Considerations in applying neutron depth profiling (NDP) to Li-ion battery research

Abstract

Li distribution within micron-scale battery electrode materials is quantified with neutron depth profiling (NDP). This method allows the determination of intra- and inter-electrode parameters such as lithiation efficiency, electrode morphology change, and Li transport. In this work, a Sn electrode was lithiated at a constant potential and in situ Li movement was monitored and quantified. This contrasts to traditional methods where Li diffusion is inferred based on the passed electrochemical charge. Diffusion constants obtained through Fick's 1st and 2nd laws using this direct detection method, ranging from 1 × 10⁻¹² cm² s⁻¹ to 10 × 10⁻¹² cm² s⁻¹, are in good agreement with each other and reduce the range from the literature reported values for this system by over an order of magnitude. A significant difference between the electrochemical charge passed and Li incorporated into the Sn electrode as measured by NDP was detected. This indicates that NDP can be used to separate lithiation current from other parasitic currents. Advantages, challenges, improvements, and opportunities for using NDP to investigate many battery-related phenomena are presented.