Enhancing the intrinsic safety of nickel-rich lithium-ion batteries by an ethylene carbonate-free electrolyte with ethoxy(pentafluoro) cyclotriphosphazene additive

Abstract

The increasing energy density of lithium-ion batteries is leading to frequent accidents represented by thermal runaway (TR), greatly limiting the large-scale application of power batteries. The fundamental problem to be solved is the intense exothermic reaction between the Nickel-rich cathode and ethylene carbonate (EC), as well as the catastrophic flame during thermal runaway. Herein, we design an EC-free electrolyte for single crystal LiNi0.8Co0.1Mn0.1O2/Graphite cells and introduce Ethoxy(pentafluoro) cyclotriphosphazene (PFPN) flame-retardant as additive. Eliminating EC helps to mitigate the thermal runaway triggering reaction, and the PFPN additive rich in elements such as P and F can capture the highly reactive free radicals. Thermal abuse tests of the NCM811/Gr cell show that the TR triggering temperature is increased by 69 °C. Furthermore, the cell with FPN electrolyte doesn't trigger thermal runaway during the nail penetration test. The cell with FPN electrolyte enhances electrical performance, retaining 94.43 % of its capacity after 600 cycles at 4.3 V. Post-mortem characterization reveals that an inorganic-rich interface has been built to maintain the cyclic and thermal stability of the electrodes. This study presents a new approach in electrolyte design for the development of high safety and long-life cells.