Effect of Electrochemical Pre-Lithiation on Layered Oxide Cathodes for Anode-Free Lithium-metal Batteries.

Due to high energy density and lower manufacturing cost, anode-free lithium-metal batteries (AFLMBs) are attracting increasing attention. The challenges for developing them lie in inferior Coulombic efficiency and short cycle life due to the highly reactive lithium metal. Herein, an electrochemical pre-lithiation strategy is applied to layered oxide cathodes, specifically LiNiO 2 and LiCoO 2 , aiming to provide an additional lithium source and understand the effect on the cathode structure for AFLMBs. The mechanism for accommodating the excess Li depends on the structural stability of the cathodes where LiNiO 2 forms lithiated Li 2 NiO 2 with the excess lithium in the crystalline lattice while the excess lithium in LiCoO 2 forms a Li 2 O phase. More importantly, an optimal amount of Li excess is necessary to maintain decent cycle stability and specific capacity in AFLMB, with 40% excess Li for LiNiO 2 and 150% for LiCoO 2 . While the pre-lithiation process causes particle pulverization depending on the amount of Li excess, LiCoO 2 offers a much better cycle performance than LiNiO 2 with a promising capacity retention of 80% after 300 cycles in AFLMB (vs 76% after 100 cycles for 40% Li excess in LiNiO 2 ). This study provides a promising avenue for developing tailor-made layered oxide cathodes for AFLMBs.