过渡金属酞菁化合物作为锂硫电池液相催化剂的研究

The demand for energy increases steadily with time due to population and economic growth, high energy density rechargeable batteries based on renewable sources need to be developed and adopted. In recent years, lithium–sulfur (Li–S) batteries have been considered as one of promising candidates for the next-generation of rechargeable batteries, which affords a high theoretical energy density of 2600 Wh/kg. Although, several approaches have been made to improve the performance of Li-S batteries, such as confining sulfur in conducting materials or introducing inorganic solid materials as immobilizer and catalysts, the utilization of sulfur during the charge/discharge process is far below the theoretical value especially under high current density or after long cycling. It is still a great challenge for further improving utilization efficiency of sulfur during charge/discharge for Li-S batteries. Is there any possible to improve the utilization efficiency of sulfur by introducing liquid-phase catalysts? Nevertheless, liquid-phase catalysts (such as redox-mediator) have shown great potential in Li-O2 batteries by improving the transformation of Li2O2. Herein, we propose that metal phthalocyanine compounds (such as Iron(II) phthalocyanine) are used as liquid-phase catalysts to improve sulfur utilization for Li-S batteries. We will evaluate the electrochemical performance of Li-S batteries by introducing metal phthalocyanine compounds and study the mechanism of catalysis process. It is our hope that this study will give fresh impetus to the research community to realize the high performance Li-S batteries.

随着人口和经济的发展，能源需求不断增大，高比能储能体系成为人们关注的焦点。质量比能量高达2600 Wh/kg的锂硫电池，成为最具潜力的下一代储能体系之一。然而，目前通过复合导电性材料等手段，首周硫的利用效率普遍只在60-80%之间；通过结构的设计、引入一些具有吸附和催化作用的无机固体材料，首周硫的利用效率已提高至近100%，但是长循环之后硫的利用效率迅速下降，尤其在大倍率下，硫的利用效率普遍在60%以下。如何进一步的提高硫在长周期充放电过程中的转化和利用效率，仍然是锂硫电池发展的关键问题。能否通过引入液相催化剂来提高硫的利用效率呢？液相催化剂在锂氧气电池体系的成功应用表明液相催化剂在改善充放电产物转化方面具有巨大潜力。本项目将采用具有催化作用的过渡金属酞菁类化合物作为液相催化剂，研究其对锂硫电池电化学性能的影响，并通过金属酞菁类化合物对多硫化物/硫化锂催化机制的研究，获得高性能锂硫电池。

锂硫电池具有较高的理论能量密度，成为下一代二次电池体系发展的研究热点之一。本项目首次提出利用液相催化剂来改善锂硫电池多硫化物/硫化锂转化，从液相催化剂的角度出发提高硫的转化利用效率。本项目系统的研究了酞菁铁作为锂硫电池液相催化剂的电化学性能和低温性能。添加了液相催化剂的锂硫电池，在室温0.1C倍率下可以提供1467mAh/g的容量，10C大倍率下仍然可以提供460mAh/g的容量，在2C的倍率下循环700周之后仍然有566mAh/g的容量（容量保持率约80%）；并且在零下20度时，0.5C的倍率下可以提供约735mAh/g的容量，在1C倍率下循环300周之后仍然有422mAh/g的容量。展示出以酞菁铁为液相催化剂的锂硫电池具有优异的电化学性能。同时，研究揭示了酞菁铁液相催化的作用机制。酞菁铁作为一个具有导电能力的分子，通过改善多硫化物以及产物和石墨烯基底之间的界面和电荷转移过程，有效的降低阻抗、提高锂硫电池反应动力学。本项目的研究展示了液相催化在锂硫电池中应用的潜力，有力的推进了锂硫电池的实用化进程，并以此研究为基础探索新型的电池材料，获得高性能锂硫电池。