Tetraethylammonium tetrafluoroborate additives for suppressed gas formation and increased cycle stability of dual-ion battery

Effect of tetraethylammonium tetrafluoroborate (TEABF4) additives on the charge and discharge properties and gas formation in dual ion battery using graphitic carbon and Li4Ti5O12 for positive and negative electrode, respectively was investigated. Although cycle stability was poor and large amount of gas was formed in dual ion battery using LiPF6 for a support salt, it was found that the reversibility of charge and discharge and cycle stability was much increased by addition of TEABF4. By using LiPF6 + TEABF4 in dimethyl carbonate (DMC)-methyl ethyl carbonate (MEC)-propylene carbonate (PC) (1:1:1), discharge capacity of 60% of initial capacity was sustained after 1017 cycles with 99% coulomb efficiency and negligible amount of gas was formed. These positive effects of TEABF4 addition were assigned to the suppression of side reaction on electrode, in particular, at Li4Ti5O12 negative electrode. Lewis acidity in electrolyte seems to be related with electrolyte decomposition and decreased cycle stability was caused by the unbalanced capacity of interaction between positive and negative electrode.