A positive electrode material, a positive electrode sheet, and a battery

Abstract

The application provides a positive electrode material, a positive electrode sheet and a battery, the positive electrode material comprising a lithium iron phosphate material, the lithium iron phosphate material comprising first particles and second particles, and a particle size distribution curve of the positive electrode material comprising: a first peak corresponding to the first particles and a second peak corresponding to the second particles, a particle size corresponding to the first peak being B1, a particle size corresponding to a position of 1 / 2 of a vertical height of the first peak to the horizontal coordinate being B2 and B3, a particle size corresponding to the second peak being C1, a particle size corresponding to a position of 1 / 2 of the vertical height of the first peak to the horizontal coordinate being C2 and C3, C1 / B1=k1, C2 / B2=k2, C3 / B3=k3, |k2-k1|=m, |k3-k2|=n, m and n satisfying: 0.005<=m<=7.97, 0.008<=n<=8.42, and the positive electrode material being capable of reducing the DCR of the battery while improving the energy density of the battery.

Description

Technical Field

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

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy vehicles, energy storage systems, power tools, and consumer electronics due to their excellent thermal stability, long cycle life, and low cost. In the field of new energy vehicles, their energy density and internal resistance directly affect the vehicle's driving range and charging speed.

[0003] The compaction density of lithium iron phosphate cathode active material is one of the key factors affecting battery energy density. In addition, in current technology, traditional lithium iron phosphate materials have inherent defects such as low electronic conductivity and small lithium-ion diffusion coefficient, resulting in high DC internal resistance of the battery and rapid capacity decay at high rates, making it difficult to meet the requirements of electric vehicles for driving range and fast charging speed. Summary of the Invention

[0004] Based on the above problems, the main objective of this invention is to provide a positive electrode material, a positive electrode sheet, and a battery. This positive electrode material can reduce the DC internal resistance of the battery and simultaneously increase its energy density, thus enabling it to meet the requirements of electric vehicles for driving range and fast charging speed.

[0005] In detail, in a first aspect, the present invention provides a cathode material, including lithium iron phosphate material, wherein the lithium iron phosphate material comprises a first particle and a second particle, and the particle size distribution curve of the cathode material has particle size on the x-axis and volume percentage on the y-axis. The particle size distribution curve includes a first peak corresponding to the first particle and a second peak corresponding to the second particle. The particle size corresponding to the vertex of the first peak is B1, where 0.12µm≤B1≤0.8µm, and the vertical height from the vertex of the first peak to the x-axis is... The particle sizes corresponding to the 1 / 2 position are B2 and B3, where B2 is smaller than B3; the particle size corresponding to the apex of the second peak is C1, where 1µm≤C1≤4µm; the particle sizes corresponding to the 1 / 2 position of the vertical height from the apex of the first peak to the horizontal axis are C2 and C3, where C2 is smaller than C3; where C1 / B1=k1, C2 / B2=k2, C3 / B3=k3, |k2-k1|=m, |k3-k2|=n, and m and n satisfy: 0.005≤m≤7.97, 0.008≤n≤8.42.

[0006] In a second aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer comprises the positive electrode material of the first aspect.

[0007] Thirdly, the present invention provides a battery comprising a negative electrode, an electrolyte, and a positive electrode as described above.

[0008] This invention defines the peak shape parameter relationship between the first and second peaks in the particle size distribution curve of the cathode material, ensuring that the first and second peaks satisfy the following conditions: C1 / B1=k1, C2 / B2=k2, C3 / B3=k3, |k2-k1|=m, |k3-k2|=n, 0.005≤m≤7.97, 0.008≤n≤8.42. This achieves precise gradation between the first (small) and second (large) particles, which can improve the electrode compaction density while maintaining unobstructed lithium-ion transport channels between particles, thus enabling the battery to achieve both high energy density and low DC internal resistance. Specifically, k1 represents the ratio of the vertex diameters of the large and small particles, reflecting the degree of difference in the center diameter of the particles; k2 represents the ratio of the right boundary diameters of the two peaks, and k3 represents the ratio of the left boundary diameters of the two peaks. By limiting the ranges of m and n respectively, this invention can ensure that the particle size distribution of the first particle and the particle size distribution of the second particle have good size connection at the vertex diameter and the diameter corresponding to half the height, achieving precise gradation of large and small particles, thereby improving the electrode compaction density while maintaining unobstructed lithium-ion transport channels between particles. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 The particle size distribution curve of the positive electrode active material provided in a specific embodiment of the present invention is shown. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0012] This invention reveals that the particle size distribution of lithium iron phosphate (LFP) particles has a decisive influence on their electrochemical performance. To simultaneously meet the requirements of high energy density and low DC internal resistance in lithium-ion batteries, this invention further investigates and finds that using a single particle size distribution or simple bimodal gradation is insufficient to achieve both low DC internal resistance and high energy density. This is because: while small particles are beneficial for shortening the lithium-ion diffusion path, they are prone to breakage under high compaction density, leading to electrode structure damage and deteriorated interfacial contact, thus limiting further improvements in electrode compaction density; while large particles, although possessing better structural stability, have low particle packing efficiency and large gaps between particles, making it impossible to achieve ideal particle gradation, which also restricts the improvement of electrode compaction density. Therefore, there is an urgent need to develop a particle size distribution scheme that can achieve synergistic gradation of large and small particles, balancing high compaction density and unobstructed ion channels, to meet the dual requirements of high energy density and low DC internal resistance in batteries.

[0013] To address the above problems, the present invention provides the following technical solution:

[0014] In a first aspect, the present invention provides a cathode material, comprising lithium iron phosphate material, the lithium iron phosphate material comprising a first particle and a second particle, wherein the particle size distribution curve of the cathode material has particle size on the x-axis (µm) and volume percentage on the y-axis (%). The particle size distribution curve includes a first peak corresponding to the first particle and a second peak corresponding to the second particle. The particle size corresponding to the vertex of the first peak is B1, where 0.12µm ≤ B1 ≤ 0.8µm, and the vertical height from the vertex of the first peak to the x-axis is 1. The particle sizes corresponding to the 1 / 2 position are B2 and B3, with B2 being smaller than B3; the particle size corresponding to the apex of the second peak is C1, where 1µm ≤ C1 ≤ 4µm; the particle sizes corresponding to the 1 / 2 position of the vertical height from the apex of the first peak to the horizontal axis are C2 and C3, with C2 being smaller than C3. Where C1 / B1 = k1, C2 / B2 = k2, C3 / B3 = k3, |k2-k1| = m, |k3-k2| = n, and m and n satisfy: 0.005 ≤ m ≤ 7.97, 0.008 ≤ n ≤ 8.42.

[0015] The cathode material provided by this invention can significantly reduce the DC internal resistance of the battery while ensuring high compaction of the electrode, thereby contributing to the synergistic improvement of battery energy density and rate performance. The main reason for this is that the lithium iron phosphate material of this invention includes a first particle (small particle) and a second particle (large particle). The first particle fills the gaps formed by the stacking of the second particle to improve the compaction density and volumetric energy density of the electrode. Furthermore, since the two particles form independent and distinguishable particle size peaks in the particle size distribution curve, this invention, by precisely controlling the matching relationship between the first and second peaks, ensures that the particle size distribution of the first particle and the particle size distribution of the second particle have good dimensional connection at the vertex particle size and the particle size corresponding to half the height. This allows the small particle to be embedded to the maximum extent in the gaps formed by the stacking of the large particle, maximizing the contact area between the small and large particles. This constructs a continuous and efficient electron conduction and ion transport network at the particle scale, significantly reducing the DC internal resistance of the battery while ensuring high compaction, thus contributing to the synergistic improvement of battery energy density and rate performance.

[0016] Furthermore, controlling C1 within the range of 1μm to 4μm not only ensures that the size of the second particle is appropriate, allowing it to serve as the main framework in the electrode, providing stable mechanical support and contributing the main capacity, but also further ensures a more suitable lithium-ion solid-phase diffusion path. This, in turn, maintains the battery's low DC internal resistance while ensuring high compaction of the positive electrode. Controlling B1 within the range of 0.12μm to 0.8μm ensures that the first particle can effectively embed into the micron-level gaps formed by the stacking of the second particle, thereby significantly improving the compaction density of the positive electrode. For example, C1 can be any value from 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, or any range between two of these values. B1 can be any value or a range between any two of the following: 0.12 μm, 0.15 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm.

[0017] It can be understood that the vertical axis of the particle size distribution curve is a volume percentage, which means that the volume of the particle corresponding to that particle size accounts for the percentage of the total volume of all particles.

[0018] In some specific embodiments, the particle size distribution curve of the cathode material is obtained through the following process:

[0019] 1) Place a certain amount of positive electrode material sample on the sample stage and observe it using a scanning electron microscope (SEM); first adjust the magnification to low magnification (5000~10000 times): observe the overall dispersion state of the sample and exclude areas with severe agglomeration; then adjust to high magnification (50000~80000 times): clearly distinguish the particle size differences of different particles, save the SEM image for subsequent statistics.

[0020] 2) Open image analysis software (such as ImageJ) and import the SEM image to be analyzed. Use the diagonal line method to measure the particle size of the particles in the image. Select 5 different non-overlapping regions (to avoid local area bias), and take a clear SEM photo of each region, avoiding edges and agglomeration areas. Ensure that the particles in the photo are independently dispersed and have no obvious overlap. Convert the statistically obtained particle size and quantity proportions into a particle size-volume proportion distribution map. For example, the conversion method may include the following steps: ① For the i-th particle, record its particle size as Di; ② The corresponding volume weight of this particle is: Vi' = Di 3 ; ③ Normalization yields the volume percentage of the particle: Vi = Vi' / ∑Vi'.

[0021] It is understandable that if the sample to be tested is a finished battery, it is necessary to disassemble the battery to obtain the positive electrode material. For example, the battery is discharged at 0.33C to the lower limit voltage of 2.5V, the empty battery is taken out, the positive electrode sheet is disassembled, the positive electrode sheet is soaked in dimethyl carbonate (DMC) solution for 4 hours, the positive electrode sheet is taken out and dried in a vacuum environment, and the powder on the surface of the electrode sheet is scraped off with a ceramic knife to obtain the positive electrode material to be tested.

[0022] Figure 1 The particle size distribution curve of the positive electrode active material provided in a specific embodiment of the present invention is shown.

[0023] For example, m can be any value or a range between any two of 0.005, 0.01, 0.05, 0.10, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 7.00, 7.97, etc.; n can be any value or a range between any two of 0.008, 0.01, 0.05, 0.10, 0.50, 1.00, 2.00, 3.00, 4.00, 5.00, 6.00, 7.00, 8.00, 8.42, etc.

[0024] In some embodiments, m ≤ 6, which further ensures good connection between the second particle and the first particle at the tail end of the high-particle-size distribution, avoiding unfillable voids in the particle accumulation due to distribution gaps, thereby further improving the compaction density of the positive electrode sheet. In some more preferred embodiments, m ≤ 0.5.

[0025] In some embodiments, n ≤ 6.1, which further ensures good connection between the first and second particles at the lower particle size end, avoiding the situation where some particles are between the first and second particles due to the excessively wide distribution of the first particle, and cannot effectively fill the gaps between large particles, thereby further improving the compaction density of the positive electrode sheet. In some more preferred embodiments, n ≤ 0.5.

[0026] m and n also satisfy: |mn|≤0.83.

[0027] Specifically, |mn|≤0.83 can significantly improve the consistency of particle contact while further increasing the compaction density of the positive electrode sheet, thereby significantly reducing the DC internal resistance of the battery while ensuring high energy density. For example, |mn| = any value from 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.83, or any value between two of these.

[0028] In some implementations, the peak value of the ordinate corresponding to B1 is greater than the peak value of the ordinate corresponding to C1.

[0029] In the above implementation, by limiting the peak value of the ordinate corresponding to B1 to be greater than the peak value of the ordinate corresponding to C1, the first particle occupies a dominant position in the particle size distribution, ensuring that the first particle fully fills the gap between the second particles, thereby improving the electrode compaction density.

[0030] In some implementations, the ratio of the peak value of the ordinate corresponding to B1 to the peak value of the ordinate corresponding to C1 is 0.33-3.

[0031] In the above implementation, the ratio of the peak value of the ordinate corresponding to B1 to the peak value of the ordinate corresponding to C1 is controlled within the range of 0.33-3. This ensures that the first particle fully fills the gap between the second particle and increases the electrode compaction density, while preventing the second particle from being excessive. This avoids an increase in lithium-ion insertion / extraction paths due to an excessive proportion of the second particle, which would affect the battery's kinetic performance. For example, the ratio of the peak value of the ordinate corresponding to B1 to the peak value of the ordinate corresponding to C1 can be any value from 0.33, 0.5, 0.7, 1.0, 1.2, 1.5, 1.8, 2.0, 2.5, 3.0, or any range between two values.

[0032] To further balance the electrode compaction density and lithium ion insertion / extraction pathways, in some embodiments, the peak value of the ordinate corresponding to C1 is Fc, where 3% ≤ Fc ≤ 9%. Exemplarily, any value or a range between any two of 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc.

[0033] In some implementations, 1.65 ≤ k1 ≤ 19.5.

[0034] In the above embodiments, k1 is controlled within the range of 1.65-19.5, which ensures that the first particle can be effectively embedded in the gaps formed by the stacking of the second particle, while avoiding insufficient filling efficiency due to too small a difference in particle size, or significant differences in lithium-ion transport paths due to too large a difference. For example, k1 can be any value from 1.65, 2.0, 3.0, 5.0, 8.0, 10.0, 12.0, 15.0, 18.0, 19.5, or any range between two of these. In some preferred embodiments, 3 ≤ k1 ≤ 10.

[0035] In some implementations, 1.75 ≤ k2 ≤ 16.75.

[0036] In the above embodiments, k2 is controlled within the range of 1.75-16.75. This ensures that the first particle can effectively embed itself in the gaps formed by the stacking of the second particle, while avoiding insufficient filling efficiency due to too small a difference in particle size, or significant differences in lithium-ion transport paths due to too large a difference. For example, k2 can be any value from 1.75, 2.0, 3.0, 5.0, 8.0, 10.0, 12.0, 14.0, 16.0, 16.75, or any range between two of these values. In some preferred embodiments, 3 ≤ k2 ≤ 10.

[0037] In some implementations, 1.5 ≤ k3 ≤ 15.84.

[0038] In the above embodiments, k3 is controlled within the range of 1.5-15.84. This ensures that the first particle can effectively embed itself in the gaps formed by the stacking of the second particle, while avoiding insufficient filling efficiency due to too small a difference in particle size, or significant differences in lithium-ion transport paths due to too large a difference. For example, k3 can be any value from 1.5, 2.0, 3.0, 5.0, 8.0, 10.0, 12.0, 14.0, 15.0, 15.84, or any range between two of these. In some preferred embodiments, 3 ≤ k3 ≤ 10.

[0039] In some implementations, 0.8µm≤C2≤3.5µm.

[0040] In the above embodiments, controlling C2 within the range of 0.8 μm to 3.5 μm ensures that the smaller particles in the second particle are of suitable size, further guaranteeing the gradation efficiency of large and small particles. This, in turn, further improves the electrode compaction density while ensuring the uniformity of electron and ion transport within the electrode, thereby further reducing the DC internal resistance of the battery. For example, C2 can be any value from 0.8 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, or any range between two such values.

[0041] In some implementations, 1.2µm≤C3≤5µm.

[0042] In the above embodiments, controlling C3 within the range of 1.2 μm to 5 μm ensures that the size of the larger particles in the second particle is appropriate, further guaranteeing the gradation efficiency of particles of different sizes. This, in turn, improves the electrode compaction density while ensuring the uniformity of electron and ion transport within the electrode, thereby further reducing the DC internal resistance of the battery. For example, C3 can be any value from 1.2 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any range between two values.

[0043] In some implementations, 0.1µm ≤ B2 ≤ 0.6µm.

[0044] In the above implementation, the particle size B2 at the left boundary of the first peak's half-width at half-maximum is controlled within the range of 0.1 μm to 0.6 μm. This ensures that there are not too many excessively fine particles (<0.1 μm) in the first particle distribution, avoiding problems such as a surge in specific surface area, increased powder resistance, and difficulty in slurry dispersion caused by an excessively high proportion of ultrafine particles. Simultaneously, it can further optimize particle packing density to further ensure the compaction density of the positive electrode sheet. For example, B2 can be any value or a range between any two of the following: 0.10 μm, 0.12 μm, 0.15 μm, 0.18 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm.

[0045] In some implementations, 0.15µm≤B3≤1.0µm.

[0046] In the above implementation method, the particle size B3 at the right boundary of the first peak's half-width at half-maximum is controlled within the range of 0.15 μm to 1.0 μm, which effectively controls the broadening of the first particle size distribution at the high-particle-size end. This range ensures that too many larger particles with sizes close to the second particle are not mixed into the small particle distribution, allowing the first particle to be more fully embedded in the pores of the second particle packing, thereby further optimizing the filling efficiency of the particle gradation and further improving the compaction density of the positive electrode sheet. For example, B3 can be any value or a range between any two of the following: 0.15 μm, 0.18 μm, 0.20 μm, 0.25 μm, 0.30 μm, 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 1.0 μm.

[0047] In some embodiments, the lithium iron phosphate material further includes a third particle, and the particle size distribution curve of the cathode material includes a third peak corresponding to the third particle; the particle size corresponding to the apex of the third peak is A1, wherein 0.02µm≤A1≤0.075µm.

[0048] In this embodiment, a third particle, which is even finer, is introduced into the lithium iron phosphate material. This third particle further fills the pores remaining after the first and second particles are stacked, maximizing the compaction density of the electrode and thus ensuring the battery's energy density. Simultaneously, the third particle has extremely high surface activity, forming more conductive contact points between particles and reducing electron transport resistance. This further reduces the battery's DC internal resistance while maintaining high compaction and high energy density. For example, A1 can be any value or a range of any combination of 0.02µm, 0.04µm, 0.045µm, 0.05µm, 0.055µm, 0.06µm, 0.065µm, 0.07µm, and 0.075µm.

[0049] In some implementations, the peak value corresponding to the ordinate of the third peak is F. A Where 0.5%≤F A ≤5%.

[0050] Among them, the above implementation methods will F A By controlling the proportion of the third particle within the range of 0.5%-5%, the third particle occupies an appropriate volume percentage in the particle size distribution. This ensures that the third particle can fully fill the pores remaining after the first and second particles are stacked, thereby maximizing the compaction density of the positive electrode sheet and ensuring the energy density of the battery. For example, F AIt can be any value from 0.5%, 1%, 2%, 3%, 4%, 5%, or any range between two.

[0051] In some implementations, the particle sizes corresponding to half the vertical height from the apex of the third peak to the horizontal axis are A2 and A3, where B2 / A2=h2, B3 / A3=h3, B1 / A1=h1, |h2-h1|≤8.2, and / or, |h3-h1|≤10.2.

[0052] The above implementation further ensures that the third particle can fully fill the pores remaining after the first and second particles are stacked, thereby maximizing the compaction density of the positive electrode sheet. Simultaneously, the high surface activity of the third particle allows for the formation of more conductive contact points between particles, reducing electron transport resistance and further lowering the battery's DC internal resistance. For example, |h2-h1| = any value from 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.2, or a range between any two. |h3-h1| = any value from 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.2, etc., or a range between any two. In some preferred embodiments, |h2-h1| ≤ 1.1; in other preferred embodiments, |h3-h1| ≤ 1.21.

[0053] In some implementations, 2.4 ≤ h1 ≤ 17.31. This ratio ensures that the third particle is neither too small to be uniformly dispersed or agglomerated, nor too large to be effectively embedded in the pores remaining after the first and second particles are stacked, thereby maximizing the compaction density of the positive electrode sheet. For example, h1 can be any value from 2.4, 3.0, 5.0, 8.0, 10.0, 12.0, 15.0, 17.31, or a range between any two.

[0054] In some implementations, 3.14 ≤ h2 ≤ 20. h2 reflects the ratio of the left boundary diameter of the first particle's half-width at half-maximum (WHM) to the left boundary diameter of the third particle's WHM. Limiting it to the range of 3.14 to 20 allows the third particle to more effectively fill the pores remaining after the first and second particles are stacked, thereby further increasing the compaction density of the positive electrode sheet. Simultaneously, the third particle, by uniformly filling the spaces between particles, forms more conductive contact points, enabling the battery to achieve high energy density while maintaining lower DC internal resistance. Exemplarily, h2 can be any value from 3.14, 4.0, 5.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 18.0, 20.0, or a range between any two.

[0055] In some implementations, 2.2 ≤ h3 ≤ 14.93. h3 reflects the ratio of the right boundary diameter of the first particle's half-width at half-maximum (WHM) to the right boundary diameter of the third particle's WHM. Limiting it to the range of 2.2 to 14.93 ensures a good transition between the particle size distributions of the first and third particles at the higher particle size end. This prevents the particle size distribution of the third particle from excessively extending towards larger particle sizes, while ensuring that the particle size distribution of the third particle is sufficiently broad to fully fill the residual gaps between the framework particles, thereby further improving the compaction density of the positive electrode sheet. Exemplarily, h3 can be any value from 2.2, 3.0, 5.0, 8.0, 10.0, 12.0, 14.0, 14.93, etc., or a range between any two.

[0056] In some implementations, 0.01μm≤A2≤0.06μm, 0.05μm≤A3≤0.09μm.

[0057] In the above implementation, the left boundary particle size A2 of the third peak's half-width at half-maximum (HWHM) is controlled within the range of 0.01 μm to 0.06 μm, and the right boundary particle size A3 is controlled within the range of 0.05 μm to 0.09 μm. This ensures that the third particles can uniformly and effectively fill the pores remaining after the first and second particles are stacked, maximizing the filling efficiency of the particle gradation. Simultaneously, it avoids introducing mismatched particles due to excessively wide distribution, which could affect the packing density or cause localized stress concentration. For example, A2 can be any value among 0.01 μm, 0.03 μm, 0.04 μm, 0.05 μm, and 0.06 μm, and A3 can be any value among 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, and 0.09 μm, or any range between two of these values.

[0058] In some embodiments, the lithium iron phosphate material further includes a fourth particle, and the particle size distribution curve of the cathode material includes a fourth peak corresponding to the fourth particle; the particle size corresponding to the vertex of the fourth peak is D1, wherein 4μm≤D1≤18μm.

[0059] In this embodiment, a fourth particle is introduced into the lithium iron phosphate material, and the vertex particle size D1 of the fourth peak is limited to the range of 4 μm to 18 μm. This fourth particle serves as an auxiliary filler material to further fill the micron-level macroscopic gaps that may still exist after the second particle is stacked, thereby further improving the compaction density of the positive electrode sheet. For example, D1 can be any value from 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, etc., or any range between two of these values.

[0060] In some implementations, the peak value of the ordinate corresponding to the fourth peak is F. D , where 1%≤F D ≤10%.

[0061] Among them, the above implementation methods will F D By controlling the proportion of the fourth particle within the range of 1%-10%, a low volume percentage is achieved in the particle size distribution. This allows the fourth particle to participate in particle stacking as an auxiliary component, avoiding problems such as reduced inter-particle contact points, prolonged electron transport paths, and increased lithium-ion solid-phase diffusion distances caused by an excessively high proportion of the fourth particle. This further reduces the battery's DC internal resistance while maintaining high energy density. For example, F... D It can be any value from 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between two of them.

[0062] In some implementations, the particle size corresponding to half the vertical height from the apex of the fourth peak to the horizontal axis is D2 and D3, where D2 / C2=S1, D3 / C3=S2, D1 / C1=S, S1-S≤3μm; S2-S≤2.59μm.

[0063] The limitation that S1-S≤3μm and S2-S≤2.59μm indicates that the particle size distribution of the fourth particle is more suitable for the connection with the second particle, which enables the fourth particle to effectively fill the gaps that still exist after the second particle is stacked, and at the same time achieves a smooth particle size transition from the fourth particle to the second particle. This further improves the battery energy density while taking into account its low DC internal resistance. For example, S1-S can be any value or a range between any two of 0μm, 0.01μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, etc.; S2-S can be any value or a range between any two of 0μm, 0.01μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 2.59μm, etc.

[0064] In some embodiments, at least a portion of the surface of the lithium iron phosphate material is provided with a carbon coating layer, the thickness of which is 0.5 nm to 120 nm.

[0065] In the above embodiments, the thickness of the carbon coating layer is controlled within the range of 0.5 nm to 120 nm, which can form a continuous and dense conductive protective layer on the surface of the lithium iron phosphate material. This significantly improves the electron transport efficiency between particles, thereby reducing the powder resistance of the material and further reducing the DC internal resistance of the battery. Simultaneously, the carbon coating layer can effectively isolate the electrolyte from direct contact with the active particles, suppress interfacial side reactions, and ensure the structural stability of the lithium iron phosphate material during long-term cycling, thus contributing to improved battery fast-charging performance and cycle life. For example, the thickness of the carbon coating layer can be any value or a range between 0.5 nm, 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, and 120 nm.

[0066] By way of example and not limitation, the thickness of the carbon coating layer can be directly obtained by TEM testing. In some specific embodiments, the thickness of the carbon coating layer can be obtained by the following process: First, take a small amount of lithium iron phosphate material to be tested and place it in a sample tube, add anhydrous ethanol, and ultrasonically disperse for 40 min to make the sample uniformly dispersed; use a pipette to draw an appropriate amount of dispersion liquid and drop it onto a copper mesh support film, let it air dry naturally, and then place it in a vacuum drying oven to dry it thoroughly. Place the dried copper mesh on the sample stage and transfer it to the transmission electron microscope chamber. Observe the cross-sectional morphology of the particles at high magnification (e.g., 50k~200kx) to clearly identify the interface between the carbon coating layer and the particle matrix. Randomly select at least 5 cross-sectional areas of different particles, measure the thickness of the carbon coating layer, and take the arithmetic mean as the thickness of the carbon coating layer of the sample.

[0067] Lithium iron phosphate (LFP) is a cathode active material with an olivine-type crystal structure. It boasts advantages such as low cost and high safety. The general chemical formula for lithium iron phosphate is LiFe. 1-x M x PO y Q z Where x≤0.1, 3.85≤y≤4, 0≤z≤0.05, and M includes at least one of Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni.

[0068] In some implementations, the specific surface area of ​​the cathode material is 5 m². 2 / g-40 m 2 / g.

[0069] In the above embodiments, the specific surface area of ​​the cathode material is controlled at 5 m². 2 / g~40 m 2 Within a range of / g, sufficient electrochemical reaction interfaces can be provided on the material surface to ensure rapid exchange of lithium ions between the electrolyte and active particles, thereby guaranteeing the battery's rate performance and fast charging capability. For example, the specific surface area can be 5 m² / g. 2 / g、8 m 2 / g、10 m 2 / g、12m 2 / g、15 m 2 / g、18 m 2 / g、20 m 2 / g、22 m 2 / g、25 m 2 / g、28 m 2 / g、30 m 2 / g、32 m 2 / g、35 m 2 / g、38m 2 / g、40 m 2 Any value in / g or any range between the two.

[0070] In some examples, the specific surface area of ​​the cathode material can be tested through the following process:

[0071] At 25℃, the BET test was performed using a nitrogen adsorption analyzer, referring to the test method in GB / T24533-2019. Specifically, in an environment of 25℃ and 60% humidity, the total mass of the empty small test tube and the stopper was weighed. The sample was immersed in anhydrous ethanol for 4 hours, then removed and dried in an oven at 100℃ for 0.5 hours. The dried sample was removed with tweezers and placed in a sample tube. The total mass of the sample, small test tube, and stopper was weighed again to obtain the mass of the dried sample. The degassing station was turned on, and the small test tube was placed in the degassing station at 100℃. Nitrogen (pure nitrogen) was purged for 30 minutes, cooled for 15 minutes, and then placed on the instrument. The test was performed in an environment of 25℃ and 60% humidity. P / P0, with points in the range of 0.05-0.25, was used as the x-axis, and P / V(P0) was calculated. P) is the Y-axis. Plot the BET equation to obtain a curve and perform linear fitting to obtain a straight line. The slope and intercept are used to calculate the specific surface area of ​​the sample. V is the adsorption amount, P is the adsorption equilibrium pressure, and P0 is the saturated vapor pressure of the adsorbate at the adsorption temperature.

[0072] As an example, and not a limitation, in some implementations, the preparation of lithium iron phosphate materials includes the following processes:

[0073] S1. Preparation methods for the first and second particles:

[0074] ① The first iron phosphate precursor, the second iron phosphate precursor, lithium source, carbon source, optional dopant, and solvent are mixed and dispersed in a certain proportion to obtain slurry 1;

[0075] ② After sand milling slurry 1, slurry 2 with Dv50=200-500nm is obtained;

[0076] ③ Slurry 2 is spray-dried with an inlet air temperature of 180-220℃ and a feed rate of 25-70m. 3 / h; outlet air temperature 80-100℃, after solvent evaporation, raw material with Dv50=20-60µm is obtained;

[0077] ④ The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere, with a sintering temperature of 700-820℃ and a holding time of 6-12h to obtain sintered material;

[0078] ⑤ The sintered material is crushed and deagglomerated at a crushing pressure of 300-500 MPa and a classification frequency of 40-60 Hz to obtain lithium iron phosphate containing the first and second particles;

[0079] In step S1, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate, and lithium acetate; the carbon source includes one or more of glucose, sucrose, citric acid, polyvinyl alcohol, polyethylene glycol, and starch; the dopant includes one or more of Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni compounds; and in lithium iron phosphate, the content of the dopant element is 300-30000 ppm (exemplarily, the content of the dopant element is any value or a range of any two of 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 2000 ppm, 5000 ppm, 10000 ppm, 15000 ppm, 20000 ppm, 25000 ppm, and 30000 ppm); and the solvent includes one or more of water, ethanol, and isopropanol.

[0080] In step ①, the Fe / P ratios of the first and second iron phosphate precursor particles are 0.960-1:0.950-1, respectively.

[0081] The volume percentage and particle size of the first and second particles can be adjusted by adjusting the sintering temperature, time, airflow breaking frequency, and classification frequency.

[0082] For example, the Dv50 of slurry 2 can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm; the inlet air temperature for spray drying can be 180°C, 190°C, 200°C, 210°C, or 220°C, and the feed rate can be 25 m / s. 3 / h, 30m 3 / h, 40 m 3 / h, 50 m 3 / h、60 m 3 / h、70 m 3 / h, the outlet air temperature can be 80℃, 85℃, 90℃, 95℃, 100℃; the Dv50 of the raw material can be 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 50 μm, 60 μm; the high-temperature sintering temperature can be 700℃, 720℃, 750℃, 780℃, 800℃, 820℃, and the isothermal time can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h; the crushing and deagglomeration pressure can be 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, and the grading frequency can be any value or a range between 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, etc.

[0083] S2, Preparation of the third particle:

[0084] ① Mix lithium source, iron source, phosphorus source and solvent in a certain proportion to obtain slurry 3;

[0085] ② Transfer slurry 3 to a hydrothermal reactor and react at 150-250℃ for 6-12 hours to obtain lithium iron phosphate powder;

[0086] ③ Mix lithium iron phosphate powder with carbon source, optional dopant and solvent in a certain proportion to obtain slurry 4;

[0087] ④ The slurry 4 is ground, wherein the grinding speed is 800-1500 rpm, the grinding number is 6-15 times, and the zircon bead size is 0.3-0.8 mm, to obtain slurry 5;

[0088] ⑤ After spray drying, the solvent in slurry 5 is evaporated to obtain raw material;

[0089] ⑥ The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere, with a sintering temperature of 650-750℃ and a holding time of 6-12h to obtain sintered material;

[0090] ⑦ The sintered material is subjected to air jet milling at a pressure of 300-500 MPa and a grading frequency of 40-60 Hz to obtain the third-stage lithium iron phosphate particles.

[0091] In step S2, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate, and lithium acetate; the iron source includes one or more of ferrous oxalate, iron phosphate, iron nitrate, ferrous sulfate, ferric oxide, and iron(II,III) oxide; the phosphorus source includes one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, iron phosphate, and lithium dihydrogen phosphate; the carbon source includes one or more of glucose, sucrose, citric acid, polyvinyl alcohol, polyethylene glycol, and starch; the dopant includes one or more of Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni compounds. In lithium iron phosphate, the content of the dopant element is 300-30000 ppm (exemplarily, the content of the dopant element is 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 2000 ppm, 5000 ppm, 10000 ppm, 15000 ppm, 20000 ppm, 25000 ppm, 30000 ppm). (Any value in ppm or a range of any two of them); solvents include one or more of water, ethanol, and isopropanol.

[0092] The volume percentage and particle size of the third particle can be adjusted by adjusting the hydrothermal reaction temperature, sintering temperature, time, and airflow crushing conditions. For example, increasing the hydrothermal reaction temperature increases the particle size of the third particle, and increasing the high-temperature sintering temperature also increases the particle size of the third particle.

[0093] For example, the hydrothermal reaction temperature can be 150℃, 180℃, 200℃, 220℃, or 250℃, and the time can be 6h, 8h, 9h, 10h, or 12h; the Dv50 of the ground slurry can be 100nm, 150nm, 200nm, 250nm, or 300nm; the inlet air temperature for spray drying can be 180℃, 190℃, 200℃, 210℃, or 220℃, and the feed rate can be 25 m / s. 3 / h、30 m 3 / h, 40 m 3 / h, 50m 3 / h、70 m 3 / h, the outlet air temperature can be 80℃, 85℃, 90℃, 95℃, 100℃; the high-temperature sintering temperature can be 650℃, 680℃, 700℃, 720℃, 750℃, and the constant temperature time can be 6h, 7h, 8h, 9h, 10h, 11h, 12h; the air pressure of airflow pulverization can be 300 MPa, 350 MPa, 400 MPa, 450 MPa, 500 MPa, and the grading frequency can be any value or any range between 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, etc.

[0094] S3, Preparation method of the fourth particle:

[0095] ① The fourth particle of iron phosphate, lithium source, carbon source, optional dopant, and solvent are mixed and dispersed in a certain proportion to obtain slurry 6;

[0096] ② After sand milling slurry 6, slurry 7 with Dv50=100-400nm is obtained;

[0097] ③ After the slurry 7 is sprayed with two fluids or multiple fluids to evaporate the solvent, a raw material with Dv50=4-40µm is obtained;

[0098] ④ The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere, with a sintering temperature of 700-820℃ and a holding time of 6-12h to obtain sintered material;

[0099] ⑤ Vibrate the sintered material through a sieve with a mesh size of 50-500 to remove caking material and obtain the fourth granular lithium iron phosphate.

[0100] In step S3, the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium nitrate, and lithium acetate; the carbon source includes one or more of glucose, sucrose, citric acid, polyvinyl alcohol, polyethylene glycol, and starch; the dopant includes one or more of Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni compounds; and in lithium iron phosphate, the content of the dopant element is 300-30000 ppm (exemplarily, the content of the dopant element is any value or a range of any two of 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 2000 ppm, 5000 ppm, 10000 ppm, 15000 ppm, 20000 ppm, 25000 ppm, and 30000 ppm); and the solvent includes one or more of water, ethanol, and isopropanol.

[0101] In step ①, the Fe / P ratio of the iron phosphate precursor in the fourth particle was 0.960-1.

[0102] The volume percentage and particle size of the fourth particle can be adjusted by the compounding ratio, vibration, and pore size specifications.

[0103] For example, the Dv50 of slurry 7 can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, or 400 nm; the inlet air temperature of spray drying can be 180°C, 190°C, 200°C, 210°C, or 220°C; the feed rate can be 25 m³ / h, 30 m³ / h, 40 m³ / h, 50 m³ / h, 60 m³ / h, or 70 m³ / h; and the outlet air temperature can be 80°C, 85°C, 90°C, 95°C, or 100°C; the Dv50 of raw material can be 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm. μm; the high-temperature sintering temperature can be 700℃, 720℃, 750℃, 780℃, 800℃, or 820℃, and the constant temperature time can be 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, or 12 h; the screen aperture specification of the vibrating screen can be any value or any range between 50 mesh, 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 400 mesh, or 500 mesh.

[0104] In a second aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising the positive electrode material of the first aspect.

[0105] It is understood that the positive electrode active material layer also includes a conductive agent and a binder. For example, the conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, graphene, conductive graphite, etc.; the binder may be selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, polyacrylic acid, polyimide, etc.; the positive electrode current collector may be a conventional positive electrode current collector in the art, such as aluminum foil, specifically aluminum metal, aluminum alloy, etc.

[0106] In some implementations, the sheet resistance of the positive electrode is 0.2Ω-2Ω.

[0107] The above embodiments control the sheet resistance of the positive electrode within the range of 0.2Ω-2Ω, ensuring rapid electron transport within the positive electrode active material layer, reducing ohmic polarization during battery charging and discharging, thereby improving rate performance and fast charging capability. Simultaneously, this sheet resistance range promotes uniform current distribution within the positive electrode, collaboratively ensuring battery cycle stability. For example, the sheet resistance of the positive electrode can be any value or a range between 0.2Ω, 0.3Ω, 0.4Ω, 0.5Ω, 0.6Ω, 0.7Ω, 1.0Ω, 1.2Ω, 1.5Ω, 1.7Ω, and 2.0Ω.

[0108] In some examples, the sheet resistance of the positive electrode can be measured by the following process:

[0109] 1) Pretreatment: Discharge the battery at 0.33C to the lower limit voltage of 2.5V, take out the empty battery, disassemble the positive electrode, soak the positive electrode in dimethyl carbonate (DMC) solution for 4 hours; and air dry.

[0110] 2) Set the test pressure to 0.4 MPa on the resistance meter software and start the four-probe method test. The software will automatically read the resistivity of the positive electrode in Ω·cm.

[0111] In a second aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, and an electrolyte.

[0112] In some embodiments, the electrolyte includes a carboxylic acid ester solvent, which accounts for 15%-40% of the total mass of the electrolyte.

[0113] The above embodiments control the proportion of carboxylic acid ester solvents in the total mass of the electrolyte within the range of 15% to 40%, which can significantly reduce the viscosity of the electrolyte and increase the migration rate of lithium ions in the liquid phase, thereby improving the low-temperature performance and rate performance of the battery. Simultaneously, an appropriate amount of carboxylic acid ester solvent has good interfacial compatibility with the cathode material, helping to reduce the electrode / electrolyte interfacial impedance, further reducing the battery's DC internal resistance and cycle life. For example, the carboxylic acid ester solvent can be ethyl acetate, methyl acetate, etc., and the mass percentage of the carboxylic acid ester solvent can be any value or a range between 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0114] In some examples, the percentage of carboxylic acid ester solvents in the total mass of the electrolyte can be determined by the following process:

[0115] 1) Electrolyte Collection: The secondary battery under test is discharged using a battery charging / discharging device. Discharge conditions: current 0.3C, cutoff voltage 2.5V. After recording the battery number / barcode, the battery is disassembled and the electrolyte collected in a glove box (H2O≤0.1ppm, O2≤0.1ppm). There are three methods for collecting the electrolyte: After removing the battery cover, ① if there is free electrolyte, collect it into a 5mL sample tube using a pipette and seal it with sealing tape to prevent leakage. ② if there is no free electrolyte, a hydraulic press (Beijing Heng'ao Technology Co., Ltd.'s FY-30 hydraulic press) can be used to continuously pressurize until free electrolyte appears. Collect the electrolyte into a sample tube and seal it. ③ Add an appropriate amount of dichloromethane extractant to the battery and record the dichloromethane content. After adding dichloromethane, put the battery into an aluminum-plastic bag and seal it with a heat sealer. Transfer it to an ultrasonic oscillator and oscillate for 12 hours to allow the electrolyte in the electrode to mix thoroughly with the dichloromethane. Then, use a pipette to draw the mixture of dichloromethane and electrolyte into a 5mL sample tube and seal the sample tube with sealing glue.

[0116] 2) The collected electrolyte sample was injected into an Agilent Intuvo 9000 gas chromatograph-mass spectrometer using a microsyringe for testing, obtaining GC-MS chromatograms. Carboxylic acid esters were dissolved in EMC solvent to prepare solutions of different concentrations, and these solutions were injected into the Agilent Intuvo 9000 gas chromatograph-mass spectrometer to obtain standard GC-MS chromatograms. The GC-MS chromatograms of the electrolyte to be tested were compared with the standard GC-MS chromatograms to confirm the presence of corresponding components. The content of each component was then determined based on its peak area in the electrolyte to be tested.

[0117] In some embodiments, the electrolyte also includes carbonate solvents; the carbon chain length of the carbonate solvent is less than or equal to 3.

[0118] The above embodiments limit the carbon chain length of the carbonate solvent to less than or equal to 3 (e.g., dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc.), which can ensure that the electrolyte has a low viscosity and a high dielectric constant, promoting lithium salt dissociation and ion migration. At the same time, short-chain carbonate solvents and carboxylic acid ester solvents have good miscibility, which helps to form a stable interface film, suppress side reactions, thereby synergistically reducing the battery internal resistance and increasing energy density.

[0119] In some embodiments, the mass ratio of carboxylic acid ester solvent to carbonate solvent is 1:1.5-4.

[0120] The above embodiments control the mass ratio of carboxylic acid ester solvent to carbonate solvent within the range of 1:1.5 to 4, which allows the electrolyte to have both low viscosity and high lithium salt dissolving capacity, optimizing the transport kinetics of lithium ions in the liquid phase, while maintaining good interfacial film-forming properties. This avoids interfacial instability due to an excessively high proportion of carboxylic acid ester solvent or increased viscosity due to an excessively high proportion of carbonate solvent, thereby achieving a balance between rate performance and cycle stability. For example, the mass ratio of carboxylic acid ester solvent to carbonate solvent can be any value from 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or any range between two of these values.

[0121] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode material, which includes at least one of graphite and silicon-based materials.

[0122] The anode material can be flexibly selected according to the energy density and rate requirements of the battery. For example, graphite can provide stable cycle performance, while silicon-based materials contribute high specific capacity.

[0123] In some embodiments, the particle size Dv50 of the negative electrode material is 5µm-20µm.

[0124] Controlling the particle size Dv50 of the anode material within the range of 5 μm to 20 μm allows for the formation of an optimized particle packing structure, shortens the lithium-ion diffusion path, and further ensures low internal resistance in the battery. For example, the particle size Dv50 of the anode material can be any value or a range between 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, and 20 μm.

[0125] The particle size Dv50 of the negative electrode material can be measured using a laser particle size distribution measuring instrument (Mastersizer 3000) based on the particle size distribution laser diffraction method (specific steps refer to GB / T19077-2016). The particle size corresponding to the cumulative particle size distribution percentage reaching 50% is Dv50.

[0126] If the sample to be tested is a finished battery, it is necessary to disassemble the battery to obtain the positive electrode material. For example, discharge the battery at 0.33C to the lower limit voltage of 2.5V, take the empty battery, disassemble the positive electrode sheet, soak the positive electrode sheet in dimethyl carbonate (DMC) solution for 4 hours, take out the positive electrode sheet and dry it in a vacuum environment, and scrape the powder on the surface of the electrode sheet with a ceramic knife to obtain the positive electrode material to be tested.

[0127] In some embodiments, the negative electrode material layer further includes a conductive agent, a binder, and a dispersant. These are examples, not limitations. The conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, graphene, etc.; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, sodium polyacrylate, etc.; the dispersant may be at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, sodium dodecyl sulfate, etc.; the negative electrode current collector may be a conventional negative electrode current collector in the art, such as copper foil.

[0128] In some specific embodiments, the preparation of the positive electrode sheet includes the following process: mixing positive electrode active material, conductive agent, binder, and dispersant, adding solvent and continuing mixing to obtain a positive electrode slurry, wherein the mass ratio of positive electrode active material: conductive agent: binder: dispersant is (95-98):(0-1):(0.5-3):(0-0.5); coating the positive electrode slurry onto at least one surface of the positive electrode current collector, drying, rolling, and slitting to obtain the positive electrode sheet. The areal density of the positive electrode sheet is 150 g / m³. 2 ~500 g / m 2 The compacted density is 2 g / cm³ 3 ~3 g / cm 3 .

[0129] In some specific embodiments, the preparation of the negative electrode sheet includes the following process: mixing negative electrode active material, conductive agent, binder, and dispersant, adding solvent and continuing mixing to obtain a negative electrode slurry, wherein the mass ratio of negative electrode active material: conductive agent: binder: dispersant is (95-99):(0.5-2):(0.3-3):(0-0.5); coating the negative electrode slurry onto at least one surface of the negative electrode current collector; drying, rolling, and slitting to obtain the negative electrode sheet. The areal density of the negative electrode sheet is 80 g / m³. 2 ~250g / m 2 The compacted density is 1.4 g / cm³. 3 ~1.8 g / cm 3 .

[0130] In some embodiments, the battery fabrication process includes the following steps:

[0131] A bare cell is obtained by winding or stacking positive electrode sheets, negative electrode sheets, and separators in an orderly manner; the bare cell is placed in an outer packaging shell, dried, injected with electrolyte, and then packaged, left to stand, formed, and calibrated to obtain a lithium-ion battery.

[0132] The outer packaging shell includes aluminum-plastic film, metal shell, etc.; the metal shell specifically includes, but is not limited to, aluminum metal, aluminum alloy metal (aluminum-magnesium alloy, aluminum-manganese alloy, etc.); steel, stainless steel, nickel-plated steel, carbon steel, etc.; titanium metal, titanium alloy, etc.

[0133] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0134] To further understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0135] Example 1

[0136] The cathode material in this embodiment includes lithium iron phosphate, and the preparation of lithium iron phosphate includes the following process:

[0137] 1. The first granule of iron phosphate precursor (Fe / P ratio of 0.97) and the second granule of iron phosphate precursor (Fe / P ratio of 0.96) are mixed at a mass ratio of 1:1 to form a precursor mixture. The precursor mixture, lithium carbonate, sucrose, titanium dioxide, and pure water are mixed at a mass ratio of 1:0.25:0.08:0.005:2.5 to obtain slurry 1.

[0138] 2. The slurry 1 was sand-milled at a speed of 900 rpm for 16 times, with a zircon bead size of 0.4 mm, to obtain slurry 2 with Dv50=400±10nm;

[0139] 3. Slurry 2 is spray-dried with an inlet air temperature of 200℃ and a feed rate of 45m. 3 / h; The outlet air temperature is 90℃, and the raw material is obtained after the solvent is evaporated;

[0140] 4. The raw materials are sintered at high temperature under a nitrogen atmosphere at 720℃ for 7 hours to obtain sintered material.

[0141] 5. The sintered material is crushed and deagglomerated at a crushing pressure of 480 MPa and a classification frequency of 56 Hz to obtain the first and second lithium iron phosphate particles.

[0142] Example 2

[0143] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 20, the sintering temperature in step 4 is 700℃, the constant temperature time is 6h, the pulverizing pressure in step 5 is 500Mpa, and the grading frequency is 60Hz.

[0144] Example 3

[0145] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 13, the sintering temperature in step 4 is 750℃, the constant temperature time is 7h, the pulverizing pressure in step 5 is 460Mpa, and the grading frequency is 45Hz.

[0146] Example 4

[0147] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 760℃, the constant temperature time is 8h, the pulverizing pressure in step 5 is 435Mpa, and the grading frequency is 40Hz.

[0148] Example 5

[0149] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 9, the sintering temperature in step 4 is 790℃, the constant temperature time is 10h, the pulverizing pressure in step 5 is 400Mpa, and the grading frequency is 40Hz.

[0150] Example 6

[0151] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 760℃, the constant temperature time is 8.5h, the pulverizing pressure in step 5 is 430Mpa, and the grading frequency is 42Hz.

[0152] Example 7

[0153] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 815℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 350Mpa, and the grading frequency is 40Hz.

[0154] Example 8

[0155] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 810℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 360Mpa, and the grading frequency is 40Hz.

[0156] Example 9

[0157] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 815℃, the constant temperature time is 12h, the pulverizing pressure in step 5 is 320Mpa, and the grading frequency is 40Hz.

[0158] Example 10

[0159] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 770℃, the constant temperature time is 9h, the pulverizing pressure in step 5 is 420Mpa, and the grading frequency is 40Hz.

[0160] Example 11

[0161] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 760℃, the constant temperature time is 8h, the pulverizing pressure in step 5 is 440Mpa, and the grading frequency is 40Hz.

[0162] Example 12

[0163] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 11, the sintering temperature in step 4 is 775℃, the constant temperature time is 9h, the pulverizing pressure in step 5 is 415Mpa, and the grading frequency is 40Hz.

[0164] Example 13

[0165] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 755℃, the constant temperature time is 8h, the pulverizing pressure in step 5 is 450Mpa, and the grading frequency is 42Hz.

[0166] Example 14

[0167] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 755℃, the constant temperature time is 8h, the pulverizing pressure in step 5 is 440Mpa, and the grading frequency is 42Hz.

[0168] Example 15

[0169] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 7, the sintering temperature in step 4 is 815℃, the constant temperature time is 12h, the pulverizing pressure in step 5 is 370Mpa, and the grading frequency is 45Hz.

[0170] Example 16

[0171] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 6, the sintering temperature in step 4 is 800℃, the constant temperature time is 10.5h, the pulverizing air pressure in step 5 is 370Mpa, and the grading frequency is 40Hz.

[0172] Example 17

[0173] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 6, the sintering temperature in step 4 is 800℃, the constant temperature time is 10.5h, the pulverizing air pressure in step 5 is 375Mpa, and the grading frequency is 40Hz.

[0174] Example 18

[0175] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 2, the sintering temperature in step 4 is 820℃, the constant temperature time is 12h, the pulverizing pressure in step 5 is 300Mpa, and the grading frequency is 40Hz.

[0176] Example 19

[0177] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 7, the sintering temperature in step 4 is 795℃, the constant temperature time is 10h, the pulverizing pressure in step 5 is 395Mpa, and the grading frequency is 40Hz.

[0178] Example 20

[0179] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 3, the sintering temperature in step 4 is 810℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 355Mpa, and the grading frequency is 40Hz.

[0180] Example 21

[0181] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 800℃, the constant temperature time is 10.5h, the pulverizing air pressure in step 5 is 390Mpa, and the grading frequency is 48Hz.

[0182] Example 22

[0183] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 5, the sintering temperature in step 4 is 805℃, the constant temperature time is 10.5h, the pulverizing air pressure in step 5 is 365Mpa, and the grading frequency is 40Hz.

[0184] Example 23

[0185] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 10, the sintering temperature in step 4 is 805℃, the constant temperature time is 11h, the pulverizing pressure in step 5 is 415Mpa, and the grading frequency is 40Hz.

[0186] Example 24

[0187] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 12, the sintering temperature in step 4 is 760℃, the constant temperature time is 8h, the pulverizing pressure in step 5 is 438Mpa, and the grading frequency is 42Hz.

[0188] Example 25

[0189] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 17, the sintering temperature in step 4 is 700℃, the constant temperature time is 6h, the pulverizing pressure in step 5 is 490Mpa, and the grading frequency is 58Hz.

[0190] Example 26

[0191] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 5, the sintering temperature in step 4 is 805℃, the constant temperature time is 10.5h, the pulverizing air pressure in step 5 is 372Mpa, and the grading frequency is 40Hz.

[0192] Example 27

[0193] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 2, the sintering temperature in step 4 is 810℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 355Mpa, and the grading frequency is 40Hz.

[0194] Example 28

[0195] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 15, the sintering temperature in step 4 is 710℃, the constant temperature time is 6.5h, the pulverizing pressure in step 5 is 480Mpa, and the grading frequency is 54Hz.

[0196] Example 29

[0197] The cathode material in this embodiment includes lithium iron phosphate, and the preparation of lithium iron phosphate includes the following process:

[0198] 1. Preparation of the first and second particles:

[0199] 1.1 The first granule of iron phosphate precursor (Fe / P ratio of 0.97) and the second granule of iron phosphate precursor (Fe / P ratio of 0.96) are mixed at a mass ratio of 1:1 to form a precursor mixture. The precursor mixture, lithium carbonate, sucrose, titanium dioxide, and pure water are mixed at a mass ratio of 1:0.25:0.08:0.005:2.5 to obtain slurry 1.

[0200] 1.2. The slurry 1 was sand-milled at a speed of 900 rpm for 13 times, with a zircon bead size of 0.4 mm, to obtain slurry 2 with Dv50=400±10nm;

[0201] 1.3. Slurry 2 is spray-dried with an inlet air temperature of 200℃ and a feed rate of 45m. 3 / h; The outlet air temperature is 90℃, and the raw material is obtained after the solvent is evaporated;

[0202] 1.4 The raw materials are sintered at high temperature under a nitrogen atmosphere at 745℃ for 8 hours to obtain sintered material;

[0203] 1.5 The sintered material is crushed and deagglomerated at a crushing pressure of 480 MPa and a classification frequency of 45 Hz to obtain the first and second lithium iron phosphate particles.

[0204] 2. Preparation of the third particle:

[0205] 2.1. Lithium hydroxide (lithium source), ferrous sulfate (iron source), and phosphoric acid (phosphoric acid source) are mixed in a mass ratio of 1:1:1, and pure water is added and the mixture is continued to be mixed to obtain slurry 3;

[0206] 2.2 Transfer slurry 3 to a hydrothermal reactor and react at 205℃ for 8 hours to obtain lithium iron phosphate powder 1;

[0207] 2.3. Lithium iron phosphate powder 1 is mixed with carbon source (a mixture of glucose and polyethylene glycol in a mass ratio of 2:1) and dopant (tetrabutyl titanate and vanadium pentoxide in a mass ratio of 1:1) in a ratio of 1:0.1:0.03. Water is added as a solvent and the mixture is continued to be mixed to obtain slurry 4.

[0208] 2.4 After grinding, slurry 4 yields slurry 5 with Dv50=200nm;

[0209] 2.5. Slurry 5 is spray-dried with an inlet air temperature of 200℃ and a feed rate of 45m. 3 / h; The outlet air temperature is 90℃. After the solvent evaporates, raw material is obtained.

[0210] 2.6 The raw materials are sintered at high temperature under a nitrogen atmosphere at 700℃ for 10 hours to obtain the sintered material.

[0211] 2.7 The sintered material is subjected to air jet milling at a pressure of 450 MPa and a grading frequency of 48 Hz to obtain the third type of lithium iron phosphate particles.

[0212] 3. Mixing:

[0213] The mixture of the first and second lithium iron phosphate particles and the third lithium iron phosphate particle is mixed, wherein the third lithium iron phosphate particle accounts for 15.14% of the total mass of lithium iron phosphate.

[0214] Example 30

[0215] The process is basically the same as in Example 1, except that: the grinding is repeated twice in step 1.2; the sintering temperature in step 1.4 is 810°C and the holding time is 11.5 h; the pulverizing pressure in step 1.5 is 355 MPa and the grading frequency is 40 Hz; the hydrothermal reactor in step 2.2 reacts at 160°C; the sintering temperature in step 2.6 is 660°C; and the third particle in step 3 contains 12.12% lithium iron phosphate by mass of the total lithium iron phosphate.

[0216] Example 31

[0217] The process is basically the same as in Example 1, except that: the number of grinding cycles in step 1.2 is 16; the sintering temperature in step 1.4 is 710℃ and the isothermal time is 6.5h; the pulverizing pressure in step 1.5 is 485MPa and the grading frequency is 58Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 150℃; the sintering temperature in step 2.6 is 655℃; and the third lithium iron phosphate particle in step 3 accounts for 7.45% of the total lithium iron phosphate mass.

[0218] Example 32

[0219] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 12; the sintering temperature in step 1.4 is 755℃ and the holding time is 8.5h; the pulverizing pressure in step 1.5 is 445MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 250℃; the sintering temperature in step 2.6 is 750℃; and the third particle in step 3 contains 10.45% lithium iron phosphate by mass of the total lithium iron phosphate.

[0220] Example 33

[0221] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 7; the sintering temperature in step 1.4 is 795℃ and the holding time is 10h; the pulverizing pressure in step 1.5 is 400MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 230℃; the sintering temperature in step 2.6 is 725℃; and the third particle of lithium iron phosphate in step 3 accounts for 11.23% of the total mass of lithium iron phosphate.

[0222] Example 34

[0223] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 19; the sintering temperature in step 1.4 is 700℃ and the holding time is 6h; the pulverizing pressure in step 1.5 is 500MPa and the grading frequency is 58Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 200℃; the sintering temperature in step 2.6 is 690℃; and the third particle in step 3 contains 15.34% of the total lithium iron phosphate mass.

[0224] Example 35

[0225] The process is basically the same as in Example 1, except that: the grinding is repeated twice in step 1.2; the sintering temperature in step 1.4 is 820°C and the holding time is 12h; the pulverizing pressure in step 1.5 is 305MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 185°C; the sintering temperature in step 2.6 is 685°C; and the third particle in step 3 contains 9.02% lithium iron phosphate by mass of the total lithium iron phosphate.

[0226] Example 36

[0227] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 8; the sintering temperature in step 1.4 is 790℃ and the holding time is 10h; the pulverizing pressure in step 1.5 is 410MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 170℃; the sintering temperature in step 2.6 is 670℃; and the third particle in step 3 contains 3.67% lithium iron phosphate by mass of the total lithium iron phosphate.

[0228] Example 37

[0229] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 14; the sintering temperature in step 1.4 is 740℃ and the holding time is 7h; the pulverizing pressure in step 1.5 is 460MPa and the grading frequency is 47Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 205℃; the sintering temperature in step 2.6 is 705℃; and the third particle in step 3 contains 19.54% lithium iron phosphate by mass of the total lithium iron phosphate.

[0230] Example 38

[0231] The process is basically the same as in Example 1, with the only differences being: the number of grinding cycles in step 1.2 is 14; the sintering temperature in step 1.4 is 735℃ and the holding time is 7h; the pulverizing pressure in step 1.5 is 475MPa and the grading frequency is 48Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 170℃; the sintering temperature in step 2.6 is 665℃; and the third lithium iron phosphate particle in step 3 accounts for 2.45% of the total lithium iron phosphate mass.

[0232] Example 39

[0233] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 14; the sintering temperature in step 1.4 is 740℃ and the holding time is 7.5h; the pulverizing pressure in step 1.5 is 470MPa and the grading frequency is 45Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 208℃; the sintering temperature in step 2.6 is 705℃; and the third particle of lithium iron phosphate in step 3 accounts for 16.45% of the total mass of lithium iron phosphate.

[0234] Example 40

[0235] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 9; the sintering temperature in step 1.4 is 790℃ and the isothermal time is 9.5h; the pulverizing pressure in step 1.5 is 410Mpa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 155℃; the sintering temperature in step 2.6 is 660℃; and the third lithium iron phosphate particle in step 3 accounts for 1.23% of the total lithium iron phosphate mass.

[0236] Example 41

[0237] The process is basically the same as in Example 1, except that: the number of grinding times in step 1.2 is 13; the sintering temperature in step 1.4 is 745℃ and the holding time is 7.5h; the pulverizing pressure in step 1.5 is 470MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 178℃; the sintering temperature in step 2.6 is 675℃; and the third particle of lithium iron phosphate in step 3 accounts for 1.52% of the total mass of lithium iron phosphate.

[0238] Example 42

[0239] The cathode material in this embodiment includes lithium iron phosphate, and the preparation of lithium iron phosphate includes the following process:

[0240] 1. Preparation of the first and second particles:

[0241] 1.1 The first granule of iron phosphate precursor (Fe / P ratio of 0.97) and the second granule of iron phosphate precursor (Fe / P ratio of 0.96) are mixed at a mass ratio of 1:1 to form a precursor mixture. The precursor mixture, lithium carbonate, sucrose, titanium dioxide, and pure water are mixed at a mass ratio of 1:0.25:0.08:0.005:2.5 to obtain slurry 1.

[0242] 1.2. The slurry 1 was sand-milled at a speed of 900 rpm for 13 times, with a zircon bead size of 0.4 mm, to obtain slurry 2 with Dv50=400±10nm;

[0243] 1.3. Slurry 2 is spray-dried with an inlet air temperature of 200℃ and a feed rate of 45m3 / h; the outlet air temperature is 90℃. After the solvent is evaporated, the raw material is obtained.

[0244] 1.4 The raw materials are sintered at high temperature under a nitrogen atmosphere at a temperature of 785℃ for 9.5 hours to obtain sintered material;

[0245] 1.5 The sintered material is crushed and deagglomerated at a crushing pressure of 410 MPa and a classification frequency of 40 Hz to obtain the first and second lithium iron phosphate particles.

[0246] 2. Preparation of the third particle:

[0247] 2.1. Lithium hydroxide (lithium source), ferrous sulfate (iron source), and phosphoric acid (phosphoric acid source) are mixed in a mass ratio of 1:1:1. Water is added as a solvent and the mixture is continued to be mixed to obtain slurry 3.

[0248] 2.2 Transfer slurry 3 to a hydrothermal reactor and react at 153℃ for 8 hours to obtain lithium iron phosphate powder 1;

[0249] 2.3. Lithium iron phosphate powder 1 is mixed with a carbon source (a mixture of glucose and polyethylene glycol in a mass ratio of 2:1) and a dopant (tetrabutyl titanate and vanadium pentoxide in a mass ratio of 1:1) at a ratio of 1:0.1:0.03. Water is added as a solvent and the mixture is further mixed to obtain slurry 4. The carbon source accounts for 15% of the mass of lithium iron phosphate powder 1.

[0250] 2.4 After grinding, slurry 4 yields slurry 5 with Dv50=200nm;

[0251] 2.5. Slurry 5 is spray-dried with an inlet air temperature of 200℃ and a feed rate of 45m³ / h; the outlet air temperature is 90℃. After the solvent evaporates, raw material is obtained.

[0252] 2.6 The raw materials are sintered at high temperature under a nitrogen atmosphere at 650℃ for 10 hours to obtain the sintered material.

[0253] 2.7 The sintered material is subjected to air jet milling at a pressure of 450 MPa and a grading frequency of 48 Hz to obtain the third type of lithium iron phosphate particles.

[0254] 3. Preparation of the fourth particle:

[0255] 3.1. Provide the fourth particle of ferric phosphate (Fe / P ratio 0.970). Mix ferric phosphate, lithium carbonate, sucrose, titanium dioxide, and pure water in a mass ratio of 1:0.25:0.08:0.005:2.5 to obtain slurry 6.

[0256] 3.2. The slurry 6 was sand-milled at a speed of 1000 rpm for 12 times, with a zircon bead size of 0.4 mm; thus, a slurry 7 with Dv50 = 400 ± 10 µm was obtained.

[0257] 3.3. The slurry 7 is sprayed with a two-fluid or multi-fluid spray at an inlet air temperature of 200℃ and a feed rate of 45m3 / h; the outlet air temperature is 90℃. After the solvent evaporates, the raw material is obtained.

[0258] 3.4 The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere. The sintering temperature is 790℃ and the holding time is 8h to obtain the sintered material.

[0259] 3.5. Vibrate and sieve the sintered material. The vibrating sieve has a mesh size of 500 to remove the caking material and obtain the fourth lithium iron phosphate particle.

[0260] 4. Mixing:

[0261] The mixture of the first and second lithium iron phosphate particles is mixed with the third and fourth lithium iron phosphate particles, wherein the third lithium iron phosphate particles account for 9.45% of the total lithium iron phosphate mass and the fourth lithium iron phosphate particles account for 9.56% of the total lithium iron phosphate mass.

[0262] Example 43

[0263] The process is basically the same as Example 42, with the only differences being: the number of grinding cycles in step 1.2 is 7; the sintering temperature in step 1.4 is 795℃ and the holding time is 10.5h; the pulverizing pressure in step 1.5 is 390MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 165℃; the sintering temperature in step 2.6 is 665℃; the sieve aperture of the vibrating screen in step 3.5 is 400 mesh; and the third lithium iron phosphate particle in step 4 accounts for 8.15% of the total lithium iron phosphate mass, while the fourth lithium iron phosphate particle accounts for 17.65% of the total lithium iron phosphate mass.

[0264] Example 44

[0265] The process is basically the same as Example 42, with the only differences being: the number of grinding cycles in step 1.2 is 6; the sintering temperature in step 1.4 is 800℃ and the holding time is 10.5h; the pulverizing pressure in step 1.5 is 380MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 180℃; the sintering temperature in step 2.6 is 680℃; the sieve aperture of the vibrating screen in step 3.5 is 380 mesh; and the third lithium iron phosphate particle in step 4 accounts for 10.14% of the total lithium iron phosphate mass, while the fourth lithium iron phosphate particle accounts for 22.58% of the total lithium iron phosphate mass.

[0266] Example 45

[0267] The process is basically the same as Example 42, with the only differences being: the number of grinding cycles in step 1.2 is 6; the sintering temperature in step 1.4 is 805℃ and the holding time is 10.5h; the pulverizing pressure in step 1.5 is 370MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 190℃; the sintering temperature in step 2.6 is 685℃; the sieve aperture of the vibrating screen in step 3.5 is 120 mesh; and the third lithium iron phosphate particle in step 4 accounts for 18.43% of the total lithium iron phosphate mass, while the fourth lithium iron phosphate particle accounts for 18.23% of the total lithium iron phosphate mass.

[0268] Example 46

[0269] The process is basically the same as Example 42, with the only differences being: the number of grinding cycles in step 1.2 is 5; the sintering temperature in step 1.4 is 805℃ and the holding time is 11.5h; the pulverizing pressure in step 1.5 is 365MPa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 205℃; the sintering temperature in step 2.6 is 690℃; the sieve aperture of the vibrating screen in step 3.5 is 50 mesh; and the third lithium iron phosphate particle in step 4 accounts for 14.35% of the total lithium iron phosphate mass, while the fourth lithium iron phosphate particle accounts for 30.53% of the total lithium iron phosphate mass.

[0270] Example 47

[0271] The process is basically the same as Example 42, except that: the grinding times in step 1.2 are 3 times; the sintering temperature in step 1.4 is 820℃ and the holding time is 12h; the pulverizing pressure in step 1.5 is 310Mpa and the grading frequency is 40Hz; the hydrothermal reactor in step 2.2 reacts at a temperature of 250℃; the sintering temperature in step 2.6 is 735℃; the sieve aperture of the vibrating screen in step 3.5 is 480 mesh; and the third lithium iron phosphate particle in step 4 accounts for 17.65% of the total lithium iron phosphate mass, while the fourth lithium iron phosphate particle accounts for 49.30% of the total lithium iron phosphate mass.

[0272] Comparative Example 1

[0273] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 6, the sintering temperature in step 4 is 805℃, the constant temperature time is 11h, the pulverizing pressure in step 5 is 370Mpa, and the grading frequency is 45Hz.

[0274] Comparative Example 2

[0275] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 810℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 358Mpa, and the grading frequency is 40Hz.

[0276] Comparative Example 3

[0277] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 16, the sintering temperature in step 4 is 735℃, the constant temperature time is 7h, the pulverizing pressure in step 5 is 485Mpa, and the grading frequency is 55Hz.

[0278] Comparative Example 4

[0279] It is basically the same as Example 1, except that: the number of grinding times in step 2 is 4, the sintering temperature in step 4 is 810℃, the constant temperature time is 11.5h, the pulverizing air pressure in step 5 is 350Mpa, and the grading frequency is 40Hz.

[0280] Application Example 1

[0281] The positive electrode sheet is prepared by using the positive electrode active materials of the above embodiments and comparative examples, including the following steps:

[0282] The prepared lithium iron phosphate, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed evenly at a mass ratio of 97:1.5:1.5 and dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was coated on the upper and lower surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After that, it was rolled and cut to obtain a positive electrode sheet with an areal density of 400 g / m². 2 .

[0283] Application Example 2

[0284] The above-mentioned positive electrode sheet is used to prepare a battery, including the following steps:

[0285] 1. Preparation of negative electrode sheet

[0286] Artificial graphite, conductive carbon black SP, sodium carboxymethyl cellulose, and polyvinylpyrrolidone (PVP) were mixed in a mass ratio of 96:0.6:3:0.4. Water was then added and the mixture was further mixed to obtain a negative electrode slurry. This slurry was coated onto the upper and lower surfaces of the negative electrode current collector. After drying, rolling, and slitting, a negative electrode sheet was obtained with an areal density of 160 g / cm³. 2 The compacted density is 1.45 g / cm³. 2 .

[0287] 2. Preparation of electrolyte

[0288] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0289] 3) Diaphragm

[0290] PE films with aluminum oxide on their surface are selected.

[0291] 4) Assembly and formation

[0292] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode sheets. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained with dimensions of 72mm × 173mm × 204mm.

[0293] Test case

[0294] 1. Particle size distribution curve:

[0295] 1) Place a certain amount of positive electrode material sample on the sample stage and observe it using a scanning electron microscope (SEM); first adjust the magnification to low magnification (5000~10000 times): observe the overall dispersion state of the sample and exclude areas with severe agglomeration; then adjust to high magnification (50000~80000 times): clearly distinguish the particle size differences of different particles, save the image for subsequent statistics.

[0296] 2) Open ImageJ software and import the SEM image to be analyzed. Use the diagonal line method to measure the particle size of the particles in the image. Select 5 different non-overlapping regions (to avoid local area deviation). Take a clear SEM photo of each region, avoiding edges and agglomerated areas, to ensure that the particles in the photo are independently dispersed and have no obvious overlap. Convert the statistical particle size and quantity ratio into particle size-volume ratio. The conversion method includes the following steps: ① For the i-th particle, record its particle size as Di; ② The volume weight corresponding to this particle is: Vi'=Di3; ③ Normalize to obtain the volume ratio of this particle Vi=Vi' / ∑Vi'.

[0297] If the sample to be tested is a finished battery, it is necessary to disassemble the battery to obtain the positive electrode material. For example, discharge the battery at 0.33C to the lower limit voltage of 2.5V, take the empty battery, disassemble the positive electrode sheet, soak the positive electrode sheet in dimethyl carbonate (DMC) solution for 4 hours, take out the positive electrode sheet and dry it in a vacuum environment, and scrape the powder on the surface of the electrode sheet with a ceramic knife to obtain the positive electrode material to be tested.

[0298] From the particle size distribution curve, the first peak, second peak, third peak, and fourth peak, as well as their respective parameter information, can be read. The lithium iron phosphate parameter information of the first and second particles of Examples 1-47 and Comparative Examples 1-4 is shown in Table 1. The lithium iron phosphate parameter information of the third particles of Examples 29-47 is shown in Table 2. The lithium iron phosphate parameter information of the fourth particles of Examples 42-47 is shown in Table 3.

[0299] 2. Battery DC internal resistance test

[0300] 1) Place the battery at room temperature and let it stand for 2 hours until thermal equilibrium is reached;

[0301] 2) Charge the battery at 1 / 3C to the upper limit voltage of 3.65V, then discharge it at 1 / 3C to the lower limit voltage of 2.5V. This constitutes one cycle, and the battery is charged and discharged 3 times. The discharge capacity of the third cycle is taken as the standard capacity C of the battery.

[0302] 3) Adjust to the test temperature of 25℃ until thermal equilibrium is reached;

[0303] 4) Charge the battery to 50% SOC at a 1 / 3C discharge rate and let it stand for 10 minutes;

[0304] 5) Discharge at a current of 1C for 18s, then let it stand for 5min. Calculate the DC internal resistance R1 using the formula R1=(U2-U1) / I, where U2 refers to the instantaneous voltage after 18s of discharge, I refers to the instantaneous current after 18s of discharge, and U1 refers to the voltage after 18s of discharge and 5min of standing.

[0305] 3. Battery energy density test:

[0306] Weigh the battery and record the weight as m. Place the battery in a fixture, apply a force of 3000N, charge it with a constant current of 0.33C to the upper limit voltage of 3.65V, let it rest for 30 minutes, discharge it with a constant current of 0.33C to the lower limit voltage of 2.5V, let it rest for 30 minutes, and repeat the cycle 3 times. Obtain the discharge capacity (in Ah) and energy E1 (average of three cycles), and energy density = E1 / m (in Wh / kg).

[0307] The test results for the DC internal resistance and energy density of the above batteries are shown in Table 4:

[0308] Table 1

[0309]

[0310]

[0311] Table 2:

[0312]

[0313] Table 3:

[0314]

[0315] Table 4

[0316]

[0317]

[0318] As can be seen from Tables 1-4, compared with Comparative Examples 1-4, the cathode material provided in Examples 1-47 achieves precise gradation of the first and second particles by limiting the peak shape parameter relationship between the first and second peaks in the particle size distribution curve, which satisfies: 0.005≤m≤7.97, 0.008≤n≤8.42. This enables the material to improve the battery energy density while having low DC internal resistance. Specifically, the cathode materials provided in Examples 1-47 can increase the battery's energy density to over 140 Wh / kg and reduce the DC internal resistance to below 0.9 Ω. However, the cathode materials provided in Comparative Examples 1 and 2 only satisfy 0.005 ≤ m ≤ 7.97 or 0.008 ≤ n ≤ 8.42, resulting in battery energy densities no higher than 134 Wh / kg and DC internal resistance greater than 1 Ω. The cathode material in Comparative Example 3 has excessively large m and n values, resulting in a battery energy density of only 125 Wh / kg and a DC internal resistance as high as 1.213 Ω. The cathode material in Comparative Example 4 has excessively small m and n values, resulting in a battery energy density of 138.2 Wh / kg and a DC internal resistance as high as 0.984 Ω.

[0319] Furthermore, the cathode materials in Examples 1-10, since they satisfy |mn|≤0.83, can further ensure that the energy density of the battery is in the range of 168-180 Wh / kg and the DC internal resistance is in the range of 0.33-0.425Ω.

[0320] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A positive electrode material, characterized in that, The cathode material includes lithium iron phosphate material, which comprises a first particle and a second particle. The particle size distribution curve of the cathode material has particle size on the x-axis (µm) and volume percentage on the y-axis (%). The particle size distribution curve includes a first peak corresponding to the first particle and a second peak corresponding to the second particle. The particle size corresponding to the vertex of the first peak is B1, where 0.12µm ≤ B1 ≤ 0.8µm. The particle size corresponding to the point where the vertical distance from the vertex of the first peak to the x-axis is 1 / 2 is... The particle sizes are B2 and B3, where B2 is smaller than B3; the particle size corresponding to the apex of the second peak is C1, where 1µm≤C1≤4µm; the particle sizes corresponding to the point where the apex of the first peak is at half the vertical height from the horizontal axis are C2 and C3, where C2 is smaller than C3; where C1 / B1=k1, C2 / B2=k2, C3 / B3=k3, |k2-k1|=m, |k3-k2|=n, and m and n satisfy: 0.005≤m≤7.97, 0.008≤n≤8.

42.

2. The cathode material according to claim 1, characterized in that, The m and the n also satisfy: m≤6; And / or, n≤6.1; And / or, |mn|≤0.

83.

3. The cathode material according to claim 2, characterized in that, The m and n also satisfy: m ≤ 0.5; And / or, n≤0.

5.

4. The cathode material according to claim 1, characterized in that, The peak value of the ordinate corresponding to B1 is greater than the peak value of the ordinate corresponding to C1.

5. The positive electrode material according to claim 1, characterized in that, The ratio of the peak value of the ordinate corresponding to B1 to the peak value of the ordinate corresponding to C1 is 0.33-3; And / or, the peak value of the ordinate corresponding to C1 is Fc, where 3%≤Fc≤9%.

6. The cathode material according to claim 1, characterized in that, 1.65≤k1≤19.5； And / or, 1.75≤k2≤16.75; And / or, 1.5≤k3≤15.

84.

7. The cathode material according to claim 6, characterized in that, 3≤k1≤10； And / or, 3≤k2≤10; And / or, 3≤k3≤10.

8. The positive electrode material according to claim 1, characterized in that, 0.8µm≤C2≤3.5µm; And / or, 1.2µm≤C3≤5µm; And / or, 0.1µm≤B2≤0.6µm; And / or, 0.15µm≤B3≤1.0µm.

9. The positive electrode material according to claim 1, characterized in that, The lithium iron phosphate material also includes a third particle, and the particle size distribution curve of the cathode material includes a third peak corresponding to the third particle; the particle size corresponding to the vertex of the third peak is A1, wherein 0.02µm≤A1≤0.075µm.

10. The cathode material according to claim 9, characterized in that, The peak value of the ordinate corresponding to the third peak is F. A Where 0.5%≤F A ≤5%.

11. The cathode material according to claim 10, characterized in that, The particle sizes corresponding to half the vertical height from the apex of the third peak to the horizontal axis are A2 and A3, where B2 / A2=h2, B3 / A3=h3, B1 / A1=h1; |h2-h1|≤8.2, and / or, |h3-h1|≤10.

2.

12. The cathode material according to claim 11, characterized in that, 2.4≤h1≤17.31, and / or, 3.14≤h2≤20, and / or, 2.2≤h3≤14.

93.

13. The cathode material according to claim 11, characterized in that, |h2-h1|≤1.1; |h3-h1|≤1.

21.

14. The cathode material according to claim 11, characterized in that, 0.01μm≤A2≤0.06μm, 0.05μm≤A3≤0.09μm.

15. The cathode material according to any one of claims 1-14, characterized in that, The lithium iron phosphate material also includes a fourth particle, and the particle size distribution curve of the cathode material includes a fourth peak corresponding to the fourth particle; the particle size corresponding to the vertex of the fourth peak is D1, where 4≤D1≤18μm.

16. The cathode material according to claim 15, characterized in that, The peak value corresponding to the fourth peak is F. D , where 1%≤F D ≤10%.

17. The cathode material according to claim 15, characterized in that, The particle sizes corresponding to half the vertical height from the apex of the fourth peak to the horizontal axis are D2 and D3, where D2 / C2=S1, D3 / C3=S2, D1 / C1=S, S1-S≤3μm; S2-S≤2.59μm.

18. The cathode material according to claim 1, characterized in that, At least a portion of the surface of the lithium iron phosphate material is provided with a carbon coating layer, the thickness of which is 0.5 nm to 120 nm.

19. The cathode material according to claim 1, characterized in that, The specific surface area of ​​the cathode material is 5 m². 2 / g-40 m 2 / g.

20. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes the positive electrode material according to any one of claims 1-19.

21. The positive electrode sheet according to claim 20, characterized in that, The surface resistance of the positive electrode is 0.2Ω-2Ω.

22. A battery, characterized in that, It includes a negative electrode, an electrolyte, and a positive electrode as described in claim 20 or 21.

23. The battery according to claim 22, characterized in that, The electrolyte includes a carboxylic acid ester solvent, which accounts for 15%-40% of the total mass of the electrolyte.

24. The battery according to claim 23, characterized in that, The electrolyte also includes carbonate solvents; the carbon chain length of the carbonate solvents is less than or equal to 3. And / or, the mass ratio of the carboxylic acid ester solvent to the carbonate solvent is 1:1.5-4.

25. The battery according to any one of claims 22-24, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode material, which includes at least one of graphite and silicon-based materials.

26. The battery according to claim 25, characterized in that, The particle size Dv50 of the negative electrode material is 5µm-20µm.

Images