Efficiently Suppressing Oxygen Evolution in High Voltage Graphite/NCM Pouch Cell with Tributyl Borate as Electrolyte Additive

Abstract Energy density of lithium ion batteries based on transition metal oxide cathodes can be enhanced by increasing the end-off charge voltage to a great extent, because the cathodes can deliver a larger specific discharge capacity under an elevated charge voltage. However, this operation is always accompanied by the oxygen evolution from the cathode oxides, which might cause the crystal destruction of the cathode oxides and the severe electrolyte decomposition on the cathodes, leading to the fast failure of the batteries. In this work, we report a new finding that the oxygen evolution in graphite/LiNi0.6Mn0.2Co0.2O2 pouch cell can be efficiently suppressed and thus the cyclic stability of the cell is significantly improved by using tributyl borate (TBB) as electrolyte additive, even under 4.5 V. Electrochemical tests indicate that, with adding 1 wt% TBB to the electrolyte, the capacity retention of the cell is enhanced from in 35.1% to 94.9% after 120 cycles. The physical characterizations combining theoretical calculations demonstrate that the B-containing species in the cathode electrolyte interphase, originated from the oxidation of TBB, present a strong combination with oxygen and suppress efficiently the oxygen evolution.