Pretreatment of Lithium Surface by Using Iodic Acid - ACS Publications

Jan 31, 2017 - ... University of Electronic Science and Technology of China (UESTC), .... Toward Safe Lithium Metal Anode in Rechargeable Batteries: A...
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Pretreatment of Lithium Surface by Using Iodic Acid (HIO3) To Improve Its Anode Performance in Lithium Batteries Weishang Jia, Qingji Wang, Jingyi Yang, Cong Fan,* Liping Wang, and Jingze Li* State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Microelectronics and Solid-state Electronics, University of Electronic Science and Technology of China (UESTC), Chengdu 610054, People’s Republic of China S Supporting Information *

ABSTRACT: Iodic acid (HIO3) was exploited as the effective source to build an artificial solid-electrolyte interphase (SEI) on the surface of Li anode. On one hand, HIO3 is a weak solid-state acid and can be easily handled to remove most ioninsulating residues like Li2CO3 and/or LiOH from the pristine Li surface; on the other hand, both the products of LiI and LiIO3 resulted from the chemical reactions between Li metal and HIO3 are reported to be the ion-conductive components. As a result, the lower voltage polarization and impedance, longer cycling lifetime and higher Coulombic efficiency have been successfully achieved in the HIO3-treated Li− Li and Li−Cu cells. By further using the HIO3-treated Li anode into practical Li−S batteries, the impressive results also have been obtained, with average discharge capacities of 719 mAh g−1 for 200 cycles (0.2 C) and 506 mAh g−1 for 500 cycles (0.5 C), which were better than the Li−S batteries using the pristine Li anode (552 and 401 mAh g−1, respectively) under the same conditions. KEYWORDS: iodic acid, lithium anode, solid-electrolyte interphase, lithium battery, Li−S battery

1. INTRODUCTION Nowadays, to meet the increasing need in electronic devices (consumer electronics, electric vehicles, etc.), it is extremely desirable to develop new batteries with higher electrical energystorage capability. Lithium (Li) metal as the anode has long been regarded as the “Holy Grail” in battery technologies (e.g., Li−S and Li−O2 batteries), because of its low gravimetric density (0.53 g cm−3), low redox potential (−3.04 V vs. standard hydrogen electrode), and high theoretical specific capacity (3860 mAh g −1 vs. 372 mAh g −1 for the commercialized graphite anode).1−8 However, the problem of dendritic and mossy Li formation has been hindering the practical application of Li anode in the past four decades.9 On one hand, the uncontrolled growth of Li dendrites during charging process could easily penetrate into cathode, causing battery short circuiting and safety problems; on the other hand, the discharging process starts from the bottom of Li dendrites, probably leading to their electrical disconnection from Li matrix and consequently the gradual capacity loss.10 Advantageously, the initial contact between active Li metal and liquid electrolyte could cause complicated reactions, and the resulting products could construct the solid-electrolyte interphase (SEI), which is an ionic-conductive layer but could prevent the further chemical reactions of Li anode as well as the formation of Li dendrites.11 However, the volume change induced by Li deposition/stripping during repeated charging/discharging processes could cause SEI to crack and then repeatedly expose fresh Li metal. To overcome this key issue, most attentions are currently focused on the novel anode design and/or enhancing the SEI stability without sacrificing its ionic conductivity.12−16 © 2017 American Chemical Society

One simple and useful method for enhancing the SEI stability is to directly add electrolyte additive into the liquid electrolyte.17 Once fresh Li metal is exposed, the added electrolyte additive could quicken the SEI formation by involving the side reactions. At present, several effective electrolyte additives have been reported. For example, Cui et al. reported the synergetic effect of lithium polysulfide and LiNO3 could prevent the Li-dendrite growth in Li−Cu cells.18 Our group unveiled that KNO3 could have the same effectiveness as the widely used LiNO3 in Li−Cu and Li−S batteries.19 However, it is notable that this well-known modification may not remain long effective during cycling, since both Li metal and electrolyte additive are still being gradually consumed. Another effective methodology is to build the artificial SEI directly onto Li anode.20−23 For instance, Kim et al. reported a modified Li anode by spin-coating a uniform polymer layer of P(VC-co-AN), which could effectively stabilize the SEI and improve the performance of Li-LiCoO2 batteries,24 and Basile et al. also demonstrated the modified SEI on Li anode by immersing it into ionic liquids.25 Very recently, Guo et al. coated ionic-conductive Li3PO4 onto Li surface via solution immersion and the resulting Li anode exhibited impressive Lidendrite suppression.26 Regardless, it is remarkable that the artificial SEI is usually mechanically and/or chemically fragile. Once broken, the artificial SEI cannot be easily recovered. Received: November 14, 2016 Accepted: January 31, 2017 Published: January 31, 2017 7068

DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

Research Article

ACS Applied Materials & Interfaces In this article, we report that iodic acid (HIO3) could be a very useful source to build an effective artificial SEI on Li anode. On one hand, HIO3 is a weak solid-state acid and can be easily handled to remove most residual Li2CO3 and/or LiOH on the pristine Li foil, which are produced by Li exposure to trace of water/air and have been reported to be the ionicinsulating species.27 The resulting product of LiIO3 was reported to be an ionic-conductive material.28 On the other hand, HIO3 is an oxidative reagent and the reduced product of LiI has also been reported as an effective electrolyte additive in symmetric Li−Li cells by Archer’s group.29 Indeed, after the treatment of Li surface by HIO3 solution, the resulting Li anode could exhibit significantly reduced voltage hysteresis (∼30 mV) in symmetric Li−Li cell than the pristine Li anode (∼70 mV) at the current density of 0.5 mA cm−2 for 400 h. By applying the HIO3-treated Li anode into practical Li−S batteries, the improved cell performance was realized, with average discharge capacity of 506 mAh g−1 during 500 cycles at the current rate of 0.5 C and the efficiency enhancement of 26% from the pristine Li−S battery (average 401 mAh g−1).

2. RESULTS AND DISCUSSION 2.1. Pretreatment of Li Foil by HIO3. The treatment process of Li foil by HIO3 solution was illustrated in Figure 1.

Figure 2. SEM images of the polished Li surface (a,b) and the HIO3treated Li surface (c,d), respectively.

were shown and compared in Figure 3. Encouragingly, the HIO3-treated Li−Li cell exhibited distinctively smaller voltage polarization of ∼30 and ∼60 mV than the pristine Li−Li cell (∼70 and ∼90 mV) at both current densities of 0.5 and 1 mA cm−2, respectively. The selected galvanostatic cycling profiles at the 10th cycle tested at higher current densities of 2 and 3 mA cm−2 for the pristine and the HIO3-treated Li−Li cells also displayed the same trend (Figure S1). The small voltage polarization of the HIO3-treated Li anode was probably originated from the ion-conductive film induced by HIO3 treatment, whereas the Li-ion transportation was hampered by the residues (Li2CO3 and LiOH, etc.) on the pristine Li surface.31 Meanwhile, the charge−discharge voltage plateau of the HIO3-treated Li−Li cell was also observed to be much smoother than that of the pristine Li−Li cell, as widely reported.14,32,33 Furthermore, the long-time operation of the HIO3-treated Li−Li cell was also superior to the pristine one, with 400/100 h (0.5/1 mA cm−2) compared to 212/84 h, respectively. Remarkably, these achievements were comparable to the results of the Li−Li cell with LiF as the electrolyte additive (350 h, 0.5 mA cm−2),29 and significantly higher than the Li−Li cell with mechanical surface modification (170 h, 0.53 mA cm−2)34 or the Li−Li cell modified by (CH3)3SiCl treatment (16 h, 0.1 mA cm−2).35 In the other aspect, the lifetime of the Li−Li cells was 234 and 98 h for the polished anode at the same conditions, respectively (Figure S2). Subsequently, the EIS experiments of the symmetric Li−Li cells based on the pristine and the HIO3-treated Li anodes were separately carried out to inspect the impedance change at different standing time. The EIS plots of the two symmetric Li−Li cells with increased standing time were depicted in Figure 4. As the standing time increases, the charge-transfer impedance (Rct) of the pristine cell was significantly increased from 280 to 650 Ω (Figure 4a). The impedance of the cell with the polished Li anode increased from 230 to 397 Ω (Figure S3). These results indicated the ion-insulating passivation layer containing Li2CO3 and LiOH, etc. was getting thicker by the slow reactions between Li metal and liquid electrolyte. On the contrary, the HIO3-treated cell showed only a small amount of

Figure 1. (a) Schematic process for the HIO3-treated Li surface; (b) the artificial SEI and the possible main reactions.

The pristine Li foil was initially polished to remove most impurities, and then the polished Li foil was immersed into the as-prepared HIO3 solution for 10 min to afford the HIO3treated Li foil (see details in the Experimental Section). The SEM images of Li surface after polish and HIO3 treatment were shown in Figure 2. Before treatment, the polished Li foil exhibited unsmooth and porous morphology (Figure 2a,b); after the HIO3 treatment, the resulting Li foil displayed smooth and tight surface (Figure 2c,d), which could be benefited to the even distribution of current density and then the prevention of Li-dendrite formation.30 On the other hand, with many efforts,24,26 we were unable to offer the thickness data of the artificial film built at the current stage. 2.2. Li−Li Cell. To judge the anode performance of the HIO3-treated Li foil, the symmetric Li−Li cells were initially constructed to test the cell polarization at different current densities. The galvanostatic cycling diagrams of the symmetric Li−Li cells for the pristine and the HIO3-treated Li anodes 7069

DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

Research Article

ACS Applied Materials & Interfaces

Figure 3. Galvanostatic cycling diagrams of the symmetric Li−Li cells for the pristine and the HIO3-treated Li anodes. (a) The galvanostatic density was 0.5 mA cm−2 for 0.5 mAh cm−2; (b) the galvanostatic density was 1 mA cm−2 for 1 mAh cm−2.

Figure 4. EIS plots of the symmetric Li−Li cells with the pristine Li anode (a) and the HIO3-treated Li anode (b) at different standing time.

impedance augment from 69 to 120 Ω under the same conditions. Notably, the small initial impedance of 69 Ω for the HIO3-treated cell probably manifested that most ion-insulating components residing on the pristine Li surface were successfully removed by HIO3 treatment, and simultaneously the remaining products could be ion conductive and should effectively delay the reactions between Li metal and liquid electrolyte, which ultimately resulted in the slow impedance increase up to 120 Ω. Accordingly, the EIS plots (Figure S4) after cycling also manifested that the HIO3-treated Li−Li cell displayed the smaller impedance than the untreated one. 2.3. Li−Cu Cell. The same efficiency of the HIO3-treated Li anode was also confirmed in Li−Cu cells. As shown in Figure S5a, although the Coulombic efficiency (CE) therein determined in fact only reflected the efficiency on the Cu

side when the counter electrode was able to give the excess amount of Li, the CE value of the HIO3-treated Li−Cu cell could still get promoted from average 82% (pristine) to 91% for the initial 50 cycles, since the stable artificial SEI on the Li electrode could effectively reduce the side reactions between Li metal and liquid electrolyte, and simultaneously benefit the Liion transportation from its improved ionic conductivity. Moreover, the CE stability was also enhanced in the HIO3treated Li−Cu cell during long-time cycling, with the value of 84% at the 100th cycle, whereas the pristine one showed significantly decreased CE value (75%) after the 50th cycle. Notably, the CE value deviation from 100% for the HIO3treated Li−Cu cell was probably caused by the Li plating/ stripping on the Cu working electrode, where the formation of Li dendrites and the side reactions cannot be stopped. 7070

DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

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ACS Applied Materials & Interfaces

Figure 5. SEM images for the pristine Li surface (a and c) and the HIO3-treated Li surface (b−d); and the cross-sectional (side-view) images for the pristine Li foil (e) and the HIO3-treated Li foil (f), respectively. The current density was 0.5 mA cm−2 with the capacity of 0.5 mAh cm−2 for 30 cycles.

At the same time, the voltage polarization of the HIO3treated Li−Cu cell was also smaller than the pristine one during cycling. For example, the polarization values were ∼30 and ∼40 mV for the HIO3-treated and the pristine Li−Cu cells at the selected 10th cycle (Figure S5b), respectively, which was in accordance with the results observed in the symmetric Li−Li cells that the artificially formed SEI is advantageous for Li-ion transportation. 2.4. Functionality of HIO3. To get more insights about the functionality of HIO3 on the Li foil, the SEM images for the HIO3-treated and the pristine Li anodes were respectively collected and compared by disassembling the related Li−Li cells after 30 cycles. As depicted in Figure 5a,c, the intensively grown mossy/porous Li, which is related to the formation of sharp needle-like lithium dendrites,36 is clearly observed on the pristine Li foil. However, the mossy Li growth was effectively suppressed on the HIO3-treated Li foil, which displayed a smoother morphology (Figure 5b,d). Furthermore, as confirmed in the cross-sectional images for the pristine Li foil (Figure 5e) and the HIO3-treated Li foil (Figure 5f), the thickness of mossy Li was effectively reduced from ∼75 to ∼40 μm after the HIO3 treatment. Next, the EDX experiments were performed for the HIO3treated Li−Li cell. As shown in Figure S6 and S7, the intensive iodine(I) signal was observed in the EDX mapping both before and after the cycling, along with the detection of the common residue elements (C and O, etc.). The existence of I element could confirm that the I-containing compounds make contribution to the SEI formation. To further classify the Icontaining compounds, the XPS experiments on the HIO3treated Li surface were carried out to inspect the valence state of I element. As displayed in Figure 6, there were four clear XPS peaks of I element, where the two peaks located at 618.8 and 624.3 eV could be easily assigned to be the electrons from the I3d5/2 level of LiI and LiIO3, respectively;37,38 while the higher energy peaks located at 629.9 and 635.9 eV may be attributed to the electrons from the I3d3/2 level of LiI and LiIO3,39 respectively. The XPS spectra for other elements (Li,

Figure 6. XPS spectra of I element for the HIO3-treated Li surface.

C, and O) were depicted in Figure S8. No XPS signal of I2 molecule resulted from the comproportionation between LiI and LiIO3 was detected. These above results could confirm the contribution of the ion-conductive components (LiI and LiIO3) for the SEI construction. 2.5. Li−S Battery. Finally, the efficacy of the HIO3-treated Li anode was proved in practical Li−S batteries, where the S cathode with theoretical capacity of ∼1675 mAh g−1 is among the highest values of rechargeable Li battery systems.17 The detailed fabrication procedures were presented in the experimental section and the added ether-based liquid electrolyte volume should be optimized.40 Notably, the performance of the symmetric Li−Li cell after HIO3 treatment was still better than the pristine one by using the same etherbased liquid electrolyte but these results exhibited no superiority than the treated one with the carbonate-based electrolyte (Figure S9). For comparison, the untreated battery using the pristine Li anode was also fabricated under the same conditions. As depicted in Figure 7a, both batteries displayed comparable discharge capacities of 1066 and 1060 mAh g−1 in the first cycle at the current rate of 0.2 C, respectively. However, in the subsequent cycles, the superiority of the HIO3treated Li−S battery was observed and expected, with average discharge capacity of 719 mAh g−1 during 200 cycles and the 7071

DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

Research Article

ACS Applied Materials & Interfaces

Figure 7. Long-cycle profiles of the HIO3-treated and untreated Li−S batteries tested at the current rates of (a) 0.2 C and (b) 0.5 C, respectively. 4.2. Preparation of Sulfur Cathode. The carbon/sulfur (C/S) composite as the cathode was prepared by heating the mixture (C:S = 1:2 by weight) of carbon black (Ketjen Black) and sublimed S powder (99.5%, Alddin) in the Ar-filled tube furnace at 155 °C for 12 h. Afterward, the C/S composite, acetylene black and LA132 (binder, Chengdu Indigo Power Sources Co., Ltd.) with the weight ratio of 8:1:1 were manually mixed with deionized water to form a uniform slurry. Subsequently, the slurry was casted onto Al foil and dried at 60 °C in vacuum for 12 h. The sulfur mass loading on the cathode was about 1 mg cm−2. The cathode was finally punched into a disk (Φ = 10 mm) for assembling Li−S batteries. 4.3. Cell Assembly. The symmetric Li−Li cells were initially fabricated, where Li foil, Celgard 2325, and Li foil were used as the working electrode, the separator, and the counter electrode, respectively. Unless otherwise noted, all of the pristine/untreated cells directly made use of the commercial Li foil without polishing. The current density is 0.5 mA cm−2 or 1 mA cm−2, and the related discharge capacity is 0.5 mAh cm−2 or 1 mAh cm−2 in Li−Li cells. The Li−Cu cells were fabricated as the same procedure except using Cu foil as the working electrode. Before the assembly, Cu foil was washed with distilled water, ethanol and finally dried for 6 h in vacuum at 110 °C. The current density is 0.5 mA cm−2, and the discharge capacity is 0.5 mAh cm−2 in Li−Cu cells. The electrolyte was 1 M LiPF6 dissolved in a mixture of ethylene carbonate/dimethyl carbonate/diethyl carbonate (EC:DMC:DEC = 1:1:1 by volume) for both Li−Li and Li−Cu cells. The Li−S batteries were assembled by the same way except using S disk as the positive electrode. 1 M lithium bis(trifluoromethanesulphonyl)imide (LiTFSI) in 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) (1:1 by volume, Zhangjiagang Guotai-Huarong New Chemical Materials Co. Ltd.) was used as the electrolyte in Li−S batteries. The volume of the electrolyte added in our Li−S batteries was optimized to be 40 μL. 1 C means the current density of 1675 mA g−1 in Li−S batteries. The specific capacity was calculated according to the S mass. The Li−S batteries were tested in the voltage range of 1.7−2.8 V (vs. Li/Li+) at the current rate of 0.2 or 0.5 C. 4.4. Electrochemical Measurements and Characterization. All batteries were tested using a CT2001A cell test instrument (LAND Electronic Co. Ltd.) at room temperature. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were tested on electrochemical workstation (Parstat 2263). CV measurements were performed at a scan rate of 10 mV s−1 in the voltage range of −0.5 V to open-circuit potential (vs. Li+/Li). EIS tests were carried out at open-circuit potential in the frequency range of 1 MHz to 10 mHz with a perturbation amplitude of 10 mV. The morphology of Li foil was observed by field-emission scanning electron microscopy (FE-SEM, Hitachi, S3400N). The composition of Li foil surface was determined by energy dispersive X-ray spectroscopy (EDX, Oxford INCA PentaFET-x3). X-ray photoelectron spectroscopy (XPS, Kratos XSAM800) was used to analyze the surface

efficiency enhancement of 30% from the untreated battery (552 mAh g−1). Noticeably, the discharge capacity of the HIO3treated Li−S battery could remain 590 mAh g−1 at the 200th cycle, which was higher than our previous work by directly using KNO3 as the electrolyte additive (562 mAh g−1 at the 100th cycle).19 More importantly, the same trend was still obvious in another group of Li−S batteries tested at higher current rate of 0.5 C for 500 cycles. As shown in Figure 7b, both average CE value and discharge capacity were apparently promoted by 6% and 26% from the untreated Li−S battery (93 vs. 88% and 506 vs. 401 mAh g−1), respectively. Regardless, the significant capacity loss and the non-100% CE value were still apparent in both the HIO3-treated and untreated Li−S batteries, which were largely attributed to the shuttle effect caused by the dissolution of S cathode.30,41 However, we do believe that the capacity stability will get significantly improved once the problems occurred in S cathode are alleviated. The related work is ongoing.

3. CONCLUSIONS We initially exploited iodic acid (HIO3) as the useful source to build an effective artificial SEI on Li anode. The superior anode performance and the reduced Li-dendrite growth have been successfully achieved in Li−Li and Li−Cu cells when compared to the untreated Li anode. By further testing the HIO3-treated Li anode in practical Li−S batteries, the satisfactory discharge capacities of average 506 mAh g−1 were obtained for 500 cycles at 0.5 C, which was promoted by 26% from the untreated Li−S battery. 4. EXPERIMENTAL SECTION 4.1. Treatment of Li Foil by HIO3 Solution. Anhydrous iodic acid (HIO3, solid, 99.5%) was purchased from Aladdin without further purification. A total of 220 mg of HIO3 was dissolved into DMSO (50 mL) to prepare the resulting HIO3 solution. Li foil was repeatedly scraped and polished by a plastic blade to remove most impurities and the inherently passive film until the surface of the Li foil was extremely shiny. After that, Li foil was immersed into the HIO3 solution, and the Li foil with 10 min immersion exhibited the best performance. Some gas (e.g., CO2, H2) was slowly produced during the immersion. Upon removal from the solution, the Li foil was dried under vacuum for 1 h at room temperature, and all the procedures were performed in an Arfilled glovebox. After the polishing or the HIO3 treatment, there were no obvious impurities (e.g., silicone-based oils from the rollers) on Li surface based on the results from SEM and EDX tests. The mechanical and flexible properties of the treated Li foil showed no difference when compared to the untreated one. 7072

DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

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by a Mixed-Conductive Li2S Nanocomposite. Nano Lett. 2016, 16, 4521−4527. (7) Zhang, H.; Deng, Q.; Mou, C.; Huang, Z.; Wang, Y.; Zhou, A.; Li, J. Surface Structure and High-Rate Performance of Spinel Li4Ti5O12 Coated with N-Doped Carbon as Anode Material for Lithium-Ion Batteries. J. Power Sources 2013, 239, 538−545. (8) Zhang, H.; Deng, Q.; Zhou, A.; Liu, X.; Li, J. Porous Li2C8H4O4 Coated with N-Doped Carbon by Using CVD as an Anode Material for Li-Ion Batteries. J. Mater. Chem. A 2014, 2, 5696−5702. (9) Zu, C.-X.; Li, H. Thermodynamic Analysis on Energy Densities of Batteries. Energy Environ. Sci. 2011, 4, 2614−2624. (10) Lu, D.; Shao, Y.; Lozano, T.; Bennett, W. D.; Graff, G. L.; Polzin, B.; Zhang, J.; Engelhard, M. H.; Saenz, N. T.; Henderson, W. A.; Bhattacharya, P.; Liu, J.; Xiao, J. Failure Mechanism for FastCharged Lithium Metal Batteries with Liquid Electrolytes. Adv. Energy Mater. 2015, 5, 1400993. (11) Xu, K. Nonaqueous Liquid Electrolytes for Lithium-Based Rechargeable Batteries. Chem. Rev. 2004, 104, 4303−4418. (12) Cao, R.; Xu, W.; Lv, D.; Xiao, J.; Zhang, J.-G. Anodes for Rechargeable Lithium-Sulfur Batteries. Adv. Energy Mater. 2015, 5, 1402273. (13) Yun, Q.; He, Y. B.; Lv, W.; Zhao, Y.; Li, B.; Kang, F.; Yang, Q. H. Chemical Dealloying Derived 3D Porous Current Collector for Li Metal Anodes. Adv. Mater. 2016, 28, 6932−6939. (14) Liang, Z.; Lin, D.; Zhao, J.; Lu, Z.; Liu, Y.; Liu, C.; Lu, Y.; Wang, H.; Yan, K.; Tao, X.; Cui, Y. Composite Lithium Metal Anode by Melt Infusion of Lithium into a 3D Conducting Scaffold with Lithiophilic Coating. Proc. Natl. Acad. Sci. U. S. A. 2016, 113, 2862−2867. (15) Zhang, R.; Cheng, X. B.; Zhao, C. Z.; Peng, H. J.; Shi, J. L.; Huang, J. Q.; Wang, J.; Wei, F.; Zhang, Q. Conductive Nanostructured Scaffolds Render Low Local Current Density to Inhibit Lithium Dendrite Growth. Adv. Mater. 2016, 28, 2155−2162. (16) Cheng, X. B.; Peng, H. J.; Huang, J. Q.; Wei, F.; Zhang, Q. Dendrite-Free Nanostructured Anode: Entrapment of Lithium in a 3D Fibrous Matrix for Ultra-Stable Lithium-Sulfur Batteries. Small 2014, 10, 4257−4263. (17) Aurbach, D.; Pollak, E.; Elazari, R.; Salitra, G.; Kelley, C. S.; Affinito, J. On the Surface Chemical Aspects of Very High Energy Density, Rechargeable Li-Sulfur Batteries. J. Electrochem. Soc. 2009, 156, A694−A702. (18) Li, W.; Yao, H.; Yan, K.; Zheng, G.; Liang, Z.; Chiang, Y.-M.; Cui, Y. The Synergetic Effect of Lithium Polysulfide and Lithium Nitrate to Prevent Lithium Dendrite Growth. Nat. Commun. 2015, 6, 7436. (19) Jia, W.; Fan, C.; Wang, L.; Wang, Q.; Zhao, M.; Zhou, A.; Li, J. Extremely Accessible Potassium Nitrate (KNO3) as the Highly Efficient Electrolyte Additive in Lithium Battery. ACS Appl. Mater. Interfaces 2016, 8, 15399−15405. (20) Liu, Q. C.; Xu, J. J.; Yuan, S.; Chang, Z. W.; Xu, D.; Yin, Y. B.; Li, L.; Zhong, H. X.; Jiang, Y. S.; Yan, J. M.; Zhang, X. B. Artificial Protection Film on Lithium Metal Anode toward Long-Cycle-Life Lithium-Oxygen Batteries. Adv. Mater. 2015, 27, 5241−5247. (21) Zhu, B.; Jin, Y.; Hu, X.; Zheng, Q.; Zhang, S.; Wang, Q.; Zhu, J. Poly(dimethylsiloxane) Thin Film as a Stable Interfacial Layer for High-Performance Lithium-Metal Battery Anodes. Adv. Mater. 2017, 29, 1603755. (22) Liu, Y.; Lin, D.; Liang, Z.; Zhao, J.; Yan, K.; Cui, Y. LithiumCoated Polymeric Matrix as a Minimum Volume-Change and Dendrite-Free Lithium Metal Anode. Nat. Commun. 2016, 7, 10992. (23) Zheng, G.; Wang, C.; Pei, A.; Lopez, J.; Shi, F.; Chen, Z.; Sendek, A. D.; Lee, H.-W.; Lu, Z.; Schneider, H.; Safont-Sempere, M. M.; Chu, S.; Bao, Z.; Cui, Y. High-Performance Lithium Metal Negative Electrode with a Soft and Flowable Polymer Coating. ACS Energy Lett. 2016, 1, 1247−1255. (24) Choi, S. M.; Kang, I. S.; Sun, Y.-K.; Song, J.-H.; Chung, S.-M.; Kim, D.-W. Cycling Characteristics of Lithium Metal Batteries Assembled with a Surface Modified Lithium Electrode. J. Power Sources 2013, 244, 363−368.

composition of Li surface by using Al Kα (1486.6 eV) radiation as the primary excitation source operated at 180 W, and the binding energies were calibrated using the C 1s level (284.6 eV) as an internal reference. The preparation of Li sample was as follows: The symmetric Li−Li cells were disassembled after 30 cycles at the current density of 0.5 mA cm−2 with the capacity fixed at 0.5 mAh cm−2. Then the resulting Li foil was rinsed with anhydrous EC/DMC (1:1 by weight) and finally dried in the Ar-filled glovebox at room temperature. A special transfer system was employed to deliver the air-sensitive Li samples to SEM and XPS systems.42

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b14614. Voltage profiles of Li−Li cells selected at the 10th cycle (Figure S1); the galvanostatic cycling diagrams of the symmetric Li−Li cells for the polished Li electrode (Figure S2); the EIS plots of the symmetric Li−Li cells with the polished Li electrode at different standing time (Figure S3); the EIS plots of symmetric Li−Li cells with pristine and treated Li electrodes after 10 cycles (Figure S4); the Coulombic efficiency of the Li−Cu cells with different Li anodes and the voltage curves selected at the 10th cycle (Figure S5); the EDX mapping for the HIO3treated Li surface (Figure S6); the EDX of Li surface after 30 cycles (Figure S7); XPS spectra for the HIO3treated Li surface (Figure S8); the galvanostatic cycling diagrams for the treated and untreated Li−Li cells by using DOL/DME electrolyte (Figure S9). (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Cong Fan: 0000-0002-9603-1594 Jingze Li: 0000-0002-8455-7601 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the National Science Foundation of China (Nos. 11234013, 21473022, 21673033, and 51603028), the Science and Technology Bureau of Sichuan Province of China (No. 2015HH0033), and the Startup Grant of UESTC (No. ZYGX2015KYQD058).

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REFERENCES

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DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074

Research Article

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DOI: 10.1021/acsami.6b14614 ACS Appl. Mater. Interfaces 2017, 9, 7068−7074