By coating germanium nanowires with silicon, the researchers stopped nearly all surface diffusion of lithium ions into the nanowires. Instead, lithium diffusion, known as lithiation, occurred layer by layer along the axis of the nanowire. This is in contrast to lithiation from the surface of nanowires not covered with silicon.
"These results demonstrate for the first time that interface and bandgap engineering of electrochemical reactions can be utilized to control the nanoscale ionic transport / insertion paths and thus may be a new tool to define the electrochemical reactions in Li-ion batteries," the researchers write in their Nano Letters paper.
This work builds on research demonstrating excellent control over germanium / silicon (Ge/Si) heterostructuring, which Dayeh and colleagues recently published as a cover article in Applied Physics Letters and a cover letter in the journal Nano Letters.
Dayeh grew the nanowires during his time as a postdoctoral researcher at Los Alamos National Laboratory (LANL). Lithiation experiments were performed by two postdoctoral researchers from Sandia National Laboratories, Drs. Yang Liu and Xiaohua Liu, and Dayeh's postdocdoral researchers working at LANL. Dayeh formulated the mechanism and performed the analysis and simulations after joining the faculty of the Electrical and Computer Engineering Department at the UC San Diego Jacobs School of Engineering.
This is a video of radial diffusion of lithium into an uncoated germanium nanowire as well as axial lithiation of a silicon-coated nanowire's germanium core. This research on nanowires could lead to tailored volume expansion of lithium ion battery electrodes, a step that could minimize their cracking, improve their durability, and perhaps influence how one could think about different electrode architectures.
A related audio conversation with UC San Diego electrical engineer Shadi Dayeh is available at: https://soundcloud.com/daniel-kane-16/better-lithium-ion-batteries
(Photo Credit: UC San Diego Jacobs School of Engineering)
By coating germanium nanowires with silicon, researchers led by a UC San Diego electrical engineer stopped nearly all surface diffusion of lithium ions into the nanowires. This work could lead to improved lithium-ion batteries through new electrode architectures with precise nano-scale designs.
(Photo Credit: UC San Diego / Electrical and Computer Engineering)