Ion-Solvent Interplay in Concentrated Electrolytes Enables Subzero Temperature Li-Ion Battery Operations

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Ethylene carbonate (EC) is crucial for solid electrolyte interphase (SEI) formation but limits lithium-ion battery performance at low temperatures due to high Li+ desolvation barriers and melting point.
• Sluggish Li+ reaction kinetics at subzero temperatures hinder the practical application of lithium-ion batteries in cold environments.

Purpose of the Study:

• To develop an ethylene carbonate-free high salt concentration electrolyte (HSCE) for enhanced low-temperature lithium-ion battery operation.
• To investigate the ion transport mechanisms and SEI properties of the novel HSCE at subzero temperatures.
• To evaluate the electrochemical performance of HSCE in full cells at extreme low temperatures.

Main Methods:

• Synthesis and characterization of an EC-free HSCE using lithium bis(fluorosulfonyl)imide and tetrahydrofuran.
• Experimental techniques (e.g., electrochemical measurements) and theoretical calculations (e.g., molecular dynamics simulations) to study Li+ transport.
• Fabrication and testing of LiNi0.6Co0.2Mn0.2O2||graphite half-cells and full cells at subzero temperatures, including -40 °C.

Main Results:

• The HSCE exhibits unusually rapid low-temperature Li+ transport, dominated by intra-aggregate ion transport.
• A thin (<5 nm) LiF-rich SEI layer derived from the anion is formed, showing excellent compatibility with graphite electrodes.
• Full cells with tailored HSCE demonstrate superior charge-discharge performance at -40 °C compared to conventional EC-based electrolytes.

Conclusions:

• The developed EC-free HSCE significantly enhances lithium-ion battery performance at subzero temperatures.
• The intra-aggregate ion transport mechanism is key to achieving efficient low-temperature Li+ conductivity.
• This work presents a promising strategy for developing robust low-temperature lithium-ion battery technology.