Multifunctional solvent molecule design enables high-voltage Li-ion batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Increasing energy density of lithium-ion batteries (LIBs) is crucial for advanced applications.
• Elevating charging cut-off voltage boosts energy density but causes detrimental parasitic reactions at interfaces.
• Existing electrolytes face limitations in stabilizing high-voltage interfaces.

Purpose of the Study:

• To design a non-flammable electrolyte for stable high-voltage operation in LIBs.
• To enable the formation of protective interphases on both cathode and anode.
• To enhance the energy density and cycle life of commercial LIBs.

Main Methods:

• Development of a fluorinated sulfonate electrolyte using multifunctional solvent molecules.
• Electrolyte composition: 1.9 M LiFSI in a 1:2 v/v mixture of trifluoroethyl trifluoromethanesulfonate and trifluoroethyl methanesulfonate.
• Testing of graphite||LiCoO2 and graphite||NCM811 cells at elevated cut-off voltages (4.55 V and 4.6 V).

Main Results:

• Formation of an inorganic-rich cathode electrolyte interphase (CEI) and a hybrid organic/inorganic solid electrolyte interphase (SEI).
• Graphite||LiCoO2 batteries charged to 4.55 V retained 89% capacity over 5329 cycles.
• Graphite||NCM811 batteries charged to 4.6 V retained 85% capacity over 2002 cycles, showing significant capacity retention.
• Achieved 33% and 16% energy density increases for LiCoO2 and NCM811 cells, respectively, compared to 4.3 V charging.

Conclusions:

• The novel electrolyte effectively suppresses parasitic reactions at high voltages.
• The designed electrolyte enables significant improvements in energy density and cycle life for LIBs.
• This strategy offers a practical approach for upgrading commercial lithium-ion batteries.