Water‐Soluble Cross‐Linking Functional Binder for Low‐Cost and High‐Performance Lithium–Sulfur Batteries

Abstract

Binders play an important role in battery systems. The lithium-sulfur (Li-S) batteries have poor cycling performance owing to large volume alteration of sulfur and shuttle effect. Herein, a novel water-soluble functional binder (named GN-BA) is prepared by the cross-linking effect between gelatin and boric acid. The excellent binder can effectively maintain the integrated electrode stable, buffer the volume changes, prevent active materials exfoliation from current collectors, and anchor polysulfides by chemical bonding. Sulfur electrodes in this binder also exhibit a loosely stacked porous structure, which is advantageous to the electrolyte permeation and fast ion diffusion. X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, and density functional theory calculations further verified that the binder can anchor polysulfides by forming BOLi, COLi, and CNLi chemical bonds. At 0.5 C, a high initial capacity of 980 mA h g −1 can be obtained, which is higher than those sulfur cathodes with traditional poly(vinylidene fluoride) binder. When the sulfur loading is up to 5.0 mg cm −2 , a high areal specific capacity of 5.7 mA h cm −2 and excellent cycling stability are achieved. This study proposes an economical and environmentally friendly strategy for the construction of advanced binders and promotes the practical application of high-energy Li-S batteries.

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

“…[29] Sulfate signals produced by the reaction between sulfur species and air are also detected at 168.5 and 169.7 eV. One intense peak in the Li 1s spectrum (Figure S9d, Supporting Information) can be fitted by three small peaks which correspond to the Li-N, Li-S, and Li-O signals, [31,49] again illustrating the strong chemical linking between the PVP-PEI binder and the discharge products. DFT calculations were also performed to systematically study the chemical adsorption ability of the PVP-PEI binder for LiPSs (Li 2 S 8 , Li 2 S 6 , and Li 2 S 4 as representatives).…”

“…As displayed in Figure 2a, Nyquist plots of all the electrodes show a semicircle in the high-frequency region which represents the charge transfer resistance (R ct ) and the electrolyte resistance (R s ), while the slope in the low-frequency region indicates the Warburg impedance. [31,32] Table S1, Supporting Information shows the values of R s and R ct for the cells with different binders, among which S@PVP-PEI has the smallest R ct (20.91 Ω), suggesting that the S@PVP-PEI cathode has fast charge transport kinetics. Satisfactory charge transfer behavior is due to the excellent adhesion ability that closely binds sulfur and conductive carbon black (CB) together to form conductive paths, which significantly increases the conductivity of the electrode.…”

“…For the PVDF binder, the non-polar fluorine-containing groups do not provide strong anchoring sites for polysulfides, resulting in inferior conversion efficiency and worse electrochemical performance. [31] In addition to a high sulfur loading, lean electrolyte conditions are increasingly regarded as important indexes to evaluate the practical application potential of Li-S batteries. [46,47] Given this, we also assembled a S@PVP-PEI electrode with a relatively low E/S ratio of 8 µL mg −1 and a sulfur loading as high as 7.1 mg cm −2 and the corresponding electrochemical performance is shown in Figure 2k.…”

Polymers in Lithium–Sulfur Batteries

“…Sun et al. [ 153 ] recently synthesized a novel water‐soluble binder (GN–BA) through the crosslinking of gelatin (GN) and boric acid (BA) (Figure 13d). GN as a well‐known natural polymer contains rich hydrophilic group like CONH, NH 2 , and COOH, which exhibits good solubility in water.…”

“…d) The schematic diagram of water-soluble GN-BA crosslinked binder. Reproduced with permission [153]. Copyright 2021, Wiley-VCH.…”