High-Coulombic-Efficiency Carbon/Li Clusters Composite Anode without Precycling or Prelithiation.

Lithium metal has attracted much research interest as a possible anode material for high-energy-density lithium-ion batteries in recent years. However, its practical use is severely limited by uncontrollable deposition, volume expansion, and dendrite formation. Here, a metastable state of Li, Li cluster, that forms between LiC6 and Li dendrites when over-lithiating carbon cloth (CC) is discovered. The Li clusters with sizes in the micrometer and submicrometer scale own outstanding electrochemical reversibility between Li+ and Li, allowing the CC/Li clusters composite anode to demonstrate a high first-cycle coulombic efficiency (CE) of 94.5% ± 1.0% and a stable CE of 99.9% for 160 cycles, which is exceptional for a carbon/lithium composite anode. The CC/Li clusters composite anode shows a high capacity of 3 mAh cm-2 contributed by both Li+ intercalation and Li-cluster formation, and excellent cycling stability with a signature sloping voltage profile. Furthermore, the CC/Li clusters composite anode can be assembled into full cells without precycling or prelithiation. The full cells containing bare CC as the anode and excessive LiCoO2 as the cathode exhibit high specific capacity and good cyclic stability in 200 cycles, stressing the advantage of controlled formation of Li clusters.