A preparation method of titanium nitride and carbon double-coated lithium manganese iron phosphate composite material

Abstract

The invention discloses a preparation method for a lithium manganese iron phosphate composite coated by both titanium nitride and carbon. The preparation method comprises the following steps: adding a certain amount of a carbon source during synthesis of a precursor; and then during sintering, introducing NH3 in a protective atmosphere, introducing TiCl4 with N2 as carrying gas and uniformly depositing a layer of a titanium nitride coating on the surface of lithium manganese iron phosphate by using a chemical vapor deposition method so as to prepare the lithium manganese iron phosphate composite uniformly coated by both titanium nitride and carbon. According to the invention, through adjustment of a carbon source addition amount during synthesis and the flow and deposition time of the three gases during vapor deposition, the granularity, thickness and bulk density of the coating can be adjusted, and the lithium manganese iron phosphate composite uniformly coated by both titanium nitride and carbon can be obtained. The coating has good uniformity and consistency; the composite has high tap density and good conductivity; a lithium ion positive electrode material using the composite has good charge and discharge rate and cycle stability; and the preparation method is simple, controllable and easy for industrial production.

Description

technical field [0001] The invention relates to the field of positive electrode materials for lithium ion batteries, in particular to a preparation method of a titanium nitride and carbon double-coated lithium manganese iron phosphate composite material. Background technique [0002] Phosphate-like material LiMPO with olivine structure 4 (M=Fe, Mn, Ni, Co) is used as a lithium-ion battery material, its theoretical capacity is about 170mAh / g, and it has many advantages such as stable structure, low reactivity with electrolyte, high safety, and good battery cycle performance. advantage. Among such phosphate materials, LiFePO 4 The synthesis of materials is relatively simple, and large-scale production and sales have been realized. However, LiFePO 4 Due to the low potential platform (about 3.4V) of lithium deintercalation, the material reduces the overall energy density of the battery and limits its development in electric vehicles. while LiMnPO 4 The working voltage for ...

AI Technical Summary

Problems solved by technology

Although it has been reported that nano-scale lithium manganese phosphate materials have been obtained by hydrothermal method, sol-gel and other methods, the preparation method is complicated, the cost is high, and the tap density of the dispersed nanoparticles is very low, resulting in a very low volumetric energy density. , which is not conducive to practical application

In addition, since LiMnPO 4 It does not have a good affinity with carbon, and the effect of carbon coating in the existing preparation methods is generally unsatisfactory. In order to obtain a higher discharge capacity, it is necessary to add a proportion of up to 20-30wt% carbon, which further reduces the power density of the battery.

[0004] LiMnxFe as an olivine structure 1 -xPO 4 The material is in LiMnPO 4 developed on the basis of the modified, LiMnxFe 1 -xPO 4 The material has two charging and discharging platforms, compared to LiFePO 4 The specific energy is higher than that of LiMnPO 4 The conductivity is good, and it has good cycle and rate; however, although Fe 2+ The introduction of lithium manganese phosphate can improve the conductivity of lithium manganese phosphate, but the range of improvement is limited, and it is difficult to make full use of the electrochemical performance of the material.

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