A kind of preparation method of nano-silicon composite negative electrode material for lithium ion battery

Abstract

The invention relates to a nano-silicon composite negative electrode material for lithium-ion batteries. The composite negative electrode material is an "egg" model structure, and the egg yolk is a nano-silicon material uniformly dispersed inside and on the surface of the graphite matrix, and the protein is uniformly dispersed. On the graphite matrix and graphene on the surface of nano-silicon, the eggshell is a conductive carbon coating. The invention combines nanocomposite, surface modification and surface coating technologies to prepare a silicon alloy negative electrode material with an "egg" model structure, which has high specific capacity, high initial charge and discharge efficiency and excellent cycle stability. The preparation process of the invention is simple, environment-friendly and pollution-free.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a nano-silicon composite negative electrode material for lithium ion batteries, a preparation method thereof, and a lithium ion battery prepared by using the negative electrode material. Background technique [0002] At present, with the shortage of global oil resources and the continuous deterioration of the climate environment, the development of clean and energy-saving new energy vehicles has been highly valued by countries all over the world. The key to the development of new energy vehicles lies in their power sources. At present, commercial lithium-ion batteries mainly use graphite-based negative electrode materials, but its theoretical specific capacity is only 372mAh / g, which cannot meet the demand for high energy density of lithium-ion batteries in the future. Therefore, the development of new high-performance electrode materials has become a r...

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Problems solved by technology

[0003] Silicon has an ultra-high theoretical specific capacity (4200mAh / g) and a low delithiation potential (<0.5V), and the voltage platform of silicon is slightly higher than that of graphite. It is difficult to cause lithium precipitation on the surface during charging, and the safety performance is better. Silicon has become one of the potential choices for the replacement of carbon-based anodes in lithium-ion batteries, but silicon also has disadvantages as an anode material for lithium-ion batteries: (1) Silicon materials are prone to volume expansion during charging and discharging, resulting in the collapse of the conductive network and affecting the battery life. Cycle performance; (2) Silicon is a semiconductor material with low electrical conductivity. During the charge-discharge cycle, the deintercalation of lithium ions will cause the volume expansion and contraction of more than 300% of the material, resulting in damage to the material structure and Pulverization, resulting in rapid loss of capacity and deterioration of cycle performance

(3) The silicon material is easy to corrode during the cycle, and the capacity fades; (4) Due to the volume effect of the silicon material, it is difficult to form a stable solid electrolyte interface (SEI) film in the electrolyte, and with the destruction of the electrode structure, the exposed A new SEI film is continuously formed on the exposed silicon surface, which intensifies the corrosion and capacity fading of silicon.

However, the composite material prepared by this method has more internal pores, lower tap density, and lower volumetric energy density.

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