Elucidating Degradation Mechanisms of Silicon-graphite Electrodes in Lithium-ion Batteries by Local Electrochemistry

The integrity of the solid electrolyte interphase (SEI) formed on the negative electrode of lithium-ion batteries (LIB) is especially critical for the performance of next-generation LIBs comprising silicon-carbon based electrode materials. The protecting character of the SEI is compromised due to volume expansion and shrinking during de/intercalation of Li ions leading to irreversible changes upon long-term cycling. Scanning electrochemical microscopy (SECM) is proposed as local electrochemical technique to investigate the degradation mechanisms of advanced negative electrodes. The impact of charge/discharge cycling on the SEI properties on Si-C electrodes was investigated, and the sensitivity of SECM successfully reveals inhomogeneities at an early stage of the cycling already at about 5 cycles. Macroscopic EIS measurements and evaluation of the coulombic efficiency may result in misleading interpretations of degradation. SECM is demonstrated to be a powerful and complementary technique for revealing & mu;m-heterogeneities in the SEI surface reactivity after a few charge/discharge cycles.

Automated summary

The integrity of the solid electrolyte interphase (SEI) on the negative electrode of lithium-ion batteries (LIB) is crucial for next-generation LIBs with silicon-carbon electrodes. The SEI protection is compromised by volume changes during Li ion de/intercalation, leading to irreversible degradation. Scanning electrochemical microscopy (SECM) is a useful technique for investigating the degradation mechanisms of advanced negative electrodes and revealing SEI surface reactivity heterogeneities after a few charge/discharge cycles.