Zhaohui Chen

Bio: Zhaohui Chen is an academic researcher. The author has contributed to research in topics: Carbon & Specific energy. The author has an hindex of 1, co-authored 1 publications receiving 749 citations.

Reducing Carbon in LiFePO4 / C Composite Electrodes to Maximize Specific Energy, Volumetric Energy, and Tap Density

Abstract: Efforts were made to synthesize LiFePO 4 /C composites showing good rale capability and high energy density while attempting to minimize the amount of carbon in the composite. First, three carbon-coated samples, one coated with carbon after the synthesis of pure LiFePO 4 , one synthesized with sugar added before the heating steps, and one synthesized with sugar added before heating and subsequently coated with carbon, were studied. The resulting carbon contents for these samples arc 2.7, 3.5, and 6.2 wt %, respectively. Electrochemical tests showed that the latter two samples had comparable rate capabilities to the LiFePO 4 /C composite (15 wt % carbon) recently reported by Huang et al. We believe the synthesis of LiFePO 4 with sugar added before heating is the best method because it gives particles having uniform small size that are covered by carbon. Further studies of samples made by this method show that a very small percentage of carbon, even less than 1 wt %, causes a significant increase in rate capability, hut unfortunately, a dramatic decrease in tap density. To make LiFePO 4 /C composites having good rate capability, high energy density, and high tap density, the carbon content and method for coating carbon onto the LiFePO 4 particles must he given careful attention. However, based on the studies reported here, we are not certain that all desired parameters can he simultaneously achieved, and this may limit the usefulness of LiFePO 4 in some practical applications.

Lithium Batteries and Cathode Materials

Abstract: In the previous paper Ralph Brodd and Martin Winter described the different kinds of batteries and fuel cells. In this paper I will describe lithium batteries in more detail, building an overall foundation for the papers that follow which describe specific components in some depth and usually with an emphasis on the materials behavior. The lithium battery industry is undergoing rapid expansion, now representing the largest segment of the portable battery industry and dominating the computer, cell phone, and camera power source industry. However, the present secondary batteries use expensive components, which are not in sufficient supply to allow the industry to grow at the same rate in the next decade. Moreover, the safety of the system is questionable for the large-scale batteries needed for hybrid electric vehicles (HEV). Another battery need is for a high-power system that can be used for power tools, where only the environmentally hazardous Ni/ Cd battery presently meets the requirements. A battery is a transducer that converts chemical energy into electrical energy and vice versa. It contains an anode, a cathode, and an electrolyte. The anode, in the case of a lithium battery, is the source of lithium ions. The cathode is the sink for the lithium ions and is chosen to optimize a number of parameters, discussed below. The electrolyte provides for the separation of ionic transport and electronic transport, and in a perfect battery the lithium ion transport number will be unity in the electrolyte. The cell potential is determined by the difference between the chemical potential of the lithium in the anode and cathode, ∆G ) -EF. As noted above, the lithium ions flow through the electrolyte whereas the electrons generated from the reaction, Li ) Li+ + e-, go through the external circuit to do work. Thus, the electrode system must allow for the flow of both lithium ions and electrons. That is, it must be both a good ionic conductor and an electronic conductor. As discussed below, many electrochemically active materials are not good electronic conductors, so it is necessary to add an electronically conductive material such as carbon * To whom correspondence should be addressed. Phone and fax: (607) 777-4623. E-mail: stanwhit@binghamton.edu. 4271 Chem. Rev. 2004, 104, 4271−4301

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Abstract: We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

Challenges Facing Lithium Batteries and Electrical Double‐Layer Capacitors

Abstract: Energy-storage technologies, including electrical double-layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double-layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double-layer capacitors.

Self-assembled TiO2-Graphene Hybrid Nanostructures for Enhanced Li-ion Insertion

Abstract: We used anionic sulfate surfactants to assist the stabilization of graphene in aqueous solutions and facilitate the self-assembly of in situ grown nanocrystalline TiO2, rutile and anatase, with graphene. These nanostructured TiO2-graphene hybrid materials were used for investigation of Li-ion insertion properties. The hybrid materials showed significantly enhanced Li-ion insertion/extraction in TiO2. The specific capacity was more than doubled at high charge rates, as compared with the pure TiO2 phase. The improved capacity at high charge-discharge rate may be attributed to increased electrode conductivity in the presence of a percolated graphene network embedded into the metal oxide electrodes.