Nonflammable electrolyte with low exothermic design for safer lithium-based batteries

Battery safety has always been a concern for high-energy-density configurations with nickel-rich cathode (Ni>0.6). Tremendous heat released from the reaction between highly flammable electrolyte and cathode under mechanical, thermal or electrical abuse may cause thermal runaway. Herein, we explore the heat release of various solvents with fully charged cathodes and summarized the solvent/heat release phase diagram. On this basis, we select fluorinated bis(2,2,2-trifluoroethyl) carbonate to prepare a nonflammable, low exothermic electrolyte. This electrolyte significantly reduces the maximum temperature by one-third and decreases the maximum heating rate from 206.0 °C s−1 to 82.6 °C s−1 during the thermal runaway process of commercial lithium-ion pouch cell. Moreover, it demonstrates remarkable compatibility with lithium metal anode. Benefited from the uniform solid-electrolyte interphase (SEI) rich in -CF3 organic layer, the Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) full cell exhibits a capacity retention rate of 80% after 240 cycles. Notably, a 1.5 Ah Li metal pouch cell with a high energy density of 365 Wh kg−1 displays an excellent capacity retention of 90.02% after 98 cycles under realistic conditions. This work provides a novel approach to construct safer and longer-lasting lithium-based batteries by designing nonflammable and low exothermic electrolyte.