Abstract
Modifying a polypropylene (PP) separator with a polysulfide barrier layer can improve the cycling performance of lithium–sulfur (Li–S) batteries. However, conventional slurry-coating- and vacuum-filtration-designed barriers usually show poor particle connection and require extra binder. Herein, we propose a facile in situ growth method and a subsequent compression strategy to design multifunctional NiCo2S4 (NiCoS) nanosheet arrays on a PP membrane for high-performance Li–S batteries. The in situ grown NiCoS nanosheet arrays are interconnected, conductive and closely adhered to the PP membrane without using any binder. After mechanical compression treatment, the overall NiCoS film is compacted, lightweight (0.148 mg cm−2) and ultrathin (0.8 μm). Density functional theory calculations combined with adsorption and diffusion tests prove that the NiCoS nanosheets have highly efficient physical/chemical entrapping capabilities for preventing polysulfide shuttling. Moreover, in situ electrochemical impedance spectroscopy demonstrated that the NiCoS barrier could efficiently suppress polysulfide diffusion and concurrently facilitate redox reactions. When applying this multifunctional separator, a sulfur/carbon nanotube (S/CNT) cathode with high sulfur content (75 wt%) delivers significantly improved long-term cycling performance, with 0.056% capacity decay per cycle over 500 cycles. This work opens up new opportunities to design multifunctional separators by an in situ growth strategy for high-performance Li–S batteries.
Highlights
With the ever-growing demands for higher energy density, conventional lithium-ion batteries (LIBs) can no longer satisfy applications in portable electronics and electric vehicles[1,2,3]
A thin layer of Ni–Co layered double hydroxide (LDH) nanosheet arrays was grown onto the PP membrane through a facile hydrothermal reaction at a low temperature of 90 °C
The presence of functional groups in PP may assist in the capture of LDH crystal seeds on the PP membrane, which improves the adherence and mechanical stability of the thin film compared with the standard solution and colloidal deposition techniques such as spin coating, dip coating, vacuum filtration, and doctor blading[27]
Summary
With the ever-growing demands for higher energy density, conventional lithium-ion batteries (LIBs) can no longer satisfy applications in portable electronics and electric vehicles[1,2,3]. The low electrical conductivity of S and its discharge product (Li2S) leads to increased polarization and low sulfur utilization, and the dissolution of lithium polysulfide intermediates causes irreversible capacity loss and corrosion of Li-metal anode[8]. To address these issues, tremendous efforts have been devoted to the development of porous cathode host materials to immobilize polysulfides by confining sulfur in porous carriers, such as porous carbon materials[9,10], heteroatom-doped carbon/graphene materials[11], and polar inorganic materials[12,13]. It is desirable to fabricate Li–S batteries with both a high sulfur content and a stable cycling performance
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