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In this paper, we report a facile ultrasonic method to synthesize well-dispersed CoO quantum dots (3~8 nm) on graphene nanosheets at room temperature by employing Co4(CO)12 as cobalt precursor. The prepared CoO/graphene composites displayed high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity (1592 mAh g-1 after 50 cycles), high coulombic efficiency (over 95%), excellent cycling stability and high rate capability (1008 mAh g-1 with a total retention of 77.6% after 50 cycles at a current density of 1000 mA g-1, dramatically raised from the initial 50 mA g-1). The extraordinary performance arises from the structure advantages of the composites: the nanosized CoO quantum dots with high dispersity on conductive graphene substrates supply not only large quantity of accessible active sites for lithium ion insertion, but also good conductivity and short diffusion length for lithium ions, which are beneficial for high capacity and rate capability. Meanwhile, the isolated CoO quantum dots anchored tightly on the graphene nanosheets can effectively circumvent the volume expansion/contraction associating with lithium insertion/extraction during discharge/charge processes, which is good for high capacity as well as cycling stability. Moreover, regarding the anomalous behavior of capacity increase with cycles (activation effect) observed, we proposed a tentative hypothesis stressing the competition between the conductivity increase and the amorphorization of the composite electrodes during cycling in determining the trends of the capacity, in the hope to gain a fuller understanding of the inner working of the novel nanostructured electrodes based lithium-ion batteries.
This article was published in the following journal.
Name: ACS nano
Many methods have been reported for synthesizing graphene oxide (GO) and graphene oxide quantum dots (GOQDs) where a tedious operational procedure and long reaction time are generally required. Herein...
We report here on the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15-35 nm, these quantum dots maintain strong visible ligh...
The deficiencies of the recently reported improved Hummers method for the synthesis of graphene oxide (GO), such as high reaction temperature (60°C) and long reaction time (10h), were successfully so...
Mesoporous graphite encapsulated Fe3C/Fe nanosheet composites have been synthesized by a facile template free method using ferric nitrate, glycine and glucose as raw materials. X-ray diffraction, tran...
High quality graphene oxide (GO) with low layer number (less than five layers) and large inter-layer space was produced via a new and efficient method using environmentally friendly, fast and economic...
The Composites and Urinary Bisphenol-A Study (CUBS) is a clinical study of dental composite for its effects on urinary bisphenol-A levels. The study will enroll approximately 139 children ...
The purpose of the study is to evaluate the safety and efficacy of the composite Nail - the Quantum interlocking intramedullary nailing system in the reduction of humeral fractures.
The purpose of this clinical study was to compare the effectiveness of passive ultrasonic irrigation with that of traditional syringe irrigation on the removal of bacteria and endotoxin (l...
Percutaneous nephrolithotomy (PNL), in conjunction with intracorporeal lithotripsy, allows for the rapid removal of any kidney stone regardless of size. Currently, the choice of intracorp...
This study is planned to compare the results of ultrasonic and Orbscan pachymetry in corneal haze not related to surgery. Corneal haze is graded with slit-lamp by a single examiner. Ultras...
Nanometer sized fragments (the dots) of semiconductor crystalline material which emit PHOTONS. The wavelength is based on the quantum confinement size of the dot. They are brighter and more persistent than organic chemical INDICATORS. They can be embedded in MICROBEADS for high throughput ANALYTICAL CHEMISTRY.
A subfield of acoustics dealing in the radio frequency range higher than acoustic SOUND waves (approximately above 20 kilohertz). Ultrasonic radiation is used therapeutically (DIATHERMY and ULTRASONIC THERAPY) to generate HEAT and to selectively destroy tissues. It is also used in diagnostics, for example, ULTRASONOGRAPHY; ECHOENCEPHALOGRAPHY; and ECHOCARDIOGRAPHY, to visually display echoes received from irradiated tissues.
The theory that the radiation and absorption of energy take place in definite quantities called quanta (E) which vary in size and are defined by the equation E=hv in which h is Planck's constant and v is the frequency of the radiation.
Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues using a transducer placed in the esophagus.
Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.