Temperature‐Inert Interface Enables Safe and Practical Energy‐Dense LiNi0.91Co0.07Mn0.02O2 Pouch Cells

Abstract Safety concerns significantly hinder the practical implementation of ultrahigh‐nickel cathodes in lithium‐ion batteries. The solid electrolyte interphase (SEI) derived from conventional ester‐based electrolyte is susceptible to thermal decomposition, resulting in battery safety degradation. Herein, a temperature‐inert and inorganic‐rich SEI is developed for the ultrahigh‐nickel LiNi 0.91 Co 0.07 Mn 0.02 O 2 |graphite (NCM91|Gr) battery by employing a flame‐retardant diluted weakly solvated electrolyte. Temperature‐dependent X‐ray photoelectron spectroscopy reveals that SEI's inorganic components of LiF, Li 2 SO 3 , Li 2 SO 4 , and Li 3 N exhibit exceptional thermotolerance under thermal attack. Further evidence from temperature‐dependent X‐ray diffraction indicates that this thermally stable interface effectively mitigates the anode phase transition from the original LiC 6 to LiC 12 state, resulting in a remarkable improvement in intrinsic safety and a 32% reduction in gas emission for battery. The 1.2 Ah NCM91|Gr pouch cell exhibits a thermal failure onset temperature as high as 183.1 °C and maintains stability at 180 °C for 60 min. Furthermore, a 360 Wh kg −1 12.3 Ah LiNi 0.92 Co 0.06 Mn 0.02 O 2 |graphite@20% silicon dioxide cell experiences no thermal runaway even at 200 °C. The 1.2 Ah NCM91|Gr pouch cell also delivers outstanding capacity retention of 90.5% after 1200 cycles with enhanced electrochemical performance. This study provides a promising approach for developing safer energy‐dense batteries through electrolyte and interface design.