Li-ion diffusion in Li intercalated graphite C₆Li and C₁₂Li probed by μ⁺SR

Abstract

In order to study a diffusive behavior of Li⁺ in Li intercalated graphites, we have measured muon spin relaxation (μ⁺SR) spectra for C₆Li and C₁₂Li synthesized with an electrochemical reaction between Li and graphite in a Li-ion battery. For both compounds, it was found that Li⁺ ions start to diffuse above 230 K and the diffusive behavior obeys a thermal activation process. The activation energy (E_a) for C₆Li is obtained as 270(5) meV, while E_a = 170(20) meV for C₁₂Li. Assuming a jump diffusion of Li⁺ in the Li layer of C₆Li and C₁₂Li, a self-diffusion coefficient D_Li at 310 K was estimated as 7.6(3) × 10^-11 (cm² s^-1) in C₆Li and 14.6(4) × 10^-11 (cm² s^-1) in C₁₂Li.