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 LiC 6 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 LiCoO 2 as the cathode exhibit high specific capacity and good cyclic stability in 200 cycles, stressing the advantage of controlled formation of Li clusters.