Suppression of dendrites and granules in surface-patterned Li metal anodes using CsPF6

Abstract

Unexpected Li deposition during plating, which causes low Coulombic efficiency and safety issues, limits the use of Li metal as an anode in commercial secondary batteries. With the recently developed micro-patterned Li metal anodes, dendrite formation during high current Li plating (2.4 mA cm−2) has successfully been reduced, as Li ions are guided into the patterned holes. However, the uncontrolled formation of granular Li is still observed in this material. To overcome these shortcomings, we have introduced cesium hexafluorophosphate into micro-patterned Li metal anodes. This additive employs the self-healing electrostatic shield mechanism to effectively reduce the formation of granular Li and Li dendrites, thereby significantly improving the electrochemical performance of the anodes even when only small amounts (0.05 M) of electrolyte are used. Our experiments revealed that batteries employing surface-patterned Li metal anodes with cesium hexafluorophosphate maintained 88.7% (96.6 mAh g−1) of their initial discharge capacity after the 900th cycle (Charging current density: C/2, 0.6 mA cm−2, Discharging current density: 1C, 1.2 mA cm−2), which is three times higher than the capacity observed with surface-patterned Li metal anodes without the additive (discharge capacity starts to decrease from 300 cycles).