电解液组成对固相转化机制硫电极性能的影响

doi:10.19799/j.cnki.2095-4239.2019.0282

摘要/Abstract

摘要：

锂硫二次电池由于潜在的高比能优势，被认为是最具发展潜力的新一代电化学储能体系。然而，构建高活性、长寿命的硫电极遇到了巨大的技术挑战。主要原因是常规硫电极在其充放电过程中伴随着多硫离子中间产物的溶解和流失，导致其循环稳定性较差。我们前期工作证实，利用碳酸亚乙烯酯（VC）溶剂与多硫离子之间的亲核反应在硫电极表面原位生成一层SEI膜，可以有效隔离硫与电解液的直接接触，实现硫与硫化锂之间的固-固转换，从而避免多硫离子的产生和溶出。为了获得更符合实际应用的研究结果，本工作中我们采用高面载量硫电极（7mg/cm²）为研究对象，探究了电解液组成，包括VC含量、LiTFSI锂盐浓度，对固相转化硫电极性能的影响。结果表明，在高VC含量和高LiTFSI浓度的“双高”共溶剂电解液[2.5 mol/L LiTFSI + VC/DOL/DME（体积比为10:5:5）]中，高面载量S/C复合电极展现出高的可逆比容量（1090mA·h·g^-1）和优异的循环性能（50周容量保持率97.2%）。研究结果为构建高循环稳定性硫电极提供了可行的技术途径。

关键词: 锂硫电池, 硫正极, 共溶剂电解液, 固相转化, 高载量电极

Abstract:

Lithium-sulfur battery (Li-S) shows a great promise as a new generation electric energy storage technology due to its very high theoretical energy density (2600 W·h/kg). However, fabricating a sulfur cathode with acceptable high electrochemical utilization and long-term cyclability is a great challenge, mainly due to the unavoidable generation, dissolution and deactivation of soluble lithium polysulfide (PS) intermediates generated during the discharge process. Our previous study has demonstrated that the redox chemistry of sulfur cathodes can be converted from dissolution-deposition mechanism to a solid-phase conversion (SPC) reaction by in situ formation of a thin and compact solid electrolyte interface (SEI) on the sulfur surface through a prompt nucleophilic reaction of soluble PSs with vinyl carbonate (VC) molecule specially designed as a co-solvent in the ether-based electrolyte, thus separating the direct contact of electrolyte with the active sulfur and completely suppressing the generation and dissolution of PSs. To obtain the research results more in line with the practical application, we prepared a high-sulfur loading sulfur/carbon composite cathode (7mg/cm²) in this work, and investigated the influence of electrolyte composition, including VC content and LiTFSI concentration, on the performance of solid-phase conversion sulfur electrode. The experimental results demonstrated that, in a co-solvent electrolyte of 2.5 mol/L LiTFSI + VC/DOL/DME (volume ratio is 10:5:5) with high VC content and high LiTFSI concentration, thus-prepared high sulfur loading cathode can exhibit a high reversible specific capacity of 1090 mA·h/g and excellent cycling performance with a capacity retention of 97.2% after 50 cycles. This study provides a new insight for future development of high sulfur loading, structurally and electrochemically stable sulfur cathodes for new generation advanced Li-S batteries.

Key words: Li-S battery, sulfur electrode, co-solvent electrolyte, solid-phase conversion mechanism, high loading cathode

中图分类号:

TM 911

吴湘江, 何丰, 曹余良, 艾新平. 电解液组成对固相转化机制硫电极性能的影响[J]. 储能科学与技术, 2020, 9(2): 331-338.

WU Xiangjiang, HE Feng, CAO Yuliang, AI Xinping. Effect of electrolyte composition on the performance of sulfur cathode based on solid-phase conversion mechanism[J]. Energy Storage Science and Technology, 2020, 9(2): 331-338.

图/表 5

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种类	VC与醚类溶剂的体积比	LiTFSI浓度/mol·L^-1
“低VC低LiTFSI”电解液	1：10	1.0
“高VC低LiTFSI”电解液	10：10	1.0
“低VC高LiTFSI”电解液	1：10	2.5
“高VC高LiTFSI”电解液	10：10	2.5

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