Curvature-driven chlorine capture mechanism on carbon nanotube cathodes for lithium-chlorine batteries

초록

Lithium-chlorine (Li-Cl) secondary batteries have been widely investigated as a candidate for next-generation energy storage systems. The efficient capture and storage of chlorine (Cl0) generated during charging are considered key factors governing the battery performance. Herein, the atomistic mechanism of chlorine capture on carbon nanotubes (CNTs) is investigated using ab initio molecular dynamics and density functional theory calculations. It is revealed by simulations that chlorine capture is highly dependent on the CNT diameter, where Cl atoms are actively bound by smaller-diameter CNTs with higher intrinsic curvature. Charge distribution and chemical bonding analyses utilising formal DDEC6 bond orders and Bader atomic charges indicate that the Cl-C bond is predominantly covalent with a slight polarity, and it is suggested that a tetrahedral structural deformation is necessitated for its stable formation, driving the transition from a planar arrangement to the sp & sup3; hybridisation of the C atoms. Furthermore, complementary graphene models are evaluated as an auxiliary reference to corroborate this curvature mechanism, illustrating how covalent anchoring is facilitated by localised out-of-plane carbon displacements. It is suggested from this trend that the atomic-level structural engineering of carbon surfaces to manage localised strains is essential for efficient chlorine storage on the surface of carbonaceous materials.

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