Morphological Evolution and Solid-Electrolyte Interphase Formation on LiNi_0.6Mn_0.2Co_0.2O₂ Cathodes Using Highly...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• High-voltage nickel-rich cathodes in lithium metal batteries (LMBs) face challenges with electrode/electrolyte interface stability.
• Key issues include the formation of a stable solid-electrolyte interphase (SEI) and preventing active material pulverization for efficient long-term cycling.

Purpose of the Study:

• To investigate the performance of NMC622 cathodes using a highly concentrated ionic liquid electrolyte (ILE).
• To evaluate the stability and protective capabilities of the SEI formed by the ILE at the cathode interface.

Main Methods:

• Utilized NMC622 cathodes (1 mAh cm^-2) with a highly concentrated ionic liquid electrolyte: N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (C₃mpyrFSI) and 50 mol % lithium bis(fluorosulfonyl)imide (LiFSI).
• Conducted cycling performance tests and impedance spectroscopy at 50 °C.
• Analyzed ion mixing and lattice expansion.

Main Results:

• The ILE facilitated the formation of a stable SEI on the NMC622 cathode, leading to excellent cycling performance with 98.13% capacity retention after 100 cycles.
• Observed minimal ion mixing and lattice expansion even at elevated temperatures (50 °C).
• Impedance analysis showed low and stable SEI resistivity (R_SEI), while active material pulverization increased charge transfer resistance (R_CT).

Conclusions:

• The developed ionic liquid electrolyte effectively stabilizes the electrode/electrolyte interface in high-voltage LMBs.
• The stable SEI layer is crucial for suppressing active material degradation and achieving long-term cycling stability.
• This approach offers a promising strategy for enhancing the performance of next-generation lithium metal batteries.