Lithium iron phosphate cathode active material, method for preparing the same, and lithium-ion battery

Abstract

A lithium iron phosphate cathode active material, a method for preparing the same, and a lithium-ion battery are provided. The cathode active material is formed by mixing first and second lithium iron phosphate materials. When the volume distribution percentages of the first and second lithium iron phosphate materials reach a maximum value, the corresponding particle sizes are D 1 mo μm and D 2 mo μm, 0.3≦D 1 mo ≦3.2 and 1≦D 2 mo ≦5, D 1 mo <D 2 mo The sphericity of the first and second lithium iron phosphate materials is A1 and A2, respectively. The first lithium iron phosphate material satisfies the following relationship: 0.49<0.643D 1 mo +0.439A1<2.3. The second lithium iron phosphate material satisfies the following relationship: 0.41<1.07D 2 mo +2.44A2-1.70D 2 mo ×A2<1.9.

Description

[Technical Field]

[0001] Cross-reference of related applications This disclosure claims priority to Chinese Patent Application No. 202210228577.2, filed on March 7, 2022, titled "Lithium iron phosphate positive electrode active material, preparation method thereof, positive electrode sheet and lithium ion battery," which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to the field of lithium-ion batteries, and more specifically to lithium iron phosphate cathode active materials, methods for preparing the same, and lithium-ion batteries. [Background technology]

[0003] Lithium iron phosphate materials are widely used due to their high safety, low cost, environmental compatibility, and other advantages. However, lithium iron phosphate materials also have obvious drawbacks, such as a low maximum compressive density (2.1-2.5 g / cm³). 3 As a result, batteries prepared with lithium iron phosphate materials have a lower energy density, which fails to meet the requirement for batteries with a long lifespan. To improve the energy density of batteries, lithium iron phosphate materials with high compressive density have become a common direction of development in industry. However, with lithium iron phosphate materials with high compressive density, the electrochemical performance of the battery is often reduced as the compressive density of lithium increases. [Overview of the Initiative] [Means for solving the problem]

[0004] To solve the above technical problems, the present disclosure provides a lithium iron phosphate cathode active material, a method for preparing the same, and a lithium-ion battery. By adjusting the particle size and sphericity parameters of two lithium iron phosphate materials that form the lithium iron phosphate cathode active material, the cathode active material obtained by mixing the two materials in any ratio can have a high compression density, and the battery prepared thereby has excellent electrochemical performance.

[0005] In a first aspect, the present disclosure provides a lithium iron phosphate cathode active material. The lithium iron phosphate cathode active material is formed by mixing a first lithium iron phosphate material and a second lithium iron phosphate material. The first lithium iron phosphate material satisfies the following relational expression, that is, 0.49 < 0.643D 1 mo + 0.439A1 < 2.3. The second lithium iron phosphate material satisfies the following relational expression, that is, 0.41 < 1.07D 2 mo + 2.44A2 - 1.70D 2 mo × A2 < 1.9. When the volume distribution percentage of the first lithium iron phosphate material reaches the maximum value, the corresponding particle size is D 1 mo μm, and 0.3 ≤ D 1 mo ≤ 3.2. When the volume distribution percentage of the second lithium iron phosphate material reaches the maximum value, the corresponding particle size is D 2 mo μm, 1 ≤ D 2 mo ≤ 5, and D 1 mo < D 2 mo is satisfied. A1 and A2 respectively represent the sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material.

[0006] Regarding positive electrode active materials, the compressive density of the positive electrode active material is generally controlled by the particle size and particle size distribution of the lithium iron phosphate material, and the contribution of particle sphericity to particle packing is hardly considered. This results in an increase in the compressive density of the mixed lithium iron phosphate positive electrode material, which impairs the charge-discharge cycle performance of the lithium-ion battery. According to the lithium iron phosphate positive electrode active material provided in this disclosure, D mo The range, and the D of the two-component lithium iron phosphate material mo By defining the range of the relevant relation for sphericity A, it is ensured that the positive electrode active material obtained by mixing two lithium iron phosphate materials in any ratio has a high packing density, and the positive electrode sheet prepared therefrom has a packing density of 2.6 g / cm³. 3 It has a potentially high compressive density, which promotes an improvement in the energy density of batteries prepared with this positive electrode active material. In addition, batteries prepared with this positive electrode active material have excellent electrochemical performance, and in particular, their cycle performance is not degraded. The maximum compressive density of the positive electrode sheet containing the positive electrode active material is 2.6 g / cm³. 3 The above conditions can be met, and the battery prepared therein will have excellent electrochemical performance.

[0007] In some embodiments, D 1 mo The value of is 0.32 ≤ D 1 mo It is within the range of ≤2.45.

[0008] In some embodiments, D 1 mo The value of is 0.40 ≤ D 1 mo It is within the range of ≤2.45.

[0009] In some embodiments, D 2 mo The value of is 1.2 ≤ D 2 mo It is within the range of ≤5.

[0010] In some embodiments, D2 mo The value of is 1.25 ≤ D 2 mo It is within the range of ≤4.95.

[0011] In some embodiments, the values ​​of A1 and A2 are within the ranges of 0.5 ≤ A1 < 1 and 0.5 ≤ A2 < 1, respectively.

[0012] In some embodiments, the value of A1 is within the range of 0.51 ≤ A1 ≤ 0.95.

[0013] In some embodiments, the value of A2 is within the range of 0.51 ≤ A2 ≤ 0.95.

[0014] In some embodiments, the first lithium iron phosphate material satisfies the following relationship, i.e., 0.5 ≤ 0.643D 1 mo The condition +0.439A1 ≤ 2.29 is satisfied.

[0015] In some embodiments, the first lithium iron phosphate material is given by the following relationship, i.e., 0.6 ≤ 0.643D 1 mo The condition +0.439A1 ≤ 2.29 is satisfied.

[0016] In some embodiments, the second lithium iron phosphate material satisfies the following relationship, i.e., 0.42 ≤ 1.07D 2 mo +2.44A2-1.70D 2 mo The condition ×A2 ≤ 1.89 is satisfied.

[0017] In some embodiments, the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is in the range of 1:(0.25~3).

[0018] In some embodiments, the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is in the range of 1:(0.25~2.5).

[0019] In some embodiments, the first lithium iron phosphate material and the second lithium iron phosphate material have a carbon coating layer on their surface.

[0020] According to the lithium iron phosphate positive electrode active material provided in a first aspect of this disclosure, the positive electrode active material is formed by mixing two lithium iron phosphate materials in any ratio that meet the requirements of particle size and sphericity parameters, has a high compressive density, and batteries prepared with this positive electrode active material have good cycle performance and rate performance. The maximum compressive density of a positive electrode sheet containing the positive electrode active material is 2.6 g / cm³. 3 The above conditions can be met, and the battery prepared therein will have excellent electrochemical performance.

[0021] In a second embodiment, the present disclosure provides a method for preparing lithium iron phosphate cathode active material. The method comprises the following steps: A first lithium iron phosphate material and a second lithium iron phosphate material are provided. When the volume distribution percentage of the first lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 1 mo It is μm, and 0.3≦D 1 mo ≤3.2. When the volume distribution percentage of the second lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 2 mo The value is μm, where 1 ≤ D 2 mo ≤ 5, D 1 mo <D 2 mo The sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material are A1 and A2, respectively. The first lithium iron phosphate material is given by the following relationship, i.e., 0.49 < 0.643D 1 mo The second lithium iron phosphate material satisfies the following relationship, i.e., 0.41 < 1.07D. 2 mo +2.44A2-1.70D 2 moThe condition ×A2 < 1.9 is satisfied. The first lithium iron phosphate material and the second lithium iron phosphate material are mixed to obtain a lithium iron phosphate cathode active material.

[0022] In a method for preparing lithium iron phosphate cathode active material, two lithium iron phosphate materials satisfying specific particle size parameter requirements are mixed in any ratio to ensure that the resulting cathode active material has a high compressive density, and batteries prepared with this cathode active material have good cycle performance and rate performance. This preparation method has a simple process and is easy to operate, making it suitable for use in large-scale production.

[0023] In a third aspect, the Disclosure provides a lithium-ion battery. The lithium-ion battery includes a positive electrode sheet. The positive electrode sheet includes a lithium iron phosphate positive electrode active material according to a first aspect of the Disclosure, or a lithium iron phosphate positive electrode active material prepared according to a method described in a second aspect of the Disclosure.

[0024] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, as well as an electrolyte and separator disposed between the positive electrode sheet and the negative electrode sheet.

[0025] In some embodiments, the maximum compressed density of the positive electrode sheet is 2.6 g / cm³. 3 It is larger than that.

[0026] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector.

[0027] In some embodiments, the positive electrode active material layer comprises lithium iron phosphate positive electrode active material, a binder, and a conductive agent.

[0028] Lithium-ion batteries using this positive electrode sheet have high energy density and excellent cycle performance. [Brief explanation of the drawing]

[0029] [Figure 1] The cycle performance curves of each pouch-type battery in embodiments 1 to 5 of this disclosure and comparative embodiments 1 and 2 are shown. [Figure 2] This is a process flow chart of a method for preparing lithium iron phosphate cathode active material according to the embodiments of this disclosure. [Modes for carrying out the invention]

[0030] This disclosure provides a lithium iron phosphate cathode active material, a method for preparing the same, and a lithium-ion battery. By adjusting the particle size and sphericity parameters of two lithium iron phosphate materials, a cathode active material obtained by mixing the two materials in any ratio can be made to have a high compressive density, and a battery prepared therefrom has excellent electrochemical performance.

[0031] In a first aspect, the present disclosure provides a lithium iron phosphate cathode active material. The lithium iron phosphate cathode active material is formed by mixing a first lithium iron phosphate material and a second lithium iron phosphate material. The first lithium iron phosphate material satisfies the following relationship, i.e., 0.49 < 0.643D 1 mo The second lithium iron phosphate material satisfies the following relationship, i.e., 0.41 < 1.07D. 2 mo +2.44A2-1.70D 2 mo The condition ×A2 < 1.9 is satisfied. When the volume distribution percentage of the first lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 1 mo It is μm, and 0.3≦D 1 mo ≤3.2. When the volume distribution percentage of the second lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 2 mo μm, 1≦D 2 mo ≤ 5, D 1 mo <D 2mo That is. A1 and A2 respectively represent the sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material.

[0032] Regarding the positive electrode active material, the compression density of the positive electrode active material is generally controlled by considering the particle size and particle size distribution of the lithium iron phosphate material, and the contribution of the sphericity of the particles to the packing of the particles is hardly considered. This results in the degradation of the charge-discharge cycle performance and the like of the lithium-ion battery when the compression density of the mixed lithium iron phosphate positive electrode material increases. According to the lithium iron phosphate positive electrode active material provided in the embodiments of the present disclosure, D mo range, and the D of the two-component lithium iron phosphate material mo and the corresponding relational expression range of the sphericity A are defined, so that the positive electrode active material obtained by mixing the two lithium iron phosphate materials in any ratio is ensured to have a high packing density, and the positive electrode sheet prepared therefrom has a high compression density that can be 2.6 g / cm 3 or more, which promotes the improvement of the energy density of the battery prepared with the positive electrode active material. In addition, the battery prepared with the positive electrode active material has excellent electrochemical performance, and in particular, the cycle performance is not deteriorated. The maximum compression density of the positive electrode sheet containing the positive electrode active material can be 2.6 g / cm 3 or more, and the battery prepared therefrom has excellent electrochemical performance.

[0033] In some embodiments, 0.5 ≦ 0.643D 1 mo + 0.439A1 ≦ 2.29, and further, 0.6 ≦ 0.643D 1 mo + 0.439A1 ≦ 2.29.

[0034] In some embodiments, 0.42 ≦ 1.07D 2 mo + 2.44A2 - 1.70D 2 mo × A2 ≦ 1.89.

[0035] In some embodiments, the first lithium iron phosphate material D 1 mo The value of the second lithium iron phosphate material D 2 mo The values ​​can be obtained from the respective laser particle size distribution diagrams. The test method can be found in GB / T 19077-2016 / ISO 13320:2009 Particle size analysis-Laser diffraction methods. Specifically, the test equipment is a laser particle size analyzer (such as the Malvern 3000).

[0036] Sphericity values ​​A1 and A2 can be obtained by averaging the ratio of the longest diameter to the shortest diameter of multiple particles (typically 400-800 particles) in scanning electron microscopy (SEM) images of the first and second lithium iron phosphate materials. In particular, A1 is obtained by determining the longest to shortest diameter of each particle in the SEM image of the first lithium iron phosphate material using the software Image J. The sphericity of each particle is defined as the ratio of the longest diameter to the shortest diameter. The sphericity A1 of the first lithium iron phosphate material is the average of the sphericity of all particles in the SEM image. The closer A1 and A2 are to 1, the more desirable the sphere of the material tends to be.

[0037] In some embodiments, D 1 mo <D 2 mo This is the D of lithium iron phosphate material. 1 mo When the D of lithium iron phosphate material is small, the diffusion pathway of lithium ions is relatively short, and the prepared battery has good electrical performance. 2 mo When is large, the compressible density of the positive electrode active material can be increased. Combined with the relationship between sphericity A1 and A2, the particle size D within the above range can be expressed. moGiven that two lithium iron phosphate materials can be made to form a dense packing when they are uniformly mixed in any ratio, thereby increasing the compressive density of the positive electrode sheet prepared with the positive electrode active material prepared therefrom without impairing the battery's cycle performance.

[0038] In some embodiments, D 1 mo The value is 0.32μm≦D 1 mo It is within the range of ≤2.45μm. Furthermore, D 1 mo The value is 0.40μm≦D 1 mo It is within the range of ≤2.45 μm.

[0039] In some embodiments, D 2 mo The value is 1.2μm ≤ D 2 mo It is within the range of ≤5μm. Furthermore, D 2 mo The value is 1.25 μm ≤ D 2 mo It is within the range of ≤4.95 μm.

[0040] D 1 mo and D 2 mo If it is within the above range, D 1 mo <D 2 mo In this case, the two lithium iron phosphate materials can adequately ensure a high compressive density of the positive electrode sheet and good electrochemical performance of the battery.

[0041] In some embodiments, 0.5 ≤ A1 < 1 and 0.5 ≤ A2 < 1. When the sphericity of the two lithium iron phosphate materials is within the above range, it can be reliably ensured that the positive electrode sheet has a high compressive density. Furthermore, in some embodiments, the value of A1 is within the range of 0.51 ≤ A1 ≤ 0.95. The value of A2 is within the range of 0.51 ≤ A2 ≤ 0.95. In this disclosure, the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material may be any ratio, in which case the maximum compressive density of the positive electrode sheet prepared with the lithium iron phosphate positive electrode active material is high, and the cycle performance of the battery prepared therewith is good. In some embodiments of this disclosure, the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is within the range of 1:(0.25~3), and further within the range of 1:(0.25~2.5), for example, within the range of 1:(0.4~1.5). In this case, the positive electrode active material formed by mixing two lithium iron phosphate materials can sufficiently ensure a high compressive density of the electrode sheet and good cycle performance of the battery.

[0042] In some embodiments, the first lithium iron phosphate material and the second lithium iron phosphate material may have a carbon coating layer on their surface, which can be obtained by sequentially polishing, spray-drying, and sintering a mixed slurry of a phosphorus source, an iron source, a lithium source, and a carbon source. In this disclosure, the specific methods for preparing the two lithium iron phosphate materials are not limited. The presence of the carbon coating layer allows the first and second lithium iron phosphate materials to have good electrical conductivity and fewer side reactions with the electrolyte. The positive electrode active material obtained by mixing the two has good electrical conductivity and good battery cycle performance.

[0043] According to the lithium iron phosphate positive electrode active material provided in a first aspect of this disclosure, the positive electrode active material is formed by mixing two lithium iron phosphate materials in any ratio that meet the requirements of particle size and sphericity parameters, has a high compressive density, and batteries prepared with this positive electrode active material have good cycle performance and rate performance. The maximum compressive density of a positive electrode sheet containing the positive electrode active material is up to 2.6 g / cm³. 3 The above conditions can be met, and the battery prepared therein will have excellent electrochemical performance.

[0044] In a second embodiment, the present disclosure provides a method for preparing lithium iron phosphate cathode active material. As shown in Figure 2, the method comprises the following steps: S101: A first lithium iron phosphate material and a second lithium iron phosphate material are provided. When the volume distribution percentage of the first lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 1 mo It is μm, and 0.3≦D 1 mo ≤3.2. When the volume distribution percentage of the second lithium iron phosphate material reaches its maximum value, the corresponding particle size is D 2 mo μm, 1≦D 2 mo ≤ 5, D 1 mo <D 2 mo The sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material are A1 and A2, respectively, where 0.49 < 0.643D. 1 mo +0.439A1 < 2.3 and 0.41 < 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 < 1.9. S102: The first lithium iron phosphate material and the second lithium iron phosphate material are mixed to obtain a lithium iron phosphate cathode active material.

[0045] In a method for preparing lithium iron phosphate cathode active material, two lithium iron phosphate materials satisfying specific particle size parameter requirements are mixed in any ratio to ensure that the resulting cathode active material has a high compressive density, and batteries prepared with this cathode active material have good cycle performance and rate performance. This preparation method has a simple process and is easy to operate, making it suitable for use in large-scale production.

[0046] A positive electrode sheet is provided. The positive electrode sheet comprises a lithium iron phosphate positive electrode active material according to a first aspect of this disclosure, or a lithium iron phosphate positive electrode active material prepared according to a method described in a second aspect of this disclosure.

[0047] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The positive electrode active material layer includes lithium iron phosphate positive electrode active material, a binder, and a conductive agent.

[0048] In some embodiments, the maximum compressed density of the positive electrode sheet is 2.6 g / cm³. 3 That concludes the explanation. In some embodiments, the maximum compressed density is 2.65 to 2.8 g / cm³. 3 Furthermore, 2.67~2.75 g / cm³ 3 It should be understood that the maximum compressive density of the positive electrode sheet refers to the corresponding compressive density of the electrode sheet when the active material particles in the positive electrode sheet are compressed under a certain pressure.

[0049] The positive electrode material layer can be formed by coating a positive electrode paste containing lithium iron phosphate positive electrode active material, a conductive agent, a binder, and a solvent onto a positive electrode current collector. The solvent may be one or more of N-methylpyrrolidone (NMP), acetone, and dimethylacetamide (DMAC). The positive electrode current collector contains one of aluminum foil, carbon-coated aluminum foil, and perforated aluminum foil. The conductive agent may include, but is not limited to, one or more of carbon nanotubes, graphene, carbon black, carbon fibers, etc. The binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylate, polyacrylonitrile (PAN), sodium carboxymethylcellulose (CMC), and sodium alginate.

[0050] In a third embodiment, the disclosure provides a lithium-ion battery, which includes a positive electrode sheet.

[0051] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, as well as an electrolyte and separator disposed between the positive electrode sheet and the negative electrode sheet.

[0052] Lithium-ion batteries using this positive electrode sheet have high energy density and excellent cycle performance.

[0053] The following descriptions represent several implementations of this disclosure. It should be noted that several improvements and modifications can be made by those skilled in the art without departing from the principles of this disclosure, provided that they remain within the scope of protection of this disclosure.

[0054] The technical solutions of this disclosure will be described below in combination with specific embodiments.

[0055] Exemplary Example 1

[0056] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0057] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage of LFP-1 reached its maximum value, the corresponding particle size was 0.46 μm and the sphericity was 0.8. That is, D 1 mo A1 is 0.46, A1 is 0.8, and 0.643D 1 mo +0.439A1 = 0.65. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage of LFP-2 reached its maximum value, the corresponding particle size was 1.08 μm and the sphericity was 0.7. That is, D 2 mo A is 1.08, A2 is 0.7, and 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 1.58.

[0058] LFP-1 material and LFP-2 material were mixed in a weight ratio of 4:6. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0059] The lithium iron phosphate cathode active material LFP-3 was prepared into a cathode sheet as follows: The lithium iron phosphate cathode active material LFP-3 was mixed with a conductive agent, namely carbon nanotubes, a binder (specifically polyvinylidene fluoride (PVDF)), and a solvent N-methylpyrrolidone (NMP) in a weight ratio of 100:3:2:60 and uniformly mixed to obtain a cathode paste. The cathode paste was coated on both sides of a carbon-coated aluminum foil and dried to a thickness of 360 g / m². 2 A double-sided positive electrode sheet with a surface density was obtained. The maximum compressed density of the positive electrode sheet without particle damage was determined. The maximum compressed density of the positive electrode sheet was 2.72 g / cm³. 3 That was the case.

[0060] Preparation of a pouch-type lithium-ion battery. A negative electrode plate was prepared by coating copper foil with a mixed paste containing graphite, conductive agent (carbon black), binder (specifically SBR), and water in a ratio of 100:2:5:120 (by weight), and drying it. In Example 1, a positive electrode sheet prepared with lithium iron phosphate positive electrode active material LFP-3 was used as the positive electrode. A polypropylene film was used as the separator. A solution containing 1.0 mol / L of LiPF6 in an ethylene carbonate (EC) to dimethyl carbonate (DMC) ratio of 1:1 (by volume) was used as the electrolyte. After assembly, a pouch-type lithium-ion battery was obtained.

[0061] Exemplary Example 2

[0062] The method for preparing the lithium iron phosphate cathode active material in Example 2 differed from that in Example 1 in that the LFP-1 material and the LFP-2 material were mixed in a weight ratio of 7:3.

[0063] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 2 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 2 was 2.68 g / cm³. 3 It was determined that this was the case.

[0064] Exemplary Example 3

[0065] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0066] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 2.41 μm (i.e., D 1 mo (is 2.41), sphericity A1 is 0.7, and 0.643D 1 mo+0.439A1 = 1.86. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage of LFP-2 reached its maximum value, the corresponding particle size was 4.36 μm (i.e., D 2 mo (is 4.36), sphericity A2 is 0.6, and 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 1.68.

[0067] LFP-1 material and LFP-2 material were mixed in a weight ratio of 8:2. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0068] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 3 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 3 was 2.65 g / cm³. 3 It was determined that this was the case.

[0069] Exemplary Example 4

[0070] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0071] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.46 μm (i.e., D 1 mo (is 0.46), sphericity A1 is 0.8, and 0.643D 1 mo +0.439A1 = 0.65. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 3.45 μm (i.e., D 2 mo (is 3.45), sphericity A2 is 0.7, and 1.07D 2 mo +2.44A2-1.70D 2 mo×A2 = 1.29.

[0072] LFP-1 material and LFP-2 material were mixed in a 5:5 weight ratio. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0073] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 4 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 4 was 2.70 g / cm³. 3 It was determined that this was the case.

[0074] Exemplary Example 5

[0075] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0076] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 1.32 μm (i.e., D 1 mo (is 1.32), sphericity A1 is 0.7, and 0.643D 1 mo +0.439A1 = 1.16. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 2.31 μm (i.e., D 2 mo (is 2.31), sphericity A2 is 0.6, and 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 1.58.

[0077] LFP-1 material and LFP-2 material were mixed in a weight ratio of 4:6. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0078] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 5 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 5 was 2.68 g / cm³. 3 It was determined that this was the case.

[0079] Exemplary Example 6

[0080] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0081] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 3.16 μm (i.e., D 1 mo (is 3.16), sphericity A1 is 0.58, and 0.643D 1 mo +0.439A1 = 2.29. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 4.94 μm (i.e., D 2 mo (is 4.94), sphericity A2 is 0.57, and 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 1.89.

[0082] LFP-1 and LFP-2 materials were mixed in a weight ratio of 3:7. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0083] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 6 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 6 was 2.68 g / cm³. 3 It was determined that this was the case.

[0084] Exemplary Example 7

[0085] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0086] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.32 μm (i.e., D 1 mo (is 0.32), sphericity A1 is 0.9, and 0.643D 1 mo +0.439A1 = 0.60. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 3.96 μm (i.e., D 2 mo (is 3.96), sphericity A2 is 0.89, and 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 0.42.

[0087] LFP-1 material and LFP-2 material were mixed in a weight ratio of 4:6. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0088] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Example 7 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Example 7 was 2.66 g / cm³. 3 It was determined that this was the case.

[0089] To highlight the beneficial effects of this disclosure, the following exemplary comparative examples 1 to 5 are provided.

[0090] Exemplary Example 1

[0091] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0092] The first lithium iron phosphate material LFP-1 is used, D1 mo The size was 3.32 μm, and A1 was 0.8, but 0.643 D 1 mo +0.439A1 = 2.49, which was outside the range of (0.49, 2.3) as defined in this disclosure. A second lithium iron phosphate material LFP-2 was used, D 2 mo The size was 3.98 μm, and A2 was 0.9, but 1.07 D 2 mo +2.44A2-1.70D 2 mo ×A2 = 0.37, which was outside the range of (0.41, 1.9) as defined in this disclosure.

[0093] LFP-1 material and LFP-2 material were mixed in a 1:1 weight ratio. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0094] Following the method described in Example 1, the lithium iron phosphate positive electrode active material LFP-3 obtained in Comparative Example 1 was prepared into a positive electrode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the positive electrode sheet in Comparative Example 1 was 2.65 g / cm³. 3 It was determined that the maximum compressed density of the positive electrode sheet in Comparative Example 1 was 2.6 g / cm³. 3 Although the above was achieved, the battery's charge-discharge cycle stability was poor. As shown in Table 1 below, the first cycle discharge ratio capacity and capacity retention rate after 1000 cycles of the battery with a positive electrode sheet in Comparative Example 1 were clearly lower than those in Example 1.

[0095] Exemplary Comparative Example 2

[0096] A lithium iron phosphate cathode material was provided in which only one lithium iron phosphate material was used as the cathode active material. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.88 μm and the sphericity A was 0.9.

[0097] Following the method described in Example 1, the positive electrode material was prepared into a positive electrode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the pouch-type battery was 2.53 g / cm³. 3 That was the case.

[0098] Exemplary Comparative Example 3

[0099] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0100] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.31 μm (i.e., D 1 mo (It was 0.31), and the sphericity A1 was 0.6, but 0.643D 1 mo +0.439A1 = 0.46, which was outside the range (0.49, 2.3) specified in this disclosure. A second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 5.36 μm (i.e., D 2 mo (It was 5.36), and the sphericity A2 was 0.55, but 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 2.07, which was outside the scope of (0.41, 1.9) as defined in this disclosure.

[0101] LFP-1 material and LFP-2 material were mixed in a 5:5 weight ratio. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0102] Following the method described in Example 1, the lithium iron phosphate positive electrode active material LFP-3 obtained in Comparative Example 3 was prepared into a positive electrode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the positive electrode sheet in Comparative Example 3 was 2.63 g / cm³. 3 It was determined that the maximum compressed density of the positive electrode sheet in Comparative Example 3 was 2.6 g / cm³.3 Although the above was achieved, the battery's charge-discharge cycle stability was poor. As shown in Table 1 below, the capacity retention rate after 1000 cycles of the battery with a positive electrode sheet in Comparative Example 3 was clearly lower than that of Example 1.

[0103] Exemplary Comparative Example 4

[0104] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0105] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.52 μm (i.e., D 1 mo (is 0.52), sphericity A1 is 0.6, and 0.643D 1 mo +0.439A1 = 0.60. The second lithium iron phosphate material, LFP-2, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 4.23 μm (i.e., D 1 mo (It was 4.23), and the sphericity A2 was 0.9, but 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 0.25, which was outside the range of (0.41, 1.9) as defined in this disclosure.

[0106] LFP-1 and LFP-2 materials were mixed in a weight ratio of 2:8. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0107] Following the method described in Example 1, the lithium iron phosphate cathode active material LFP-3 obtained in Comparative Example 4 was prepared into a cathode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the cathode sheet in Comparative Example 4 was 2.64 g / cm³. 3 It was determined that the maximum compressed density of the positive electrode sheet in Comparative Example 4 was 2.6 g / cm³. 3Although the above was achieved, the battery's charge-discharge cycle stability was poor. As shown in Table 1 below, the first cycle discharge ratio capacity and capacity retention rate after 1000 cycles of the battery with a positive electrode sheet in Comparative Example 4 were clearly lower than those in Example 1.

[0108] Exemplary Comparative Example 5

[0109] A method for preparing lithium iron phosphate cathode active material includes the following steps:

[0110] The first lithium iron phosphate material, LFP-1, was used. When the volume distribution percentage reached its maximum value, the corresponding particle size was 0.34 μm (i.e., D 1 mo (is 0.34), sphericity A1 is 0.8, and 0.643D 1 mo +0.439A1 = 0.57. The second lithium iron phosphate material, LFP-2, was used. The sphericity A2 was 0.85, and when the volume distribution percentage reached its maximum value, the corresponding particle size was 0.65 μm (i.e., D 2 mo (This is 0.65), which is outside the range of 1 to 5 μm as defined in this disclosure, and is 1.07D 2 mo +2.44A2-1.70D 2 mo ×A2 = 1.83, which was outside the range of (0.41, 1.9) as defined in this disclosure.

[0111] LFP-1 material and LFP-2 material were mixed in a weight ratio of 4:6. Lithium iron phosphate cathode active material LFP-3 was obtained.

[0112] Following the method described in Example 1, the lithium iron phosphate positive electrode active material LFP-3 obtained in Comparative Example 5 was prepared into a positive electrode sheet and assembled into a pouch-type lithium-ion battery. The maximum compressed density of the positive electrode sheet in Comparative Example 5 was 2.52 g / cm³. 3 It was determined that this was the case.

[0113] To support the beneficial effects of the exemplary embodiments of this disclosure, the cycle performance of pouch-type batteries in each example and comparative example was tested. Each pouch-type battery was subjected to a charge-discharge cycle test at 0.5C / 0.5C and 25°C. The voltage range was 2.0 to 3.8V. Figure 1 shows the cycle performance curves of each pouch-type battery in Examples 1 to 7 and Comparative Examples 1 to 5. The first-cycle discharge ratio capacity, first-cycle Coulomb efficiency, and capacity retention rate after 1000 cycles for the batteries in the examples and comparative examples are summarized in Table 1 below. [Table 1]

[0114] As can be seen from Figure 1 and Table 1, in Comparative Example 2, where only one lithium iron phosphate material was used as the positive electrode active material, the battery's charge-discharge cycle performance was good, but the maximum compressive density of the electrode sheet was low, which did not contribute to improving the battery's energy density. When two lithium iron phosphate materials are mixed by the method provided in this disclosure, the compressive density of the positive electrode sheet prepared with the positive electrode active material is high, at 2.6 g / cm³. 3 In addition, depending on the circumstances, it may be 2.68 to 2.75 g / cm³. 3 This is possible. In addition, the battery has excellent electrochemical performance, a high first-cycle discharge ratio capacity, and a high first-cycle Coulomb efficiency, and its cycle performance (Examples 1-7) is comparable to that of the low-compression-density battery in Comparative Example 2. However, when a positive electrode active material obtained by mixing two raw materials that do not meet the specific requirements of this disclosure (Comparative Examples 1 and 3-5) is used, the compression density of the electrode sheet is too low, for example, in Comparative Examples 2 and 5 the compression density is 2.6 g / cm³. 3 It is less than, or the compressed density is in some cases 2.6 g / cm³ 3 While the above can be achieved, the charge-discharge cycle stability of the battery is poor; for example, the charge-discharge cycle stability of the batteries in Comparative Examples 1, 3, and 4 was poor. In general, high compressive density and good cycle performance of electrode sheets cannot be achieved simultaneously.

[0115] The embodiments described above illustrate only a number of implementations of the Disclosure and are described in detail, but these should not be construed as limitations on the scope of the Disclosure. Those skilled in the art will understand that several modifications and improvements can be made by those skilled in the art without departing from the ideas of the Disclosure, all of which are envisioned within the scope of the Disclosure. Therefore, the scope of the Disclosure shall be defined by the appended claims.

Claims

1. A lithium iron phosphate cathode active material formed by mixing a first lithium iron phosphate material and a second lithium iron phosphate material, wherein the first lithium iron phosphate material satisfies the following relational expression, namely 0.49 < 0.643D １ ｍｏ + 0.439A １ < 2.3, and the second lithium iron phosphate material satisfies the following relational expression, namely 0.41 < 1.07D ２ ｍｏ + 2.44A ２ - 1.70D ２ ｍｏ × A ２ < 1.9, When the volume distribution percentage of the first lithium iron phosphate material reaches its maximum value, the corresponding particle size is D １ ｍｏ It is μm, and 0.3 ≤ D １ ｍｏ When ≤ 3.2 and the volume distribution percentage of the second lithium iron phosphate material reaches its maximum value, the corresponding particle size is D ２ ｍｏ It is μm, and 1 ≤ D ２ ｍｏ ≤ 5, D １ ｍｏ <D ２ ｍｏ A １ and A ２ These represent the sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material, respectively. Lithium iron phosphate cathode active material.

2. D １ ｍｏ The value of is 0.32 ≤ D １ ｍｏ The lithium iron phosphate cathode active material according to claim 1, wherein the value is within the range of ≤2.

45.

3. D １ ｍｏ The value of is 0.40 ≤ D １ ｍｏ The lithium iron phosphate cathode active material according to claim 1, wherein the value is within the range of ≤2.

45.

4. D ２ ｍｏ The value of is 1.2 ≤ D ２ ｍｏ The lithium iron phosphate cathode active material according to claim 1, wherein it is within the range of ≤ 5.

5. D ２ ｍｏ The value of is 1.25 ≤ D ２ ｍｏ The lithium iron phosphate cathode active material according to claim 1, wherein the value is within the range of ≤4.

95.

6. A １ and A ２ The values ​​are 0.5 ≤ A １ <1, and 0.5 ≤ A ２ The lithium iron phosphate cathode active material according to claim 1, wherein it is within the range of <1.

7. A １ The value of is 0.51 ≤ A １ The lithium iron phosphate cathode active material according to claim 1, wherein the value is within the range of ≤0.

95.

8. A ２ The value of is 0.51 ≤ A ２ The lithium iron phosphate cathode active material according to claim 1, wherein the value is within the range of ≤0.

95.

9. The first lithium iron phosphate material is given by the following relationship, i.e., 0.5 ≤ 0.643D １ ｍｏ +0.439A １ A lithium iron phosphate cathode active material according to claim 1, satisfying ≤2.

29.

10. The first lithium iron phosphate material is given by the following relationship, i.e., 0.6 ≤ 0.643D １ ｍｏ +0.439A １ A lithium iron phosphate cathode active material according to claim 1, satisfying ≤2.

29.

11. The second lithium iron phosphate material is given by the following relationship, i.e., 0.42 ≤ 1.07D ２ ｍｏ +2.44A ２ -1.70D ２ ｍｏ ×A ２ A lithium iron phosphate cathode active material according to claim 1, satisfying ≤ 1.

89.

12. The lithium iron phosphate cathode active material according to claim 1, wherein the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is in the range of 1:(0.25 to 3).

13. The lithium iron phosphate cathode active material according to claim 1, wherein the mixed weight ratio of the first lithium iron phosphate material and the second lithium iron phosphate material is in the range of 1:(0.25 to 2.5).

14. The lithium iron phosphate cathode active material according to claim 1, wherein the first lithium iron phosphate material and the second lithium iron phosphate material have a carbon coating layer on their surfaces.

15. A method for preparing lithium iron phosphate cathode active material, (S101) To provide a first lithium iron phosphate material and a second lithium iron phosphate material, wherein when the volume distribution percentage of the first lithium iron phosphate material reaches its maximum value, the corresponding particle size is D １ ｍｏ It is μm, and 0.3 ≤ D １ ｍｏ When ≤ 3.2 and the volume distribution percentage of the second lithium iron phosphate material reaches its maximum value, the corresponding particle size is D ２ ｍｏ It is μm, and 1 ≤ D ２ ｍｏ ≤ 5, D １ ｍｏ <D ２ ｍｏ The sphericity of the first lithium iron phosphate material and the second lithium iron phosphate material is A, respectively. １ and A ２ Therefore, the first lithium iron phosphate material is given by the following relationship, namely 0.49 < 0.643D １ ｍｏ +0.439A １ The second lithium iron phosphate material satisfies <2.3 and is given by the following relationship, i.e., 0.41 < 1.07D ２ ｍｏ +2.44A ２ -1.70D ２ ｍｏ ×A ２ <1. To provide something that satisfies 1.9, (S102) The lithium iron phosphate cathode active material is obtained by mixing the first lithium iron phosphate material and the second lithium iron phosphate material. A method for preparing a lithium iron phosphate cathode active material comprising the following:

16. A lithium-ion battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises a lithium iron phosphate positive electrode active material according to any one of claims 1 to 14.

17. The lithium-ion battery according to claim 16, further comprising a negative electrode sheet, and an electrolyte and separator disposed between the positive electrode sheet and the negative electrode sheet.

18. The maximum compressed density of the positive electrode sheet is 2.65 to 2.8 g / cm³, the lithium-ion battery according to claim 16.

19. The lithium-ion battery according to claim 16, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector.

20. The lithium-ion battery according to claim 19, wherein the positive electrode active material layer comprises the lithium iron phosphate positive electrode active material, a binder, and a conductive agent.

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