Enhancing Hydrophilicity of Thick Electrodes for High Energy Density Aqueous Batteries

Abstract

Thick electrodes can substantially enhance the overall energy density of batteries. However, insufficient wettability of aqueous electrolytes toward electrodes with conventional hydrophobic binders severely limits utilization of active materials with increasing the thickness of electrodes for aqueous batteries, resulting in battery performance deterioration with a reduced capacity. Here, we demonstrate that controlling the hydrophilicity of the thicker electrodes is critical to enhancing the overall energy density of batteries. Hydrophilic binders are synthesized via a simple sulfonation process of conventional polyvinylidene fluoride binders, considering physicochemical properties such as mechanical properties and adhesion. The introduction of abundant sulfonate groups of binders (i) allows fast and sufficient electrolyte wetting, and (ii) improves ionic conduction in thick electrodes, enabling a significant increase in reversible capacities under various current densities. Further, the sulfonated binder effectively inhibits the dissolution of cathode materials in reactive aqueous electrolytes. Overall, our findings significantly enhance the energy density and contribute to the development of practical zinc-ion batteries.

Synthesis of Aminopolyolefins with Tunable Hydrophilicity and Chain Flexibility for Application as Binders in Aqueous Rechargeable Batteries

“…Cells with a higher discharge capacity and capacity retention are desired. Recent findings have demonstrated the importance of the wettability/hydrophilicity of binders in enhancing the cycling performance in near-neutral aqueous ZIBs. , We propose the hydrophobic nature of both these materials, consistent with the high water contact angles (WCA > 100°, vide infra ), lacked efficient wetting of the electrode and active materials. Hence, we took advantage of the tunability of our APO synthesis to target low WCA values and high hydrophilicity for improved electrode performance.…”

“…However, as the mass loading of the active material increases, so does the thickness of the electrode. Consequently, this results in higher internal ionic and electronic resistance as well as poor mass transport, , ultimately translating to lower specific capacity and energy, poor cycle life, and irreproducible Coulombic efficiency. Low-loading MnO 2 /Zn batteries have been extensively studied in the scientific literature, including our own research, and excellent cyclability has been achieved. , However, to transition to commercial applications, achieving optimal performance with thicker electrodes becomes imperative.…”

Dendrite-Free Zn Anode Endowed by Facile Al-Complex Coating for Long-Cycled Aqueous Zn-Ion Batteries

“…Recently, many efforts have been made to solve the dendritic problem of zinc anode. − For example, electrolyte additives (sodium dodecyl sulfate (SDS), poly­(ethylene glycol), triethyl phosphate (TEP), cetyltrimethylammonium bromide (CTAB), thiourea, and polyacrylamide (PAM)) have been shown to have a positive effect on improving the stability of zinc anode. − Nevertheless, these methods are at the expense of the intrinsic advantages of low cost and safety for AZIBs. Moreover, coating the zinc anode with a protective layer was proved to be effective. − Solid polymer coating acts as an artificial solid/electrolyte interface phase (SEI), such as artificial polyamide (PA) and highly viscoelastic poly­(vinyl butyral) (PVB) layer. , These solid polymer coating strategies usually result in strong polarization, which is not conducive to fast reaction kinetics.…”

“…Although these simple and convenient methods have achieved good results, spin-coating is not easy for large-scale production, and the doctor-blade coating method is difficult to achieve uniform coating and adjust the coating thickness accurately. In addition, since PVDF is hydrophobic, the introduction of PVDF would inhibit the contact of aqueous electrolyte and Zn electrode and inevitably increase the polarization of Zn deposition/stripping . Atomic layer deposition (ALD) technology is a strategy to achieve coating delicately.…”

“…In addition, since PVDF is hydrophobic, the introduction of PVDF would inhibit the contact of aqueous electrolyte and Zn electrode and inevitably increase the polarization of Zn deposition/ stripping. 16 Atomic layer deposition (ALD) technology is a strategy to achieve coating delicately. For instance, a thin and homogeneous Al 2 O 3 layer was successfully coated on a Zn plate using the ALD technique.…”