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 LiNiO2 and LiCoO2, 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 LiNiO2 forms lithiated Li2NiO2 with the excess lithium in the crystalline lattice while the excess lithium in LiCoO2 forms a Li2O 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 LiNiO2 and 150% for LiCoO2. While the pre-lithiation process causes particle pulverization depending on the amount of Li excess, LiCoO2 offers a much better cycle performance than LiNiO2 with a promising capacity retention of 80% after 300 cycles in AFLMB (vs 76% after 100 cycles for 40% Li excess in LiNiO2). This study provides a promising avenue for developing tailor-made layered oxide cathodes for AFLMBs. An electrochemical pre-lithiation method is employed on LiNiO2 and LiCoO2 cathodes and its impact on the cathode structure and cycle life of anode-free lithium metal batteries is presented. While both LiNiO2 and LiCoO2 have a similar structure, the mechanism in accommodating the excess Li is different where LiNiO2 forms the Li2NiO2 phase and LiCoO2 forms a Li2O surface layer.image