Selection method of positive electrode material

Abstract

The invention belongs to the technical field of batteries, and discloses a selection method of a positive electrode material. The selection method comprises the steps that the Sp2 / Sp1 value and the A / A0 value of the positive electrode material are measured, and Sp1 is the initial (D90-D10) / D50 of the positive electrode material; sp2 is (D90 '-D10') / D50 'after the positive electrode material is subjected to powder pressing under the pressure of 10T-30T; a is an initial D50 / S value of the positive electrode material; a0 is a D50 ' / S' value of the positive electrode material after powder pressing under the pressure of 10T-30T; s is the initial specific surface area of the positive electrode material; s'is the specific surface area of the positive electrode material after powder pressing under the pressure of 10T-30T, and if the measured Sp2 / Sp1 value meets the condition that Sp2 / Sp1 is larger than or equal to 1 and smaller than or equal to 2.0 and the A / A0 value meets the condition that A / A0 is larger than or equal to 1 and smaller than or equal to 2.50, the positive electrode material is the target positive electrode material.The positive electrode material obtained through the selection method can have good cycle performance on the premise that the capacity is not sacrificed.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for selecting a positive electrode material. Background Art

[0002] With the rapid development of modern industry and technology, traditional fossil energy represented by coal and oil has been consumed at an accelerated rate, further exacerbating global environmental pollution and climate problems. Therefore, the development and application of clean energy has become the key to the development of human society in the 21st century. However, renewable clean energy such as wind energy, solar energy, and tidal energy has certain geographical limitations and intermittency, making it difficult to provide long-term and stable energy security. It is urgent to develop efficient energy storage and conversion devices to realize the large-scale application of renewable energy in the future society.

[0003] Lithium-ion batteries stand out from many energy storage devices due to their high energy density, energy conversion efficiency and long cycle life. Their applications are no longer limited to portable consumer electronics. Emerging fields such as electric vehicles, energy storage power stations and smart grids provide a broader space for the development of lithium-ion batteries. At the same time, they also pose higher challenges to their energy density, service life and safety.

[0004] Currently, the common cathode materials for commercial lithium-ion batteries include lithium iron phosphate, lithium cobalt oxide, nickel-cobalt-manganese ternary materials, etc. However, due to the anisotropy of particles in the existing cathode material crystals, microcracks are easily generated during the charge and discharge process, causing the electrolyte to react with the cathode material, resulting in irreversible capacity loss, reducing cycle stability, and severely limiting its commercial application. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, one object of the present invention is to provide a method for selecting a positive electrode material, and the positive electrode material obtained by the selection method provided by the present application can have good cycle performance without sacrificing capacity.

[0006] In the first aspect of the present invention, the present invention proposes a method for selecting a positive electrode material. According to an embodiment of the present invention, the selection method comprises: determining the Sp2 / Sp1 value and A / A0 value of the positive electrode material, wherein Sp1 is the initial (D90-D10) / D50 of the positive electrode material; Sp2 is the (D90'-D10') / D50' of the positive electrode material after powder pressing at a pressure of 10T-30T; A is the initial D50 / S value of the positive electrode material; A0 is the positive electrode material at a pressure of 10T-30T. D50' / S' value after powder pressing; S is the initial specific surface area of ​​the positive electrode material; S' is the specific surface area of ​​the positive electrode material after powder pressing at a pressure of 10T-30T; if the Sp2 / Sp1 value obtained by measurement satisfies: 1≤Sp2 / Sp1≤2.0, and the A / A0 value satisfies: 1≤A / A0≤2.50, then it is the target positive electrode material, and the positive electrode material includes at least one of a layered metal oxide positive electrode material, a spinel metal oxide positive electrode material and a polyanion salt positive electrode material.

[0007] According to the selection method of the above embodiment of the present invention, by measuring and calculating the Sp2 / Sp1 value and A / A0 value of the positive electrode material to be tested, when the positive electrode material satisfies 1≤Sp2 / Sp1≤2.0 and 1≤A / A0≤2.50 at the same time, it is the selected target positive electrode material, wherein 1≤Sp1 / Sp2≤2.0 ensures that the initial particle size distribution span of the positive electrode material and the particle size distribution span after powder pressing under a pressure of 10T-30T do not increase significantly, that is, the size distribution of the positive electrode material remains relatively uniform, which helps to maintain the mechanical strength of the positive electrode material particles, reduces the breakage during the battery manufacturing process, and thus can maintain the initial capacity of the battery. 1≤A / A0≤2.50 ensures that the ratio of the initial average size of the positive electrode material to the specific surface area and the ratio of the average size of the positive electrode material to the specific surface area after powder pressing under a pressure of 10T-30T do not increase significantly, that is, the morphology and structure of the positive electrode material remain relatively stable, which helps to reduce the breakage of the positive electrode material and the side reaction of the electrolyte, thereby improving the cycle stability of the battery. Therefore, when the measurement results of the positive electrode material satisfy the above relationship at the same time, the mechanical strength of the positive electrode material can be improved, reducing the breakage of the positive electrode material during the rolling process and the cycle process, thereby avoiding the breakage of the positive electrode material and the side reaction of the new interface with the electrolyte, which is beneficial to improve the cycle performance of the battery without sacrificing capacity.

[0008] In addition, the selection method according to the above embodiment of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, Sp1 of the layered metal oxide positive electrode material satisfies: 0<Sp1≤1.3, which is beneficial to improve the cycle performance of the battery.

[0010] In some embodiments of the present invention, Sp1 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp1≤8.25. This is beneficial to improve the cycle performance of the battery.

[0011] In some embodiments of the present invention, the Sp2 of the layered metal oxide positive electrode material satisfies: 0<Sp2≤2.6, which is beneficial to improve the cycle performance of the battery.

[0012] In some embodiments of the present invention, Sp2 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp2≤8.3, which is beneficial to improve the cycle performance of the battery.

[0013] In some embodiments of the present invention, the A of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 . As a result, the cycle performance of the battery can be improved without sacrificing capacity.

[0014] In some embodiments of the present invention, the A of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0.05 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 . As a result, the cycle performance of the battery can be improved without sacrificing capacity.

[0015] In some embodiments of the present invention, the A0 of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 Thus, the increase in specific surface area due to the crushing of the layered metal oxide positive electrode material particles is avoided, the contact with the electrolyte is reduced, which is beneficial to reduce the occurrence of side reactions, thereby improving the cycle performance of the battery.

[0016] In some embodiments of the present invention, the A0 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material meets the following requirements: 0.05 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 Thus, the specific surface area increased due to the crushing of lithium iron phosphate positive electrode material particles is avoided, the contact with the electrolyte is reduced, which is conducive to reducing the occurrence of side reactions, thereby improving the cycle performance of the battery.

[0017] In some embodiments of the present invention, the initial D50 particle size of the layered metal oxide positive electrode material is 2.5 μm-15 μm, thereby balancing the electrochemical and mechanical properties of the layered metal oxide positive electrode material, reducing the agglomeration of the layered metal oxide positive electrode material particles, and improving the overall strength of the positive electrode active material layer.

[0018] In some embodiments of the present invention, the initial D50 particle size of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 100nm-15μm. Thus, the electrochemical properties and mechanical properties of the lithium iron phosphate positive electrode material are balanced, the agglomeration of the lithium iron phosphate positive electrode material particles is reduced, and the overall strength of the positive electrode active material layer is improved.

[0019] In some embodiments of the present invention, the initial specific surface area of ​​the layered metal oxide positive electrode material is 0.15 m 2 / g-1.3m 2 / g. Thus, it can be ensured that the layered metal oxide positive electrode material has an appropriate initial specific surface area, can provide sufficient active sites to improve the electrochemical activity, and at the same time reduce the side reaction with the electrolyte, thereby improving the cycle performance of the battery.

[0020] In some embodiments of the present invention, the initial specific surface area of ​​the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 0.15 m 2 / g-20m 2 / g. Thus, it can be ensured that the lithium iron phosphate positive electrode material has an appropriate initial specific surface area, can provide sufficient active sites to improve the electrochemical activity, and at the same time reduce the side reaction with the electrolyte, thereby improving the cycle performance of the battery.

[0021] In some embodiments of the present invention, the layered structured metal oxide includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide and lithium-rich manganese-based oxide.

[0022] In some embodiments of the present invention, the spinel structure metal compound positive electrode material includes at least one of lithium manganese oxide and lithium nickel manganese oxide.

[0023] In some embodiments of the present invention, the polyanion salt positive electrode material includes at least one of lithium iron phosphate and lithium iron manganese.

[0024] In some embodiments of the present invention, the positive electrode material includes polycrystalline lithium nickel cobalt manganese oxide.

[0025] In some embodiments of the present invention, the positive electrode material includes polycrystalline lithium nickel cobalt manganese oxide with a coating layer.

[0026] In some embodiments of the present invention, the thickness of the coating layer is ≤100 nm.

[0027] In some embodiments of the present invention, the chemical formula of the lithium nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) O2, where 0.7≤x<1, 0<y≤0.3, 0<x+y<1.

[0028] In some embodiments of the present invention, the chemical formula of the lithium iron phosphate is LiFePO4, LiMn x1 Fe (1-x1) PO4, LiMn2O4, x2Li2MnO3·(1-x2)LiMO2, wherein 0<x1<1, 0<x2<1, and M is at least one of nickel, cobalt, and manganese.

[0029] In some embodiments of the present invention, the compaction density of the electrode sheet prepared from the layered metal oxide positive electrode material is not less than 3.5 g / cm 3 The compaction density of the electrode sheet prepared by one of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is not less than 2.5g / cm 3 Therefore, the electrode can ensure better cycle performance.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0032] Figure 1 A flow chart showing a method for selecting a positive electrode material according to an embodiment of the present invention is shown;

[0033] Figure 2 The SEM image of the positive electrode material of Example 1 of the present application is shown. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0035] In a first aspect of the present invention, the present invention provides a lithium ion battery, referring to Figure 1According to an embodiment of the present invention, the selection method comprises: S10, determining the Sp2 / Sp1 value and A / A0 value of the positive electrode material, wherein Sp1 is the initial (D90-D10) / D50 of the positive electrode material; Sp2 is the (D90'-D10') / D50' of the positive electrode material after being pressed at a pressure of 10T-30T; A is the initial D50 / S value of the positive electrode material; A0 is the D50' / S' value of the positive electrode material after being pressed at a pressure of 10T-30T; S is the initial specific surface area of ​​the positive electrode material; S' is the specific surface area of ​​the positive electrode material after powder compaction at a pressure of 10T-30T; S20, if the Sp2 / Sp1 value obtained by measurement satisfies: 1≤Sp2 / Sp1≤2.0, and the A / A0 value satisfies: 1≤A / A0≤2.50, then it is the target positive electrode material, and the positive electrode material includes at least one of a layered metal oxide positive electrode material, a spinel metal oxide positive electrode material and a polyanion salt positive electrode material.

[0036] For example, the value of Sp2 / Sp1 can be 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, etc.; the value of A / A0 can be 1.00, 1.30, 1.50, 1.70, 1.90, 2.10, 2.30, 2.50, etc.

[0037] It should be noted that (D90-D10) / D50 represents the particle size distribution span of the initial positive electrode material, wherein D10 is the D10 particle size of the initial positive electrode material, and the D10 particle size refers to the particle size at which the cumulative distribution of the positive electrode material particles is 10%, that is, the volume content of the positive electrode material particles smaller than this particle size accounts for 10% of all the positive electrode material particles; D50 is the D50 particle size of the initial positive electrode material, and the D50 particle size refers to the particle size at which the cumulative distribution of the positive electrode material particles is 50%, that is, the volume content of the positive electrode material particles smaller than this particle size accounts for 50% of all the positive electrode material particles. D90 is the D90 particle size of the initial positive electrode active material, and the D90 particle size refers to the particle size at which the cumulative distribution of the positive electrode material particles is 90%, that is, the volume content of the positive electrode material particles smaller than this particle size accounts for 90% of all the positive electrode material particles. Similarly, (D90'-D10') / D50' represents the particle size distribution span of the positive electrode material after 10T-30T pressure powder compaction.

[0038] It should be noted that powder pressing refers to the process of applying a certain pressure to the positive electrode material in a press to form the powder material, and then grinding and crushing the formed material for testing to simulate the pole piece rolling. There is no special limitation on the pressure of the positive electrode material powder pressing, and technicians in this field can flexibly select it according to needs. According to other embodiments of the present invention, the pressure of the powder pressing can be 10T-30T, for example, 10T, 15T, 20T, etc. At present, the pole piece compaction density of the positive electrode material is usually 3.5g / cm 3 -3.6g / cm3 To achieve this compaction density, the roller press needs a pressure of about 10T, so the pressure applied during the evaluation should be at least 10T. In theory, the higher the pressure that can be tolerated, the better. However, considering the actual use of positive electrode materials and the compaction capacity of equipment, the general powder pressing pressure is between 10-20, which can improve the mechanical strength of the positive electrode material particles and is beneficial to improving the cycle performance of the battery without sacrificing capacity.

[0039] According to the selection method of the above embodiment of the present invention, by measuring and calculating the Sp2 / Sp1 value and A / A0 value of the positive electrode material to be tested, when the positive electrode material satisfies 1≤Sp2 / Sp1≤2.0 and 1≤A / A0≤2.50 at the same time, it is the selected target positive electrode material, wherein 1≤Sp1 / Sp2≤2.0 ensures that the initial particle size distribution span of the positive electrode material and the particle size distribution span after powder pressing under a pressure of 10T-30T do not increase significantly, that is, the size distribution of the positive electrode material remains relatively uniform, which helps to maintain the mechanical strength of the positive electrode material particles, reduces the breakage during the battery manufacturing process, and thus can maintain the initial capacity of the battery. 1≤A / A0≤2.50 ensures that the ratio of the initial average size of the positive electrode material to the specific surface area and the ratio of the average size of the positive electrode material to the specific surface area after powder pressing under a pressure of 10T-30T do not increase significantly, that is, the morphology and structure of the positive electrode material remain relatively stable, which helps to reduce the breakage of the positive electrode material and the side reaction of the electrolyte, thereby improving the cycle stability of the battery. Therefore, when the measurement results of the positive electrode material satisfy the above relationship at the same time, the mechanical strength of the positive electrode material can be improved, reducing the breakage of the positive electrode material during the rolling process and the cycle process, thereby avoiding the breakage of the positive electrode material and the side reaction of the new interface with the electrolyte, which is beneficial to improve the cycle performance of the battery without sacrificing capacity.

[0040] It should be noted that there is no particular limitation on the type of positive electrode material, and those skilled in the art can flexibly select it as needed. According to some embodiments of the present invention, the positive electrode material includes but is not limited to at least one of a layered metal oxide positive electrode material, a spinel metal oxide positive electrode material, and a polyanion salt positive electrode material. The above types of positive electrode materials have high capacity and excellent energy density, and are widely used positive electrode materials in lithium-ion batteries.

[0041] As an example, the layered structure metal oxide positive electrode material includes but is not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide and lithium-rich manganese base.

[0042] As an example, the spinel structure metal compound positive electrode material includes at least one of lithium manganese oxide and lithium nickel manganese oxide.

[0043] Optionally, the positive electrode material includes polycrystalline lithium nickel cobalt manganese oxide.

[0044] Optionally, the chemical formula of the lithium nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) O2, wherein 0.7≤x<1, 0<y≤0.3, 0<x+y<1. For example, x can be 0.7, 0.8, 0.9, etc.; y can be 0.1, 0.2, 0.3, etc.

[0045] Optionally, the chemical formula of the lithium iron phosphate is LiFePO4, LiMn x1 Fe (1-x1) PO4, LiMn2O4, x2Li2MnO3·(1-x2)LiMO2, wherein 0<x1<1, 0<x2<1, M is at least one of nickel, cobalt, and manganese, for example, x1 can be 0.1, 0.3, 0.5, 0.7, 1, etc.; x2 can be 0.1, 0.3, 0.5, 0.7, 1, etc.

[0046] There is no special limitation on the preparation method of the positive electrode material, and those skilled in the art can flexibly select it according to needs. According to a specific embodiment of the present invention, the method for preparing polycrystalline nickel cobalt manganese oxide includes: 1) preparing a spherical precursor using nickel salt, cobalt salt and manganese salt, and controlling the primary particle morphology of the precursor by controlling the ammonia concentration, pH value, ammonia flow rate, etc.; 2) mixing the spherical precursor and lithium salt and calcining to obtain a primary sintered material; 3) mixing the primary sintered material with cobalt salt and a material containing metal element N and calcining to obtain a polycrystalline nickel cobalt manganese oxide positive electrode material, wherein the metal N is at least one of rare earth elements such as La, Ce, Nd, etc.

[0047] According to some embodiments of the present invention, in the process of preparing polycrystalline nickel cobalt lithium manganese oxide positive electrode material, the polycrystalline nickel cobalt lithium manganese oxide positive electrode material also needs to be modified. The modification method is not particularly limited. For example, the polycrystalline nickel cobalt lithium manganese oxide positive electrode material can be modified by doping, coating, precursor regulation and other technologies. Among them, doping can be performed during the precursor synthesis process, or during the first sintering or the second sintering. Coating can be performed during the second sintering or the last tertiary sintering to coat oxides, solid electrolytes, etc. Precursor regulation can control the sphericity of the particles, the size of the primary particles, and the orientation of the primary particles (growth direction (001), (100), etc.) according to the conditions of the precursor synthesis. Technical personnel in this field can flexibly select according to needs.

[0048] According to some embodiments of the present invention, the Sp1 of the layered metal oxide positive electrode material satisfies: 0<Sp1≤1.3. For example, it can be 0.1, 0.5, 1.0, 1.3, etc. Sp1 represents the particle size distribution span of the initial layered metal oxide positive electrode material particles. By limiting Sp1 within the above range, the uniformity of the particle size distribution of the layered metal oxide positive electrode material particles is ensured, and the particle size is relatively concentrated, which can avoid uneven lithium extraction from the pole piece caused by the non-concentrated distribution of the layered metal oxide positive electrode material particles, thereby affecting the cycle performance of the battery. This is conducive to improving the cycle performance of the battery.

[0049] According to some embodiments of the present invention, the Sp1 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp1≤8.25. For example, it can be 0.1, 0.5, 1, 3, 5, 8.25, etc. The Sp1 represents the particle size distribution span of the initial polyanion salt positive electrode material particles or the spinel metal oxide positive electrode material particles. By limiting Sp1 within the above range, the uniformity of the particle size distribution of the positive electrode material is ensured, and the particle size is relatively concentrated, which can avoid uneven lithium extraction of the pole piece caused by the non-concentrated distribution of the positive electrode material particles, thereby affecting the cycle performance of the battery. As a result, it is beneficial to improve the cycle performance of the battery.

[0050] According to some embodiments of the present invention, the Sp2 of the layered metal oxide positive electrode material satisfies: 0<Sp2≤2.6. For example, it can be 0.1, 0.5, 1.0, 1.5, 2.0, 2.6, etc. Sp2 represents the particle size distribution span of the layered metal oxide positive electrode material after powder pressing under a pressure of 10T-30T, which can reflect the change and distribution uniformity of the particle size of the layered metal oxide positive electrode material during the powder pressing process under a pressure of 10T-30T. By limiting Sp2 to the above range, it is ensured that the particle size distribution of the layered metal oxide positive electrode material after powder pressing under a pressure of 10T-30T is uniform, and the particle size of the layered metal oxide positive electrode material is relatively concentrated, which can avoid the particle breakage during the pole piece rolling process and the charging and discharging process caused by the low strength of the positive electrode material particles, thereby reducing the cycle life of the battery. As a result, it is beneficial to improve the cycle performance of the battery.

[0051] According to some embodiments of the present invention, the Sp2 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp2≤9. For example, it can be 0.1, 0.5, 1, 1.5, 3, 5, 7, 9, etc. The Sp2 represents the particle size distribution span of the particles of the polyanion salt positive electrode material or the spinel metal oxide positive electrode material after powder pressing under a pressure of 10T-30T, which can reflect the change and distribution uniformity of the particle size of the positive electrode material during the powder pressing process under a pressure of 10T-30T. By limiting Sp2 to the above range, it is ensured that the particle size distribution of the positive electrode material after powder pressing under a pressure of 10T-30T is uniform, and the particle size of the positive electrode material is relatively concentrated, which can avoid the particle breakage during the pole piece rolling process and the charging and discharging process caused by the low strength of the positive electrode material particles, thereby reducing the cycle life of the battery. Therefore, it is beneficial to improve the cycle performance of the battery.

[0052] According to some embodiments of the present invention, the A of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 , for example, can be 1.9 (μm·g) / m 2 , 10(μm·g) / m 2 , 30(μm·g) / m 2 , 50(μm·g) / m 2 , 70(μm·g) / m 2 , 100(μm·g) / m 2 Etc. A represents the ratio of the initial D50 particle size of the layered metal oxide positive electrode material particles to the specific surface area (S), which can reflect the morphology and structure of the layered metal oxide positive electrode material particles. By limiting A to the above range, on the one hand, it can ensure that the size of the layered metal oxide positive electrode material particles is large enough and the specific surface area is not too large, thereby reducing the contact area with the electrolyte, reducing the occurrence of interfacial side reactions, avoiding excessive consumption of active substances, and being beneficial to the battery capacity and improving the battery cycle life. On the other hand, it can ensure that the size of the layered metal oxide positive electrode material particles is not too large and the specific surface area is not too small, thereby ensuring that the diffusion path of lithium ions is not too long and maintaining the electrochemical activity of the positive electrode material. As a result, the cycle performance of the battery can be improved without sacrificing capacity.

[0053] According to some embodiments of the present invention, the A of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0.05 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 For example, it can be 0.05 (μm·g) / m 2, 0.1(μm·g) / m 2 , 1(μm·g) / m 2 , 5(μm·g) / m 2 , 10(μm·g) / m 2 , 20(μm·g) / m 2 , 50(μm·g) / m 2 , 100(μm·g) / m 2 Etc. A represents the ratio of the initial D50 particle size of the polyanion salt positive electrode material particles or the spinel metal oxide positive electrode material particles to the specific surface area (S), which can reflect the morphology and structure of the positive electrode material particles. By limiting A to the above range, on the one hand, it can ensure that the size of the positive electrode material particles is large enough and the specific surface area is not too large, thereby reducing the contact area with the electrolyte, reducing the occurrence of interfacial side reactions, avoiding excessive consumption of active substances, and being beneficial to the battery capacity and improving the battery cycle life. On the other hand, it can ensure that the size of the positive electrode material particles is not too large and the specific surface area is not too small, thereby ensuring that the diffusion path of lithium ions is not too long and maintaining the electrochemical activity of the positive electrode material. As a result, the cycle performance of the battery can be improved without sacrificing capacity.

[0054] According to some embodiments of the present invention, the A0 of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 For example, it can be 1.9 (μm·g) / m 2 , 10(μm·g) / m 2 , 20(μm·g) / m 2 , 30(μm·g) / m 2 , 40(μm·g) / m 2 A0 represents the ratio of the particle size D50' of the layered metal oxide positive electrode material particles after powder pressing at a pressure of 10T-30T to the specific surface area (S'), which can reflect the morphology and structure of the layered metal oxide positive electrode material particles. By limiting A0 to the above range, the increase in specific surface area due to the crushing of the layered metal oxide positive electrode material particles can be avoided, the contact with the electrolyte is reduced, which is conducive to reducing the occurrence of side reactions, thereby improving the cycle performance of the battery.

[0055] According to some embodiments of the present invention, the A0 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material meets the following requirements: 0.05 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 For example, it can be 0.05 (μm·g) / m 2 , 0.1(μm·g) / m2 , 1(μm·g) / m 2 , 5(μm·g) / m 2 , 10(μm·g) / m 2 , 20(μm·g) / m 2 , 40(μm·g) / m 2 Etc. The A0 represents the ratio of the D50' particle size to the specific surface area (S') of the polyanion salt positive electrode material particles or spinel metal oxide positive electrode material particles after powder pressing at a pressure of 10T-30T, which can reflect the morphology and structure of the positive electrode material particles. By limiting A0 to the above range, the increase in specific surface area due to the crushing of the positive electrode material particles is avoided, the contact with the electrolyte is reduced, which is conducive to reducing the occurrence of side reactions, thereby improving the cycle performance of the battery.

[0056] According to some embodiments of the present invention, the initial D50 particle size of the layered metal oxide positive electrode material is 2.5 μm-15 μm. For example, it can be 2.5 μm, 5 μm, 10 μm, 15 μm, etc. By limiting the initial D50 particle size of the layered metal oxide positive electrode material to the above range, the electrochemical properties and mechanical properties of the layered metal oxide positive electrode material are balanced, the agglomeration of the layered metal oxide positive electrode material particles is reduced, and the overall strength of the positive electrode active material layer is improved.

[0057] According to some embodiments of the present invention, the initial D50 particle size of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 100nm-15μm. For example, it can be 100nm, 1μm, 5μm, 10μm, 15μm, etc. By limiting the initial D50 particle size of the polyanion salt positive electrode material or the spinel metal oxide positive electrode material to the above range, the electrochemical properties and mechanical properties of the positive electrode material are balanced, the agglomeration of the positive electrode material particles is reduced, and the overall strength of the positive electrode active material layer is improved.

[0058] According to some embodiments of the present invention, the initial specific surface area of ​​the layered metal oxide positive electrode material is 0.15 m 2 / g-1.3m 2 / g. For example, it can be 0.15m 2 / g,0.3m 2 / g,0.5m 2 / g,1.0m 2 / g, 1.3m 2 / g, etc. To ensure that the layered metal oxide positive electrode material has a suitable specific surface area, on the one hand, it can avoid the specific surface area of ​​the layered metal oxide positive electrode material being too small, resulting in the layered metal oxide positive electrode material particles having a larger size, increasing the diffusion distance of lithium ions, and reducing the activity of the layered metal oxide positive electrode material. On the other hand, it can avoid the specific surface area of ​​the layered metal oxide positive electrode material being too large, resulting in an increase in the interfacial side reactions between the layered metal oxide positive electrode material and the electrolyte, affecting the battery capacity. Therefore, by limiting the initial specific surface area of ​​the layered metal oxide positive electrode material to the above range, it can be ensured that the layered metal oxide positive electrode material has an appropriate initial specific surface area, which can provide sufficient active sites to improve the electrochemical activity, while reducing the side reactions with the electrolyte, thereby improving the cycle performance of the battery.

[0059] According to some embodiments of the present invention, the initial specific surface area of ​​the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 0.15 m 2 / g-20m 2 / g. For example, it can be 0.15m 2 / g,0.2m 2 / g,0.5m 2 / g,1m 2 / g,5m 2 / g,15m 2 / g,20m 2 By limiting the initial specific surface area of ​​the polyanion salt positive electrode material or the spinel metal oxide positive electrode material within the above range, it can be ensured that the positive electrode material has an appropriate initial specific surface area, can provide sufficient active sites to improve the electrochemical activity, and reduce the side reaction with the electrolyte, thereby improving the cycle performance of the battery.

[0060] According to some embodiments of the present invention, the compaction density of the electrode sheet prepared from the layered metal oxide positive electrode material is not less than 3.5 g / cm 3 For example, it can be 3.5 g / cm 3 , 3.55g / cm 3 , 3.6g / cm 3 , 3.65g / cm 3 , 3.7g / cm 3 The compaction density of the electrode sheet prepared by one of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is not less than 2.5 g / cm 3 , for example, can be 2.5 g / cm 3 , 2.55g / cm 3 , 2.6g / cm 3 , 2.65g / cm3 , 2.7g / cm 3 Etc. Therefore, the pole piece can ensure better cycle performance.

[0061] According to some embodiments of the present invention, the positive electrode material includes polycrystalline nickel cobalt lithium manganese oxide having a coating layer; the thickness of the coating layer is ≤100nm. For example, the coating layer can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc. By limiting the thickness of the coating layer to the above range, the particle strength of the polycrystalline nickel cobalt lithium manganese oxide positive electrode material can be effectively improved, thereby improving the cycle performance of the positive electrode material.

[0062] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will appreciate that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not indicated in the examples, the techniques or conditions described in the literature in this area or the product instructions are used. Where the manufacturers of reagents or instruments are not indicated, they are all conventional products that can be obtained commercially.

[0063] Example 1

[0064] The method for selecting the positive electrode material includes the following steps:

[0065] Step S1: Prepare the positive electrode material, taking polycrystalline lithium nickel cobalt manganese oxide with a coating layer as an example, specifically:

[0066] S11: dissolving nickel salt (NiSO4·6H2O), cobalt salt (CoSO4·7H2O) and manganese salt (MnSO4·H2O) in deionized water, mixing them evenly, and preparing a 1 mol / L soluble salt solution; wherein the feeding amounts of nickel salt, cobalt salt and manganese salt are calculated according to the molar ratio of Ni:Co:Mn being 90:5:5;

[0067] S12: adding the soluble salt solution, NaOH solution and NH3·H2O complexing agent obtained in step S11 into the reactor at a certain flow rate, introducing nitrogen with a purity of 99.5%, turning on the stirring device of the continuous stirred tank reactor, controlling the temperature of the continuous stirred tank reactor at 50°C, and continuously monitoring the pH value of the reaction system during the reaction. Within the first 4 hours of the reaction, the pH value of the reaction system is regulated to be 10.5, and after 4 hours, the pH value of the system is regulated to be 11.2. The total reaction time is 24 hours. After coprecipitation reaction, a precursor slurry is obtained, and then through washing, drying, screening and other processes, a precursor powder is obtained. The spherical precursor is [Ni 90 Co5Mn5](OH2), where the thickness of the precursor primary particles is about 280nm;

[0068] S13: The precursor obtained in step S12 is added with LiOH in a Li / Me (Me is the total molar amount of nickel, cobalt and manganese in the precursor) ratio of 1.03, and the mixture is evenly mixed. The mixture is placed in a tubular furnace and oxygen is introduced for calcination. The temperature is first increased to 450°C at a heating rate of 2°C / min and kept constant for 4h, and then the temperature is increased to 740°C at a heating rate of 4°C / min and kept constant for 12h to obtain a primary sintered material, which is then crushed and screened.

[0069] S14: Evenly mix the primary sintering material powder obtained in step S13 with Co(OH)2 and La2O3, place the mixture in a tubular furnace, introduce oxygen for calcination, first heat the temperature to 450°C at a heating rate of 2°C / min, keep the temperature constant for 4 hours, then heat the temperature to 670°C at a heating rate of 4°C / min, keep the temperature constant for 10 hours, to obtain a secondary sintering material, crush and screen the secondary sintering material to obtain a coated polycrystalline nickel cobalt lithium manganese oxide layered polycrystalline positive electrode material, with a coating layer thickness of 20nm.

[0070] Step S2: Testing the D50, D90, D10 and specific surface area S of the positive electrode material prepared in step S1, which are: D50 = 12.8 μm, specific surface area S = 0.55 m 2 / g, D90=20.2, D10=7.

[0071] Step S3: The positive electrode material prepared in step S1 is powder-pressed under a pressure of 10T, and the D50, D90, D10 and specific surface area S of the positive electrode material after powder pressing are tested and marked as D50', D90', D10', S', which are respectively: D50'=9.04, D90'=16.4, D10'=7.4, S'=0.9.

[0072] Comparative Example 1

[0073] The difference between Comparative Example 1 and Example 1 is that:

[0074] S14. Evenly mix the primary sintering material powder obtained in step S13 with Co(OH)2, place the mixture in a tubular furnace, introduce oxygen for calcination, first heat the temperature to 450°C at a heating rate of 2°C / min, keep the temperature constant for 4 hours, then heat the temperature to 670°C at a heating rate of 4°C / min, keep the temperature constant for 10 hours, to obtain a secondary sintering material, crush and screen the secondary sintering material to obtain a positive electrode material with D50=12.5, specific surface area S=0.55, D90=18.04, and D10=9.13.

[0075] S15. Powder-press the coated NCM layered polycrystalline positive electrode material obtained in step S14 under a pressure of 10 T to obtain a pressed positive electrode material. The pressed positive electrode material has a D50'=9, a specific surface area S'=0.99, a D90'=17.43, and a D10'=1.01.

[0076] The positive electrode materials of Examples 2-8 and Comparative Examples 1-3 are the same as those of Example 1 except for some parameters (see Table 1).

[0077] Example 9

[0078] The method for selecting the positive electrode material includes the following steps:

[0079] Step S1: Prepare positive electrode materials, taking single crystal lithium iron phosphate as an example, specifically:

[0080] S11, weigh a certain amount of FeSO4·7H2O, pour LiOH into H3PO4, stir to make it completely dissolved, and add an appropriate amount of citric acid solution;

[0081] S12, slowly pour the LiOH solution into the mixed solution of S1, stir evenly, and adjust the pH of the mixed solution to neutral;

[0082] S13, the solution is sealed in a polytetrafluoroethylene hydrothermal autoclave, and kept at 180°C for 5 hours, and a LiFePO4 powder sample is obtained through the steps of suction filtration, washing, vacuum drying, etc.;

[0083] S14. Conductive polymer PNAI is uniformly plated on the surface of LiFePO4 by in-situ electroplating. During the in-situ electroplating process, the constant voltage is 1V, the electroplating time is 10min, and the electrolyte is 0.05mol·L -1 of H2SO4, the concentration of PANI is 0.1 mol·L -1 , and then washed several times with distilled water and acetone respectively, the obtained PANI / LiFePO4 was carbonized at 700℃ for 5h in a nitrogen atmosphere to form a dense carbon layer to obtain C / LiFePO4.

[0084] Step S2: Testing the D50, D90, D10 and specific surface area S of the positive electrode material prepared in step S1, which are: D50 = 1.05 μm, specific surface area S = 13.7 m 2 / g, D90=15.2, D10=0.4.

[0085] Step S3: The positive electrode material prepared in step S1 is powder-pressed under a pressure of 10T, and the D50, D90, D10 and specific surface area S of the positive electrode material after powder pressing are tested and marked as D50', D90', D10', S', which are: D50'=1.04, D90'=15.2, D10'=0.4, S'=13.8 respectively.

[0086] Some parameters of the positive electrode materials of Examples 1-9 and Comparative Examples 1-3 are shown in Table 1.

[0087] Table 1

[0088]

[0089]

[0090] Testing and analysis

[0091] Under the same conditions, the positive electrode materials selected from the above Examples 1-9 and Comparative Examples 1-3 were respectively subjected to gram capacity test and cycle performance test, and the specific test methods are as follows:

[0092] Gram capacity test: The positive electrode material, conductive agent (SP) and polyvinylidene fluoride (PVDF) were homogenized in a ratio of 92:5:3 and the double-sided surface density was 300g / cm 2 The compaction density of lithium nickel cobalt manganese oxide and lithium iron phosphate is 3.6g / cm 3 and 2.5g / cm 3 The negative electrode is a lithium sheet, assembled into a single half-cell, the test voltage of lithium nickel cobalt manganese oxide and lithium iron phosphate are 2.7V-4.25V and 2.5V-3.65V respectively, and the capacity is fixed for 3 cycles under 0.33C conditions, the first cycle charging capacity and discharge capacity are recorded, and the first efficiency is calculated.

[0093] Cycle performance test: The positive electrode material, SP and PVDF were homogenized in a ratio of 92:5:3 and the double-sided surface density was 300g / cm 2 The compaction density of lithium nickel cobalt manganese oxide and lithium iron phosphate is 3.6g / cm 3 and 2.5g / cm 3 , the negative electrode is graphite, assembled into a soft pack battery, the test voltage of lithium nickel cobalt manganese oxide and lithium iron phosphate are 2.7V-4.25V and 2.5V-3.65V, 0.1C conditions for 3 cycles, and then 2.7V-4.25V, 0.5C conditions for 200 cycles, calculate the cycle retention rate;

[0094] Cycle retention rate = discharge capacity of the last cycle at 0.5C / discharge capacity of the first cycle at 0.5C.

[0095] The test results are shown in Table 2.

[0096] Table 2

[0097] Gram capacity (mAh / g) Capacity retention after 200 cycles (%) Example 1 211.7 93.1 Example 2 205 97.6 Example 3 213 92.9 Example 4 206.4 96.3 Example 5 210.1 96.5 Example 6 210.1 94.2 Example 7 210.1 92.7 Example 8 210.4 91.8 Example 9 162 98.8 Comparative Example 1 211.5 83.1 Comparative Example 2 210 85.6 Comparative Example 3 211.7 86.7

[0098] Combining Table 1 and Table 2, it can be obtained that compared with the positive electrode materials of Comparative Examples 1-3, the positive electrode materials of Examples 1-9 use different modification methods to ensure that the particle size and specific surface of the materials satisfy the relationship 1≤Sp2 / Sp1≤2.0 and 1≤A / A0≤2.50, ensuring that the initial and powder-pressed particle size distributions of the positive electrode materials remain relatively concentrated, which helps to maintain the mechanical strength of the positive electrode material particles, reduce particle breakage during rolling and cycling, reduce the generation of new interfaces, and reduce interface side reactions, thereby improving the cycle performance of the positive electrode materials. Among them, the gram capacity of Example 2 and Example 4 is lower than that of other examples and comparative examples. This is because the D50 particle sizes of the initial positive electrode materials of Example 2 and Example 4 are 2.5 μm and 3.5 μm, respectively, which are single crystal materials, so the capacity is slightly lower; while the D50 particle size of the initial positive electrode materials of other examples and comparative examples is large, belonging to polycrystalline materials, and polycrystalline materials are composed of many small crystals. There are a large number of defects and active sites at the grain boundaries, which can react with ions in the electrolyte to increase the capacity of the positive electrode material. Therefore, the gram capacity of other examples and comparative examples is slightly higher.

[0099] Figure 2 The SEM photograph of the positive electrode material of Example 1 of the present application is shown. From the figure, it can be seen that by changing the precursor conditions to control the particle size and thickness of the polycrystalline primary particles and coating them with rare earth elements, the particle strength of the polycrystalline material can be effectively improved, thereby improving the cycle performance of the material.

[0100] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", "some implementation schemes" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0101] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for selecting a positive electrode material, characterized in that: include: Determine the Sp2 / Sp1 value and A / A0 value of the positive electrode material, wherein Sp1 is the initial (D90-D10) / D50 of the positive electrode material; Sp2 is the (D90'-D10') / D50' of the positive electrode material after 10T-30T pressure powder pressing; A is the initial D50 / S value of the positive electrode material; A0 is the D50' / S' value of the positive electrode material after 10T-30T pressure powder pressing; S is the initial specific surface area of ​​the positive electrode material; S' is the specific surface area of ​​the positive electrode material after 10T-30T pressure powder pressing; If the Sp2 / Sp1 value obtained by measurement satisfies: 1≤Sp2 / Sp1≤2.0, and the A / A0 value satisfies: 1≤A / A0≤2.50, then it is the target positive electrode material; The positive electrode material includes at least one of a layered metal oxide positive electrode material, a spinel metal oxide positive electrode material and a polyanion salt positive electrode material.

2. The selection method according to claim 1, characterized in that: The Sp1 of the layered metal oxide positive electrode material satisfies: 0<Sp1≤1.3; Preferably, Sp1 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp1≤8.

25.

3. The selection method according to claim 1, characterized in that: The Sp2 of the layered metal oxide positive electrode material satisfies: 0<Sp2≤2.6; Preferably, Sp2 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0<Sp2≤8.

3.

4. The selection method according to claim 1, characterized in that: The A of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 ; Preferably, the A of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0.05 (μm·g) / m 2 ≤A≤100(μm·g) / m 2 .

5. The selection method according to claim 1, characterized in that: The A0 of the layered metal oxide positive electrode material satisfies: 1.9 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 ; Preferably, the A0 of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material satisfies: 0.05 (μm·g) / m 2 ≤A0≤40(μm·g) / m 2 .

6. The selection method according to any one of claims 1 to 5, characterized in that: The initial D50 particle size of the layered metal oxide positive electrode material is 2.5 μm-15 μm; Preferably, the initial D50 particle size of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 10 nm-15 μm.

7. The selection method according to any one of claims 1 to 5, characterized in that: The initial specific surface area of ​​the layered metal oxide positive electrode material is 0.15 m 2 / g-1.3m 2 / g; Preferably, the initial specific surface area of ​​the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is 0.15 m 2 / g-20m 2 / g.

8. The selection method according to any one of claims 1 to 5, characterized in that: The layered metal oxide positive electrode material comprises at least one of lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide and lithium-rich manganese base; Preferably, the spinel structure metal compound positive electrode material includes at least one of lithium manganese oxide and lithium nickel manganese oxide; Preferably, the polyanion salt positive electrode material includes at least one of lithium iron phosphate and lithium iron manganese; Preferably, the positive electrode material comprises polycrystalline lithium nickel cobalt manganese oxide; Preferably, the positive electrode material comprises polycrystalline lithium nickel cobalt manganese oxide having a coating layer; Preferably, the coating layer has a thickness of ≤100 nm.

9. The selection method according to claim 8, characterized in that: The chemical formula of the lithium nickel cobalt manganese oxide is LiNi x Co y Mn (1-x-y) O2, where 0.7≤x<1, 0<y≤0.3, 0<x+y<1; Preferably, the chemical formula of the lithium iron phosphate is LiFePO4, LiMn x1 Fe (1-x1) PO4, LiMn2O4, x2Li2MnO3·(1-x2)LiMO2, wherein 0<x1<1, 0<x2<1, and M is at least one of nickel, cobalt, and manganese.

10. The selection method according to any one of claims 1 to 5, characterized in that: The compaction density of the electrode sheet prepared by the layered metal oxide positive electrode material is not less than 3.5g / cm 3 The compaction density of the electrode sheet prepared by one of the polyanion salt positive electrode material and the spinel metal oxide positive electrode material is not less than 2.5g / cm 3 .

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