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Owing to their high theoretical capacity and low material cost, lithium-sulfur batteries (LSBs) are considered the most promising next-generation energy storage devices. In response to existing LSBs problems, facilitating the conversion of lithium polysulfides (LiPSs) is considered an effective method, and the LiPSs conversion in the liquid phase provides the majority of the capacity of LSBs. Understanding the kinetics of redox processes of LiPSs in liquid-electrolyte LSBs is crucial. In this study, we have designed a new flowing electrolyte three-electrode system, equipped with a tiny H-type electrolytic cell isolated using the Nafion membrane, to quantitatively measure the intrinsic kinetics of LiPSs conversion. As a result, the onset redox potentials, exchange current densities, reaction orders, and apparent activation energy of the LiPSs conversion were obtained on the basis of the steady-state polarization curves. The onset reduction potentials of main LiPSs were 2.427, 2.348, 2.281, 2.212, and 2.139 V (vs Li+/Li) for S8, Li2S8, Li2S6, Li2S4, and Li2S2, respectively. The calculated exchange current density of Li2S6 redox was the highest (188.55 µA/cm2), while the S8 reduction was the minimal (0.97 µA/cm2). In addition, the reaction orders and apparent activation energies of Li2S8, Li2S6, Li2S4 were studied. The kinetic parameters obtained were related to the formation of the potential plateaus and the sloping regions, especially for the exchange current densities associated with LSBs charge/discharge process. These parameters were used to decipher the charge/discharge curves and CV profile of S8 in detail. This study could assist in understanding of the LSBs reaction mechanism.

The shuttle effect of soluble intermediate polysulfide toward lithium anode, the sluggish redox kinetics of polysulfides conversion and the low lithium ion/electrical conductivity severely limited the commercialization of lithium-sulfur (Li-S) battery. To overcome the bottleneck, herein we designed a Nickel foam/graphene/sulfonated carbon nanotubes (NG/CNTs-SO3−) three-dimensional (3D) interconnected electrode. Nickel foam weaved with 1D multi-wall carbon nanotubes (MWCNT) and 2D graphene (named as NG/CNTs) is used as the host for sulfur accommodation, forming a continuously ion-electronic conductive 3D network and boosting fast redox reaction kinetic. Moreover, the negatively charged –SO3− groups transform the cathode surface from hydrophobic to hydrophilic, and it not only acts as constructing ion-selective layer for suppressing the shuttle effect of polysulfides, but also accelerates the polysulfides conversion process by strong adsorption sites to anchor polysulfides. In addition, the grafted –SO3− groups reinforce the rapid transportation of lithium-ion five times than none negatively charged groups decorated ones. The Li-S batteries with NG/CNTs-SO3− cathode delivers an initial capacity of 1380 mAh g−1 at 0.2 C, retaining a capacity of 1043.5 mAh g−1 after 100 cycles. Furthermore, the cells with NG/CNTs-SO3− cathode also exhibits excellent cycling stability with capacity decay of 0.031% at 2 C and rate capability, which confirms it is outstanding to improve the electrochemical performance and inhibit the shuttle effect.

This study demonstrates the preparation of well aligned-carbon nanotube (WA-CNT) arrays onto a carbon paper substrate with a conductive carbon-black layer by the catalyst seed-impregnated chemical vapor deposition method. The prepared WA-CNT arrays were then characterized by scanning electron microscopy for different growth temperatures, standard linear velocities of feed vapors, and ferrocene-to-xylene ratios in the feed vapors. Results indicate that the optimal WA-CNT arrays of length 40–50 μm and diameter 30–40 nm were obtained at the growth temperature range of 750–800 °C, standard linear velocity of 1.40 cm s −1 , and ferrocene-to-xylene molar ratio of 1:50–1:30. These results provide new insights into the growth mechanism of CNT arrays, which involves cross-coupling of chemical reaction and mass transfer based on reaction engineering theory. The samples prepared in the study can be used as catalyst supports in air electrodes considering their three-dimensional porous structure, approximately linear channel, controllable length and diameter distribution, and excellent CNT conductivity. Electrochemical measurement indicated that the WA-CNT arrays/carbon-black layer/carbon paper substrate composites achieved relatively high discharge capacity of 2930 mAh g −1 (CNTs) at a current density of 0.05 mA cm −2 in Li–air batteries, which far exceeded other carbonaceous materials in Li–air batteries.