Weakly Solvating Co-Solvent Strategy for Propylene Carbonate-Based Electrolytes Enabling Low-Temperature and High-Voltage Operation of Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have garnered significant attention due to their high energy density and excellent cycling stability, making them indispensable for applications such as energy storage systems and electric vehicles. However, conventional ethylene carbonate (EC)-based electrolytes suffer from performance degradation under extreme conditions, including low temperatures, high voltages, and high charge/discharge rates. In particular, the high melting point of EC (~35 o C) restricts Li⁺ transport and hinders efficient desolvation at low temperatures. To overcome these limitations, propylene carbonate (PC) has been explored as a promising alternative due to its wide liquid temperature range (−49 to 240 °C) and superior anodic stability. Nonetheless, the strong coordination between PC and Li⁺ results in persistent solvent co-intercalation into graphite anodes, causing exfoliation and ultimately battery failure. To address this issue, various weakly solvating co-solvents (WSSs) have been introduced to tailor the Li⁺ solvation sheath, effectively weakening the PC–Li⁺ interaction. This WSS-modified solvation structure prevents PC co-intercalation and facilitates rapid Li⁺ desolvation, thereby improving the reversibility of Li⁺ intercalation/deintercalation. Additionally, the inclusion of WSSs promotes anion involvement in the solvation sheath, enabling the formation of a highly ion-conductive, anion-derived solid electrolyte interphase (SEI) on the graphite surface. In this work, we designed a PC-based electrolyte incorporating WSSs to fine-tune solvent–Li⁺ interactions. Raman and nuclear magnetic resonance (NMR) spectroscopy were employed to investigate the distinctive solvation structures. The electrochemical performance of graphite/LiNi₀.₈Co₀.₁Mn₀.₁O₂ full cells using the PC-based electrolyte was evaluated under high-voltage conditions (~4.4 V). The cells demonstrated enhanced cycling stability at both 25 °C and 45 °C compared to EC-based electrolytes, and exhibited exceptional performance even at −20 °C.