Stable interfaces in lithium metal batteries constructed via in-situ electrolyte reformulation

• Introducing Li2CO3 into LiPF6-based electrolytes and storing at 40 °C generates LiPO2F2 and LiF in situ, forming a stable interface. • The reformulated electrolyte significantly enhances cycling stability of Li||Li cells, achieving over 800 h at 0.5 mA/cm2 and 300 h at 1.0 mA/cm2. • Coulombic efficiency is markedly improved from 81.99% (standard) to 91.56% with optimal Li2CO3 content. • Full cells with NCM cathodes (9.6 mg/cm2) show improved compatibility and rate performance, indicating practical applicability.