Excellent electrochemical properties of graphene-like carbon obtained from acid-treating natural black talc as Li-ion battery anode

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g^-1 to 450 F∙g^-1 at the current density of 1 A∙g^-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg^-1 at the specific power of 1520 W∙kg^-1.

Fluorination of MXene by Elemental F2 as Electrode Material for Lithium-Ion Batteries

The transformation of MXene sheets into TiOF₂ 2D sheets with superior electrochemical performance was developed. MXene synthesized from Ti₃ AlC₂ was fluorinated for 3, 6, and 24 h, respectively, by means of a direct fluorination process. Exposure of MXene powder to elemental fluorine for 3 h induced the formation of CF₂ groups and TiF₃ on the surface, which have beneficial effects on the electrochemical performance. X-ray photoelectron spectroscopy suggested that after fluorinating the MXene sample for 6 h Ti²⁺ and Ti³⁺ were not present on the surface but only Ti⁴⁺ , indicating the formation of TiOF₂ . XRD indicated that TiOF₂ was present after fluorinating for 3 h, and after 24 h the MXene had transformed to TiOF₂ with minor impurities remaining, maintaining its 2D layer morphology. The 24 h fluorinated sample with its TiOF₂ phase showed superior capacity that increased with cycle number. It also had a better rate capability than non-2D-layered TiOF₂ , indicating the advantage of the 2D-layered morphology derived from the parent MXene phase.