Three-Dimensional Holey Graphene Enwrapped Li3 V2 (PO4 )3 /N-Doped Carbon Cathode for High-Rate and Long-Life Li-Ion Batteries

Monoclinic Li₃ V₂ (PO₄ )₃ is a promising cathode material for high-power Li-ion batteries. Herein, a three-dimensional holey graphene enwrapped Li₃ V₂ (PO₄ )₃ /N-doped carbon (LVPNCHG) nanocomposite has been successfully synthesized. The holes could be in-situ and directly introduced in graphene through H₂ O₂ chemical etching in the synthesis process, which could remarkably enhance the ion and electron transport and greatly improve the electrochemical performance of the LVPNCHG electrode: 78 mAh g^-1 at 150 C, 86.1 % capacity retention over 2000 cycles at 10 C, and 96 % capacity retention over 500 cycles at 1 C under -20 °C. Moreover, in-situ distribution of relaxation time analysis was used to study LVPNCHG cathode during charge/discharge at 3.0-4.8 V, combined with in-situ X-ray diffraction measurement, and the results showed that a two-phase reaction mechanism was involved during the insertion of Li⁺ in the discharge process. Further demonstration of graphite//LVPNCHG full cell indicated great potential of the as-synthesized materials for practical application.

FeOF/TiO2 Hetero-Nanostructures for High-Areal-Capacity Fluoride Cathodes

Iron fluoride compounds offer an exciting pathway toward low-cost and high-capacity conversion-type lithium-ion battery (LIB) cathodes. However, due to the sluggishness of the electronic and ionic transport in iron fluorides, mass loadings of active materials in previous studies are typically less than 2.5 mg cm^-2, which is too low for practical applications. Herein, we improve the charge transport in fluoride electrodes at both nano- and mesoscales to enable high-mass-loading fluoride electrodes. At the nanoscale, we prepare electronically conducting Li_xTiO₂ composites with FeOF nanoparticles to reduce electron transport distance to 5-10 nm, which is one of the shortest among reports. At the mesoscale, we design a percolating three-dimensional porous carbon nanotube (CNT) network to enable fast pathways for both electrons and ions. The resulting spongelike material, FeOF/TiO₂@CNT, substantially enhances the kinetics of the conversion reaction in FeOF, boosts extra lithium storage capacity, and reduces the voltage hysteresis. Steady cycling over 300 cycles is achieved at a high mass loading of 8.7 mg cm^-2 (FeOF/TiO₂) (1.74 mAh cm^-2). Such areal capacity of lithium storage is significantly higher than previously reported iron fluorides-based structures, a significant step forward toward the development of low-cost metal fluoride electrodes.