聚吡咯修饰氧化铁纳米片改善锂硫电池性能

Polypyrrole Modified Iron Oxide Nanosheets for Improving Li-S Battery Electrochemical Performance

采用酸刻蚀诱导的原位生长法在α-Fe_(2)O_(3)纳米片表面修饰聚吡咯,其中对甲苯磺酸起到刻蚀与掺杂的作用,Fe_(2)O_(3)纳米片表面被刻蚀出的Fe^(3+)作为氧化剂,使得吡咯在Fe_(2)O_(3)纳米片表面聚合生长,对甲苯磺酸根作为对阴离子掺杂于聚吡咯分子结构中,得到Fe_(2)O_(3)@PPy复合纳米片。通过调节刻蚀环境与Fe_(2)O_(3)纳米片的投料量控制聚吡咯的修饰量,制得系列Fe_(2)O_(3)@PPy复合纳米片。当对甲苯磺酸和Fe_(2)O_(3)摩尔比为12:1时,Fe_(2)O_(3)@PPy复合纳米片获得优异的电化学性能。1 C下的初始容量为468.7 mA·h·g^(-1),循环500次后仍保持414.5 mA·h·g^(-1)的容量,容量保持率为86.2%,表现出良好的循环稳定性。该材料可应用于动力电池的开发。

Introduction Lithium sulfur batteries have attracted recent attention as the secondary batteries with a high specific energy,a long lifespan,and a high safety.Inhibiting the shuttle effect of polysulfides and improving reaction kinetics become challenges.The chemical interactions between polar metal compounds and polysulfide ions(i.e.,polarity polarity interactions,Lewis acid-base interactions,and sulfur bond chain reactions)have some advantages in inhibiting the shuttle effect of polysulfide ions.In addition,many metal compounds exhibit an electrocatalytic activity during the conversion of polysulfides,promoting the conversion rate of polysulfide ions during charging and discharging,suppressing the uneven deposition of insoluble sulfides Li2S2/Li2S on the electrode surface,and thus achieving a goal of improving the utilization rate of active substances,inhibiting shuttle,and reducing the loss of active substances.The inherent conductive properties of conductive polymers are conducive to electron conduction,and their soft and elastic properties can effectively buffer the volume expansion of active substances during charge and discharge processes.The functional groups rich in them have a strong affinity for Li PSs and can inhibit shuttle effects.In this paper,Fe_(2)O_(3)@PPy composite materials were prepared via in-situ growth of polypyrrole on Fe_(2)O_(3) nanosheets by acid etching.Methods Fe_(2)O_(3) nanosheets were modified by a simple one-step method with polypyrrole to prepare high-performance lithium sulfur battery composite cathode materials.Fe_(2)O_(3) nanosheets were placed in a solution of p-toluenesulfonic acid,and the surface was exposed to Fe^(3+)by acid etching.Fe^(3+)acted as an oxidant to promote the oxidation polymerization reaction of pyrrole monomers on the surface of the nanosheets.Also,p-toluenesulfonic acid was doped into the molecular structure of polypyrrole to obtain Fe_(2)O_(3)@PPy composite nanosheets.A series of Fe_(2)O_(3)@PPy composite nanosheets were prepared via adjusting the etching environment and the feeding amount of Fe_(2)O_(3) nanosheets to control the modification amount of polypyrrole.Results and discussion The in-situ growth method induced by acid etching was used to modify the surface ofα-Fe_(2)O_(3) nanosheets with polypyrrole,in which p-toluenesulfonic acid played an etching and doping role.Fe^(3+)ion etched on the surface of Fe_(2)O_(3) nanosheets is used as an oxidant,allowing pyrrole to polymerize and grow on the surface of Fe_(2)O_(3) nanosheets.P-toluenesulfonic acid is doped into the molecular structure of polypyrrole as a para anion,resulting in Fe_(2)O_(3)@PPy composite nanosheets.The obtained Fe_(2)O_(3)@PPy nanocomposites combine the catalytic active sites exposed by Fe_(2)O_(3) nanosheets with a high conductivity and a high specific surface area of polypyrrole.This increases the chemical adsorption of polysulfides and inhibits their shuttle,and accelerates the conversion of soluble Li PSs to insoluble products,greatly improving the utilization rate of sulfur,helping to improve the ion/electron transfer rate of nanosheets,and enhancing the reaction kinetics of electrode materials.Fe_(2)O_(3) nanosheets form reinforced chemical bonds with Li PSs and promote the conversion of polysulfides,which effectively alleviates the shuttle effect of polysulfides,and improves the Coulomb efficiency,cycle stability and capacity retention of batteries.Polypyrrole enhances the conductivity of Fe_(2)O_(3) nanosheets,their surface ion and electron conductivity,and improves Li+diffusion kinetics.At a molar ratio of p-toluenesulfonic acid to Fe_(2)O_(3) of 12:1,Fe_(2)O_(3)@PPy composite nanosheets exhibit a superior electrochemical performance.The discharge specific capacities of the S@Fe_(2)O_(3)@PPy-3 cathode at 0.1,0.2,0.5 C and 1.0 C are 734.7,576,468.7 m A·h·g^(-1)and 405.2 m A·h·g^(-1),respectively.At a current density of 0.1C,S@Fe_(2)O_(3)@PPy-3 cathode can recover more reversible capacity with a discharge specific capacity of 519.5 m A·h·g^(-1),having a superior rate performance.S@Fe_(2)O_(3)@PPy-3 provides an excellent cycling performance,maintaining a capacity of 414.5 m A·h·g^(-1)even after 500 cycles at a high rate of 1 C with a capacity retention rate of 86.2%.This material can be used to the development of power batteries.Conclusions The synergistic effect of Fe_(2)O_(3) and PPy on the electrochemical performance improvement of lithium sulfur batteries was effective.According to the change in the relative content of polypyrrole on the surface of Fe_(2)O_(3) nanosheets,the conductivity of Fe_(2)O_(3) nanosheets improved with the increase of polypyrrole content.However,the excess polypyrrole nanoparticles covered the surface of Fe_(2)O_(3) nanosheets at the excessive polypyrrole,leading to a decrease in active sites and in battery performance.In summary,as a carrier for sublimation of sulfur,Fe_(2)O_(3)@PPy could promote the adsorption of polysulfides and alleviate their shuttle effect,improving the utilization rate of sulfur in lithium sulfur batteries.