Enhanced Electrochemical Performance of Ultracentrifugation-Derived nc-Li3VO4/MWCNT Composites for Hybrid Supercapacitors

Nanocrystalline Li3VO4 dispersed within multiwalled carbon nanotubes (MWCNTs) was prepared using an ultracentrifugation (uc) process and electrochemically characterized in Li-containing electrolyte. When charged and discharged down to 0.1 V vs Li, the material reached 330 mAh g–1 (per composite) at an average voltage of about 1.0 V vs Li, with more than 50% capacity retention at a high current density of 20 A g–1. This current corresponds to a nearly 500C rate (7.2 s) for a porous carbon electrode normally used in electric double-layer capacitor devices (1C = 40 mA g–1 per activated carbon). The irreversible structure transformation during the first lithiation, assimilated as an activation process, was elucidated by careful investigation of in operando X-ray diffraction and X-ray absorption fine structure measurements. The activation process switches the reaction mechanism from a slow “two-phase” to a fast “solid-solution” in a limited voltage range (2.5–0.76 V vs Li), still keeping the capacity as high as 115 mAh g–1 (per composite). The uc-Li3VO4 composite operated in this potential range after the activation process allows fast Li+ intercalation/deintercalation with a small voltage hysteresis, leading to higher energy efficiency. It offers a promising alternative to replace high-rate Li4Ti5O12 electrodes in hybrid supercapacitor applications

Cation-Disordered Li3VO4: Reversible Li Insertion/Deinsertion Mechanism for Quasi Li-Rich Layered Li1+x[V1/2Li1/2]O2 (x = 0–1)

The reversible lithiation/delithiation mechanism of the cation-disordered Li3VO4 material was elucidated, including the understanding of structural and electrochemical signature changes during cycling. The initial exchange of two Li induces a progressive and irreversible migration of Li and V ions from tetrahedral to octahedral sites, confirmed by the combination of in situ/operando X-ray diffraction and X-ray absorption fine structure analyses. The resulting cation-disordered Li3VO4 can smoothly and reversibly accommodate two Li and shows a Li+ diffusion coefficient larger by 2 orders of magnitude than the one of pristine Li3VO4, leading to improved electrochemical performance. This cation-disordered Li3VO4 negative electrode offers new opportunities for designing high-energy and high-power supercapacitors. Furthermore, it opens new paths for preparing disordered compounds with the general hexagonal close-packing structure, including most polyanionic compounds, whose electrochemical performance can be easily improved by simple cation mixing

Enhanced Electrochemical Performance of Ultracentrifugation-Derived nc-Li₃VO₄/MWCNT Composites for Hybrid Supercapacitors

Nanocrystalline Li₃VO₄ dispersed within multiwalled carbon nanotubes (MWCNTs) was prepared using an ultracentrifugation (uc) process and electrochemically characterized in Li-containing electrolyte. When charged and discharged down to 0.1 V <i>vs</i> Li, the material reached 330 mAh g^–1 (per composite) at an average voltage of about 1.0 V <i>vs</i> Li, with more than 50% capacity retention at a high current density of 20 A g^–1. This current corresponds to a nearly 500<i>C</i> rate (7.2 s) for a porous carbon electrode normally used in electric double-layer capacitor devices (1<i>C</i> = 40 mA g^–1 per activated carbon). The irreversible structure transformation during the first lithiation, assimilated as an activation process, was elucidated by careful investigation of <i>in operando</i> X-ray diffraction and X-ray absorption fine structure measurements. The activation process switches the reaction mechanism from a slow “two-phase” to a fast “solid-solution” in a limited voltage range (2.5–0.76 V <i>vs</i> Li), still keeping the capacity as high as 115 mAh g^–1 (per composite). The uc-Li₃VO₄ composite operated in this potential range after the activation process allows fast Li⁺ intercalation/deintercalation with a small voltage hysteresis, leading to higher energy efficiency. It offers a promising alternative to replace high-rate Li₄Ti₅O₁₂ electrodes in hybrid supercapacitor applications