Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage

Unusual pseudocapacitive lithium-ion storage on defective Co3O4nanosheets

Secondary lithium-ion batteries are restricted in large-scale applications including power grids and long driving electric vehicles owing to the low specific capacity of conventional intercalation anodes possessing sluggish Li-ion diffusion kinetics. Herein, we demonstrate an unusual pseudocapacitive lithium-ion storage on defective Co₃O₄nanosheet anodes for high-performance rechargeable batteries. Cobalt-oxide nanosheets presented here composed of various defects including vacancies, dislocations and grain boundaries. Unique 2D holey microstructure enabled efficient charge transport as well as provided room for volume expansions associated with lithiation-delithiation process. These defective anodes exhibited outstanding pseudocapacitance (up to 87%), reversible capacities (1490 mAh g^-1@ 25 mA g^-1), rate capability (592 mAh g^-1@ 30 A g^-1), stable cycling (85% after 500 cycles @ 1 A g^-1) and columbic efficiency (∼100%). Exceptional Li-ion storage phenomena in defective Co₃O₄nanosheets is accredited to the pseudocapacitive nature of conversion reaction resulting from ultrafast Li-ion diffusion through various crystal defects. The demonstrated approach of defect-induced pseudocapacitance can also be protracted for various low-cost and/or eco-friendly transition metal-oxides for next-generation rechargeable batteries.

Rational Functionalization Towards Redox-Active TEMPO Stable Free-Radical-Hydrochar Composites

Although both stable free organic radicals and biomass-derived hydrochars have emerged as appealing, green, multifunctional materials, their association has not been explored. In this study, strength is found to lie in their union, which primarily leads to stable redox-active free-radical-hydrochar composites that can generate unexpected opportunities for the development of advanced metal-free sustainable materials. The composites are obtained by a straightforward green one-pot hydrothermal procedure. The loading of stable free radicals of nitroxide type and their localization is engineered by the nature of the carbohydrate and the reaction status; vigorous reaction parameters promote faster nucleation and growth kinetics of the hydrochar products, leading to a covalent immobilization of redox species on the surface of the carbonaceous microspherical aggregates. The nitroxide free-radical-hydrochar materials demonstrate enhancements in terms of both electrocatalytic activity and capacitive features.

A g-C3N4 self-templated preparation of N-doped carbon nanosheets@Co-Co3O4/Carbon nanotubes as high-rate lithium-ion batteries' anode materials

A novel N-doped graphene-like carbon nanosheets (CNs) and carbon nanotubes (CNTs)-encapsulated Co-Co₃O₄ nanoparticles (NPs) (CN@Co-Co₃O₄/CNTs) were synthesized successfully by a simple hydrothermal and annealing method with graphite carbon nitride (g-C₃N₄) as self-template. By annealing Co²⁺/g-C₃N₄ under N₂ atmosphere, g-C₃N₄ was transformed into CN/CNTs, and Co²⁺ was reduced into CoNPs which were embedded in CNs. Further annealing in air, a shell of Co₃O₄ was formed around CoNPs. The amount of CNs, CNTs, and CoNPs can be adjusted by changing the ratio of Co²⁺ in Co²⁺/g-C₃N₄. The graphene-like CNs provided a large number of active sites and a large specific surface area for loading lots of small CoNPs uniformly. The CNTs with a diameter of 100 nm could not only improve the conductivity but also provide a buffer space for the aggregation and volume expansion of Co₃O₄. CNTs also enlarged the interlayer distance of CNs, which prevented the re-stacking of CNs and provided great convince for the intercalation and de-intercalation of Li⁺. When applied for anode material of lithium-ion batteries, CN@Co-Co₃O₄/CNTs exhibited a high discharge capacity of 460.0 mAh g^-1 at 5000 mA g^-1 after 300 cycles with a Coulombic efficiency of 98% and excellent higher-rate capacity (401.0 mAh g^-1 at 2000 mA g^-1 and 329.0 mAh g^-1 at 5000 mA g^-1).

Insight into the Superior Lithium Storage Properties of Ultrafine CoO Nanoparticles Confined in a 3 D Bimodal Ordered Mesoporous Carbon CMK-9 Anode

Ultrafine CoO particles immobilized into the mesopores of three-dimensional cubic bimodal ordered mesoporous carbon CMK-9 is successfully prepared by using a combination of nanocasting and wet-impregnation methods. It is found that the cubic bimodal interconnected mesoporous framework of CMK-9 plays a crucial role in achieving the excellent electrochemical performances by assisting the rapid mass and charge transfer. Among the prepared nanocomposites, CoO(10)@CMK-9 delivers a discharge capacity of 830 mAh g^-1 after 200 cycles at a current density of 100 mA g^-1 in lithium-ion batteries. At a higher current density of 1000 mA g^-1 , the anode presents an outstanding discharge capacity of 636 mAh g^-1 after 200 cycles. In sodium-ion batteries, the anode provides a discharge capacity of 296 mAh g^-1 after 250 cycles at a current density of 100 mA g^-1 . The remarkable performances of CoO(10)@CMK-9 demonstrate the promising potentials of the nanocomposite as the anode for rechargeable batteries.