The increasing demand for smaller, lighter, cheaper, and more stable power sources for portable electronics, vehicles and aircrafts spurs intensive research of the lithium ion batteries. Rational battery engineering, including design of smart electrode materials, is impossible without in-depth understanding of the chemical and physical processes in galvanic cells at the microscopic, nanoscopic, and eventually, molecular levels. Reaction mechanisms, cathode expansion, formation of cracks and SEI layer, electrolyte decomposition etc., are being extensively studied with a variety of ex and in situ microscopic, spectroscopic and electrochemical techniques. However, a significant drawback of the existing methodologies is their inability to deliver Li⁺ ions and control their concentration at the nanoscale level. In addition, the classic electrochemical techniques imply existence of liquid-solid interfaces and inevitable formation of SEI layer. This is a significant impediment for studying lithium diffusion and associated morphological changes in cathode materials.

We report progress in developing Li⁺ focused ion beams (FIB) as a novel probe for exploring nanoscale electrochemistry in battery-relevant materials. This work focuses on implantation of lithium ions in crystalline silicon to benchmark this technique and builds on recent, qualitative studies of FIB implantation in Sn microspheres [Takeuchi et al. JES 163 (6), A1010-A1012]. FIB implantation opens the possibility of precise spatial control of nanoscale lithium concentration though variation of the beam positioning and current. Experiments are performed in vacuo without the presence of electrolytes or associated solid-electrolyte interface. The Li⁺ ion beam operates with energies ranging from 0.5 to 5 keV, currents up to 15 pA, and minimum spot size of 27 nm using a magneto-optical trap ion source (MOTIS).

WRM acknowledges support from the National Research Council Research Associateship Program. ES and JG acknowledge support under the Cooperative Research Agreement between the University of Maryland and the National Institute of Standards and Technology Center for Nanoscale Science and Technology, Award 70NANB14H209, through the University of Maryland.