Synergistic effects of film-forming and film-modifying additives for enhanced all-climate performance of graphite/NMC622 pouch cells

Abstract

The increasing demand for lithium-ion batteries (LIBs) with wide temperature adaptability arises from their growing utilization in extreme environments. However, LIB performance significantly deteriorates under such conditions. Electrolyte additives have demonstrated promise in addressing this issue; however, most fail to achieve a balance in performance across all temperature ranges due to the typical offering of either high stability or low impedance by additive-derived electrode/electrolyte interphases. In this study, we propose a dual-additive strategy to overcome this trade-off by employing a Film-Forming Additive (FFA), specifically an anhydride compound, and a Film-Modifying Additive (FMA), specifically a boron-containing compound. The FFA forms a robust interphase that enhances stability against interfacial side reactions, while the FMA, possessing high electrochemical activity, modifies the FFA-derived interphase by reducing impedance and facilitating rapid Li⁺ de-solvation through the formation of conductive B-O bonds. This synergistic interphase combines both high stability and low impedance, enabling graphite/NMC622 pouch cells to retain 76 % capacity after 500 cycles at 25 °C and 77 % after 700 cycles at 55 °C compared to respective values of 28 % and 66 % for cells without additives. Additionally, cells with the dual additives exhibit over a 20 % improvement in discharge capacity at subzero temperatures. This dual-additive design provides a valuable framework for developing electrolytes tailored for all-climate batteries.