Nickel Foam Coated by Ni Nanoparticle-Decorated 3D Nanocarbons as a Freestanding Host for High-Performance Lithium-Sulfur Batteries.

Nanocarbons (NCs) consisting of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were coated on the surface of nickel foam (NF) via a chemical vapor deposition method. The CNFs formed conductive networks on NF, while the CNTs grew perpendicular to the surface of the CNFs, accompanied with the formation of Ni nanoparticles (Ni NPs) at the end of CNTs. The unique Ni-NCs-coated NF with a porous structure was applied as the three-dimensional (3D) current collector of lithium-sulfur (Li-S) batteries, which provided enough space to accommodate the electrode materials inside itself. Therefore, the 3D interconnected conductive framework of the coated NF collector merged in the electrode materials shortened the path of electron transport, and the generated Ni NPs could adsorb lithium polysulfides (LiPSs) and effectively accelerated the conversion kinetics of LiPSs as well, thereby suppressing the "shuttle effect". Moreover, the rigid framework of NF would also constrain the movement of the electrode compositions, which benefited the stability of the Li-S batteries. As a matter of fact, the Li-S battery based on the Ni-NCs-coated NF collector delivered an initial discharge capacity as high as 1472 mAh g-1 at 0.1C and outstanding high rate capability at 3C (802 mAh g-1). Additionally, low decay rates of 0.067 and 0.08% at 0.2C (300 cycles) and 0.5C (500 cycles) have been obtained, respectively. Overall, our prepared Ni-NCs-coated NF collector is promising for the application in high-performance Li-S batteries.

Formation mechanism of critical nucleus during nucleation process of liquid metal sodium.

To deeply understand the formation mechanism of a critical nucleus during the nucleation process of liquid metal sodium, a system consisting of 10 000 Na atoms has been simulated by using molecular dynamics method. The evolutions of nuclei are traced directly, adopting the cluster-type index method. It is found that the energies of clusters and their geometrical constraints interplay to form the favorable microstructures during the nucleation process. The nucleus can be formed through many different pathways, and the critical size of the nucleus would be different for each pathway. It is also found that the critical nucleus is nonspherical and may include some metastable structures. Furthermore, the size of the cluster and its internal structure both play a crucial role in determining whether it is a critical nucleus, and this is in agreement with the simulations by computing the free energy of the Lennard-Jones system [D. Moroni, P. R. ten Wolde, and P. G. Bolhuis, Phys. Rev. Lett. 94, 235703 (2005)].