Robust Benzimidazole-Based Electrolyte Overcomes High-Voltage and High-Temperature Applications in 5 V Class Lithium Ion Batteries

Abstract

Electric vehicles (EVs) are poised to dominate the next generation of transportation, but meeting the power requirements of EVs with lithium ion batteries is challenging because electrolytes containing LiPF6 and carbonates do not perform well at high temperatures and voltages. However, lithium benzimidazole salt is a promising electrolyte additive that can stabilize LiPF6 through a Lewis acid–base reaction. The imidazole ring is not eligible for high-voltage applications owing to its resonance structure, but in this research, electron-withdrawing (−CF3) and electron-donating (−CH3) substitutions on imidazole rings were investigated. According to the calculation results, the CF3 substitution facilitates a high electron cloud density on imidazole ring structures to resist the electron releases from bezimidazole in oxidation reactions. In addition, through CF3 substitution, electrons are accepted from the lattice oxygen (O2–) in lithium-rich layer material and O– is converted by an electron released. The O– is then adsorbed with the ethylene carbonate and catalyzed to alkyl carbonate by Ni2+. The −CF3 substituted benzimidazole triggers a further reaction with alkyl carbonate and forms a new polyionic liquid solid electrolyte interphase on the cathode’s surface. Furthermore, the cycle performance tested at 60 °C and 4.8 V showed that the CF3 substitution maintains the battery retention effectively and exhibits almost no fading compared with both the blank electrolyte and the CH3 substitution.

Fluorine and Lithium: Ideal Partners for High‐Performance Rechargeable Battery Electrolytes

“…The influence of fluorine on the single electron transfer decomposition mechanism of ethyl methyl carbonate (EMC) and (2,2,2‐trifluoroethyl)methyl carbonate (FEMC), as examples, is shown in Scheme , supported by DFT calculations performed by Xing et al . The improved cycling performance is related to the composition of the CEI layer as well as the decreased overall impedance …”

“…In the case of imidazole‐based additives, the substitution of hydrogen by fluorine atoms inhibits the Lewis acid/base neutralization reaction (decomposition reaction of LiPF 6 ) through the formation of a pentafluorophosphate imidazole anion …”

Improving Stability of LiCoO2 Cathode by Using Lithium Bis(Trifluoroborane)‐5‐Cyano‐2‐(Trifluoromethyl) Benzimidazolide as Additive

“…The formation of SEI species using reference electrolyte 1 M LiPF 6 /EC+DEC can be attributed to the acid‐base interaction of EC and PF 6 anion with oxygen intermediates extracted from oxide surface . The SEI species like acyl fluoride, lithium alkyl carbonates, and Li 2 CO 3 are similarly formed with/without the additive, attributable to the Lewis acid/base sites on LiCoO 2 .…”

“…Additives that can simultaneously resolve these two challenges are reported only recently. Using Li salts as additives can be expected leading to SEI with good Li ion conductivity, of which many examples are recently reported to improve the efficiencies and cycling stability of LIBs and a low impedance and thin SEI (CEI) is frequently attributed for the improved performance . However, none of these salt additive reports used LiCoO 2 as the cathode.…”

High‐Voltage Li‐Ion Full‐Cells with Ultralong Term Cycle Life at Elevated Temperature

“…Thus, any electrolyte optimization strategy should not neglect the compatibility with cathode and reversibility toward commercial anode (graphite and Si), which substantially raise the difficulty of modification. Additionally, elevated temperature derived from practical cell operation environment would exacerbate the cell deterioration due to the poor thermal stability of typical LiPF 6 carbonate‐based electrolyte . In a word, improving the energy density of cell can be likened as extend the capacity of wood bucket.…”