Na-s - Tmmob Metalurji Ve Malzeme Mühendisleri Odası

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Bildiriler Kitabı TMMOB Metalurji ve Malzeme Mühendisleri Odası The Use of Polysulfide Barriers to Improve the Performance of Room-Temperature Sodium-Sulfur (Na-S) Batteries Abstract Limited resources of lithium paves a way to extensive research of room temperature sodiumsulfur batteries with the reason of being earthabundant nature and cheapness of sodium element. However, LWIDFHV³6KXWWOH(IIHFW´as seen in lithiumsulfur batteries. To suppress this effect, an ion selective membrane was inserted between the separators located among cathode and anode. It is expected that this design would entrap soluble polysulfides on the cathode side and suppress the shuttle effect. 1. Introduction Lithium-Sulfur (Li-S) batteries are one of the most promising type among lithium-based batteries with high theoretical capacity (1672 mAh/g) and energy density (2600 Wh/kg). However limited resource of lithium makes researchers find alternative anodic materials. Sodium is one of the most suitable anode materials among them. By combining sulfur with sodium at room temperature provides all advantages of lithium-sulfur batteries besides decreasing battery cost. Na-S batteries have similar charge-discharge process and same limitations with Li-S batteries which are i) insulating nature of sulfur, (ii) dissolution of polysulfides in electrolyte which results in loss of active material and capacity fading, (iii) shuttle effect of dissolved polysulfides, (iv) dendrite formation on lithium metal anode which causes safety problems. 1-12 Herein, in order to eliminate the poisoning of the sodium anode from polysulfide attacks, an ion selective membrane was used between anode and Elif Ceylan Cengiz, Rezan Demir-Çakan Gebze Technical University - Türkiye cathode as barrier, Na2S5 dissolved into electrolyte (so-called catholyte) was used as cathode while sodium is as anode side. With this configuration, we aim to keep dissolved polysulfides on the cathode side and thereafter their electrochemical performance was investigated. Firstly, different solvent-salt combinations were tried to determine the best performing combination for Na-S batteries followed by determination of solvent-salt complex. Additionally, different cut-off voltages were tried to observe their effect on the cell performance. 2. Experimental Procedure 2.1. Synthesis of Na2S5 Powder and Preparation of Catholyte Stochiometric amounts of sulfur powder and sodium particles were dissolved into ethylene glycol diethyl HWKHU DW  ƒ& IRU VHYHUDO GD\V $IWHU GU\LQJ procedure, catholyte was prepared as including 0.1 M Na2S5 powder in electrolytes. Catholyte was used directly as active material. 2.2. Preparation of C/S Composite Mesoporous Carbon/Sulfur (MCS) composite which gave the one of the best result in Li-S batteries was used for comparison.13 For the synthesis of mesoporous carbon, a sacrificial SBA-15 template was synthesized according to the method described by Stucky et al.15. After the synthesis, the pores of the SBA-15 template were completely filled with an aqueous solution of sucrose/H2SO4. The resulting wet sucrose/SBA- ZDVFDOFLQHGDWƒ&XQGHU an inert atmosphere. The silica was thereafter removed from the composites using a 4 M aqueous solution of ammonium hydrogen difluoride yielding carbon replicas. Then mesoporous carbon and sulfur 18. Uluslararası Metalurji ve Malzeme Kongresi | IMMC 2016 749 UCTEA Chamber of Metallurgical & Materials Engineers 2.3. Cell Assembly Measurements and electrolytes (catholyte) were at cathode side. Since Nafion has SO3- groups, the polysulfides Sn2- formed during discharge are pushed from the membrane. Thus, they are not able to migrate from anode side and are kept at cathode side. According to Fig. 1, 1 M NaOTF in TEGDME gave the best   9ROWDJH9 YV1D (50/55 wt%) were placed in a crucible and mixed. 7KHPL[WXUHZDVKHDWHGWRƒ&DQGQRDGGLWLRQDO washing procedure was applied afterward. The carbon/sulfur composite (MCS) after impregnation DW  ƒ& KDV  ZW  sulfur, as proven by thermogravimetric analysis (TGA) (data not shown). Prior to testing, the composite was hand-milled with 20 wt% Ketjen Black carbon. Final composite contains 40% S. For the battery in which MCS was used as cathode, 0.2 mL bare electrolyte (1 M NaOTF in TEGDME) is used. Proceedings Book Electrochemical Classical two-electrode Swagelok-typeTM cells were assembled in an Argon filled glove box. At first, different solvent-salt combinations were tried. These are 1 M NaClO4 (Sodium perchlorate) in TEGDME (Tetra ethylene glycol dimethyl ether), 1 M NaCF3SO3 (Sodium trifluoromethanesulfonateNaOTF) in TEGDME, 1 M NaOTF in TMS (Tetra methylene sulfone), 1 M NaOTF in DOL:DME (1,3Dioxolane: 1,2-Dimethoxyethane). Each Na/dissolved polysulfide cell includes 0.1 mL of Na2S5 containing 1 M salt in solvent and 0.1 mL bare electrolyte. After seeing that "1 M NaOTF in TEDGME" gave the best result, the other cells were made with this electrolyte. And additionally, different cut-off voltages were used to see their effect on battery performance. 3. Results and Discussion Electrolytes are very important component in Li-S battery systems, because they effect the chargedischarge mechanism substantially. Thus, herein the performance of electrolytes were investigated at first. Figure 1 shows the effect of electrolyte on Na/polysulfide batteries. To do so, four different combinations of electrolytes were prepared, these are 1 M NaOTF salt in TEGDME, 1 M NaOTF in TMS, 1 M NaOTF in DOL:DME, 1 M NaClO4 in TEGDME. All of these batteries had Nafion between the separators which were both located between anode and cathode. While bare electrolytes were present at the anode side, 0.1 M Na2S5 contained 750 IMMC 2016 | 01D27)LQ7(*'0( 01D27)LQ706               &DSDFLW\P$KJ  01D27)LQ'2/'0( 01D&O2LQ7(*'0(  'LVFKDUJH&DSDFLW\P$KJ Galvanostatic cycling measurements were performed using with the C/10 current density using a galvanostat/potentiostat VMP3. The voltage range is between 1.2-2.8 V vs Na. The amount of catholyte was fixed to 0.1 mL for all batteries. Nafion NR-212 membranes were used directly during battery assembly. 01D27)'2/'0( 01D&O27(*'0(   01D27)LQ7(*'0( 01D27)LQ706                 &\FOH1XPEHU Fig. 1 Na-S cells with different electrolytes. (a) galvanostatic charge/discharge curves (C/10), (b) Discharge capacities as a function of the cycle number. result, because TEGDME which is a glyme-based solvent can dissolve polysulfides to a large extent, since it has high donor number and low dielectric constant. Although DOL:DME is commonly used in Li-S batteries, by means of showing good performances, which did not perform well in Na-S batteries. Moreover, polarization is lower than the RWKHUHOHFWURO\WHVLQWKHFDVHRIXVLQJ³0NaOTF LQ7(*'0(´HOHFWURO\WH Conventional C/S cathode and Na/polysulfide batteries with and without Nafion were compared. These cells were operated between 1.2-2.8 V at C/10 current density. The capacity of the battery with Nafion has higher capacity than conventional C/S cathode and battery without Nafion. The reason of the low capacity of the battery with Nafion at first 18 th International Metallurgy & Materials Congress  Bildiriler Kitabı cycle can be because of non-wettability of Nafion. After several cycles, capacity started to increase and even at 40th cycle, ~300 mAh/g discharge capacity was obtained. Thus, Nafion barrier enhances the sulfur utilization of Na-S batteries. In addition to these, the reduction of polarization can be clearly seen in the case of battery with Nafion. The end-of discharge product Na2S is the main reason of capacity fading. Eliminating of this product may enhance the capacity and stability of cells. Na2S formation can be prevented by varying the cut-off voltages. It is known that Na2S is formed approximately 1.5 V, so if battery operates above this voltage, i.e. 1.7 V, it is thought that Na2S formation can be hindered. In this regard, different cut-off voltages which are 1.2-2.2 V, 1.7-2.8 V and 1.2-2.8 V were applied to the cells. Expectedly, 1.72.8 V results the best performance. CONCLUSION In this work, using Nafion barrier in roomtemperature Na-S batteries was investigated. It is obvious that confinement of sulfur into carbon pores is not a permanent solution, so different ideas are needed. Adding barrier to battery system is a good option for this reason. In this article, NR-212 type Nafion was used to prevent polysulfide shuttle and results show that this configuration is very effective to increase discharge capacity. In addition to this, it was thought that tuning the cut-off voltage may prevent the Na2S formation which is one of the biggest problems seen in Na-S batteries. TMMOB Metalurji ve Malzeme Mühendisleri Odası [5] S. Wenzel, H. Metelmann, C. Raiss, A. K. Durr, J. Janek, P. Adelhelm, J. Power Sources 2013,243, 758. [6] I. Kim, J.Y. Park, C.H. Kim, J.W. Park, J.P. Ahn, J.-H. Ahn, K.W. Kim, H.J. Ahn, J. Power Sources,2016, 301, 332-337. [7] I. Bauer, M. Kohl, H. Althues, S. Kaskel, Chem. Commun. 2014, 50, 3208. [8] X. W. Yu, A. Manthiram, J. Phys. Chem. Lett. 2014, 5, 1943. [9] X.W.Yu,A.Manthiram, ChemElectroChem 2014 , 1, 1275. [10] X. W. Yu., A. Manthiram, J. Phys. Chem. C 2014, 118, 22952. [11] X. W. Yu., A. Manthiram, Adv. Energy Mater. 2015, 1500350. [12] X.Y. Liu, Z.Q. Shan, K.L. Zhu, J.Y. Du, Q.W. Tang, J.H. Tian, J. Power Sources, 2015, 274 85±93. [13] X. Ji, K. T. Lee and L. F. Nazar, Nat. Mater., 2009, 8, 500. ACKNOWLEDGEMENTS This work is partially supported by National Young Researchers Career Development Grant of TUBITAK (contract no: 213M374). REFERENCES [1] C. W. Park, J. H. Ahn, H. S. Ryu, K. W. Kim, H. J. Ahn, Electrochem. Solid St. 2006, 9, A123. [2] D. J. Lee, J. W. Park, I. Hasa, Y. K. Sun, B. Scrosati, J. Hassoun, J. Mater. Chem. A 2013, 1, 5256. [3] T. H. Hwang, D. S. Jung, J. S. Kim, B. G. Kim, J. W. Choi, Nano Lett. 2013, 13, 4532. [4] S. Xin, Y. X. Yin, Y. G. Guo, L. J. Wan, Adv. Mater. 2014, 26, 1261. 18. Uluslararası Metalurji ve Malzeme Kongresi | IMMC 2016 751