Biphasic MoO₂/Mo₂C-Passivated Graphite Anodes for Fast-Charging Lithium-Ion Batteries.

Abstract

Fast charging of commercial lithium-ion batteries severely compromises long-term cycle durability, particularly in cells using high mass-loading thick electrodes. Such performance decay originates from interfacial kinetic limitations in the graphite anode as follows: (i) a sluggish Li⁺ desolvation at the electrolyte-graphite interface, (ii) a hindered Li⁺ diffusion across the solid electrolyte interphase (SEI), and (iii) a restricted Li⁺ insertion into the graphite, which collectively lead to an undesirable Li plating. Herein, we introduce an ultrathin and uniform MoO₂/Mo₂C biphasic passivation layer, achieved through a sequential cationic polyelectrolyte-assisted molybdate adsorption approach. The outer MoO₂ layer does not only suppress an excessive SEI formation but also stabilizes the electrolyte interface by promoting the formation of Li₂O and LiF-rich SEI that are both ionically conductive and chemically robust. The inner Mo₂C layer provides a low Li⁺ adsorption energy (-0.97 eV), a reduced surface diffusion barrier (43 meV), and a high electrical conductivity (∼10⁴ S cm^-1), consequently enabling capacitive behavior and fast intercalation kinetics at the edge plane. The biphasic layer-passivated graphite anode delivers a fast-charging capability, reaching the 80% state of charge in just 7.4 min at a current density of 6 C and retaining 78.3% of its initial capacity after 600 fast-charge cycles with a practically viable high areal capacity of 3.2 mAh cm^-2. These results represent a notable advancement over previously reported surface-engineered graphite anodes, particularly under industrially demanding conditions including high mass-loading and fast-charging.