On-Demand Capacity Extraction of Cu Current Collector for Li Batteries

Irreversible loss of lithium due to its high reactivity lead to decrease in the energy density of lithium batteries. The decomposition of electrolyte forms electrochemically inactive solid electrolyte interface (SEI) layer on the surface of anodes, and lithium used to form SEI cannot be retrieved. Especially, large portion of Li⁺ from cathodes are consumed during the initial cycle of LIB, and the energy density of full cells are significantly decreased afterwards. In order to supplement this loss, various prelithiation strategies such as introducing additional lithium compounds on either anodes or cathodes have been reported. However, Cu current collector, has not been considered as a source of extra lithium and considered as dead weight, mainly due to its electrochemical inactivity with lithium.<br/>Here, we introduce a novel concept that involves utilizing Cu current collector as a lithium reservoir and extracting lithium on-demand during cycling to enhance the capacity of lithium batteries. By annealing Li and Cu, we show that Li-Cu alloy, a two-phase alloy, is formed with controllable capacity of lithium at an extraction potential of 1.2 V vs Li/Li⁺. Electrochemical and structural analyses revealed the irreversible extraction of Li during the phase transformation of the alloy. Based on electrochemical analyses, we demonstrated that Li-Cu alloy can serve as a prelithiated current collector in LIB, resulting in substantial increase of initial coulombic efficiency of anodes of half cells. Furthermore, relatively high extraction potential of Li-Cu alloy enabled on-demand extraction of lithium during discharging in full cells. In addition, prelithiated current collectors can also be employed to anode-free Li metal batteries, and capacity retention and cycle life of were observed to be improved. We anticipate that using current collector for lithium storage could enhance energy density of batteries while reducing reactivity of Li.