Liberating the Electrolyte via In Situ Conversion of an Amide, Sulfonate‐Containing Monomer Precursor for High‐Temperature Graphite/NCM Batteries

Abstract High‐temperature (HT) operation and storage performance of Li‐ion batteries (LIBs) are essential for applications in electric vehicles, grid storage, or defense missions. Unfortunately, severe capacity fading is witnessed due to growing instability of the electrode/electrolyte interphase at HT. Herein, the study liberates the electrolyte from the task of film‐formation. Instead, it takes advantage of the favorable solid‐electrolyte interphase (SEI)‐forming functional groups by priorly anchoring them on graphite surface. Specifically, via molecular design, unsaturated CC bond, together with amide and sulfonate groups, are concurrently involved, namely the lithium‐2‐acrylamido‐2‐methyl‐1‐propanesulfonate (Li‐AMPS). Upon electrochemical cycle, the unsaturated CC bond in Li‐AMPS turns into a radical that induces polymerization between CC bonds to construct a polymeric network. The presence of amide and sulfonate groups endows the SEI with nitrogen, sulfur‐based reduction products OSO 2 Li and Li 3 N, etc. As such, the designed interphase makes the use of propylene carbonate‐based electrolyte possible. By assembling full cells with the modified graphite and LiNi 0.5 Co 0.2 Mn 0.3 O 2 (cathode loading of ≈18.5 mg cm −2 ), the capacity retention of the full cell has increased from 53.2% (with pristine graphite) to 77.8% after 300 cycles under 60 °C. A 2 Ah, 265 Wh kg −1 pouch cell is also able to operate for 200 cycles at an extreme temperature of 80 °C with the modified graphite.