能源的儲存已成為再生能源供電穩定的關鍵，其中鋰離子電池為大型儲能設備的首選。然而，鋰離子電池可以提供儲存的最高能量已無法滿足交通等市場需求，因此科學家們致力發展於尋找更高電容及能量密度的電池，而鋰硫電池因其具有高電容、高能量密度，且硫因價格低廉且對環境友善，因此被譽為下一世代的電池。但是在鋰硫電池運轉時產生的穿梭效應大幅降低鋰硫電池效能，其中溶劑化電解液因其具有抑制穿梭效應的能力，因此被視為抑制穿梭效應並提升鋰硫電池性能的解決方案。
本實驗分別使用傳統鋰硫電池電解液(1 M LiTFSI 溶於DOL/DME 1:1(v/v))和不同的溶劑化電解液，包括：4.2 M LiTFSI 溶於ACN/TTE 1:1(v/v)、4.2 M LiTFSI 溶於DME/TTE 1:1(v/v)和4.2 M LiTFSI 溶於THF/TTE 1:1(v/v)進行電化學性能的測試，更使用了循環伏安法、臨場拉曼光譜及臨場X光吸收光譜等分析技術探討在不同電解液下，硫電極在充放電過程中的反應機制，並進一步的探討反應機制對電池性能的影響。
本研究結果顯示，溶劑化電解液相對於傳統鋰硫電池電解液具有更高的電容及更穩定的循環壽命。在臨場拉曼光譜中發現傳統鋰硫電池電解液會涉及複數個電化學及化學反應，因此可以觀察到各種不同的多硫化物，包括：S82-, S7-, S62-, S42-, S3●-，此現象也證明歧化反應的發生。然而若使用溶劑化電解液，只可觀察到中間產物S82-和S42-的生成，此說明了溶劑化電解液的電子轉移途徑較為單純且可以抑制歧化反應的發生。在臨場拉曼光譜實驗中更發現了除了濃度效應以外，不同溶劑對於鋰鹽的溶劑化能力不同，抑制歧化反應的能力也不同。在臨場X光吸收光譜中可以觀察到溶劑化電解液相較於傳統鋰硫電池電解液可溶解較少量的多硫化物。根據實驗結果，我們發現抑制歧化反應的發生可以讓電池具有更優異的電化學性能。

Sparingly solvated electrolytes have been proposed as one of the solutions to prevent shuttle effect in lithium-sulfur (Li-S) batteries. However, the sulfur reduction mechanisms occurred in different solvent systems are still unclear. In this study, we use in situ Raman/X-ray absorption spectroscopy to investigate the effect of conventional electrolyte (DOL/DME) and solvated electrolytes (ACN-based, DME-based and THF-based electrolyte) on the Li-S battery performance and sulfur reduction mechanism. In situ Raman spectroscopy shows that polysulfides, such as S82-, S7-, S62-, S42-, S3●- are formed through multiple electrochemical and chemical reactions in conventional ether-based electrolyte system, suggesting that disproportionation processes occur in the dilute electrolyte during discharge process. In contrast, in situ Raman spectroscopy shows that sulfur is reduced and forms S82-, S42- in solvated electrolyte during discharge process which suggests that solvated electrolyte could suppress disproportionation and has an uniform electron transfer pathway. Moreover, the solvated electrolyte with good solvation ability consists of less amount of free solvent which can suppress the disproportionation process efficiently. The solvation ability of solvated electrolytes was studied in the present work in detail.
In situ X-ray absorption spectroscopy of sulfur-carbon cathode suggests that less amount of polysulfide dissolution is formed in the solvated electrolyte than that of in the conventional ether-based electrolyte. Our results demonstrate that solvated electrolyte could suppress disproportionation processes resulted from the polysulfide dissolution and lead to an enhanced Li-S battery performance.

[1] S. Connor, "Global warming: Scientists say temperatures could rise by 6C by 2100 and call for action ahead of UN meeting in Paris," 2015.
[2] K. Fletcher, "EIA releases 2016 International Energy Outlook," 2016.
[3] S. Evers and L. F. Nazar, "New Approaches for High Energy Density Lithium–Sulfur Battery Cathodes," Accounts of Chemical Research, vol. 46, no. 5, pp. 1135-1143, 2013.
[4] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J.-M. Tarascon, "Li–O2 and Li–S batteries with High Energy Storage," Nature Materials, vol. 11, no. 1, pp 19-29, 2011.
[5] M. Pressman, "Understanding Tesla's Lithium Ion Batteries," 2017.
[6] P. G. Bruce, L. J. Hardwick, and K. Abraham, "Lithium-Air and Lithium-Sulfur Batteries, " MRS bulletin , vol. 36, no. 7, pp. 506-512, 2011.
[7] L. Carbone, S. Greenbaum, and J. Hassoun, "Lithium Sulfur and Lithium Oxygen Batteries: New Frontiers of Sustainable Energy Storage," Sustainable Energy & Fuels, vol. 1, no. 2, pp. 228-247, 2017.
[8] S. A. Freunberger ,Chen, Yuhui, Bruce, Peter G., "Reactions in the Rechargeable Lithium–O2 Battery with Alkyl Carbonate Electrolytes," Journal of the American Chemical Society, vol. 133, no. 20, pp. 8040-8047, 2011.
[9] X. Ji and L. F. Nazar, "Advances in Li–S batteries," Journal of Materials Chemistry, vol. 20, no. 44, pp. 9821-9826, 2010.
[10] Y.-X. Yin, S. Xin, Y.-G. Guo, and L.-J. Wan, "Lithium–Sulfur Batteries: Electrochemistry, Materials, and Prospects," Angewandte Chemie International Edition , vol. 52, no. 50, pp. 13186-13200, 2013.
[11] M. Hagen, D. Hanselmann, K. Ahlbrecht, R. Maça, D. Gerber, and J. Tübke, "Lithium–Sulfur Cells: the Gap between the State-of-the-Art and the Requirements for High Energy Battery Cells," Advanced Energy Materials, vol. 5, no. 16, pp. 1401986-1401996, 2015.
[12] W. Xu et al., "Lithium Metal Anodes for Rechargeable Batteries," Energy & Environmental Science, vol. 7, no. 2, pp. 513-537, 2014.
[13] L. Gireaud, S. Grugeon, S. Laruelle, B. Yrieix, and J. M. Tarascon, "Lithium Metal Stripping/Plating Mechanisms Studies: A Metallurgical Approach," Electrochemistry Communications, vol. 8, no. 10, pp. 1639-1649, 2006.
[14] R. Demir-Cakan, M. Morcrette, A. Guéguen, J.-M. Tarascon, and G. Babu, "Li-S Batteries: Simple Approaches for Superior Performance," Energy & Environment Science, vol. 6, no. 1, pp. 176-182, 2012.
[15] G. Ma, Z. Wen, Q. Wang, C. Shen, J. Jin, and X. Wu, "Enhanced Cycle Performance of a Li–S Battery Based on a Protected Lithium Anode," J. Mater. Chem. A, vol. 2, no. 45, pp. 19355-19359, 2014.
[16] J.-Q. Huang, T.-Z. Zhuang, Q. Zhang, H.-J. Peng, C.-M. Chen, and F. Wei, "Permselective Graphene Oxide Membrane for Highly Stable and Anti-Self-Discharge Lithium–Sulfur Batteries," ACS Nano, vol. 9, no. 3, pp. 3002-3011, 2015.
[17] Z. Yuan et al., "Powering Lithium–Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts," Nano Letters, vol. 16, no. 1, pp. 519-527, 2016.
[18] X. Liang et al., "Improved Cycling Performances of Lithium Sulfur Batteries with LiNO3-Modified Electrolyte," Journal of Power Sources, vol. 196, no. 22, pp. 9839-9843, 2011.
[19] S. Xiong, K. Xie, Y. Diao, and X. Hong, "Characterization of the Solid Electrolyte Interphase on Lithium Anode for Preventing the Shuttle Mechanism in Lithium–Sulfur Batteries," Journal of Power Sources, vol. 246, no. 246, pp. 840-845, 2014.
[20] T. Mandai, K. Yoshida, K. Ueno, K. Dokko, and M. Watanabe, "Criteria for Solvate Ionic Liquids," Physical Chemistry Chemical Physics, vol. 16, no. 19, pp. 8761-8772, 2014.
[21] Y. Yamada et al., "Unusual Stability of Acetonitrile-Based Superconcentrated Electrolytes for Fast-Charging Lithium-Ion Batteries," J. Am. Chem. Soc., vol. 136, no. 13, pp. 5039-5046, 2014.
[22] M. Cuisinier, P. E. Cabelguen, B. D. Adams, A. Garsuch, M. Balasubramanian, and L. F. Nazar, "Unique Behaviour of Nonsolvents for Polysulphides in Lithium–Sulphur Batteries," Energy Environ. Sci., vol. 7, no. 8, pp. 2697-2705, 2014.
[23] M. Wild and G. Offer, Lithium–Sulfur Batteries. 2019.
[24] R. Miao, J. Yang, Z. Xu, J. Wang, Y. Nuli, and L. Sun, "A New Ether-Based Electrolyte for Dendrite-Free Lithium-Metal Based Rechargeable Batteries," Scientific Reports, vol. 6, pp. 21771, 2016.
[25] W. Li et al., "The synergetic effect of lithium polysulfide and lithium nitrate to prevent lithium dendrite growth," Nature Communications, vol. 6, no.1, pp. 7436, 2015.
[26] M. Cuisinier, C. Hart, M. Balasubramanian, A. Garsuch, and L. Nazar, "Radical or Not Radical: Revisiting Lithium–Sulfur Electrochemistry in Nonaqueous Electrolytes," Advanced Energy Materials, vol.5, no.16, pp. 1401801, 2015.
 
[27] Q. Zou and Y.-C. Lu, "Solvent-Dictated Lithium Sulfur Redox Reactions: An Operando UV-Vis Spectroscopic Study," The Journal of Physical Chemistry Letters, vol. 7, no.8, pp. 1518-1525, 2016.
[28] O. J. Murphy, S. Srinivasan, and B. E. Conway, Electrochemistry in Transition: From the 20th to the 21st Century, New York: Plenum Press, 1992.
[29] C. O. Laoire, S. Mukerjee, K. Abraham, E. J. Plichta, and M. A Hendrickson," Influence of Nonaqueous Solvents on the Electrochemistry of Oxygen in the Rechargeable Lithium− Air Battery," The Journal of Physical Chemistry C, vol. 114, no.19, pp. 9178-9186, 2010.
[30] C. Wohlfarth, Static Dielectric Constant of the Pure Liquid and Binary Liquid Mixtures, New York: Springer 2015.
[31] G. Xiong, A. Kundu, and T. S. Fisher, Thermal effects in supercapacitors, New York: Springer International Publishing, 2015.
[32] S. A. Campbell, C. Bowes, and R. S. McMillan, "The Electrochemical Behaviour of Tetrahydrofuran and Propylene Carbonate without Added Electrolyte," Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, vol. 284, no. 1, pp. 195–204, 1990.
[33] R. E. Ruther et al., "Stable Electrolyte for High Voltage Electrochemical Double-Layer Capacitors," Journal of The Electrochemical Society, vol. 164, no. 2, pp. 277-283, 2017.
[34] F. Cataldo, "A Revision of The Gutmann Donor Numbers of a Series of Phosphoramides Iincluding TEPA". Eur. Chem. Bull., vol. 4, no. 2, pp. 92-97, 2015.
[35] M. Hagen et al., "In-Situ Raman Investigation of Polysulfide Formation in Li-S Cells," Journal of The Electrochemical Society, vol. 160, no. 8, pp. 1205-1214, 2013.
[36] J. D. McBrayer, T. E. Beechem, B. R. Perdue, C. A. Apblett, and F. H. Garzon, "Polysulfide Speciation in the Bulk Electrolyte of a Lithium Sulfur Battery," Journal of The Electrochemical Society, vol. 165, no. 5, pp. 876-881, 2018.
[37] J.-J. Chen et al., "Conductive Lewis Base Matrix to Recover the Missing Link of Li2S8 during the Sulfur Redox Cycle in Li–S Battery," Chemistry of Materials, vol. 27, no. 6, pp. 2048-2055, 2015.
[38] W. Zhu et al., "Investigation of the Reaction Mechanism of Lithium Sulfur Batteries in Different Electrolyte Systems by In Situ Raman Spectroscopy and In Situ X-ray Diffraction," Sustainable Energy & Fuels, vol. 1, no. 4, pp. 737-747, 2017.
[39] H. L. Wu, L. A. Huff, and A. A. Gewirth, "In Situ Raman Spectroscopy of Sulfur speciation in lithium-sulfur batteries," ACS Appl. Mater. Interfaces, vol. 7, no. 3, pp. 1709-1719, 2015.
[40] J. Hannauer, J. Scheers, J. Fullenwarth, B. Fraisse, L. Stievano, and P. Johansson, "The Quest for Polysulfides in Lithium-Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study," Chem. Phys. Chem., vol. 16, no. 13, pp. 2709-2709, 2015.
[41] J. T. Yeon, J. Y. Jang, J.-G. Han, J. Cho, K. Tae Lee, and N.-S. Choi, "Raman Spectroscopic and X-ray Diffraction Studies of Sulfur Composite Electrodes during Discharge and Charge, " Journal of the Electrochemical Society, vol. 159, no. 8, pp. 1308-1314, 2012,.
[42] J. Nelson et al., "In Operando X-ray Diffraction and Transmission X-ray Microscopy of Lithium Sulfur Batteries," Journal of the American Chemical Society, vol. 134, no. 14, pp. 6337-6343, 2012.
[43] S. Waluś et al., "New Insight into the Working Mechanism of Lithium–Dulfur Batteries: In Situ and Operando X-ray Diffraction Characterization," Chemical Communications, vol. 49, no. 72, pp. 7899-7901, 2013.
[44] T. Chivers, "Ubiquitous Trisulphur Radical Ion S3−·," Nature, vol. 252, no. 5478, pp. 32-33, 1974.
[45] M. Vijayakumar et al., "Molecular Structure and Stability of Dissolved Lithium Polysulfide Species," Physical Chemistry Chemical Physics, vol. 16, no. 22, pp. 10923-10932, 2014.
[46] T. Chivers and P. J. W. Elder, "Ubiquitous Trisulfur Radical Anion: Fundamentals and Applications in Materials Science, Electrochemistry, Analytical Chemistry and Geochemistry," Chemical Society Reviews, vol. 42, no. 14, pp. 5996-6005, 2013.
[47] T. Chivers and I. Drummond, "Characterization of the Trisulfur Radical Anion S3- in Blue Solutions of Alkali Polysulfides in Hexamethylphosphoramide," Inorganic Chemistry, vol. 11, no. 10, pp. 2525-2527, 1972.
[48] Y.-S. Su, Y. Fu, T. Cochell, and A. Manthiram, "A strategic approach to recharging lithium-sulphur batteries for long cycle life," Nature Communications, vol. 4, no. 1, pp. 2985,2013.
[49] M. Cuisinier et al., "Sulfur Speciation in Li–S Batteries Determined by Operando X-ray Absorption Spectroscopy," The Journal of Physical Chemistry Letters, vol. 4, no. 19, pp. 3227-3232, 2013.
[50] I. Seo and S. W. Martin, "Structural Properties of Lithium Thio-Germanate Thin Film Electrolytes Grown by Radio Frequency Sputtering," Inorganic Chemistry, vol. 50, no. 6, pp. 2143-2150, 2011.
[51] T. A. Pascal et al., "X-ray Absorption Spectra of Dissolved Polysulfides in Lithium–Sulfur Batteries from First-Principles," The Journal of Physical Chemistry Letters, vol. 5, no. 9, pp. 1547–1551, 2014.
[52] M. Cuisinier et al., "Sulfur Speciation in Li–S Batteries Determined by Operando X-ray Absorption Spectroscopy," The Journal of Physical Chemistry Letters, vol. 4, no.19, pp. 3227-3232, 2013.