Customized Structure Design and Functional Mechanism Analysis of Carbon Spheres for Advanced Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next-generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe "shuttle effect" of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above-mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state-of-the-art advances of CSs for advanced high-energy LSBs, including their preparation strategies and applications in inhibiting the "shuttle effect" of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.

Strong Surface-Bound Sulfur in Carbon Nanotube Bridged Hierarchical Mo2 C-Based MXene Nanosheets for Lithium-Sulfur Batteries

In this work, hydroxyl-functionalized Mo₂ C-based MXene nanosheets are synthesized by facilely removing the Sn layer of Mo₂ SnC. The hydroxyl-functionalized surface of Mo₂ C suppresses the shuttle effect of lithium polysulfides (LiPSs) through strong interaction between Mo atoms on the MXenes surface and LiPSs. Carbon nanotubes (CNTs) are further introduced into Mo₂ C phase to enlarge the specific surface area of the composite, improve its electronic conductivity, and alleviate the volume change during discharging/charging. The strong surface-bound sulfur in the hierarchical Mo₂ C-CNTs host can lead to a superior electrochemical performance in lithium-sulfur batteries. A large reversible capacity of ≈925 mAh g^-1 is observed after 250 cycles at a current density of 0.1 C (1 C = 1675 mAh g^-1 ) with good rate capability. Notably, the electrodes with high loading amounts of sulfur can also deliver good electrochemical performances, i.e., initial reversible capacities of ≈1314 mAh g^-1 (2.4 mAh cm^-2 ), ≈1068 mAh g^-1 (3.7 mAh cm^-2 ), and ≈959 mAh g^-1 (5.3 mAh cm^-2 ) at various areal loading amounts of sulfur (1.8, 3.5, and 5.6 mg cm^-2 ) are also observed, respectively.

A 3D conductive network of porous carbon nanoparticles interconnected with carbon nanotubes as the sulfur host for long cycle life lithium-sulfur batteries

Constructing an interlinked three-dimensional conductive carbon structure as a sulfur host is considered to be an effective strategy for suppressing the capacity decay over long-term cycling and improving the rate performance of lithium-sulfur (Li-S) batteries, because it can not only facilitate rapid electronic and ionic transportation in the cathode, but also be conducive to confine lithium polysulfide (LiPS) dissolution and shuttling. In this report, we designed a novel 3D conductive network structure (CNTs/Co-NC), which is composed of Co-NC (cobalt embedded in an N-doped porous carbon composite) derived from ZIF-67 polyhedra and inserted carbon nanotubes (CNTs), and applied it as a sulfur host for Li-S batteries. The CNT/Co-NC network structure is firstly prepared via the in situ nucleation of small ZIF-67 crystals on the surface of CNTs and eventually grown into CNT/ZIF-67 hybrid materials; after subsequent carbonization and infiltration of sulfur procedures, the S@CNT/Co-NC cathode is obtained. Li-S batteries based on the S@CNT/Co-NC cathode show an improved rate capability of 772.6 mA h g^-1 at the 2 C rate, enhanced long cycling stability under a large current density with a low capacity decay rate of ∼0.067% per cycle at the 0.5 C rate after 500 cycles and ∼0.072% per cycle at the 1 C rate after 700 cycles and an excellent coulombic efficiency of about 95% up to 500 cycles at 0.5 C and 91% up to 700 cycles at 1 C. The superior performance of S@CNTs/Co-NC should be ascribed to the rapid charge transfer, excellent electron conductivity, improved adsorption capability for LiPSs and enhanced redox kinetics of this 3D conductive network structure.

Doping-template approach of porous-walled graphitic nanocages for superior performance anodes of lithium ion batteries

Removal of the N-doped template creates nanopores in the shells of nanocages. The created nanopores enhance fast ion diffusion.