The electrocatalytic activity of BaTiO3 nanoparticles towards polysulfides enables high-performance lithium-sulfur batteries

The slow redox dynamics and dissolution of polysulfides in lithium-sulfur(Li-S)batteries result in poor rate performance and rapid decay of battery capacity,thus limiting their practical application.Ferroelectric barium titanate(BT)nanoparticles have been reported to effectively improve the electrochemical performance of Li-S batteries due to the inherent self-polarization and high adsorption capacity of the BT nanoparticles towards polysulfides.Here in this paper,BT nanoparticles,behave as highly efficient electrocatalyst and demonstrate much higher redox dynamics towards the conversion reaction of polysulfides and Li2S than TiO2,as shown by both electrochemical measurements and density functional theory calculation.The coupling of the sulfur host of the hollow and graphitic carbon flakes(HGCF)and the BT nanoparticles(HGCF/S-BT)enable excellent electrochemical performance of Li-S batteries,delivering a0.047%capacity decay per cycle in 1000 cycles at 1 C,788 mAh g^-1 at 2 C and a reversible capacity of613 mAh g^-1 after 300 cycles at a current density of 0.5 C at a S loading of 3.4 mg cm^-2.HGCF/S-BT also shows great promise for practical application in flexible devices as demonstrated on the soft-packaged Li-S batteries.

Pyrrole derivatives as interlayer modifier of Li-S batteries:Modulation of electrochemical performance by molecular perturbation

The electrochemical performance of lithium-sulfur(Li-S)batteries is strongly hampered by the shuttle effect and slow redox kinetics of lithium polysulfides(Li PSs).Surface modified interlayer of a separator of Li-S batteries is demonstrated to be an effective strategy to overcome this problem.Herein,cobalt nanoparticles confined in nitrogen co-doped porous carbon framework(Co-CN)were developed from pyrolysis of ZIF-67 and used as interlayer of PP separator for Li-S batteries,and were functionalized by four pyrrole derivatives,1-phenylpyrrole,1-methyl pyrrole,1-(p-toluenesulfonyl)pyrrole,and 1-pyrrole,respectively,which were screened in terms of the electron-withdrawing/donating ability of the substituent groups on the pyrrolic nitrogen.The impact of the molecular structure of pyrrole derivatives on the interaction with Li PSs and the electrochemical performance of Li-S batteries were explored by nuclear magnetic resonance and theoretical calculation.It is uncovered that 1-phenylpyrrole shows the highest enhancement of redox kinetics of Li PSs,attributing to the optimal interaction with Co nanoparticles and Li PSs.Therefore,1-phenylpyrrole modified Co-CN interlayer enables the best electrochemical performance for the Li-S batteries,delivering a specific capacity of 562 m Ah g^(-1)at 5 C and a capacity of 538,526,and 449 m Ah g^(-1)after 500 cycles at 1,2,and 3 C,respectively.At a high sulfur loading of 5.5 mg cm^(-2),it achieves a capacity of 440 m Ah g^(-1)after 500 cycles at 1 C.This work reveals the interaction mechanism among Li PSs,Co nanoparticles and the molecular modifiers in improving the electrochemical performance of Li-S batteries.