The role of active passivated interface in poly (ethylene oxide) electrolyte for 4.2 V solid-state lithium metal batteries

Solid-state lithium metal batteries (LMBs) show great potential in high-energy density storage with enhanced safety. However, the uncontrollable dendrite growth and limited operating voltage hampers its practical application. Herein, a stable passivated interface is constructed on Li metal surface via the active decomposition of LiPO2F2, which significantly reduce the interfacial resistance. The active passivated interface effectively suppresses parasitic reactions and inhibits the sprawl of Li dendrites, enabling long lifetime for more than 1200 h at 0.2 mA cm−2 for symmetric Li/Li cells. Moreover, the oxidation voltage of PEO-based solid electrolyte is elevated to >4.5 V, which makes it possible to pair with 4.2 V LiNi0.6Co0.2Mn0.2 (NCM622) cathode. The NCM622/Li cells can deliver 147.8 mAh/g after 100 cycles, with 88.5 % capacity retention. According to the variation in relaxation time, three independent electrochemical processes are identified. It has confirmed the existence of interface contact for flexible polymer electrolytes and the predominance of Li+ migration process in constituting interfacial resistance. Of note, it is critical to accelerate Li+ diffusion through the PEO/Li interface to regulate Li deposition behavior and achieve dendrite-free anodes. This work puts forward an effective strategy to enable long-term cycling of high-voltage cathodes in PEO-based electrolyte and opens a new understanding of interfacial resistance.