Quadrupled Cycle Life of High-Voltage Nickel-Rich Cathodes: Understanding the Effective Thiophene-Boronic Acid-Based CEI via Operando SHINERS

Abstract

Increasing the cell voltage of lithium-ion batteries (LIBs) is a straightforward approach to increasing their capacity and energy density. However, state-of-the-art cathode materials like LiNixMnyCo1-x-yO2 (NMC) suffer from severe failure mechanisms at high operating voltages, significantly degrading the performance and cycle life of the cells. Notably, an effective cathode electrolyte interphase (CEI) mitigates these failure mechanisms. Nevertheless, a deep understanding of the formation mechanisms and properties of the CEI is necessary to tailor effective interphases. This study introduces a promising electrolyte additive for high operating voltage NMC811||graphite cells. Implementing an optimized concentration of 3-thiophene boronic acid (3-Thp-BOH) significantly enhances the cells' performance and reduces capacity fading, resulting in a quadrupled cycle life and a six-times higher accumulated specific energy. Operando shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to shed light on the formation mechanism and molecular composition of CEI during cell operation, proving that the presence of the additive results in the formation of a complex 3-Thp-BOH-based polymeric CEI on the NMC811 surface. The CEI investigation is additionally supported by scanning electron microscopy and energy dispersive X-ray analysis and highly accurate quantum chemistry modeling of the suggested polymerization mechanisms.