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

Abstract

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.

Li0.5La0.5TiO3 as an Ionic Conducting Additive Enhancing the High-Voltage Performance of LiNi0.8Mn0.1Co0.1O2 Cathodes in Lithium-Ion Batteries

“…The graphite paired with the bare NMC811 cathode shows a thick SEI layer covering most of the surface of the graphite particles. Even the morphology of the graphite underneath the SEI layer is not observable due to the thick SEI associated with severe parasitic reactions, which is a typical phenomenon observed in high-voltage LIBs . In contrast, the anodes paired with the 1 and 5 wt % LLTO blended cathodes revealed cleaner graphite surfaces, indicating less electrolyte decomposition and thinner SEI.…”

“…31−33 First two rows in Figure 5 compare the C 1s, O 1s, F 1s, and Mn 2p spectra of bare NMC811 and NMC811 + 5 wt % LLTO cathodes, which were recovered from SLPCs after 100 cycles with 4.4 V cutoff at 25 °C. As reported earlier, 21,29,34 the CEIs on cycle-aged cathodes at high voltages contain several species such as lithium alkoxides (ROLi), lithium carbonates, alkyl carbonate (ROCOOLi), certain lithium fluorophosphate (Li x PO y F z ), and LiF, which are responsible for parasitic reactions and capacity fading in full-cells. The C 1s spectra show two peaks located at ∼284.7 and ∼290.6 eV, respectively, corresponding to C−C and C−F from conductive carbon black and PVdF binder.…”

“…The Nyquist plots were fitted using an electrical circuit model, which comprises two parallel resistance ( R ) – constant phase element (CPE) components connected in series, followed by a Warburg diffusion segment: R Ohmic – [ R Int /CPE Int ] – [ R CT /CPE CT ] – W Diff . The high-frequency [ R Int /CPE Int ] component originates from the interfacial impedance of the electrodes/electrolyte interfaces, and the mid-to-low frequency [ R CT /CPE CT ] component originates from the charge transfer (CT) process Table S3 lists the fitted values of the electrolyte ohmic resistance ( R Ohmic ), interfacial resistance ( R Int ), and CT resistance ( R CT ) of the full-cells.…”

“…Even the morphology of the graphite underneath the SEI layer is not observable due to the thick SEI associated with severe parasitic reactions, which is a typical phenomenon observed in high-voltage LIBs. 29 In contrast, the anodes paired with the 1 and 5 wt % LLTO blended cathodes revealed cleaner graphite surfaces, indicating less electrolyte decomposition and thinner SEI. In conjunction with XPS and EIS data, these SEM results provide conclusive evidence that LLTO-blended NMC811 cathodes can effectively mitigate oxidative decomposition at CEI, thereby reducing parasitic reactions at the graphite SEI.…”

“…The high-frequency [R Int /CPE Int ] component originates from the interfacial impedance of the electrodes/electrolyte interfaces, and the mid-to-low frequency [R CT /CPE CT ] component originates from the charge transfer (CT) process. 29 Table S3 lists the fitted values of the electrolyte ohmic resistance (R Ohmic ), interfacial resistance (R Int ), and CT resistance (R CT ) of the full-cells.…”