Morphological Evolution and Solid–Electrolyte Interphase Formation on LiNi_0.6Mn_0.2Co_0.2O₂ Cathodes Using Highly Concentrated Ionic Liquid Electrolytes

Abstract

Employing high-voltage Ni-rich cathodes in Li metal batteries (LMBs) requires stabilization of the electrode/electrolyte interfaces at both electrodes. A stable solid–electrolyte interphase (SEI) and suppression of active material pulverization remain the greatest challenges to achieving efficient long-term cycling. Herein, studies of NMC622 (1 mAh cm–2) cathodes were performed using highly concentrated N-methyl-N-propylpyrrolidinium bis­(fluorosulfonyl)­imide (C3mpyrFSI) 50 mol % lithium bis­(fluorosulfonyl)­imide (LiFSI) ionic liquid electrolyte (ILE). The resulting SEI formed at the cathode enabled promising cycling performance (98.13% capacity retention after 100 cycles), and a low degree of ion mixing and lattice expansion was observed, even at an elevated temperature of 50 °C. Fitting of acquired impedance spectra indicated that the SEI resistivity (R SEI) had a low and stable contribution to the internal resistivity of the system, whereas active material pulverization and secondary grain isolation significantly increased the charge transfer resistance (R CT) throughout cycling.

Enhancing the Electrochemical Properties of Nickel-Rich Cathode by Surface Coating with Defect-Rich Strontium Titanate

“…The lower R s of NCA-STOx could be ascribed to the uniform STOx coating layer that influences the CEI deposition on the NCA cathode surface. Furthermore, STOx possesses lower electrical resistance than the bare NCA cathode surface and the CEI on NCA when in contact with the electrolyte . The OV defects in the STOx layer not only provide higher conductivity for electrons but may also offer migration paths for Li + , triggering relatively faster charge carrier transfer kinetics and lower R ct in NCA-STOx than in NCA at the initial cycling stage .…”

Locally Concentrated Ionic Liquid Electrolyte with Partially Solvating Diluent for Lithium/Sulfurized Polyacrylonitrile Batteries

“…[14,15] Therefore, the development of more practical Li/SPAN cells requires electrolytes that can form stable electrolyte/electrode interphases (EEIs) simultaneously on LMAs and SPAN cathodes. [16][17][18][19] Ionic liquid electrolytes (ILEs) with low flammability and high compatibility toward LMAs are promising candidates for safe and long-lifespan LMBs, [20,21] but their high viscosity and sluggish Li + transport at room temperature limit their further application. [22] Recently, diluting ILEs with non-solvating co-solvents, e.g., hydrofluoroethers or fluorinated aromatic compounds, has been proven to be an effective approach in mitigating the aforementioned deficiencies without compromising the high compatibility toward LMAs, [12,[23][24][25] inspired by organic-solvent-based concentrated electrolytes.…”

Understanding the Capacity Decay of Si/NMC622 Li-Ion Batteries Cycled in Superconcentrated Ionic Liquid Electrolytes: A New Perspective

“…However, their intensity is noticeably less than those in the negative electrode, for example, ∼3× less based on integrated intensity for the P 111i4 FSI–LiFSI system. This suggests a possible preferential involvement of IL components in the SEI formation on the negative electrode or a sign of a thinner CEI on the positive electrode side …”

“…This suggests a possible preferential involvement of IL components in the SEI formation on the negative electrode or a sign of a thinner CEI on the positive electrode side. 62 Figure 6a,b presents the 7 Li NMR spectra of the Si electrodes cycled in the phosphonium-based electrolytes and stopped at the end of the 5th and 100th delithiation. The normalized integrated intensities show one major resonance at about 0 ppm, which is typically associated with diamagnetic Li species.…”