Trace water in nonaqueous electrolytes has been supposed to be detrimental to Li metal, which may induce formation of HF and corrode battery materials. Herein, we propose that a controllable AlCl3 is an efficient electrolyte additive for dendrite-free Li deposition. The additive could react with trace water in the electrolyte to form a stable Al2O3-rich solid electrolyte interphase (SEI) layer on the surface of Li and Al-based positively charged colloidal particles (PCCPs) in the electrolyte. PCCPs could form a positively charged electrostatic shield around the protruding lithium during the deposition process and induce the subsequent deposition of Li to the adjacent regions of the protruding Li, enabling a uniform and dendrite-free Li morphology. The assembled Li|Se and Li|Li4Ti5O12 batteries benefit from the synergism of SEI layer and PCCPs, thereby demonstrating the impressive capability for dendrite suppression of Li anode and improved electrochemical performance.