Tuning Reaction Pathways via Symmetric Fluorination Enables High-Temperature and High-Voltage Electrolytes

Ni-rich layered oxide cathodes deliver high capacity, but they suffer from severe interfacial instability and thermal safety risks when operated at high voltages and elevated temperatures. Here we propose an electrolyte design strategy based on molecular fluorination symmetry. This approach employs difluoro-symmetric substitution to precisely steer decomposition pathways towards preferential ring-opening reactions, thereby effectively suppressing defluorination decomposition and the concomitant formation of acidic byproducts at elevated temperatures. Through rational molecular engineering of synergistic fluorination, we achieve directed interfacial chemistry control. Under harsh operational conditions (4.5 V, 45°C), the modified cells retain 83% of their capacity after 300 cycles, along with significantly reduced gas generation and an elevated thermal runaway onset temperature. Furthermore, 2 Ah graphite||LiNi_0.8Co_0.1Mn_0.1O₂ pouch cells exhibit a capacity retention of 90% after 480 cycles at 45°C and 91% after 200 cycles at 60°C. These results establish molecular fluorination symmetry as a practical design principle for electrolytes that enhance high-temperature performance and intrinsic safety in Ni-rich cathodes under demanding operational conditions.