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

Abstract 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.