Positive electrode active materials, positive electrodes, secondary batteries and electrical equipment

Abstract

This application provides a positive electrode active material, a positive electrode, a secondary battery, and an electrical device. The particle size distribution curve of the positive electrode active material satisfies a special mathematical relationship, which can have both high compaction density and better initial charge specific capacity and high initial cycle efficiency.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to positive electrode active materials, positive electrodes, secondary batteries, and electrical equipment. Background Technology

[0002] To meet market demand for devices with long battery life, battery manufacturers are committed to continuously improving battery energy density. Increasing the compaction density of the positive electrode active material is one of the key technological routes for improving battery energy density. Currently, the industry generally controls compaction density by mixing positive electrode active materials with different average particle sizes and simply adjusting their average particle size ratio or parameters such as D50 and D90. However, this method ignores the influence of the particle size distribution of the positive electrode active material on compaction density, resulting in poor precision in controlling compaction density. This leads to a limited final compaction density of the positive electrode active material. Alternatively, while a higher compaction density of the positive electrode active material can be obtained, it may result in poor performance in other electrochemical aspects of the final battery. Summary of the Invention

[0003] In view of this, embodiments of this application provide a positive electrode active material, a positive electrode, a secondary battery, and an electrical device. The particle size distribution curve of the positive electrode active material satisfies a special mathematical relationship, which can have both high compaction density and better initial charge capacity and high initial cycle efficiency.

[0004] The first aspect of this application provides a positive electrode active material, wherein the particle size distribution curve of the positive electrode active material has only a first peak, and the positive electrode active material satisfies:

[0005] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10; or,

[0006] The particle size distribution curve of the positive electrode active material includes a first peak and a second peak sequentially along a first direction, and the positive electrode active material satisfies:

[0007] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10;

[0008] Wherein, the abscissa of the particle size distribution curve is particle size, in μm; the ordinate of the particle size distribution curve is volume percentage; the first direction is the direction from 0 to positive infinity on the abscissa of the particle size distribution curve;

[0009] Dfp is the particle size in μm corresponding to the peak value of the first peak; f Dfp The peak value of the first peak;

[0010] Dsp is the particle size in μm corresponding to the peak value of the second peak; f Dsp The peak value of the second peak; Dspn = (D90 - D10) / D50, Cu = D60 / D10;

[0011] f D70 This represents the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material.

[0012] D10, D50, D60, D70, and D90 are the particle sizes corresponding to the cumulative volume percentage of the positive electrode active material reaching 10%, 50%, 60%, 70%, and 90%, respectively, with units of μm.

[0013] The two specific mathematical relationships mentioned above can respectively reflect the comprehensive influence of multiple particle size factors on the achievable compaction density and electrochemical performance of positive electrode active materials with particle size distribution curves having one or multiple peaks. By controlling the values ​​of the above mathematical formulas within the range of 7-10, the positive electrode active material can achieve a high compaction density while also maintaining good electrochemical performance.

[0014] In some embodiments of this application, 1% ≤ f Dfp ≤20%; and / or 0.1 ≤ Dfp ≤ 1. Preferably, 1% ≤ f Dfp ≤11%.

[0015] In some embodiments of this application, 0 <f D70 ≤20%; and / or 0.5μm≤D70≤10μm. Preferably, 1%≤f D70 ≤8%.

[0016] In some embodiments of this application, Dspn≤5.

[0017] In some embodiments of this application, 1.5 ≤ Cu ≤ 6.

[0018] In some embodiments of this application, 0.1 μm ≤ D10 ≤ 0.8 μm.

[0019] In some embodiments of this application, 0.3μm≤D50≤3μm.

[0020] In some embodiments of this application, 0.4μm≤D60≤8μm.

[0021] In some embodiments of this application, 0.6 μm ≤ D90 ≤ 12 μm.

[0022] In some embodiments of this application, 0.5 ≤ Dsp ≤ 10; and / or 0 <f Dsp ≤20%. Preferably, 1% ≤fDsp ≤8%.

[0023] In some embodiments of this application, the positive electrode active material includes modified or unmodified lithium iron phosphate.

[0024] In some embodiments of this application, the aspect ratio of the positive electrode active material is in the range of (1-10 / 7):1.

[0025] A second aspect of this application provides a positive electrode, including the aforementioned positive electrode active material provided in the first aspect of this application. Due to the presence of the positive electrode active material provided in this application, the positive electrode can achieve a higher compaction density and also superior electrochemical performance.

[0026] A third aspect of this application provides a secondary battery, including a negative electrode, a positive electrode provided in the second aspect of this application, and an electrolyte located between the positive and negative electrodes. Due to the presence of the positive electrode provided in this application, the secondary battery can achieve a high energy density and simultaneously exhibit superior electrochemical performance.

[0027] A fourth aspect of this application provides an electrical device including the secondary battery provided in the third aspect of this application. Because this electrical device uses the secondary battery provided in this application for power supply, it has good market competitiveness. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the particle size distribution curve of the positive electrode active material provided in an embodiment of this application;

[0029] Figure 2 This is a schematic diagram of the particle size distribution curve of the positive electrode active material provided in another embodiment of this application. Detailed Implementation

[0030] Understandably, the particle size distribution curve of a cathode active material can flexibly reflect its particle size distribution, such as parameters like D10, D50, and D90, which are also key areas of focus in the industry. However, particle size distribution curves can actually reveal more differences between various cathode active materials. For example, based on the number of peaks in the curve, they can be categorized as single-peak materials (containing only one peak), double-peak materials (containing two peaks), or even multi-peak materials (containing three or more peaks). The industry often controls the particle size of cathode active materials based on single parameters like D10, D50, and D90, which has a limited effectiveness and often results in low compaction density or an inability to balance compaction density and electrochemical performance.

[0031] To address the aforementioned issues, the applicant, through extensive theoretical derivation and experimental verification, discovered that parameters such as the ordinate and peak position of the sharp peak in the particle size distribution curve of the positive electrode active material, as well as the particle size distribution width, all affect the compaction density of the positive electrode active material. Furthermore, by adjusting these parameters to satisfy specific mathematical relationships, a positive electrode active material with both high compaction density and superior electrochemical performance can be obtained.

[0032] Specifically, this application provides a positive electrode active material; please refer to [link to relevant documentation]. Figure 1 The particle size distribution curve of the positive electrode active material has only a first peak (for ease of description, this type of positive electrode active material will be referred to as "single-peak material" below), and the positive electrode active material satisfies:

[0033] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10, Equation (1);

[0034] or,

[0035] Please see Figure 2 The particle size distribution curve of the positive electrode active material includes a first peak and a second peak sequentially along the first direction (for ease of description, this type of positive electrode active material will be referred to as "multi-peak material" below), and the positive electrode active material satisfies:

[0036] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10, Equation (2).

[0037] Wherein, the abscissa of the particle size distribution curve is particle size, in μm; the ordinate of the particle size distribution curve is volume percentage; the first direction is the direction from 0 to positive infinity on the abscissa of the particle size distribution curve;

[0038] In equations (1) and (2), Dfp is the particle size in μm corresponding to the peak value of the first peak (that is, the x-coordinate corresponding to the point with the maximum ordinate value on the first peak); f Dfp The value of the first peak (that is, the maximum value of the ordinate of the first peak);

[0039] In equation (2), Dsp is the particle size in μm corresponding to the peak value of the second peak (that is, the x-coordinate corresponding to the point with the maximum ordinate value on the second peak); f Dsp This is the peak value of the second peak (that is, the maximum value of the ordinate of the second peak).

[0040] Dspn=(D90-D10) / D50, where Dspn represents the particle size distribution width; Cu=D60 / D10, where Cu represents the non-uniformity coefficient of the positive electrode active material;

[0041] f D70 This represents the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material.

[0042] D10, D50, D60, D70, and D90 are the particle sizes corresponding to the cumulative volume percentage of the positive electrode active material reaching 10%, 50%, 60%, 70%, and 90%, respectively, with units of μm.

[0043] For ease of description, the cathode active material with only one peak in its particle size distribution curve will be referred to as "single-peak material" in the following text. Single-peak materials have a relatively high particle size concentration, making it difficult to obtain a high compaction density by combining larger and smaller particles. While multi-peak materials themselves have a combination of larger and smaller particles, making it easier to achieve a higher compaction density than single-peak materials, the industry still hopes to further improve their compaction density and achieve better electrochemical performance.

[0044] While increasing the particle size distribution width (Dspn) and / or the non-uniformity coefficient (Cu) can increase the compaction density of the cathode active material, simply increasing Dspn and / or Cu can cause battery polarization due to differences in lithium-ion diffusion coefficients and surface current densities among cathode active materials of different particle sizes. This is also detrimental to battery capacity, rate capability, and low-temperature performance. However, relying solely on these parameters is insufficient to precisely control the particle size distribution of the cathode active material, nor can its particle size distribution curve be clearly defined. The influence of peak particle size, D70 particle size, and their volume fraction—which have the highest particle size distribution frequency and the greatest impact on particle size distribution—is ignored. Furthermore, all of these parameters affect the compaction density of the cathode active material, and their effects on compaction density and electrochemical performance are intertwined. Therefore, improving the compaction density of the cathode active material while maintaining its electrochemical performance remains a challenge.

[0045] The applicant's extensive research revealed that f of unimodal materials Dfp Cu, Dispn, f D70 These parameters establish a quantitative relationship, linking the f of multi-peak materials. Dfp Cu, Dispn, f Dsp A quantitative relationship is established between the parameters, and the first particle size index M1 (M1 = -6 × f) is defined respectively. Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu) and the second particle size index M2 (M2=-6×f Dfp +80×f Dsp+Dsp+1.2×Dspn+0.3×Cu), M1 and M2 can respectively reflect the comprehensive influence of particle size factors, achievable compaction density, and electrochemical performance in single-peak and multi-peak materials. Controlling the values ​​of M1 and M2 within the range of 7-10 allows the positive electrode active material to achieve both high compaction density and good electrochemical performance, such as high initial charge capacity and initial cycle efficiency. When calculating using values ​​from a specific embodiment, for example, when f... Dfp =10%, f D70 When 10% = 6%, then simply substitute 10% and 6% into the formula for M1 for calculation.

[0046] For example, the values ​​of M1 and M2 can be independently 7.0, 7.2, 7.5, 7.8, 8.0, 8.2, 8.5, 8.8, 9.0, 9.2, 9.5, 9.8, 10.0, etc., but are not limited to these. If the value of M1 or M2 is too small (less than 7), it will result in the overall particle size of the positive electrode active material being too small, resulting in poor processing performance and concentrated particle size distribution, leading to reduced electrode compaction. If the value of M1 or M2 is too large (greater than 10), it will result in too many oversized particles in the positive electrode active material, increasing the ion diffusion path, reducing capacity, and worsening particle flowability, leading to reduced compaction.

[0047] It should be noted that in the embodiments of this application, the particle size distribution curve of the above-mentioned positive electrode active material was obtained by laser particle size analyzer. Therefore, parameters such as D10, D50, D60, D70, and D90 were also obtained by laser particle size analyzer. It can be understood that (D70 / μm) refers to the value obtained by dividing D70 by the unit μm.

[0048] In some embodiments of this application, the positive electrode active material includes, but is not limited to, modified or unmodified lithium iron phosphate. In some specific embodiments, the modified lithium iron phosphate includes, but is not limited to, doped modified lithium iron phosphate, for example, Li. 1- a A a Fe 1-x M x (P 1-y E yThe modified lithium iron phosphate (LFP) is defined as follows: O₄, 0 ≤ a < 1, 0 ≤ x < 1, 0 ≤ y < 1, and x, y, and a are not simultaneously 0; where A includes, but is not limited to, at least one alkali metal element such as Na and K; M is selected from at least one transition metal element; and E includes, but is not limited to, at least one element such as B, Si, or S. In some specific embodiments, the modified LFP can also be LFP with a coating layer on its surface. For example, the coating layer material includes, but is not limited to, conductive carbon materials, fast ion conductor materials, etc. In some specific embodiments, the modified LFP includes doped modified LFP with a coating layer. The above-mentioned modified or unmodified LFP materials can be prepared by solid-state method or synthesized by liquid-phase method.

[0049] In some embodiments of this application, 1% ≤ f Dfp ≤20%. The above applies to both unimodal and multimodal materials. For unimodal materials, controlling f... Dfp Within the aforementioned range, the risk of reduced compaction density due to the high particle size concentration of the positive electrode active material can be reduced; for multi-peak materials, controlling f Dfp Within the above range, it will not significantly reduce the volume percentage of other peaks (e.g., the volume percentage f of the second peak). Dsp This facilitates the production of positive electrode active materials with higher compaction density. For example, f Dfp The value can be, but is not limited to, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. In some specific embodiments, 1% ≤ f Dfp ≤11%.

[0050] In some embodiments of this application, 0.1 ≤ Dfp ≤ 1. Understandably, current cathode electrode production primarily employs a wet process, where the positive electrode active material is first dispersed with other substances (e.g., conductive agents, binders) in a dispersion medium to obtain a positive electrode slurry, which is then coated onto the surface of the positive electrode current collector. Controlling 0.1 ≤ Dfp ≤ 1, whether for single-peak or multi-peak materials, allows for appropriate control of the viscosity of the subsequent positive electrode slurry, thereby improving the processing capability of the positive electrode slurry. Simultaneously, it facilitates shorter diffusion paths for active ions in the positive electrode active material, resulting in a more suitable specific surface area and electrochemical reactivity, which is beneficial for the full release of material capacity. Especially when the battery is discharged at low temperatures and high rates, the contact resistance between particles is lower, thus benefiting the battery's low-temperature performance and rate performance, as well as its rate performance at low temperatures. Furthermore, it reduces the risk of agglomeration of positive electrode active material particles. For example, Dfp can be, but is not limited to, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc. In some specific embodiments, 1% ≤ fDfp ≤20%, and 0.1≤Dfp≤1. More preferably, 1%≤f Dfp ≤11%, and 0.1≤Dfp≤1.

[0051] In some embodiments of this application, Dspn ≤ 5. When the values ​​of M1 or M2 of the positive electrode active material are in the range of 7-10, further controlling the particle size distribution width Dspn of the positive electrode active material to ≤ 5 is beneficial for balancing the surface current density of different particles in the positive electrode active material during charge-discharge cycles, reducing the risk of battery polarization, and improving battery performance. Specifically, D... spn The value can be, but is not limited to, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, etc.

[0052] In some embodiments of this application, 1.5 ≤ Cu ≤ 6. Thus, for both single-peak and multi-peak materials, the positive electrode active material possesses a certain degree of inhomogeneity while effectively reducing the risk of discontinuous gradation due to the lack of intermediate particle sizes, making it easier to achieve a higher compaction density. Exemplarily, the value of Cu can be, but is not limited to, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, etc.

[0053] In some embodiments of this application, 0.1 μm ≤ D10 ≤ 0.8 μm. D10 is applicable to both single-peak and multi-peak materials. Adjusting the value of D10 can simultaneously affect the values ​​of Dispn and Cu, and has a significant impact on M1 and M2. By controlling D10 within the above range, while satisfying the limitations on M1 and M2 in the embodiments of this application, Dispn and Cu can be adjusted to further improve the compaction density and electrochemical performance of the cathode active material, and also help reduce the risk of agglomeration of the cathode active material. For example, the D10 of the cathode active material can be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, etc.

[0054] In some embodiments of this application, 0.3 μm ≤ D50 ≤ 3 μm. D50 is applicable to both single-peak and multi-peak materials. This facilitates controlling the Dispn of the cathode active material within a suitable range; furthermore, D50 is a key parameter affecting the slurry preparation performance of the cathode active material, and adjusting D50 also helps improve the process capability of the cathode slurry. Exemplarily, the D50 of the cathode active material can be, but is not limited to, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, etc.

[0055] In some embodiments of this application, 0.4 μm ≤ D60 ≤ 8 μm. D60 is applicable to both single-peak and multi-peak materials. Adjusting the D60 of the positive electrode active material can work in conjunction with D10 to control the value of Cu, thereby further facilitating the balance of the performance of the positive electrode active material. Exemplarily, the D60 of the positive electrode active material can be, but is not limited to, 0.4 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, etc.

[0056] In some embodiments of this application, 0.6 μm ≤ D90 ≤ 12 μm. Controlling D90 within this range allows for compatibility with the D10 and D50 of the cathode active material (including single-peak and multi-peak materials), thereby enabling more suitable adjustment of the particle size distribution width Dspn of the cathode active material and improving its overall performance. Furthermore, it avoids the risk of oversized particles in the cathode material, prevents lithium-ion diffusion path growth leading to reduced capacity, and also prevents oversized particles from cracking during cycling, exposing new surfaces, and sending side reactions to the electrolyte, thus reducing cycle capacity. For example, the D90 of the positive electrode active material can be, but is not limited to, 0.6 μm, 0.8 μm, 1.0 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, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, etc.

[0057] In some embodiments of this application, for unimodal materials, 0 <f D70 ≤20%. That is, for positive electrode active materials with only one sharp peak in their particle size distribution curve, the volume percentage corresponding to D70 in the particle size distribution curve is greater than 0 and less than or equal to 20%. This is beneficial for increasing the compaction density of the material. In some specific embodiments, 1% ≤ f D70 ≤20%. Furthermore, 1% ≤f D70 ≤8%. For example, the f of the positive electrode active material... D70 Possible values ​​include, but are not limited to, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, and 20%. It should also be noted that although f can be measured for multi-peak materials... D70 However, for multi-peak materials, attention should be paid to f. Dsp That's all.

[0058] In some embodiments of this application, 0.5 μm ≤ D70 ≤ 10 μm. For single-peak materials, controlling the particle size of the positive electrode active material particles, which constitute 70% of the cumulative volume percentage, within the above range can effectively reduce the path length of active ions within the positive electrode active material particles and appropriately increase their specific surface area, thereby improving the rate performance and low-temperature performance of the final battery, including rate performance at low temperatures; simultaneously, it also facilitates the release of material capacity. Exemplarily, the D70 of the positive electrode active material can be, but is not limited to, 0.5 μm, 1.0 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, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, etc. In some specific embodiments, 0 <f D70 ≤20%, and 0.5μm≤D70≤10μm. More preferably, 1%≤f D70 ≤8%, and 0.5μm≤D70≤10μm. It should also be noted that although multi-peak materials also have D70, for multi-peak materials, Dsp has a greater impact on their final electrochemical performance, and D70 can be ignored for multi-peak materials.

[0059] In some embodiments of this application, for multimodal materials, especially bimodal materials, 0% <f Dsp ≤20%. f Dsp If kept within the above range, it will not excessively crowd out f. Dfp Furthermore, the value of M2 can be controlled within the range of 7-10 while maximizing the compaction density of the positive electrode active material. In some specific embodiments, 1% ≤ f Dsp ≤20%. Furthermore, 1% ≤f Dsp ≤8%. For example, f Dsp The value can be, but is not limited to, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0060] In some embodiments of this application, for multimodal materials, especially bimodal materials, 0.5 ≤ D sp ≤10. Controlling the peak particle size of the second peak in the positive electrode active material within the above range can effectively reduce the risk of particle agglomeration. The diffusion path of active ions is also shorter, and the specific surface area is more suitable. This reduces the risk of side reactions between the positive electrode active material particles and the electrolyte, and also ensures a suitable number of contact points between particles, thereby facilitating the utilization of material capacity, improving the battery's initial efficiency, and also benefiting the battery's low-temperature and rate performance. For example, D... spThe denominator can be, but is not limited to, 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, etc. In some specific embodiments, 0.5 ≤ Dsp ≤ 10, and 0 <f Dsp ≤20%. More preferably, 0.5≤Dsp≤10, and 1≤f Dsp ≤8%.

[0061] In some embodiments of this application, the multi-peak material is a bi-peak material, that is, the particle size distribution curve of the positive electrode active material has only a first peak and a second peak arranged sequentially along the first direction.

[0062] In some embodiments of this application, the aspect ratio of the positive electrode active material is in the range of (1-10 / 7):1. That is, the length of the positive electrode active material particle is L, and the radial length (short side dimension) is d, where 1≤L / d≤10 / 7. This makes it easier to achieve close packing of the positive electrode active material and ensures a suitable specific surface area while maintaining the particle size, thereby improving the initial cycle retention rate. For example, the L / d ratio of the positive electrode active material can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.42:1, 1.428:1, etc. In the embodiments of this application, a scanning electron microscope (SEM) can be used to determine the L / d ratio of the positive electrode active material. Specifically, the cross-section of the positive electrode active material layer or particles is obtained through ion cutting, SEM images are taken, and the cross-section of the particles in the SEM images is statistically analyzed and calculated.

[0063] In this embodiment, the morphology of the positive electrode active material can also be characterized by the cross-sectional roundness of the positive electrode active material particles instead of the aspect ratio, where 0.74 ≤ cross-sectional roundness of the positive electrode active material ≤ 1. Specifically, cross-sectional roundness = diameter of the equivalent circle of the same area of ​​the cross-section of the positive electrode active material particle / length of the longest side of the cross-section. The cross-sectional roundness of the positive electrode active material particles can also be determined using SEM. Exemplarily, the cross-sectional roundness of the positive electrode active material particles can be, but is not limited to, 0.74, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, etc.

[0064] Accordingly, based on the positive electrode active material provided in the embodiments of this application, a method for preparing positive electrode active material particles can also be provided, comprising:

[0065] A positive electrode active material is provided, mixed, wherein the particle size distribution curve of the positive electrode active material has only a first peak, and the f of the positive electrode active material is provided.Dfp f D70 The values ​​of D70, Dspn, and Cu satisfy:

[0066] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10, or,

[0067] The particle size distribution curve of the positive electrode active material includes a first peak and a second peak sequentially along a first direction, and the f of the positive electrode active material Dfp f Dsp The values ​​of Dsp, Dspn, and Cu satisfy:

[0068] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10.

[0069] The above preparation method is of guiding significance for regulating the compaction density and electrochemical performance data of positive electrode active materials. Specifically, those skilled in the art can mix different positive electrode active materials according to the particle size distribution curve model (M1, M2) of the positive electrode active material provided in the embodiments of this application, and determine the selection of raw materials and the mixing ratio through the model.

[0070] Understandably, in order to improve the overall performance of the positive electrode active material, or to obtain a positive electrode active material that meets the above particle size distribution requirements, it is often necessary to mix different positive electrode active particles. Specifically, different positive electrode active particles are materials with different particle size distributions, and other characteristics are not used as distinguishing features for "whether two materials belong to the same positive electrode active material".

[0071] In some embodiments of this application, the positive electrode active material includes two or more types of positive electrode active particles. For ease of description, the different positive electrode active materials are referred to as the first positive electrode active material, the second positive electrode active material, and the Nth positive electrode active material (N is a positive integer greater than or equal to 3), and the particle size distribution of each positive electrode active particle is different.

[0072] S01. Test the particle size distribution curves of N types of positive electrode active particles respectively, and predict the volume percentage of each particle size in the mixed material. For example, for each positive electrode active particle, the volume percentage of particles with a size of a1μm is b11, b12, ..., b1n, the volume percentage of particles with a size of a2μm is b21, b22, ..., b2n, the volume percentage of particles with a size of an is bn1, bn2, ..., bnn, and so on. Therefore, taking the total volume of the mixed positive electrode active materials as the benchmark, the volume percentages of the first positive electrode active material, the second positive electrode active material, and the Nth positive electrode active material are x1, x2, ..., xn, respectively. Then, the volume percentage of particles with a size of a1μm after mixing is b1'=a1×b11+a1×b12+……+a1×b2n; the volume percentage of particles with a size of a2μm after mixing is b2'=a2×b21+a2×b22+……+a2×b2n, ...; and the volume percentage of particles with a size of anμm after mixing is bn'=an×bn1+an×bn2+……+an×bnn;

[0073] S02. Based on the predicted volume percentage of each particle size in the mixed material, plot the predicted particle size distribution curve, analyze the particle size distribution curve, calculate M1 or M2, and adjust x1, x2, ..., xn so that 7≤M1≤10 or 7≤M2≤10, determine the final x1, x2, ..., xn, and mix each positive electrode active particle according to the above volume percentage to obtain the positive electrode active material.

[0074] In some embodiments of this application, the volume percentages x1, x2, ..., xn of each positive electrode active particle are adjusted so that M1 or M2 approaches 10. In this case, the compaction density of the final positive electrode active material can be further increased.

[0075] The above preparation method is simple, easy to implement, and highly efficient, making it suitable for large-scale industrial production. Furthermore, this method can be used to quickly determine whether the mixing ratio of positive electrode active particles is sufficient to produce positive electrode active materials with high compaction density and good electrochemical performance, significantly saving time and costs in industrial production and providing valuable guidance.

[0076] In this embodiment of the application, when mixing two or more positive electrode active particles, each positive electrode active particle does not need to satisfy 7≤M1≤10 or 7≤M2≤10. As long as the positive electrode active material obtained by the final mixing satisfies 7≤M1≤10 or 7≤M2≤10, it is sufficient.

[0077] In some embodiments of this application, the positive electrode active particles are lithium iron phosphate particles, obtained by a solid-state method. In some specific embodiments of this application, a lithium source, an iron source, a phosphorus source, and a carbon source are mixed, sintered, crushed, and sieved to obtain lithium iron phosphate particles. The lithium source includes, but is not limited to, lithium carbonate and lithium dihydrogen phosphate; the iron source includes, but is not limited to, anhydrous iron phosphate and ferrous oxalate; the phosphorus source includes, but is not limited to, anhydrous iron phosphate and lithium dihydrogen phosphate; and the carbon source includes, but is not limited to, glucose, sucrose, starch, polyethylene glycol (PEG), phenolic resin, or other commonly used carbon sources in the field.

[0078] In other embodiments of this application, lithium iron phosphate particles are prepared by a liquid-phase method. The liquid-phase method can be either a self-heating evaporation process or a hydrothermal process. When using a self-heating evaporation process, the iron source includes, but is not limited to, iron blocks, ferric nitrate, or other iron salts commonly used in the field; the lithium source includes, but is not limited to, lithium carbonate, lithium hydroxide, or other lithium salts commonly used in the field; the phosphorus source includes, but is not limited to, phosphoric acid; and the carbon source includes, but is not limited to, glucose, sucrose, starch, polyethylene glycol (PEG), phenolic resin, or other carbon sources commonly used in the field. When using a hydrothermal process, the iron source includes, but is not limited to, ferrous sulfate or other ferrous salts commonly used in the field; the lithium source includes, but is not limited to, lithium hydroxide or other lithium salts commonly used in the field; the phosphorus source includes, but is not limited to, phosphoric acid; and the carbon source includes, but is not limited to, glucose, sucrose, starch, polyethylene glycol (PEG), phenolic resin, or other carbon sources commonly used in the field.

[0079] This application also provides a positive electrode, including the aforementioned positive electrode active material provided in this application embodiment. Due to the presence of the positive electrode active material provided in this application embodiment, the positive electrode can achieve a higher compaction density and superior electrochemical performance, such as a higher initial discharge specific capacity and a higher initial cycle efficiency.

[0080] In some embodiments of this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one side surface of the positive current collector. The positive electrode material layer includes the positive electrode active material, binder, and optional conductive agent provided in the embodiments of this application.

[0081] In this embodiment, the positive electrode current collector is any known current collector suitable for positive electrodes, such as aluminum foil suitable for lithium-ion battery positive electrodes. The binder is any known binder in the art suitable for positive electrodes, such as polyvinylidene fluoride. The conductive agent is any known conductive agent in the art suitable for positive electrodes, such as Super P, graphene, carbon nanotubes, etc.

[0082] This application also provides a secondary battery, including the positive electrode provided in this application embodiment. Due to the presence of the positive electrode provided in this application embodiment, the secondary battery can achieve a high energy density and simultaneously exhibit superior electrochemical performance.

[0083] In some embodiments of this application, the secondary battery includes a positive electrode, a negative electrode, and an electrolyte located between the positive electrode and the negative electrode, as provided in the embodiments of this application.

[0084] In some embodiments of this application, the secondary battery is a lithium secondary battery.

[0085] In this embodiment of the application, the secondary battery can be a liquid battery using a liquid electrolyte, a solid battery using a solid electrolyte, or a semi-solid battery.

[0086] In this embodiment, the secondary battery is fully discharged and disassembled. The positive electrode is removed and immersed in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte. The positive electrode material layer on the positive electrode current collector is scraped off with a ceramic scraper and placed in an aluminum box. It is then dried in a vacuum oven at 105°C for 6-12 hours to obtain a dried powder sample. The particle size distribution curve of the positive electrode active material is then tested according to GB / T19077.1 "Particle Size Analysis by Laser Diffraction".

[0087] This application also provides an electrical device, including the secondary battery provided in this application embodiment. Because it uses the secondary battery provided in this application embodiment for power supply, this electrical device has good market competitiveness.

[0088] In some embodiments of this application, the aforementioned electrical equipment includes, but is not limited to, vehicles and 3C electronic products. Among them, vehicles include, but are not limited to, new energy vehicles and electric vehicles.

[0089] The technical solution of this application is further described below with reference to several embodiments.

[0090] Example 1

[0091] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve with a first peak and a second peak arranged sequentially along a first direction. Specifically, the f of the positive electrode active material... Dfp =6.03%, f Dsp =4.9%, Dfp=0.46, Dsp=1.651, Dspn=2.75, Cu=3.64, D10=0.364μm, D50=0.981μm, D60=1.326μm, D90=3.06μm;

[0092] -6×f Dfp +80×f Dsp+Dsp+1.2×Dspn+0.3×Cu=9.600.

[0093] Example 2

[0094] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve with only one peak. Specifically: the f... Dfp =10.42%, Dfp=0.405, f D70 =6.19%, D70=0.675μm, Dspn=2.3, Cu=1.98, D10=0.311μm, D50=0.532μm, D60=0.615μm, D90=1.532μm;

[0095] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=8.349.

[0096] Example 3

[0097] A positive electrode active material, obtained by mixing the positive electrode active materials of Example 1 and Example 2 at a volume ratio of 9:1, wherein the particle size distribution curve of the positive electrode active material of Example 3 has a first peak and a second peak arranged sequentially along a first direction, specifically: the f of the positive electrode active material Dfp =5.97%, Dfp=0.405, f Dsp =4.75%, Dsp=1.45, Dspn=2.794, Cu=3.583, D10=0.314μm, D50=0.872μm, D60=1.125μm, D90=2.75μm;

[0098] -6×f Dfp +80×f Dsp +Dsp+1.2×Dsp n +0.3×Cu=9.323.

[0099] Example 4

[0100] A positive electrode active material, obtained by mixing the positive electrode active materials of Example 1 and Example 2 at a volume ratio of 5:5, wherein the particle size distribution curve of the positive electrode active material of Example 4 has only one peak, specifically: the f of this positive electrode active material Dfp =7.77%, Dfp=0.357, f D70=3.358%, D70=0.932μm, Dspn=2.746, Cu=3.1535, D10=0.3355, D50=0.820μm, D60=1.058μm, D90=2.585μm;

[0101] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=7.390.

[0102] Example 5

[0103] A positive electrode active material, obtained by mixing the positive electrode active materials of Example 1 and Example 2 at a volume ratio of 1:9, wherein the particle size distribution curve of the positive electrode active material of Example 5 has only one peak, specifically: the f of this positive electrode active material Dfp =9.811%, Dfp=0.314, f D70 =5.53%, D70=0.559μm, Dspn=2.72, Cu=2.95, D10=0.3355μm, D50=0.767μm, D60=0.991μm, D90=2.421μm;

[0104] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=8.543.

[0105] To highlight the beneficial effects of the embodiments of this application, the following comparative examples are provided.

[0106] Comparative Example 1

[0107] A lithium iron phosphate cathode active material, the particle size distribution curve of which sequentially includes a first peak and a second peak along a first direction, its f Dfp =9.65%, f Dsp =1.88%, Dsp=3.125, Dspn=5.4, Cu=2.08, D10=0.323μm, D50=0.575μm, D60=0.671μm, D90=3.428μm;

[0108] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=11.153.

[0109] Comparative Example 2

[0110] A lithium iron phosphate cathode active material, the particle size distribution curve of which sequentially includes a first peak and a second peak along a first direction, its f Dfp=6.38%, f Dsp =4.21%, Dsp=3.55, Dspn=4.74, Cu=4.98, D10=0.388μm, D50=1.06μm, D60=1.931μm, D90=5.412μm;

[0111] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=13.716.

[0112] Comparative Example 3

[0113] A lithium iron phosphate cathode active material, obtained by mixing Comparative Example 1 and Comparative Example 2 at a volume ratio of 5:5, has a particle size distribution curve that sequentially includes a first peak and a second peak along a first direction, and its f Dfp =8.02%, f Dsp =3.01%, Dsp=3.34, Dspn=5.863, Cu=2.61; D10=0.314μm, D50=0.6345μm, D60=0.8195μm, D90=4.034μm;

[0114] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=13.075.

[0115] Comparative Example 4

[0116] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve with only one peak. Specifically: the f... Dfp =7.72%, f D70 =7.565%, D70=9.2675μm, Dspn=1.81, Cu=3.41, D10=2.238μm, D50=7.457μm, D60=7.637μm, D90=15.758μm;

[0117] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=18.056.

[0118] Comparative Example 5

[0119] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve with only one peak. Specifically: the f... Dfp =10.96%, f D70=10.57%, D70=40.146μm, Dspn=1.21, Cu=2.13, D10=16.60μm, D50=34.40μm, D60=35.34μm, D90=58.20μm;

[0120] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=50.034.

[0121] Comparative Example 6

[0122] A lithium iron phosphate cathode active material, the particle size distribution curve of which sequentially includes a first peak and a second peak along a first direction, its f Dfp =11.27%, f Dsp =7.91%, Dsp=0.594, Dspn=3.68, Cu=1.74; D10=0.30μm, D50=0.50μm, D60=0.52μm, D90=2.14μm;

[0123] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=11.180.

[0124] Comparative Example 7

[0125] A lithium iron phosphate cathode active material, the particle size distribution curve of which sequentially includes a first peak and a second peak along a first direction, its f Dfp =5.78%, f Dsp =5.14%, Dsp=2.75, Dspn=3.022, Cu=6.61; D10=0.366μm, D50=2.018μm, D60=2.421μm, D90=6.465μm;

[0126] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=12.126.

[0127] The particle size distribution curves of the above-mentioned embodiments and comparative materials were measured according to GB / T 19077.1 "Particle size analysis by laser diffraction method", and the results are summarized above.

[0128] Performance testing

[0129] (1) Preparation of the positive electrode and testing of compaction density: The positive electrode active material, binder (specifically PVDF) and conductive agent (specifically conductive carbon black) of each embodiment and comparative example are mixed in a mass ratio of 90:5:5 and dispersed in a solvent (specifically N-methylpyrrolidone). The mixture is mixed evenly to obtain the positive electrode slurry.

[0130] The positive electrode slurry is coated on both sides of the positive electrode current collector (specifically, carbon-coated aluminum foil). (The areal density on both sides remains consistent in all embodiments, at 440 g / cm³.) 3 The samples were dried and cut into 4*20cm strips. Using a Kejing MSK-DPC-B320 precision roller press, the front and back sides of the electrode samples were pressed once each at a pressure of 35T, a roll gap of 0.12mm, and a conveyor speed of 1.5m / min. Five small circular pieces with a diameter of 30mm were removed from the strip electrode sheets to measure the thickness of the positive electrode material layer and calculate the compaction density of each positive electrode active material. The compaction density of the positive electrode material is calculated as follows: (Weight of positive electrode circular piece - Weight of 30mm diameter carbon-coated aluminum foil circular piece) / (Area of ​​30mm diameter positive electrode circular piece * Thickness of positive electrode material layer). The results are summarized in Table 1.

[0131] (2) Preparation of the test battery: The positive electrode sheet was cut into 14mm small round pieces using a punching machine. After baking in an empty drying oven at 105℃ for 2 hours, it was transferred to a glove box and assembled with the negative electrode (specifically, a lithium sheet with a diameter of 16mm). Electrolyte was injected, and the cells were sealed using a sealing machine. The cells were then left to stand at room temperature for 12-24 hours to obtain the 2016 button battery. The electrolyte was an organic solvent containing lithium salt (specifically lithium hexafluorophosphate), with a lithium salt concentration of 1 mol / L. The organic solvent included ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and vinylene carbonate. The mass ratio of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in the organic solvent was 3:6:1, and the mass fraction of vinylene carbonate was 1%.

[0132] (3) Electrochemical performance test: Connect each test battery prepared in step (2) above to the battery cabinet, charge it to 3.8V with a constant current of 0.1C, then charge it with a constant voltage until the current is ≤0.02C, let it stand for 10 minutes, and then discharge it to 2.5V with a constant current of 0.1C. Record the first charge capacity and calculate the first charge specific capacity of the battery. The first charge specific capacity = first charge capacity / mass of positive electrode active material, and the first cycle efficiency = first discharge capacity / first charge capacity × 100%. The results are summarized in Table 1.

[0133] Table 1

[0134]

[0135] As can be seen from the data in Table 1, when the particle size distribution curve of the positive electrode active material meets the limitations of the embodiments of this application, the positive electrode active material achieves high compaction density while also possessing high initial charge specific capacity and high initial cycle efficiency. The positive electrode active material of the comparative example does not meet the limitations of the embodiments of this application; it cannot achieve high compaction density in the positive electrode manufacturing process. When the comparative example positive electrode is assembled into a battery, although the initial charge specific capacity and initial cycle efficiency are good, the low compaction density of the positive electrode active material results in low energy density in the comparative example battery, which cannot meet the requirements of high-endurance power devices.

[0136] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized in that, The particle size distribution curve of the positive electrode active material has only a first peak, and the positive electrode active material satisfies: 7≤ -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10; or, The particle size distribution curve of the positive electrode active material includes a first peak and a second peak sequentially along a first direction, and the positive electrode active material satisfies: 7≤ -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10; Wherein, the abscissa of the particle size distribution curve is particle size, in μm; the ordinate of the particle size distribution curve is volume percentage; the first direction is the direction from 0 to positive infinity on the abscissa of the particle size distribution curve; Dfp is the particle size in μm corresponding to the peak value of the first peak; f Dfp The peak value of the first peak; Dsp is the particle size in μm corresponding to the peak value of the second peak; f Dsp The peak value of the second peak; Dspn=(D90-D10) / D50, Cu=D60 / D10; f D70 This represents the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material. D10, D50, D60, D70, and D90 are the particle sizes corresponding to the cumulative volume percentage of the positive electrode active material reaching 10%, 50%, 60%, 70%, and 90%, respectively, with units of μm.

2. The positive electrode active material according to claim 1, characterized in that, 1%≤f Dfp ≤20%; and / or 0.1≤Dfp≤1.

3. The positive electrode active material according to claim 2, characterized in that, 1%≤f Dfp ≤11%。 4. The positive electrode active material according to claim 1, characterized in that, 0 <f D70 ≤20%; and / or 0.5μm≤D70≤10μm.

5. The positive electrode active material according to claim 4, characterized in that, 1%≤f D70 ≤8%。 6. The positive electrode active material according to claim 1, characterized in that, Dspn≤5.

7. The positive electrode active material according to claim 1, characterized in that, 1.5≤Cu≤6.

8. The positive electrode active material according to claim 1, characterized in that, 0.1μm≤D10≤0.8μm.

9. The positive electrode active material according to claim 1, characterized in that, 0.3μm≤D50≤3 μm.

10. The positive electrode active material according to claim 1, characterized in that, 0.4 μm≤D60≤8 μm.

11. The positive electrode active material according to claim 1, characterized in that, 0.6 μm≤D90≤12 μm.

12. The positive electrode active material according to claim 1, characterized in that, 0.5 ≤ Dsp ≤ 10; and / or 0 <f Dsp ≤20%.

13. The positive electrode active material according to claim 12, characterized in that, 1%≤f Dsp ≤8%。 14. The positive electrode active material according to any one of claims 1-13, characterized in that, The positive electrode active material includes modified or unmodified lithium iron phosphate.

15. The positive electrode active material according to any one of claims 1-13, characterized in that, The aspect ratio of the positive electrode active material is in the range of (1-10 / 7):

1.

16. A positive electrode, characterized in that, Includes the positive electrode active material as described in any one of claims 1-15.

17. A secondary battery, characterized in that, The secondary battery includes the positive electrode as described in claim 16.

18. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 17.

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