The passivation efficiency of the solid electrolyte interphase on Si anodes

• Applicant: Professor Dr. Hans-Georg Steinrück
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517694212

Electrolyte breakdown leads to capacity fading in high energy density lithium-ion batteries (LIBs), which impedes their utilization. To overcome this issue, a molecular-level understanding of the electrolyte behavior near electrodes and of the time-evolution of the electrodes is imperative. Of particular relevance is the solid electrolyte interphase (SEI), a nanoscale surface layer occurring on the anodes of LIBs. It consists of electrolyte decomposition products and determines cell lifetime and kinetics. The passivation efficiency of the SEI corresponds to its ability to prevent continued electrolyte decomposition and is its most important property. Despite its relevance, only sparse knowledge exists. This is due the experimental challenge to accurately differentiate capacity losses originating from (i) limited passivation efficiency, (ii) uncontrolled SEI growth on new, non-passivated surfaces resulting from SEI cracking and/or delamination upon electrode particle breathing, and (iii) active material deactivation. This hurdle is particularly high for alloying anodes such as Si. It represents a roadblock towards finding future electrolytes. The goal of this proposal is to utilize the concept of SEI passivation efficiency together with its experimental quantification as a criterion for electrolyte performance. The main hypothesis is: Foundational molecular level understanding of the root causes for high passivation efficiency based on model system investigations allows for tailored electrode passivation through rational electrolyte chemistry engineering. Towards this goal, we aim to develop a correlation between electrolyte chemistry, resulting SEI structure, morphology and composition, and the passivation efficiency. We will achieve this goal by a comprehensive multi-method and multi-property approach to systematically study different electrolyte classes, using advanced experimental tools in conjunction with well-defined model systems. This includes a combination of precision electrochemical cycling measurements and operando surface X-ray scattering using model amorphous Si thin film electrodes. By this combination, we can quantify SEI capacities and therefore the passivation efficiency. Several complementary electroanalytical and structural probes will unravel the structure-chemistry-property relationship. Based on our findings, we will develop concepts for future electrolytes and propose new electrolyte chemistries. We anticipate that our results will render the process of finding new electrolytes more efficient in general, because the candidate pool is constrained to systems with high passivation efficiency.

• DFG Programme: Research Grants