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High energy density Li-ion battery with ultra-stable electrolyte is essential to facilitate the massive application of electric vehicles. Despite being used ubiquitously in Li-ion batteries, lithium hexafluorophosphate (LiPF6) is not stable both chemical and electrochemically, rendering the battery using LiPF6 based electrolyte. While lithium bis(fluorosulfonyl)imide (LiFSI) based electrolyte possesses both higher conductivity and better compatibility with the electrode materials compared to the traditional LiPF6 electrolyte, the high cost and the inability to suppress aluminum corrosion hinder its application in Li-ion batteries. In this work, we developed a bi-salt electrolyte by blending LiPF6 and LiFSI, as well as introducing Lithium difluoroborate (LiDFOB) as the anti-corrosion additive to mitigate the Al corrosion. Although the newly formulated electrolyte shows promising result at coin cell level, the big format pouch cell using the new electrolyte failed after prolonged cycling due to the detachment of the Cu tab. Based on the NMR results, we revealed that Al corrosion was accelerated by the change in the electrolyte formulation during cycling, and the situation was further escalated by the high state of charge (SOC). Most importantly, the Al3+ ions dissolved from the cathode side migrated to the anode side and formed alloy with Li and Cu, triggering the detachment of Cu tab, which was confirmed by SEM, ICP-MS and HRXRD. Owing to the higher current density and temperature on the tab region, it has significantly higher chance to be torn apart. In sum, it is imperative to precisely control both the SOC and the amount of LiFSI added to minimize the corrosion problem.

To facilitate the massive commercialization of electric vehicles, it is imperative to enhance the energy density of the state-of-the-art lithium battery technology. [1] Lithium metal battery (LMB) is considered as a promising energy storage system because of the exceptionally low electrochemical potential and ultrahigh specific capacity of the lithium metal anode. [2-4] Yet, the extensive application of LMBs is still obstructed by the extreme reactivity of lithium metal, which leads to severe safety problems. [5-6] To tackle this issue, the re-design of the electrolyte is viewed as the most practical approach due to its cost effectiveness. [7-8] In this presentation, we successfully establish a solvation rule for the SEI enabler to achieve stable cycling of the lithium metal anode through a variety of electrochemical and solvation studies such as a Li/Cu cell test and IR-DOSY analysis. Fluoroethylene carbonate (FEC) was used as the exemplary solid-electrolyte interphase (SEI) enabler because it is the most common SEI enabler in the LMB electrolyte, and it is able to form a desirable SEI on the lithium metal surface. The results of all electrochemical studies point to the existence of a critical ratio between FEC and a co-solvent (e.g., DMC, EMC, and EA) for the stable cycling of LMBs. If the FEC/co-solvent ratio is lower than the critical ratio, not only will an unstable SEI be formed, but the SEI will also be gradually deteriorated by the significant decomposition of lithium complexes, with Li+ solvated solely by the co-solvent/non-SEI enabler. We discovered that the solvation number of FEC must be ≥ 1 to ensure the formation of a stable SEI, which mainly resulted from the sacrificial reduction of the SEI enabler and subsequent repair of the SEI to facilitate stable cycling of LMBs. This finding is crucial for the future development of functional electrolytes in that the ratio of FEC to co-solvent must exceed the critical volume/molar ratio for the solvation number of FEC to be ≥ 1. Reference: Schmuch, R.; Wagner, R.; Hörpel, G.; Placke, T.; Winter, M., Nature Energy 2018, 3, 267–278. Li, X.; Zheng, J.; Engelhard, M. H.; Mei, D.; Li, Q.; Jiao, S.; Liu, N.; Zhao, W.; Zhang, J. G.; Xu, W., ACS Applied Materials & Interfaces 2018, 10 (3), 2469-2479. Xu, W.; Wang, J.; Ding, F.; Chen, X.; Nasybulin, E.; Zhang, Y.; Zhang, J.-G., Energy Environ. Sci. 2014, 7 (2), 513– Fang, C.; Li, J.; Zhang, M.; Zhang, Y.; Yang, F.; Lee, J. Z.; Lee, M. H.; Alvarado, J.; Schroeder, M. A.; Yang, Y.; Lu, B.; Williams, N.; Ceja, M.; Yang, L.; Cai, M.; Gu, J.; Xu, K.; Wang, X.; Meng, Y. S., Nature 2019, 572, 511. Alvarado, J.; Schroeder, M. A.; Pollard, T. P.; Wang, X.; Lee, J. Z.; Zhang, M.; Wynn, T.; Ding, M.; Borodin, O.; Meng, Y. S.; Xu, K., Environ. Sci. 2019, 12, 780. Liang, X.; Pang, Q.; Kochetkov, I. R.; Sempere, M. S.; Huang, H.; Sun, X.; Nazar, L. F. Nature Energy 2017, 2 (9), 17119. Zheng, J.; Engelhard, M. H.; Mei, D.; Jiao, S.; Polzin, B. J.; Zhang, J.-G.; Xu, W. Nature Energy 2017, 2, 17012. Cao, X.; Ren, X.; Zou, L.; Engelhard, M. H.; Huang, W.; Wang, H.; Matthews, B. E.; Lee, H.; Niu, C.; Arey, B. W.; Cui, Y.; Wang, C.; Xiao, J.; Liu, J.; Xu, W.; Zhang, J.-G., Nature Energy 2019, 4, 796.

Developing a high-voltage enabling electrolyte is extremely critical for the success of the next generation high-energy density lithium-ion battery especially for electric vehicles. Material scientists have developed new cathode materials with improved specific capacity[1,2] and operating voltage (5 V vs. Li+/Li).[3,4] However, designed for a 4V-class lithium-ion chemistry, the conventional electrolyte suffers from oxidation instability on the charge cathode/electrolyte interface at high charging voltages which leads to severe transition metal (TM) dissolution and rapid capacity fading. The voltage instability of electrolyte becomes the bottleneck for the extensive application of the high voltage cathode materials. Thus, new electrolytes with elevated voltage stability has been widely explored.[5-8] Here we report a new class of fluorinated electrolytes comprising novel fluorinated sulfones including ((trifluoromethyl)sulfonyl)ethane (FMES), 1-((trifluoromethyl)sulfonyl)propane (FMPS) and 2-((trifluoromethyl)sulfonyl)propane (FMIS).[9] These compounds have been synthesized via new synthetic routes and evaluated as electrolyte materials under high voltage operation. The results indicate that sulfones with an α-trifluoromethyl group possess enhanced oxidative potential and reduced viscosity as compared to their non-fluorinated counterparts. The α-fluorinated sulfones also show enhanced wetting ability with polyolefin separator. A facile synthesis method for a reported sulfone 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS) was also developed. With the new reaction method, large quantity of material was obtained and comprehensive electrochemical properties of FPMS as high voltage electrolyte was evaluated. Unlike the α-fluorinated sulfones, the γ-fluorinated sulfones resemble the property of the non-fluorinated ones. References: [1] Nyten, A.; Abouimrance, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochem. Commun., 2005, 7, 156-160. [2] Ellis, B. L.; Makahnoul, R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F., Nat. Mater., 2007, 6, 749-753. [3] Hu, M.; Pang, X.; Zhou, Z. J., Power Sources, 2013, 237, 229-242. [4] Santhanam, R.; Rambabu, B. J., Power Sources, 2010, 195, 5442-5451. [5] He, M.; Su, C. C.; Feng, Z.; Zeng, L.; Wu, T.; Bedzyk, M. J.; Fenter, P.; Wang, Y.; Zhang, Z., Adv. Energy Mater., 2017, 7, 1700109. [6] He, M.; Su, C. C.; Peebles, C.; Feng, F.; Connell, J. G.; Liao, C.; Wang, Y.; Shkrob, I. A.; Zhang, Z., ACS Appl. Mater. Interface, 2016, 8(18), 11450-11458. [7] Kunduraciz, M.; Amatucci, G.G., J. Electrochem. Soc., 2006, 153, A1345-A1352. [8] Wolfenstine, J.; Aleen, J., J. Power Sources, 2005, 142, 389-390. [9] Su, C. C.; He, M.; Redfern, P. C.; Curtiss, L. A.; Shkrob, I. A.; Zhang, Z., Energy Environ. Sci., 2017, 10, 900-904. Figure 1

Lithium-ion batteries have been widely applied in portable electronics due to its high energy density. [1] It is essential to improve the state-of-the-art LIBs, which are far from their maximum theoretical energy density, in order to power up electric vehicles. [2] Researchers have shown that the physiochemical properties, such as conductivity, electrochemical window and ability to form solid electrolyte interphase (SEI), depend on the solution structures of the electrolyte. [3] Thus, it is crucial to determine the solution structures of the electrolyte and the relative solvating ability of various solvents for designing advanced electrolyte systems. Novel method utilizing specific 2D-NMR technique was successfully developed to probe the solvation state of different electrolyte solvents. The result obtained by this technique agreed with the measurement by vibrational spectroscopy. Most importantly, unlike the vibrational spectroscopy measurement, this method can be easily applied to electrolyte system with two or more electrolyte solvents. For example, it is not impossible to determine the solvation state of a ternary-solvent electrolyte comprising EC, EMC and DMC by vibrational spectroscopy due to the severe overlapping of peaks. However, the solvation state can be easily determined with the new method developed. Therefore, this new technique provides an important experimental tool in examining the solvation state of different electrolyte solvents. Application of this newly developed technique in revealing the electrochemical performance of various electrolytes on Li-ion batteries will also be discussed. References: [1] (a) Tarascon, J.-M.; Armand, M., Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414, 359-367. (b) Armand, M.; Tarascon, J.-M., Building Better Batteries. Nature 2008, 451, 652-657. [2] Goodenough, J. B.; Park, K.-S., The Li-Ion Rechargeable Battery: A Perspective. Journal of the American Chemical Society 2013, 135, 1167-1176. [3] (a) Seo, D. M.; Reininger, S.; Kutcher, M.; Redmond, K.; Euler, W. B.; Lucht, B. L., Role of Mixed Solvation and Ion Pairing in the Solution Structure of Lithium Ion Battery Electrolytes. The Journal of Physical Chemistry C 2015, 119 (25), 14038-14046. (b) Xu, K., Electrolytes and interphases in Li-ion batteries and beyond. Chemical reviews 2014, 114 (23), 11503-618.

Lithium sulfur (Li-S) battery is a promising alternative technology of lithium ion batteries. However, due to the complicity of the chemistry in Li-S batteries, the mechanism is not well understood. In addition, the co-existence of soluble species and insoluble species limits the application of other characterization techniques. The sensitivity and element selectivity make NMR spectroscopy a powerful tool to study the changes in local chemical environment and speciation process in Li-S batteries. In this study, in situ 7Li NMR spectroscopy was employed where plastic pouch cells were assembled and cycled in the magnet while NMR spectra were acquired simultaneously. Method to quantitatively study entire lithium inventory in a Li-S battery is developed and implemented, and the cell design is optimized for electrochemical performance and spectroscopic resolution. This methodology can be readily extended to Li-S batteries with other electrolytes where the speciation process can be tracked and analyzed. The development of electrolyte will also benefit greatly from the detailed understanding of the Li-S battery speciation process as well as the additive development. [1] See, et. al., J. Am. Chem. Soc., 2014, 136 (46), pp 16368–16377 [2] Xiao, et. al., Nano Lett., 2015, 15, 3309-3316

Organic carbonate electrolytes are commonly used in lithium ion batteries due to their wide electrochemical stability window and high lithium salt solubility. However, the high voltage of some cathode materials is above the stability of these conventional carbonate electrolytes (>4.5V vs. Li+/Li). One method of increasing the anodic stability of the organic carbonates is through substitution of the solvents with a fluorinated carbonates. In this work, we evaluate the stability of electrolyte formulations comprising combinations of either ethylene carbonate, fluoroethylene carbonate, or difluoroethylene carbonate as cyclic carbonates, and ethyl methyl carbonate or hexafluorodiethyl carbonate as linear carbonates. Stability of these electrolytes at both positive and negative electrodes was determined by lithium/graphite half cell tests, as well as 60 hour potentiostatic hold tests at 4.6 V vs. Li+/Li with NMC (LiNi0.5Mn0.3 Co0.2O2) cathodes and either graphite or LTO (Li4Ti5O12) anodes. In potentiostatic holds with NMC cathodes, the fluorinated electrolytes show enhanced stability (lower oxidation current) with the graphite anodes, while fluorethylene carbonate containing formulations show higher oxidation currents with the LTO anodes. These results indicate the feasibility of fluorinated electrolytes in enabling high voltage cathodes through stability of the cathode/electrolyte interface. Acknowledgements The work at Argonne National Laboratory was performed under the auspices of the U.S. Department of Energy (DOE), Office of Vehicle Technologies, under Contract No. DE-AC02-06CH11357. The submitted issue has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W-31-109-Eng-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, non-exclusive, irrevocable, worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

The use of electrolyte additives has been and continues to be an economical and effective approach to enhance the performance and increase the lifetime of lithium ion battery systems. In the presence of additives, the baseline performance of electrolytes can be improved due to the formation of surface films on the electrodes, HF scavenging in the bulk electrolyte, etc. However, the interaction between electrolytes and small molecule additives are rarely studied due to the assumed inertness of the system. While this inert relationship may hold true for many additives, we have found that one commonly used additive, tris(trimethylsilyl) phosphite (TMSPi), demonstrates a dynamic (reactive) relationship when used with a LiPF6-based electrolyte (1.2 M LiPF6 in EC/EMC, 3/7 wt/wt). Our findings suggest that immediately after the addition of TMSPi into the electrolyte, the nature of the electrolyte changes and the properties of the bulk electrolyte are drastically different between immediately making the solution and waiting less than a week. We present electrochemical data comparing freshly prepared (same day) and “aged” (one week) TMSPi-based electrolyte formulations. Our results indicate that the effect of electrolyte aging on cell electrochemistry (LiNi0.5Mn0.3Co0.2O2 /graphite full cells operating between 3.0-4.4 V) can be dramatic with observable differences in impedance, redox behavior, surface film formation and transition metal dissolution from the positive electrode. The data presented sheds considerable light on the possible interactions between additives and electrolyte and are of utmost importance when considering electrolyte formulations for lithium ion batteries.

The lithium-ion battery is an ideal power source for electrified vehicles due to its long cycle life and high energy and power density. To further increase the energy density, the general approach is to use cathode materials with high operating voltages (5 V vs. Li+/Li) and high specific capacity (250 mAh/g). Tremendous attention has been paid to raising the specific capacity and the discharge voltage of the cathode materials. For example, two-Li+-ion material such as silicate Li2FeSiO4 and fluorophosphate Li2FePO4F has been proposed and investigated as a high capacity cathode. The theoretical capacity of these two materials is high, 323 and 292 mAh/g, respectively. There also have been many studies on expanding the operating voltage. Cathode materials with a potential of more than 5 V have been proposed, for example, olivine-type LiNiPO4 and LiCoPO4, and normal spinel-type LiNi0.5Mn1.5O4 and LiCoMnO4. However, these cathodes require an electrolyte with high oxidation stability to deliver the full capacity. Okada et al. proposed Li2CoPO4F as both a high-capacity and a high-voltage cathode material. However, its practical capacity is 120 mAh/g, and its energy density showed no advantage over LiCoPO4 because of electrolyte decomposition above 5 V. The conventional lithium-ion battery employs organic carbonate esters as the electrolyte solvent, in particular, mixtures of ethylene carbonate (EC) with dimethyl carbonate (DMC), diethyl carbonate (DEC), and/or ethyl methyl carbonate (EMC) dissolved in LiPF6 salt. This electrolyte continuously decomposes above 4.5 V vs. Li+/Li, limiting its application to a cathode chemistry that delivers capacity at a high charging voltage. Therefore, the demand for a high-voltage electrolyte has become a high priority for the development of lithium-ion batteries with high energy density. Several studies have been dedicated to the development of high voltage electrolytes such as sulfones, ionic liquids, and dinitriles, as well as electrolyte additives that stabilize the charged cathode surface to afford a reversible Li+-intercalation chemistry in the coveted 5-V region. These electrolyte materials can provide high anodic stability, but they suffer from their intrinsic high viscosity, low dielectric constant, and low conductivity. More importantly, they do not form a solid-electrolyte interphase (SEI) on carbonaceous anode material. Moreover, it is a major challenge to develop an electrolyte additive for these new electrolytes that will provide the SEI formation required for extended cycling performance, especially under abuse conditions. Although an additive for cathode SEI formation was reported to be able to suppress the reactivity of the charged electrode and electrolyte, a superior electrolyte system comprising solvents with intrinsic anodic stability is the ultimate solution for high voltage electrolytes. In this presentation, new electrolyte based on fluorinated carbonate solvents were designed, syntehsized and evaluated with high voltage cathode materials at elevated temperature. The theoretically high anodic stability of these new electrolytes was supported by electrochemical evaluation results using LiNi0.5Mn1.5O4 spinel cathodes and LiNi0.5Co0.2Mn0.3O2 cathodes. Fluorinated carbonate appears to be a suitable electrolyte candidate for transition metal oxide cathodes at high voltage.

Lithium ion batteries have dominated the portable electronics market and have the potential to dominate large-scale battery applications including hybrid and electric vehicles as well as grid storage because of their high energy and power densities.[1] It is well known that conventional electrolytes (such as 1.2 M LiPF6 in EC/EMC 3/7) show poor anodic stabilities above 4.5 V versus Li/Li+.[2] However, high voltage electrolytes play an intrinsic role in many applications such as hybrid and electrical vehicles, aerospace uses and power grids. As a result, high voltage electrolytes are essential for the development of next generation lithium ion batteries. One possible solution is to develop fluorinated electrolytes which not only form kinetically stable SEI interphase, but also are resistant to oxidative decomposition due to their high oxidation potential. [3] In this work, a novel fluorinated electrolyte was introduced in a graphite-LiNi0.5Mn0.3Co0.2O2 full cell operated between 3.0 - 4.6 V. The electrolyte contains 1.0 M LiPF6 dissolved in a mixture of FEC and HFDEC solvent with 1wt % LiDFOB used as the additive. Compared to a conventional EC and EMC based electrolyte, the fluorinated electrolyte shows an excellent cycle life under a 4.6V cut off voltage. NMR and GC-MS were used to analyze the harvested electrolyte post-cycling while SEM, XPS and FTIR were employed to study the interface between the electrolyte and the bulk electrodes. Most importantly, HR-XRD and XANS were conducted to investigate and compare the cycled bulk cathode electrode in different electrolytes. To the best of our knowledge, the structural change of the cycled cathode material in different electrolytes has never been reported. Therefore, we believe this research is a crucial breakthrough for studying the interaction between the electrolyte and electrode. The methodology developed could be fundamental in the design and investigation of better electrolytes for next generation lithium ion batteries. [1]Xu, Kang. "Nonaqueous liquid electrolytes for lithium-based rechargeable batteries." Chemical reviews 104.10 (2004): 4303-4418. [2] Xu, Kang. "Electrolytes and interphases in Li-ion batteries and beyond." Chemical reviews 114.23 (2014): 11503-11618. [3] Zhang, Zhengcheng, et al. "Fluorinated electrolytes for 5 V lithium-ion battery chemistry." Energy Environ. Sci. 6.6 (2013): 1806-1810.

One of the more promising cathode materials for high-energy high-voltage lithium ion batteries (LIBs) are Ni-rich layered cathode materials such as LiNixMnyCozO2 (where x + y + z = 1). Although these cathode materials are attractive from a high capacity standpoint, they commonly suffer from poor structural stability at highly delithiated (charged) states leading to poor electrochemical performance.1-3 To help aid these issues, surface coatings are becoming a widely adopted method to improve the cycling performance of high-voltage cathode materials. More widely investigated coating materials include oxide coatings (Al2O3, TiO2, etc.)4 while comparatively fewer studies have investigated organic monomer or polymer coatings (PEDOT, polyimide, etc.).5 In this work, the surface of LiNi0.5Mn0.3Co0.2O2 cathode materials were coated with organosilane reagents to investigate their effect on cell electrochemical performance. The impact of the weight percentage of organosilane used and the functionality of the organosilane used will be presented. Characterization of the organosilane coating using XRD, XPS and FTIR confirm the presence of a Si-containing coating. Cycling performance for half cells (Li/ LiNi0.5Mn0.3Co0.2O2) using the organosilane coated cathodes will be shown. In conclusion, a new type of organic coating was utilized on Ni-rich cathode materials and this research explores a new type of coating for high voltage cathodes. 1) Son, I. H.; Park, J. H.; Kwon, S.; Mun, J. and Choi, J. W. Chem. Mat. 2015, 27, 7370-7379. 2) Bak, S.-M.; Hu, E.; Zhou, Y.; Yu, X.; Senanayake, S. D.; Cho, S.-J.; Kim, K.-B.; Chung, K. Y.; Yang, X.-Q. and Nam, K.-W. ACS Appl. Mater. Interfaces 2014, 6, 22594-22601. 3) Lin, F.; Markus, I. M.; Doeff, M. M.; Xin, H. L. Sci. Rep., 2014, 4, 5694. 4) Xu, S.; Jacobs, R. M.; Nguyen, H. M.; Hao, S.; Mahanthappa, M.; Wolverton, C.; Morgan, D. J. Mater. Chem. A, 2015, 3, 17248. 5) Zhang, J.; Lu, Q.; Fang, J.; Wang, J.; Yang, J. and NuLi, Y. ACS Appl. Mater. Interfaces 2014, 6, 17965-17973.

High-voltage electrolytes (HVEs) for Li-ion battery refer to the electrolytes that are intrinsically stable towards oxidative decomposition on the cathode at high charging potential. To develop HVEs that are compatible with 5 V spinel LiNi0.5Mn1.5O4 (LNMO), we focus on incorporating fluorinated solvents in the electrolyte formulation. In the meantime, we also take into account the stability of such electrolytes on the anode. A combination of cathode-compatible fluorinated solvents with anode-protecting additives is envisaged to be a promising solution for a successful HVE. A new HVE containing fluorinated carbonates was evaluated against LNMO cathode and showed excellent oxidative stability. Several additives were found to form solid-electrolyte interphase (SEI) layers that effectively prevented significant decomposition of the HVE on the graphite anode. Cell performance was evaluated at both ambient and elevated temperatures. The fluorinated HVE exhibited much improved performance compared with conventional non-fluorinated carbonate-based electrolyte especially at high temperature. Cycling results and electrochemical impedance spectroscopy (EIS) data clearly demonstrated the synergetic effect of the fluorinated solvents and the SEI forming additives.

High-voltage Li-ion battery draws great interest due to the promise to deliver high power and energy which are essential to transportation applications. The bottleneck to this technology is the anodic stability of the organic electrolyte. Approaches to solve this problem include developing additives to kinetically stabilize the cathode/electrolyte interface and developing novel electrolyte systems that are intrinsically stable toward oxidation at high potential . Our group has been taking the second approach with a focus on fluorinated compounds as electrolyte solvents. We have synthesized a series of fluorinated cyclic carbonates and linear carbonates and evaluated their electrochemical stability and other physical characteristics. Electrolytes formulated from these fluorinated compounds have demonstrated excellent anodic stability and some of the formulations also showed enhanced cell performance for LiNi0.5Mn1.5O4(LNMO)/ graphite full cells. Characterization of harvested electrolyte with NMR and GC-MS revealed that less soluble decomposition products were generated in the fluorinated electrolyte compared with the conventional electrolyte. Investigation of the cycled electrodes with SEM and TEM revealed that the high stability of the fluorinated electrolyte on the cathode not only helped with the electrolyte decomposition problem, but also reduced the degradation of the electrode material as well.

Silicon is a highly promising high capacity anode material for high energy lithium-ion batteries for electric vehicle application. Great progress has been made especially in the area of material level on the nano scale.1 However, the electrolyte research tailored to further improve the performance of the Si anode is limited.2 In this paper, we present a new electrolyte additive N, N-diethyltrimethylsilylamine (DETMSA) which showed great improvement over the conventional carbonate electrolyte using the fluoroethylene carbonate as additive. Our experiment data showed that with addition of 0.5 wt. % of DETMSA to the baseline electrolyte 1.2 M LiPF6 EC/EMC+10% FEC, the Li/Si-graphite cell gained a 10% improvement in capacity retention increase with high coulombic efficiency at room temperature. The functioning mechanism of the new electrolyte additive for Si anode was investigated by the XPS, SEM/EDX and FT-IR. 3 References: He, M., Sa, Q., Liu, G., & Wang, Y. (2013). Caramel Popcorn Shaped Silicon Particle with Carbon Coating as a High Performance Anode Material for Li-Ion Batteries. ACS applied materials & interfaces, 5(21), 11152-11158. Zhang, S. S. (2006). A review on electrolyte additives for lithium-ion batteries.Journal of Power Sources, 162(2), 1379-1394. Zhang, S., Ding, M. S., Xu, K., Allen, J., & Jow, T. R. (2001). Understanding solid electrolyte interface film formation on graphite electrodes. Electrochemical and Solid-State Letters, 4(12), A206-A208.

In an effort to enhance the energy and power density of Li-ion battery technology to facilitate the commercialization of electric vehicles, material researchers have developed new cathode materials with improved specific capacity [1] and operating voltage (5 V vs. Li+/Li).[2] However, the state-of-the-art electrolyte containing 1.2 M lithium hexafluorophosophate (LiPF6) in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) decomposes at above 4.5 V vs. Li+/Li which prevents the extensive use for the high voltage cathode materials. [3] Thus, the exploration of new electrolytes with elevated voltage stability has been actively pursued. [2] In this paper, we present a novel electrolyte candidate of fluorinated sulfones for high voltage Li-ion battery. Aided by DFT computation, fluorinated sulfones with various chemical structures (trifluoromethyl)sulfonylethane (FMES), 1-(trifluoromethyl)sulfonylpropane (FMPS) and 2-(trifluoromethyl)sulfonylpropane (FMIS) were designed, synthesized and characterized with analytical methods including NMR, GC-MS and FT-IR and their oxidation stability were examined by a floating method using LiNi0.5Mn1.5O4/Li cell. Sulfone with trifluoromethyl (-CF3) substitution at alpha position possesses enhanced oxidative stability and reduced viscosity as compared to their non-fluorinated counterparts. The alpha-substituted fluorinated sulfones also showed improved wetting ability with PE/PP separators. A facile method for the synthesis of 1,1,1-trifluoro-3-(methylsulfonyl)propane (FPMS), which enabled us to produce adequate amount of FPMS for electrolyte testing, was also developed. Unlike alpha-substituted fluorinated sulfones, the gamma-substituted fluorinated sulfones resemble the properties of their non-fluorinated ones. References: [1] (a) Nyten, A.; Abouimrance, A.; Armand, M.; Gustafsson, T.; Thomas, J. O. Electrochem. Commun., 2005, 7, 156-160. (b) Ellis, B. L.; Makahnoul, R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F. Nat. Mater., 2007, 6, 749-753. [2] (a) Zhang, Z.; Hu, L.; Wu, H.; Weng, W.; Koh, M.; Redfern, P. C.; Curtiss, L. A.; Amine, K. Energy Environ. Sci., 2013, 6, 1806-1810. (b) Hu, M.; Pang, X.; Zhou, Z. J. Power Sources, 2013, 237, 229-242. (c) Xu, M.; Zhou, L.; Done, Y.; Chen, Y.; Garsuch, A.; Lucht, B. L. J Electrochem. Soc. 2013, 160, A2005-A2013. (d) Von Cresce, A.; Xu, K. ECS Trans., 2012, 41, 17-22. (e) Santhanam, R.; Rambabu, B. J. Power Sources, 2010, 195, 5442-5451. [3] a) Kunduraciz, M.; Amatucci, G.G. J Electrochem. Soc. 2006, 153, A1345-A1352. (b) Wolfenstine, J.; Aleen, J. J. Power Sources, 2005, 142, 389-390. Figure 1