Simple, robust metal fluoride coating on layered Li1.23Ni0.13Co0.14Mn0.56O2 and its effects on enhanced electrochemical properties

Highlights: • Loosely arranged decahedral particles formed larger bulk particles on fluorine substitution. • At high potentials, fluorine coating reduces surface damage and improves lithium diffusion and thereby capacity retention. • Fluorine substitution triggers the formation of layered–layered–spinel, which stabilized the electrode structures. • Formation of layered-layered-spinel counters voltage decay upon subsequent cycling. -- Abstract: In present study, fluorine substituted Li1.23Ni0.13Co0.14Mn0.56O2−zFz (z = 0–0.20) are synthesized by simple and low-temperature co-precipitation process and observed enhancement in their electrochemical properties are investigated as function of fluorine substitutions. 19F MAS NMR analyses revealed the presence of fluorine as metal fluoride on the surface, and as oxy-fluoride in bulk Li1.23Ni0.13Co0.14Mn0.56O2−zFz. Li1.23Ni0.13Co0.14Mn0.56O2−zFz (z = 0.15) showed improved cycling performance and reduced cell impedance as a result of the fluorine doping. In addition, fluorine substitution controlled the amount of stabilizing transition metals in the lithium layers of spinel-like regions, which in turn resulted in countering the capacity loss and voltage decay compared to Li1.23Ni0.13Co0.14Mn0.56O2