New insight into liquid electrolyte of rechargeable lithium/sulfur battery

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• 作者：Sheng S. Zhang ; ^{shengshui.zhang.civ@mail.mil} ; ^{shengshui@gmail.com}
• 关键词：Lithium/sulfur battery ; Liquid electrolyte ; Polysulfide ; Quaternary ammonium ; Ionic liquid
• 刊名：Electrochimica Acta
• 出版年：2013
• 出版时间：1 May, 2013
• 年：2013
• 卷：97
• 期：Complete
• 页码：226-230
• 全文大小：622 K

文摘

The lithium/sulfur (Li/S) cell is a liquid electrochemical system, in which the dissolution of lithium polysulfide (PS, the series of the sulfur reduction intermediates) plays an essential role in the cell's performance. In solution, the PS undergo a series of complicated disproportionations, as described by a general equation of Li₂S_n ¡ú m/8S₈ + Li₂S_n?m, to form the less soluble sulfur and low-order PS, which become inactive once precipitated out of the liquid electrolyte or deposited into the pores of separator. Based on the hard and soft acids and bases (HSAB) theory, quaternary ammonium cations are expected to stabilize the PS anions through a chemical interaction between the soft acid and soft base. In this paper, we report a significant improvement in the capacity retention of a Li/S cell by introducing a tetrabutylammonium triflate (NBu₄SO₃CF₃) or an N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) into the liquid electrolyte. For example, by using an electrolyte of 0.25 mol kg^?1 LiNO₃-0.25 mol kg^?1 PYR₁₄TFSI dissolved in a 1:1 (wt.) mixture of dimethyl ether (DME) and 1,3-dioxolane (DOL), a Li/S cell with a cathode containing 77 % sulfur and a 2 mg cm^?2 sulfur loading exhibited an initial capacity of 1227 mAh g^?1 and retained a capacity of 875 mAh g^?1 after 40 cycles when cycled at 0.2 mA cm^?2 between 1.7 V and 2.8 V. We contribute the improved performance to the stabilized PS anions by the added quaternary ammonium cations.