Polypyrrole/Graphene Composite Interlayer: High Redox Kinetics of Polysulfides and Electrochemical Performance of Lithium–Sulfur Batteries Enabled by Unique Pyrrolic Nitrogen Sites

Abstract

It is still a grand challenge to achieve high performance lithium-sulfur (LiÀ S) batteries of high capacity, high-rate performance and long cycling performance, especially at lean electrolyte condition. Herein, a multi-functional composite interlayer is developed by in-situ polymerizing pyrrole (PPy) on graphene nanosheet (PPy/G) and examined by Fourier Transformed infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The graphene layers in PPy/G assure the high conductivity of the composite interlayer, while the high content of pyrrolic nitrogen sites of PPy in PPy/G composite interlayer can effectively trap the polysulfides (PSs) and promote the redox kinetics of PSs, which is valuable to suppress PSs dissolution and enhance utilization of sulfur content in LiÀ S batteries. Besides, the composite interlayer also facilitates the homogenous flux of Li + and inhibits the growth of Li dendrite on Li metal anode. As a result, PPy/G interlayer delivers an impressive capacity of 535 mAh g À 1 at 5 C and an area capacity of 5.18 mAh cm À 2 at a sulfur load of 5.8 mg cm À 2 after 100 cycles. A steady capacity of 664 mAh g À 1 is also accomplished in lean-electrolyte condition after 100 cycles.

Effect of Nitrogen Dopant Agents in the Performance of Graphene-Based Cathodes for Li-S Batteries

“…This test was replicated at a higher rate, concretely, at C/5 (335 mA g −1 ), achieving, once again, an outstanding electrochemical performance for the S@NH 3 -rGO based electrode over 800 cycles, as illustrated in Figure 8 e. It commenced with an initial specific capacity of 1867 mAh g −1 , stabilising at around 1100 mAh g −1 . Notably, this outperforms the cell employing the S@en-rGO electrode ( Figure S5b ), which could be attributed to the electrocatalytic effect of the pyridinic nitrogen on the polysulfides reaction, as was previously described [ 62 ]. The capacity fading behaviour remained consistent at C/5.…”

“…These data confirm the excellent properties of the ammonia-functionalised graphene material as a sulphur matrix in Li-S technology. According to the conductivity and diffusion data, and as previously reported in the literature [ 62 ], this specific type of functionalised graphene material serves as a crucial factor in optimising the battery’s performance. It functions adeptly as an efficient matrix and an excellent electrocatalyst during the conversion reaction of lithium polysulfides.…”

Recent advances in modified commercial separators for lithium–sulfur batteries

“…185 This is important because pyrrolic nitrogen sites have shown excellent poly-sulde adsorption and catalytic conversion compared to the other nitrogen sites. 186,187 In a recent study, Zhang et al 188 used DFT to show that a composite comprising PANI chains and a-ZrP nanosheets was highly catalytic to polysulde conversion. The Li polysuldes adsorbed by the a-ZrP nanosheets acted as an electronic switch that allowed electrons to ow between PPy and a-ZrP, which triggered the multiphase conversion of the adsorbed polysulde.…”

Polypyrrole-coated cobalt sulfide as an effective host for sulfur cathode

“…Among different sulfur hosts, the easy-to-synthesize conductive polymers with abundant functional groups can suppress the shuttle effect and improve the electronic conductivity of sulfur electrodes. 8,9 For example, Li et al designed a polypyrrole-coated sulfur nanofiber electrode with a first discharge of 1064 mA h g −1 . 10 Although conductive polymers can limit the shuttle of LiPSs and improve sulfur utilization to a certain extent, the weak physical adsorption between non-polar conductive polymers and polar LiPSs limits the adsorption capacity of conductive polymers toward LiPSs.…”

“…Among different sulfur hosts, the easy-to-synthesize conductive polymers with abundant functional groups can suppress the shuttle effect and improve the electronic conductivity of sulfur electrodes. 8,9 For example, Li et al designed a polypyrrole-coated sulfur nanofiber electrode with a first discharge of 1064 mA h g −1 . 10…”