graphite-like silicon nanospheres (Si @ C) have a high specific capacity, but in the process of lithiation, the mechanical stress inside the silicon sphere will cause the silicon sphere to expand rapidly and destroy the outer mesh coating, so it has not been widely used. Recently, PicoFemto®Helping Professor Wang Xi of Beijing Jiaotong University and researcher Chen Shimou of the Institute of Process of Chinese Academy of Sciences to make new discoveries in the research of Si @ NG-based lithium ion battery anode materials. The relevant research results are published in the international journal Nano Energy (IF = 15.46) under the title of "Stress-relieving defects enable ultra-stable silicon anode for Li-ion storage.

Figure 1. In-situ experiment details

Figure 2. PicoFemto®Schematic diagram of in-situ electrical sample rod (JEOL or FEI electron microscope compatible)

Figure 3. In situ TEM measurements of Si @ NG and Si @ G materials.(from original)

Researchers use PicoFemto®In situ electrical sample rod (TEM-STM holder) studied the structural stability of Si @ NG negative material in the process of lithium in the transmission electron mirror, and found that the nitrogen-doped carbon layer wrapped on the silicon nanosphere can effectively alleviate the volume expansion of the silicon ball in the lithium process. They carefully studied and found that the homogeneous doping of N in the carbon layer produced uniformly distributed "hole" defects in the NG network, which fully ensured the stress release of the silicon ball during the expansion process. The battery cycle performance test results show that Si @ NG exhibits good cycle stability (at a current density of 2100 mA g-1, a specific capacity of 1321 mAh g-1 after 100 cycles, and a retention rate of about 96.6). In addition, the initial coulombic efficiency (ICE) reached 90.3%. Conclusion: In-situ transmission electron microscopy studies combined with finite element analysis show that the nitrogen-doped Carbon matrix can effectively alleviate the mechanical stress caused by the volume expansion of silicon spheres during lithiation, keep the internal silicon spheres intact, and ensure the cycle stability and good rate performance of Si @ NG anode materials. This study validates a reliable method to improve the electrochemical performance of Si/C-based electrode materials, paving the way for their practical application in lithium-ion batteries (LIBs).

Original DOI Link: https://doi.org/10.1016/j.nanoen. 2020.104568