Nano silicon material and preparation method thereof

Abstract

The invention relates to a nano silicon material with an amorphous / nanocrystalline composite structure. In the application of a lithium / sodium ion battery, after lithium / sodium is embedded into a crystalline silicon material for the first time, a composite structure of an amorphous region (silicon-lithium alloy) and a crystalline region (not embedded with lithium) is formed, and volume expansion and structural change are generated; after lithium / sodium removal, volume shrinkage causes structure collapse, i.e., silicon particle fracture and pulverization. In order to provide enough lithium / sodium embedding space in advance and inhibit the volume change of lithium / sodium embedding / removal for the first time, the invention provides an amorphous / nanocrystalline composite structure and a controllable preparation method thereof, i.e., a nano silicon material with the amorphous / nanocrystalline composite structure is prepared by adopting a spark discharge and high-energy ball milling combined process, the amorphous region surrounds the nanocrystalline, the crystal face orientation of the nanocrystalline is randomly distributed, the proportion range of the amorphous region is controllable, and the amorphous region belongs to an isotropic material. In the application of lithium and sodium ion batteries, the structure can effectively relieve the problems of material fracture and pulverization caused by silicon material expansion / shrinkage due to embedding / removal of lithium / sodium, so that the cycle performance of the silicon negative electrode is improved.

Description

technical field [0001] The invention relates to a nano-silicon material with an amorphous / nano-crystalline composite structure, and belongs to the technical field of negative electrode materials for lithium batteries. Background technique [0002] In recent years, with the rapid development of new energy pure electric vehicles, plug-in hybrid electric vehicles and electric tools, higher requirements have been placed on the energy density, safety and cycle stability of lithium-ion batteries. Graphite is used as a commercial anode material for lithium-ion batteries (theoretical specific capacity is 372 mAh g -1 ), has been unable to meet the market demand for large batteries with high energy density. Silicon-based anode materials have a high theoretical specific capacity of 4200 mAh g -1 , lower charge and discharge platform (close to the potential platform of graphite), green environmental protection and high safety, etc., is considered to be the most lithium-ion battery ...

AI Technical Summary

Problems solved by technology

However, the above-mentioned material synthesis methods are mainly chemical vapor deposition, laser ablation, electron beam evaporation, magnetron sputtering, and metal-assisted chemical etching. However, these preparation methods have extremely high requirements for equipment, harsh process conditions, Mainly use silane or silicon tetrachloride as silicon source, high cost and difficult to scale production

Most of the nano-materials prepared by the above method are crystalline nano-silicon, and the volume expansion has anisotropy during charge and discharge, resulting in uneven distribution of mechanical stress, which is easy to cause material cracking and crushing, and it is difficult to maintain long-term cycle performance.

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