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_0.91Co_0.07Mn_0.02O₂|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, Li₂SO₃, Li₂SO₄, and Li₃N 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 LiC₆ to LiC₁₂ 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_0.92Co_0.06Mn_0.02O₂|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.