Impact of Surface Modification on the Lithium, Sodium, and Potassium Intercalation Efficiency and Capacity of Few-Layer Graphene Electrodes.

In a conventional lithium-ion battery (LIB), graphite forms the negative electrode or anode. Although Na is considered one of the most attractive alternatives to Li, achieving reversible Na intercalation within graphitic materials under ambient conditions remains a challenge. More efficient carbonaceous anode materials are desired for developing advanced LIBs and battery technologies. We hypothesized that two-dimensional materials with distinct surface electronic properties create conditions for ion insertion into few-layer graphene (FLG) anodes. This is because modification of the electrode/electrolyte interface potentially modifies the energetics and mechanisms of ion intercalation in the thin bulk of FLG. Through first-principles calculations; we show that the electronic, structural, and thermodynamic properties of FLG anodes can be fine-tuned by a covalent heteroatom substitution at the uppermost layer of the FLG electrode, or by interfacing FLG with a single-side fluorinated graphene or a Janus-type hydrofluorographene monolayer. When suitably interfaced with the 2D surface modifier, FLG exhibits favorable thermodynamics for the Li, Na, and K intercalation. Remarkably, the reversible binding of Na within carbon layers becomes thermodynamically allowed, and a large storage capacity can be achieved for the Na intercalated modified FLG anodes. The origin of charge-transfer promoted electronic tunability of modified FLGs is rationalized by various theoretical methods.