It is estimated that the world will need to double its energy supply by 2050. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. Comparing to conventional energy materials, carbon nanomaterials possess unique size-/surface-dependent (e.g., morphological, electrical, optical, and mechanical) properties useful for enhancing the energy-conversion and storage performances. During the past 25 years or so, therefore, considerable efforts have been made to utilize the unique properties of carbon nanomaterials, including fullerenes, carbon nanotubes, and graphene, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion (e.g., solar cells and fuel cells) and storage (e.g., supercapacitors and batteries) devices. This article reviews progress in the research and development of carbon nanomaterials during the past twenty years or so for advanced energy conversion and storage, along with some discussions on challenges and perspectives in this exciting field.

Carbon Nanomaterials for Advanced Energy Conversion and Storage

Lithium ion batteries are receiving considerable attention in applications, ranging from portable electronics to electric vehicles, due to their superior energy density over other rechargeable battery technologies. However, the societal demands for lighter, thinner, and higher capacity lithium ion batteries necessitate ongoing research for novel materials with improved properties over that of state-of-the-art. Such an effort requires a concerted development of both electrodes and electrolyte to improve battery capacity, cycle life, and charge–discharge rates while maintaining the highest degree of safety available. Carbon nanotubes (CNTs) are a candidate material for use in lithium ion batteries due to their unique set of electrochemical and mechanical properties. The incorporation of CNTs as a conductive additive at a lower weight loading than conventional carbons, like carbon black and graphite, presents a more effective strategy to establish an electrical percolation network. In addition, CNTs have the capability to be assembled into free-standing electrodes (absent of any binder or current collector) as an active lithium ion storage material or as a physical support for ultra high capacity anode materials like silicon or germanium. The measured reversible lithium ion capacities for CNT-based anodes can exceed 1000 mAh g−1 depending on experimental factors, which is a 3× improvement over conventional graphite anodes. The major advantage from utilizing free-standing CNT anodes is the removal of the copper current collectors which can translate into an increase in specific energy density by more than 50% for the overall battery design. However, a developmental effort needs to overcome current research challenges including the first cycle charge loss and paper crystallinity for free-standing CNT electrodes. Efforts to utilize pre-lithiation methods and modification of the single wall carbon nanotube bundling are expected to increase the energy density of future CNT batteries. Other progress may be achieved using open-ended structures and enriched chiral fractions of semiconducting or metallic chiralities that are potentially able to improve capacity and electrical transport in CNT-based lithium ion batteries.

Carbon nanotubes for lithium ion batteries

Carbon anode materials for lithium ion batteries

Recent advancement of nanostructured carbon for energy applications

4.3. Manganese Oxide-Based Compounds 1291 4.3.1. MnO2-Type Compounds 1291 4.3.2. Ternary Lithiated LixMnOy Compounds 1293 4.4. Vanadium Pentoxide V2O5 1298 4.4.1. V2O5 Structure 1298 4.4.2. LixV2O5 Bulk Phases 1300 4.4.3. LixV2O5 Crystallized Thin Films 1303 4.5. Titanium Oxide-Based Compounds 1305 4.5.1. Lithium Titanate Li4Ti5O12 1306 4.5.2. TiO2 Anatase 1308 5. Phospho-olivine LiFePO4 Compound 1312 6. General Conclusion 1314 7. Acknowledgments 1315 8. References 1315

Raman Microspectrometry Applied to the Study of Electrode Materials for Lithium Batteries

Electrochemical intercalation of lithium into multiwall carbon nanotubes

Electrochemical lithium intercalation into multiwall carbon nanotubes : a micro-Raman study

Electrochemical intercalation of lithium into multiwall carbon nanotubes produced by the arc-electric technique has been carried out in button cells to estimate the solid state diffusion coefficients of lithium. An extension of the Galvanostatic Intermittent Titration Technique (G.I.T.T.) of Weppner and Huggins and further developed by Honders is employed. The results are interpreted providing that the lithium species enter the nanotubes perpendicularly to their walls and thus give rise to a necklace structure as observed by Transmission Electron Microscopy (TEM). Finally, the results are compared with the data obtained for different kinds of carbon: carbon fiber, petroleum coke and graphite.

B. Simon

Papers

Electrochemical intercalation of lithium into multiwall carbon nanotubes

Electrochemical lithium intercalation into multiwall carbon nanotubes : a micro-Raman study

Determination of the chemical diffusion coefficient of lithium in multiwall carbon nanotubes