High-concentration LiPF/sulfone electrolytes: structure, transport properties, and battery application

• Published in: Physical chemistry chemical physics : PCCP Vol. 25; no. 43; pp. 29566 - 29575
• Main Authors: Ugata, Yosuke, Chen, Yichuan, Miyazaki, Shuhei, Sasagawa, Shohei, Ueno, Kazuhide, Watanabe, Masayoshi, Dokko, Kaoru
• Format: Journal Article
• Published: 08.11.2023
• DOI: 10.1039/d3cp04561g
• ISSN: 1463-9076

Non-flammable and oxidatively stable sulfones are promising electrolyte solvents for thermally stable high-voltage Li batteries. In addition, sulfolane-based high-concentration electrolytes (HCEs) show high Li + ion transference numbers. However, LiPF 6 has not yet been investigated as the main salt in sulfone-based HCEs for Li batteries. In this study, we investigated the phase behaviors, solvate structures, and transport properties of binary and ternary mixtures of LiPF 6 and the following sulfone solvents: sulfolane (SL), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), and 3-methyl sulfolane (MSL). The stable crystalline solvates Li(SL) 4 PF 6 and Li(DMS) 2.5 PF 6 with high melting points were formed in the LiPF 6 /SL and LiPF 6 /DMS mixtures, respectively. In contrast, LiPF 6 /EMS, LiPF 6 /MSL, and LiPF 6 /SL/another sulfone mixtures remained liquids over a wide temperature range. Raman spectroscopy revealed that SL and another sulfone are competitively coordinated to Li + ions to dissociate LiPF 6 in the ternary mixtures. Although the ionic conductivity decreased with increasing LiPF 6 concentration due to an increase in viscosity, Li + ions diffused faster than PF 6 − via exchanging ligands in the HCE [LiPF 6 ]/[SL]/[DMS] = 1/2/2, resulting in a higher Li ion transference number than that in conventional Li battery electrolytes. LiPF 6 and sulfolane form a stable crystalline solvate at a 1 : 4 molar ratio; however, the partial substitution of sulfolane with another sulfone suppresses solvate crystallization, enabling its use as a liquid electrolyte in Li batteries.