Dominant Solvent-Separated Ion Pairs in Electrolytes Enable Superhigh Conductivity for Fast-Charging and Low-Temperature Lithium Ion Batteries

Xinping Chen; Zelin Li; He Zhao; Jie Li; Wenting Li; Ce Han; Yujuan Zhang; Lisi Lu; Jinxing Li; Xinping Qiu

doi:10.1021/acsnano.3c12877

Dominant Solvent-Separated Ion Pairs in Electrolytes Enable Superhigh Conductivity for Fast-Charging and Low-Temperature Lithium Ion Batteries

ACS Nano. 2024 Mar 19;18(11):8350-8359. doi: 10.1021/acsnano.3c12877. Epub 2024 Mar 11.

Authors

Xinping Chen¹, Zelin Li², He Zhao¹, Jie Li¹, Wenting Li^{1

3}, Ce Han¹, Yujuan Zhang¹, Lisi Lu¹, Jinxing Li², Xinping Qiu^{1

3}

Affiliations

¹ Key Laboratory of Organic Optoelectronics and Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China.
² School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, P. R. China.
³ Institute of Tsinghua University Hebei, Beijing 100084, P. R. China.

PMID: 38465598
DOI: 10.1021/acsnano.3c12877

Abstract

The low ionic conductivities of aprotic electrolytes hinder the development of extreme fast charging technologies and applications at low temperatures for lithium-ion batteries (LIBs). Herein, we present an electrolyte with LiFSI in acetone (DMK). In DMK electrolytes, the solvation number is three, and solvent-separated ion pairs (SSIPs) are the dominant structure, which is largely different from other linear aprotic electrolytes where salts primarily exist as contact ion pairs (CIPs). With incompact solvation structures due to the weak solvation ability of DMK with Li⁺, the ionic conductivity reaches 45 mS/cm at room temperature. The percentage of SSIPs increases as temperatures decrease in DMK electrolytes, which is totally different from the carbonate-based electrolytes but greatly beneficial to low-temperature ionic conductivity. With the appropriate addition of VC and FEC, DMK-based electrolytes still exhibit a superhigh ionic conductivity. Even at -40 °C, the ionic conductivity is greater than 10 mS/cm. With DMK-based electrolytes, LIBs with thick LiFePO₄ electrodes can be cycled at high rates and at low temperatures.

Keywords: acetone electrolytes; extreme fast charging; low-temperature cycling; solvation structures; solvent-separated ion pairs; superhigh ionic conductivity; thick LiFePO4 electrodes.