Homogeneous Li deposition through the control of carbon dot assisted Li dendrite morphology for high-performance Li metal batteries
Lithium metal as a battery anode is the most promising energy storage materials owing to its high theoretical capacity and low working potential. However, uncontrollable Li growth during cycling raises safety issues in the battery due to dendrite formation and poor Coulombic reversibility. Here, a design of carbon nanodots (CDs) as electrolyte additives is introduced, which significantly improve the morphology of the Li plating and cycling stability of lithium metal batteries (LMBs). These CDs are suitable for electrolyte additives because they show good dispersibility against organic solvent which originated from their 2–5 nm small-sized particles. In addition, CDs include surface negative charges and various functional groups, which are easily controllable through modulating the amount and types of precursors. The surface negative charges and the functional groups in CDs draw Li cations by electrostatic force and provide a strong Li-ion affinity, respectively. This synergistic combination enables uniform Li-ion transportation to the current collector, resulting in a metal reduction with the smooth surface during plating/stripping process. Moreover, the control of CD-assisted Li dendrite morphology is examined by ex-situ transmission electron microscopy. In the LMB full-cell tests with limited 20-μm-thick Li metal, the CD-containing electrolytes exhibit capacity retention value of 99.9% after 100 cycles. The CD-assisted Li deposition minimizes the risks originating from Li dendrite growth, thus stabilizing the cycling ability of LMBs.