Synergistic Catalysis by Single-Atom Catalysts and Redox Mediator to Improve Lithium-Oxygen Batteries Performance.

Lithium-oxygen (Li-O2 ) batteries with ultrahigh theoretical energy density have attracted widespread attention while there are still problems with high overpotential and poor cycle stability. Rational design and application of efficient catalysts to improve the performance of Li-O2 batteries is of significant importance. In this work, Co single atoms catalysts are successfully combined with redox mediator (lithium bromide [LiBr]) to synergistically catalyze electrochemical reactions in Li-O2 batteries. Single-atom cobalt anchored in porous N-doped hollow carbon spheres (CoSAs-NHCS) with high specific surface area and high catalytic activity are utilized as cathode material. However, the potential performances of batteries are difficult to adequately achieve with only CoSAs-NHCS, owing to the blocked electrochemical active sites covered by insulating solid-state discharge product Li2 O2 . Combined with LiBr as redox mediator, the enhanced OER catalytic effect extends throughout all formed Li2 O2 during discharge. Meantime, the certain adsorption effect of CoSAs-NHCS on Br2 and Br3 - can reduce the shuttle of RMox . The synergistic effect of Co single atoms and LiBr can not only promote more Li2 O2 decomposition but also reduce the shuttle effect by absorbing the oxidized redox mediator. Li-O2 batteries with Co single atoms and LiBr achieve ultralow overpotential of 0.69 V and longtime stable cyclability.

Kirkendall effect modulated hollow red phosphorus nanospheres for high performance sodium-ion battery anodes.

Hollow nanospheres are desirable to resolve the volume expansion of red phosphorus anodes for sodium-ion batteries. Here, we developed a mild molten salt method to prepare hollow red phosphorus in the NaCl-KCl-AlCl3 system by using the Kirkendall effect. As an anode for sodium-ion batteries, the prepared hollow nanospheres exhibit a highly reversible capacity of 624 mA h g-1 at 4.0C and 737 mA h g-1 at 1.0C even after 600 cycles with a low capacity fading rate of 0.06% per cycle.

Fully integrated hierarchical double-shelled Co9S8@CNT nanostructures with unprecedented performance for Li-S batteries.

The insulating and dissoluble features of sulfur and polysulfide intermediates significantly hinder the cycling performance and coulombic efficiency of Li-S batteries. We herein design fully integrated hierarchical double-shelled Co9S8@CNT hollow nanospheres as a sulfur host, where each shell owns a tri-layer sandwich structure and six functional layers are constructed in total. Uniquely, the hierarchical structures integrate the beneficial functions of electrical conductivity, ion diffusion, polysulfide immobilization and polysulfide redox kinetics. The Co9S8@CNT/S delivers a reversible specific capacity of 1415 mA h g-1 at 0.2C, which is very close to the theoretical capacity of sulfur. Moreover, even at a high rate of 10C, an unprecedented capacity of 676.7 mA h g-1 can still be achieved, which represents the best rate capability among the ever-reported sulfur cathodes with similar sulfur content. More importantly, the Co9S8@CNT/S also displays a high coulombic efficiency of nearly 100% and an excellent cycling performance for up to 1000 cycles with a capacity fading rate of only 0.0448% per cycle. Even at the loading amount of 5.5 mg cm-2, the areal capacity can still reach 4.3 mA h cm-2. The concept to rationally integrate distinct components into fully functional units could provide valuable insights for the development of Li-S batteries and beyond.

Hierarchical Graphene-Scaffolded Silicon/Graphite Composites as High Performance Anodes for Lithium-Ion Batteries.

To better couple with commercial cathodes, such as LiCoO2 and LiFePO4 , graphite-based composites containing a small proportion of silicon are recognized as promising anodes for practical application in lithium-ion batteries (LIBs). However, the prepared Si/C composite still suffers from either rapid capacity fading or the high cost up to now. Here, the facile preparation of hierarchical graphene-scaffolded silicon/graphite composite is reported. In this designed 3D structure, Si nanoparticles are homogeneously dispersed on commercial graphites and then uniformly encapsulated in the hierarchical graphene scaffold. This hierarchical structure is also well characterized by the synchrotron X-ray computed nanotomography technique. When evaluated as anodes for LIBs, the hierarchical composite, with the Si weight ratio of 5 wt%, exhibits a reversible capacity of 559 mA h g-1 at 75 mA g-1 , suggesting an unprecedented utilization of Si up to 95%. Even at 372 mA g-1 , the composite can still maintain a high capacity retention of 90% after 100 cycles. Coupled with the LiFePO4 cathode, the full cell shows the high capacity of 114 mA h g-1 at 170 mA g-1 . The excellent Li-storage properties can be ascribed to the unique designed hierarchical structure.

Synchronous synthesis of Kirkendall effect induced hollow FeSe2/C nanospheres as anodes for high performance sodium ion batteries.

In this work, we have developed a simple and facile method to synchronously synthesize hollow FeSe2/C nanospheres using the Kirkendall effect. When evaluated as an anode for SIBs, the hollow FeSe2/C nanospheres exhibit a high discharge capacity retention of 474.1 mA h g-1 at 0.05 A g-1 (based on the calculation of FeSe2), which is very close to the theoretical capacity of FeSe2 (∼500 mA h g-1). Meanwhile, hollow FeSe2/C also has a superior rate capability of 364.5 and 316.5 mA h g-1 even at 2.0 and 5.0 A g-1, respectively. The high performance of the hollow FeSe2/C nanospheres can be ascribed to the unique carbon coated hollow nanostructure.