A C/Ni composite was prepared via thermal decomposition of a nickel oleate complex at 700 °C, yielding disperse Ni nanocrystals with an average size of 20 nm, encapsulated by carbon nanosheets as deduced from transmission electron microscopy (TEM) images and confirmed from X-ray photoelectron spectroscopy (XPS). Furthermore, the X-ray diffraction pattern revealed a good ordering of the carbon layers, forced by the Ni encapsulation to adopt a bending structure. Considering the close interaction between the graphitized framework and the metallic nanoparticles we have studied the properties of the composite as an anode for Li-ion batteries. Compared with other nanostructured synthetic carbons, this carbon composite has a low voltage hysteresis and a modest irreversible capacity value, properties that play a significant role in its behaviour as electrodes in full cell configuration. At moderate rate values, 0.25 C, the electrode delivers an average capacity value around 723 mAh·g^-1 on cycling, among the highest values so far reported for this carbon type. At higher rate values, 1 C, the average capacity values delivered by the cell on cycling decrease, around 205 mAh·g^-1, but it maintains good capacity retention, a coulombic efficiency close to 100% after the first cycles and recovery of the capacity values when the rate is restored from 3 to 0.1 C.

Graphene nanosheets are a promising scaffold to accommodate S for achieving high performance Li/S battery. Nanosheet activation is used as a viable strategy to induce a micropore system and further improve the battery performance. Accordingly, chemical activation methods dominate despite the need of multiple stages, which slow down the process in addition to making them tiresome. Here, a three-dimensional (3D) N-doped graphene specimen was physically activated with CO₂, a clean and single step process, and used for the preparation of a sulfur composite (A-3DNG/S). The A-3DNG/S composite exhibited outstanding electrochemical properties such as an excellent rate capability (1, 000 mAh·g^-1 at 2C), high reversible capacity and cycling stability (average capacity ~ 800 mAh·g^-1 at 1C after 200 cycles), values which exceed those measured in chemically activated graphene. Therefore, these results support the use of physical activation as a simple and efficient alternative to improve the performance of carbons as an S host for high-performance Li-S batteries.

A micro- and mesoporous carbon obtained from cherry pit waste and activated with H₃PO₄ acid has been studied as the sulfur host for Li/S batteries. The carbon has a high specific surface area of 1, 662 m²·g^–1 (SBET) and micropore and mesopore volumes of 0.57 and 0.40 cm³·g^–1, respectively. The S/C composite, with a sulfur content of 57% deposited by the disproportionate reaction of a S₂O₃^2- solution in an acid medium without an additional heating step above the S melting point, delivers an initial specific capacity of 1, 148 mAh·g^–1 at a current of C/16. It also has a high capacity retention of 915 mAh·g^–1 after 100 cycles and a Coulombic efficiency close to 100%. The good performance of the composite was also observed under higher current rates and long-term cycling tests. The capacities delivered by the cell after 200 cycles were 707 and 410 mAh·g^–1 at C/2 and 1C (1C = 1, 675 mA·g^–1), respectively, maintaining the high Coulombic efficiency. The overall electrochemical response of this carbon as the sulfur matrix is among the best reported so far among the other biomass-derived carbons, probably because of the micro- and mesopore system formed upon activation.