Grain-Boundary-Enriched SEI via Field Regulation Enables Anode-Less Potassium Metal Batteries

Anode-less alkali metal battery has garnered wide attention in fundamental and technological realms, where its electrochemical performance is closely associated with the solid electrolyte interphase (SEI) design. However, knowledge regarding the SEI structure, content and related property remain elusive especially in the potassium metal battery realm. Here we report a graphene-based current collector modification strategy to render an inorganic SEI with grain boundary enrichment in a potassium anode system, with the aim of addressing the chronic electrochemical stability issue of anode-less metal battery. We show comprehensive quantification of inorganic/organic interphase and predominant grain boundary proportions, realizing decoupled analysis of interface dynamics related to ion transport across the interphases and electron transfer at the anode surface. The derived SEI endows admirable interface stability and mechanical strength, affording 10 000 h cycling of potassium electrodes in symmetric cell configurations under 5.0 mA cm⁻²/5.0 mAh cm⁻². Our optimized interphase with rich grain boundary minimizes the consumption of active species in anode-less potassium metal battery (with an N/P ratio of 5) during the formation stage, leading to a 12-fold increase in cycling lifespan and 3.4-fold improvement in capacity output.