Low-temperature lithium-metal batteries improved by hierarchical solvation

What the study found: The study found that a hierarchically solvating electrolyte made from tetrahydropyran (a weakly coordinating ether), methyl propionate (a strongly coordinating ester), lithium difluoro(oxalato)borate, and trifluorotoluene supported high-performance lithium-metal batteries at low temperature.
Why the authors say this matters: The authors conclude that tailoring solvation chemistry may help address the sluggish lithium-ion transport and high desolvation energy that limit lithium-metal batteries in extreme conditions such as low temperatures.
What the researchers tested: The researchers engineered a multicomponent electrolyte system and examined how its solvation structure affected lithium-ion desolvation and solid electrolyte interphase (SEI) formation. They also tested Li||Li symmetric cells and Li||LiCoO2 full cells at cryogenic temperatures.
What worked and what didn't: The electrolyte promoted an anion-enriched primary solvation sheath and, with trifluorotoluene as a non-solvating diluent, shifted the local solvation structure toward aggregate dominance. The resulting SEI was described as compact, homogeneous, and mechanically balanced, and Li||Li symmetric cells cycled for over 6000 h at -25°C. In Li||LiCoO2 full cells, the system supported 400 stable cycles and retained 85.5% and 66.2% of nominal room-temperature capacity at -25°C and -45°C, respectively.
What to keep in mind: The abstract does not describe specific limitations beyond the low-temperature focus of the tests, and the results are reported for the electrolyte compositions and cell types studied here.

Key points

• A hierarchically solvating electrolyte was built from THP, MP, LiDFOB, and trifluorotoluene.
• The authors say the design reduces the activation energy needed for lithium-ion desolvation.
• The electrolyte helped form a compact, homogeneous SEI with organic and inorganic components.
• Li||Li symmetric cells cycled for more than 6000 hours at -25°C.
• Li||LiCoO2 full cells ran for 400 stable cycles and retained 85.5% capacity at -25°C and 66.2% at -45°C.