Positive electrode material, secondary battery and electrical device

Abstract

Provided in the present application are a positive electrode material, a secondary battery and an electrical device. With regard to the positive electrode material of the present application, a layer of lithium iron phosphate doped with metal ions other than Mn is coated on the surface of lithium manganese iron phosphate, the content of the doping metal ions and the content of Mn in the lithium manganese iron phosphate are controlled, and the valence state h and the radius r<Å> of the doping metal ions are controlled to satisfy: 1.8≤h*r / 0.8<2, such that the coating layer material and the internal lithium manganese iron phosphate can be crystallographically fused, greatly improving the coating effect, and suppressing manganese dissolution of the internal lithium manganese iron phosphate, thereby improving the electrochemical performance of secondary batteries prepared by using the positive electrode material.

Description

Cathode material, secondary battery and electric device

[0001] This application claims priority to the Chinese patent application No. 202410864883.4 filed on June 28, 2024, and entitled "Cathode material, secondary battery and electric device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a cathode material, a secondary battery and an electric device. BACKGROUND

[0003] The lithium manganese iron phosphate system secondary battery is a derivative of the lithium iron phosphate system secondary battery. It has attracted widespread attention in the industry due to its high voltage platform and high energy density advantages. One prominent disadvantage of the lithium manganese iron phosphate system is manganese dissolution, which can cause rapid cycle decay, gas production and a series of other problems, affecting its electrochemical performance. SUMMARY

[0004] The purpose of the present application is to provide a cathode material, a secondary battery and an electric device to improve the electrochemical performance of the lithium manganese iron phosphate system secondary battery.

[0005] To achieve the above purpose, the first aspect of the present application provides a cathode material, which comprises lithium manganese iron phosphate and a coating layer arranged on at least part of the surface of the lithium manganese iron phosphate, wherein the coating layer comprises lithium iron phosphate.

[0006] The lithium manganese iron phosphate comprises a compound with a chemical formula of Li b Mn d Fe (1-d) PO4, and the lithium iron phosphate comprises a compound with a chemical formula of Li c M f Fe (1-f) PO4, wherein 0.95≤b≤1.05, 0.95≤c≤1.05, 0.1≤d≤0.9, 0.1≤f≤0.9, d-f≤0.1 or f-d≤0.1, M is a metal ion other than Mn, the valence h of the M ion and the radius r of the M ion satisfy: 1.8≤h*r / 0.8<2.

[0007] As an embodiment of the present application, the M comprises one or more of Zn, Cu, Ni and Co.

[0008] As an embodiment of the present application, the unit cell parameter a of the lithium manganese iron phosphate is a1, the unit cell parameter a of the lithium iron phosphate is a2, and 0.94≤a1 / a2≤1.0 is satisfied. ​

[0009] As an embodiment of the present application, the unit cell volume of the lithium manganese iron phosphate is V1, the unit cell volume of the lithium iron phosphate is V2, and the following is satisfied: 0.85≤V1 / V2≤1.00.

[0010] As an embodiment of the present application, the thickness of the coating layer is T, and the unit cell parameter a of the lithium iron phosphate is a2, and the following is satisfied: 10≤T / a2≤30.

[0011] As an embodiment of the present application, the thickness of the coating layer is T, and the following is satisfied:

[0012] As an embodiment of the present application, the specific surface area of the positive electrode material is 0.5m 2 / g~10m 2 / g.

[0013] As an embodiment of the present application, the powder compaction density of the positive electrode material under a pressure of 40KN is 2g / cm 3 ~3.5g / cm 3 .

[0014] In a second aspect of the present application, a secondary battery is provided, which comprises the positive electrode material according to the first aspect of the present application.

[0015] In a third aspect of the present application, an electric device is provided, which comprises the secondary battery according to the second aspect of the present application.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] The positive electrode material according to the present application is prepared by coating a layer of lithium iron phosphate doped with metal ions other than Mn on the surface of lithium manganese iron phosphate, and controlling the content of the doped metal ions, the content of Mn in the lithium manganese iron phosphate, and the valence h and radius r of the doped metal ions to satisfy: 1.8≤h*r / 0.8<2, so that the coating layer material and the internal lithium manganese iron phosphate can be fused into the same whole in crystallography, greatly improving the coating effect, inhibiting the dissolution of manganese in the internal lithium manganese iron phosphate, and thus improving the electrochemical performance of the secondary battery prepared using the positive electrode material. DETAILED DESCRIPTION

[0018] For better illustrating the purpose, technical scheme and advantages of the present application, the present application will be further illustrated by specific examples below, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and devices used in the present application are conventional reagents, methods and devices in the technical field. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0019] Embodiments of the present application provide a positive electrode material, which comprises lithium manganese iron phosphate and a coating layer arranged on at least part of the surface of the lithium manganese iron phosphate, wherein the coating layer comprises lithium iron phosphate;

[0020] The lithium manganese iron phosphate comprises a compound with a chemical formula of Li b Mn d Fe (1-d) PO4, and the lithium iron phosphate comprises a compound with a chemical formula of Li c M f Fe (1-f) PO4, wherein 0.95≤b≤1.05, 0.95≤c≤1.05, 0.1≤d≤0.9, 0.1≤f≤0.9, d-f≤0.1 or f-d≤0.1, M is a metal ion other than Mn, the valence h of the M ion and the radius r of the M ion satisfy: 1.8≤h*r / 0.8<2. The valence h of the M ion and the radius r of the M ion satisfy: 1.8≤h*r / 0.8<2.

[0021] The inventors of the present application have found that, by coating a layer of lithium iron phosphate doped with a metal ion other than Mn on the surface of lithium manganese iron phosphate, and controlling the content of the doped metal ion, the content of Mn in the lithium manganese iron phosphate, and the valence h of the doped metal ion and its radius r satisfy: 1.8≤h*r / 0.8<2, the cell channel for manganese dissolution can be narrowed, and the coating layer material and the internal lithium manganese iron phosphate can be fused in crystallography, the coating effect is improved, manganese dissolution is inhibited, and the electrochemical performance of the secondary battery is ultimately improved.

[0022] In some embodiments, the M comprises one or more of Zn, Cu, Ni, and Co.

[0023] The type of the M ion is determined by SEM (scanning electron microscope)-EDS (energy dispersive spectroscopy), the valence of the M ion is determined by XANES (X-ray absorption near edge structure), and the radius of the M ion is determined by EXAFS (Extended x-ray absorption fine structure).

[0024] In some embodiments, the unit cell parameter a of the lithium manganese iron phosphate is a1, the unit cell parameter a of the lithium iron phosphate is a2, and 0.94≤a1 / a2≤1.0 is satisfied. For example, a1 / a2 can be 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or a range between any two of the foregoing values. When a1 / a2 is within the above range, the coating effect can be further improved, and the manganese elution can be reduced.

[0025] In some embodiments, a1 satisfies: For example, a1 can be or a range between any two of the foregoing values.

[0026] In some embodiments, a2 satisfies: For example, a2 can be or a range between any two of the foregoing values.

[0027] In some embodiments, the unit cell volume of the lithium manganese iron phosphate is V1, and the unit cell volume of the lithium iron phosphate is V2, and 0.85≤V1 / V2≤1.00 is satisfied. For example, V1 / V2 can be 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or a range between any two of the foregoing values. When V1 / V2 is within the above range, the coating effect can be further improved, thereby inhibiting manganese elution and ultimately improving the electrochemical performance of the secondary battery.

[0028] In some embodiments, V1 satisfies: For example, V1 can be or a range between any two of the foregoing values.

[0029] In some embodiments, V2 satisfies: For example, V2 can be or a range between any two of the foregoing values.

[0030] It should be noted that the unit cell parameter and the unit cell volume of the positive electrode material described in the present application can be obtained by performing XRD (X-Ray Diffraction) testing on the material, and then performing structure refinement on the testing graph using the Rietveld method.

[0031] In some embodiments, the thickness of the coating layer is T, the unit cell parameter a of the lithium iron phosphate is a2, and 10≤T / a2≤30 is satisfied. For example, T / a2 can be 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, or a range defined by any two of the above values.

[0032] In some embodiments, the thickness T of the coating layer satisfies: For example, T can be or a range defined by any two of the above values. The thickness T of the coating layer in the above range can further improve the coating effect and reduce the dissolution of manganese.

[0033] In some embodiments, the specific surface area of the positive electrode material is 0.5m 2 / g to 10m 2 / g. For example, the specific surface area of the positive electrode material can be 0.5m 2 / g, 1m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, or a range defined by any two of the above values. The specific surface area of the positive electrode material in the above range can further balance the fast-charging performance and the cycle performance, and improve the energy density of the secondary battery.

[0034] In some embodiments, the powder compaction density of the positive electrode material under a pressure of 40KN is 2g / cm 3 to 3.5g / cm 3 . For example, the powder compaction density of the positive electrode material under a pressure of 40KN can be 2g / cm 3 , 2.2g / cm 3 , 2.4g / cm 3 , 2.6g / cm 3 , 2.8g / cm 3 , 3.0g / cm 3 , 3.2g / cm 3 , 3.5g / cm 3 , or a range defined by any two of the above values. The powder compaction density of the positive electrode material under a pressure of 40KN in the above range can further improve the energy density of the secondary battery.

[0035] In some embodiments, the application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode material according to the application.

[0036] In some embodiments, the application provides an electric device, which comprises the secondary battery according to the application.

[0037] For example, the electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0038] The following are specific embodiments of the application, and the technical solutions of the application are further described in combination with the embodiments. However, the application is not limited to these embodiments. The reagents, methods and devices used in the application are conventional reagents, methods and devices in the technical field unless otherwise specified.

[0039] Embodiment 1

[0040] This embodiment provides a lithium ion battery, and the preparation method comprises the following steps:

[0041] (1) Preparation of the positive electrode material:

[0042] S1. Li2CO3, FePO4 and MnPO4 are mixed according to a molar ratio of 0.5:0.4:0.6, ball-milled at a speed of 200 revolutions per minute for 6 hours, and then the powder is taken out and pressed into a sheet, calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0043] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4 and ZnPO4 are mixed according to a molar ratio of 100:0.5:0.4:0.6, ball-milled at a speed of 200 revolutions per minute for 6 hours, the powder is taken out and pressed into a sheet, calcined at 1200°C for 6 hours, and then naturally cooled to obtain the positive electrode material (LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4).

[0044] (2) Preparation of the positive electrode sheet:

[0045] The positive electrode material, conductive agent carbon black, and binder PVDF are mixed in a mass ratio of 96.5:2:1.5, a solvent NMP is added, and stirring is performed under the action of a vacuum stirrer to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on a positive electrode current collector aluminum foil, and after air drying at room temperature, the positive electrode slurry is transferred to an oven for continuous drying, and then after rolling, slitting, and cutting, a positive electrode sheet is obtained.

[0046] (3) Preparation of a negative electrode sheet:

[0047] The negative electrode active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber, and dispersant sodium carboxymethyl cellulose are mixed in a mass ratio of 96.5:1.5:1.5:0.5, a solvent deionized water is added, and stirring is performed under the action of a vacuum stirrer to obtain a negative electrode slurry; the negative electrode slurry is uniformly coated on a negative electrode current collector copper foil, and after air drying at room temperature, the negative electrode slurry is transferred to an oven for continuous drying, and then after rolling, slitting, and cutting, a negative electrode sheet is obtained.

[0048] (4) Preparation of an electrolyte:

[0049] Vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1, and then LiPF6 is added and mixed uniformly to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0050] (5) Preparation of a lithium ion battery:

[0051] The positive electrode sheet, a separator (polyethylene), and the negative electrode sheet are sequentially stacked with the separator exactly between the positive electrode and the negative electrode to play a role of isolating the two electrodes, and then the stack is wound into a bare cell and placed in an aluminum plastic film, and the bare cell is baked at 80°C to remove moisture, and after the moisture is removed, the electrolyte is injected, and then the cell is sealed, hot and cold pressed, double-sealed, formed, and finally, the finished battery is obtained.

[0052] Example 2

[0053] The difference between Example 2 and Example 1 is that the preparation method of the positive electrode material is different. In this embodiment, the preparation method of the positive electrode material is as follows:

[0054] S1. Li2CO3, FePO4, and MnPO4 are mixed in a molar ratio of 0.5:0.2:0.8, ball-milled at 200 revolutions per minute for 6 hours, and then the powder is taken out and pressed into a sheet, calcined at 1200°C for 6 hours, and naturally cooled to obtain an internal material LiMn 0.8 Fe 0.2 PO4;

[0055] S2. The internal material LiMn 0.8 Fe 0.2Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.2:0.8, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.8 Fe 0.2 PO4-coated LiMn 0.8 Fe 0.2 PO4.

[0056] Example 3

[0057] Example 3 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0058] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.1:0.9, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain an internal material LiMn 0.9 Fe 0.1 PO4;

[0059] S2. The internal material LiMn 0.9 Fe 0.1 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.1:0.9, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.9 Fe 0.1 PO4-coated LiMn 0.9 Fe 0.1 PO4.

[0060] Example 4

[0061] Example 4 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0062] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.6:0.4, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain an internal material LiMn 0.4 Fe 0.6 PO4;

[0063] S2. The internal material LiMn 0.4 Fe 0.6Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.6:0.4, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.4 Fe 0.6 PO4-coated LiMn 0.4 Fe 0.6 PO4.

[0064] Example 5

[0065] Example 5 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0066] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.9:0.1, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain an internal material LiMn 0.1 Fe 0.9 PO4;

[0067] S2. The internal material LiMn 0.1 Fe 0.9 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.9:0.1, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.1 Fe 0.9 PO4-coated LiMn 0.1 Fe 0.9 PO4.

[0068] Example 6

[0069] Example 6 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0070] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain an internal material LiMn 0.6 Fe 0.4 PO4;

[0071] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, CuPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiCu 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0072] Example 7

[0073] Example 7 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0074] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0075] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, NiPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiNi 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0076] Example 8

[0077] Example 8 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0078] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0079] S2. The internal material LiMn 0.6 Fe 0.4PO4, Li2CO3, FePO4, CoPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiCo 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0080] Example 9

[0081] Example 9 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0082] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1100°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0083] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1100°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0084] Example 10

[0085] Example 10 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0086] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1000°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0087] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1000°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0088] Example 11

[0089] Example 11 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0090] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1300°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0091] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1300°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0092] Example 12

[0093] Example 12 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0094] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1400°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0095] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1400°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0096] Example 13

[0097] Example 13 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0098] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 5 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0099] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 5 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0100] Example 14

[0101] Example 14 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0102] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 4 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0103] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 4 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0104] Example 15

[0105] Example 15 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0106] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6.5 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0107] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6.5 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0108] Example 16

[0109] Example 16 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0110] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 7 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0111] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 7 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0112] Example 17

[0113] Example 17 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0114] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0115] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 125:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0116] Example 18

[0117] Example 18 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0118] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0119] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 150:0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0120] Example 19

[0121] Example 19 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0122] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0123] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 75:0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0124] Example 20

[0125] Example 20 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0126] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0127] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 50:0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0128] Example 21

[0129] Example 21 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0130] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 3 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0131] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 3 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0132] Example 22

[0133] Example 22 differs from Example 1 in the method of preparing the positive electrode material. In this example, the method of preparing the positive electrode material is as follows:

[0134] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 12 hours at a speed of 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0135] S2. The internal material LiMn 0.6 Fe 0.4PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 12 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the LiZn 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0136] Comparative Example 1

[0137] Comparative Example 1 differs from Example 1 in the method of preparing the positive electrode material. In this comparative example, the positive electrode material was prepared by the following method:

[0138] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0139] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.2:0.8, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the LiZn 0.8 Fe 0.2 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0140] Comparative Example 2

[0141] Comparative Example 2 differs from Example 1 in the method of preparing the positive electrode material. In this comparative example, the positive electrode material was prepared by the following method:

[0142] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at a speed of 200 revolutions per minute, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0143] S2. The internal material LiMn 0.6 Fe 0.4Li2CO3, FePO4, ZnPO4 were mixed in a molar ratio of 100:0.5:0.6:0.4, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiZn 0.4 Fe 0.6 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0144] Comparative Example 3

[0145] Comparative Example 3 differs from Example 1 in the method of preparing the positive electrode material. In this comparative example, the positive electrode material was prepared by the following method:

[0146] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0147] S2. The internal material LiMn 0.6 Fe 0.4 PO4, Li2CO3, FePO4, CaPO4 were mixed in a molar ratio of 100:0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiCa 0.6 Fe 0.4 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0148] Comparative Example 4

[0149] Comparative Example 4 differs from Example 1 in the method of preparing the positive electrode material. In this comparative example, the positive electrode material was prepared by the following method:

[0150] S1. Li2CO3, FePO4, and MnPO4 were mixed in a molar ratio of 0.5:0.4:0.6, ball-milled for 6 hours at 200 rpm, and then pressed into a sheet shape. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain the internal material LiMn 0.6 Fe 0.4 PO4;

[0151] S2. The internal material LiMn 0.6 Fe 0.4PO4, Li2CO3, FePO4, MgPO4 were mixed in a molar ratio of 100:0.5:0.6:0.4, ball-milled for 6 hours at a rotation speed of 200 rpm, and then pressed into a sheet. The sheet was calcined at 1200°C for 6 hours, and then naturally cooled to obtain LiMg 0.4 Fe 0.6 PO4-coated LiMn 0.6 Fe 0.4 PO4.

[0152] The parameters of the positive electrode materials obtained in Examples 1 to 22 and Comparative Examples 1 to 4 are shown in Table 1 and Table 2.

[0153] Table 1

[0154] Table 2

[0155] The performance of the secondary batteries obtained in the examples and comparative examples was tested, and the specific testing methods were as follows:

[0156] 1) Gas production performance test: The injection port of the secondary battery was connected to a gas pressure gauge, and was adjusted to zero. The battery was placed in a charge-discharge test cabinet, and was kept at a constant temperature of 25°C. The voltage range was 2.5 to 4.25 V, the charge rate was 1C, and the discharge rate was 1C. The test was stopped when the number of cycles reached 100, and the pressure of the gas pressure gauge was read.

[0157] 2) Rate performance test: Fresh secondary batteries that had not undergone electrochemical testing were placed in a charge-discharge tester, and were kept at room temperature. The batteries were charged at 0.33C to 4.25 V, and were discharged at 0.33C to 2.5 V. The capacity was Q1. The batteries were then charged at 0.33C to 4.25 V, and were discharged at 6C to 2.5 V. The capacity was Q2, and the rate performance was Q2 / Q1*100%.

[0158] 3) Cycle performance test: The secondary batteries were placed in a charge-discharge test cabinet, and were kept at a constant temperature of 25°C. The voltage range was 2.5 to 4.25 V, the charge rate was 1C, and the discharge rate was 1C. The test was stopped when the capacity decreased to 80% of the initial capacity, and the number of cycles was recorded.

[0159] The test results of the secondary batteries obtained in Examples 1 to 22 and Comparative Examples 1 to 4 are shown in Table 3.

[0160] Table 3

[0161] From the above embodiments and comparative examples, it can be seen that the cathode material described in this application involves coating a layer of lithium iron phosphate doped with metal ions other than Mn onto the surface of lithium manganese iron phosphate, and controlling the content of the doped metal ions, the content of Mn in the lithium manganese iron phosphate, and the valence state h and radius r of the doped metal ions. The condition 1.8≤h*r / 0.8<2 is satisfied, which improves the coating effect, inhibits the dissolution of manganese from the internal lithium manganese iron phosphate, and thus improves the electrochemical performance of the secondary battery prepared using this cathode material.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A cathode material, wherein, The cathode material comprises lithium manganese iron phosphate and a coating layer disposed on at least a portion of the surface of the lithium manganese iron phosphate, the coating layer comprising lithium iron phosphate; The lithium manganese iron phosphate contains the chemical formula Li b Mn d Fe (1-d) The compound of PO4, wherein the lithium iron phosphate contains the chemical formula Li c M f Fe (1-f) A compound of PO4, wherein 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.1 ≤ d ≤ 0.9, 0.1 ≤ f ≤ 0.9, df ≤ 0.1 or fd ≤ 0.1, M is a metal ion other than Mn, and the valence state h of the M ion is related to the radius r of the M ion. It satisfies: 1.8≤h*r / 0.8<2.

2. The cathode material according to claim 1, wherein, M includes one or more of Zn, Cu, Ni, and Co.

3. The cathode material according to claim 1, wherein, The cell parameter a of the lithium manganese iron phosphate is a1, and the cell parameter a of the lithium iron phosphate is a2, satisfying: 0.94≤a1 / a2≤1.

0.

4. The cathode material according to claim 3, wherein, The value of a1 / a2 is a range consisting of 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any two of these values.

5. The cathode material according to claim 3, wherein, a1 satisfies:

6. The cathode material according to claim 5, wherein, a1 is Or a range consisting of any two of these values.

7. The cathode material according to claim 3, wherein, The a2 satisfies:

8. The cathode material according to claim 7, wherein, a2 is Or a range consisting of any two of these values.

9. The cathode material according to claim 1, wherein, The cell volume of the lithium manganese iron phosphate is V1, and the cell volume of the lithium iron phosphate is V2, satisfying: 0.85≤V1 / V2≤1.

00.

10. The cathode material according to claim 9, wherein, The V1 / V2 is a range consisting of 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any two of these values.

11. The cathode material according to claim 9, wherein, V1 satisfies:

12. The cathode material according to claim 11, wherein, The V1 is Or a range consisting of any two of these values.

13. The cathode material according to claim 9, wherein, V2 satisfies:

14. The cathode material according to claim 13, wherein, The V2 is Or a range consisting of any two of these values.

15. The cathode material according to claim 1, wherein, The thickness of the coating layer is T, and the cell parameter a of the lithium iron phosphate is a2, satisfying: 10≤T / a2≤30.

16. The cathode material according to claim 1, wherein, The thickness of the coating layer is T, and it satisfies:

17. The cathode material according to claim 1, wherein, The specific surface area of ​​the positive electrode material is 0.5 m². 2 / g~10m 2 / g.

18. The cathode material according to claim 1, wherein, The compaction density of the positive electrode material under 40 kN pressure is 2 g / cm³. 3 ~3.5g / cm 3 .

19. A secondary battery, wherein, It includes a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 18.

20. An electrical appliance, wherein, The electrical device includes the secondary battery as described in claim 19.

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