Phosphorus-Doped Silicon for Li-ion Battery Applications: Studied with Electrochemical Isothermal Microcalorimetry, ATR-FTIR and XPS

Silicon (Si) has garnered significant attention as a potential anode material for lithium-ion batteries due to its high theoretical specific capacity. However, there are considerable challenges to address before practical implementation, primarily stemming from issues such as very large volume changes upon Li insertion/extraction, poor electrical conductivity, and an unstable solid-electrolyte interphase (SEI). We report here investigations on P-doped Si (SiPx) using electrochemical isothermal micro-calorimetry (EIMC), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) techniques. The EIMC measurements on SiPxrevealed decreased parasitic reaction heat flows during the lithiation/de-lithiation cycles. The first cycle cell voltage profiles show decreased electrochemical reactivity for the SiPx. Analyses using ATR-FTIR and XPS on cycled electrodes suggest that the parasitic reaction products originate from solvent and electrolyte salt decomposition, with significantly lower amounts observed on the SiPx. Collectively, these findings endorse P-doping of Si as a promising strategy for Li-ion battery applications and demonstrate the unique advantages of performing EIMC measurements by focusing on the intrinsic losses from parasitic reactions, regardless of the electrode and cell configurations being optimized. In contrast, fully optimized configurations are necessary when using coulombic efficiency as the metric for cycle stability of the battery chemistry.