2D spinel ZnCo_(2)O_(4) microsheet-coated functional separator for promoted redox kinetics and inhibited polysulfide dissolution

Lithium-sulfur(Li-S)batteries are receiving increasing attention as one of the potential next-generation batteries,owing to their high energy densities and low cost.However,practical Li-S batteries with high energy densities are extremely hindered by the sulfur loss,low Coulombic efficiency,and short cycling life originating from the polysulfide(LiPS)shuttle.In this study,two-dimensional(2D)ZnCo_(2)O_(4) microsheets fabricated by a facile hydrothermal process are employed to modify the separator,for improving the electrochemical performances of Li-S cells.The resulting 2D Zn Co_(2)O_(4)-coated separator features a coating thickness of approximately 10 lm,high ionic conductivity of 1.8 m S/cm,and low mass loading of 0.2 mg/cm^(2).This 2D ZnCo_(2)O_(4)-coated separator effectively inhibits Li PS shuttle by a strong chemical interaction with Li PS as well as promotes the redox kinetics by Zn CO2O4-coated layers,as determined by X-ray photoelectron spectroscopy analysis,self-discharge,time-dependent permeation test,Li symmetric cell test,and Li2S nucleation analyses.Consequently,the Li-S batteries based on the 2D Zn Co_(2)O_(4)-coated separator exhibit a high initial discharge capacity of 1292.2 m Ah/g at 0.1 C.Moreover,they exhibit excellent long cycle stability at 1 and 2 C with capacity retention of 84%and 86%even after800 cycles,corresponding to a capacity fading rate of 0.020%and 0.016%per cycle,respectively.Effectively,these Li-S cells with a high sulfur loading at 5.3 mg/cm^(2) and low electrolyte concentration of 9 l L/mg deliver a high discharge capacity of 4.99 m Ah/cm^(2) after 200 cycles at 0.1 C.

High Na-ion conductivity andmechanical integrity of anion-exchanged polymeric hydrogel electrolytes for flexible sodium ion hybrid energy storage

The polymeric gel electrolytes are attractive owing to their higher ionic conductivities than those of dry polymer electrolytes and lowered water activity for enlarged potential window.However,the ionic conductivity and mechanical strength of the Na-ion conducting polymeric gel electrolytes are limited by below 20 mS cm−1 and 2.2 MPa.Herein,we demonstrate Na-ion conducting and flexible polymeric hydrogel electrolytes of the chemically coupled poly(diallyldimethylammonium chloride)-dextrin-N,N′-methylene-bisacrylamide film immersed in NaClO_(4) solution(ex-DDA-Dex+NaClO_(4))for flexible sodium-ion hybrid capacitors(f-NIHC).In particular,the anion exchange reaction and synergistic interaction of ex-DDA-Dex with the optimum ClO_(4)−enable to greatly improve the ionic conductivity up to 27.63 mS cm−1 at 25◦C and electrochemical stability window up to 2.6 V,whereas the double networking structure leads to achieve both the mechanical strength(7.48 MPa)and softness of hydrogel electrolytes.Therefore,the f-NIHCs with the ex-DDA-Dex+NaClO_(4) achieved high specific and high-rate capacities of 192.04 F g^(−1)at 500 mA g^(−1)and 116.06 F g^(−1)at 10000 mA g^(−1),respectively,delivering a large energy density of 120.03Wh kg^(−1)at 906Wkg^(−1)and long cyclability of 70%over 500 cycles as well as demonstrating functional operation under mechanical stresses.