芘对聚苯胺锂硫电池低温性能的影响机制研究

Studies on the Influence of Pyrene on the Low Temperature Performance of Polyaniline Containing Lithium-sulfur Battery

提出在电解液中加入电荷转移中间体改善锂硫电池低温性能的思路,在电解液中添加芘作为电荷转移中间体,加速低温下聚苯胺锂硫电池电化学反应的平衡过程.循环伏安研究证明,芘在锂硫电池放电过程中的高压平台附近具有电化学活性,并通过X射线光电子能谱证实芘的引入能够使锂硫电池在低温下提高多硫化物平衡速率,延长第一平台,生成更多长链多硫化锂.对同样电极材料组成的聚苯胺/硫复合正极材料构成的锂硫电池,当在电解液中加入0.1 mol/L的芘时,相比于不含芘的锂硫电池,其第50次充放电循环下容量在0oC时能够提升22.8%,而在-15oC时能提升25.1%.

Conductive polyaniline is an important material to improve the capacity and cycle stability ofLithium-sulfur battery, but lithium-sulfur cathode with conductive polyaniline still faces poor capacity retentionand cycle stability at temperature below 0 ℃ due to slow equilibration of sulfur or polysulfides. A novel conceptusing redox mediator to accelerate electrochemical reaction at low temperature was proposed. By adding a redoxmediator with its redox potential below S and between Li and S, the electrochemical reaction is accelerated andthe low temperature performance of Li-S battery is therefore improved. More specifically, when pyrene is used asthe redox mediar （RM）, it can be oxidized to RM＋at the cathode surface by sulfur or polysulfides, then RM＋attains electron from cell system regenerating RM. The mediator acts as an electron transfer agent permittingefficient reduction of sulfur or polysulfides. Pyrene is identified from cyclic voltammogram （CV） test aselectrochemical active substance around the high-plateau in discharge process, which meets the requirement ofredox mediator in Li-S battery at low temperature. When pyrene was dissolved in electrolyte, it may act as aneffective electron transfer agent to increSase the electron transfer rate, permitting efficient reduction of sulfur topolysulfides Li2Sx （4〈 X 〈8）, thereby accelerating the equilibration process, and finally enhanced the lowtemperature performance of Li-S battery. To analyze the influence of pyrene on the composition of reductionproducts of sulfur, ex situ X-ray photoelectron spectroscopy （XPS） is used to test the cathode material afterdischarging to 2.2 V at the 10th cycle. XPS experiments confirm that the addition of pyrene may accelerate thepolysulfides equilibration rate and prolong the first plateau. When ultrathin sulfur-wrapped PANI nanocomposite（S-PANI） is used as cathode material, taking the capacity of 25 ℃ as reference, the addition of 0.1 mol/L pyreneinto electrolyte could raise the 50th capacity retention rate from 68.9% to 84.6% at 0 ℃, i.e. by 22.8%. Thiscapacity retention rate is increased by 25.2% from 56.0% to 70.1% at -15 ℃.