High-energy-density lithium-ion battery using a carbon-nanotube-Si composite anode and a compositionally graded Li[Ni0.85Co0.05Mn0.10]O2 cathodeElectronic supplementary information (ESI) available. See DOI: 10.1039/c6ee01134a

A fully operational practical Li-rechargeable battery system delivering unprecedented high energy density with excellent cycle life was proposed using the state-of-the-art cathode and anode technologies. Based on the simple ball-milling process, a carbon nanotube (CNT)-Si composite anode with extremely stable long-term cycling, while providing a discharge capacity of 2364 mA h g −1 at a tap density of 1.103 g cm −3 , was developed. For the cathode, a two-sloped full concentration gradient (TSFCG) Li[Ni 0.85 Co 0.05 Mn 0.10 ]O 2 cathode, designed to obtain maximum possible discharge capacity by having a Ni-enriched core and to simultaneously ensure high chemical and thermal stability by having an outer Mn-enriched layer, yielded a discharge capacity of 221 mA h g −1 . Integrating the CNT-Si composite and the TSFCG cathode in a full cell configuration, the full cell generated an energy density of 350 W h kg −1 with excellent capacity retention for 500 cycles at 1 C rate, satisfying the energy density limit imposed by the drive range requirement for EVs. The proposed battery system satisfied the demands for energy storage for vehicle applications in terms of energy density, power and cycle life. A Li-rechargeable battery system based on state-of-the-art cathode and anode technologies demonstrated high energy density, meeting demands for vehicle application.