Electrolyte engineering is a promising strategy to enable practical lithium metal batteries. For a promising electrolyte, several key requirements are marked: (1) consistently high Coulombic efficiency (CE) to minimize Li loss, including that in the initial cycles; (2) functionality under lean electrolyte and limited-excess Li conditions for maximized energy density; (3) oxidative stability towards high-voltage cathodes; (4) rmoderate salt concentration for cost-effectiveness; (5) high boiling point and low flammability for safety and processability. Several reports on electrolyte engineering improved the cyclability of Li metal batteries, such as high-concentration electrolytes, local high-concentration electrolytes, additive optimization, solvent combination, and liquified gas electrolytes. But a detailed methodology of rational electrolyte design is still highly demanded. In our work, we target new solvent molecules that not only dissolve Li salt but also stay compatible when confronted with both Li metal anodes and high-voltage cathodes. Thus we design a first-time synthesized liquid molecule, fluorinated 1,4-dimethoxybutane (FDMB), solely as the electrolyte solvent. It is paired with 1 molar lithium bis(fluorosulfonyl)imide (1 M LiFSI) in a single-salt, single-solvent formulation (1 M LiFSI/FDMB) to enable stable and high-energy-density Li metal batteries. Theoretical simulations show a unique Li+-solvent interaction in 1 M LiFSI/FDMB and thus higher anion-solvent ratio in the Li+ solvation structure, endowing the electrolyte with both Li metal compatibility and high-voltage tolerance. A high CE (~99.52%) and fast activation (CE ramps up to &gt;99% within 5 cycles) for Li metal anodes are achieved. The Li|NMC full cells with limited-excess Li retain 90% capacity after 420 cycles with an average CE of 99.98%. Industrial anode-free Cu|NMC 811 pouch cells achieve ~325 Wh kg-1 single-cell energy density while Cu|NMC532 ones show 80% capacity retention after 100 cycles, which is one of the best performing anode-free cells. Our rational design concept for electrolyte provides a promising path to high-energy, practical Li metal batteries with high cyclability and processability.

Molecular design for electrolyte solvents enables long-cycling anode-free lithium metal batteries

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.