Taming the Ion-Dipole Interaction via Rational Diluent Selection for Low-Temperature Li-Metal Batteries

Area of Science:

• Electrochemistry
• Materials Science

Background:

• Advanced electrolytes with high lithium (Li) affinity are crucial for long-cycling lithium metal batteries (LMBs).
• Strong Li+-solvent interactions in conventional electrolytes hinder Li+ desolvation, especially at low temperatures, leading to unstable electrode interfaces and poor cycling stability in LMBs.

Purpose of the Study:

• To investigate the influence of diluents on Li+ desolvation in electrolytes.
• To develop a parameter for selecting optimal diluents to enhance Li+ desolvation and improve low-temperature performance of LMBs.

Main Methods:

• Introducing various diluents into lithium hexafluorophosphate in 1,2-dimethoxyethane electrolyte.
• Analyzing the impact of diluent-solvent and diluent-anion interactions on Li+ desolvation.
• Proposing and utilizing a diluent selection parameter (DSP) based on interaction energies.

Main Results:

• Li+ desolvation is influenced by both diluent-solvent and diluent-anion interactions.
• A higher DSP value promotes Li+ desolvation and enhances low-temperature battery performance.
• The selected 1,2-dichloroethane diluent (DSP=3.95) demonstrated excellent Li reversibility (98.5% after 300 cycles) in Li|Cu cells.
• Li|LiFePO4 cells showed minimal capacity loss at -20°C over 300 cycles.
• Li|LiNi0.8Co0.1Mn0.1O2 cells retained 87% capacity after 100 cycles.

Conclusions:

• The study provides new insights into managing strong Li-solvent interactions in electrolytes.
• A novel diluent selection parameter (DSP) offers a new approach for designing advanced electrolytes for improved LMB performance.
• The findings pave the way for enhanced cycling stability and low-temperature operation in lithium metal batteries.