Structure Design And Electrochemical Performance Of Porous Polymer Interlayer Materials For Lithium-Sulfur Battery

The rapid development of science and technology has led to an increasing demand for clean and renewable secondary battery with a high specific capacity,high energy density and low cost.Lithium-sulfur(Li-S)battery is considered as the most promising next-generation energy storage device due to its high theoretical specific capacity(1675 m Ah g^-1),high energy density(2600 Wh kg^-1)and low price.However,several Li-S battery issues,such as the shuttle of lithium polysulfides(Li PSs),the insulation of active material sulfur,and the slow conversion between Li PSs,affect its stability and safety.In this dissertation,four types of porous organic polymers(POPs)based multifunctional interlayers were designed and employed to improve the performance of the Li-S battery.The main research contents and results are as follows:(1)Covalent triazine framework(CTF)was synthesized by condensation polymerization of aldehydes and amidines under the conditions of temperature below 120?and without strong acid.And then the CTF-interlayer was prepared by the blade-coating method.The CTF with nitrogen-doped and layered microporous structure can chemically adsorb and physically block Li PSs simultaneously,and its high specific surface area can improve the wettability of the electrolyte,thereby inhibiting the shuttle of Li PSs and promoting the diffusion of lithium ions.The discharge specific capacity of the battery assembled with CTF-interlayer is as high as 802 m Ah g^-1 at a current density of 2 C.(2)The CTF/MWCNT-interlayer was prepared by composing the CTF with multi-walled carbon nanotubes(MWCNT)through the mechanical blending method.CTF is utilized as chemically and physically anchors for Li PSs,and high conductive MWCNT is beneficial for electron transfer,thus inhibiting the shuttle of Li PSs and improving the utilization of active material sulfur.The discharge specific capacity of the battery assembled with CTF/MWCNT-interlayer is as high as 982 m Ah g^-1 at a current density of 2 C,which is 22.4%higher than that with CTF-interlayer.(3)The poly dimethyl diallyl ammonium chloride(PDDA)wrapped CTF(PDDA@CTF)and poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate)(PEDOT:PSS)were layer-by-layer assembled on both sides of the commercial separator,thus the layered PDDA@CTF/PEDOT:PSS-interlayer was prepared.PDDA@CTF is utilized as chemically and physically anchors for Li PSs,and high conductive PEDOT:PSS is beneficial for electron transfer,thus inhibiting the shuttle of Li PSs and improving the utilization of active material sulfur.Besides,the interlayer can also inhibit the growth of lithium dendrites due to the double-sided functional interlayer.The discharge specific capacity of the battery assembled with PDDA@CTF/PEDOT:PSS-interlayer is as high as992 m Ah g^-1 at a current density of 2 C,which is 23.7%higher than that with CTF-interlayer.(4)The polyporphyrin Mg(Co)complex(Por-POPs-Mg(Co))that can catalyze the conversion of Li PSs were designed and composited with graphene nanosheets(GNs)to prepare the Por-POPs-Mg(Co)/GNs-interlayers.Por-POPs-Mg(Co)can chemically and physically anchor Li PSs as well as catalyze the conversion of Li PSs simultaneously,and the highly conductive GNs can improve the transfer of electron,thereby inhibiting the shuttle of Li PSs,promoting the conversion of Li PSs,and improving the utilization of active material sulfur.The discharge specific capacity of the battery assembled with Por-POPs-Mg/GNs-interlayer and Por-POPs-Co/GNs-interlayer are as high as 835 and 860 m Ah g^-1 at a current density of 2 C,which are 4.1%and 7.2%higher than that with CTF-interlayer respectively.