Cobalt Phosphide Nanoflake-Induced Flower-like Sulfur for High Redox Kinetics and Fast Ion Transfer in Lithium-Sulfur Batteries

Abstract

Sulfur reactivity in lithium−sulfur batteries highly depends on its distribution and morphology during cycling, which is of great significance to suppress the shuttle effect and promote conversion reaction. Herein, cobalt phosphide nanoflakes are prepared and used as a sulfur host. An improved redox kinetics from sulfur to lithium sulfide and the corresponding fast lithium-ion diffusion are observed to greatly promote the electrochemical performance of lithium−sulfur batteries. Meanwhile, for the first time, we propose "effective triple phase contact" and "insulated dead sulfur" to account for cycling performance differences of CoP@S and rGO@S batteries. The flower-like sulfur induced by CoP nanoflakes during cycling provides extra lithium-ion diffusion and electron transfer ways compared with agglomerated sulfur in the rGO@S cathode. The CoP@S battery shows good rate performance and delivers 520 mA h g −1 after 1000 cycles with an excellent Coulombic efficiency of 99%. In contrast, no conversion reaction happens after 600 cycles in the rGO@S battery, implying no existence of reactive sulfur. This research reveals the effect of morphological evolution of sulfur on the cycling performance and affords an insight for developing high-performance lithium−sulfur batteries.

Metallic MoS2 Nanoflowers Decorated Graphene Nanosheet Catalytically Boosts the Volumetric Capacity and Cycle Life of Lithium–Sulfur Batteries

“…Scanning electron microscopy (SEM) and transmission electron microscope (TEM) observations clearly reveal an intimate contact between the 2D nanosheet‐composed MoS 2 nanoflowers and graphene, which is highly beneficial for rapid interfacial charge transfer ( Figure 2a –c, Figure S1, Supporting Information). [ 33,34 ] The nanoflowers are well distributed on graphene surface without agglomeration, suggesting GO serves as a perfect 2D template to induce the homogeneous nucleation and growth of MoS 2 . High‐resolution TEM image exhibits that the interval between two adjacent lattice fringes is 0.476 nm (Figure 2c), which corresponds to the (004) lattice plane of metallic 1T phase of MoS 2 .…”

CoSe2/MoS2 Heterostructures to Couple Polysulfide Adsorption and Catalysis in Lithium‐Sulfur Batteries†

“…Despite a strong polysulfides adsorption ability, the CoSe 2 cathodes show rapid capacity fading owing to relatively low electronic conductivity of CoSe 2 and poor catalytic activities. [ 39‐40 ] At a high sulfur loading of 5 mg·cm −2 (Figure S6), CC@CoSe 2 /MoS 2 can still deliver a capacity of 689.4 mAh·g −1 at 1 C after 100 cycles. Figure 5e shows the long‐term cycle performances.…”

An Organodiselenide Comediator to Facilitate Sulfur Redox Kinetics in Lithium–Sulfur Batteries

“…However, the blank cell only provided an initial capacity of 979 mAh g −1 and a cyclic decay rate of 0.156% per cycle, which exhibited a sharp capacity decay after 150 cycles probably due to the deposition of a “dead sulfur” layer and sharply deteriorated voltage polarization (Figures S11 and S12, Supporting Information). [ 41 ] Furthermore, Li anodes with DPDSe after 50 cycles exhibited a more flatter morphology with a thinner deposition layer than the anode without DPDSe (Figure S13, Supporting Information).The high capacity of the DPDSe‐cells can be attributed to the effective and sustainable comediation process, and the high stability approximately benefits from the protective effect of the aromatic group on the lithium anode. [ 42 ] Nevertheless, excessive concentration of DPDSe led to sharp capacity decay due to deteriorated shuttle effect and lithium anode corrosion (Figure S14, Supporting Information).…”