example 1 is that: in step 1, after fine grinding, materials with a D50 particle size of 205 nm and materials with a D50 particle size of 282 nm are obtained respectively; in step 2, the materials with a D50 particle size of 205 nm and materials with a D50 particle size of 282 nm are mixed at a mass ratio of 3:7; in step 4, the conditions for high-temperature sintering are: temperature of 745℃ and time of 6 h.

[0288] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 14, and the compaction density of this positive electrode sheet is 2.75 g / cm³. 3 .

[0289] Example 15

[0290] This embodiment provides a positive electrode active material and a battery cell.

[0291] A positive electrode active material, lithium iron phosphate, comprises the following: 91% of primary particles have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 7% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 2% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.68 g / cm³. 3 Its specific surface area is 9.8 m². 2 / g.

[0292] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 525 nm; and the conditions for high-temperature sintering in step 4 are: temperature 750 °C and time 8 h.

[0293] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 15, and the compaction density of this positive electrode sheet is 2.74 g / cm³. 3 .

[0294] Example 16

[0295] This embodiment provides a positive electrode active material and a battery cell.

[0296] A positive electrode active material, lithium iron phosphate, comprises the following: 91% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 7% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 2% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.36 g / cm³. 3 Its specific surface area is 12.1 m². 2 / g.

[0297] The difference between this method for preparing lithium iron phosphate and Example 1 is that: in step 1, after fine grinding, materials with a D50 particle size of 180 nm and materials with a D50 particle size of 282 nm are obtained respectively; in step 2, materials with a D50 particle size of 205 nm and materials with a D50 particle size of 282 nm are mixed at a mass ratio of 6:4; in step 4, the conditions for high-temperature sintering are: temperature of 730℃ and time of 6 h.

[0298] A battery cell differs from Example 1 in that: the positive electrode sheet is prepared using the positive electrode active material provided in Example 14, and the compaction density of this positive electrode sheet is 2.46 g / cm³. 3 .

[0299] Comparative Example 1

[0300] This comparative example provides a positive electrode active material and a battery cell.

[0301] A positive electrode active material, lithium iron phosphate, comprises the following: 64% of primary particles have a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm; 30.8% have a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm; 4% have a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm; and 1.2% have a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.35 g / cm³. 3 Its specific surface area is 13.5 m². 2 / g.

[0302] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 282 nm; and the conditions for high-temperature sintering in step 4 are: temperature 705 °C and time 6 h.

[0303] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Comparative Example 1 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.45 g / cm³. 3 .

[0304] Comparative Example 2

[0305] This comparative example provides a positive electrode active material and a battery cell.

[0306] A positive electrode active material, lithium iron phosphate, comprises 73% primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm, and 27% primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm. The powder compaction density of this positive electrode active material under 3T pressure is 2.21 g / cm³. 3 Its specific surface area is 14.7 m². 2 / g.

[0307] The difference between this method for preparing lithium iron phosphate and Example 1 is that the D50 particle size of the finely ground material in step 1 is 180 nm; and the conditions for high-temperature sintering in step 4 are: temperature 690 °C and time 6 h.

[0308] A battery cell differs from Example 1 in that it uses the positive electrode active material provided in Comparative Example 2 to prepare the positive electrode sheet, and the compaction density of this positive electrode sheet is 2.35 g / cm³. 3 .

[0309] Performance testing

[0310] (1) Primary particle size test

[0311] The method for testing the primary average particle size of lithium iron phosphate is as follows: 0.05 g of the test material is dissolved in 40 ml of anhydrous ethanol, and then an appropriate amount of dispersant is added. The mixture is stirred until a suspension is obtained. 2 ml of the suspension is mixed with 2 ml of anhydrous ethanol and then subjected to ultrasonic treatment at a power of 480 W for 5 min. A uniformly dispersed suspension is obtained. An appropriate amount of the middle layer suspension is subjected to transmission electron microscopy (TEM). The projection area of ​​each primary particle in the TEM image is counted, which is the cross-sectional area S of the primary particle. The equivalent circle diameter of the primary particle is obtained using the equivalent circle method, which is the primary particle diameter d. In the above statistical process of primary particles and their primary particle diameters, primary particles with a primary particle diameter less than 50 nm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50 nm are considered effective particles). At least 500 effective particles are tested for their cross-sectional area S and primary particle diameter d. The primary average particle size of the test material = the sum of the primary particle diameters of all primary particles / the total number of primary particles.

[0312] (2) Room temperature cycling performance test

[0313] At 25°C, the battery cells prepared in Examples 1-16 and Comparative Examples 1-2 were first charged at a constant current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) to a voltage of 3.48V, then charged at a constant current of 0.5C to a voltage of 3.5V, then charged at a constant current of 1 / 3C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of 0.05C. After resting for 5 minutes, the battery cells were discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery cells were subjected to multiple charge-discharge cycles using the above method until the discharge capacity of the lithium-ion secondary battery decreased to 80%, and the number of cycles of the lithium-ion battery cells was recorded.

[0314] (3) High-temperature cycling performance

[0315] At 60°C, the battery cells prepared in Examples 1-16 and Comparative Examples 1-2 were first charged at a constant current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) to a voltage of 3.48V, then charged at a constant current of 0.5C to a voltage of 3.5V, then charged at a constant current of 1 / 3C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of 0.05C. After resting for 5 minutes, the battery cells were discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery cells were subjected to multiple charge-discharge cycles using the above method, and the discharge capacity of the 500th cycle was measured.

[0316] The capacity retention rate of a single battery cell after 500 cycles at 60°C = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0317] (4) Initial capacity

[0318] At room temperature, the battery cells provided in Examples 1-16 were discharged at a constant current of 1 / 3C to a voltage of 2.5V, allowed to stand for 5 minutes, charged at a constant current of 1 / 3C to a voltage of 3.65V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 10 minutes, discharged at a constant current of 1 / 3C to a voltage of 2.5V, and allowed to stand for 10 minutes; this process was repeated: charged at a constant current of 1 / 3C to a voltage of 3.65V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 10 minutes, discharged at a constant current of 1 / 3C to a voltage of 2.5V, and allowed to stand for 10 minutes; then charged at a constant current of 1C to a voltage of 3.48V, charged at a constant current of 0.5C to a voltage of 3.5V, charged at a constant current of 1 / 3C to a voltage of 3.65V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 10 minutes, and discharged at a constant current of 1C to a voltage of 2.5V. The discharge capacity at this point is the initial capacity of the battery cell.

[0319] Example 1 and Comparative Example 1 were tested under normal temperature cycling performance test conditions, and the results are shown in Figure 4. As can be seen from Figure 4, after the battery is assembled using the positive electrode active material provided in Example 1, the battery has a significant capacity improvement in the early stage of cycling, and the capacity decay trend in the later stage is significantly reduced.

[0320] The performance test results of the battery cells provided in Examples 1-16 and Comparative Examples 1-2 are listed below, as shown in Tables 1 and 2.

[0321] Table 1

[0322] As can be seen from Table 1, compared with Comparative Examples 1-2, in the embodiments of this application, the proportion of primary particles with a primary particle size greater than 0.8 μm in the positive electrode active material is greater than or equal to 7%, so that there are enough primary particles in the positive electrode active material to play a capacity-releasing role, thereby effectively improving the cycle performance of the battery, such as increasing the number of cycles and improving the cycle capacity retention rate.

[0323] Table 2

[0324] Based on the data in Tables 1-2, the performance test data from Examples 6-11 show that as the proportion of primary particles with a diameter greater than 0.8 μm increases, the initial capacity of the battery cell decreases. This is because these particles have a larger diameter and a relatively smaller specific surface area, resulting in limited actual contact area with the electrolyte. Consequently, there are insufficient active sites for the electrical chemical reactions, preventing the full utilization of capacity and ultimately leading to a lower initial capacity. Therefore, controlling the proportion of primary particles with a diameter greater than 0.8 μm to 7%-30% can effectively improve the overall cycle performance of the battery without significantly reducing the initial capacity of the battery cell, achieving a balance between the two.

[0325] Based on the data in Tables 1-2, the performance test data from Examples 1 and 12 show that as the particle size of primary particles (greater than 0.8 μm) increases, the cycle retention rate, such as the number of cycles at room temperature and the cycle retention rate at high temperature, also increases. However, in stark contrast, the initial capacity of the battery decreases significantly. Therefore, controlling the particle size of primary particles within the range of greater than 0.8 μm and less than or equal to 2.5 μm allows the positive electrode active material to exhibit good performance in both initial capacity and cycle characteristics.

[0326] Based on the data in Tables 1-2, the performance test data of Examples 1 and 13-14 show that: compared with Example 1, Example 13 has lower cycle performance, such as cycle count and cycle retention rate, but higher initial capacity; Example 14 has higher cycle performance, such as cycle count and cycle retention rate, but lower initial capacity. This indicates that, under the premise that the proportion of primary particles with a primary particle size less than or equal to 0.8 μm remains unchanged, adjusting the distribution of primary particles larger than 0.8 μm in a certain proportion within the two ranges of greater than 0.8 μm and less than or equal to 1.2 μm and greater than 1.2 μm and less than or equal to 2.5 μm is more conducive to the positive electrode active material having an appropriate initial capacity and also exhibiting better cycle performance.

[0327] Based on the data in Tables 1-2, the performance test data of Examples 1 and 15-16 show that: compared with Example 1, Example 15 has higher cycle performance, such as cycle count and cycle retention rate, but lower initial capacity; Example 16 has lower cycle performance, such as cycle count and cycle retention rate, but higher initial capacity. This indicates that, under the premise that the proportion of primary particles with a primary particle size greater than 0.8 μm remains unchanged, adjusting the distribution of primary particles smaller than or equal to 0.8 μm in a certain proportion within the two ranges of greater than or equal to 0.05 μm and less than or equal to 0.4 μm and greater than 0.4 μm and less than or equal to 0.8 μm not only makes it easier for the positive electrode active material to obtain a suitable initial capacity, but also significantly improves its cycle performance.

[0328] The above are merely optional embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

A battery cell characterized by The device includes a positive electrode sheet, which comprises a positive current collector and a positive electrode film layer bonded to at least one surface of the positive current collector. The positive electrode film layer contains a positive electrode active material, which includes a lithium phosphate material. The positive electrode active material comprises, with the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%. The battery cell of claim 1, wherein Taking the total number of primary particles of the lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is 7%-30%. The battery cell as claimed in claim 1 or 2, characterized in that Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%. The battery cell according to any one of claims 1 to 3, characterized in that Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%. The battery cell according to any one of claims 1 to 4, characterized in that Taking the total number of primary particles of the lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-12%; the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-5%. The battery cell according to any one of claims 1 to 5, characterized in that Taking the total number of primary particles of the lithium phosphate material as 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%. The battery cell according to any one of claims 1 to 6, characterized in that Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%. The battery cell of any one of claims 1 to 7, wherein The volumetric particle size distribution curve of the positive electrode active material is a single-peak curve. The battery cell of any one of claims 1 to 8, wherein The molecular formula of the lithium phosphate material is Li a Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in, M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr; Q includes at least one element selected from B, S, Si, and N; R includes one or more elements selected from S, F, Cl, and Br; Q and R are not both elements of S; 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.

1. The battery cell of any one of claims 1 to 9, wherein The powder compacting density of the positive electrode active material is 2.4-2.6 g / cm3 after pressure compaction at 3T 3 ; and / or, The specific surface area of the positive electrode active material is 9-13 m 2 / g. The battery cell of any one of claims 1 to 10, wherein The compacted density of the positive electrode plate is 2.5-2.7 g / cm 3 ; and / or, The porosity of the positive electrode sheet is 15%-30%. A battery device characterized by comprising: It includes multiple battery cells as described in any one of claims 1-10. An electric power utilization device characterized by comprising: Includes a battery cell as described in any one of claims 1-11 or a battery device as described in claim 12. A positive electrode active material characterized by comprising: The positive electrode active material includes lithium phosphate material, and based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm is greater than or equal to 7%. The positive electrode active material according to claim 14, characterized in that Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 2.5 μm is 7%-30%; the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.8 μm is 70%-93%. The positive electrode active material according to any one of claims 14 to 15, characterized in that, Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 5%-15%; the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-10%. The positive electrode active material according to any one of claims 14 to 16, characterized in that, Based on the total number of primary particles of the lithium phosphate material being 100%, the proportion of primary particles with a primary particle size greater than or equal to 0.05 μm and less than or equal to 0.4 μm is 40%-55%; the proportion of primary particles with a primary particle size greater than 0.4 μm and less than or equal to 0.8 μm is 30%-38%; the proportion of primary particles with a primary particle size greater than 0.8 μm and less than or equal to 1.2 μm is 7%-10%; and the proportion of primary particles with a primary particle size greater than 1.2 μm and less than or equal to 2.5 μm is 2%-4%. The positive electrode active material according to any one of claims 14 to 17, characterized in that, The molecular formula of the lithium phosphate material is Li a Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ,in, M includes at least one element selected from Ni, Co, Mg, Zn, Ca, Ti, V, and Cr; Q includes at least one element selected from B, S, Si, and N; R includes one or more elements selected from S, F, Cl, and Br; Q and R are not both elements of S; 0.9≤a≤1.2; 0≤x≤1; 0≤y≤1; 0≤1-xy<1; 0≤m≤0.1; 0≤n≤0.1.

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