Wrapping Sb₂Te₃ with a Graphite Layer toward High Volumetric Energy and Long Cycle Li-Ion Batteries

Many recent efforts on the electrode design for advanced Li-ion batteries (LIBs) are often devoted to increasing the gravimetric capacity, but little attention is paid to the volumetric capacity which is more critical for practical application. Though the alloying-type anode materials are quite attractive, the challenge is that they must be composited with a large amount of carbon materials (e.g., GO, rGO, CNT) to buffer their large volume change, which would undoubtedly sacrifice the volumetric energy density of the whole electrode due to the carbon's low tap density (∼0.05 g/cm³). Herein, we propose the unique layered Sb₂Te₃, which possesses high conductivity and a large volumetric capacity (3419 mAh/cm³), to be served as the alternative anode for LIBs. Furthermore, we introduce natural graphite, which is low price and with high density (2.25 g/cm³), into Sb₂Te₃ to successfully build a novel Sb₂Te₃@Gra composite in which the Sb₂Te₃ particles are wrapped by graphite layers. Interestingly, this modified Sb₂Te₃@Gra exhibits much more superior cycle stability (570 mAh/g after 200 cycles, 96% retention) than pure Sb₂Te₃ (130 mAh/g after 200 cycles, 22% retention), while keeping its original large volumetric capacity output (∼3200 mAh/cm³) at the same time. More specially, it enables a reversible structure recovery of Sb₂Te₃, guaranteeing the electrode integrity and cyclability. These extraordinary phenomena are investigated in detail, whose results display that the outer graphite layer plays an important role by facilitating the intimate contact with Sb₂Te₃ particles and protecting them from pulverization. Besides, such graphite layer greatly promotes the electron-transfer during lithiation, helping to improve the rate capability (372 mAh/g at 2000 mA/g, 60% retention). Consequently, the assembled Sb₂Te₃//LiCoO₂ full cell delivers a large capacity of 500 mAh/g, with stable discharge plateau and cycle stability, revealing its high potential for practical application.