Synergistic suppression of the shuttle effect and absorption of electrolytes using a functional rich amine porous organic polymer/acetylene black-polypropylene separator in Li-S batteries

Nanoscale melamine-based porous organic frameworks as host material for efficient polysulfides chemisorption in lithium-sulfur batteries

In order to improve the electrochemical capacity of lithium-sulfur batteries (LiSBs), it is necessary to introduce the porous organic frameworks with well-defined hetero atom species in cathode. In this work, porous nanomaterials with ultra-high nitrogen containing and adjustable porosity named Schiff-based networks (SNWs) were selected as potential candidate for sulfur host in LiSBs. Two SNW samples have been constructed by reacting melamine with phenyl or biphenyl dialdehydes through microwave-assisted method, respectively. The high BET surface area provided sufficient room to impregnate sulfur and mitigated volume changes during the cycling performance. Besides, the high density and homogeneous distribution of pyridinic-N and aminic-N in SNW nanoparticles can cooperatively form lithium polysulfides (LiPSs) chemisorption via enhanced Li⁺-N interactions to effectively suppressed the 'shuttle effect'. Attributed to its structural superiorities, SNW/S cathode demonstrates excellent electrochemical performance in LiSBs. In particular, SNW-2/S cathode delivers an excellent cyclability with a specific capacity of 620 mAh · g^-1 after 500 cycles at 0.5 C, counting with a low capacity fading of 0.0508% per cycle. This work highlights the importance of rational design for effective LiPSs chemisorption and pioneers a facile strategy for developing suitable sulfur host materials towards high-performance LiSBs.

A Trifunctional Separator Based on a Blockage-Adsorption-Catalysis Synergistic Effect for Li-S Batteries

To address the obstinate problem of the shuttle effect in lithium-sulfur (Li-S) batteries, cathode materials are usually given multifunctions to immobilize sulfur, which increases the processing difficulty of cathode materials and weakens the advantage in energy density of Li-S batteries. Herein, a single-source decomposition approach is employed to synthesize a pomegranate-like nitrogenous carbon-coated ZnS (ZnS@NC) precursor that is acid etched to obtain the partially etched ZnS@NC (PE-ZnS@NC) composite. PE-ZnS@NC is coated on a commercial PP separator to a fabricate PE-ZnS@NC/PP functional separator that is used to assemble a coin cell with the sulfur/super P cathode. The 3D network carbon framework of PE-ZnS@NC provides additional active sites for electrochemical reaction and a space barrier for the diffusion of the dissolved lithium polysulfides (LPS). Well-distributed N-containing functional groups and polar ZnS could chemically anchor LPS. Also, the ZnS nanoparticles inside could facilitate a fast kinetic process by catalyzing the liquid-liquid and liquid-solid conversion. Since the shuttle effect is greatly suppressed by the synergistic trifunctions of blockage-chemisorption catalysis, PE-ZnS@NC/PP delivers remarkable electrochemical performances that a self-discharge rate of 0.4% per day is achieved in the shelving test and a capacity retention of 97.0% is gained after 50 cycles at 0.5 C, under a sulfur-areal density of around 3 mg cm^-2.