De-solvation of heteroalkali cations enabling stable solid electrolyte interphase for dendrite-free lithium metal batteries

Li metal is highly sought after as a negative electrode material due to its high specific capacity and low electrode potential. However, the brittle solid electrolyte interphase and undesirable coulombic efficiency have severely hindered its commercial application. Here we propose a formation mechanism of stable solid electrolyte interphase based on the de-solvation of heteroalkali cations rather than the simple electrostatic shielding effect. Cesium trifluoroacetate (CsTFA), characterized by high electron-donor anion and weak solvent-binding heteroalkali cation, was incorporated into commercial electrolytes to foster an inorganic-rich solid electrolyte interphase. The de-solvation of absorbed Cs⁺ dominates the initial solid electrolyte interphase formation on the Li surface. Simultaneously, the preferential reduction of TFA^- promotes the enrichment of LiF within the solid electrolyte interphase. Owing to the synergistic effect of CsTFA, Li | |Cu half cells deliver a high CE of 99.77%, and Li | |LFP full cells exhibit satisfactory stability over 300 cycles with a 94.3% capacity retention at a negative/positive electrode capacity ratio of 1.36. Moreover, the added CsTFA in conventional ester electrolyte demonstrates improved stability of Li | |NCM811 full cells with an 80% capacity retention over 222 cycles at a negative/positive electrode capacity ratio of 1.