Edge‐NFx (x=1 or 2) Protected Graphitic Nanoplatelets as a Stable Lithium Storage Material

• Published in: Batteries & supercaps 2020-09, Vol.3 (9), p.928-935
• Main Authors: Noh, Hyuk‐Jun, Liu, Shenghong, Yu, Soo‐Young, Fan, Qinghua, Xiao, Feng, Xu, Jiantie, Jeon, In‐Yup, Baek, Jong‐Beom
• Format: Article
• Language: English
• Subjects: Anode; Edge-protection; Graphitic nanoplatelets; Lithium storage; NF3 functionalization
• ISSN: 2566-6223; 2566-6223
• DOI: 10.1002/batt.202000056

Edge‐NFx (x=1 or 2) protected graphitic nanoplatelets (NFGnPs) are synthesized for the first time as a stable anode material for lithium storage. The NFGnPs are prepared via mechanochemical reaction, by ball‐milling graphite in the presence of nitrogen trifluoride (NF3) gas. The average grain size of the NFGnPs is dramatically reduced compared to the starting graphite. The ball‐milling effectively unzips graphitic C−C bonds, generating active carbon species (C.), which form edge C−NFx bonds and delaminate the graphite layers into a few layered NFGnPs. The resulting NFGnPs have a large specific surface area (671.0 m2 g−1). The edge functionalities of the NFGnPs consist of major C(C)=NF1 and minor C−NF2 moieties. Because of their large specific surface area, the NFGnPs display high average reversible capacities of 850.5, 722.4, 576.4, 482.0, 369.1, 229.7, 127.5 mAh g−1 at 0.2, 0.5, 1, 2, 5 and 10 C, respectively, with excellent rate capability. More importantly, due to the edge protection provided by the stable C(C)=NF1 bonds (pseudo‐aromatic), the NFGnPs maintain a high reversible charge capacity of 421.6 mAh g−1 at 2 C, with an initial capacity retention of 78.3 % after 200 cycles. Mill and protect: Edge‐NFx (x=1 or 2) protected graphitic nanoplatelets (NFGnPs) are produced via a facile ‘one‐step’ mechanochemical ball‐milling graphite in the presence of nitrogen trifluoride (NF3) gas instead of dangerous F2 gas. The NFGnPs have a large surface area and unique C(C)=NF1/C−NF2 protection at their edges with well‐preserved crystalline basal plane, exhibiting remarkable performance as an anode for lithium‐ion batteries (LIBs).