Nanometer silicon composite negative electrode material used for lithium ion battery

Abstract

The invention relates to a nanometer silicon composite negative electrode material used for a lithium ion battery. The composite negative electrode material adopts an ''egg'' model structure, whereinthe egg yolk comprises a graphite substrate and a nanometer silicon material uniformly dispersed in the interior and on the surface of the graphite substrate; the egg white is graphene uniformly dispersed on the surfaces of the graphite substrate and the nanometer silicon; and the egg shell is a conductive carbon coating layer. By combination of nanometer compounding, surface medication and surface coating technologies, the silicon alloy negative electrode material with the ''egg'' model structure is prepared, and the negative electrode material has high specific capacity, high initial charging-discharging efficiency and excellent cycle stability; and the preparation process is simple, environment friendly and free of pollution.

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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