Lithium bisoxalatodifluorophosphate (LiBODFP) is a promising multifunctional lithium salt-type electrolyte additive used to enhance the performance of 5 V LiNi0.5Mn1.5O4 (LNMO)-based lithium-ion batteries (LIBs).
Enhancing
the flame retardancy of electrolytes and the quality
of interface films is of great significance to improve the safety
performance of lithium-ion batteries (LIBs). In this work, the effects
of (ethoxy)pentafluorocyclotriphosphazene (PFPN), hexafluorocyclotriphosphazene
(FPPN), and pentafluoro(phenoxy)cyclotriphosphazene (HFPN) as flame-retardant
additives in the functional electrolyte on the performances of LiNi0.6Mn0.2Co0.2O2 (NCM622)/graphite
pouch cells are comprehensively investigated. It is indicated that
the contents of PFPN, FPPN, and HFPN, respectively, reach 5, 8, and
8% to achieve the purpose of flame retardancy in the 1 M LiPF6/EC + EMC (EC/EMC = 1:2 in weight) system. When the cells
without and with PFPN, FPPN, and HFPN additives are, respectively,
charge–discharged in the voltage range of 3.0–4.4 V
at 1C, their capacity retentions are 36.1, 60.7, 74.7, and 73.8% after
150 cycles. The interface analysis and theoretical calculation show
that PFPN, FPPN, and HFPN can facilitate the formation of stable interface
films on two electrodes and subsequently improve the battery performance.
The addition of cyclotriphosphazene flame retardant in the electrolyte
ultimately improves the safety of NCM622/graphite pouch cells without
sacrificing electrochemical performance. The as-prepared additive-containing
electrolyte exhibits promising prospects in the application, and the
evaluation method is also useful to develop the functional electrolyte
with flame retardant and film-forming properties.
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