Discovery Sagaサイレントキーワード俯瞰

Lithium-ion battery / nonflammable electrolyte / high-voltage / SEI formation / cyclic phosphate / electrolyte / non-flammable

The lack of a suitable alternative solvent has hindered further exploration of new functional electrolytes. Herein we design and synthesize a fluorinated cyclic phosphate solvent, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphospholane 2-oxide (TFEP), for use in LIBs. An electrolyte formula composed of 0.95 M LiN(SO2F)2 in TFEP/2,2,2-trifluoroethyl methyl carbonate shows excellent non-flammability with zero self-extinguishing time and enables the highly stable operation of graphite anodes (ca. 0.1 V vs lithium) and high-voltage LiNi0.5Mn1.5O4 cathodes (ca. 4.7 V vs lithium), thereby outperforming the traditional electrolytes. This work opens new frontiers in electrolyte developments toward safe LIBs with higher energy densities, which was recently accepted for publication on Nature Energy.

sodium-ion battery / lithium-ion battery / electrolyte / safety / high voltage

Severe safety concerns are currently impeding the large-scale employment of lithium/sodium batteries. Conventional electrolytes are highly flammable and volatile, which may cause catastrophic fires or explosions. Efforts to introduce flame-retardant solvents into the electrolytes have generally resulted in compromised battery performance because those solvents do not suitably passivate carbonaceous anodes. We propose a salt-concentrated electrolyte design to resolve this dilemma via the formation of a robust inorganic passivation film on the anode. We demonstrated that a concentrated electrolyte using a salt and a popular flame-retardant solvent (trimethyl phosphate), without any additives or soft binders, realized stable charge-discharge cycling of both hard carbon and graphite anodes for more than 1000 cycles (over one year) with negligible degradation; this performance is comparable or superior to that of conventional flammable carbonate electrolytes. The unusual passivation character of the concentrated electrolyte coupled with its fire-extinguishing property contributes to developing safe and long-lasting batteries, and unlocking the limit toward development of much higher energy-density batteries. Moreover, we found that this concentrated electrolyte potentially enables the battery operation from -20 to 100 °C.