Further development of high-voltage lithium-ion batteries (LIBs) depend on electrolytes stable against oxidation or modifications of the unstable cathode-electrolyte interface. In this work different metal salts of the bis(trifluoromethanesulfonyl)imide (TFSI) or the trifluoromethanesulfonate (OTf) anions, including the metal cations Li~+, Na~+, Mg~(2+), Al~(3+), Ca~(2+), Sc~(3+), Cr~(3+), Ni~(2+), Cu~(2+) and Zn~(2+), were investigated as electrolyte additives with regard to their effect on the cycling performance of LiNi_(1/3)Mn_(1/3)Co_(1/3)O_2 (NMC) based cathodes at the elevated upper cut-off potential of 4.6 V vs. Li/Li~+. Obtained results point out that several additives, but Mg(TFSI)2 in particular, can suppress electrolyte decomposition, stabilize the cathode/electrolyte interface, reduce the overall internal battery impedance and prevent the degradation of the active material. Ex-situ analysis of the harvested NMC electrodes after cycling indicates that the addition of Mg(TFSI)2 leads to the formation of an artificial cathode passivation layer, probably containing MgF2.
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