CN-122000324-A - Lithiated nano-cellulose carbon coated lithium iron phosphate composite material, preparation method thereof, positive electrode material, positive electrode plate and battery

CN122000324ACN 122000324 ACN122000324 ACN 122000324ACN-122000324-A

Abstract

The invention focuses on the technical field of lithium ion battery anode materials, and particularly relates to a lithiated nanocellulose carbon-coated lithium iron phosphate composite material, a preparation method of the material, an anode material based on the material, an anode plate and a battery. The lithium ion battery comprises a lithium iron phosphate matrix and a carbon layer coated on the surface of the matrix, wherein the carbon layer is formed by lithiation nano cellulose gel through a carbonization process and is a conductive layer with a three-dimensional continuous porous network structure, and lithium elements in the lithiation nano cellulose gel can migrate to the lithium iron phosphate matrix in the carbonization process so as to play an in-situ lithium compensation role on the lithium iron phosphate matrix. Under the condition of extremely low carbon content, the continuous three-dimensional conductive network is successfully constructed, and the carbon layer is used as a structural framework, so that the particle aggregation phenomenon is effectively inhibited. The accurate and gradient compensation of lithium loss from the surface and the inner is realized, and the crystal lattice is effectively repaired. The obtained material has high specific capacity, excellent multiplying power performance and ultra-long cycle life.

Inventors

Bi Shengsheng
SHU XINGJUAN
ZHANG RONGHUI
REN YUANYUAN
LI HUANGE
MA XIANG
SHEN BEIBEI

Assignees

河南科高辐射化工科技有限公司
河南省科学院

Dates

Publication Date: 20260508
Application Date: 20260203

Claims (10)

1. The lithium nanocellulose carbon-coated lithium iron phosphate composite material is characterized by comprising a lithium iron phosphate matrix and a carbon layer coated on the surface of the lithium iron phosphate matrix, wherein the carbon layer is formed by carbonizing a lithium nanocellulose gel, the carbon layer is a conductive layer with a three-dimensional continuous porous network structure, and lithium elements in the lithium nanocellulose gel can migrate to the lithium iron phosphate matrix in the carbonization process to play an in-situ lithium compensation role.
2. The lithiated nanocellulose carbon-coated lithium iron phosphate composite material of claim 1, wherein the lithiated modified nanocellulose is obtained by ion exchange and partial esterification double modification of nanocellulose prepared by irradiation degradation method, and the surface of the lithiated modified nanocellulose simultaneously contains lithium ions loaded by ion exchange and substances bonded with cellulose hydroxyl groups through phosphate bonds.
3. The lithiated nanocellulose carbon-coated lithium iron phosphate composite material of claim 1, wherein the mass ratio of lithiated nanocellulose gel to lithium iron phosphate matrix is from 1:1 to 10:1.
4. The lithiated nanocellulose carbon-coated lithium iron phosphate composite material of claim 1, wherein the carbon layer has a thickness of 5-50nm and the composite material has a particle size in the range of 100-500nm.
5. A method for preparing the lithiated nanocellulose carbon-coated lithium iron phosphate composite material of claims 1-3, comprising the steps of: s1, preparing a lithium iron phosphate matrix; S2, preparing lithiation modified nanocellulose gel, namely taking nanocellulose prepared by an irradiation degradation method as a raw material, performing ion exchange reaction with a lithium salt solution, and performing partial esterification reaction with a lithium dihydrogen phosphate solution to obtain modified nanocellulose gel; and S3, preparing a core-shell precursor, namely uniformly dispersing the lithium iron phosphate matrix powder obtained in the step S1 into the lithiation modified nanocellulose sol obtained in the step S2, and drying to obtain a dried precursor with a lithium iron phosphate core-modified cellulose shell structure. S4, sectional controlled release carbonization, namely, performing two-stage heat treatment on the dry precursor in inert atmosphere: the first stage, heat treatment is carried out at 300-500 ℃ to promote the lithiation modified nanocellulose to crosslink and release first part of lithium, and lithium compensation is carried out on the surface layer of the lithium iron phosphate particles; and in the second stage, heat treatment is carried out at 500-750 ℃ to carbonize the crosslinked cellulose skeleton, construct a three-dimensional network carbon layer and release a second part of lithium, wherein the second part of lithium diffuses into the lithium iron phosphate particles to form a concentration gradient. The lithium iron phosphate matrix is synthesized by a liquid phase method, and comprises the steps of mixing a lithium source, an iron source and a phosphorus source according to a molar ratio of 1:1:1-1.2, and reacting for 2-8 h at 120-200 ℃.
6. The method for lithiating a nanocellulose carbon-coated lithium iron phosphate composite material of claim 5, wherein in step S2, the lithium salt is lithium hydroxide or lithium acetate, and the radiation adopted by the irradiation degradation method is gamma rays or electron beams.
7. The method of preparing a lithiated nanocellulose carbon coated lithium iron phosphate composite material of claim 5, wherein said heat treatment is a staged calcination comprising: Heating from room temperature until The calcination temperature of the first section is 300-500 ℃ and the heat preservation time is 2-4 h; The second stage calcining temperature is 500-750 ℃ and the heat preservation time is 4-8 h; the temperature rising rate is 5-15 ℃ per minute.
8. A lithium ion battery positive electrode material comprising the lithiated nanocellulose carbon-coated lithium iron phosphate composite material of any one of claims 1-3.
9. A positive electrode sheet for a lithium ion battery comprising the positive electrode material according to claim 8.
10. A lithium ion battery comprising the positive electrode sheet of claim 9.

Description

Lithiated nano-cellulose carbon coated lithium iron phosphate composite material, preparation method thereof, positive electrode material, positive electrode plate and battery Technical Field The invention relates to the technical field of lithium ion battery anode materials, in particular to a lithiated nanocellulose carbon-coated lithium iron phosphate composite material, a preparation method thereof, an anode material, an anode plate and a battery. Background Lithium iron phosphate) The positive electrode material has higher safety and longer cycle life, and is widely applied to lithium ion batteries. But its inherent low electron conductivity and lithium ion diffusion coefficient limit its performance in terms of rapid charge and discharge performance of the battery. The carbon coating technology is to promoteOne of the effective means of the electrochemical performance of the material is to optimize the structure and the characteristics of the carbon coating layer by utilizing different materials, so that the conductivity and the lithium ion diffusion rate of the composite electrode material can be obviously improved. In the prior art, natural small molecular organic matters such as glucose, sucrose, citric acid and the like, or artificial high molecular polymers such as polyacrylonitrile, phenolic resin and the like are often adopted as carbon sources. In the high-temperature carbonization process of the carbon sources, the coating layer is often caused by severe pyrolysis and shrinkage, so that the problems of (1) poor continuity, incomplete coating to form island-shaped or dot-shaped coating and limited electron conduction path, (2) compact structure, which can promote electron conductivity but possibly prevent diffusion of lithium ions, and (3) uneven combination with a matrix, and easy secondary agglomeration of active particles are caused. Furthermore, lithium migration of lithium iron phosphate during high temperature solid phase sintering is unavoidable, which can deviate the final product from stoichiometry, yielding e.g.And isophase, the integrity of the crystal structure is damaged, and further, the active lithium is continuously and irreversibly consumed and structurally degenerated in the charge and discharge process, which is a key intrinsic factor for limiting the stability of the long-cycle life of the active lithium. Therefore, a novel composite material which integrates the two functions of uniformly constructing a conductive network and controllable lithium compensation and realizes high-efficiency coating under low carbon content and a simple preparation method thereof are developed, and breakthrough is madeThe electrochemical performance bottleneck of the positive electrode material is significant in promoting the development of next-generation high-performance batteries. In recent years, natural polymer materials are valued for their advantages such as wide sources, green and renewable properties. Cellulose is taken as a natural polymer material, is rich in hydroxyl functional groups, can obtain good hydrophilicity and three-dimensional network gel forming capability after being decomposed into a micro-size form, and is regarded as an ideal carbon precursor. The nano-cellulose is prepared by adopting the irradiation oxidative degradation method, the nano-carbon source with large length-diameter ratio and high reactivity can be efficiently and cleanly obtained, and the process does not need a large amount of strong acid and strong alkali and is environment-friendly. In addition, the nano cellulose is easy to form a porous network structure after carbonization, and after lithiation modification and carbonization of coated lithium iron phosphate, a carbon network with cooperatively enhanced physical crosslinking and chemical bonding can be formed, so that the electron transmission is more efficient, and the structure is more stable in circulation. Disclosure of Invention In order to solve the problems in the prior art, the invention provides a lithiated nanocellulose carbon-coated lithium iron phosphate composite material and a preparation method thereof, and a positive electrode material, a positive electrode plate and a battery based on the material. The invention aims to solve the existing problemsThe problems of incomplete conductive network, uncontrollable lithium cycle loss and the like of the anode material under the low-carbon coating condition are solved. The method specifically comprises 1) realizing uniform and firm three-dimensional conductive coating under the condition of lower carbon content, 2) accurately and efficiently compensating lithium loss in the high-temperature preparation process and repairing lattice defects, and 3) strengthening the interface between a carbon layer and a matrix, thereby prolonging the long cycle life of the material. In order to achieve the above purpose, the present invention adopts the following technical scheme: The lithium nanocellulos