Regulating Polysulfide Redox Kinetics on a Self‐Healing Electrode for High‐Performance Flexible Lithium‐Sulfur Batteries

Abstract

Wearable electronics require lightweight and flexible batteries, of which lithiumsulfur (Li-S) batteries are of great interest due to their high gravimetric energy density. Nevertheless, flexible Li-S batteries have unsatisfactory electrochemical performance owing to electrode fracture during repeated bending, the volume change of sulfur species and the severe shuttle effect. Binders play essential roles in these batteries but have always lacked attention. Herein, a self-healing polyvinylpyrrolidone-polyethyleneimine (PVP-PEI) binder cross-linked by hydrogen bonds, which also regulates polysulfide redox kinetics, is reported. The dynamic hydrogen-bonding networks repair the cracks and ensure the integrity of the electrode while numerous polar groups such as CO and -NH 2 suppress the shuttle effect by immobilizing polysulfides. Therefore, Li-S batteries with the PVP-PEI binder exhibit excellent cycling stability (a capacity decay rate of 0.0718% per cycle at 1 C after 450 cycles), an outstanding areal capacity of 7.67 mAh cm −2 even under a high sulfur loading (7.1 mg cm −2 ) and relatively lean electrolyte conditions (E/S ratio = 8 µL mg −1 ). Flexible Li-S pouch cells using the PVP-PEI binder show a stable performance for 140 cycles and a favorable capacity retention of over 95% after 2800 bending cycles, confirming its application potential in high-performance flexible Li-S batteries.

Enhanced Polysulfide Conversion with Highly Conductive and Electrocatalytic Iodine‐Doped Bismuth Selenide Nanosheets in Lithium–Sulfur Batteries

“…[55,56] The second discharge plateau corresponds to the conversion of soluble LiPS to lithium sulfide (S 4 → Li 2 S 2 → Li 2 S) at about 2.1 V. [57,58] The voltage difference between the oxidation and the second reduction plateaus is considered as © 2022 Wiley-VCH GmbH the polarization potential, ∆E. [59,60] Among the tested materials, I-Bi 2 Se 3 /S showed the lowest ∆E, at 131 mV, well below that of Bi 2 Se 3 /S, 162 mV, and Super P/S, 205 mV (Figure 4b).…”

Synergistic Cation–Anion Regulation of Polysulfides by Zwitterionic Polymer Binder for Lithium–Sulfur Batteries

“…Moreover, the binding energies between ZIP binder and high‐order Li 2 S n are significantly higher than those between PVDF and Li 2 S n species. [ 44 ] Beyond that, the interaction energy between cationic quaternary ammonium group and polysulfide anions (e.g., S 2 2− , S 4 2− , S 6 2− , and S 8 2− ) exhibits negative binding energy values indicating the electrostatic interaction between quaternary ammonium cations and polysulfide anions (Figure S16, Supporting Information). Furthermore, other two possible adsorption sites in ZIP matrix were considered and summarized in Figure S17 (Supporting Information).…”

“…[38] Inspired by biology, self-healing chemistry has been applied in the binder to spontaneously repair microcracks in electrodes via dynamic crosslinking networks of noncovalent bonds, such as hydrogen bonding, ionic interaction, and metal chelation. [39][40][41][42][43][44] Regarding to lithium polysulfide regulation, the binders featuring polar functional groups have been also designed to expedite chemically or electrostatically adsorbing of soluble polysulfides and immobilize active species within the cathode. [45][46][47][48] Apart from that, the Li ion conductivity of binders is critical for affecting sulfur reaction kinetics.…”

Multimodal Capturing of Polysulfides by Phosphorus‐Doped Carbon Composites for Flexible High‐Energy‐Density Lithium–Sulfur Batteries

“…[ 22 ] However, flexible batteries need to work under bending conditions, which may cause delamination of active material layers from the current collectors and fracture of the electrodes. [ 23 ] Thus, the use of metal collectors should be avoided in flexible or foldable Li–S batteries, because active materials can easily detach from the current collector under mechanical stress conditions. [ 14,24 ] To address these issues, previous studies have designed freestanding S cathodes without metal collectors to improve the performance of Li–S cells, [ 25 ] such as a freestanding bilayer carbon‐S cathode, [ 26 ] a carbon nanofiber (CNF)–S composites via S vapor deposition, [ 27 ] infiltration of melted elemental S in microporous active carbon cloth, [ 28 ] sandwiching S between two carbon layers, [ 29 ] and multistacked reactivation layers of graphene flakes and Al‐coated tissue paper.…”