Ultra-lightweight PANiNF/MWCNT-functionalized separators with synergistic suppression of polysulfide migration for Li–S batteries with pure sulfur cathodes

Abstract

A custom separator with an ultra-lightweight polyaniline nanofibers/multiwall carbon nanotubes (PANiNF/MWCNT) coating has been utilized in lithium-sulfur (Li-S) battery for investigating the electrochemical performance of a hybrid conductive-polymer/carbon coating.The cells employing the PANiNF/MWCNT-functionalized separators facilitate high reversible capacities of 709, 641, and 612 mA h g -1 at, respectively, C/5, C/2, and 1C rates after 100 cycles.High charge-storage capacity retention was also found in the cell with the PANiNF/MWCNTfunctionalized separator after a resting time of 12 h. Such dynamically and statically electrochemical stability could be ascribed to the synergistic physical adsorption and chemical immobilization of the polysulfides by the ultra-lightweight PANiNF/MWCNT coating (only 0.01 mg cm -2 ). This demonstrates that the design of hybrid polymer/carbon-coated-separators has the potential to become a viable approach for successfully developing practical Li-S batteries. 7 contrast, cells employing the bare Celgard separator have poor R QH and R QL (Q H : 78 %, R QH: 31 %; Q L 40 %; R QL 37 %) after only 50 cycles (Fig. S5d in ESI).The comparative analysis between the two functionalized separators shows that the MWCNT-functionalized separator has the higher discharge capacity during the initial several cycles since the use of sp 2 carbon network alone can assist fast electron transport (Fig. 4a). 7Nevertheless, the capacities fade relatively fast due to the easy detachment of polysulfides from the ultra-lightweight MWCNT layer during the discharge process. [10][11][12] In contrast, the PANiNF/MWCNT-functionalized separator displays excellent capacity utilization and retention at various cycling rates during long cycles in spite of the extremely lightweight functional layer. This is because the PANiNF/MWCNT coating possesses (i) the hybrid conductive PANiNF/MWCNT network to guarantee the high redox accessibility and (ii) the functional groups to strengthen the chemical polysulfide-immobilizing capability. [10][11][12] The strong interaction between the PANi and sulfur-containing species for the improved cycle stability is much debated in the literature. [10][11][12][14][15][16] Subsequently, the hybrid polymer/carbon coating may allow reducing the weight of the coating layer immensely, yet retain the stable cyclability. This finding is supported by the enhanced cycle stability of the cells employing the ultra-lightweight PANiNF/MWCNT-functionalized separators, which exhibit a high reversible discharge capacity of 709 mA h g -1 after 100 cycles. The corresponding capacity retention rate and capacity fade rate approach, respectively, 70 % and 0.3 % per cycle. As a reference, the capacity fade rates of the reference cells using the MWCNT-functionalized separator and the Celgard separator are, respectively, 1.29 % per cycle and 1.31 % per cycle after 50 cycles.The rate performance of the PANiNF/MWCNT-functionalized separator is shown in Fig. 4a. The initial discharge capacities approach 1020, 867...

Enhanced Cycling Performance for Lithium–Sulfur Batteries by a Laminated 2D g‐C3N4/Graphene Cathode Interlayer

“…The voltage hysteresis (Δ E ) between charge and discharge curves at the point of 50 % of the discharge capacity was considered an important parameter for assessing the energy efficiency of the sulfur cathode. The S/KB@C 3 N 4 /GS cathode shows a Δ E value of approximately 0.18 V, which is slightly smaller than the values reported in previous studies . It was found that Δ E values increased as the rate increased; nevertheless, the speed of the increase was different for the two cathodes.…”

“…There have been many efforts to apply interlayers of various structures and compositions—including conductive polymers, metal–organic frameworks (MOFs), transition‐metal sulfides,, oxides, and nitrides,, and carbonaceous materials—to improve the electrochemical performance of Li–S batteries. Conductive polymer‐type interlayers, such as polypyrrole (PPy), polyaniline (PANI), and poly(3,4‐ethylenedioxythiophene) (PEDOT), not only can generate N−S, O−S, S−S, and hydrogen bonds with lithium polysulfides but also can tightly adhere to the polymer separator surface. Nevertheless, these novel conductive polymers are not appropriate for large‐scale production owing to the necessity of precisely controlled polymerization and an unreacted monomer separation process.…”

Advanced Separators for Lithium‐Ion and Lithium–Sulfur Batteries: A Review of Recent Progress

“…PANI, which is electronically conductive, can interact with S species through the imine group. A hybrid coating of PANI and MWCNT was applied onto a PP separator to improve the battery performance of separator (Figure C) . Such a hybrid coating can trap polysulfide species through both chemical bonding and physical absorption.…”

Rational Integration of Polypropylene/Graphene Oxide/Nafion as Ternary‐Layered Separator to Retard the Shuttle of Polysulfides for Lithium–Sulfur Batteries

“…Our group has fabricated ion‐selective separators with a Nafion coating layer of 0.7–3.5 mg cm −2 (1.4–7.0 μm) to reject the diffusion of polysulfides . Together with other interlayers of reduced graphene oxide (GO), cellular graphene framework, graphene/TiO 2 , CNTs/PANiNF, as well as functional layers of Al 2 O 3 , glass fiber, GO, SuperP carbon black, carbon nanotube@polyethylene glycol, and poly(acrylic acid), the introduction of binary separators (polymer matrix and functional layer) renders the effective strategy to improve the stable utilization of sulfur.…”