Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries
Electrolyte Concentration Effect on Sulfur Utilization of Li-S Batteries
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DOI：
10.1149/2.0161902jes
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发表时间：
2019-01
影响因子：
3.9
通讯作者：
K. Sun;Na Li;D. Su;H. Gan
中科院分区：
文献类型：
--
作者：
K. Sun;Na Li;D. Su;H. Gan
电解质是锂硫电池的关键组成部分。过去的研究已经揭示了当电解质盐浓度增加到盐中溶剂状态时Li-S电池的行为，并证明了极大改善的循环寿命。然而，当电解质盐浓度从标准1.0M条件降低时，没有对Li-S电池的系统研究。这项工作通过使用具有相对高负载（> 6 mg cm− 2）的硫电极对DME：DOL组合中的标准LiTFSI进行系统研究来研究较低的盐浓度范围。虽然降低电解质盐浓度降低了离子电导率，但发现Li-S电池的硫利用率和倍率性能受益于该过程。当用LiI和LiBr代替LiTFSI时也发现了类似的观察结果，在相同的浓度水平下，LiI和LiBr形成比LiTFSI导电性更低的电解质。数据相关性表明Li-S电池的倍率性能与电解质电导率之间的相关性比与电解质粘度之间的相关性更强。在这项工作中，提出了自由Li+浓度，这是成比例的电解质的电导率，是真实的率能力的决定参数。降低电解质盐浓度和用更少的可解离盐（LiI、LiBr）代替LiTFSI都将减少电解质中的游离Li+，这将允许更高的Li 2 S 2/Li 2 S饱和点。这可能会延迟绝缘层在阴极导电网络上的积累，并提高溶解的Li-多硫化物到Li 2S 2/Li 2S的转化效率。阻抗和阴极形态都支持这一定理。
Electrolyte is the critical component of the Li-S battery. Past studies have shed light on the behavior of the Li-S cells when the electrolyte salt concentration is increased to the solvent-in-salt regime and demonstrated tremendously improved cycle life. However, there is no systematic study on the Li-S cell when the electrolyte salt concentration is reduced from the standard 1.0 M condition. This work investigates the lower salt concentration regime by doing a systematic study with the standard LiTFSI in DME: DOL combination, using sulfur electrodes with relatively high loading (> 6 mg cm− 2). Although reducing the electrolyte salt concentration lowers the ionic conductivity, it is found that the sulfur utilization and rate capability of the Li-S cells benefits from this process. Similar observations are also found when LiTFSI is replaced with LiI and LiBr, which form less conductive electrolytes than LiTFSI at the same concentration levels. Data correlation indicates a stronger correlation between the Li-S cell's rate-capability and the electrolyte conductivity than electrolyte viscosity. It is proposed in this work that free Li+ concentration, which is proportional to the electrolyte conductivity, is the real rate-capability determining parameter. Reducing the electrolyte salt concentration and replacing LiTFSI with less dissociable salts (LiI, LiBr) both will reduce the free Li+ in the electrolyte, which will allow a higher saturation point of Li 2 S 2/Li 2 S. This probably will delay the insulating layer buildup on the cathode conductive network and improve the dissolved Li-polysulfide to Li 2 S 2/Li 2 S conversion efficiency. Both impedance and cathode morphology support this theorem.