Cathode active material, positive electrode, secondary battery, and electric device

Abstract

Provided are a cathode active material, a positive electrode, a secondary battery, and an electric device. A particle size distribution curve of the cathode active material satisfies a special mathematical relationship, and therefore the cathode active material has a relatively high compacted density, a relatively large first charge specific capacity, and a relatively high initial coulombic efficiency.

Description

Positive electrode active material, positive electrode, secondary battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 29, 2024, with application number 202410389552.X and application name “Positive Electrode Active Material, Positive Electrode, Secondary Battery and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of battery materials, and in particular to positive electrode active materials, positive electrodes, secondary batteries and electrical equipment. Background Art

[0003] In order to meet the market demand for long-lasting electrical equipment, battery manufacturers are committed to continuously improving the energy density of batteries. Improving the compaction density of positive electrode active materials in batteries is one of the key technical routes to improve battery energy density. At present, the industry generally controls the 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 treatment method ignores the effect of the particle size distribution of the positive electrode active material on the compaction density, and the accuracy of the control of the compaction density is poor, resulting in a limited compaction density of the final positive electrode active material. Alternatively, a positive electrode active material with a higher compaction density can be obtained, but this will lead to poor performance of other electrochemical properties of the final battery.

[0004] Summary of the Invention

[0005] In view of this, the embodiments of the present 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, and can have both a higher compaction density and a better first charge gram capacity and a higher first cycle efficiency.

[0006] In a first aspect, an embodiment of the present application provides a positive electrode active material, wherein a particle size distribution curve of the positive electrode active material has only a first peak, and the positive electrode active material satisfies:

[0007] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10; or

[0008] The particle size distribution curve of the positive electrode active material includes a first peak and a second peak in sequence along a first direction, and the positive electrode active material satisfies:

[0009] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10;

[0010] The abscissa of the particle size distribution curve is the particle size in μm; the ordinate of the particle size distribution curve is the volume percentage; the first direction is the direction from 0 to positive infinity of the abscissa of the particle size distribution curve;

[0011] f Dfp is the peak value of the first peak;

[0012] Dsp is the particle size corresponding to the peak value of the second peak in μm; f Dsp is the peak value of the second peak;

[0013] Dspn=(D90-D10) / D50, Cu=D60 / D10;

[0014] f D70 is the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material;

[0015] The D10, D50, D60, D70, and D90 are the particle sizes corresponding to when the cumulative volume percentages of the positive electrode active material reach 10%, 50%, 60%, 70%, and 90%, respectively, and the unit is μm.

[0016] The above two specific mathematical relationships can respectively reflect the comprehensive influence of multiple particle size factors on the achievable compaction density and electrochemical performance of the positive electrode active material with a particle size distribution curve of one peak 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 higher compaction density while also taking into account good electrochemical performance.

[0017] In some embodiments of the present application, 1%≤f Dfp ≤20%; and / or, 0.1≤Dfp≤1, where Dfp is the value of the particle size corresponding to the peak value of the first peak in μm.

[0018] In some embodiments of the present application, 1%≤f Dfp ≤11%.

[0019] In some embodiments of the present application, 0 <f D70 ≤20%; and / or, 0.5μm≤D70≤10μm.

[0020] In some embodiments of the present application, 1%≤f D70 ≤8%.

[0021] In some embodiments of the present application, Dspn≤5.

[0022] In some embodiments of the present application, 1.5≤Cu≤6.

[0023] In some embodiments of the present application, 0.1 μm≤D10≤0.8 μm.

[0024] In some embodiments of the present application, 0.3 μm≤D50≤3 μm.

[0025] In some embodiments of the present application, 0.4 μm≤D60≤8 μm.

[0026] In some embodiments of the present application, 0.6 μm ≤ D90 ≤ 12 μm.

[0027] In some embodiments of the present application, 0.5≤Dsp≤10; and / or, 0 <f Dsp ≤20%.

[0028] In some embodiments of the present application, 1%≤f Dsp ≤8%.

[0029] In some embodiments of the present application, the positive electrode active material includes modified or unmodified lithium iron phosphate.

[0030] In some embodiments of the present application, the aspect ratio of the positive electrode active material is in the range of (1-10 / 7):1.

[0031] A second aspect of the present invention provides a positive electrode comprising the positive electrode active material of the first aspect of the present invention. Due to the positive electrode active material provided in the present invention, the positive electrode can achieve a higher compaction density and better electrochemical performance.

[0032] The third aspect of the embodiment of the present application provides a secondary battery, including a negative electrode, the positive electrode provided by the third aspect of the embodiment of the present application, and an electrolyte located between the above-mentioned positive electrode and the negative electrode. The secondary battery can achieve a higher energy density and at the same time have better electrochemical performance.

[0033] The fourth aspect of the present application provides an electric device, including the secondary battery provided in the fourth aspect of the present application. Since the electric device is powered by the secondary battery provided in the embodiment of the present application, it has good market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the implementation methods or the description of the prior art. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] FIG1 is a schematic diagram of a particle size distribution curve of a positive electrode active material provided in one embodiment of the present application;

[0036] FIG2 is a schematic diagram of a particle size distribution curve of a positive electrode active material provided in another embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used in this application includes any and all combinations of one or more of the relevant listed items.

[0039] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0040] Understandably, the particle size distribution curve of the positive electrode active material can flexibly reflect the particle size distribution of the positive electrode active material, such as parameters such as D10, D50, and D90, which are also the focus of the industry. However, based on the particle size distribution curve, we can actually find more differences between different positive electrode active materials. For example, based on the number of peaks in the particle size distribution curve, it can be divided into single-peak materials containing only one peak, double-peak materials containing two peaks, and even multi-peak materials containing three or more peaks. The industry often controls the particle size of the positive electrode active material based on a single parameter such as D10, D50, and D90. The effect is relatively simple, which often leads to a low compaction density of the positive electrode active material, or it is impossible to take into account both the compaction density and the electrochemical performance of the positive electrode active material.

[0041] To solve the above problems, the applicant, through a large amount of theoretical derivation and experimental verification, found that parameters such as the vertical coordinate and peak position corresponding to the peak value of the sharp peak in the particle size distribution curve of the positive electrode active material, the particle size distribution width, etc. will affect the compaction density of the positive electrode active material. By regulating the above parameters so that they satisfy specific mathematical relationships, a positive electrode active material with both higher compaction density and better electrochemical performance can be obtained.

[0042] Specifically, the present embodiment provides a positive electrode active material. As shown in FIG1 , the particle size distribution curve of the positive electrode active material has only a first peak (for the convenience of description, this type of positive electrode active material is referred to as a “single-peak material” hereinafter), and the positive electrode active material satisfies the following conditions:

[0043] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10, formula (1);

[0044] or,

[0045] Referring to FIG2 , the particle size distribution curve of the positive electrode active material includes a first peak and a second peak in sequence along a first direction (for the convenience of description, this type of positive electrode active material is referred to as a “multi-peak material” hereinafter), and the positive electrode active material satisfies:

[0046] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10, formula (2).

[0047] The abscissa of the particle size distribution curve is the particle size in μm; the ordinate of the particle size distribution curve is the volume percentage; the first direction is the direction from 0 to positive infinity of the abscissa of the particle size distribution curve;

[0048] In formula (1) and formula (2), f Dfp is the peak value of the first peak (i.e., the maximum value of the ordinate of the first peak);

[0049] In formula (2), Dsp is the value of the particle size corresponding to the peak value of the second peak in μm (that is, the abscissa corresponding to the point with the maximum value of the ordinate on the second peak); f Dsp is the peak value of the second peak (that is, the maximum value of the ordinate of the second peak).

[0050] Dspn = (D90-D10) / D50, Dspn represents the particle size distribution width; Cu = D60 / D10, Cu represents the heterogeneity coefficient of the positive electrode active material;

[0051] f D70 is the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material;

[0052] The D10, D50, D60, D70, and D90 are the particle sizes corresponding to when the cumulative volume percentages of the positive electrode active material reach 10%, 50%, 60%, 70%, and 90%, respectively, and the unit is μm.

[0053] For the convenience of description, the positive electrode active material with only one peak in the particle size distribution curve is referred to as a "single-peak material" below. The particle size concentration in the single-peak material is relatively high, and it is not easy to obtain a material with a high compaction density by combining larger particles and smaller particles. Although the multi-peak material itself has a combination of larger particles and smaller particles, it is easier to achieve a higher compaction density than the single-peak material, but the industry still hopes to further improve its compaction density and exert better electrochemical performance.

[0054] Although increasing the particle size distribution width Dspn and / or the inhomogeneity coefficient Cu can increase the compaction density of the positive electrode active material, due to the different lithium ion diffusion coefficients and particle surface current densities of positive electrode active materials with different particle sizes, simply increasing Dspn and / or Cu will cause battery polarization, which is not conducive to the battery capacity, rate capability, and low-temperature performance. However, relying solely on the above parameters, it is impossible to accurately control the particle size distribution of the positive electrode active material, let alone to clearly define its particle size distribution curve. The peak particle size, D70 particle size, and its volume fraction, which have the highest frequency and the greatest impact on the particle size distribution, are ignored. The above parameters will affect the compaction density of the positive electrode active material, and even the effects on its compaction density and electrochemical performance are intertwined. It is still difficult to improve the compaction density of the positive electrode active material while taking into account the electrochemical performance of the positive electrode active material.

[0055] The applicant has found through extensive research that the f of the single-peak material Dfp 、Cu、Dspn、f D70 These parameters establish a quantitative relationship between the f Dfp 、Cu、Dspn、f Dsp Quantitative relationships are established between the parameters, and the first particle size index M1 (M1 = -6 × f 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 combined effects of various particle size factors in single-peak materials and multi-peak materials, the achievable compaction density of the materials, and the electrochemical performance. By controlling the values ​​of M1 and M2 in the range of 7-10, the positive electrode active material can achieve a higher compaction density while also taking into account better electrochemical performance, such as higher first charge capacity and first cycle efficiency. When the values ​​of a specific embodiment are substituted for calculation, for example, when f Dfp =10%, f D70 =6%, then directly substitute 10% and 6% into the formula of M1 for calculation.

[0056] 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 thereto. If the value of M1 or M2 is too small (less than 7), the particle size of the positive electrode active material will be small as a whole, the processing performance will be poor, the particle size distribution will be concentrated, and the compaction of the electrode will be reduced; if the value of M1 or M2 is too large (greater than 10), there will be too many oversized particles of the positive electrode active material, the ion diffusion path will increase, the capacity will decrease, and the particle fluidity will deteriorate, resulting in reduced compaction.

[0057] It should be noted that in the examples of this application, the particle size distribution curve of the positive electrode active material was obtained using a laser particle size analyzer. Therefore, parameters such as D10, D50, D60, D70, and D90 were also obtained using a laser particle size analyzer. It should be understood that (D70 / μm) refers to the value obtained by dividing D70 by the unit μm.

[0058] In some embodiments of the present 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 y )O4, 0≤a<1, 0≤x<1, 0≤y<1, and x, y, and a are not 0 at the same time; wherein A includes but is not limited to at least one of alkali metal elements such as Na and K; the M element is selected from at least one of transition metal elements, and the E element includes but is not limited to at least one of elements such as B, Si or S. In some specific embodiments, the modified lithium iron phosphate can also be a lithium iron phosphate having a coating layer on the surface. For example, the material of the coating layer includes but is not limited to a conductive carbon material, a fast ion conductor material, etc. In some specific embodiments, the modified lithium iron phosphate includes a doped-modified lithium iron phosphate having a coating layer. The above-mentioned modified or unmodified lithium iron phosphate material can be prepared by a solid phase method, or can be synthesized by a liquid phase method.

[0059] In some embodiments of the present application, 1%≤f Dfp ≤20%. The above situation is applicable to both single-peak materials and multi-peak materials. For single-peak materials, control f Dfp Within the above range, the risk of reduced compaction density due to high particle size concentration of the positive electrode active material can be reduced; for multi-peak materials, controlling f Dfp In the above range, the volume percentage of other peaks (such as the volume percentage of the second peak f Dsp), which is conducive to obtaining a positive electrode active material with a higher compaction density. For example, f Dfp The value of 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%.

[0060] In some embodiments of the present application, 0.1≤Dfp≤1, where Dfp is the value of the particle size corresponding to the peak value of the first peak in μm (i.e., the abscissa corresponding to the point with the maximum ordinate on the first peak). It is understandable that the current production of positive electrode sheets mostly adopts a wet process, that is, the positive electrode active material and other substances (e.g., a conductive agent, a binder) are first dispersed in a dispersion medium to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the surface of the positive electrode current collector. By controlling 0.1≤Dfp≤1, whether for single-peak materials or multi-peak materials, the viscosity of the subsequent positive electrode slurry can be controlled within an appropriate range, thereby improving the process capability of the positive electrode slurry; at the same time, it is also beneficial to control the diffusion path of active ions in the positive electrode active material to be shorter, and the specific surface area is more appropriate, and the electrochemical reaction activity of the positive electrode active material is more appropriate, which is beneficial to the full release of the material capacity, especially when the battery is discharged at a high rate at low temperature, the contact resistance between the particles is small, which is beneficial to the low temperature performance and rate performance of the battery, and also to the rate performance of the battery at low temperatures. In addition, the risk of agglomeration of positive electrode active material particles can also be reduced. Exemplarily, 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%≤f Dfp ≤20%, and 0.1≤Dfp≤1. More preferably, 1%≤f Dfp ≤11%, and 0.1≤Dfp≤1.

[0061] In some embodiments of the present application, Dspn ≤ 5. When the value of M1 or M2 of the positive electrode active material is within 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 of the positive electrode active material during the charge and discharge cycle, reducing the risk of battery polarization, and promoting battery performance. Specifically, the value of Dspn 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.

[0062] In some embodiments of the present application, 1.5 ≤ Cu ≤ 6. This allows for both unimodal and multimodal materials to achieve a certain degree of heterogeneity in the positive electrode active material while effectively reducing the risk of missing intermediate particle sizes and resulting in discontinuous grading, thereby facilitating the achievement of a higher compaction density. For example, 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, and the like.

[0063] In some embodiments of the present application, 0.1μm≤D10≤0.8μm. D10 is applicable to both single-peak materials and multi-peak materials. Regulating the value of D10 can simultaneously affect the values ​​of Dspn and Cu, and has a greater impact on M1 and M2; controlling D10 within the above range, while meeting the limitations of M1 and M2 in the embodiments of the present application, can regulate Dspn and Cu to further improve the compaction density and electrochemical performance of the positive electrode active material, and also help reduce the risk of agglomeration of the positive electrode active material. Exemplarily, the D10 of the positive electrode active material can be, but is not limited to, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, etc.

[0064] In some embodiments of the present application, 0.3 μm ≤ D50 ≤ 3 μm. D50 is applicable to both unimodal and multimodal materials. This helps to control the Dspn of the positive electrode active material within an appropriate range; in addition, D50 is a key parameter affecting the slurrying performance of the positive electrode active material. By regulating D50, it is also beneficial to improve the process capability of the positive electrode slurry. For example, the D50 of the positive electrode 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.

[0065] In some embodiments of the present application, 0.4μm≤D60≤8μm. D60 is applicable to both unimodal and multimodal materials. Regulating the D60 of the positive electrode active material can be coordinated with D10 to regulate the value of Cu, thereby further facilitating the balance of the performance of the positive electrode active material. For example, the D60 of the positive electrode active material can be, but is not limited to, 0.4μm, 0.5μm, 0.8μm, 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3.5μm, 3.8μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, 8.0μm, etc.

[0066] In some embodiments of the present application, 0.6 μm ≤ D90 ≤ 12 μm. Controlling D90 within the above range can be compatible with the D10 and D50 of the positive electrode active material (including unimodal and multimodal materials), thereby adjusting the particle size distribution width Dspn of the positive electrode active material to be more appropriate, which is beneficial to improving the overall performance of the positive electrode active material. In addition, it can avoid the risk of oversized particles in the positive electrode material, avoid the increase in lithium ion diffusion path leading to reduced capacity, and avoid the cracking of oversized particles during the cycle, exposing new surfaces and sending side reactions with the electrolyte, which reduces the cycle capacity. For example, the D90 of the positive active material may 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.

[0067] In some embodiments of the present application, for a single-peak material, 0 <f D70 ≤20%. That is, the volume percentage of D70 of the positive electrode active material with only one sharp peak in the particle size distribution curve is greater than 0 and less than or equal to 20%. This is conducive to improving the compaction density of the material. In some specific embodiments, 1%≤f D70 ≤20%. Further, 1%≤f D70 ≤8%. Exemplarily, the positive electrode active material f D70 It can be, but is not limited to, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. It should also be noted that although multimodal materials can also measure f D70 , but for multimodal materials, focus on f Dsp That's it.

[0068] In some embodiments of the present application, 0.5μm≤D70≤10μm. For single-peak materials, controlling the particle size of the positive electrode active material particles with a cumulative volume percentage of 70% within the above range can effectively reduce the path length of the active ions in 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 the rate performance at low temperatures; at the same time, it is also beneficial to the release of material capacity. Exemplarily, the D70 of the positive electrode active material can be, but is not limited to, 0.5μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 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 multimodal materials also have D70, for multimodal materials, Dsp has a greater impact on their final electrochemical performance, and multimodal materials do not need to pay attention to their D70.

[0069] In some embodiments of the present application, for multimodal materials, especially bimodal materials, 0% <f Dsp ≤20%. Dsp Control within the above range and do not occupy too much f Dfp , and the value of M2 can be controlled within the range of 7-10 while increasing the compaction density of the positive electrode active material as much as possible. In some specific embodiments, 1%≤f Dsp ≤20%. Further, 1%≤f Dsp ≤8%. For example, f Dsp The value of can be, but is not limited to, 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0070] In some embodiments of the present application, for multi-peak materials, especially bimodal materials, 0.5≤Dsp≤10. Controlling the peak particle size of the second peak of the positive electrode active material within the above range can effectively reduce the risk of agglomeration of the positive electrode active material particles, the diffusion path of the active ions is also shorter, and the specific surface area is more appropriate, which can not only reduce the risk of side reactions between the positive electrode active material particles and the electrolyte, but also ensure that there are a suitable number of contact points between the particles, thereby facilitating the utilization of the material capacity, improving the first efficiency of the battery, and also facilitating the low temperature and rate performance of the battery. Exemplarily, Dsp 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%.

[0071] In some embodiments of the present application, the multimodal material is a bimodal material, that is, the particle size distribution curve of the positive electrode active material only has a first peak and a second peak sequentially arranged along a first direction.

[0072] In some embodiments of the present 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, the radial length (short side dimension) is d, and 1≤L / d / ≤10 / 7. In this way, the positive electrode active material is easier to achieve dense stacking, and the specific surface area of ​​the positive electrode active material can be ensured to be more appropriate while ensuring the particle size of the positive electrode active material, thereby facilitating the improvement of the first cycle retention rate of the positive electrode active material. Exemplarily, the L / d 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 embodiment of the present application, the L / d of the positive electrode active material can be measured by scanning electron microscope (SEM). Specifically, by ion cutting, a cross section of the positive electrode active material layer or the positive electrode active material particle is cut, an SEM photo is taken, and the particle cross section in the SEM photo is statistically analyzed and calculated.

[0073] In the embodiment of the present application, the cross-sectional circularity of the positive electrode active material particles can also be used instead of the aspect ratio to characterize the above-mentioned morphology of the positive electrode active material, 0.74≤cross-sectional circularity of the positive electrode active material≤1. Specifically, cross-sectional circularity = diameter of the equivalent circle of the same area of ​​the cross section of the positive electrode active material particle / longest side dimension of the cross section. SEM can also be used to measure the cross-sectional circularity of the positive electrode active material particles. For example, the cross-sectional circularity 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.

[0074] According to the positive electrode active material provided in the embodiments of the present application, a method for preparing positive electrode active material particles can also be provided, comprising:

[0075] 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 Dfp 、f D70 , D70, Dspn and Cu values ​​satisfy:

[0076] 7≤-6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu≤10, or

[0077] The particle size distribution curve of the positive electrode active material includes a first peak and a second peak in sequence along the first direction, and the ... Dfp 、f Dsp , Dsp, Dspn and Cu satisfy the following values:

[0078] 7≤-6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu≤10.

[0079] The above preparation method has guiding significance for regulating the compaction density and electrochemical performance data of the positive electrode active material. Specifically, a person 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 embodiment of the present application, and determine the selection of raw materials and the mixing ratio through the model.

[0080] It is understandable that in order to improve the comprehensive performance of the positive electrode active material, or in order to obtain a positive electrode active material that meets the above-mentioned 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 the other characteristics are not used as distinguishing features of "whether two materials belong to the same positive electrode active material".

[0081] In some embodiments of the present application, the positive electrode active material includes two or more positive electrode active particles. For the convenience 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:

[0082] 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 of the mixed material. For example, for each positive electrode active particle, the volume percentage of particles with a particle size of a1μm is b11, b12, ..., b1n, the volume percentage of particles with a particle size of a2μm is b21, b22, ..., b2n, the volume percentage of particles with a particle size of an is bn1, bn2, ..., bnn, and so on. Then, based on the total volume of the mixed positive electrode active material, 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 particle size of a1 μm after mixing is b1'=a1×b11+a1×b12+...+a1×b2n; the volume percentage of particles with a particle size of a2 μm after mixing is b2'=a2×b21+a2×b22+...+a2×b2n, ...; the volume percentage of particles with a particle size of an μm after mixing is bn'=an×bn1+an×bn2+...+an×bnn;

[0083] S02. Based on the predicted volume percentages of the various particle sizes of the mixed material, a predicted particle size distribution curve is drawn, and the particle size distribution curve is analyzed to calculate M1 or M2, and x1, x2, ..., xn are adjusted to make 7≤M1≤10, or 7≤M2≤10, to determine the final x1, x2, ..., xn, and to mix the positive electrode active particles according to the above volume percentages to obtain the positive electrode active material.

[0084] In some embodiments of the present application, the volume percentages x1, x2, ..., xn of the positive electrode active particles are adjusted so that M1 or M2 infinitely approaches 10. In this case, the compaction density of the final positive electrode active material can be further improved.

[0085] The above preparation method is simple, easy to implement, and highly efficient, making it suitable for large-scale industrial production. Furthermore, the above preparation method can be used to quickly determine whether the mixing ratio of positive electrode active particles can produce a positive electrode active material with a high compaction density and good electrochemical performance, significantly saving time and costs in industrial production and providing valuable guidance.

[0086] In the embodiments of the present application, when two or more positive electrode active particles are mixed, each positive electrode active particle does not need to satisfy 7≤M1≤10, or 7≤M2≤10, as long as the final mixed positive electrode active material satisfies 7≤M1≤10, or 7≤M2≤10.

[0087] In some embodiments of the present application, the positive electrode active particles are lithium iron phosphate particles and are produced by a solid-phase method. In some specific embodiments of the present 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, lithium dihydrogen phosphate, etc.; the iron source includes, but is not limited to, anhydrous ferric phosphate, ferrous oxalate, etc.; the phosphorus source includes, but is not limited to, anhydrous ferric phosphate, lithium dihydrogen phosphate, etc.; 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.

[0088] In some other embodiments of the present application, lithium iron phosphate particles are prepared by a liquid phase method. The liquid phase method can be a self-heating evaporation process or a hydrothermal process; when the self-heating evaporation process is used, the iron source includes but is not limited to iron blocks, ferric nitrate or other iron salts commonly used in other fields; the lithium source includes but is not limited to lithium carbonate, lithium hydroxide or other lithium salts commonly used in other fields; the phosphorus source includes but is not limited to phosphoric acid; the carbon source includes but is not limited to glucose, sucrose, starch, polyethylene glycol (PEG), phenolic resin or other carbon sources commonly used in other fields. When the hydrothermal process is used, the iron source includes but is not limited to ferrous sulfate or other ferrous salts commonly used in other fields; the lithium source includes but is not limited to lithium hydroxide or other lithium salts commonly used in other fields; the phosphorus source includes but is not limited to phosphoric acid; the carbon source includes but is not limited to glucose, sucrose, starch, polyethylene glycol (PEG), phenolic resin or other carbon sources commonly used in other fields.

[0089] The present invention also provides a positive electrode comprising the aforementioned positive electrode active material provided in the present invention. Due to the inclusion of the positive electrode active material provided in the present invention, the positive electrode can achieve a higher compaction density and also achieve superior electrochemical performance, such as a higher initial discharge specific capacity and a higher initial cycle efficiency.

[0090] In some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode material layer arranged on at least one side of the positive electrode current collector. The positive electrode material layer includes the positive electrode active material provided in the embodiments of the present application, a binder, and an optional conductive agent.

[0091] In the embodiments of the present application, the positive electrode current collector is any known current collector suitable for positive electrodes, for example, aluminum foil suitable for lithium-ion battery positive electrodes. The binder is any known binder suitable for positive electrodes, for example, polyvinylidene fluoride. The conductive agent is any known conductive agent suitable for positive electrodes, for example, super P, graphene, carbon nanotubes, etc.

[0092] The present invention also provides a secondary battery comprising the positive electrode provided in the present invention. Due to the positive electrode provided in the present invention, the secondary battery can achieve a higher energy density and simultaneously have better electrochemical performance.

[0093] In some embodiments of the present application, the secondary battery includes a positive electrode and a negative electrode provided in the embodiments of the present application, and an electrolyte located between the positive electrode and the negative electrode.

[0094] In some embodiments of the present application, the secondary battery is a lithium secondary battery.

[0095] In the embodiment of the present application, the secondary battery may be a liquid battery using a liquid electrolyte, a solid-state battery using a solid-state electrolyte, or a semi-solid-state battery.

[0096] In the embodiment of the present application, the secondary battery is completely discharged and disassembled, the positive electrode is removed, and the positive electrode is immersed in dimethyl carbonate (DMC) for 10 min-20 min 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. The sample is dried in a vacuum oven at 105°C for 6 h-12 h to obtain a dry powder sample. The particle size distribution curve of the positive electrode active material is tested according to GB / T 19077.1 "Particle Size Analysis by Laser Diffraction Method".

[0097] The present invention also provides an electric device including the secondary battery provided in the present invention. As the electric device is powered by the secondary battery provided in the present invention, it has good market competitiveness.

[0098] In some embodiments of the present application, the above-mentioned electrical equipment includes but is not limited to vehicles, 3C electronic products, etc. Among them, vehicles include but are not limited to new energy vehicles, electric vehicles, etc.

[0099] The technical solution of this application is further illustrated below with multiple embodiments.

[0100] Example 1

[0101] A positive electrode active material (specifically lithium iron phosphate), whose particle size distribution curve has a first peak and a second peak arranged in sequence along a first direction, specifically: the f of the positive electrode active material Dfp =6.03%, fDsp =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;

[0102] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=9.600.

[0103] Example 2

[0104] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve having only one peak, specifically: the particle size distribution curve of the positive electrode active material has only one peak. 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;

[0105] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=8.349.

[0106] Example 3

[0107] A positive electrode active material is obtained by mixing the positive electrode active material of Example 1 and the positive electrode active material of Example 2 in a volume ratio of 9:1. The particle size distribution curve of the positive electrode active material of Example 3 has a first peak and a second peak arranged in sequence 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;

[0108] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=9.323.

[0109] Example 4

[0110] A positive electrode active material is obtained by mixing the positive electrode active material of Example 1 and the positive electrode active material of Example 2 in a volume ratio of 5:5. The particle size distribution curve of the positive electrode active material of Example 4 has only one peak. Specifically: the positive electrode active material has a particle size distribution curve of only one peak. 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;

[0111] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=7.390.

[0112] Example 5

[0113] A positive electrode active material is obtained by mixing the positive electrode active material of Example 1 and the positive electrode active material of Example 2 in a volume ratio of 1:9. The particle size distribution curve of the positive electrode active material of Example 5 has only one peak. Specifically: the positive electrode active material has a particle size distribution curve of only one peak. 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;

[0114] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=8.543.

[0115] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0116] Comparative Example 1

[0117] A lithium iron phosphate positive electrode active material, wherein the particle size distribution curve includes a first peak and a second peak in sequence along a first direction, and ... 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;

[0118] -6×f Dfp +80×f Dsp+Dsp+1.2×Dspn+0.3×Cu=11.153.

[0119] Comparative Example 2

[0120] A lithium iron phosphate positive electrode active material, wherein the particle size distribution curve includes a first peak and a second peak in sequence along a first direction, and ... 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;

[0121] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=13.716.

[0122] Comparative Example 3

[0123] A lithium iron phosphate positive electrode active material, which is obtained by mixing comparative example 1 and comparative example 2 in a volume ratio of 5:5, wherein the particle size distribution curve thereof includes a first peak and a second peak in sequence along a first direction, and the 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;

[0124] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=13.075.

[0125] Comparative Example 4

[0126] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve having only one peak, specifically: the particle size distribution curve of the positive electrode active material has only one peak. 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;

[0127] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=18.056.

[0128] Comparative Example 5

[0129] A positive electrode active material (specifically lithium iron phosphate) has a particle size distribution curve having only one peak, specifically: the particle size distribution curve of the positive electrode active material has only one peak. 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;

[0130] -6×f Dfp +80×f D70 +(D70 / μm)+1.2×Dspn+0.3×Cu=50.034.

[0131] Comparative Example 6

[0132] A lithium iron phosphate positive electrode active material, wherein the particle size distribution curve includes a first peak and a second peak in sequence along a first direction, and ... 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;

[0133] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=11.180.

[0134] Comparative Example 7

[0135] A lithium iron phosphate positive electrode active material, wherein the particle size distribution curve includes a first peak and a second peak in sequence along a first direction, and ... 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;

[0136] -6×f Dfp +80×f Dsp +Dsp+1.2×Dspn+0.3×Cu=12.126.

[0137] The particle size distribution curves of the materials in the above embodiments and comparative examples were measured according to GB / T 19077.1 “Particle size analysis by laser diffraction method”, and the results are summarized above.

[0138] Performance Testing

[0139] (1) Preparation of 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 were mixed in a mass ratio of 90:5:5, dispersed in a solvent (specifically N-methylpyrrolidone), and mixed uniformly to obtain a positive electrode slurry;

[0140] The positive electrode slurry is coated on the opposite sides of the positive electrode current collector (specifically, carbon-coated aluminum foil) (the double-sided surface density of each embodiment is consistent, which is 440 g / cm 3 ), dried, and cut into 4*20cm strips. The electrode samples were rolled once on both sides using a Kejing MSK-DPC-B320 precision roller press at a pressure of 35T, a roll gap of 0.12mm, and a speed of 1.5m / min. Five small discs with a diameter of 30mm were removed from the strips to measure the thickness of the positive electrode material layer and calculate the compacted density of each positive electrode active material. The compacted density of the positive electrode material = (weight of the positive electrode disc - weight of the 30mm diameter carbon-coated aluminum foil disc) / (area of ​​the 30mm diameter positive electrode disc * thickness of the positive electrode material layer). The results are summarized in Table 1.

[0141] (2) Preparation of test battery: The positive electrode sheet was cut into 14 mm small discs using a punching machine, baked in an empty drying oven at 105°C for 2 h, and then transferred to a glove box for assembly with the negative electrode (specifically, a lithium sheet with a diameter of 16 mm). The electrolyte was injected, sealed using a sealing machine, and allowed to stand at room temperature for 12 h to 24 h to prepare a 2016 button battery. The electrolyte is an organic solvent containing a lithium salt (specifically, lithium hexafluorophosphate), wherein the lithium salt concentration is 1 mol / L, and the organic solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and vinylene carbonate. In the organic solvent, the mass ratio of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate is 3:6:1, and the mass fraction of vinylene carbonate is 1%.

[0142] (3) Electrochemical Performance Test: Each test battery prepared in step (2) above was connected to a battery cabinet and charged to 3.8 V at a constant current of 0.1 C. Then, the battery was charged at a constant voltage to a current of ≤ 0.02 C, allowed to stand for 10 min, and then discharged to 2.5 V at a constant current of 0.1 C. The first charge capacity was recorded and the first charge gram capacity of the battery was calculated: first charge gram capacity = first charge capacity / mass of positive electrode active material, first cycle efficiency = first discharge capacity / first charge capacity × 100%. The results are summarized in Table 1.

[0143] Table 1

[0144] As can be seen from the data in Table 1, when the particle size distribution curve of the positive electrode active material meets the requirements of the embodiments of the present application, the positive electrode active material achieves a high compaction density while also having a high first charge gram capacity and a high first cycle efficiency. The positive electrode active material of the comparative example does not meet the requirements of the embodiments of the present application, and it is unable to achieve a high compaction density during the positive electrode manufacturing process. When the comparative example positive electrode is assembled into a battery, although the first charge gram capacity and first cycle efficiency are good, the compaction density of the positive electrode active material is low, resulting in a low energy density of the comparative example battery, which cannot meet the requirements of high-endurance electrical equipment.

[0145] The above is an exemplary embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made thereto without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A positive electrode active material, wherein The particle size distribution curve of the positive electrode active material has only the 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 in sequence 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; The abscissa of the particle size distribution curve is the particle size in μm; the ordinate of the particle size distribution curve is the volume percentage; the first direction is the direction from 0 to positive infinity of the abscissa of the particle size distribution curve; f Dfp is the peak value of the first peak; Dsp is the particle size corresponding to the peak value of the second peak in μm; f Dsp is the peak value of the second peak; Dspn=(D90-D10) / D50, Cu=D60 / D10; f D70 is the volume percentage corresponding to D70 in the particle size distribution curve of the positive electrode active material; The D10, D50, D60, D70, and D90 are the particle sizes corresponding to when the cumulative volume percentages of the positive electrode active material reach 10%, 50%, 60%, 70%, and 90%, respectively, and the unit is μm.

2. The positive electrode active material according to claim 1, wherein 1%≤f Dfp ≤20%; and / or, 0.1≤Dfp≤1, where Dfp is the value of the particle size corresponding to the peak value of the first peak in μm.

3. The positive electrode active material according to claim 2, wherein 1％≤f Dfp ≤11％。 4. The positive electrode active material according to any one of claims 1 to 3, wherein 0 <f D70 ≤20%; and / or, 0.5μm≤D70≤10μm.

5. The positive electrode active material according to claim 4, wherein 1％≤f D70 ≤8％。 6. The positive electrode active material according to any one of claims 1 to 5, wherein Dspn≤5.

7. The positive electrode active material according to any one of claims 1 to 6, wherein 1.5≤Cu≤6.

8. The positive electrode active material according to any one of claims 1 to 7, wherein 0.1μm≤D10≤0.8μm.

9. The positive electrode active material according to any one of claims 1 to 8, wherein 0.3μm≤D50≤3μm.

10. The positive electrode active material according to any one of claims 1 to 9, wherein 0.4μm≤D60≤8 μm.

11. The positive electrode active material according to any one of claims 1 to 10, wherein 0.6μm≤D90≤12μm.

12. The positive electrode active material according to any one of claims 1 to 11, wherein 0.5≤Dsp≤10; and / or, 0 <f Dsp ≤20%.

13. The positive electrode active material according to claim 12, wherein 1％≤f Dsp ≤8％。 14. The positive electrode active material according to any one of claims 1 to 13, wherein 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 to 14, wherein The aspect ratio of the positive electrode active material is in the range of (1-10 / 7):

1.

16. A positive electrode, wherein The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 15.

17. A secondary battery, wherein: The secondary battery includes the positive electrode according to claim 16.

18. An electrical device, wherein: The electric device includes the secondary battery according to claim 14.

Images