Molecular pillaring driven microcrystalline structure engineering of hard carbon for high-rate sodium storage

Hard carbon (HC) is a promising anode for commercial sodium-ion batteries. However, the slow intercalation kinetics of Na+ ions in HC anodes results in the inferior rate capability. Developing a pseudo-graphite-rich structure with expanded interlayer spacing in HC is beneficial for high-rate sodium-ion storage. Herein, a molecular pillaring strategy was developed to expand the interlayer spacing of lignin-derived HC, using perylene3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the guest molecule. During the initial carbonization process, lignin decomposed into a carbonaceous skeleton at low pyrolysis temperatures. PTCDA underwent decomposition at lignin pyrolysis temperatures, in which the decomposed radicals of PTCDA connect and pillar the ligninderied carbon skeleton. Surprisingly, extensive pseudo-graphite structures with unprecedented interlayer spacing (0.397 nm) enlargement were built in the matrix of HC. As a result, the intercalation-dominated sodium-ionstorage HC anode exhibited more superior rate performance than lignin-derived HC (193 vs 97 mAh g- 1 at 1 A g- 1). This study opens up a new path for the development of high-rate sodium-ion-storage HC anodes.