CN-118083937-B - Manganese iron phosphate precursor, manganese iron lithium phosphate positive electrode material, preparation method and application

CN118083937BCN 118083937 BCN118083937 BCN 118083937BCN-118083937-B

Abstract

The invention relates to the field of lithium ion batteries, in particular to a manganese iron phosphate precursor, a manganese iron phosphate lithium positive electrode material, a preparation method and application, wherein the manganese iron phosphate precursor comprises manganese element, iron element and carbon element, the content of the manganese element is decreased from an inner core to the surface, the content of the iron element is increased, the content of the carbon element is decreased, the contents of the three elements show gradient distribution synergistic effect, and the battery containing the manganese iron phosphate lithium positive electrode material prepared from the precursor can achieve both higher discharge gram capacity and discharge platform voltage, and the dissolution amount of the manganese element is reduced.

Inventors

LI WEI
XU KAIHUA
CHEN YUJUN
Dong Yuanchu
ZHANG ZHILI

Assignees

格林美（无锡）能源材料有限公司

Dates

Publication Date: 20260505
Application Date: 20240226

Claims (12)

1. The manganese iron phosphate precursor is characterized by comprising manganese element, iron element and carbon element, wherein the content of the manganese element is decreased progressively, the content of the iron element is increased progressively and the content of the carbon element is decreased progressively from the inner core to the surface; at the inner core, the molar ratio of the manganese element to the iron element is (8-9): (1-2); Taking the mass of the ferric manganese phosphate precursor at the inner core as a reference, the content of the carbon element is 5-8wt%; The molar ratio of the manganese element to the iron element is (6-7.5) (2.2-4) in the middle of the inner core and the surface; the content of the carbon element is 2-4wt% based on the mass of the manganese iron phosphate precursor in the middle of the inner core and the surface; at the surface, the molar ratio of the manganese element to the iron element is (3-5): 5-7; The content of the carbon element is 1-2wt% based on the mass of the manganese iron phosphate precursor at the surface.
2. The manganese iron phosphate precursor according to claim 1, wherein the manganese iron phosphate precursor has an average particle size of 3-5 μm.
3. A method for preparing the manganese iron phosphate precursor according to claim 1 or 2, comprising the steps of: step 1, mixing a first manganese source, a first iron source, a first phosphorus source and a first carbon source to obtain a base solution; Step 2, adding a manganese source solution, an iron source solution, a carbon source solution and a complexing agent into the base solution at an initial flow rate for reaction, and respectively reducing the flow rates of the manganese source solution and the carbon source solution to 2/3-9/10 of the initial flow rate when the average grain size is 1.5-2 mu m, and improving the flow rate of the iron source solution to 2-4 times of the initial flow rate; When the reaction is carried out until the average grain size is 2.5-2.8 mu m, respectively reducing the flow rate of the manganese source solution and the flow rate of the carbon source solution to 1/3-3/4 of the initial flow rate, and improving the flow rate of the iron source solution to 3-7 times of the initial flow rate; and step 3, ageing the material obtained after the reaction in the step2, and separating to obtain a manganese iron phosphate precursor.
4. The method according to claim 3, wherein in step 1, the molar ratio of the first manganese source, the first iron source, the first phosphorus source, and the first carbon source is (5-10): 0.5-2): 5-12): 1.
5. The method of claim 4, wherein the molar ratio of the first manganese source, the first iron source, the first phosphorus source, and the first carbon source is (8-9): 1-1.5): 9-10): 1.
6. A method according to claim 3, wherein in step1, a dispersing agent is further added before mixing.
7. The method of claim 6, wherein the mass ratio of the dispersant to the first iron source is 8-12:1; and/or the dispersing agent comprises polyethylene glycol and/or polyacrylamide.
8. The method of claim 3, wherein in step 2, the molar ratio of the complexing agent to the first iron source is from 0.3 to 0.6:1; and/or, in step 2, the complexing agent comprises ferrous phosphate and/or oxalic acid dihydrate; And/or in the step2, the manganese source solution comprises a second manganese source and water, wherein the concentration of the second manganese source is 1.8-2.2mol/L; and/or in the step2, the iron source solution comprises a second iron source and water, wherein the concentration of the second iron source is 0.7-1.3mol/L; and/or in the step 2, the carbon source solution contains a second carbon source and water, wherein the concentration of the second carbon source is 0.3-0.5g/L; and/or, the first manganese source and the second manganese source are each independently selected from at least one of manganese nitrate, manganese sulfate and manganese carbonate; and/or, the first iron source and the second iron source are each independently selected from ferric nitrate; and/or, the first carbon source and the second carbon source are each independently selected from at least one of glucose and fructose.
9. A method of preparation according to claim 3, wherein in step 2, the initial flow rate is 0.005-0.1L/s; And/or the reaction conditions include a reaction temperature of 50-80 ℃.
10. A lithium manganese iron phosphate positive electrode material, characterized in that the lithium manganese iron phosphate positive electrode material is prepared by sintering a lithium source and the lithium manganese iron phosphate precursor according to claim 1 or 2 or the manganese iron phosphate precursor prepared by the preparation method according to any one of claims 3 to 9.
11. The lithium iron manganese phosphate positive electrode material according to claim 10, wherein the molar ratio of the lithium source to the iron manganese phosphate precursor is 0.5-1.2:1.
12. Use of the lithium manganese iron phosphate positive electrode material according to claim 10 or 11 in a lithium ion battery.

Description

Manganese iron phosphate precursor, manganese iron lithium phosphate positive electrode material, preparation method and application Technical Field The invention relates to the field of lithium ion batteries, in particular to a manganese iron phosphate precursor, a manganese iron lithium phosphate positive electrode material, a preparation method and application. Background Lithium iron phosphate (LiMn xFe1-xPO4, abbreviated as LMFP) is a positive electrode material of a lithium ion battery, and gradually becomes a further selection for replacing lithium iron phosphate by virtue of the advantages of high safety performance, long cycle life, high voltage, wide raw material sources and the like, and becomes an important selection for new energy automobiles and energy storage markets in the future. However, lithium iron manganese phosphate also has problems of poor electron conductivity, manganese elution, and the like, because in a nonlinear MnO 6 octahedron, mn 3+ in a high spin state has a very large magnetic moment, and only one electron exists in a double degenerate eg orbit (including dx 2-y2 and dz 2 orbitals), resulting in an asymmetric distribution of electrons. Meanwhile, electrons in dx 2-y2 and dz 2 orbitals show different degrees of shielding effect on Mn nuclei in different directions, and in order to stabilize Mn 3+ migration in molecules, longitudinal Mn-O bonds are gradually elongated, and horizontal Mn-O bonds are shortened, so that linear MnO 2 alignment is elongated along the axial direction, and Jahn-Teller distortion is generated. In order to avoid Jahn-Teller distortion, the material can be modified, the performance of the material is improved, and the modification process comprises the processes of carbon coating, particle size nanocrystallization, ion doping, manganese content optimization and the like. However, the current technology has the problems that the conductivity of the material is obviously reduced due to the introduction of manganese element, and meanwhile, the problem of manganese element dissolution occurs. Disclosure of Invention Therefore, the technical problem to be solved by the invention is to overcome the defect that the battery in the prior art cannot achieve both higher discharge gram capacity and discharge platform voltage, and the manganese element in the battery can be dissolved out, so as to provide a manganese iron phosphate precursor, a manganese iron lithium phosphate anode material, a preparation method and application. Therefore, the invention provides the following technical scheme: the first aspect of the invention provides a manganese iron phosphate precursor, which comprises manganese element, iron element and carbon element, wherein the content of manganese element is decreased progressively, the content of iron element is increased progressively and the content of carbon element is decreased progressively from an inner core to a surface. The manganese iron phosphate precursor provided by the invention has the advantages that from the inner core to the surface, the content of manganese element is reduced, the content of iron element is increased, the content of carbon element is reduced, and the battery containing the manganese iron phosphate lithium anode material prepared from the manganese iron phosphate precursor can give consideration to higher discharge gram capacity and discharge platform voltage, wherein the gradient distribution of the content of carbon enhances the electronic conductivity, promotes the migration and diffusion of lithium ions, and improves the conductivity of the battery. According to the invention, the molar ratio of manganese element to iron element at the core is (8-9): (1-2). According to the invention, the content of the carbon element is 5-8wt% based on the mass of the manganese iron phosphate precursor at the core. According to the invention, the molar ratio of manganese element to iron element is (6-7.5) (2.2-4) in the middle of the core and the surface. According to the invention, the content of carbon element is 2-4wt% based on the mass of the manganese iron phosphate precursor in the middle of the core and the surface. According to the invention, the molar ratio of manganese element to iron element at the surface is (3-5): (5-7). According to the invention, the content of carbon element is 1-2wt% based on the mass of the manganese iron phosphate precursor at the surface. In the invention, the average particle size of the manganese iron phosphate precursor is 0-1.8 mu m at the inner core, the average particle size of the manganese iron phosphate precursor is 1.8-2.5 mu m (excluding 1.8 mu m) at the middle between the inner core and the surface, and the average particle size of the manganese iron phosphate precursor is 2.5-5 mu m (excluding 2.5 mu m) at the surface. According to the invention, the content of different metal elements at different parts of the ferromanganese phosphate precursor is determined by adopt