A kind of silicon matrix composite material and its preparation method and application

Abstract

The invention provides a silicon-based composite material and a preparation method and application thereof. The composite material consists of silicon and / or silicon oxide as the inner core, and the outer surface of the inner core is covered by a composite layer of carbon and carbon fluoride. The composite layer has a continuous and dense structure, and the carbon content of the coating layer gradually increases from the inside to the outside. The fluorinated carbon content gradually increases, and the fluorinated carbon coating layer formed by this structure has a better effect. During the battery cycle, the fluorine on the surface reacts with the lithium in the battery system to form lithium fluoride, and the formed fluorinated interface energy Better maintain structural stability, reduce the occurrence of side reactions, and reduce the thickness of SEI, thereby effectively improving the cycle performance of composite materials.

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 dramatically. Li-ion batteries are widely used due to their advantages of large specific energy, high operating voltage, and low self-discharge rate. in the field of mobile electronic terminal equipment. And with the growing demand for high-energy power sources, lithium-ion batteries are developing towards higher energy density. At present, most of the commercial lithium-ion batteries use the lithium iron phosphate / graphite system. Due to the low theoretical capacity of the electrodes ...

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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