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

Abstract

The application provides a positive electrode active material, a positive electrode sheet and a battery. The positive electrode active material comprises a lithium iron phosphate material, the lithium iron phosphate material comprises first particles and second particles with decreasing particle sizes, the particle size of the first particles is smaller than that of the second particles, and the positive electrode active material comprises a first peak corresponding to the first particles and a second peak corresponding to the second particles in a particle size distribution curve, the peak intensity of the first peak is A1%, the peak intensity of the second peak is B1%, there is a first peak valley between the first peak and the second peak, the intensity of the first peak valley is E%, and the powder resistivity of the positive electrode active material is b Ω.m. The positive electrode active material satisfies n=E / (A1+B1), 0.1<=1000*n / b<=192.5, and the positive electrode active material can reduce the DCR of the battery and improve 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 active material, a positive electrode sheet, and a battery. Background Technology

[0002] Lithium iron phosphate (LFP) batteries have become a core power source in new energy vehicles, energy storage systems, power tools, and aerospace due to their high safety, long cycle life, and excellent thermal stability. With the increasing demands for driving range and charging speed from electric vehicles and energy storage systems, LFP materials need to further combine high energy density with low internal resistance. However, traditional LFP materials have inherent defects such as low electronic conductivity and a small lithium-ion diffusion coefficient, resulting in high DC internal resistance and rapid capacity decay at high rates, making it difficult to meet the requirements of fast charging and high energy density.

[0003] Therefore, developing a lithium iron phosphate material that combines high energy density and low DC internal resistance (DCR) is one of the important research directions in the field of lithium-ion batteries. Summary of the Invention

[0004] Based on the above problems, the main objective of this invention is to provide a positive electrode active material, a positive electrode sheet, and a battery that can reduce the DCR of the battery while simultaneously increasing its energy density.

[0005] In detail, in a first aspect, the present invention provides a positive electrode active material, the positive electrode active material comprising lithium iron phosphate material, the lithium iron phosphate material comprising a first particle and a second particle, the first particle having a smaller particle size than the second particle, the particle size distribution curve of the positive electrode active material including: a first peak corresponding to the first particle, a second peak corresponding to the second particle, the peak intensity of the first peak being A1, the peak intensity of the second peak being B1, a first valley being formed between the first peak and the second peak, the intensity of the first valley being E, and the powder resistivity of the positive electrode active material being b; the positive electrode active material satisfies the following formulas 1 and 2:

[0006] n = E / (A1+B1) Equation 1,

[0007] 0.1≤1000×n / b≤192.5 Equation 2.

[0008] In a second aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector, wherein the positive electrode material layer comprises a positive electrode active material in the first aspect.

[0009] Thirdly, the present invention provides a battery comprising a negative electrode, an electrolyte, and a positive electrode as described above.

[0010] The positive electrode active material provided by the present invention significantly improves the filling efficiency of the interparticle gaps of the positive electrode active material by controlling the relationship between the first peak intensity A1, the second peak intensity B1, the peak-valley intensity E between the first peak and the second peak in the particle size distribution curve of the first and second particles, and the powder resistivity b of the positive electrode active material as shown in Equations 1 and 2. This helps to improve the compaction density and electrode uniformity of the positive electrode sheet, and ultimately reduces the DCR of the battery and increases its energy density. Attached Figure Description

[0011] 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.

[0012] 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

[0013] 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.

[0014] This invention reveals that the particle size distribution of lithium iron phosphate (LFP) cathode active material particles has a decisive influence on its electrochemical performance. To simultaneously meet the requirements of high energy density and low DC internal resistance (DCR) in lithium-ion batteries, this invention further investigates and finds that existing LFP materials are typically prepared by mixing particles with a single particle size or a simple bimodal particle size distribution. For example, some techniques improve electrode compaction density by mixing small-sized (<1 μm) and large-sized (>5 μm) particles, but they do not quantitatively control the peak and valley characteristics of the particle size distribution curve. This results in an excessively high proportion of particles with intermediate sizes between large and small particles, which hinders the filling of gaps between large particles and limits the improvement in compaction density. Furthermore, existing technologies do not design a correlation between particle size distribution characteristics and ion transport paths, failing to address the issue of differences in lithium-ion transport paths caused by insufficient continuity in particle distribution. Therefore, to improve the energy density of lithium-ion batteries while simultaneously enhancing their rate performance, thereby expanding the application of lithium-ion batteries in high-power scenarios, this invention provides the following technical solution:

[0015] In a first aspect, the present invention provides a positive electrode active material, comprising lithium iron phosphate material, the lithium iron phosphate material comprising a first particle and a second particle, the first particle having a smaller particle size than the second particle, the particle size distribution curve of the positive electrode active material including: a first peak corresponding to the first particle, a second peak corresponding to the second particle, the peak intensity of the first peak being A1, the peak intensity of the second peak being B1, a first valley being formed between the first peak and the second peak, the intensity of the first valley being E, and the powder resistivity of the positive electrode active material being b; the positive electrode active material satisfies the following equations 1 and 2:

[0016] n = E / (A1+B1) Equation 1,

[0017] 0.1≤1000×n / b≤192.5 Equation 2.

[0018] This invention controls the relationship between the peak-valley intensity E between the first and second peaks in the particle size distribution curve of the positive electrode active material, the peak intensity A1 of the first peak, the peak intensity B1 of the second peak, and the powder resistivity b of the positive electrode active material. This ensures that these four factors satisfy Equations 1 and 2, improving the consistency of ion transport between particles and reducing the DC internal resistance of the battery while maintaining the high compaction density of the electrode. This contributes to the synergistic improvement of battery energy density and rate performance. Specifically, this invention finds that when E / (A1+B1) is too small, the peak-valley intensity ratio is too low, the continuity of the particle size distribution deteriorates, resulting in a lack of transition between the first and second particles. This increases the difference in the extraction / insertion paths of lithium ions between different particles, causing local current density unevenness and intensified polarization, leading to an increase in the DC internal resistance of the battery. When E / (A1+B1) is too small, the peak-valley intensity ratio is too low, the continuity of the particle size distribution deteriorates, resulting in a lack of transition between the first and second particles. This increases the difference in lithium ion extraction / insertion paths between different particles, causing local current density unevenness and intensified polarization, thus increasing the DC internal resistance of the battery. When A1+B1 is too large, the peak-valley intensity ratio is too high, and there are many intermediate particles in the particle size distribution located between the first peak and the second peak. The particle size of these particles is between the first particle (small particle) and the second particle (large particle). They cannot effectively fill the large gaps formed by the accumulation of large particles, and their filling efficiency is lower than that of small particles. This leads to a decrease in electrode compaction density and a limitation on battery energy density. Based on this, in order to control the peak-valley intensity ratio within a suitable range, this invention introduces the powder resistivity value b of the positive electrode active material and makes it satisfy the above relationship. This not only promotes the first particle to fully fill the gaps between the second particles and improves the intrinsic electronic conductivity of the positive electrode active material, but also compensates for the kinetic degradation that may be caused by the discontinuous particle size distribution. Therefore, while ensuring the energy density of the battery, it can also reduce the DC internal resistance of the battery.

[0019] It can be understood that the x-axis of the particle size distribution curve of the positive electrode active material is the particle size, and the y-axis is the peak intensity. The unit of peak intensity is %, which means that the number of particles corresponding to that particle size accounts for the percentage of the total number of particles. n is a dimensionless parameter of the relative depth of the valley in the particle size distribution curve, which can be understood as the degree of separation between the first particle (small particle size) and the second particle (large particle size) in the particle size distribution. Formula 1 and Formula 2 are both purely numerical calculations.

[0020] In some specific embodiments, the particle size distribution curve of the positive electrode active material is obtained through the following process:

[0021] 1) Place a certain amount of positive electrode active 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 difference between the first and second particles, save the image for subsequent statistics.

[0022] 2) Open the 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 areas (to avoid local area deviation). Take a clear SEM photo of each area, avoiding the edges and agglomeration areas, and ensure that the particles in the photo are independently dispersed and have no obvious overlap. Generate a particle size-frequency distribution map from the statistically obtained particle size and quantity for parameter reading and calculation.

[0023] in, Figure 1 The figure shows the particle size distribution curve of the positive electrode active material according to a specific embodiment of the present invention. In the figure, the peak intensity (A1) of the first peak is the maximum value of dV / dlogD, the peak intensity (B1) of the second peak is the maximum value of dV / dlogD, and the valley E is located at the minimum point between the first peak and the second peak.

[0024] In some specific embodiments, the powder resistivity of the positive electrode active material is measured by the following process:

[0025] The positive electrode active material to be tested is ball-milled at a speed of 300 r / min using 0.6 mm diameter zirconia balls with a ball-to-material ratio of 5:1 for 20-40 min. After ball milling, the material is placed on the electrodes of a four-probe resistivity meter (such as the ST2722 semiconductor powder resistivity meter from Suzhou Jingge Electronics Co., Ltd.). Pressure is applied to the powder on the other electrode at a pressure intensity of 10 MPa, and the resistivity value of the powder is read.

[0026] For example, 1000×n / b is any value or a range between any two of 0.1, 20, 40, 60, 80, 100, 120, 140, 160, 180, 192.5, etc.

[0027] In some implementations, 6.6 ≤ 1000 × n / b ≤ 36. Positive electrode active materials that satisfy the above relationship can further ensure the high real density of the positive electrode sheet while reducing the DC internal resistance of the battery.

[0028] In some implementations, 0.03 ≤ n ≤ 0.42. This further ensures that the first particle fully fills the gaps between the second particles, thereby further guaranteeing the energy density of the battery. Exemplarily, n is any value or a range between any two of 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24, 0.27, 0.30, 0.33, 0.36, 0.39, 0.42, etc.

[0029] In some implementations, 2 ≤ b ≤ 500. Positive electrode active materials that satisfy this range can further reduce the DC internal resistance of the battery. Exemplarily, b is any value or a range of any two of the following: 2, 5, 10, 20, 50, 100, 150, 200, 300, 500, etc.

[0030] In some implementations, 0.27 ≤ n ≤ 0.38. This further ensures that the first particle fully fills the gap between the second particles, thereby further guaranteeing the energy density of the battery.

[0031] In some implementations, 10 ≤ b ≤ 50. Positive electrode active materials that meet this range can further reduce the DC internal resistance of the battery.

[0032] In some implementations, 0.5 ≤ E ≤ 6.

[0033] The above embodiments, by limiting the range of E, further ensure that the proportion of intermediate-sized particles between the first and second particles is within a more suitable range, reducing the accumulation of intermediate-sized particles. This can further improve the compaction density of the positive electrode and the uniformity of the lithium-ion transport path, thereby further ensuring the energy density and low DC resistance of the battery. If E is too small, i.e., the first peak and valley are too deep, it means that there is a gap in intermediate-sized particles, and there is a lack of transition bridges between large and small particles. The porosity increases during accumulation, and the improvement in compaction density is not significant. If the first peak and valley are too shallow, it indicates that the size distinction between small and large particles is insufficient, the gradation effect fails, and small particles cannot effectively embed into the gaps in the large particle skeleton, which also reduces the accumulation efficiency. Moreover, excessive intermediate-sized particles will consume too much binder, which is not conducive to electrode processing. Preferably, 3.5≤E≤4.5. For example, E is any value of 0.5, 0.7, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, or any range between any two.

[0034] In some implementations, 4 ≤ A1 ≤ 10.

[0035] In this embodiment, by limiting the range of the peak intensity A1 of the first peak, it is further ensured that the first particle occupies an appropriate proportion in the particle size distribution, enabling it to effectively fill the gaps formed by the accumulation of the second particle, thereby further improving the compaction density and volumetric energy density of the positive electrode sheet. Simultaneously, this range also avoids an excessively high proportion of small particles leading to a surge in specific surface area and an increase in powder resistance, thus further reducing the DC internal resistance of the battery while ensuring high energy density. Preferably, 5 ≤ A1 ≤ 7. Exemplarily, A1 is any value from 4, 5, 6, 7, 8, 9, 10, etc., or a range between any two.

[0036] In some implementations, 3 ≤ B1 ≤ 10.

[0037] The above embodiments, by limiting the range of the peak intensity B of the second peak, further ensure that the proportion of the second particle in the particle size distribution is within a suitable range. On the one hand, this provides stable mechanical support and the main capacity contribution for the positive electrode, while reducing interfacial side reactions by utilizing its lower specific surface area. On the other hand, this range allows sufficient filling space between the second particles, creating favorable conditions for the embedding of the first particle and lithium-ion transport channels, thereby further reducing the DC internal resistance of the battery while ensuring the high compaction density of the positive electrode. Preferably, 5 ≤ B1 ≤ 6. Exemplarily, B1 is any value of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 9.5, 10, etc., or a range between any two.

[0038] In some implementations, the positive electrode active material satisfies: 0.27≤E / (A1+B1)≤0.38.

[0039] Specifically, the positive electrode active material that satisfies the above relationship can further promote the first particle to fully fill the gap between the second particles, improving the intrinsic electronic conductivity of the positive electrode active material while compensating for the kinetic degradation that may be caused by the discontinuous particle size distribution. This further reduces the DC internal resistance of the battery while ensuring the high compaction density of the positive electrode sheet. For example, E / (A1+B1) is any value or a range between any two of 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, and 0.38. In some examples, 7≤A1+B1≤20, and preferably, 10≤A1+B1≤13.

[0040] In some implementations, the particle size corresponding to the first peak is I. E 0.2µm≤I E ≤1µm.

[0041] The above embodiments, by limiting the particle size range corresponding to the first peak and valley, can further optimize particle filling efficiency and reduce the void volume of the positive electrode active material, thereby helping to further ensure the high compaction density of the positive electrode sheet. For example, I E It is any value or a range of any two of the following: 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm.

[0042] In some implementations, the particle size corresponding to the apex of the first peak is I. A The particle size corresponding to the apex of the second peak is I. B Where 120nm≤I A ≤800nm, 1µm≤I B ≤4µm.

[0043] In the above embodiments, the particle size I of the first particle is... A The particle size I of the second particle is controlled within the range of 120 nm to 800 nm. B By controlling the particle size within the range of 1 μm to 4 μm, the first particle can effectively fill the micron-level gaps formed by the stacking of the second particle, ensuring the compaction density and volumetric energy density of the positive electrode. Simultaneously, I A The lower limit is 120 nm, avoiding the surge in specific surface area, increased powder resistivity, and difficulties in slurry processing caused by excessively fine particles. A The upper limit is 800 nm to ensure that the first particle still has sufficient filling efficiency and a short lithium-ion diffusion path; I BThe lower limit is 1 μm, ensuring that the second particle has a low specific surface area to reduce interfacial side reactions. B The upper limit of 4 μm is used to avoid excessively large particle size of the second particle, which would prolong the lithium-ion solid-phase diffusion path and intensify polarization. For example, I A It can be 120 nm, 150 nm, 200 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or 800 nm, and IB can be any value or a range between any two of 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, or 4.0 μm.

[0044] In some implementations, 2≤I B / I A ≤20.

[0045] In the above embodiments, the particle size ratio I of the second particle to the first particle is used. B / I A By controlling the particle size ratio within the range of 2 to 20, a suitable size difference can be formed between the second and first particles, allowing the first particle to be fully embedded in the gaps formed by the stacking of the second particles, thereby increasing the compaction density of the electrode sheet. Simultaneously, this particle size ratio range avoids insufficient filling efficiency due to excessively small size differences or significantly increased differences in lithium-ion extraction / insertion paths due to excessively large differences. This ensures a more balanced transport path for lithium ions between different particles, reducing local current density unevenness and polarization, thus synergistically achieving the goal of high energy density and low DC internal resistance in the battery. For example, I... B / I A It can be any value from 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 20, etc., or a range between any two.

[0046] In some implementations, I E / I A= k1, I E / I B= k2, where 1.1≤k1≤6, 0.1≤k2≤0.9.

[0047] In this embodiment, by limiting 1.1≤k1≤6 and 0.1≤k2≤0.9, the peak and valley positions in the particle size distribution curve are positioned within a suitable range between the second and first particles. This ensures effective control of the proportion of intermediate-sized particles, thereby creating a smooth transition from the first to the second particle and reducing adverse effects on filling the gap between the second and first particles. For example, k1 can be any value or a range of any combination of 1.1, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, etc., or k2 can be any value or a range of any combination of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc.

[0048] In some implementations, 2 ≤ k1 / k2 ≤ 20.

[0049] In this embodiment, by limiting the ratio of k1 / k2, the particle size ratio between the second particle and the first particle is also indirectly limited. When the ratio of k1 / k2 is in the range of 2 to 20, a significant size difference can be formed between the second particle and the first particle, ensuring that the first particle can be fully embedded in the gaps formed by the stacking of the second particles, thereby further improving the compaction density and energy density of the positive electrode sheet. At the same time, this ratio range avoids insufficient filling efficiency due to excessively small particle size differences or a significant increase in the difference in lithium ion extraction / insertion paths due to excessively large differences, making the transport path of lithium ions between different particles tend to be balanced, thereby further reducing the DC internal resistance of the battery. For example, k1 / k2 can be any value of 2, 4, 6, 8, 10, 12, 15, 17, 20, or any combination of both.

[0050] In some embodiments, the lithium iron phosphate material further includes a third particle with a smaller particle size than the first particle, and the particle size distribution curve of the positive electrode active material includes a third peak corresponding to the third particle; the peak intensity of the third peak is C1%, where 0.5≤C1≤4.

[0051] In this embodiment, the introduction of a third particle fills the submicron or even nanometer-sized pores remaining after the first and second particles are stacked, further improving the compaction density and volumetric energy density of the positive electrode. Simultaneously, controlling its peak intensity C1 within the range of 0.5 to 4 effectively controls the overall proportion of the third particle (ultra-small particle), avoiding problems such as increased interfacial side reactions, increased powder resistance, and difficulties in slurry processing caused by an excessively large specific surface area of ​​the third particle. For example, C1 can be any value from 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or any range between two such values.

[0052] In some implementations, the particle size corresponding to the apex of the third peak is I. C Where 20nm≤I C ≤100 nm.

[0053] In the above embodiments, the particle size I of the third particle is... C By controlling the particle size within the range of 20 nm to 100 nm, it is further ensured that, as the smallest filler component (ultra-small particles), it can effectively embed itself in the submicron or even nanometer-scale pores remaining after the first and second particles are stacked, thereby further improving the compaction density and volumetric energy density of the positive electrode. For example, I C It can be any value from 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc., or a range between any two.

[0054] In some embodiments, the lithium iron phosphate material further includes a fourth particle, the fourth particle having a larger particle size than the second particle, and the particle size distribution curve of the positive electrode active material includes a fourth peak corresponding to the fourth particle; the peak intensity of the fourth peak is D1%, where D1 <C1。

[0055] In the above implementation, by introducing a fourth particle and limiting its peak intensity D1 to be less than C1, the fourth particle, as an ultra-large particle component, accounts for a low proportion in the particle size distribution and only participates in particle stacking as an auxiliary framework. This avoids problems such as reduced contact points between particles and extended electron transport paths caused by too many ultra-large particles. Thus, while further improving the battery energy density, it maintains good electron conduction and ion transport uniformity inside the electrode and synergistically reduces the DC internal resistance of the battery.

[0056] In some implementations, the particle size corresponding to the apex of the fourth peak is I. D , where 4µm≤I D ≤35µm.

[0057] In the above implementation, by introducing a fourth particle (an ultra-large particle size), which, together with the first, second, and third particles, constructs a quaternary particle gradation system, a hierarchical close packing is achieved, which helps to improve the overall compaction density and structural stability of the electrode. For example, I D It can be any value or a range of any two of the following: 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm.

[0058] In some implementations, 0.4% ≤ D1 ≤ 3.5. The fourth particle in this range further improves the compaction density of the positive electrode while avoiding the problem of increased point contact ratio between particles and interruption of electron transport path due to excessive number of ultra-large particles. For example, D1 can be any value of 0.4, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, or any range between two of them.

[0059] In some implementations, there is a second valley between the second peak and the fourth peak; the intensity of the second valley is F%, where 0.5 ≤ F ≤ 3.

[0060] In the above implementation method, by limiting the intensity F of the second valley between the second and fourth peaks to the range of 0.5 to 3, the proportion of intermediate-sized particles located between the second and fourth particles can be effectively controlled. If the second valley is too deep, it indicates a lack of buffering particles of transitional size. The fourth and second particles will come into contact during rolling, and local stress concentration can easily lead to the fourth particle breaking and generating microcracks. At the same time, the contact resistance increases, resulting in a deterioration in battery rate and cycle performance. If the second valley is too shallow, it means that the two particles are close in size and cannot form a synergistic gradation of skeleton-secondary filler. The stacking behavior degenerates into single-size stacking, which is not only detrimental to improving compaction density, but also disrupts the subsequent filling path of small and ultra-small particles, causing the overall gradation chain to fail. For example, F can be any value of 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, or any range between two values.

[0061] In some implementations, the particle size corresponding to the second peak is I. F Where 2.5µm≤I F ≤19.5µm.

[0062] In the above implementation method, the particle size I corresponding to the second peak valley is... F By controlling the particle size distribution within the range of 2.5 μm to 19.5 μm, the transition region between the second and fourth peaks in the particle size distribution curve is located within a suitable range between the second and fourth particles. This ensures that intermediate-sized particles do not interfere with the macroscopic gap filling of the fourth particle, while maintaining appropriate continuity in the particle size distribution. This avoids excessive intermediate particles affecting the compaction density and ensures a smooth transition of the lithium-ion transport path between particles of different sizes. Therefore, while further improving the battery's energy density, it also synergistically reduces its DC internal resistance. For example, I... F It can be any value or a range between 2.5 μm, 3.0 μm, 5.0 μm, 8.0 μm, 10.0 μm, 12.0 μm, 15.0 μm, 18.0 μm, 19.5 μm, etc.

[0063] In some implementations, the third peak, the fourth peak, and the second valley satisfy the following relationship: F ​​< D1 < B1.

[0064] In this embodiment, by limiting F < D1 < B1, the proportion of particles in the transition region between the third and fourth particles can be further effectively controlled, and the proportion of intermediate transition particles can be further ensured to be moderate. This avoids the negative impact of too many transition particles on the filling efficiency of the macroscopic gap of the fourth particle, and also prevents too few transition particles from causing discontinuous particle size distribution and increased differences in lithium-ion transport paths. Thus, the energy density of the battery can be further improved and its DC internal resistance can be reduced simultaneously.

[0065] In some implementations, I F / I B =L1,I F / I D =L2, where 1≤L1 / L2≤35.

[0066] In this embodiment, by limiting L1 / L2 to the range of 1 to 35, the ratio between the second and fourth particle sizes is indirectly controlled. This ratio range ensures a significant size difference between the fourth and second particles, allowing the second particles to effectively fill the macroscopic gaps formed by the accumulation of the fourth particles, constructing a multi-level particle distribution network, and further improving the compaction density of the positive electrode sheet. Simultaneously, this range coordinates the lithium-ion extraction / insertion behavior on the surfaces of particles of different sizes, further reducing the DC internal resistance of the battery. For example, L1 / L2 can be any value from 1, 2, 3, 5, 8, 10, 12, 15, 18, 20, 25, 30, 35, or a range between any two.

[0067] 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 0.5-120 nm.

[0068] In the above embodiments, the thickness of the carbon coating layer is controlled within the range of 0.5 nm to 120 nm. This allows for the formation of a continuous and dense conductive protective layer on the surface of the positive electrode active material, significantly improving the electron transport efficiency between particles and reducing the powder resistance of the material, thereby further reducing the DC internal resistance of the battery. Simultaneously, the carbon coating layer effectively isolates the electrolyte from direct contact with the active particles, suppresses interfacial side reactions, and ensures 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.

[0069] 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.

[0070] In some embodiments, the lithium iron phosphate material includes a doped metal element, which includes at least one selected from Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni.

[0071] 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, M is a doped metal element, and Q includes F. - Cl - SO4 2- NO3 - At least one of them.

[0072] The above implementation methods introduce doped metal elements into lithium iron phosphate materials, which can improve the intrinsic electronic conductivity of lithium iron phosphate materials, improve the lithium-ion diffusion coefficient, thereby further reducing the DC internal resistance of the battery and improving fast charging performance. At the same time, after the doped elements enter the crystal lattice, they can stabilize the olivine structure, suppress lattice distortion and iron dissolution during cycling, reduce interfacial side reactions between the cathode and the electrolyte, and synergistically improve the energy density and cycle stability of the battery.

[0073] In some embodiments, the content of the doped metal element is 300~30000 ppm, depending on the mass of the lithium iron phosphate material. Specifically, the above embodiments control the content of the doped metal element within the range of 300 ppm to 30000 ppm, which, while maintaining the structural stability of the lithium iron phosphate olivine, can further improve the intrinsic electronic conductivity and lithium-ion diffusion coefficient of the material through appropriate doping. For example, the content of the doped metal element can be any value or a range between any two of the following: 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 12000 ppm, 15000 ppm, 18000 ppm, 20000 ppm, 25000 ppm, 30000 ppm.

[0074] As an example, and not a limitation, in some implementations, the preparation of lithium iron phosphate materials, in order of increasing particle size, includes the following processes:

[0075] S1, Preparation of the third particle:

[0076] ① Mix lithium source, iron source, phosphorus source and solvent in a certain proportion to obtain slurry 1;

[0077] ② Transfer slurry 1 to a hydrothermal reactor and react at 150-250℃ for 6-12 hours to obtain lithium iron phosphate powder 1;

[0078] ③ Mix lithium iron phosphate powder 1 with carbon source, optional dopant and solvent in a certain proportion to obtain slurry 2;

[0079] ④ After grinding, slurry 2 is used to obtain slurry 3 with Dv50=100-300nm;

[0080] ⑤ Slurry 3 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 the solvent evaporates, raw material is obtained;

[0081] ⑥ The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere. The sintering temperature is 650-750℃ and the holding time is 6-12h to obtain the sintered material.

[0082] 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.

[0083] In step S1, 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). The solvent includes one or more of the following: ppm, 30000 ppm, etc., or a range of any two.

[0084] The particle size of the third particle can be adjusted by adjusting the sintering temperature, airflow crushing and other conditions. For example, the higher the classification frequency of airflow crushing, the smaller the particle size, and the higher the sintering temperature, the larger the particle size.

[0085] 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 m³ / h, 30 m³ / h, 40 m³ / h, 50 m³ / h, or 70 m³ / h. The capacity is m³ / h, and the outlet air temperature can be 80℃, 85℃, 90℃, 95℃, or 100℃; the high-temperature sintering temperature can be 650℃, 680℃, 700℃, 720℃, or 750℃, and the constant temperature time can be 6h, 7h, 8h, 9h, 10h, 11h, or 12h; the air pressure for airflow pulverization can be 300 MPa, 350 MPa, 400 MPa, 450 MPa, or 500 MPa, and the grading frequency can be any value or a range between 40 Hz, 45 Hz, 50 Hz, 55 Hz, or 60 Hz.

[0086] S2, Preparation methods of the first and second particles:

[0087] 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 4.

[0088] ② After sand milling slurry 4, slurry 5 with Dv50=200-500nm is obtained;

[0089] ③ Slurry 5 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;

[0090] ④ The raw materials are sintered at high temperature in an inert atmosphere or a reducing atmosphere. The sintering temperature is 700-820℃ and the holding time is 6-12h to obtain the sintered material.

[0091] ⑤ The sintered material is crushed and deagglomerated. The crushing pressure is 300-500 MPa and the grading frequency is 40-60 Hz to obtain lithium iron phosphate containing the first and second particles.

[0092] In step S2, 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; 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.

[0093] Step ① The Fe / P ratio of the first iron phosphate precursor is 0.96-1, and the Fe / P ratio of the second iron phosphate precursor is 0.95-1.

[0094] The particle size of the first particle and the particle size of the second particle can be adjusted in the following ways: 1) The larger the Fe / P ratio of the iron phosphate precursor, the smaller the particle size, and the higher the classification frequency of the sintered material during air jet milling, the smaller the particle size; the particle size of the first particle and the peak intensity of the second particle can be adjusted by adjusting the mass ratio of the first iron phosphate precursor and the second iron phosphate precursor.

[0095] The intensity E of the first peak can be adjusted in the following ways: 1) Adjust E by adjusting the difference between Fe / P (0.96-1) of the first iron phosphate precursor and Fe / P (0.95-1) of the second iron phosphate precursor. The greater the difference, the smaller the intensity E; 2) Adjust the intensity E by adjusting the crushing and classification frequency. The higher the classification frequency, the smaller the intensity E.

[0096] For example, the Dv50 of slurry 5 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.

[0097] S3, Preparation method of the fourth particle:

[0098] ① Iron phosphate, lithium source, carbon source, optional dopant, and solvent are mixed and dispersed in a certain proportion to obtain slurry 6;

[0099] ② After sand milling slurry 6, slurry 7 with Dv50=100-400nm is obtained;

[0100] ③ The slurry 7 is sprayed with a two-fluid or multi-fluid spray, 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=4-40µm is obtained;

[0101] 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;

[0102] 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.

[0103] 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.

[0104] In step ①, the Fe / P ratio of the iron phosphate precursor in the fourth particle was 0.960-1.

[0105] The particle size of the fourth particle can be adjusted by adjusting conditions such as sintering temperature and spray feed rate. For example, the higher the sintering temperature, the larger the particle size; the higher the spray feed rate, the larger the particle size.

[0106] The intensity of the second peak can be adjusted with reference to the intensity of the first peak, the only difference being that the first and second particles are replaced with the second and fourth particles.

[0107] 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.

[0108] In addition, the resistivity of the positive electrode active material powder can be adjusted in the following ways: 1) Adjust the powder resistivity by adjusting the sintering temperature. The higher the sintering temperature, the lower the powder resistivity; 2) Adjust the powder resistivity by adjusting the amount of carbon source added. The higher the amount added (0.8-2%), the lower the powder resistivity.

[0109] In a second aspect, the present invention provides a positive electrode sheet, comprising a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector, the positive electrode material layer comprising the positive electrode active material of the first aspect.

[0110] It is understood that the positive electrode 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.

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

[0112] In some embodiments, the electrolyte includes additives, solvents, and lithium salts; the additives include tris(trimethylsilyl)borate, and / or the solvents include ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0113] In the above embodiments, tris(trimethylsilyl)borate (TMSB) is introduced into the electrolyte as an additive. This additive can form a stable interfacial protective film on the positive electrode surface, effectively inhibiting the oxidative decomposition of the electrolyte under high voltage, reducing interfacial impedance, and thus improving the cycle stability and fast charging performance of the battery. At the same time, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are selected as solvent systems. The high dielectric constant of EC promotes the dissociation of lithium salt, and the low viscosity of EMC and DEC improves the wettability and ionic conductivity of the electrolyte, so that the electrolyte has both good film-forming properties and low-temperature performance.

[0114] In some examples, the lithium salt is LIPF6.

[0115] Based on the mass of the electrolyte, the mass content of the additive is 0.05%-2.5%, the mass content of the solvent is 45%-87.5%, and the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is (1-2):(1-2):(1-2).

[0116] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one side of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, which includes at least one of graphite and silicon-based materials.

[0117] The negative electrode active 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.

[0118] The particle size of the negative electrode active material can be flexibly selected according to the energy density and rate requirements of the battery. For example, the particle size Dv50 of the negative electrode active material is controlled in the range of 5 μm to 20 μm, which can enable the negative electrode active material to form an optimized particle packing structure, shorten the lithium ion diffusion path, and further ensure that the battery has low internal resistance.

[0119] In some embodiments, the negative electrode material layer includes a negative electrode active material, a conductive agent, a binder, and a dispersant. This is illustrative and not limiting. The conductive agent may be selected from at least one of natural graphite, artificial graphite, 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.

[0120] 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):(0-2); 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 .

[0121] 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 deionized water as 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). The negative electrode slurry is coated on at least one surface of the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained. The areal density of the negative electrode sheet is 90 g / m³. 2 ~150g / m 2 The compacted density is 1.4 g / cm³. 3 ~1.8 g / cm 3 .

[0122] In some embodiments, the battery fabrication process includes the following steps:

[0123] 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.

[0124] 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.

[0125] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0126] 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.

[0127] Example 1

[0128] The positive electrode active material in this embodiment is lithium iron phosphate, and its preparation includes the following process:

[0129] Methods for preparing the first and second particles:

[0130] 1.1 The first particle of iron phosphate precursor (Fe / P ratio of 0.979, specific surface area of ​​7.3 m²) 2 / g), the second particle of iron phosphate precursor (Fe / P = 0.959, specific surface area = 8.7m²). 2The mixture of lithium carbonate (in a mass ratio of 5.38:4.62) and vanadium pentoxide (in a mass ratio of 4:5.1) is used to form a ferric phosphate precursor mixture. The ferric phosphate precursor mixture, lithium carbonate (lithium source), carbon source (a mixture of polyethylene glycol and glucose in a mass ratio of 4:5.1), vanadium pentoxide and titanium dioxide (in a mass ratio of 100:25:1.92:0.40:0.15) are mixed together. The carbon source accounts for 1.51% of the mass of the mixture. Then, deionized water is added as a solvent and the mixture is further mixed and dispersed to obtain slurry 4.

[0131] 1.2. After sand milling slurry 4, slurry 5 with Dv50=350nm is obtained;

[0132] 1.3. Slurry 5 is spray-dried with an inlet air temperature of 190℃ and a feed rate of 40m. 3 / h; outlet air temperature 90℃, after solvent evaporation, raw material with Dv50=35µm is obtained;

[0133] 1.4 The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere. The sintering temperature is 798℃ and the holding time is 6h to obtain the sintered material.

[0134] 1.5. The sintered material is crushed and deagglomerated. The crushing pressure is 450 MPa and the grading frequency is 50 Hz to obtain lithium iron phosphate containing the first and second particles.

[0135] Example 2

[0136] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.975, the Fe / P ratio of the second iron phosphate precursor particle is 0.960, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.42%, the sintering temperature in step 1.4 is 748℃, and the grading frequency in step 1.5 is 47 Hz.

[0137] Example 3

[0138] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.977, the Fe / P ratio of the second iron phosphate precursor particle is 0.959, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.58%, the sintering temperature in step 1.4 is 760℃, and the grading frequency in step 1.5 is 49 Hz.

[0139] Example 4

[0140] 1. Preparation methods of the first and second particles: basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the iron phosphate precursor of the first particle is 0.976, the Fe / P ratio of the iron phosphate precursor of the second particle is 0.960, the mass ratio of the iron phosphate precursor of the first particle to the iron phosphate precursor of the second particle is 5.54:4.46, the mass ratio of carbon source to the mixed system is 1.59%, the sintering temperature in step 1.4 is 762℃, and the grading frequency in step 1.5 is 48 Hz.

[0141] 2. Preparation method of the fourth particle:

[0142] 2.1 The fourth particle of iron phosphate (Fe / P ratio of 0.954, specific surface area of ​​11.3 m²) 2 The slurry 6 was prepared by mixing and dispersing lithium carbonate (g) with lithium source, polyethylene glycol (CG), glucose (CG), titanium dioxide (DOT) in a mass ratio of 100:25:4.0:5.1:0.40:0.15 in solvent deionized water to obtain slurry 6.

[0143] 2.2 After sand milling slurry 6, slurry 7 with Dv50=400nm is obtained;

[0144] 2.3. The slurry 7 is sprayed with two or more fluids at an inlet air temperature of 190℃ and a feed rate of 30m3 / h; the outlet air temperature is 90℃. After the solvent is evaporated, a raw material with Dv50=35 is obtained.

[0145] 2.4 The raw materials are sintered at high temperature in an inert atmosphere or a slightly reducing atmosphere. The sintering temperature is 820℃ and the holding time is 8h to obtain the sintered material.

[0146] 2.5. Vibrate and sieve the sintered material. The vibrating sieve has a mesh size of 250 mesh to remove the caking material and obtain the fourth type of lithium iron phosphate particles.

[0147] 3. The first, second and fourth lithium iron phosphate particles are mixed to obtain a lithium iron phosphate mixture, wherein the fourth lithium iron phosphate particle accounts for 1.8% of the total amount.

[0148] Example 5

[0149] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.974, the Fe / P ratio of the second iron phosphate precursor particle is 0.961, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.62%, the sintering temperature in step 1.4 is 763℃, and the grading frequency in step 1.5 is 46 Hz.

[0150] Example 6

[0151] The process is basically the same as in Example 4, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.973, the Fe / P ratio of the second iron phosphate precursor particle is 0.961, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.64%, the sintering temperature in step 1.4 is 765℃, and the grading frequency in step 1.5 is 45 Hz; in step 3, the first, second, and fourth lithium iron phosphate particles are mixed to obtain a lithium iron phosphate mixture, wherein the fourth lithium iron phosphate particle accounts for 0.5% of the total amount.

[0152] Example 7

[0153] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.972, the Fe / P ratio of the second iron phosphate precursor particle is 0.962, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.75%, the sintering temperature in step 1.4 is 782℃, and the grading frequency in step 1.5 is 44 Hz.

[0154] Example 8

[0155] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.977, the Fe / P ratio of the second iron phosphate precursor particle is 0.960, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.69%, the sintering temperature in step 1.4 is 775℃, and the grading frequency in step 1.5 is 48 Hz.

[0156] Example 9

[0157] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.980, the Fe / P ratio of the second iron phosphate precursor particle is 0.957, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.37%, the sintering temperature in step 1.4 is 742℃, and the grading frequency in step 1.5 is 52 Hz.

[0158] Example 10

[0159] The process is basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.979, the Fe / P ratio of the second iron phosphate precursor particle is 0.959, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.43%, the sintering temperature in step 1.4 is 750℃, and the grading frequency in step 1.5 is 50 Hz.

[0160] Example 11

[0161] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.988, the Fe / P ratio of the second iron phosphate precursor particle is 0.952, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 0.99%, the sintering temperature in step 1.4 is 720℃, and the grading frequency in step 1.5 is 58 Hz.

[0162] Example 12

[0163] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.985, the Fe / P ratio of the second iron phosphate precursor particle is 0.953, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 0.80%, the sintering temperature in step 1.4 is 700℃, and the grading frequency in step 1.5 is 57 Hz.

[0164] Example 13

[0165] The process is basically the same as in Example 4, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.984, the Fe / P ratio of the second iron phosphate precursor particle is 0.954, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the carbon source accounts for 0.92% of the mass ratio of the mixed system, the sintering temperature in step 1.4 is 712℃, and the grading frequency in step 1.5 is 56 Hz; in step 3, the first, second, and fourth lithium iron phosphate particles are mixed to obtain a lithium iron phosphate mixture, wherein the fourth lithium iron phosphate particle accounts for 2.3% of the total amount.

[0166] Example 14

[0167] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.983, the Fe / P ratio of the second iron phosphate precursor particle is 0.956, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.15%, the sintering temperature in step 1.4 is 730℃, and the grading frequency in step 1.5 is 54 Hz.

[0168] Example 15

[0169] The process is essentially the same as Example 1, with the following differences: In step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.981, the Fe / P ratio of the second iron phosphate precursor particle is 0.957, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the carbon source accounts for 1.21% of the mass ratio of the mixed system, the sintering temperature in step 1.4 is 735℃, and the grading frequency in step 1.5 is 53 Hz; in step 3, the first, second, and fourth lithium iron phosphate particles are mixed to obtain a lithium iron phosphate mixture, wherein the fourth lithium iron phosphate particle accounts for 4.0% of the total amount.

[0170] Example 16

[0171] The process is basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.980, the Fe / P ratio of the second iron phosphate precursor particle is 0.958, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the carbon source accounts for 1.26% of the mass ratio of the mixed system, the sintering temperature in step 1.4 is 740℃, and the grading frequency in step 1.5 is 51 Hz; in step 3, the first, second, and fourth lithium iron phosphate particles are mixed to obtain a lithium iron phosphate mixture, wherein the fourth lithium iron phosphate particle accounts for 3.3% of the total amount.

[0172] Example 17

[0173] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.983, the Fe / P ratio of the second iron phosphate precursor particle is 0.955, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.41%, the sintering temperature in step 1.4 is 745℃, and the grading frequency in step 1.5 is 55 Hz.

[0174] Example 18

[0175] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.970, the Fe / P ratio of the second iron phosphate precursor particle is 0.964, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.99%, the sintering temperature in step 1.4 is 820℃, and the grading frequency in step 1.5 is 42 Hz.

[0176] Example 19

[0177] The process is basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.970, the Fe / P ratio of the second iron phosphate precursor particle is 0.965, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.84%, the sintering temperature in step 1.4 is 795℃, and the grading frequency in step 1.5 is 40 Hz.

[0178] Comparative Example 1

[0179] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.987, the Fe / P ratio of the second iron phosphate precursor particle is 0.952, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 0.83%, the sintering temperature in step 1.4 is 705℃, and the grading frequency in step 1.5 is 58 Hz.

[0180] Comparative Example 2

[0181] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.971, the Fe / P ratio of the second iron phosphate precursor particle is 0.963, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 1.99%, the sintering temperature in step 1.4 is 820℃, and the grading frequency in step 1.5 is 43 Hz.

[0182] Comparative Example 3

[0183] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.989, the Fe / P ratio of the second iron phosphate precursor particle is 0.951, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 0.90%, the sintering temperature in step 1.4 is 710℃, and the grading frequency in step 1.5 is 60 Hz.

[0184] Comparative Example 4

[0185] The results are basically the same as in Example 1, except that: in step 1.1, the Fe / P ratio of the first iron phosphate precursor particle is 0.970, the Fe / P ratio of the second iron phosphate precursor particle is 0.968, the mass ratio of the first iron phosphate precursor particle to the second iron phosphate precursor particle is 5.54:4.46, the mass ratio of the carbon source to the mixed system is 2.04%, the sintering temperature in step 1.4 is 830℃, and the grading frequency in step 1.5 is 39 Hz.

[0186] Application Example 1

[0187] The positive electrode sheet is prepared by using the positive electrode active materials of the above embodiments and comparative examples, including the following steps:

[0188] The prepared lithium iron phosphate, conductive carbon black (SP), polyvinylidene fluoride (PVDF), and polyvinylpyrrolidone (PVP) were mixed evenly in a ratio of 97.5:1.2:0.8:0.5 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 The compacted density is 2.6 g / cm³. 3 .

[0189] Application Example 2

[0190] The above-mentioned positive electrode sheet is used to prepare a battery, including the following steps:

[0191] 1. Preparation of negative electrode sheet

[0192] A negative electrode slurry was prepared by mixing graphite (the negative electrode active material), SP (a conductive agent), and sodium carboxymethyl cellulose (CMC) (a binder), and adding deionized water as a solvent. The mass ratio of the negative electrode active material, conductive agent, and binder was 98.6:0.6:0.8. The negative electrode slurry was coated on the upper and lower surfaces of a negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet was obtained with an areal density of 100 g / m³. 2 The compacted density is 1.6 g / cm³. 3 The negative electrode sheet includes a negative electrode material layer.

[0193] 2. Preparation of electrolyte

[0194] 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 a lithium salt concentration of 1 mol / L. Subsequently, 1.5% tris(trimethylsilyl)borate ester (TMSB) was added as an additive to obtain the electrolyte.

[0195] 3. Preparation of the diaphragm

[0196] A PE film with an aluminum oxide layer (2µm) on its surface (total thickness 15µm) was selected.

[0197] 4. Assembly and formation

[0198] 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.

[0199] Test case

[0200] 1. Particle size distribution curve:

[0201] 1) Place a certain amount of positive electrode active 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 difference between the first and second particles, save the image for subsequent statistics.

[0202] 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 areas (to avoid local area deviation). Take a clear SEM photo of each area, avoiding the edges and agglomeration areas, to ensure that the particles in the photo are independently dispersed and have no obvious overlap. Generate a particle size-quantity frequency distribution map from the statistically obtained particle size and quantity for parameter reading and calculation.

[0203] From the particle size distribution curve, the intensity of the first peak, the second peak, the fourth peak, the first valley, and the second valley, as well as the corresponding particle size, can be read. In Example 4, the particle size corresponding to the apex of the first peak is 350 nm, the particle size corresponding to the apex of the second peak is 2 µm, the particle size corresponding to the apex of the fourth peak is 18 µm, the particle size corresponding to the first valley is 1 µm, and the particle size corresponding to the second valley is 12 µm.

[0204] 2. Powder resistivity test:

[0205] The sample to be tested was ball-milled at a speed of 300 r / min. The ball used was zirconia balls with a diameter of 0.6 mm, the ball-to-material ratio was 5:1, and the ball-milling time was 20~40 min. After ball milling, the sample was placed on the electrodes of a four-probe resistivity tester (ST2722 semiconductor powder resistivity tester from Suzhou Jingge Electronics Co., Ltd.). The other electrode was pressurized to the powder at a pressure of 10 MPa, and the powder resistivity value was read.

[0206] 3. Battery DC internal resistance test

[0207] 1) Place the battery at room temperature until it reaches thermal equilibrium;

[0208] 2) Perform three standard cycles at a 1 / 3C current; use the discharge capacity of the third cycle as the standard capacity C of the battery;

[0209] 3) Adjust to the test temperature in the following order (25°C / -10°C) until thermal equilibrium is reached;

[0210] 4) Adjust the battery charge to 50% SOC at a 1 / 3C discharge rate;

[0211] 5) Discharge at a 1C rate current for 18s, record the battery voltage U2, current I before the discharge stops and the battery voltage U1 after the battery voltage stabilizes. Calculate the DC internal resistance R1 according to the formula R1=(U2-U1) / I.

[0212] 4. Battery energy density test:

[0213] Weigh the battery and record the weight as m; place the battery in the fixture, apply a force of 3000N, charge it to the upper limit voltage with a constant current of 0.33C, let it rest for 30 minutes, discharge it to the lower limit voltage with a constant current of 0.33C, 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), energy density = E1 / m (in Wh / kg).

[0214] The test results are shown in Tables 1 and 2:

[0215] Table 1:

[0216]

[0217] Table 2:

[0218]

[0219] As shown in Tables 1 and 2, compared with Comparative Examples 1-4, Examples 1-19 provided by the present invention significantly improve the filling efficiency of the interparticle gaps of the positive electrode active material by controlling the first peak intensity A1, the second peak intensity B1, the peak-valley intensity E between the first and second peaks in the particle size distribution curves of the first and second particles, and the powder resistivity b of the positive electrode active material to satisfy the relationships shown in Equations 1 and 2. This helps to improve the compaction density and electrode uniformity of the positive electrode sheet, ultimately reducing the DCR of the battery and increasing its energy density. Furthermore, compared with Examples 9-19, the positive electrode active materials of Examples 1-8 satisfy: 0.27≤E / (A1+B1)≤0.38; 6.6≤1000×n / b≤36, further improving the energy density of the battery.

[0220] 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 active material, characterized in that, The positive electrode active material includes lithium iron phosphate material, which comprises a first particle and a second particle with decreasing particle size. The first particle has a smaller particle size than the second particle. The particle size distribution curve of the positive electrode active material includes a first peak corresponding to the first particle and a second peak corresponding to the second particle. The peak intensity of the first peak is A1%, and the peak intensity of the second peak is B1%. There is a first valley between the first peak and the second peak, with an intensity of E%. The powder resistivity of the positive electrode active material is bΩ·m. The positive electrode active material satisfies the following equations 1 and 2: n = E / (A1+B1) Equation 1, 0.1≤1000×n / b≤192.5 Equation 2.

2. The positive electrode active material according to claim 1, characterized in that, 6.6≤1000×n / b≤36.

3. The positive electrode active material according to claim 1, characterized in that, 0.03≤n≤0.42； And / or, 2≤b≤500.

4. The positive electrode active material according to claim 3, characterized in that, 0.27≤n≤0.38； And / or, 10≤b≤50.

5. The positive electrode active material according to claim 1, characterized in that, 0.5≤E≤6； And / or, 4≤A1≤10; And / or, 3≤B1≤10.

6. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material satisfies: 0.27≤E / (A1+B1)≤0.

38.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The particle size corresponding to the first peak and valley is I. E 0.2µm≤I E ≤1µm; And / or, the particle size corresponding to the apex of the first peak is I. A The particle size corresponding to the apex of the second peak is I. B Where 120nm≤I A ≤800nm, 1µm≤I B ≤4µm.

8. The positive electrode active material according to claim 7, characterized in that, 2≤I B / I A ≤20。 9. The positive electrode active material according to claim 7, characterized in that, I E / I A= k1, I E / I B= k2, wherein 1.1≤k1≤6 and 0.1≤k2≤0.

9.

10. The positive electrode active material according to claim 9, characterized in that, 2≤k1 / k2≤20.

11. The positive electrode active material according to claim 1, characterized in that, The lithium iron phosphate material further includes a third particle, the particle size of which is smaller than that of the first particle, and the particle size distribution curve of the positive electrode active material includes a third peak corresponding to the third particle. The peak intensity of the third peak is C1%, where 0.5 ≤ C1 ≤ 4. And / or, the particle size corresponding to the apex of the third peak is I. C Where 20nm≤I C ≤100 nm.

12. The positive electrode active material according to claim 1, characterized in that, The lithium iron phosphate material further includes a fourth particle, the particle size of which is larger than that of the second particle, and the particle size distribution curve of the positive electrode active material includes a fourth peak corresponding to the fourth particle. The peak intensity of the fourth peak is D1%, where D1 <C1, And / or, the particle size corresponding to the apex of the fourth peak is I. D , where 4µm≤I D ≤35µm.

13. The positive electrode active material according to claim 12, characterized in that, 0.4≤D1≤3.5； And / or, there is a second valley between the second peak and the fourth peak; the intensity of the second valley is F%, where 0.5≤F≤3.

14. The positive electrode active material according to claim 13, characterized in that, The corresponding particle size of the second peak and valley is I. F Where 2.5µm≤I F ≤19.5µm.

15. The positive electrode active material according to claim 13 or 14, characterized in that, The second peak, the fourth peak, and the second valley satisfy the following relationship: F ​​< D1 < B1.

16. The positive electrode active material according to claim 14, characterized in that, I F / I B =L1, I F / I D =L2, where 1≤L1 / L2≤35.

17. The positive electrode active material according to any one of claims 1-6, 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 0.5-120 nm.

18. The positive electrode active material according to claim 17, characterized in that, The lithium iron phosphate material includes a doped metal element, which includes at least one of Ti, V, Mn, Na, Cr, Mg, Co, Al, Zr, Nb, and Ni.

19. The positive electrode active material according to claim 18, characterized in that, Based on the mass of the lithium iron phosphate material, the content of the doped metal element is 300~30000ppm.

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

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

22. The battery according to claim 21, characterized in that, The electrolyte includes additives and solvents; the additives include tris(trimethylsilyl)borate, and / or the solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

23. The battery according to claim 22, characterized in that, Based on the mass of the electrolyte, the mass content of the additive is 0.05%-2.5%, the mass content of the solvent is 45%-87.5%, and the mass ratio of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate is (1-2):(1-2):(1-2).

24. The battery according to any one of claims 21-23, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one side of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, which includes at least one of graphite and silicon-based materials.

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