Energy storage devices that can deliver high powers have many applications, including hybrid vehicles and renewable energy. Much research has focused on increasing the power output of lithium batteries by reducing lithium-ion diffusion distances, but outputs remain far below those of electrochemical capacitors and below the levels required for many applications. Here, we report an alternative approach based on the redox reactions of functional groups on the surfaces of carbon nanotubes. Layer-by-layer techniques are used to assemble an electrode that consists of additive-free, densely packed and functionalized multiwalled carbon nanotubes. The electrode, which is several micrometres thick, can store lithium up to a reversible gravimetric capacity of 200mAhg 1 electrode while also delivering 100kWkg electrode 1 of power and providing lifetimes in excess of thousands of cycles, both of which are comparable to electrochemical capacitor electrodes. A device using the nanotube electrode as the positive electrode and lithium titanium oxide as a negative electrode had a gravimetric energy 5 times higher than conventional electrochemical capacitors and power delivery 10 times higher than conventional lithium-ion batteries.
Bibliographical noteFunding Information:
The authors acknowledge partial support from the Dupont–MIT Alliance for this project. Y.S.H. acknowledges support from the Office of Naval Research (N000140410400) and the MRSEC Program of the National Science Foundation (award no. DMR – 0819762). The assistance of E.L. Shaw in collecting XPS data, Y.T. Kim in carrying out surface functionalization of MWNTs, and Y.C. Lu in electrochemical measurements and XPS analysis is greatly appreciated. T. Kawaguchi is thanked for assistance with Li4Ti5O12 and LiNi0.5Mn1.5O4 synthesis and measurements. S.W.L. acknowledges a Samsung Scholarship from the Samsung Foundation of Culture, and B.M.G. acknowledges a graduate research fellowship from the National Science Foundation.
All Science Journal Classification (ASJC) codes
- Atomic and Molecular Physics, and Optics
- Biomedical Engineering
- Materials Science(all)
- Condensed Matter Physics
- Electrical and Electronic Engineering