Unraveling the Dynamic Interfacial Behavior of LiCoO₂ at Various Voltages with Lithium Bis(oxalato)borate for Lithium-Ion Batteries

Abstract

The electrochemical dynamic behavior of the solid electrolyte interface (SEI) formed on LiCoO 2 (LCO) by lithium bis(oxalato)borate (LiBOB) is investigated at various cutoff voltages. Particularly, for layered cathode active materials, various cutoff voltages are used to control the delithiation states; however, systematic investigations of the voltage and SEI are lacking. To increase the practical energy density of the LCO, a high cutoff voltage is pursued to utilize a state of high delithiation. However, this high cutoff voltage causes the electrolyte to undergo side reactions and the crystalline structure changes irreversibly, limiting the cycle life. In a lowvoltage environment (<4.7 V), LiBOB improves the initial Coulombic efficiency and cycling performance by forming an effective SEI, which suppresses side reactions. At higher voltage levels (4.7−4.9 V), LiBOB no longer effectively protects the surface, causing the electrochemical performance to decrease rapidly. The main cause of this phenomenon is the decomposition of LiBOB-SEI at a high voltage, as shown by systematic surface and electrochemical analyses comprising linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. In conclusion, LiBOB can suppress side reactions of the electrolyte by SEI formation, but the SEI decomposes at voltage levels higher than 4.7 V.

Beneficial impact of lithium bis(oxalato)borate as electrolyte additive for high‐voltage nickel‐rich lithium‐battery cathodes

“…To verify this, the electrochemical stability of the commercial organic electrolyte (LP30, 1 M LiPF 6 in EC/DMC) with/without LiBOB as additive was investigated by linear sweep voltammetry (LSV), as shown in Figure 3A. The profiles demonstrate that the oxidation peak occurs slightly earlier for the electrolyte with LiBOB than the neat LP30, in agreement with the highest occupied molecular orbital (HOMO) energy level of LiBOB with respect to the other electrolyte components 45 . The decomposition of LiBOB generates a borate‐containing layer on the surface of the cathode particles, which helps to suppress side reactions between the electrolyte and the cathode 1,32 .…”

“…The profiles demonstrate that the oxidation peak occurs slightly earlier for the electrolyte with LiBOB than the neat LP30, in agreement with the highest occupied molecular orbital (HOMO) energy level of LiBOB with respect to the other electrolyte components. 45 The decomposition of LiBOB generates a borate-containing layer on the surface of the cathode particles, which helps to suppress side reactions between the electrolyte and the cathode. 1,32 Two-electrode Li/NCM83 cells were assembled to evaluate the electrochemical performance of the positive electrode without and with LiBOB as additive.…”

Prospective Application, Mechanism, and Deficiency of Lithium Bis(oxalate)Borate as the Electrolyte Additive for Lithium‐Batteries

“…− is a strong oxidative agent at high temperatures, The performance of lithium bis(oxalate)borate (LiBOB) in different cathodes and electrolytes. [13,18,21,40,48,65] LiPF 6 alkyl carbonate solutions undergo thermal runaway when heated, even when not in contact with the electrodes. Moreover, the decomposition of LiPF 6 generates HF, the presence of which has an effect on both the cathode and the anode.…”

A review – exploring the performance degradation mechanisms of LiCoO2 cathodes at high voltage conditions and some optimizing strategies

“…51 During the charging and discharging process at high voltage, the impedance on the LiCoO 2 would show a significant increasing trend. 52 This was because the overly high voltage increases the tendency of the electrolyte to oxidize and form an SEI film, 53 whose generation would alter the double-layer structure on the electrophoretic interface, while the change in the double-layer structure on the electrophoretic surface would lead to an increase in the voltage on the SEI film. The thickness of the SEI film increased as the charging and discharging voltage increased and finally increased the charge transfer resistance on the interface (Fig.…”

“…Fig.3HR-TEM images of LiCoO 2 particles obtained under different conditions: (a) pristine LiCoO 2 powder, cycled electrode particles with 0 wt% LiBOB at (b) 4.5 V and (c) 4.9 V cut-off voltages, and cycled electrode particles with 5 wt% LiBOB at (d) 4.5 V and (e) 4.9 V. Adapted with permission 53. Copyright 2022, Applied Materials.…”