近年來，隨著技術的推進與能源需求的增加，擁有高能量密度與高安全性的無陽極鋰金屬電池被認為極具發展的潛能，但是在無陽極電池中仍有許多挑戰需解決，如鋰枝晶的生長與庫倫效率低與電池循環壽命縮短，因此為了提升電池的性能與穩定性，採用的解決方法包括優化電解液、改質電極表面等方法。
本研究著重於優化電解液並且主要分為添加劑與局部高濃度電解液兩個部分，第一部分將三種添加劑以混合物設計（mixtrue design）的實驗方法，以十種配比進行有效篩選，搭配無陽極鋰金屬電池作為電解液開發平台，成功地開發出最佳添加劑配比為1wt% DTD+1wt% LiDFOB，與商用電解液相比，可以使無陽極電池的平均庫倫效率從86%提升至95%並且經過30圈循環後放電容量保持率仍保有40%。第二部分之實驗結果顯示以1,1,2,2-四氟乙基 2,2,3,3-四氟丙基醚(1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl Ether, TTE)為稀釋劑的碳酸乙二酯/碳酸甲乙酯溶劑配方EC/EMC/TTE (v:v:v=3:7:10)，搭配LiPF6 0.1/LiTFSI0.9雙鹽，可調配1.5 M之局部高濃度電解液，其黏度從15.6 mPa*s降低至6.6 mPa*s，同時電解液對隔離膜之潤濕性提升，使用拉曼光譜分析證明電解液的溶劑化結構使得游離溶劑含量降低並且從SEM形貌分析發現局部高濃度電解液能夠讓鋰離子均勻地沉積於銅箔表面，因此具有較好的電池循環穩定性。
最後整合以上兩部分的成果，使用最佳配比之添加劑於局部高濃度電解液中進行優化，在Li||Cu電池中能夠降低電池的極化現象並減少死鋰的產生，同時利用XPS分析發現使用添加劑後有助於提升SEI組成的無機物含量。在NMC||Li電池中顯示出使用添加劑有助於提升電解液在高電壓下的穩定性並在正極上形成保護膜使得電池能夠穩定地循環完100圈，最後經過變速率性能、工作電位窗口以及安全性測試證明優化後之電解液擁有穩定的變速率性能、工作電位窗口提升至6 V並具有耐燃性。

In recent years, with the advancement of technology and the increase in energy demand, anode-free lithium metal batteries with high energy density and high safety are considered to have great potential for development. However, there are still many challenges to solve in anode-free batteries, such as the growth of lithium dendrites, low coulombic efficiency, and short battery cycle life. Therefore, to improve the performance and stability of the battery, the solutions adopted include optimizing the electrolyte and modifying the electrode surface.
This study focuses on optimizing electrolytes and is divided into additives and local high-concentration electrolytes. The first part uses the mixture design of experiments to optimize ten different combination ratios of three additives. The screening was assisted with the anode-free lithium metal battery as the electrolyte development platform. The optimal additive ratio of 1wt% DTD+1wt% LiDFOB was successfully identified. Compared with the commercial electrolyte, the average coulombic efficiency of the anode-free battery can be increased from 86 % to 95%, and the discharge capacity retention rate remained at 40% after 30 cycles. The experimental results of the second part showed that 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) is the diluent added into ethylene carbonate/ethyl methyl carbonate solvents in a ratio of EC/EMC/TTE (v:v:v=3:7:10). The addition of dual-salt with LiPF6 0.1/LiTFSI0.9 can form a localized high-concentration of 1.5 M. The viscosity of the localized high-concentration electrolyte was reduced from 15.6 mPa*s to 6.6 mPa*s, and the wettability of the electrolyte to the separator was greatly improved. Raman spectroscopy analysis proves that the solvated structure of the electrolyte reduces the free solvent content. From the SEM morphology analysis, it is found that the localized high-concentration electrolyte can make the lithium ions more evenly deposited on the surface of the copper foil, so it enables better battery cycling stability.
Finally, the results of the above two parts are integrated, and the optimal ratio of additives is used to optimize the localized high-concentration electrolyte. In Li||Cu battery, the polarization phenomenon of the battery and the amount of dead lithium can be reduced. At the same time, XPS analysis found that additives increase the inorganic content of the SEI composition. In NMC||Li battery, it shows that additives can help improve the stability of the electrolyte at high voltage and form a protective film on the positive electrode to make battery complete 100 cycles stably. Finally, the optimized electrolyte has stable variable rate performance, wide operating potential window (up to 6 V) and nonflammability, which are proved by variable rate performance, working potential window and safety tests.

1. Liang, Y.; Zhao, C. Z.; Yuan, H.; Chen, Y.; Zhang, W.; Huang, J. Q.; Yu, D.; Liu, Y.; Titirici, M. M.; Chueh, Y. L., A review of rechargeable batteries for portable electronic devices. InfoMat 2019, 1 (1), 6-32.
2. Brown, S.; Pyke, D.; Steenhof, P., Electric vehicles: The role and importance of standards in an emerging market. Energy Policy 2010, 38 (7), 3797-3806.
3. Arfwedson, A., Untersuchung einiger bei der Eisen-Grube von Utö vorkommenden Fossilien und von einem darin gefundenen neuen feuerfesten Alkali. J. Chem. Phys 1818, 22, 93-117.
4. Lewis, G. N.; Keyes, F. G., THE POTENTIAL OF THE LITHIUM ELECTRODE. Journal of the American Chemical Society 1913, 35 (4), 340-344.
5. Cheng, X.-B.; Zhang, R.; Zhao, C.-Z.; Zhang, Q., Toward safe lithium metal anode in rechargeable batteries: a review. Chemical reviews 2017, 117 (15), 10403-10473.
6. Whittingham, M. S., Electrical energy storage and intercalation chemistry. Science 1976, 192 (4244), 1126-1127.
7. Whittingham, M. S.; Yoshino, A., Lithium-Ion Batteries. 2019.
8. Hausbrand, R.; Cherkashinin, G.; Ehrenberg, H.; Gröting, M.; Albe, K.; Hess, C.; Jaegermann, W., Fundamental degradation mechanisms of layered oxide Li-ion battery cathode materials: Methodology, insights and novel approaches. Materials Science and Engineering: B 2015, 192, 3-25.
9. Tian, Y.; An, Y.; Wei, C.; Jiang, H.; Xiong, S.; Feng, J.; Qian, Y., Recently advances and perspectives of anode-free rechargeable batteries. Nano Energy 2020, 78, 105344.
10. Nanda, S.; Gupta, A.; Manthiram, A., Anode‐free full cells: a pathway to high‐energy density lithium‐metal batteries. Advanced Energy Materials 2021, 11 (2), 2000804.
11. Qian, J.; Adams, B. D.; Zheng, J.; Xu, W.; Henderson, W. A.; Wang, J.; Bowden, M. E.; Xu, S.; Hu, J.; Zhang, J. G., Anode‐free rechargeable lithium metal batteries. Advanced Functional Materials 2016, 26 (39), 7094-7102.
12. Mizushima, K.; Jones, P.; Wiseman, P.; Goodenough, J. B., LixCoO2 (0< x⩽ 1): A new cathode material for batteries of high energy density. Solid State Ionics 1981, 3, 171-174.
13. Daniel, C.; Mohanty, D.; Li, J.; Wood, D. L. In Cathode materials review, AIP Conference Proceedings, American Institute of Physics: 2014; pp 26-43.
14. Ohzuku, T.; Makimura, Y., Layered lithium insertion material of LiNi1/2Mn1/2O2: a possible alternative to LiCoO2 for advanced lithium-ion batteries. Chemistry letters 2001, 30 (8), 744-745.
15. Ohzuku, T.; Makimura, Y., Layered lithium insertion material of LiCo1/3Ni1/3Mn1/3O2 for lithium-ion batteries. Chemistry Letters 2001, 30 (7), 642-643.
16. Thackeray, M.; David, W.; Bruce, P.; Goodenough, J., Lithium insertion into manganese spinels. Materials Research Bulletin 1983, 18 (4), 461-472.
17. Matsumoto, K.; Inoue, K.; Nakahara, K.; Yuge, R.; Noguchi, T.; Utsugi, K., Suppression of aluminum corrosion by using high concentration LiTFSI electrolyte. Journal of power sources 2013, 231, 234-238.
18. Peled, E., The electrochemical behavior of alkali and alkaline earth metals in nonaqueous battery systems—the solid electrolyte interphase model. Journal of The Electrochemical Society 1979, 126 (12), 2047.
19. Zhang, S. S., A review on electrolyte additives for lithium-ion batteries. Journal of Power Sources 2006, 162 (2), 1379-1394.
20. Haregewoin, A. M.; Wotango, A. S.; Hwang, B.-J., Electrolyte additives for lithium ion battery electrodes: progress and perspectives. Energy & Environmental Science 2016, 9 (6), 1955-1988.
21. Liu, M.; Vatamanu, J.; Chen, X.; Xing, L.; Xu, K.; Li, W., Hydrolysis of LiPF6-containing electrolyte at high voltage. ACS Energy Letters 2021, 6 (6), 2096-2102.
22. Zhan, C.; Wu, T.; Lu, J.; Amine, K., Dissolution, migration, and deposition of transition metal ions in Li-ion batteries exemplified by Mn-based cathodes–a critical review. Energy & Environmental Science 2018, 11 (2), 243-257.
23. Zhang, X.-Q.; Wang, X.-M.; Li, B.-Q.; Shi, P.; Huang, J.-Q.; Chen, A.; Zhang, Q., Crosstalk shielding of transition metal ions for long cycling lithium–metal batteries. Journal of Materials Chemistry A 2020, 8 (8), 4283-4289.
24. Li, W., An unpredictable hazard in lithium-ion batteries from transition metal ions: dissolution from cathodes, deposition on anodes and elimination strategies. Journal of The Electrochemical Society 2020, 167 (9), 090514.
25. Chandra, A.; Bagchi, B., Ionic contribution to the viscosity of dilute electrolyte solutions: Towards a microscopic theory. The Journal of Chemical Physics 2000, 113 (8), 3226-3232.
26. Yamada, Y.; Yamada, A., Superconcentrated electrolytes for lithium batteries. Journal of The Electrochemical Society 2015, 162 (14), A2406.
27. Tatara, R.; Yu, Y.; Karayaylali, P.; Chan, A. K.; Zhang, Y.; Jung, R.; Maglia, F.; Giordano, L.; Shao-Horn, Y., Enhanced cycling performance of Ni-rich positive electrodes (NMC) in Li-ion batteries by reducing electrolyte free-solvent activity. ACS applied materials & interfaces 2019, 11 (38), 34973-34988.
28. Liu, W.; Li, J.; Li, W.; Xu, H.; Zhang, C.; Qiu, X., Inhibition of transition metals dissolution in cobalt-free cathode with ultrathin robust interphase in concentrated electrolyte. Nature communications 2020, 11 (1), 1-11.
29. Chen, S.; Zheng, J.; Mei, D.; Han, K. S.; Engelhard, M. H.; Zhao, W.; Xu, W.; Liu, J.; Zhang, J. G., High‐voltage lithium‐metal batteries enabled by localized high‐concentration electrolytes. Advanced materials 2018, 30 (21), 1706102.
30. Ma, G.; Wang, L.; He, X.; Zhang, J.; Chen, H.; Xu, W.; Ding, Y., Pseudoconcentrated electrolyte with high ionic conductivity and stability enables high-voltage lithium-ion battery chemistry. ACS Applied Energy Materials 2018, 1 (10), 5446-5452.
31. Su, C.-C.; He, M.; Amine, R.; Rojas, T.; Cheng, L.; Ngo, A. T.; Amine, K., Solvating power series of electrolyte solvents for lithium batteries. Energy & Environmental Science 2019, 12 (4), 1249-1254.
32. Han, J. G.; Kim, K.; Lee, Y.; Choi, N. S., Scavenging materials to stabilize LiPF6‐containing carbonate‐based electrolytes for Li‐ion batteries. Advanced Materials 2019, 31 (20), 1804822.
33. Choi, H.; Bae, Y.; Lee, S.-M.; Ha, Y.-C.; Shin, H.-C.; Kim, B. G., A LiPF 6-LiFSI Blended-Salt Electrolyte System for Improved Electrochemical Performance of Anode-Free Batteries. Journal of Electrochemical Science and Technology 2022, 13 (1), 78-89.
34. Jiang, B.; Xu, H.; Cheng, X.; Li, J.; Wang, H.; Liu, Y., Dual‐Salt Electrolyte with Synergistic Effect for Lithium Metal Batteries with Prolonging Cyclic Performance. ChemElectroChem 2022, 9 (2), e202101251.
35. Beyene, T. T.; Bezabh, H. K.; Weret, M. A.; Hagos, T. M.; Huang, C.-J.; Wang, C.-H.; Su, W.-N.; Dai, H.; Hwang, B.-J., Concentrated dual-salt electrolyte to stabilize Li metal and increase cycle life of anode free Li-metal batteries. Journal of The Electrochemical Society 2019, 166 (8), A1501.
36. Yu, B. T.; Qiu, W. H.; Li, F. S.; Cheng, L., A study on sulfites for lithium-ion battery electrolytes. Journal of power sources 2006, 158 (2), 1373-1378.
37. Li, X.; Yin, Z.; Li, X.; Wang, C., Ethylene sulfate as film formation additive to improve the compatibility of graphite electrode for lithium-ion battery. Ionics 2014, 20 (6), 795-801.
38. Zhao, W.; Zheng, G.; Lin, M.; Zhao, W.; Li, D.; Guan, X.; Ji, Y.; Ortiz, G. F.; Yang, Y., Toward a stable solid-electrolyte-interfaces on nickel-rich cathodes: LiPO2F2 salt-type additive and its working mechanism for LiNi0. 5Mn0. 25Co0. 25O2 cathodes. Journal of power sources 2018, 380, 149-157.
39. Liu, Q.; Ma, L.; Du, C.; Dahn, J., Effects of the LiPO2F2 additive on unwanted lithium plating in lithium-ion cells. Electrochimica acta 2018, 263, 237-248.
40. Dong, Q.; Guo, F.; Cheng, Z.; Mao, Y.; Huang, R.; Li, F.; Dong, H.; Zhang, Q.; Li, W.; Chen, H., Insights into the dual role of lithium difluoro (oxalato) borate additive in improving the electrochemical performance of NMC811|| Graphite cells. ACS Applied Energy Materials 2019, 3 (1), 695-704.
41. Morita, M.; Shibata, T.; Yoshimoto, N.; Ishikawa, M., Anodic behavior of aluminum in organic solutions with different electrolytic salts for lithium ion batteries. Electrochimica Acta 2002, 47 (17), 2787-2793.
42. Mukai, K.; Inoue, T.; Kato, Y.; Shirai, S., Superior low-temperature power and cycle performances of Na-ion battery over Li-ion battery. ACS omega 2017, 2 (3), 864-872.
43. Krause, L. J.; Lamanna, W.; Summerfield, J.; Engle, M.; Korba, G.; Loch, R.; Atanasoski, R., Corrosion of aluminum at high voltages in non-aqueous electrolytes containing perfluoroalkylsulfonyl imides; new lithium salts for lithium-ion cells. Journal of power sources 1997, 68 (2), 320-325.
44. Brown, Z. L.; Jurng, S.; Nguyen, C. C.; Lucht, B. L., Effect of fluoroethylene carbonate electrolytes on the nanostructure of the solid electrolyte interphase and performance of lithium metal anodes. ACS Applied Energy Materials 2018, 1 (7), 3057-3062.
45. Jurng, S.; Brown, Z. L.; Kim, J.; Lucht, B. L., Effect of electrolyte on the nanostructure of the solid electrolyte interphase (SEI) and performance of lithium metal anodes. Energy & Environmental Science 2018, 11 (9), 2600-2608.
46. Huang, C.-J.; Thirumalraj, B.; Tao, H.-C.; Shitaw, K. N.; Sutiono, H.; Hagos, T. T.; Beyene, T. T.; Kuo, L.-M.; Wang, C.-C.; Wu, S.-H., Decoupling the origins of irreversible coulombic efficiency in anode-free lithium metal batteries. Nature communications 2021, 12 (1), 1-10.