Carbon nanotubes (CNTs) are considered to be excellent candidates for high performance electrode materials in Li ion batteries. The nanometer‐sized pore structures of CNTs can provide the hosting sites for storing large numbers of Li ions. A short diffusion distance for the Li ions may bring about a high discharge rate. The long‐cycle performance of aligned multiwalled carbon nanotubes (MWNTs) directly synthesized on stainless‐steel foil as an anode material in lithium battery is demonstrated. An increase in the specific capacity with an increase in the cycle number is observed. Starting at a value of 132 mA hg−1 in the first cycle at a current rate of 1 C, the specific capacity increased about 250% to a value of 460 mA hg−1 after 1 200 cycles. This is an unusual but a welcoming behavior for battery applications. It is found that the morphology of the MWNTs with structural and surface defects and the stainless‐steel substrate play an important role in enhancing the capacity during the cycling process.

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in battery technology have come since its fi rst demonstration, the high energy demands needed to electrify the automotive industry have not yet been met with the current technology. [ 2,3 ] One considerable bottleneck is the cathode energy density. [ 2,3 ] The lithium layered oxides utilize transition metal redox pairs for charge/ discharge compensation during lithium extraction and intercalation offering a theoretical capacity of 270 mAh g −1 for complete lithium extraction. [ 3,4 ] However, practical capacities have so far shown to be ≈200 mAh g −1 due to degradation reactions and large lattice contractions at low lithium content, limiting its capability to meet future demands. One possible cathode material is the Li-rich layered oxide compounds x Li 2 MnO 3 ⋅(1 − x )LiMO 2 (M = Ni, Mn, Co) (0.5 = < x = <1.0) that exhibit capacities over 280 mAh g −1 obtainable by the combination of the typical transition metal redox pair with the additional oxygen redox reaction as the charge compensation mechanism. [ 5 ] In this class of compounds, lithium ions can reside in both lithium layer and transition metal layer of close packed oxygen framework, typical from O3 type layered oxides like LiCoO 2 . Large irreversible capacities are often observed in these materials due to irreversible oxygen loss or side reactions stemming for the electrolyte. [ 6 ] It has been also observed using ex situ NMR (nuclear magnetic resonance) that lithium reinsertion back into the transition metal layer is little to none. [ 7 ] Several different lithium extraction/insertion sites and migration pathways are available, where lithium may be extracted from lithium or transition metal layers and lithium from octahedral coordinated sites to tetrahedral sites to form Li-Li dumbbells. [ 8 ] However, these studies have not revealed the dynamic process of lithium migration for the Li-rich material under operando electrochemical cycling conditions. Neutron scattering has several distinct advantages for battery studies: (1) The sensitivity of neutron to light elements such as lithium and oxygen is signifi cant in order to determine their position in the crystal structure; (2) Compares to the X-ray, the neutron shows larger scattering contrast between neighboring elements in the periodic table specifi cally the scattering lengths, e.g., for transition metals in this case: Ni, 10.3 fm; Mn, −3.73 fm; Co, 2.49 fm; and (3) The deep penetration capability of neutron allows simultaneous observation of the cathode and

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Development of materials and structures leading to lithium ion batteries with high energy and power density is a major requirement for catering to the power needs of present day electronic industry. Here, we report an in situ formation of a sandwiched structure involving single-walled carbon nanotube film, copper oxide, and copper during the direct synthesis of nanotube macrofilms over copper foils and their electrochemical performance in lithium ion batteries. The sandwiched structure showed a remarkably high reversible capacity of 220 mAh/g at a high cycling current of 18.6 A/g (50 C), leading to a significantly improved electrochemical performance which is extremely high compared to pure carbon nanotube and any other carbon based materials.