Improved Capacity Retention for a Disordered Rocksalt Cathode via Solvate Ionic Liquid Electrolytes

Abstract

Lithium-rich disordered rocksalts (DRX) are a promising class of cathode materials for high-energy lithium ion batteries (LIBs) and lithium metal batteries (LMBs) due to the high initial specific capacities (> 200 mAh g À 1 ) as well as flexible chemical composition. However, challenges concerning severe capacity fade and voltage decay upon cycling at high cut-off voltages are still to be overcome. Moreover, state-of-the-art carbonatebased electrolytes can be decomposed by reactive oxygen species released by DRX materials during cycling. In this work, the electrochemical performance of Li 1.25 Fe 0.5 Nb 0.25 O 2 (LFNO) j j Li LMB and LFNO j j graphite LIB cells is compared for a conventional, carbonate-based electrolyte and the solvate ionic liquid (SIL) [Li(G3)][TFSI] (G3: triethyleneglycoldimethylether). Cycle life is notably improved by the chemically more stable ionic liquid electrolyte, as the anionic redox activity of LFNO is prolonged compared to the carbonate-based cells. This work represents an important step toward an improved cycle life of DRX cathodes.

Understanding the Solvation Structure of Li-Ion Battery Electrolytes Using DFT-Based Computation and 1H NMR Spectroscopy

“…1,9−12 Recent work has shown this class of electrolytes undergoes greatly reduced decomposition in full battery cells compared to standard carbonate-based systems, enabling use of more experimental electrode materials and extending cycle life. 13 Tetraglyme, which constitutes a typical molecular solvent of the SIL system, has also proven its potential in Li-ion batteries and supercapacitors; it is a small-molecule analogue of the quintessential poly(ethylene oxide) (PEO) material used as a solid-state polymer electrolyte, and its study can thus also provide insight into the ion transport mechanisms in polymer electrolytes. 14 For example, typical characteristics of tetraglyme-based electrolytes as used in battery applications are high solubility of alkaline salts as well as high ionic conductivity.…”

“…Glymes (i.e., methoxy-terminated oligoethers, CH 3 O­(CH 2 CH 2 O) n CH 3 ) are promising solvents commonly used as components of Li-ion battery electrolyte systems. Glyme-based systems, such as lithium bis­(trifluoro­methane­sulfonyl)­imide (Li­[TFSI]) salt dissolved in tetraglyme (G4), have been extensively developed and explored. ,− Recent work has shown this class of electrolytes undergoes greatly reduced decomposition in full battery cells compared to standard carbonate-based systems, enabling use of more experimental electrode materials and extending cycle life …”

“… 1 , 9 − 12 Recent work has shown this class of electrolytes undergoes greatly reduced decomposition in full battery cells compared to standard carbonate-based systems, enabling use of more experimental electrode materials and extending cycle life. 13 …”