Nanoprobing combined with SEM imaging reveals the mechanism of capacity decay in SiOx anodes.
Anodes made of silicon oxide offer a promising alternative to pure silicon anodes for Li-ion batteries due to their good volumetric stability, high capacity, and industrially scalable production by chemical vapor deposition.
One problem with SiOx anodes is that they deteriorate after several charging/discharging cycles, reducing the battery capacity.
The team of Feng Pan from School of Advanced Materials, Peking University Shenzhen Graduate School in China, and their collaborators looked into what happens with the solid electrolyte interface (SEI) during charge cycling.
They combined in-situ SEM nanoprobing with various imaging and 3D reconstruction techniques and achieved an important insight to the capacity decay mechanism in the SiOx anode material.
Turns out that morphological evolution of SEI on SiOx during long cycling includes two types of SEI structures around the SiOx particles. They undergo uneven accordion-like “breathing” and gradual densification with each cycle.
Researchers directly measured SEI conductivity by nano-probing and visualized the conductive network within SEI using EELS mapping. Electron transfer through the percolation network of conductive agents within the thick SEI gradually disappeared as SEI grew. This mechanism underlines the capacity decay.
To limit the free growth of SEI and slow down the anode aging process, researchers proposed a simple solution. A confining graphite layer on top of the SiOx electrode showed an improved cycling stability of the SiOx electrode.
More details about the paper can be found here.
