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彭翃杰:纳米碳-多孔碳联姻用于高性能锂硫电池
清华大学绿色反应工程与工艺北京市重点实验室    2014-09-25 16:51:59   

彭翃杰:纳米碳-多孔碳联姻用于高性能锂硫电池

随着个人便携式电子设备、电动汽车以及可再生能源的飞速发展,具有高能量密度和高功率密度的电化学储能系统正受到高度的关注。碳材料以其优异的导电性、化学稳定性、机械强度以及丰富的孔结构成为构建高性能电极材料的重要组成部分,支撑着电化学储能元件如锂电池、超级电容器等的储能特性。例如,锂硫电池由于其远超传统的锂离子电池接近四倍的、高达2600 Wh L-1的理论能量密度,近年来正成为储能研究的热点。然而其实际应用仍然受限于较低的活性材料利用率、较低的效率、不理想的倍率性能和较差的循环寿命。这些问题主要来源于正极材料硫及其放电产物的高度电子/离子绝缘性以及多步电化学反应中具有高度溶解性的多硫化物中间产物。具有优异性能和合理纳米结构的碳材料是解决这些问题的优良途径。在碳材料家族中,具有sp2杂化掌控的纳米碳材料如碳纳米管、石墨烯等由于其优良的石墨结构、低的结构缺陷而具有优异的导电性和机械强度,是构建复合电极材料的优良候选。但其往往受限于纳米碳由于相互堆叠造成的低比表面积和孔结构。而以活性炭、介孔碳为代表的另一类碳材料则具有很高的比表面积和丰富可调的孔结构,在早期的锂硫电池研究中起到了先锋作用,但却由于其较多的结构缺陷而具有较差的导电能力,因此限制了锂硫电池的倍率性能。鉴于上述两种典型的碳材料均不能单独满足锂硫电池正极材料发展的需要,兼具高导电性和丰富孔结构的新型碳材料需要得到进一步的研究。
近期,清华大学张强、魏飞团队通过原位的化学气相沉积、碳热解以及化学活化的方法得到了一种碳纳米管/石墨烯/多孔碳的新型碳纳米杂化结构,其三维交联的碳纳米管/石墨烯网络提供了超过商用导电炭黑、活性炭几十倍的电子导率,而表面原位沉积的多孔碳层提供了高的比表面积和丰富的微孔/介孔结构,以用于储存纳米尺度的硫分子团簇并且提供互联通的离子通道。同时其多级孔结构在一定程度上也延缓了多硫化物向电解液主体中的溶解于扩散。因此基于这种新型碳纳米结构的锂硫电池在高达16.7 A g-1的电流密度下获得了超过800 mAh g-1的电化学容量,这意味着在六分钟内完成一次充放电循环,释放出超过传统锂离子电极材料两到三倍的能量。相关工作于以《具有高导电性和交互孔的石墨烯-碳管-多孔碳杂化物及其在锂硫电池的应用》(Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium-Sulfur Batteries) 为题发表在《先进功能材料》(Advanced Functional Materials)上,相关图片作为内封底发表。该文的第一作者是清华大学化工系反应工程实验室的博士生彭翃杰,通讯作者是本实验室教师张强、魏飞教授。
该工作表明,兼具高导电性和丰富孔结构的先进碳材料在电化学储能器件的研究中仍然具有重要的地位。这种新型的杂化纳米碳还具有在超级电容器、金属-空气电池盒钠离子电池/电容中发挥重要作用的潜力。

 


Marriage of nanocarbon and nanostructured porous carbon for next-generation batteries

By hybridizing sp2 nanocarbon and nanostructured porous carbon, researchers have created a high-energy and high-power lithium-sulfur battery at Tsinghua University, appearing on Volume 24, Issue 19 of Advanced Functional Material published on May 21, 2014.
"Motivated by the rapid development of portable electronics, electric vehicles, and renewable energy harvest, advanced energy storage devices such as lithium batteries are highly sought after," said Dr. Qiang Zhang, an associate professor at Department of Chemical Engineering, Tsinghua University. "Since the traditional lithium-ion battery has met its theoretical limitation for energy density, our group explored the tremendous potential of lithium-sulfur batteries, a novel electrochemical energy storage system, and has carried out wide research for about two years."
Lithium-sulfur batteries, employing sulfur as cathode and metallic lithium as anode, theoretically delivers energy density of 2600 Wh kg-1, three to six times higher than traditional lithium-ion batteries when sulfur and lithium are fully reacted. Additionally, the cathode material sulfur is naturally abundant, low cost, and environmentally friendly. However, there are still several challenge sto meet before lithium-sulfur batteries find practical application.
"On one hand, sulfur is highly electrical and ionic insulating. Its conductivity is several-to-ten orders of magnitude lower than typical LiCoO2 or LiFePO4 cathode material found in lithium-ion batteries, requiring 25 to 40 percent more weight in conductive agents within the whole cathode, thereby hindering the full demonstration of the intrinsic high energy density," Qiang told tsinghua.edu.cn,
"On the other hand, due to the multi-step and multi-phase reaction path, the high soluble intermediate, always in the form of chain-like polysulfide anions, generates at the cathode side, diffuses through the membrane, reacts with lithium anode, and shuttles back. During the whole process, polysulfides dissolve and irreversibly react with lithium and organic components, causing the destruction of the cathode structure, depletion of lithium anode, and loss of active materials. Thus, the life cycle is very poor."
Actually, similar to advanced anode material such as silicon and tin, there is a huge volume change (about 60-70 percent) when sulfur is fully lithiated into lighter lithium sulfide, resulting in the failure of the conductive scaffold and also the poor lifespan. To solve such multifaceted problems, researchers need to develop multifunctional material with high electrical conductivity, an interconnected ion pathway, and enough space for accommodating sulfur and retarding the diffusion of polysulfides.
"Carbon material plays a vital role in advanced energy storage systems like lithium-sulfur batteries due to their excellent conductivity, mechanical flexibility, and tailored morphology and surface chemistry" said Prof. Fei Wei. "Our group has investigated nanocarbon material for a long time and developed a series of methodologies for mass production of carbon nanotubes (CNTs) and graphene, as well as their application for energy storage. The sp2 nanocarbon possesses extraordinary electron conductivity with limited specific surface area and confined space. Nanostructured porous carbon such as activated carbon and mesoporous carbon have high specific surface area and porosity but low conductivity due to the defective nature. Since both of the two cannot meet the requirement of lithium-sulfur batteries, the hybridization, or the 'marriage' of two such materials will result in a novel carbon nanoarchitecture inheriting the advantages and exhibiting superior functionality."
Based on this concept, Hong-Jie Peng, a graduate student and the first author, developed an in-situ chemical vapor deposition strategy followed by hydrocarbon pyrolysis and chemical activation. A CNT/graphene/porous carbon nanoarchitecture with extraordinary electrical conductivity and hierarchical micro-/mesopores was fabricated for an advanced carbon/sulfur composite cathode.The rational marriage of the two carbon materials realized the potential of carbon material as both electron/ion pathway and active mass reservoir. The resulting lithium-sulfur exhibited extended cycle life and superior power capability.
"We hope that the advanced carbon materials can help lithium-sulfur batteries to be comparable to the engine-driven system for future electric transportation." said Hong-Jie. Further study will focus on the increase of areal sulfur loading and actual content, as well as the innovation of membrane, anode, electrolyte, and the whole configuration of the cell. Additionally, the hybridized carbon material has amazing applications in supercapacitors, sodium-ion batteries, and metal-air batteries, and other technologies.
More information: Peng HJ, Huang JQ, Zhao MQ, Zhang Q, Liu XY, Qian WZ, Wei F. "Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium-Sulfur Batteries." Advanced Functional Materials 2014, 24(19), 2772-2781. DOI: 10.1002/adfm.201303296.

清华大学化工系 张强
联系方式:62789041, 15810694966
zhang-qiang@mails.tsinghua.edu.cn; zhangqiangflotu@tsinghua.edu.cn

主要媒体报道链接:
Phys.org: Marriage of nanocarbon and nanostructured porous carbon for next-generation batteries
http://phys.org/news/2014-05-marriage-nanocarbon-nanostructured-porous-carbon.html

Nanowerk: Two-carbon marriage for better lithium-sulfur battery
http://www.nanowerk.com/nanotechnology-news/newsid=35611.php

MaterialsViewsChina: 杂化纳米碳用于高性能锂硫电池
http://www.materialsviewschina.com/2014/05/za-hua-na-mi-tan-yong-yu-gao-xing-neng-li-liu-dian-chi/

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