To enhance the overall safety of electronic devices and energy storage systems, the development of functional electrolytes that improve the thermal stability of rechargeable batteries is of utmost importance. Here, we report a novel cyclic phosphoramidate, 2-(N,N-dimethylamino)-1,3,2-dioxaphospholane-2-oxide (DMAP), which has been newly designed and synthesized as a multifunctional solvent for safe Li-ion batteries.1 Its unique molecular structure, incorporating an amine moiety into a five-membered cyclic phosphate, provides both high electrochemical and thermal benefits: (i) a stable DMAP-derived passivation film (solid electrolyte interphase, SEI) is formed on the graphite surface, thereby suppressing electrolyte reduction, (ii) exothermic reactions induced by the thermal decomposition of the SEI and direct reactions between a lithiated graphite anode and electrolyte salt, which are known to trigger and accelerate battery temperature rise, are largely mitigated thanks to DMAP's inherently high radicals-/Lewis acids-/HF-scavenging abilities, (iii) the moisture sensitivity is improved with reduced nucleophilic attack at the P atom caused by water contamination in the electrolyte due to the presence of a substituted N atom in the DMAP, thus enhancing storage stability, and (iv) the stable cycling of LiFePO4 cathodes is achieved based on moderate oxidation stabilities and suppressed aluminum current collector dissolution in the DMAP-based electrolytes. Importantly, all these advantages can be obtained with DMAP used as both an electrolyte solvent and additive, regardless of the types of salts (LiFSI or LiPF6) and co-solvents (fluorinated ethyl methyl carbonate or dimethyl carbonate) employed.We believe that our solvent-design strategies, based on molecular modification and optimization, combined with fine-tuning the elements in the molecular structure, can endow the electrolyte with highly functional physicochemical and electrochemical properties, thus opening new possibilities for developing safe batteries with high energy densities.1,2 S.Ko, A.Matsuoka et al., R.Shang and A.Yamada, ACS Energy Lett., 9, 7, 3628–3635 (2024)Q.Zheng et al., E.Nakamura and A.Yamada, Nat. Energy, 5, 291-298 (2020) Figure 1
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