Impact of Triethyl Borate on the Performance of 5 V Spinel/Graphite Lithium-Ion Batteries

Positive roles of triethyl borate (TEB) electrolyte additive on high-voltage lithium-ion batteries were investigated in LiNi0.5Mn1.5O4(LNMO)/graphite full-cells. A capacity fading of the LNMO/graphite full-cells originates from the Mn dissolution of LNMO cathodes and a degradation of graphite SEI, which unwantedly consumes active Li+. Because the Li+ loss cannot be measured in a half-cell configuration (i.e., LNMO/Li), we designed a systematic experiment to understand the effect of TEB on the electrode–electrolyte interphases in the full-cells: cathode–electrolyte interphase (CEI) of LiNi0.5Mn1.5O4 (LNMO) and solid–electrolyte interphase (SEI) of graphite, respectively. Among various TEB contents (0–4 wt %) investigated, 1 wt % TEB offered combined advantages of high specific capacity and low full-cell impedance during extended cycling. The TEB contributed to the production of a CEI layer and suppressed Mn dissolution on LNMO cathode during long-term cycling. A combinatorial study of TEB-treated graphite and TEB-treated LNMO electrodes, however, suggested that an early-stage performance improvement shown by the full-cells was mostly contributed by an improved SEI stability on graphite anodes and a reduced Li+ loss, as evidenced by X-ray photoelectron spectroscopy data. Although literature data mostly focused on the impacts of TEB on CEI in half-cell configurations, our full-cell analyses revealed an additional benefit of TEB in significant improving stability of graphite SEI. Our results suggest that TEB can contribute to CEI and SEI simultaneously, which can offer promising performance improvements in various types of high-voltage LIBs.