Anion Intercalation into a Graphite Electrode from Trimethyl Phosphate

Lei Zhang; Hongyu Wang

doi:10.1021/acsami.0c14921

Anion Intercalation into a Graphite Electrode from Trimethyl Phosphate

ACS Appl Mater Interfaces. 2020 Oct 21;12(42):47647-47654. doi: 10.1021/acsami.0c14921. Epub 2020 Oct 8.

Authors

Lei Zhang^{1

2}, Hongyu Wang^{1

2}

Affiliations

¹ State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, China.
² School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei 230026, China.

PMID: 33030890
DOI: 10.1021/acsami.0c14921

Abstract

Trimethyl phosphate (TMP) is a flame-retardant solvent frequently used in nonaqueous electric energy storage devices. Anions can hardly intercalate into a graphite positive electrode from neat TMP at ordinary conditions. In TMP solutions, dissolving lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonimide) (LiTFSI), by means of increasing lithium salt concentration or increasing the charge cutoff voltage of Li/graphite cells, the TMP-solvated anions can successfully intercalate into graphite positive electrodes. Moreover, the effect of TFSI^- activation on a graphite electrode is addressed. Ex situ X-ray diffraction measurements in combination with traditional electrochemical tests are employed to investigate the crystal structure change and electrochemical performance of graphite electrodes, respectively. Nuclear magnetic resonance, Fourier-transform infrared, and Raman spectroscopy are employed to characterize the TMP solutions.

Keywords: anion−graphite intercalation compounds; concentrated solutions; dual-ion batteries; solvated anion; trimethyl phosphate.