Surface chemical modified lithium iron phosphate and application thereof

Abstract

The invention relates to surface chemical modification of cathode materials of lithium batteries and provides surface chemical modified lithium iron phosphate and an application of the surface chemical modified lithium iron phosphate as a cathode material of a lithium battery. The surface chemical modified lithium iron phosphate is characterized in that surfaces of lithium iron phosphate particlesare covered with surface modification layers. The surface chemical modified lithium iron phosphate has the specific discharge capacity of 125-140 mA hg<-1> after circulating 100 circles at 1 C and has the capacity retention ratio of 85%-92%. The particle surfaces of the surface chemical modified lithium iron phosphate have polymer modification layers formed in situ in a normal pressure and room temperature environment, which is favorable for inhibiting direct contact of environment air and electrolyte with active substances, and the rate performance and the circulating stability of lithium iron phosphate are improved.

Description

technical field [0001] The invention relates to the surface chemical modification of lithium ion battery (abbreviated as lithium battery) positive electrode material, in particular to the surface chemical modification of lithium iron phosphate positive electrode material of lithium battery, and belongs to the technical field of surface modification of lithium battery electrode material. Background technique [0002] Cathode materials (also known as cathode materials) are an important part of lithium batteries, which determine the energy density, cycle stability, safety and cost of lithium batteries (Electrochimica Acta, 2016, 222, 685-692). Common cathode materials for lithium batteries are: lithium cobalt oxide (LiCoO 2 , abbreviated as LCO), lithium manganate (LiMn 2 o 4 , abbreviated as LMO), lithium iron phosphate (LiFePO 4 , abbreviated as LFP) and manganese, nickel doped lithium cobalt oxide ternary electrode material (LiNi x mn y co z o 2 , x + y + z = 1)...

AI Technical Summary

Problems solved by technology

There are two important problems in the actual application of the above-mentioned positive electrode materials: one is the problem of low electronic conductivity and ionic conductivity of the positive electrode material; the other is the problem of performance attenuation of the positive electrode material exposed to ambient air, that is, the problem of aging

But, as described in CN1617371A, the way of positive electrode material of lithium ion battery, because positive electrode material is in contact with water in the process of organic coating, thereby can inevitably cause the stripping of Li, M1, M2 metal ion, impairs the electrochemical performance of positive electrode material

In the surface modification or coating of positive electrode materials described in CN102544514A and CN104600282A, since the positive electrode material has undergone a high-temperature calcination process during the surface modification or coating process, this will cause the surface modification layer to shrink, split, unevenly distribute, and coat incomplete phenomenon

Functional polymer modified LiMn provided by CN1652376A 2 o 4 It has the following disadvantages. First, the functional polymer as a surface modifier is not easy to obtain and is not conductive, and it is grafted to the active material (i.e. LiMn 2 o 4 ) will reduce the electronic conductivity of the electrode material after the surface; secondly, whether it is LiMn 2 o 4 Mixed with functional polymer solution or LiMn 2 o 4 Mix with functional polymer monomers and initiators in solution and in-situ polymerize to obtain functional polymer grafted LiMn 2 o 4 The process is bound to be accompanied by the volatilization of organic substances such as solvents and unreacted monomers, which is not environmentally friendly

The lithium-rich material covered by the carbon & nickel-cobalt alloy quantum dot heterostructure provided by CN107437617A has the advantage that the organic ligand vapor formed by the organic ligand under vacuum and heating conditions can be deposited with the lithium-rich material in the form of vapor deposition. The material particle surface is combined, which is conducive to the formation of a uniform modified layer on the surface of the lithium-rich material particle; the disadvantage is that the selected organic ligand (methylimidazole or 2-methylimidazole) has a high boiling point, and the vapor deposition process needs to be carried out in a vacuum, It is carried out under heating conditions, and the process requirements are high; the organic ligands deposited on the surface of the active material (lithium-rich material) particles are not conductive, and need further high-temperature heat treatment (450~480 °C) to convert into carbon, the steps are cumbersome, and the energy consumption is high; and , the carbon layer obtained by high-temperature heat treatment is difficult to completely cover the surface of lithium-rich material particles

The mechanical mixing method is not conducive to the coating of active material particles. The modification method based on solvent / solution has a long process route and can generate waste liquid, which may easily lead to delithiation of the active material during the modification process.

In short, none of the above methods can meet the stated requirements for secondary surface modification / coating of cathode materials.

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