Constructing Unique Cathode Interface by Manipulating Functional Groups of Electrolyte Additive for...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• High-voltage lithium-ion batteries (LIBs) require stable electrolytes to prevent performance degradation.
• Graphite/LiNi_0.6Co_0.2Mn_0.2O₂ cells face challenges cycling above 4.0 V due to electrolyte decomposition.
• Developing effective electrolyte additives is crucial for enhancing LIB stability and lifespan.

Purpose of the Study:

• To investigate the efficacy of 1-(2-cyanoethyl) pyrrole (CEP) as an electrolyte additive for high-voltage LIBs.
• To elucidate the mechanism by which CEP improves the electrochemical performance of graphite/LiNi_0.6Co_0.2Mn_0.2O₂ cells.
• To assess the impact of CEP on capacity retention and electrolyte stability at 4.5 V.

Main Methods:

• Electrochemical cycling of graphite/LiNi_0.6Co_0.2Mn_0.2O₂ cells with and without CEP additive.
• Ex situ characterization techniques including X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy.
• Theoretical modeling to understand electrolyte stabilization mechanisms.

Main Results:

• Adding 1% CEP to the baseline electrolyte significantly improved 4.5 V capacity retention from 27.4% to 81.5% after 50 cycles.
• CEP preferentially oxidizes on the cathode surface, forming a protective film that suppresses electrolyte decomposition at high voltage.
• CEP's Lewis base functional groups capture PF₅, mitigating hydrofluoric acid (HF) generation and reducing transition-metal dissolution.

Conclusions:

• 1-(2-cyanoethyl) pyrrole (CEP) is a highly effective electrolyte additive for high-voltage LIBs.
• CEP enhances electrochemical performance by forming a superior cathode interfacial film and stabilizing the electrolyte.
• The study demonstrates CEP's potential for improving the safety and longevity of next-generation lithium-ion batteries.