Potassium Underpotential Deposition for Defect-Free Lithium Deposition in Anode-Free Li-Metal Batteries

Defects in deposited lithium (Li) severely cause dendrite growth and promote reactions between Li and electrolytes, resulting in active Li loss in anode-free Li metal batteries (AFLMBs). Herein, potassium underpotential deposition (K-UPD) is systematically established to heal defective Li and create a K-Cu bimetallic interface, facilitating uniform bulk Li deposition. The K-UPD at a potential of ≈1.0 V, higher than the equilibrium potentials of bulk K⁺ (0.1 V) and Li⁺ (0.0 V), significantly lowers the nucleation barrier and mitigates Li dendrite growth due to the better lithiophilicity of K metal compared to Cu. Meanwhile, the higher surface mobility of K atoms than Li atoms enables K metal to heal defects and prevent reactions between Li and electrolytes. The lower adsorption energy (ΔE) of the K atoms (-1.56 eV) than that of Li atoms (0.032 eV) indicates favorable adsorption of the K atom, as confirmed by DFT calculations. As a result, Cu||Li cell containing 1.3 M LiFSI+0.2 M KFSI bimetallic electrolyte reaches >1600 h, while Cu||NMC532 full-cell achieves a higher average Coulombic efficiency (avg. CE) of 99.6% than the cell with 1.5 M LiFSI electrolyte (≈98.2%) after the 100^th cycle. This work offers insights into the K-UPD mechanism for enhancing interface stability and healing defects in deposited Li.