Revealing the aging process of solid electrolyte interphase on SiO_x anode.

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Silicon oxide (SiO_x) is a promising anode material for batteries, but its application is limited by rapid capacity fading.
• The aging of the Solid Electrolyte Interphase (SEI) layer on SiO_x is a critical, yet poorly understood, factor contributing to this degradation.

Purpose of the Study:

• To elucidate the microstructural characteristics and evolution of the SEI layer on SiO_x anodes.
• To understand the relationship between SEI structure, electronic conductivity, and capacity decay in SiO_x batteries.
• To propose a strategy for mitigating SEI-related capacity fading.

Main Methods:

• Utilized 3D focused ion beam-scanning electron microscopy (FIB-SEM) for tomographic imaging of SEI microstructure.
• Employed nanoprobe and electron energy loss spectroscopy (EELS) to analyze SEI composition and electronic conductivity.
• Investigated the effect of a mechanically restricting confining layer on SEI growth and electrode performance.

Main Results:

• Revealed a non-homogeneous SEI structure with an incompact inner region and a dense outer region, challenging previous assumptions.
• Discovered that SEI electronic conductivity depends on a percolation network of conductive agents within the SEI.
• Demonstrated that SEI growth attenuates this conductive network, leading to capacity decay in SiO_x anodes.
• Showcased a proof-of-concept strategy using a confining layer to restrict SEI growth and improve stability.

Conclusions:

• The study provides fundamental insights into the aging mechanisms of SEI layers on SiO_x anodes.
• Understanding SEI evolution and its impact on electronic conductivity is key to improving battery performance.
• Mechanical restriction of SEI growth presents a viable strategy for enhancing the cycle life of SiO_x-based batteries.