An oligomeric solid–electrolyte interphase (SEI) constructed by electrolyte engineering improves the cyclability of lithium (Li) metal batteries. However, to spontaneously establish a SEI with elasticity and self-healing features, as well as high ionic conductivity is still a huge challenge due to the uncontrollable SEI formation process. Herein, we first synthesize an ionic conductive elastomer (ICE) through the in situ chain scission of the polylactic acid precursor triggered by the Li metal. Firstly, different from conventional elastomers, the resulting lithiated polymer here possessed a unique Li+-crosslinked network with the presence of a trace amount of liquid electrolyte inside the ICE. Moreover, the cationic Li+ promptly generates ionic groups to establish adaptive motifs, endowing the network with remarkable dynamic reversibility and improved elasticity. Finally, the ICE offered rapid Li+-transport pathways through the molecular backbones and the liquid electrolyte present within the framework. As such, the SEI armed with the self-healing, elastic, and conductive ICE can effectively suppress the growth of Li dendrites and maintain the structural integrity, visually demonstrated by in situ transmission electron microscopy. Consequently, a surprising lifespan over 22 700 cycles (∼9110 h) at a current density of 5 mA cm−2 has been achieved in symmetric cells that largely exceeds the current records, accordingly guaranteeing stable high-capacity pouch cells. This work proposes a brand-new elastomer for robust and conductive interphase design towards achieving high-energy Li or other alkali metal batteries.