Synergistic Decomposition of Closo ‐Type Borohydrides Enables Robust Cathode–Electrolyte Interphases in Ah‐Class Lithium Cells

For the next generation of lithium metal batteries of high energy density and high‐power density, the protection of cathodes is vital, which requires a uniform cathode‐electrolyte interphase (CEI) layer with an excellent mechanical strength upon cycling. Here, we introduce closo ‐type borohydride Li 2 B 12 H 12 as an effective electrolyte additive, via a synergistic decomposition that [B 12 H 12 ] 2− and [PF 6 ] − of commercial electrolytes undergo at voltages ∼3.3 V, constructing a CEI layer rich in both fluorides and borides. The modulated CEI layer is as thin as ∼10 nm with a high Young's modulus of 8.77 GPa. This CEI enhances the electrochemical performance of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathode, as well as other ultrahigh‐voltage cathodes like Li‐rich Mn‐based (LRMO) cathodes. The Li||LRMO battery not only reaches an outstanding rate performance at 10 C, but also reaches an energy density of 392 Wh kg −1 in a 3 Ah‐class pouch cell. This synergistic decomposition strategy of the closo ‐type borohydride additive effectively provides a reference for the modulation of an ultrathin and strong CEI, balancing both energy density and power density of the battery.