Effects of lithium salt concentration on graphited carbon microbead anodes in the piperidinium-based hybrid electrolytes

• “Lithium aggregates” in piperidinium-based electrolytes are evidenced by IR and NMR.
• High LiPF6 content could decrease Li+ mobility due to “ionic aggregates”.
• Lithium salt concentration is an important factor affecting graphite performances.

The variations in LiPF6 concentration lead to the very different electrochemical performances of carbon microbeads anodes in the piperidinium-based hybrid electrolytes. The “two peaks” behaviors of lithium plating observed in cyclic voltammetry tests, and some detailed changes in infrared spectra and nuclear magnetic resonance indicates that the formation of “ionic aggregates” related to lithium ions”. Therefore, the excessive lithium salts in the piperidinium-based hybrid electrolytes, usually cause a significant decrease in Li+ mobility and transfer efficiency. The main behaviors are that, when LiPF6 concentrations increased from 0.2 to 1.2 mol kg−1, the apparent migration energies (Ea) increase largely from 8.83 to 21.16 kJ mol−1, while the lithium transference numbers (tLi+) drop markedly from 0.538 to 0.292.

“Lithium aggregates” usually cause a significant decrease in Li+ mobility and transfer efficiency. Therefore, as important as the problem of SEI, the content of lithium salt and the interaction between Li+ and ILs’ anions should be taken into consideration in the optimization of ILs-based electrolytes for Li-ion batteries.Figure optionsDownload as PowerPoint slide