CuFeS2 Quantum Dots Anchored in Carbon Frame: Superior Lithium Storage Performance and the Study of Electrochemical Mechanism.

Herein, we report a simple and quick synthetic route to prepare the pure CuFeS2 quantum dots (QDs) @C composites with the unique structure of CuFeS2 QDs encapsulated in the carbon frame. When tested as anode materials for the lithium ion battery, the CuFeS2 QDs @C composites based electrodes exhibit excellent electrochemical performances. When charge-discharge occurred with a current density of 0.5 A g-1, the electrodes exhibit a high reversible capacity (760 mA h g-1) for as long as 700 cycles, which indicates the superior cycling life. Detailed investigations of the morphological and structural changes of CuFeS2 QDs by ex situ XRD, ex situ Raman, and ex situ TEM reveal an interesting electrochemical reaction mechanism, a hybrid of a lithium-copper iron sulfide battery and lithium-sulfur battery. The direct observation of orthorhombic FeS2 by HRTEM and the existence of Li2FeS2 detected by Raman support our assertion. We believe such an electrochemical mechanism would attract more attention to the CuFeS2 nanomaterials as lithium ion battery anode materials. The excellent electrochemical properties would be derived from the unique structure, which include CuFeS2 QDs encapsulated in the carbon frame.

Fast and Universal Approach to Encapsulating Transition Bimetal Oxide Nanoparticles in Amorphous Carbon Nanotubes under an Atmospheric Environment Based on the Marangoni Effect.

Transition metal oxide nanoparticles capsuled in amorphous carbon nanotubes (ACNTs) are attractive anode materials of lithium-ion batteries (LIBs). Here, we first designed a fast and universal method with a hydromechanics conception which is called Marangoni flow to fabricate transition bimetal oxides (TBOs) in the ACNT composite with a better electrochemistry performance. Marangoni flows can produce a liquid column with several centimeters of height in a tube with one side immersed in the liquid. The key point to induce a Marangoni flow is to make a gradient of the surface tension between the surface and the inside of the solution. With our research, we control the gradient of the surface tension by controlling the viscosity of a solution. To show how our method could be generally used, we synthesize two anode materials such as (a) CoFe2O4@ACNTs, and (b) NiFe2O4@ACNTs. All of these have a similar morphology which is ∼20 µm length with a diameter of 80-100 nm for the ACNTs, and the particles (inside the ACNTs) are smaller than 5 nm. In particular, there are amorphous carbons between the nanoparticles. All of the composite materials showed an outstanding electrochemistry performance which includes a high capacity and cycling stability so that after 600 cycles the capacity changed by less than 3%.

Self-Climbed Amorphous Carbon Nanotubes Filled with Transition Metal Oxide Nanoparticles for Large Rate and Long Lifespan Anode Materials in Lithium Ion Batteries.

A composed material of amorphous carbon nanotubes (ACNTs) and encapsulated transition metal oxide (TMOs) nanoparticles was prepared by a common thermophysics effect, which is named the Marangoni effect, and a simple anneal process. The prepared ropy solution would form a Marangoni convection and climb into the channel of anodic aluminum oxide template (AAO) spontaneously. The ingenious design of the preparation method determined a distinctive structure of TMOs nanoparticles with a size of ∼5 nm and amorphous carbon coated outside full in the ACNTs. Here we prepared the ferric oxide (Fe2O3) nanoparticles and Fe2O3 mixed with manganic oxide (Fe2O3&Mn2O3) nanoparticles encapsulated in ACNTs as two anode materials of lithium ion batteries' the TMOs-filled ACNTs presented an evolutionary electrochemical performance in some respects of highly reversible capacity and excellent cycling stability (880 mA h g-1 after 150 cycles).