A positive electrode sheet and a battery

Abstract

The application relates to the technical field of batteries, in particular to a positive plate and a battery, the positive plate comprising a positive current collector and a positive active layer located on one side or both sides of the positive current collector; the positive active layer comprises a positive active material, the positive active material comprising secondary lithium iron phosphate particles, the particle size Dv50 of the secondary lithium iron phosphate particles being 5-15 mu m; the secondary lithium iron phosphate particles are composed of multiple primary particles, the particle size of the primary particles being in the range of 0.2-1.5 mu m, a carbon layer being arranged on the surface of the primary particles, and the primary particles comprising first particles, second particles and third particles. The positive plate can effectively balance the compaction density and the kinetic performance of the positive plate, so that the positive plate has a high compaction density and still has excellent fast-charging kinetic performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a positive electrode and a battery. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and the demand for large-scale energy storage, the market's requirements for battery energy density have further increased.

[0003] To further address the range anxiety issue of new energy vehicles, it is often necessary to increase the energy density of lithium iron phosphate (LFP) batteries. Calculations show that the current maximum initial charge capacity of LFP batteries has reached 162-163 mAh / g. Considering the necessary carbon layer coating and structural losses, this is already close to the theoretical capacity of LFP. Further increasing the energy density requires increasing the compaction density, which is currently below the theoretical capacity of 3.6 g / cm³. 3 There is still room for improvement in the true density. Furthermore, as the size of existing energy storage batteries increases, the requirements for capacity and energy efficiency gradually rise. Therefore, increasing the compaction density of materials, and consequently the compaction density of electrode sheets, to improve energy density is currently the main development direction. However, with increased compaction, the porosity of the electrode sheets will further decrease, especially when the electrode sheets are compacted to 2.85 g / cm³. 3 Afterwards, the electrode porosity drops below 20%. The decrease in electrode porosity will further reduce the kinetic performance of the electrode during the lithium insertion / extraction process. Studies have shown that as compaction increases, the battery's rate charge / discharge performance decreases, which in turn reduces the SOC state corresponding to the lithium plating potential of the negative electrode at high rates, increases the battery charging time, further increases the battery's DCR, increases the resistance to lithium-ion charge transfer and ion diffusion, and has a certain impact on the battery's high-temperature storage performance.

[0004] Furthermore, as compaction increases, larger particles are needed to improve the volume utilization and tap density of the filling material. However, as particle size increases, the material's kinetics decrease exponentially, especially after the particle size increases to 2μm, at which point the specific capacity and kinetic performance of the material will decrease significantly. Therefore, it is crucial to develop a battery with high electrode compaction, good fast-charging kinetics, and excellent performance in high-temperature storage and cycle life. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a positive electrode and a battery. The positive electrode of this invention can effectively balance compaction density and the kinetic performance of the electrode, enabling the electrode to have both high compaction density and excellent fast-charging kinetic performance.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active layer located on one or both sides of the positive current collector; the positive active layer comprises a positive active material, the positive active material comprising lithium iron phosphate particles, wherein the particle size Dv50 of the lithium iron phosphate particles is 5μm-15μm. The secondary lithium iron phosphate particles are composed of multiple primary particles with a particle size ranging from 0.2 μm to 1.5 μm. The surface of each primary particle is provided with a carbon layer. Each primary particle includes a first particle, a second particle, and a third particle. The first particle has a particle size of 200 nm to 400 nm, the second particle has a particle size of 401 nm to 800 nm, and the third particle has a particle size of 801 nm to 1500 nm. The ratio of the number of the first particle, the second particle, and the third particle is (5-8):(2-4):(0-1).

[0007] A second aspect of the present invention provides a battery comprising the positive electrode, negative electrode, separator, and electrolyte described in the first aspect of the present invention.

[0008] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art: The positive electrode of this invention achieves a highly efficient balance between compaction density and kinetic performance by limiting the particle size range of secondary lithium iron phosphate particles and the composition and ratio of primary particles. The first, second, and third particles of specific sizes are combined in a specific ratio. The high proportion of small-diameter first particles fully fills the gaps between particles, increasing the material packing density and thus improving the battery's kinetic and rate performance, while simultaneously increasing the electrode's compaction density. Medium-diameter second particles support the larger and smaller particles, effectively reducing polarization during charging and discharging, further improving the battery's kinetic performance. A small number of large-diameter third particles form a stable compaction framework, increasing the material's tap density and further enhancing the electrode's compaction potential. This ratio allows for a reasonable porous structure within the secondary particles, enabling full electrolyte wetting and solving the problem of hindered ion and electron transport under traditional high compaction conditions. This allows the electrode to maintain excellent fast-charging kinetic performance while achieving high compaction density and contributing to increased battery energy density.

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0010] Figure 1The diagram shown is a schematic representation of a primary particle structure provided in an example of the present invention. Figure 1 .

[0011] Figure 2 The diagram shown is a schematic representation of a primary particle structure provided in an example of the present invention. Figure 2 .

[0012] Figure 3 The diagram shown is a schematic representation of a primary particle structure provided in an example of the present invention. Figure 3 .

[0013] Figure 4 The diagram shown is a schematic diagram of the structure of the positive electrode active layer provided in an example of the present invention.

[0014] Figure 5 The image shown is a SEM image of the positive electrode active layer provided in an example of the present invention. Detailed Implementation

[0015] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0016] A first aspect of the present invention provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode active layer located on one or both sides of the positive electrode current collector; the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprising lithium iron phosphate particles, the particle size Dv50 of the lithium iron phosphate particles being 5μm-15μm (e.g., 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm); the lithium iron phosphate particles of the positive electrode active material are secondary spherical particles, and the particle size Dv50 of the lithium iron phosphate particles is within 5μm when measured using a Malvern laser particle size analyzer. Within the -15μm particle size range, lithium iron phosphate particles have a moderate specific surface area and better particle dispersion, resulting in good slurry flowability during electrode preparation. Therefore, these lithium iron phosphate particles exhibit excellent processing performance. Furthermore, the secondary spherical particles within this particle size range possess high mechanical strength and shorten the diffusion path of lithium ions in the solid phase, ensuring that the electrolyte can fully wet the pores inside the secondary spherical particles, providing ample lithium ion transport channels to meet the battery's rate charge and discharge requirements. Lithium iron phosphate particles within this particle size range can also achieve graded stacking, resulting in higher compaction density for the electrode. The secondary lithium iron phosphate particles are composed of multiple primary particles. Each primary particle has a carbon layer on its surface, and the primary particles are interconnected through conductive carbon within the carbon layer to form the secondary lithium iron phosphate particles. This facilitates ion diffusion within the particles. The particle size of the primary particles ranges from 0.2 μm to 1.5 μm (e.g., 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm). The primary particles, comprising a first particle, a second particle, and a third particle, have a particle size of 200nm-400nm (e.g., 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 1.3μm, 1.4μm, or 1.5μm). The second particle has a particle size of 401nm-800nm ​​(401nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm, 600nm, 620nm, 640nm, 660nm, 680nm, 700nm, 720nm, 740nm, 760nm, 780nm or 800nm), and the particle size of the second particle is 380nm, 390nm or 400nm. The particle size of the three particles is 801nm-1500nm (e.g., 801nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm or 1500nm), and the ratio of the first particle, the second particle and the third particle is (5-8):(2-4):(0.1-1), for example 5:4:1, 6:3:1, 7:2:1, 7.9:2:0.1, 6:3.9:0.1 or 7:2.9:0.1.Several lithium iron phosphate (LFP) particles were cut using an argon-ion milling machine, and their cross-sectional electron microscopy (TEM) analyses were performed. One particle cross-section was randomly selected for a single particle size analysis. Particles with a size range of 200 nm-400 nm were designated as the first type, particles with a size range of 401 nm-800 nm as the second type, and particles with a size range of 801 nm-1500 nm as the third type. The proportions of the three types of particles were calculated. However, the proportion of primary particles within each LFP particle was not entirely consistent, exhibiting several possible ratios. Ten LFP particles were randomly selected, and the number of each type of particle was counted, and the proportions were calculated. The results are distributed in the range (5-8). Within the range of (2-4):(0.1-1), this ratio can be used as the ratio of the number of the first, second, and third particles of all lithium iron phosphate particles in the active material; furthermore, randomly select 10 of each of the first, second, and third particles from one lithium iron phosphate particle, measure their particle size and take the average value to obtain the average particle size of the first, second, and third particles in the lithium iron phosphate particle. Finally, randomly select 10 lithium iron phosphate particles and obtain the average particle size of the three particles using the same method as described above, and then take the average of the 10 average particle sizes, which can be used as the particle size range of the three particles in all lithium iron phosphate particles in the active material. The ratio of the number of primary particles in different particle size ranges within this range enables the lithium iron phosphate active material to have the highest packing density (the ratio of the volume of a solid sphere to the volume per unit volume), thus resulting in a high compaction density. Furthermore, the larger particles (i.e., the third particles) within this ratio range can act as a skeletal support for compaction, improving vibration compaction. The medium-sized particles (i.e., the second particles) serve to support the particles of different sizes, reducing the polarization during the charging and discharging process of the material. The smaller particles (i.e., the first particles) within this ratio range can fill the gaps and improve the material dynamics, thereby achieving an efficient balance between compaction density and dynamic performance.

[0017] The first, second, and third particles of specific sizes are combined in a specific ratio. The high proportion of small-sized first particles can fully fill the gaps between particles, increasing the material's packing density and thus achieving a high compaction density. At the same time, the high proportion of small-sized first particles shortens the solid-phase diffusion path of lithium ions in the lithium iron phosphate active particles, thereby improving the battery's kinetic and rate performance, and simultaneously increasing the electrode's compaction density. The medium-sized second particles support the larger and smaller particles, effectively reducing polarization during charging and discharging, further improving the battery's kinetic performance. A small number of large-sized third particles form a stable compaction framework, increasing the material's tap density and further enhancing the electrode's compaction potential. This ratio combination allows the secondary particles to form a reasonable porous structure, enabling full electrolyte wetting and solving the problem of obstructed ion and electron transport in electrodes under traditional high compaction conditions. This allows the electrode to maintain excellent fast-charging kinetic performance while achieving high compaction density and contributing to increased battery energy density.

[0018] In one specific embodiment, the particle size distribution width (Dv90-Dv10) / Dv50 of the secondary lithium iron phosphate particles is 1-3, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 2.9, or 3. This distribution width ensures that the particle size distribution uniformity of the secondary lithium iron phosphate particles is within the optimal range, avoiding the problems of uneven particle packing voids caused by excessively wide particle sizes and insufficient packing density caused by excessively narrow particle sizes. This ensures the tight packing of the secondary particles, laying the structural foundation for high-pressure compaction of the electrode, and also forms continuous and uniform pore channels, ensuring sufficient wetting of the electrolyte and smooth transport of lithium ions, avoiding local dynamic dead zones caused by disordered particle size distribution, and increasing material concentration polarization.

[0019] In one specific embodiment, the sphericity of the lithium iron phosphate particles is 0.8-1, for example, 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 1. For the positive electrode active material, lithium iron phosphate particles, when fully dispersed, under electron microscopy, the sphericity of a single particle is between 0.8 and 1. The testing method involves magnifying the electron microscope to 2Kx, identifying single spherical secondary particles, saving the image, and using graphics software such as ImageJ to manually or automatically outline and calculate the area of ​​the spherical particle. The formula for calculating the sphericity is... High sphericity secondary particles can significantly reduce the frictional resistance between particles, making it easier to achieve close packing during electrode compaction and effectively improving the overall compaction density of the electrode. At the same time, the uniform surface curvature of the spherical structure can reduce excessive local contact between the electrolyte and the particles, reduce the probability of side reactions, and the uniform spherical structure can form a regular pore network, further optimizing the ion diffusion path and improving the electrode kinetic performance.

[0020] In one specific embodiment, the mechanical strength Cs of the secondary lithium iron phosphate particles is greater than 40 MPa. The mechanical strength of the secondary lithium iron phosphate particle agglomerates can be obtained using a mechanical strength tester by gradually applying pressure and measuring the pressure intensity at which the particles break. High mechanical strength secondary particles can withstand the extrusion pressure during high-pressure compaction of the electrode and the volumetric stress caused by lithium intercalation / deintercalation during battery cycling, preventing particle breakage. This maintains the integrity of the internal pore structure and conductive carbon network of the secondary particles, ensuring the stability of ion transport during long-term cycling and achieving high-pressure cycling performance.

[0021] In one specific embodiment, the ratio of the D peak to the G peak (Id / Ig) of the lithium iron phosphate particles in the Raman spectrum is 0.85-0.95, for example, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, or 0.95. Lithium iron phosphate particles have superior electronic conductivity. The ratio of the D peak to the G peak (Id / Ig) in the Raman spectrum can be obtained by spot scanning the positive electrode active material using a Raman spectrometer. Id / Ig is related to the graphitization degree of the carbon material. The D peak (approximately 1350 cm⁻¹)... -1 The D peak reflects the defects and disordered structure in the material. The higher the defect density, the greater the intensity of the D peak and the greater the intensity of the G peak (approximately 1580 cm⁻¹). -1 Then it corresponds to SP. 2 The higher the intensity of the G peak in the ordered vibration of hybrid carbon, the better the crystallinity of the material. The Id / Ig ratio usually reflects the graphitization degree of carbon materials. The smaller the Id / Ig ratio, the fewer defects in the material, the higher the graphitization degree, and the better the conductivity of the carbon material. The Id / Ig ratio of this lithium iron phosphate particle is in the range of 0.85-0.95, which corresponds to the optimal range of graphitization degree of carbon material. This ensures that the carbon layer has sufficient defect structure to achieve electrolyte wetting and lithium ion transport, while also having good crystallinity to improve electronic conductivity, thus significantly improving the electrode dynamics performance.

[0022] In this invention, the radius of the secondary lithium iron phosphate particle is R. The region enclosed by the center point of the secondary lithium iron phosphate particle as the center of a sphere, and a radius of 1 / 2R, is designated as the first region. The region enclosed by radii from 1 / 2R to R is designated as the second region. The distribution of the primary particles within the secondary lithium iron phosphate particle includes at least one of the following three: In one specific embodiment, such as... Figure 1 As shown, the first region includes the first particle and the second particle, and the second region includes the third particle. The ratio of the number of primary particles in the first region to the number of primary particles in the second region is (8-9):(1-2), for example, 8:2 or 9:1. This distribution, where the second region consists of large particles, reduces the surface area for side reactions with the electrolyte, while the first region consists of small to medium-sized particles with a higher specific surface area, which is beneficial for internal ion diffusion and transport. In subsequent embodiments, this distribution is referred to as S1.

[0023] In one specific implementation, such as Figure 2 As shown, the first region includes the second particle and the third particle, the second region includes the first particle, and the ratio of the number of primary particles in the first region to the number of primary particles in the second region is (2-5):(5-8), for example, 2:8, 3:7, 4:6, or 5:5. This particle distribution, with medium to large particles in the first region, makes it easier to stabilize the particle structure and avoid particle collapse during high-pressure compaction and cycling. The second region contains small particles, which can further improve the material's lithium insertion / extraction rate and significantly optimize the fast-charging kinetics of the electrode. In subsequent embodiments, this distribution is referred to as S2.

[0024] In one specific implementation, such as Figure 3 As shown, the first region includes the first particle, the second particle, and the third particle, and the second region includes the first particle, the second particle, and the third particle. The ratio of the number of primary particles in the first region to the number of primary particles in the second region is (0.8-1.2):(0.8-1.2). The uniform and random distribution of the primary particles makes the pore structure and conductive network inside the secondary particles more uniform, with no obvious dead zones for ion / electron transport, enabling rapid diffusion of lithium ions throughout the particle. At the same time, the uniform particle distribution allows the compaction stress and cyclic volume stress to be evenly dispersed inside the particle, avoiding particle cracking caused by local stress concentration, thus balancing the high compaction and kinetic stability of the electrode. In subsequent embodiments, this distribution is referred to as S3.

[0025] The method for observing the distribution of primary particles within lithium iron phosphate particles is as follows: The cathode sheet is cut into sections, and the cross-sectional sample is observed under a scanning electron microscope at 5Kx magnification. A first region and a second region are divided with the center point of the particle cross-section as the center and half the cross-sectional radius as the boundary. The total number of primary particles (first, second, and third particles) in each region is counted. The ratio of the total number of primary particles in the first region to the total number of primary particles in the second region is calculated. This ratio indicates the distribution of primary particles within a given lithium iron phosphate particle. When the ratio is in the range of (8-9):(1-2), the lithium iron phosphate particles are small and medium-sized particles in the middle and large particles on the outside. When the ratio of the number of primary particles in the first region to the number of primary particles in the second region is in the range of (2-5):(5-8), the lithium iron phosphate particles are large and medium-sized particles in the middle and small particles on the outside. When the ratio of the number of primary particles in the first region to the number of primary particles in the second region is in the range of (0.8-1.2):(0.8-1.2), the lithium iron phosphate particles are in a state of uniform distribution of primary particles.

[0026] In one specific embodiment, the distance between the primary particles within the secondary lithium iron phosphate particle is 2nm-10nm, for example, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, or 10nm. This spacing provides optimal channel space for lithium-ion transport and electrolyte wetting, avoiding both insufficient electrolyte wetting and obstructed lithium-ion transport due to excessively small spacing, and insufficient packing density and compaction due to excessively large spacing. The positive electrode sheet is cross-sectioned, and the resulting cross-sectional sample is placed under a scanning electron microscope at magnification of 30Kx or higher to observe the internal structure of the particles. Several unobstructed, clearly defined primary particle gap regions are selected, and the vertical distance between the edges of the primary particles is measured using ImageJ image analysis software. At least 50 sets of distances between primary particles are randomly tested, and the average value is calculated, which is the distance between the primary particles within the secondary lithium iron phosphate particle.

[0027] In one specific embodiment, the surface of the secondary lithium iron phosphate particles is provided with a Li-BPO coating layer, which includes Li and boron phosphate (i.e., the Li-BPO coating layer contains lithium-doped boron phosphate, or it can be understood as a composite material of Li and boron phosphate). The thickness of the Li-BPO coating layer is 3nm-10nm, for example, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, or 10nm. The thickness of the Li-BPO coating layer can also be obtained by cross-sectional cutting of the particles using an argon ion mill, and then testing the cross-sectional sample under a transmission electron microscope.

[0028] In one specific embodiment, the vertical distance from the edge of the primary particle closest to the Li-BPO coating layer to the edge of the Li-BPO coating layer is 2nm-9nm. This refers to the vertical distance between the edge of the coating layer through which the extension line connecting the edge of the primary particle closest to the coating layer and the center of the primary particle passes. The edge of the Li-BPO coating layer refers to the edge away from the primary particle. The length of this distance is between 2nm and 9nm.

[0029] The Li-BPO coating further stabilizes the spherical structure, reduces electrolyte erosion of the active material, decreases iron dissolution, and improves high-temperature storage and cycle life. The moderate thickness of the 3-10nm Li-BPO coating allows for the formation of a dense protective film on the secondary particle surface, effectively preventing direct contact between the electrolyte and the lithium iron phosphate active material, reducing iron ion dissolution rate and electrolyte oxidation decomposition. However, an excessively thick coating does not hinder lithium ion insertion / extraction and transport. Furthermore, the vertical distance from the edge of the primary particle closest to the Li-BPO coating to the edge of the Li-BPO coating surface is further set within the range of 2nm-9nm. This allows the primary particles at the edge to intercalate with the coating, resulting in a tighter coating that is less prone to detachment during high-temperature storage and cycling, further extending the battery's storage life and cycle stability.

[0030] In one specific implementation, such as Figure 4 As shown, the positive electrode active material also includes primary lithium iron phosphate particles, and the weight ratio of the secondary lithium iron phosphate particles to the primary lithium iron phosphate particles is (1-3):(7-9), for example, 1:9, 2:8, or 3:7. To further improve compaction, the positive electrode active material can be composed of a mixture of the aforementioned secondary lithium iron phosphate particles and primary lithium iron phosphate particles. The electrode slices are prepared using an argon ion mill, and SEM analysis is performed at a magnification of 5K. Figure 5 As shown, the positive electrode active material can be identified as including lithium iron phosphate particles (LFP) and lithium iron phosphate particles (LFP). When the active materials of this invention are mixed in this weight ratio, the compaction density of the electrode will not decrease but will be further increased. While maintaining the existing compaction density, it exhibits a rich porosity distribution, which further enhances the kinetic performance of the electrode.

[0031] In one specific embodiment, the particle size Dv50 of the lithium iron phosphate particles is 0.5 μm-2 μm, for example, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm. The particle size Dv50 of the lithium iron phosphate particles can also be obtained by measuring a Malvern laser particle size analyzer.

[0032] In one specific embodiment, the compacted density of the lithium iron phosphate particles is 2.6 g / cm³. 3 -2.7g / cm 3 For example, 2.6 g / cm³ 3 2.61 g / cm 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 2.66 g / cm 3 2.67 g / cm 3 2.68g / cm 3 2.69 g / cm 3 Or 2.7g / cm 3 The compacted density of lithium iron phosphate particles can be obtained by testing with a compaction density meter.

[0033] In one specific embodiment, the resistivity of the primary lithium iron phosphate particles is 1Ω.cm-5Ω.cm, for example, 1Ω.cm, 1.5Ω.cm, 2Ω.cm, 2.5Ω.cm, 3Ω.cm, 3.5Ω.cm, 4Ω.cm, 4.5Ω.cm or 5Ω.cm.

[0034] In one specific embodiment, the compacted density of the lithium iron phosphate particles is 2.5 g / cm³. 3 -2.6g / cm 3 For example, 2.5g / cm³ 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 Or 2.6g / cm 3The compacted powder density of primary lithium iron phosphate particles and the compacted powder density of secondary lithium iron phosphate particles can be obtained by testing with a compaction density meter.

[0035] In one specific embodiment, the powder resistivity of the secondary lithium iron phosphate particles is 5 Ω·cm to 30 Ω·cm, for example, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 12 Ω·cm, 14 Ω·cm, 16 Ω·cm, 18 Ω·cm, 20 Ω·cm, 22 Ω·cm, 24 Ω·cm, 26 Ω·cm, 28 Ω·cm, or 30 Ω·cm. The powder resistivity of the primary and secondary lithium iron phosphate particles can be measured using a four-probe powder resistivity meter, gradually applying pressure and taking the value at 50.93 MPa.

[0036] The small particle size and high-compaction characteristics of primary lithium iron phosphate (LFP) particles provide the foundation for high-compaction electrodes, while their low resistivity ensures the basic electronic conductivity of the electrodes, solving the problem of relatively high resistivity in secondary lithium iron phosphate (LFP) particles. Mixing primary and secondary lithium iron phosphate particles further achieves a balance between high-compaction and excellent kinetic performance.

[0037] In one specific embodiment, the positive electrode active material in the positive electrode active layer has a mass content of 95%-98.5%, for example, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, or 98.5%. The positive electrode active layer also includes a positive electrode binder and a positive electrode conductive agent. The positive electrode binder has a mass content of 1%-3%, for example, 1%, 1.5%, 2%, 2.5%, or 3%. The positive electrode conductive agent has a mass content of 1%-3%, for example, 1%, 1.5%, 2%, 2.5%, or 3%.

[0038] In one specific embodiment, the positive electrode binder includes at least one of a mixture of polyvinylidene fluoride (PVDF), polybenzimidazole (PBI), polyimide (PI), polyacrylic acid (PAA), polyamide-imide (PAI), polyether-imide (PEI), polyvinylidene fluoride (PVDF), and polyimide (PI).

[0039] In one specific embodiment, the positive electrode conductive agent includes at least one selected from conductive carbon black (SP), carbon nanotubes (CNTs), graphene, and graphite. In another specific embodiment, the positive electrode conductive agent includes a combined conductive agent of conductive carbon black and carbon nanotubes.

[0040] In one specific embodiment, the compaction density of the positive electrode sheet is 2.65 g / cm³. 3 -2.85g / cm 3For example, 2.65 g / cm³ 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 Or 2.85g / cm 3 .

[0041] In one specific embodiment, the positive electrode has a resistivity of 4 Ω·cm to 15 Ω·cm at 26 MPa, for example, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 11 Ω·cm, 12 Ω·cm, 13 Ω·cm, 14 Ω·cm, or 15 Ω·cm. The resulting positive electrode, when tested with an electrode resistivity meter, has a resistivity of 4-15 Ω·cm at 26 MPa.

[0042] A second aspect of the present invention provides a battery comprising the positive electrode, negative electrode, separator, and electrolyte described in the first aspect of the present invention.

[0043] In one specific embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating located on one or both sides of the negative electrode current collector. The negative electrode current collector is a copper foil or a composite copper foil. The negative electrode coating includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0044] In one specific embodiment, the negative electrode conductive agent includes at least one selected from graphite, carbon black, graphene, carbon nanofibers, and carbon nanotubes. In a preferred embodiment, the negative electrode conductive agent includes carbon black.

[0045] In one specific embodiment, the negative electrode binder includes at least one selected from styrene-butadiene rubber, styrene-acrylic emulsion, polyacrylic binder, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose. In a preferred embodiment, the negative electrode binder includes lithium carboxymethyl cellulose and lithium polyacrylate.

[0046] In one specific embodiment, the negative electrode active material includes at least one selected from graphite, silicon, silicon suboxide, hard carbon, soft carbon, and lithium titanate. In a preferred embodiment, the negative electrode active material includes graphite.

[0047] In one specific embodiment, the separator can be any material suitable for secondary battery separators in the art, such as, but not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0048] In one specific embodiment, the electrolyte includes a high-viscosity solvent, which includes at least one selected from ethylene carbonate (EC), propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and propyl propionate. The high-viscosity solvent in the system ensures that the electrolyte possesses a sufficient dielectric constant to promote lithium salt dissociation and form a stable interfacial film on the electrode surface, which is beneficial for improving battery cycle performance. In one specific embodiment, the high-viscosity solvent accounts for 15%-40% of the total mass of the electrolyte, for example, 15%, 20%, 25%, 30%, 35%, or 40%.

[0049] In one specific embodiment, the electrolyte includes a low-viscosity solvent, which includes at least one selected from dimethyl carbonate (DMC), ethyl propionate (EP), ethyl acetate (EA), methyl acetate, acetonitrile, and acetone. The low-viscosity solvent accounts for 30%-70% of the total mass of the electrolyte, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. To further optimize kinetic performance, a high proportion of low-viscosity solvent is introduced into the electrolyte, which can significantly reduce the overall viscosity of the electrolyte and the solvation energy barrier of lithium ions, thereby accelerating the migration rate of lithium ions and significantly reducing their desolvation energy at the interface.

[0050] In one specific embodiment, the electrolyte includes other solvents: approximately 30% cyclic carbonates and chain carbonates (EMC, DMC).

[0051] In one specific embodiment, the electrolyte includes a second additive, which includes at least one of fluorobenzene, fluoroether, and silane. To increase the wettability of the electrolyte, a wetting agent is contained in the electrolyte, and the mass content of the second additive is 0.1%-5% based on the total mass of the electrolyte.

[0052] In one specific embodiment, the second additive includes at least one of trifluorobenzene, trifluorotoluene, pentafluorotoluene, 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, tetramethylsilane, tetraethylsilane, and (trifluoromethyl)trimethylsilane.

[0053] The highly electronegative fluorine atoms in fluorobenzene and fluoroethers weaken the intermolecular forces of solvents, reducing the contact angle at the liquid-solid interface; silane compounds can adsorb onto the material surface to form a low-energy layer, further improving spreading ability. Through this synergistic effect, the electrolyte can rapidly and uniformly penetrate the porous electrode, more easily entering the spaces between the positive electrode particles and enhancing the material's kinetic properties.

[0054] In one specific embodiment, the electrolyte includes a first additive, which includes at least one of acetonitrile, propionitrile, and fluoroacetonitrile. The mass content of the first additive is 0.1%-10% based on the total mass of the electrolyte, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0055] The electrolyte additive includes a nitrile-based first additive, acetonitrile, and fluoroacetonitrile, to prevent iron from dissolving to the negative electrode and reacting with it. To prevent lithium dendrites from precipitating at the negative electrode after Fe ions dissolve from the positive electrode, a first additive is added to the electrolyte. The total content of the nitrile is 0.1-10% by mass of the electrolyte. To reduce the viscosity of the electrolyte and improve wettability, the nitrile is a short-chain nitrile, preferably acetonitrile, propionitrile, or fluoroacetonitrile. The added short-chain first additive (such as acetonitrile, propionitrile, or fluoroacetonitrile) has multiple mechanisms of action: on the one hand, its cyano group (-CN) can effectively complex the dissolved Fe through strong coordination. 2+ / 3+ These additives inhibit the migration of Fe ions to the negative electrode, preventing them from damaging the SEI film and catalyzing lithium dendrite growth. On the other hand, nitrile molecules preferentially adsorb onto the surface of the positive electrode material, forming a dynamic protective film that reduces Fe ion dissolution at the source. Simultaneously, these additives significantly reduce electrolyte viscosity, improving its wetting and penetration efficiency on the electrodes and separator, especially the high-compact positive electrode, thereby improving ion transport kinetics and enhancing the battery's cycle stability and safety.

[0056] In one specific embodiment, the electrolyte further includes other additives, including at least one of fluoroethylene carbonate, vinylene carbonate, and vinyl sulfate. The mass content of the other additives is 1%-5% based on the total mass of the electrolyte, for example, 1%, 2%, 3%, 4%, or 5%.

[0057] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0058] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0059] Example 1 (1) Preparation of secondary lithium iron phosphate particle positive electrode active material: Iron phosphate, lithium carbonate, glucose, polyethylene glycol, and titanium dioxide were mixed and ground in a certain proportion. Different sizes of zirconium balls and grinding times were used to obtain different particle sizes. The ground slurry was mixed in this proportion and then demagnetized and filtered. It was then passed through a pressure spray dryer. The atomizing air flow and feeding rate of the pressure spray dryer were adjusted to pelletize and dry the slurry, resulting in a secondary particle agglomerate precursor with a moisture content of <5%. The obtained precursor was then placed in a refractory graphite crucible and sintered at 760°C for 20 hours under an inert gas + reducing atmosphere with an oxygen content of <10ppm. Then, a lithium phosphate and boron phosphate solution was prepared, and the previously obtained particles were placed in the solution and annealed at 350°C for 1 hour. After sieving, demagnetization, and packaging, the secondary lithium iron phosphate particles were obtained. The packaging was carried out in a constant temperature and low humidity room (temperature 25°C, humidity within 15%RH) using vacuum packaging to maintain the finished product moisture content below 1000ppm. (2) Preparation of lithium iron phosphate cathode: The lithium iron phosphate particles obtained in step (1) have a particle size Dv50 of 10.14 μm; the Id / Ig ratio of these particles, obtained by Raman spectroscopy, is 0.91; their powder resistivity is 24.15 Ω·cm; and their powder compaction density is 2.51 g / cm³. 3 Its sphericity is 0.91; its mechanical strength Cs is 104 MPa; the ratio of the number of the first, second and third particles in the secondary lithium iron phosphate particles is 6:3.5:0.5 (12:7:1), and the three sizes of particles are randomly distributed. The ratio of the number of primary particles in the first region to the number of primary particles in the second region is 1:1; the thickness of the Li-BPO coating layer is 4 nm, and the vertical distance from the edge of the primary particle closest to the Li-BPO coating layer to the edge of the Li-BPO coating layer is 3 nm. A positive electrode slurry was prepared based on the positive electrode active material. The slurry consisted of lithium iron phosphate particles (the active material), a positive electrode conductive agent, a positive electrode binder, and a solvent. The active material, lithium iron phosphate particles, accounted for 96.5% of the slurry. The positive electrode conductive agent in the slurry adopted a three-dimensional composite conductive agent system, with a mass ratio of 1.4%. The positive electrode conductive agent was a combination of conductive carbon black and carbon nanotubes, with a carbon black:carbon nanotube addition ratio of 0.8%:0.6%. The positive electrode binder in the slurry was polyvinylidene fluoride (PVDF), with an addition amount of 2.1%. The positive electrode slurry is prepared and mixed separately, then filtered and impurity removed before being fed into the inner cavity of a die head. After the test piece passes the test, continuous coating is performed to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 2.75 g / cm³. 3 The electrode resistance of the positive electrode at 26MPa is 12Ω·cm; (3) Preparation of negative electrode: The negative electrode uses artificial graphite as the negative electrode material, conductive carbon black as the negative electrode conductive agent, sodium carboxymethyl cellulose (CMC) and polyacrylic acid as binders, and deionized water as solvent. After being mixed evenly, the mixture is layered and coated onto the surface of the copper foil current collector. (3) Preparation of electrolyte: The electrolyte is a mixed lithium salt system of LiPF6 and LiTFSi. The electrolyte is composed of EC, DMC, EMC and additives. The corresponding materials are dissolved in a stirred reactor in the following proportions. After stirring for 30 min, the electrolyte is obtained by filtration and demagnetization. The addition amount of each component by mass is 35% EC + 20% EP + 25% DMC + 2% acetonitrile + 1.5% FEC + 1.5% trifluorobenzene + 5% LiFSI + 10% LiPF6.

[0060] (4) Preparation of lithium iron phosphate stacked lithium-ion batteries: The positive and negative electrode sheets are die-cut into the designed shapes. The positive electrode sheets, separator, and negative electrode sheets are stacked alternately in a Z-shaped stacking method. The electrode core tabs are ultrasonically welded, with the positive electrode welded to the aluminum tabs and the negative electrode welded to the copper tabs. Then, they are placed in a shell made of aluminum-plastic film by heat sealing. The stacked core is sealed in the shell by heating. The separator is an 11μm separator of base film + ceramic + adhesive. The stacked lithium-ion battery is made by forming a Blue Electric charging cabinet. After activation at 0.2C, the battery is charged at 0.33C with constant current and constant voltage to 3.8V and discharged at 0.33C to 2.0V.

[0061] Example 2 group This embodiment is based on Embodiment 1, except that the preparation method of the secondary lithium iron phosphate particles is changed, thereby changing the particle size Dv50, as shown in Table 1.

[0062] Comparative Example 1 This comparative example group was carried out in accordance with Example 1, except that the preparation method of the secondary lithium iron phosphate particles was changed, so that the particle size Dv50 was changed, as shown in Table 1.

[0063] Example 3 Group This embodiment is based on Embodiment 1, except that the preparation method of the secondary lithium iron phosphate particles is changed, so that the weight ratio of the first particle, the second particle and the third particle is changed, as shown in Table 1.

[0064] Comparative Example 2 This comparative example group was carried out in accordance with Example 1, except that the preparation method of the secondary lithium iron phosphate particles was changed, so that the weight ratio of the first particle, the second particle and the third particle was changed, as shown in Table 1.

[0065] Example 4 group This embodiment is based on Embodiment 1, except that the preparation method of the secondary lithium iron phosphate particles is changed, so that the ratio of the number of primary particles in the first region to the number of primary particles in the second region of the secondary lithium iron phosphate particles is changed, as shown in Table 1.

[0066] Table 1 Example 5 group This embodiment is based on Embodiment 1, except that the preparation method of the secondary lithium iron phosphate particles is changed, thereby altering the thickness of the Li-BPO coating layer on the surface of the secondary lithium iron phosphate particles. Specifically: Example 5-1: The thickness of the Li-BPO coating layer is 3 nm, and the vertical distance from the edge of the primary particle closest to the Li-BPO coating layer to the edge of the Li-BPO coating layer is 2 nm. In Example 5-2, the thickness of the Li-BPO coating layer is 10 nm, and the vertical distance from the edge of the primary particle closest to the Li-BPO coating layer to the edge of the Li-BPO coating layer is 9 nm.

[0067] Example 6 group Example 6-1 was carried out in accordance with Example 1, except that lithium iron phosphate particles were added to the positive electrode active material during the preparation of the positive electrode sheet. The particle size Dv50 of these lithium iron phosphate particles was 0.89 μm, and the powder compaction density was 2.68 g / cm³. 3 The powder resistivity is 2.14 Ω·cm, and the ratio of secondary lithium iron phosphate particles to primary lithium iron phosphate particles is 3:7. Example 6-2 is the same as Example 6-1, except that the particle size Dv50 of the primary lithium iron phosphate particles is 2 μm, and the ratio of the number of secondary lithium iron phosphate particles to the number of primary lithium iron phosphate particles is 1:9. Example 6-3 is the same as Example 6-1, except that the particle size Dv50 of the primary lithium iron phosphate particles is 1.5 μm, and the ratio of the number of secondary lithium iron phosphate particles to the number of primary lithium iron phosphate particles is 4:6.

[0068] Example 7 group This embodiment is based on Embodiment 1, except that the mass content percentage of the low-viscosity solvent in the electrolyte is changed. Specifically: In Example 7-1, 35% EC + 20% EP + 25% DMC was replaced with 50% EC + 20% EP + 10% DMC, wherein the content of EC was adjusted according to the content of the low-viscosity solvents EP and DMC to ensure that the total mass content percentage of each component was 100%. In Example 7-2, 35%EC+20%EP+25%DMC was replaced with 10%EC+30%EP+40%DMC, wherein the content of EC was adjusted according to the content of the low-viscosity solvents EP and DMC to ensure that the total mass content percentage of each component was 100%.

[0069] Example 8 group This embodiment is based on Embodiment 1, except that the mass content ratio of the first additive and the second additive in the electrolyte is changed. Specifically: In Example 8-1, 2% acetonitrile + 1.5% trifluorobenzene was replaced with 0.1% acetonitrile + 5% trifluorobenzene, wherein the content of EC was adjusted according to the content of acetonitrile and trifluorobenzene to ensure that the total mass content percentage of each component was 100%. In Example 8-2, 2% acetonitrile + 1.5% trifluorobenzene was replaced with 10% acetonitrile + 0.1% trifluorobenzene, wherein the content of EC was adjusted according to the content of acetonitrile and trifluorobenzene to ensure that the total mass content percentage of each component was 100%. In Examples 8-3, 2% acetonitrile + 1.5% trifluorobenzene was replaced with 1.5% trifluorobenzene (without the first additive), wherein the content of EC was adjusted according to the content of acetonitrile and trifluorobenzene to ensure that the total mass content percentage of each component was 100%. In Examples 8-4, 2% acetonitrile + 1.5% trifluorobenzene was replaced with 2% acetonitrile (without adding a second additive), wherein the content of EC was adjusted according to the content of acetonitrile and trifluorobenzene to ensure that the total mass content percentage of each component was 100%.

[0070] Test case The lithium-ion batteries obtained in the above embodiments and comparative examples were subjected to electrochemical performance tests using a Blue Electric charge-discharge test cabinet and the following test methods. The test results are recorded in Table 2: (1) Volumetric energy density of the battery: At 25°C, the lithium-ion batteries provided in the above embodiments and comparative examples were fully charged to the charging limit voltage of 3.8 V at a constant current and constant voltage of 0.33 C, with a cutoff current of 0.05 C. After resting for 5 minutes, they were then discharged at a constant current of 0.33 C to the discharge termination voltage of 2.0 V. The capacity of this discharged battery was recorded as the battery capacity. The voltage platform can be used to obtain the energy of the battery; then the volume of the battery can be calculated based on its length, width and height. The volumetric energy density of the battery is the battery energy / battery volume, with the unit being Wh / L.

[0071] (2) Capacity retention rate after 30 days of storage at 60℃: First, the battery obtained above was charged and discharged at room temperature (25℃). It was charged to 3.8V at 0.5C, then charged at constant voltage to the cutoff current of 0.05C, and left to stand for 5 minutes. Then, it was discharged at constant current of 0.5C to the discharge termination voltage of 2.0V to obtain the initial discharge capacity C0 of the material. The battery was then charged at constant current of 0.5C to 3.8V, and then charged at constant voltage to the cutoff current of 0.05C. It was then placed in a constant temperature room at 60℃ for 30 days (30D). After that, the battery was taken out and discharged at room temperature. It was discharged at 0.5C to a capacity of 2.0V. The ratio of the discharge capacity to the initial discharge capacity C0 was the discharge capacity retention rate (%) after 30D storage at 60℃.

[0072] (3) 5C constant current charge ratio: The battery obtained above was subjected to 3T of charge and discharge at room temperature (25℃). The discharge capacity of the 3rd discharge was defined as C0. The battery was discharged at 0.33C to the lower limit voltage of 2.0V, and then charged at a constant current and constant voltage rate of 5C0 to 3.8V. Then, it was charged at a constant voltage rate to the cutoff current of 0.05C. The capacity charged in the constant current stage and the capacity charged in the constant voltage stage were recorded. The constant current stage charge capacity / (constant current stage charge capacity + constant voltage stage charge capacity) was calculated as the 5C constant current charge ratio (%) of the battery.

[0073] Table 2 This invention achieves a highly efficient balance between compaction density and kinetic performance by limiting the particle size range of secondary lithium iron phosphate particles and the composition and ratio of primary particles. This quantitative combination allows the secondary particles to form a reasonable pore structure, enabling full electrolyte wetting. It solves the problem of ion and electron transport obstruction in traditional high-compaction electrodes, allowing the electrodes to maintain excellent fast-charging kinetic performance while possessing high compaction density and contributing to the improvement of battery energy density.

[0074] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active layer located on one or both sides of the positive current collector; the positive active layer includes a positive active material, the positive active material contains lithium iron phosphate particles, and the particle size Dv50 of the lithium iron phosphate particles is 5μm-15μm; The secondary lithium iron phosphate particles are composed of multiple primary particles with a particle size ranging from 0.2 μm to 1.5 μm. The surface of each primary particle is provided with a carbon layer. Each primary particle includes a first particle, a second particle, and a third particle. The first particle has a particle size of 200 nm to 400 nm, the second particle has a particle size of 401 nm to 800 nm, and the third particle has a particle size of 801 nm to 1500 nm. The ratio of the number of the first particle, the second particle, and the third particle is (5-8):(2-4):(0.1-1).

2. The positive electrode sheet according to claim 1, characterized in that, The particle size distribution width (Dv90-Dv10) / Dv50 of the secondary lithium iron phosphate particles is 1-3; And / or, the sphericity of the secondary lithium iron phosphate particles is 0.8-1; And / or, the mechanical strength Cs of the secondary lithium iron phosphate particles is greater than 40 MPa; And / or, the ratio of the D peak to the G peak (Id / Ig) of the secondary lithium iron phosphate particles in the Raman spectrum is 0.85-0.

95.

3. The positive electrode sheet according to claim 1, characterized in that, it is provided that... The radius of the secondary lithium iron phosphate particle is R. A region enclosed by a sphere with a radius of 1 / 2R and the center point of the secondary lithium iron phosphate particle as its center is defined as the first region. A region enclosed by radii from 1 / 2R to R is defined as the second region. The distribution of the primary particles within the secondary lithium iron phosphate particle includes at least one of the following three configurations: The first region includes the first particle and the second particle, the second region includes the third particle, and the ratio of the number of primary particles in the first region to the number of primary particles in the second region is (8-9):(1-2). And / or, the first region includes the second particle and the third particle, the second region includes the first particle, and the ratio of the number of primary particles in the first region to the number of primary particles in the second region is (2-5):(5-8); And / or, the first region includes the first particle, the second particle and the third particle, the second region includes the first particle, the second particle and the third particle, and the ratio of the number of primary particles in the first region to the number of primary particles in the second region is (0.8-1.2):(0.8-1.2).

4. The positive electrode sheet according to claim 1, characterized in that, The distance between the primary particles inside the secondary lithium iron phosphate particles is 2nm-10nm; And / or, the surface of the secondary lithium iron phosphate particles is provided with a Li-BPO coating layer, the Li-BPO coating layer includes Li and boron phosphate, and the thickness of the Li-BPO coating layer is 3nm-10nm; Preferably, the vertical distance from the edge of the primary particle closest to the Li-BPO coating layer to the edge of the Li-BPO coating layer is 2nm-9nm.

5. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material also includes primary lithium iron phosphate particles, and the weight ratio of secondary lithium iron phosphate particles to primary lithium iron phosphate particles is (1-3):(7-9). Preferably, the particle size Dv50 of the primary lithium iron phosphate particles is 0.5μm-2μm; Preferably, the compacted density of the primary lithium iron phosphate particles is 2.6 g / cm³. 3 -2.7g / cm 3 ; Preferably, the resistivity of the primary lithium iron phosphate particles is 1 Ω·cm to 5 Ω·cm; Preferably, the compacted density of the lithium iron phosphate particles is 2.5 g / cm³. 3 -2.6g / cm 3 ; Preferably, the resistivity of the lithium iron phosphate particles is 5Ω·cm-30Ω·cm.

6. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active layer contains 95%-98.5% of the positive electrode active material by mass. The positive electrode active layer also includes a positive electrode binder and a positive electrode conductive agent by mass. The positive electrode binder and the positive electrode conductive agent each contain 1%-3% by mass.

7. The positive electrode sheet according to claim 1, characterized in that, The compaction density of the positive electrode is 2.65 g / cm³. 3 -2.85g / cm 3 ; And / or, the electrode resistance of the positive electrode at 26MPa is 4Ω·cm-15Ω·cm.

8. A battery, characterized in that, It comprises the positive electrode, negative electrode, separator, and electrolyte as described in any one of claims 1-7.

9. The battery according to claim 8, characterized in that, The electrolyte includes a low-viscosity solvent, which includes at least one of dimethyl carbonate, ethyl propionate, ethyl acetate, methyl acetate, acetonitrile, and acetone. The low-viscosity solvent accounts for 30%-70% of the total mass of the electrolyte.

10. The battery according to claim 8, characterized in that, The electrolyte includes a first additive, which includes at least one of acetonitrile, propionitrile, and fluoroacetonitrile. The mass content of the first additive is 0.1%-10% based on the total mass of the electrolyte. And / or, the electrolyte includes a second additive, wherein the mass content of the second additive is 0.1%-5% based on the total mass of the electrolyte, and the second additive includes at least one of fluorobenzene, fluoroether and silane.

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