Si-based Anode Materials for Lithium-ion Batteries

Abstract

Porous silicon materials were made by various synthetic methods and highlighted for anode materials for Lithium ion battery. Most of Porous Silicon has been prepared on the Si wafers but we employed 3D-interconnected pores to silicon at the bulk powder to alleviated the volume expansion during lithium alloy/dealloy. Herein, we applied metal-assisted chemical etching method at bulk silicon powder to produce urchin-like silicon of 1-3 µm in length of wires and 5-8µm sized particles. By controlling etchant concentration, deposed metal concentration, etching time and temperature, we optimized pore depth and core size of the silicon powder for good performance. However, native surface layer of silicon in which SEI layer formation occurs, influence the kinetics of lithiation/delithiation and the interfacial stability during cycling. Accordingly, surface of the sample is modified via functionalized groups (Si-OH, Si-O-Si, Si-H, Si-O-Li) through different chemical treatments, and the characteristic of each samples were confirmed from 29Si-MAS, FT-IR, XPS. Silicon, one of most promising anode, has been significantly challenged to improve the volumetric energy density related to the both material and electrode expansion, electrical conductivity and long-term cycle performance for the practical application. Herein, we demonstrated a synthesis of Si nanparticles embedded α-FeSi2 matrix in which α-FeSi2 acts as a buffer matrix for the expansion of adjacent Si expansion, and inter connected carbon enhance conductivity and reduce the side reaction of electrolyte and structural degradation. Our results reveals that the α-FeSi2/Si/Carbon (FSC) exhibits excellent electrochemical property in full lithium ion cell compared to α-FeSi2/Si (FS) and benchmarking sample of FS, FS/CNT, owing to the decreasing formation of SEI layers and good mechanical strength induced by carbon specious. The FSC anode in the full cell shows a significant improved capacity retention of 83% at 0.7C/0.5C charge/discharge rate between 4.4-3V after 200 cycles. Silicon oxide (SiOx) is one of the silicon (Si)-based candidates for next generation anode materials beyond graphite in lithium ion batteries industry. However the fading mechanisms of Si-based anode have not been researched in detail with full-cells, though the volume expansion of Si is known as foremost issue of capacity decay and half-cells cycling test is not reliable for practical use of full-cells. Here, we report practical investigation of the fading mechanisms of SiOx-graphite mixture (SG) full-cells test. We conclude that the extent of electrode swelling could determine the main fading reason of Si-based anode whether it follows rapid or gradual degradations and that of SG full-cell was estimated as the continuous SEI thickening which causes large over-potential and electrolyte depletion. The 200th cycle retention of our full-cell shows 70% with initial discharge capacity of 3.45 mAh·cm-2, which is the higher area capacity compared to previous Si-based anode full-cell publication. This work will furnish a guide to make practical strategies of Si-based anode.