Graphene-coated lithium iron phosphate composite material and preparation method thereof

Abstract

The invention discloses a graphene-coated lithium iron phosphate composite material and a preparation method thereof, and belongs to the technical field of lithium ion batteries. The preparation method comprises the following steps: coating graphene oxide and lithium iron phosphate by adopting spray drying or evaporation drying to prepare a graphene-coated lithium iron phosphate solid, and carrying out heat treatment on the obtained graphene-coated lithium iron phosphate solid to prepare a graphene-coated lithium iron phosphate composite material, wherein the ratio of the sheet diameter of the graphene oxide to the D50 of the lithium iron phosphate is 0.05-40. According to the preparation method, the specific surface area of the obtained graphene-coated lithium iron phosphate composite material is effectively controlled by controlling the matching of the sheet diameter of graphene oxide and the particle size of lithium iron phosphate, and the processability of the coated material is greatly improved. Meanwhile, the resistivity of the prepared graphene-coated lithium iron phosphate composite material is reduced, and the charge-discharge performance of the material under high multiplying power can be improved.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and relates to a graphene-coated lithium iron phosphate composite material and a preparation method thereof. Background technique [0002] The olivine-type lithium iron phosphate belongs to the orthorhombic crystal system, because Li + The one-dimensional diffusion mechanism and PO 4 The hindering effect of the tetrahedron, resulting in Li + In its diffusion rate and electronic conductivity are extremely low. This intrinsic defect greatly limits its application in the high-magnification and low-temperature markets. Therefore, effectively overcoming these two obstacles will greatly promote the electrochemical performance of LFP. [0003] Carbon coating and particle nanosizing are currently the most widely used and convenient modification methods in the industry. Good carbon coating can provide an effective electronically conductive network for electrode materials; particle nanos...

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Problems solved by technology

Good carbon coating can provide an effective electronically conductive network for electrode materials; particle nanoscale can greatly shorten the Li + The diffusion distance in the bulk phase can improve the reaction kinetics of the material, reduce the polarization, and improve its reversible capacity and rate performance, but the nano-particles also bring certain technological difficulties to subsequent processing.

In recent years, with the continuous development of the graphene industry, graphene-based coating processes have emerged in an endless stream. Although there are many reports in the literature, most of them use in-situ composite methods for coating. On the one hand, this method cannot be very good. Graphene is evenly dispersed on the surface of the particles, and at the same time, the specific surface of the original nanoparticles is further increased after coating, which aggravates the problem of material processing technology. At the same time, the preparation cost of this method is extremely high, which is not conducive to the later commercialization.

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