CN-115395012-B - Lithium iron manganese phosphate anode material and preparation method and application thereof

CN115395012BCN 115395012 BCN115395012 BCN 115395012BCN-115395012-B

Abstract

The application discloses a lithium iron manganese phosphate anode material, and a preparation method and application thereof. The lithium iron manganese phosphate anode material comprises lithium iron manganese phosphate particles, wherein the lithium manganese phosphate particles are sequentially divided into a core area, a middle area and a surface area from the center of the lithium manganese iron phosphate particles to the surface according to the content distribution of iron elements, the middle area covers the core area, the surface area covers the middle area, the iron element content in a first composite area is reduced in a gradient manner from the core area to the middle area, and the iron element content in a second composite area is increased in a gradient manner from the middle area to the surface area. The lithium iron manganese phosphate anode material has high compaction density, high energy density, high voltage platform, good cycle performance and good low-temperature performance. The preparation of the lithium iron manganese phosphate anode material can ensure the stable electrochemical performance of the prepared lithium iron manganese phosphate anode material.

Inventors

XU RONGYI
Zhe Jiayun
LIANG SHIHAN
LI HENGLI
LIU QIFENG
YANG YI

Assignees

深圳市德方纳米科技股份有限公司
佛山市德方纳米科技有限公司

Dates

Publication Date: 20260505
Application Date: 20220811

Claims (13)

1. The lithium manganese iron phosphate anode material is characterized by comprising lithium manganese iron phosphate particles and a functional coating layer, wherein the functional coating layer coats the lithium manganese iron phosphate particles; The lithium manganese iron phosphate particles are sequentially divided into a core region, a middle region and a surface region according to the content distribution of iron elements from the center of the lithium manganese iron phosphate particles to the surface direction, wherein the middle region coats the core region, the surface region coats the middle region, the content of iron elements in a first composite region is reduced in a gradient manner from the core region to the middle region, the content of iron elements in a second composite region is increased in a gradient manner from the middle region to the surface region, the molar content of iron elements in the first composite region is at the rate of the gradient reduction, and the molar content of iron elements in the second composite region is at the rate of the gradient increase, and is respectively and independently 0.00175-0.0032 mol/nm; the manganese content in the first composite region is gradually increased from the core region to the middle region, the manganese content in the second composite region is gradually reduced from the middle region to the outer surface of the surface region, so that the middle region forms a manganese-rich region, the molar content of the manganese element in the first composite region is at the gradient increasing rate, and the molar content of the manganese element in the second composite region is respectively and independently 0.00175-0.0032 mol/nm at the gradient decreasing rate; the material of the functional coating layer contains at least one of an iron simple substance and an iron compound, and the iron compound comprises at least one of lithium iron phosphate, lithium ferrite and ferric oxide.
2. The lithium iron manganese phosphate positive electrode material according to claim 1, wherein the molar content ratio of the three elements of iron, manganese and phosphorus contained in the core region, the intermediate region and the surface region satisfies that the total molar content of iron and manganese is phosphorus molar content = 1, (0.95-1.05); wherein the molar content ratio of the iron element to the phosphorus element in the first composite zone is reduced from (0.6-0.8): (0.95-1.05) to (0.95-1.05) in the gradient, and/or The molar content ratio of the iron element to the phosphorus element in the second composite region is increased from 0 (0.95-1.05) to 0.6-0.8 (0.95-1.05) in the gradient.
3. The lithium iron manganese phosphate positive electrode material according to claim 1, wherein the molar content ratio of the three elements of iron, manganese and phosphorus contained in the core region, the intermediate region and the surface region is such that the molar content of the total molar content of iron and manganese is phosphorus molar content=1 (0.95-1.05), wherein, The molar ratio of manganese element to phosphorus element in the first composite zone is increased from (0.2-0.4): (0.95-1.05) to (0.95-1.05) in the gradient.
4. The lithium iron manganese phosphate positive electrode material according to claim 1, characterized in that: the molar content ratio of the three elements of iron, manganese and phosphorus in the core region, the middle region and the surface region is satisfied that the total molar content of iron and manganese is phosphorus molar content=1 (0.95-1.05), The molar content ratio of manganese element to phosphorus element in the second composite region is reduced from 1 (0.95-1.05) to 0.2-0.4 (0.95-1.05) in the gradient.
5. The lithium iron manganese phosphate positive electrode material according to claim 1 to 4, wherein the molar content ratio of four elements of iron, manganese, phosphorus and lithium contained in the core region, the intermediate region and the surface region is such that the molar content of total molar content of iron and manganese is phosphorus and lithium is molar content=1, (0.95 to 1.05): (0.95 to 1.10), and/or Doping elements are also distributed in the lithium iron manganese phosphate particles.
6. The lithium iron manganese phosphate positive electrode material according to claim 5, wherein the content of the doping element in the first composite region is decreased in a gradient from the core region to the intermediate region, and/or The content of the doping element in the second composite region increases in the gradient from the intermediate region to the outer surface of the surface region, and/or In the lithium iron manganese phosphate particles, the molar content ratio of iron, manganese, phosphorus and doping elements contained is such that the total molar content of iron and manganese is the molar content of doping elements and the molar content of phosphorus is 1, (0.01-0.02): (0.95-1.05), and/or The doping element comprises at least one of Mg, ti, cr, co, ni, ca, mn, S, B, and/or The mole ratio of the doping element to the iron element contained in the lithium iron manganese phosphate particles is (0.0125-0.033): 1.
7. The lithium iron manganese phosphate positive electrode material according to claim 5, wherein the functional coating layer has a thickness of 5 to 20 nm and/or The iron simple substance and/or iron compound in the functional coating layer accounts for 1-10% of the total weight of the lithium iron manganese phosphate anode material, and/or The molar content ratio of the doping element to the phosphorus element in the first composite region is reduced from (0.01-0.02): 0.95-1.05 to 0 in the gradient, and/or In the second composite region, the molar content ratio of the doping element to the phosphorus element is increased from 0 to (0.01-0.02) in the gradient to (0.95-1.05).
8. The lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 4, 6 and 7, wherein the lithium iron manganese phosphate particles have a D50 particle diameter of 200 to 500 nm and/or The D50 particle size of the lithium iron manganese phosphate anode material is 400-800 nm.
9. The method for preparing a lithium iron manganese phosphate positive electrode material according to any one of claims 1 to 8, comprising the steps of: Carrying out first mixing treatment on a lithium source, a phosphorus source, a first iron source and a manganese source according to the proportion of preparing lithium iron manganese phosphate to obtain a precursor; and carrying out first sintering treatment on the precursor in a protective atmosphere to obtain lithium iron manganese phosphate particles, wherein the content of iron element is firstly reduced in a gradient manner from the inside of the lithium iron manganese phosphate particles to the surface direction, and then is increased in a gradient manner.
10. The method of claim 9, wherein the precursor is prepared by a method comprising the steps of: Preparing a precursor nucleus body by taking a part comprising a lithium source, a phosphorus source, a first iron source and a manganese source; Sequentially forming a plurality of coating layers on the surface of the precursor nucleus body to form the precursor body, wherein in the process of forming each coating layer, the mixing proportion of a first iron source and a manganese source is controlled to realize the gradient-decreasing and gradient-increasing distribution of the iron element from the precursor nucleus body to the surface of the precursor body, or the gradient-decreasing and gradient-increasing distribution of the iron element is realized at the same time as the gradient-increasing and gradient-decreasing distribution of the manganese element; And/or The lithium source, the phosphorus source, the first iron source and the manganese source are mixed according to the mole ratio of (0.95-1.10): (0.95-1.05): (0-0.8): (0.2-1) of the lithium element, the phosphorus element and the iron element provided by the first iron source The temperature of the first sintering treatment is 400-500℃, and/or In the first mixing treatment process, a doping element compound is also added according to the mole ratio of the iron source to the doping element compound of 1 (0.001-0.02) After the step of the first sintering treatment, further comprising the steps of: carrying out second mixing treatment on the lithium iron manganese phosphate particles and a second iron source or the second iron source and a reducing agent to obtain a mixture; And performing second sintering treatment on the mixture to form a functional coating layer containing an iron simple substance and/or an iron compound on the surface of the lithium manganese iron phosphate particles.
11. The method according to claim 10, wherein the reducing agent comprises at least one of a carbon source, H 2 , and S; The temperature of the second sintering treatment is 500-800 ℃; the second mixing treatment is carried out on the lithium manganese iron phosphate particles, the reducing agent and the second iron source according to the mass ratio of (3-10): (0.03-0.3): (0.1-0.5).
12. The positive electrode is characterized by comprising a current collector and a positive electrode active layer combined on the surface of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a binder and a conductive agent, and the positive electrode active material is the lithium iron manganese phosphate positive electrode material according to any one of claims 1-8 or prepared by the preparation method according to any one of claims 9-11.
13. A secondary battery comprising a positive electrode, wherein the positive electrode is the positive electrode of claim 12.

Description

Lithium iron manganese phosphate anode material and preparation method and application thereof Technical Field The application belongs to the technical field of electrode materials, and particularly relates to a lithium iron manganese phosphate anode material, a preparation method and application thereof. Background Lithium ion batteries are widely applied to various fields such as 3C electronic products, power automobiles, energy storage power stations and the like due to high energy density, small self-discharge, no memory effect and long cycle life, and are research hot spots in the current new energy storage and conversion system. The lithium iron manganese phosphate material (LiMn 1-xFexPO4 (0 < x < 1)) has the characteristics of rich raw materials, low cost, higher specific capacity, good thermal stability and the like, and has higher discharge voltage (3.8V vs 3.3V) compared with lithium iron phosphate (LiFePO 4), so that the energy density of the battery can be improved by about 15%, and the lithium iron manganese phosphate material is one of the new-generation industrialized lithium ion battery anode materials. However, the existing lithium iron manganese phosphate also has some defects, such as low electronic conductivity, insufficient compaction density, two voltage platforms (4.1V and 3.4V) and the like, and has unsatisfactory multiplying power performance, cycle performance, energy density and the like. The prior report that the modification of the lithium iron manganese phosphate is attempted to overcome part of defects of the lithium iron manganese phosphate, such as in the disclosed graphene in-situ composite lithium iron manganese phosphate positive electrode material, the graphene is used for coating the lithium iron manganese phosphate, although the growth of crystal grains is effectively controlled, the crystal grains in the material are orderly arranged, the stacking compaction performance is improved, the structural stability is improved, and the electron migration rate is accelerated. However, the modified lithium iron manganese phosphate only improves the conductivity of the lithium iron manganese phosphate obviously, and does not improve the voltage platform, the multiplying power performance, the cycle performance, the energy density and other performances of the lithium iron manganese phosphate. Disclosure of Invention The application aims to overcome the defects in the prior art, and provides a lithium iron manganese phosphate anode material and a preparation method thereof, so as to solve the technical problems of non-ideal performances such as voltage platform, multiplying power performance, cycle performance and energy density of the existing lithium iron manganese phosphate. The application further aims to provide a positive electrode and a secondary battery containing the positive electrode, so as to solve the technical problems of low voltage platform, and unsatisfactory cycle performance and gram capacity of the conventional lithium iron manganese phosphate secondary battery. In order to achieve the above object, according to a first aspect of the present application, there is provided a lithium iron manganese phosphate positive electrode material. The lithium iron manganese phosphate anode material comprises lithium iron manganese phosphate particles, wherein the lithium manganese phosphate particles are sequentially divided into a core area, a middle area and a surface area from the center of the lithium manganese iron phosphate particles to the surface according to the content distribution of iron elements, the middle area covers the core area, the surface area covers the middle area, the iron element content in a first composite area is reduced in a gradient manner from the core area to the middle area, and the iron element content in a second composite area is increased in a gradient manner from the middle area to the surface area. In a second aspect of the application, a method for preparing a lithium iron manganese phosphate positive electrode material is provided. The preparation method of the lithium iron manganese phosphate anode material comprises the following steps: Carrying out first mixing treatment on a lithium source, a phosphorus source, a first iron source and a manganese source according to the proportion of preparing lithium iron manganese phosphate to obtain a precursor; And (3) performing first sintering treatment on the precursor in a protective atmosphere to obtain lithium iron manganese phosphate particles, wherein the content of iron element is firstly reduced in a gradient manner from the inside to the surface of the lithium iron manganese phosphate particles, and then is increased in a gradient manner. In a third aspect of the present application, a positive electrode is provided. The positive electrode comprises a current collector and a positive electrode active layer combined on the surface of the current collector, wherein the positive elec