Solvation and Interfacial Engineering Enable −40 °C Operation of Graphite/NCM Batteries at Energy Density over 270 Wh kg⁻¹

Li‐ion batteries (LIBs) that can operate under low temperature (LT) conditions are essential for applications in orbital missions, subsea areas, and electric vehicles. Unfortunately, severe capacity loss is witnessed due to tremendous kinetic barriers that emerge at LT. Herein, to surmount such kinetic limitations, a low dielectric environment is tamed throughout the bulk electrolyte, which efficaciously brought the Li⁺ desolvation energy down to 30.76 kJ mol⁻¹. At the meantime, the adoption of sodium cations (Na⁺) is proposed as a hetero‐cation additive, and a Li‐Na hybrid and fluoride‐rich interphase is further identified via preferential reduction of Na⁺‐(solvent/anion) clusters, which is found to efficiently facilitate Li⁺ migration through the LiF/NaF grain boundaries. Based on a N/P ratio of 1.1, the graphite/LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) full cell (cathode loading of ≈18.5 mg cm⁻²) delivers a capacity as high as 125.1 mAh g⁻¹ under −20 °C with prolonged cycling to 100 cycles. Finally, a 270 Wh kg⁻¹ graphite/NCM pouch cell is assembled, which affords a discharge capacity of 108.7 mAh g⁻¹ under −40 °C during the initial cycles. With an eye to both fundamental and practical aspects, this work will propel additional advancements and allow LIBs to fill more roles under extreme operation temperatures than ever before.