Enhancing cycle life of nickel-rich LiNi0.9Co0.05Mn0.05O2 via a highly fluorinated electrolyte additive - pentafluoropyridine

Abstract

A highly fluorinated additive, pentafluoropyridine (PFP), is used here to enhance the interfacial stability of the Ni-rich LiNi0.9Co0.05Mn0.05O2 (NCM90) cathode at a cut-off voltage of 4.3 V vs. Li/Li+ at 30 °C. The capacity retention of the NCM90||Li cell is obviously improved from 72.3% to 80.3% after 200 cycles at 1C (1C = 180 mA g-1) when 0.2% PFP is introduced into the baseline electrolyte (1 mol L-1 LiPF6 in ethylene carbonate/diethyl carbonate). The improvement in electrochemical performance could be attributed to the formation of a compact and uniform cathode electrolyte interphase (CEI) layer enriched with F-containing polypyridine moieties and LiF species on the NCM90 particles. This CEI prevents side reactions between the electrode and electrolyte and hinders the corrosion of the cathode caused by HF attack. In addition, the formation of internal particle cracks is somewhat suppressed by the robust CEI, thus prohibiting the irreversible phase transformation and better maintaining the superior lithium-ion diffusion kinetics.