Guangmin Zhou

Graphene Anchored with Co3O4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Graphene Anchored with Co 3 O 4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Progress in flexible lithium batteries and future prospects

With the advent of flexible electronics, flexible lithium-ion batteries have attracted great attention as a promising power source in the emerging field of flexible and wearable electronic devices such as roll-up displays, touch screens, conformable active radio-frequency identification tags, wearable sensors and implantable medical devices. In this review, we summarize the recent research progress of flexible lithium-ion batteries, with special emphasis on electrode material selectivity and battery structural design. We begin with a brief introduction of flexible lithium-ion batteries and the current development of flexible solid-state electrolytes for applications in this field. This is followed by a detailed overview of the recent progress on flexible electrode materials based on carbon nanotubes, graphene, carbon cloth, conductive paper (cellulose), textiles and some other low-dimensional nanostructured materials. Then recently proposed prototypes of flexible cable/wire type, transparent and stretchable lithium-ion batteries are highlighted. The latest advances in the exploration of other flexible battery systems such as lithium–sulfur, Zn–C (MnO2) and sodium-ion batteries, as well as related electrode materials are included. Finally, the prospects and challenges toward the practical uses of flexible lithium-ion batteries in electronic devices are discussed.

Oxygen Bridges between NiO Nanosheets and Graphene for Improvement of Lithium Storage

Graphene has been widely used to dramatically improve the capacity, rate capability, and cycling performance of nearly any electrode material for batteries. However, the binding between graphene and these electrode materials has not been clearly elucidated. Here we report oxygen bridges between graphene with oxygen functional groups and NiO from analysis by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy and confirm the conformation of oxygen bridges by the first-principles calculations. We found that NiO nanosheets (NiO NSs) are bonded strongly to graphene through oxygen bridges. The oxygen bridges mainly originate from the pinning of hydroxyl/epoxy groups from graphene on the Ni atoms of NiO NSs. The calculated adsorption energies (1.37 and 1.84 eV for graphene with hydroxyl and epoxy) of a Ni adatom on oxygenated graphene by binding with oxygen are comparable with that on graphene (1.26 eV). However, the calculated diffusion barriers of the Ni adatom on the oxygenated graphene surface (2.23 and 1.69 eV for graphene with hydroxyl and epoxy) are much larger than that on the graphene (0.19 eV). Therefore, the NiO NS is anchored strongly on the graphene through a C-O-Ni bridge, which allows a high reversible capacity and excellent rate performance. The easy binding/difficult dissociating characteristic of Ni adatoms on the oxygenated graphene facilitates fast electron hopping from graphene to NiO and thus the reversible lithiation and delithiation of NiO. We believe that the understanding of this oxygen bridge between graphene and NiO will lead to the development of other high-performance electrode materials.

A Graphene–Pure‐Sulfur Sandwich Structure for Ultrafast, Long‐Life Lithium–Sulfur Batteries

Lithium-sulfur (Li–S) batteries have high specific capacities and are considered as next-generation batteries for large-scale energy storage and electric vehicles. However, rapid capacity fade and low sulfur utilisation inhibit their use. We designed a unique sandwich structure with pure sulfur between two graphene membranes, which are continuously produced over a large area, as a very simple but effective approach for the fabrication of Li–S batteries with ultrafast charge/discharge rates and long-life. One membrane was used as a graphene current collector (GCC) to replace the conventional aluminium foil current collector, and sulfur was coated onto this membrane as the active material. The other membrane was coated onto a conventional polymer separator (G-separator). This electrode showed a high specific capacity of 1340 mA h g−1 at 300 mA g−1, a Coulombic efficiency approaching 100%, excellent high-rate performance and long cyclic stability. The GCC and G-separator not only effectively reduce the internal resistance of the sulfur cathode but also function as buffer layers to trap/immobilise and reuse the dissolved lithium polysulfides. Furthermore, for the first time, three-dimensional X-ray microtomography was used to investigate sulfur diffusion during electrochemical charge/discharge.

Fibrous Hybrid of Graphene and Sulfur Nanocrystals for High-Performance Lithium–Sulfur Batteries

Graphene-sulfur (G-S) hybrid materials with sulfur nanocrystals anchored on interconnected fibrous graphene are obtained by a facile one-pot strategy using a sulfur/carbon disulfide/alcohol mixed solution. The reduction of graphene oxide and the formation/binding of sulfur nanocrystals were integrated. The G-S hybrids exhibit a highly porous network structure constructed by fibrous graphene, many electrically conducting pathways, and easily tunable sulfur content, which can be cut and pressed into pellets to be directly used as lithium-sulfur battery cathodes without using a metal current-collector, binder, and conductive additive. The porous network and sulfur nanocrystals enable rapid ion transport and short Li(+) diffusion distance, the interconnected fibrous graphene provides highly conductive electron transport pathways, and the oxygen-containing (mainly hydroxyl/epoxide) groups show strong binding with polysulfides, preventing their dissolution into the electrolyte based on first-principles calculations. As a result, the G-S hybrids show a high capacity, an excellent high-rate performance, and a long life over 100 cycles. These results demonstrate the great potential of this unique hybrid structure as cathodes for high-performance lithium-sulfur batteries.

A Flexible Sulfur-Graphene-Polypropylene Separator Integrated Electrode for Advanced Li-S Batteries

A flexible Li-S battery based on an integrated structure of sulfur and graphene on a separator is developed. The internal graphene current collector offers a continuous conductive pathway, a modified interface with sulfur, and a good barrier to and an effective reservoir for dissolved polysulfides, consequently improving the capacity and cyclic life of the Li-S battery.

Balancing surface adsorption and diffusion of lithium-polysulfides on nonconductive oxides for lithium-sulfur battery design

Lithium–sulfur batteries have attracted attention due to their six-fold specific energy compared with conventional lithium-ion batteries. Dissolution of lithium polysulfides, volume expansion of sulfur and uncontrollable deposition of lithium sulfide are three of the main challenges for this technology. State-of-the-art sulfur cathodes based on metal-oxide nanostructures can suppress the shuttle-effect and enable controlled lithium sulfide deposition. However, a clear mechanistic understanding and corresponding selection criteria for the oxides are still lacking. Herein, various nonconductive metal-oxide nanoparticle-decorated carbon flakes are synthesized via a facile biotemplating method. The cathodes based on magnesium oxide, cerium oxide and lanthanum oxide show enhanced cycling performance. Adsorption experiments and theoretical calculations reveal that polysulfide capture by the oxides is via monolayered chemisorption. Moreover, we show that better surface diffusion leads to higher deposition efficiency of sulfide species on electrodes. Hence, oxide selection is proposed to balance optimization between sulfide-adsorption and diffusion on the oxides.

A microporous–mesoporous carbon with graphitic structure for a high-rate stable sulfur cathode in carbonate solvent-based Li–S batteries

A microporous-mesoporous carbon with graphitic structure was developed as a matrix for the sulfur cathode of a Li-S cell using a mixed carbonate electrolyte. Sulfur was selectively introduced into the carbon micropores by a melt adsorption-solvent extraction strategy. The micropores act as solvent-restricted reactors for sulfur lithiation that promise long cycle stability. The mesopores remain unfilled and provide an ion migration pathway, while the graphitic structure contributes significantly to low-resistance electron transfer. The selective distribution of sulfur in micropores was characterized by X-ray photoelectron spectroscopy (XPS), nitrogen cryosorption analysis, transmission electron microscopy (TEM), X-ray powder diffraction and Raman spectroscopy. The high-rate stable lithiation-delithiation of the carbon-sulfur cathode was evaluated using galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. The cathode is able to operate reversibly over 800 cycles with a 1.8 C discharge-recharge rate. This integration of a micropore reactor, a mesopore ion reservoir, and a graphitic electron conductor represents a generalized strategy to be adopted in research on advanced sulfur cathodes.

Scalable Clean Exfoliation of High-Quality Few-Layer Black Phosphorus for a Flexible Lithium Ion Battery.

Few-layer black phosphorus (BP) nanosheets that are clean and of high quality, are efficiently produced by exfoliating bulk BP crystals, which are prepared by a scalable gas-phase catalytic transformation method in water. They are stable enough in water for further processing and applications. As an example, these BP nanosheets are combined with graphene to give high-performance flexible lithium-ion batteries.