rapidly growing topic in the sulfur/carbon cathodes. [15][16][17][24][25][26][27][28][29][30] Although the porous structures of HCS favor the sulfur loading and electrolyte transport, the interaction between the nonpolar carbon shell and polar polysulfi de intermediates is not enough to suppress the dissolution of polysulfi de intermediates. More importantly, when used as the electrode materials, the large inner cavity of HCS usually results in the relatively low volumetric energy densities. Such an inherent drawback of HCS is undesirable for practical applications. [ 31,32 ] Following the development trend of the sulfur/carbon cathodes, the design of HCS should focus on the following aspects: (i) ultrahigh surface area to maximize the electrolyte permeation and interaction between HCS and sulfur/polysulfi des; (ii) heteroatom doping (e.g., nitrogen) to enhance the electrical conductivity of HCS and chemisorption between HCS and polysulfi de intermediates; (iii) shape optimization to improve conductive pathway and volumetric energy densities; (iv) facile and low-cost methodology to facilitate the practical applications.As a special class of hollow structures, bowl-like structure is an ideal methodology to increase the packing density of HCS. When used as the electrode materials, hollow carbon bowls (HCB) stacked within each other are also benefi cial to forming a favorable conductive pathway. However, there has been little success in using HCB to directly achieve high-performance energy storage components. [ 33,34 ] Recent research has indicated the unique biomedical applications of HCB. [35][36][37] Unfortunately, the reported HCB usually exhibit a low specifi c surface area (about 700-1000 m 2 g −1 ), which is much lower than HCS reported previously. [15][16][17][24][25][26][27][28][29] Since the utilization of chemical bonding between heteroatom doped carbon host and polysulfi de intermediates has been recently demonstrated as an effective way to further reduce the dissolution of polysulfi de intermediates, [38][39][40][41][42][43][44] the reported HCB with pristine carbon shell is diffi cult to meet the requirement for bonding polysulfi de intermediates. Therefore, the desirable HCB should not only inherit the advantages of HCS but also fulfi ll all above requirements for S/HCS cathodes. From the point of structure design, N-doped HCB (N-HCB) with high specifi c surface areas would open new opportunities for the sulfur/carbon cathodes. However, a new and effective methodology is the necessary prerequisite to the targeted N-HCB.Here, we present a facile route to synthesize N-doped HCS (N-HCS) and its N-HCB counterparts. Since the structure parameters of HCS can be precisely controlled by the prefabricated templates, hard-templating method is one of the most important routes to synthesize HCS. [45][46][47][48][49][50][51][52] From early Rechargeable lithium-sulfur (Li-S) batteries with the theoretical specifi c energy (≈2600 Wh kg −1 ) have attracted considerable attention due to its favorable prospect for futu...

Although electron spins in III-V semiconductor quantum dots have shown great promise as qubits, hyperfine decoherence remains a major challenge in these materials. Group IV semiconductors possess dominant nuclear species that are spinless, allowing qubit coherence times up to 2 s. In carbon nanotubes, where the spin-orbit interaction allows for all-electrical qubit manipulation, theoretical predictions of the coherence time vary by at least six orders of magnitude and range up to 10 s or more. Here, we realize a qubit encoded in two nanotube valley-spin states, with coherent manipulation via electrically driven spin resonance mediated by a bend in the nanotube. Readout uses Pauli blockade leakage current through a double quantum dot. Arbitrary qubit rotations are demonstrated and the coherence time is measured for the first time via Hahn echo, allowing comparison with theoretical predictions. The coherence time is found to be ∼65 ns, probably limited by electrical noise. This shows that, even with low nuclear spin abundance, coherence can be strongly degraded if the qubit states are coupled to electric fields.

The manipulation and readout of spin qubits in quantum dots have been successfully achieved using Pauli blockade, which forbids transitions between spin-triplet and spin-singlet states 1 . Compared with spin qubits realized in III-V materials 2-5 , group IV materials such as silicon and carbon are attractive for this application because of their low decoherence rates (nuclei with zero spins) 6,7 . However, valley degeneracies in the electronic band structure of these materials combined with Coulomb interactions reduce the energy difference between the blocked and unblocked states 8-10 , significantly weakening the selection rules for Pauli blockade. Recent demonstrations of spin qubits in silicon devices have required strain and spatial confinement to lift the valley degeneracy 7 . In carbon nanotubes, Pauli blockade can be observed by lifting valley degeneracy through disorder 11-14 , but this makes the confinement potential difficult to control. To achieve Pauli blockade in low-disorder nanotubes, quantum dots have to be made ultrasmall 8,9 , which is incompatible with conventional fabrication methods. Here, we exploit the bandgap of low-disorder nanotubes to demonstrate robust Pauli blockade based on both valley and spin selection rules. We use a novel stamping technique to create a bent nanotube, in which single-electron spin resonance is detected using the blockade. Our results indicate the feasibility of valley-spin qubits in carbon nanotubes.Two quantum dots containing two electrons in total can be tuned to the transition between two charge states-(1,1) with one electron in each dot and (2,0) with both electrons in the first dot. The transition involves tunnelling of the electron from the second to the first dot. Even when this transition is allowed energetically, it can be blocked by selection rules 15 . In III-V quantum dots (for example, GaAs or InAs), a blockade can be set up between a (1,1)-triplet state and a (2,0)-singlet state. Important for a robust blockade is the condition that the (2,0)-triplet state be high in energy, because this excited state is not blocked by selection rules. The crucial energy difference, E ST , between the (2,0)-triplet and (2,0)-singlet states can be several meVs in III-V materials 15 . In carbon nanotubes the two-electron states are grouped into singletlike and triplet-like states. The energy difference, E ′ ST , between the singlet-like and triplet-like states can be one or two orders of magnitude smaller than in III-V materials. There are two main reasons for this: additional levels from valley degeneracy and stronger Coulomb interactions in the carbon nanotubes 8-10 . These complications have prevented a consistent observation of Pauli blockade and, as a result, spin manipulation has not been realized. We avoid these complications by using the large level spacing from the bandgap of the nanotube and demonstrate a robust valleyspin blockade. Here, we discuss our novel fabrication method for obtaining ultraclean quantum dots controlled by a set of gate electrodes with ...

The performance degradation of high-sulfur-loading cathodes caused by the migration of polysulfide intermediates from cathode to anode seriously impedes the practical use of lithium-sulfur batteries. This work presents a lightweight, porous nitrogen-doped carbon nanosheet modified commercial separator with a high polysulfide-entrapping ability, which can significantly improve the capacities, rate capabilities, and cycling stability of the high-sulfur-loading cathodes made of commercial carbon materials. This study provides useful insight into the design of low-cost and high-energy-density Li-S batteries.

Lithium–sulfur (Li–S) batteries are considered as one of the most potential next‐generation rechargeable batteries due to their high theoretical energy density. However, some critical issues, such as low capacity, poor cycling stability, and safety concerns, must be solved before Li–S batteries can be used practically. During the past decade, tremendous efforts have been devoted to the design and synthesis of electrode materials. Benefiting from their tunable structural parameters, hollow porous carbon materials (HPCM) remarkably enhance the performances of both sulfur cathodes and lithium anodes, promoting the development of high‐performance Li–S batteries. Here, together with the templated synthesis of HPCM, recent progresses of Li–S batteries based on HPCM are reviewed. Several important issues in Li–S batteries, including sulfur loading, polysulfide entrapping, and Li metal protection, are discussed, followed by a summary on recent research on HPCM‐based sulfur cathodes, modified separators, and lithium anodes. After the discussion on emerging technical obstacles toward high‐energy Li–S batteries, prospects for the future directions of HPCM research in the field of Li–S batteries are also proposed.