Silicon-based composite material as well as preparation method and application thereof

Abstract

The invention provides a silicon-based composite material as well as a preparation method and application thereof. The composite material takes silicon and / or silicon oxide as an inner core, the outer surface of the inner core is coated with a carbon and carbon fluoride composite layer, the composite layer has a continuous and compact structure, wherein the carbon content of the coating layer is gradually reduced from inside to outside, the carbon fluoride content is gradually increased from inside to outside; therefore, the carbon fluoride coating layer formed by the structure has a better effect, and in the cycle process of the battery, fluorine on the surface reacts with lithium in a battery system to generate lithium fluoride, and a formed fluorinated interface can better maintain the structural stability, reduce side reactions and reduce the thickness of SEI, so the cycle performance of the composite material is effectively improved.

Description

technical field [0001] The invention relates to a silicon-based composite material and a preparation method thereof, in particular to the application of the silicon-based composite material as a negative electrode material of a high specific energy lithium ion battery. Background technique [0002] With the wide application and rapid development of various portable electronic devices and electric vehicles, the demand and performance requirements for their chemical power sources have increased sharply. Lithium-ion batteries are widely used due to their advantages such as large specific energy, high operating voltage, and low self-discharge rate. In the field of mobile electronic terminal equipment. And with the increasing demand for high-energy power sources, lithium-ion batteries are developing towards higher energy densities. At present, most commercial lithium-ion batteries use lithium iron phosphate / graphite system. Due to the low theoretical capacity of the electrode it...

AI Technical Summary

Problems solved by technology

The composite material with multi-level structure is coated with carbon fluoride, which effectively improves the battery capacity and the first Coulombic efficiency, and has excellent cycle performance. However, the physical method of ball milling is used to coat carbon fluoride on silicon nanoparticles in the preparation of the material. The surface and the coated surface have poor density. During the ball milling process, local overheating will cause oxidation problems, and new interfaces will be generated, which will cause SEI to grow continuously and cause battery performance to decay.

Moreover, the method of preparing nano-silicon by magnesia thermal reduction in this method destroys the original silicon-oxygen structure of silicon oxide, cannot effectively buffer the volume expansion, and also deteriorates the cycle performance of the battery.

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