Structure and Surface Chemistry Optimization of Graphite Electrodes for High-Voltage Dual-Intercalation Batteries
To accomplish this goal, we subjected spherical, core-shell, and stacked graphite structures to 1100 – 1800 °C vacuum annealing, impact milling, 570 °C air oxidation, C2F6 plasma discharge, and high-temperature treatments using melamine and H2. These procedures defunctionalized surfaces , altered defects in the sp2 lattice, or selectively grafted C=O, C-F, C‑Nx, and C-H groups, respectively. Following electrochemical cycling between 4.0 and 5.2 V in 2.0 m LiPF6 in fluoroethylene carbonate (FEC), ethylmethycarbonate (EMC) electrolytes and a tris(hexafluoro-iso-propyl)phosphate (HFiP) additive, we observed different effects of specific surface chemistries on anode and cathode capacities and first-cycle efficiencies. In particular, we observe positive influences of hydrogenated anode surfaces and improved performances for oxidized cathodes. Similar modifications of spherical and layered graphite electrodes yielded asymmetric efficiencies and long-duration cyclabilities, indicating divergent influences of functionalities on specific intercalated ions. Matching the appropriate surface groups for anode and cathode dual-graphite batteries, we observe improvements in coulombic efficiencies and long-term cyclabilities. Our findings offer fundamental insights into the dual-intercalation process and provide pathways for optimization of these all-carbon, environmentally friendly energy storage systems  for grid-level applications.
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