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This article introduces a new residual life of (n − k + 1)-out-of-n systems consisting of n independent and identically distributed components, given that the total number of failures of components is not less than l at time t, and the system is still working. Some stochastic comparisons of residual lifetimes are conducted, and behaviors of DLR and ILR are given.

The derivatives of 1,3-benzodioxan (DBBD1) and 1,4-benzodioxan (DBBD2) bearing two tert -butyl groups have been synthesized as new redox shuttle additives for overcharge protection of lithium-ion batteries. Both compounds exhibit a reversible redox wave over 4 V vs Li/Li + with better solubility in a commercial electrolyte (1.2 M LiPF 6 dissolved in ethylene carbonate/ethyl methyl carbonate (EC/EMC 3/7) than the di- tert -butyl-substituted 1,4-dimethoxybenzene (DDB). The electrochemical stability of DBBD1 and DBBD2 was tested under charge/discharge cycles with 100% overcharge at each cycle in MCMB/LiFePO 4 and Li 4 Ti 5 O 12 /LiFePO 4 cells. DBBD2 shows significantly better performance than DBBD1 for both cell chemistries. The structural difference and reaction energies for decomposition have been studied by density functional calculations.

The electrolyte additive 2-(pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole (PFPTFBB, 1) was found to have a reversible redox potential at 4.43 V vs. Li+/Li. This compound can function as an overcharge protection additive as well as anion receptor for lithium-ion batteries. It has drawn a great deal of interest from industry, but its use in relatively large quantities is limited by the production challenges of tetrafluorocatechol (TFC, 3), which is the key starting chemical for the synthesis of PFPTFBB. As part of a continuous effort in our research toward improving the safety of lithium-ion batteries, we have performed the synthesis of TFC and optimized its synthesis process. The X-ray single-crystal structures of TFC and the intermediate product 5,6,7,8-tetrafluoro-1,4-benzodioxane (4) during the process of PFPTFBB synthesis are reported for the first time. Also presented is the lithium ion cell performance of PFPTFBB as redox shuttle in various electrolyte systems.

Silicon-based electrolyte has emerged as a primary candidate for the development of large lithium-ion batteries for electric vehicle (EV) and other systems in which safety is a primary consideration. Comparing to the electrolyte used in the conventional lithium-ion batteries, which are flammable, volatile, and highly reactive organic carbonate solvents, silicon-based electrolytes are thermally and chemically stable, less flammable and environmental benign. Tri(ethylene glycol)-substituted trimethylsilane (1NM3) was identified as a focus of investigation due to its high conductivity and low viscosity. We present the results of a systematic investigation of the 1NM3-based electrolytes with lithium bis(oxalate)borate (LiBOB) salt, including temperature dependent ionic conductivity and lithium cell performance. Lithium-ion cell with LiNi 1/3 Co 1/3 Mn 1/3 O 2 as the positive electrode and MAG graphite as the negative electrode has shown excellent cyclability using 1NM3-LiBOB as electrolyte.

Contrast agents for bioimaging suffer from low accumulation at lesion area and high uptake in the reticuloendothelial system (RES). Assembly of nanoparticles in vivo improves their enrichment at tumors and inflamed areas. However, uncontrollable assembly also occurs at the liver and spleen owing to the uptake of nanoparticles by the RES. This is known to probably cause a higher bioimaging background and more severe health hazards, which may hamper the clinical application. Herein, a new near-infrared (NIR)-controlled supramolecular engineering strategy is developed for in vivo assembly and disassembly between lanthanide upconversion nanoparticles and second near-infrared window (NIR-II, 1000-1700 nm) nanoprobes to realize precision bioimaging of tumors. A supramolecular structure is designed to realize assembly via host-guest interactions of azobenzene and β-cyclodextrin to enhance the retention of NIR-II nanoprobes in the tumor area. Meanwhile NIR-laser-controllable nanoprobes disassembly brings about a reduction in the bioimaging background as well as acceleration of their RES clearance rate. This strategy may also be used in other nano-to-micro-scale contrast agents to improve bioimaging signal-to-noise ratio and reduce long-term cytotoxicity.

Functionalized disiloxane compounds were synthesized by attaching oligo(ethylene glycol) chains, –(CH 2 CH 2 O)– n , n = 2–7, via hydrosilation, dehydrocoupling, and nucleophilic substitution reactions and were examined as non-aqueous electrolyte solvents in lithium-ion cells. The compounds were fully characterized by 1 H, 13 C, and 29 Si nuclear magnetic resonance (NMR) spectroscopy. Upon doping with lithium bis(oxalato)borate (LiBOB) or LiPF 6 , the disiloxane electrolytes showed conductivities up to 6.2 × 10 −4 S cm −1 at room temperature. The thermal behavior of the electrolytes was studied by differential scanning calorimetry, which revealed very low glass transition temperatures before and after LiBOB doping and much higher thermal stability compared to organic carbonate electrolytes. Cyclic voltammetry measurements showed that disiloxane-based electrolytes with 0.8 M LiBOB salt concentration are stable to 4.7 V. The LiBOB/disiloxane combinations were found to be good electrolytes for lithium-ion cells; unlike LiPF 6 , LiBOB can provide a good passivation film on the graphite anode. The LiPF 6 /disiloxane electrolyte was enabled in lithium-ion cells by adding 1 wt% vinyl ethylene carbonate (VEC). Full cell performance tests with LiNi 0.80 Co 0.15 Al 0.05 O 2 as the cathode and mesocarbon microbead (MCMB) graphite as the anode show stable cyclability. The results demonstrate that disiloxane-based electrolytes have considerable potential as electrolytes for use in lithium-ion batteries.

In this paper we obtain several mixture representations of the reliability function of the inactivity time of a coherent system under the condition that the system has failed at time t (> 0) in terms of the reliability functions of inactivity times of order statistics. Some ordering properties of the inactivity times of coherent systems with independent and identically distributed components are obtained, based on the stochastically ordered coefficient vectors between systems.

3,5-di-tert-butyl-1,2-dimethoxybenzene (DBDB) has been synthesized as a new redox shuttle additive for overcharge protection of lithium-ion batteries. DBDB can easily dissolve in carbonate-based electrolytes, which facilitates its practical use in lithium-ion batteries; however, it has poor electrochemical stability compared to 2,5-di-tert-butyl-1,4-dimethoxybenzene (DDB). The structures of DBDB and DDB were investigated using X-ray crystallography and density functional calculations. The structures differ in the conformations of the alkoxy bonds probably due to the formation of an intramolecular hydrogen bond in the case of DBDB. We investigated reaction energies for decomposition pathways of neutral DBDB and DDB and their radical cations and found little difference in the reaction energies, although it is clear that kinetically, decomposition of DBDB is more favorable.

The scalability and design flexibility make redox flow batteries highly advantageous for grid-scale energy storage applications. Traditional flow batteries are based mainly on inorganic metal species, but their broad market penetration is greatly limited by the low energy density and high chemical costs. In this regard, water-soluble organic redox-active materials have demonstrated competitive property and performance merits, which makes them promising materials candidates to enable next-generation flow batteries.1 In this contribution, we will report our recent accomplishments in developing new aqueous organic flow battery materials and systems. A variety of high-performance organic candidates with different structures and reaction mechanisms have been identified and investigated that have produced decent cyclability over extended charge/discharge cycling. We will introduce our generic approaches to gain fundamental structure-activity-stability relationships for organic redox-active materials, including solvation interactions, electronic structures, and failure mechanisms. These understandings have greatly guided our materials development strategies to achieve significant improvement in solubility, cell voltage, and stability. References X. Wei, W. Pan, W. Duan, A. Hollas, Z. Yang, B. Li, Z. Nie, J. Liu,D. Reed, W. Wang, V. Sprenkle, Materials and Systems for Organic Redox Flow Batteries: Status and Challenges. ACS Energy Lett. 2017, 2, 2187. Figure 1

Silicon (Si), with its extremely high theoretical specific capacity (up to 4200 mAhg−1), natural abundance and low toxicity, is considered as one of the most promising anode material candidates for next generation high energy density lithium-ion batteries. However, large volume expansion (~300 %) upon lithiation/delithiation makes it difficult for Si-based anode to maintain its capacity over extended cycles. Several possible mechanisms have been proposed to explain the rapid capacity fade in Si-based anode such as pulverization of the active materials, loss of electrical pathways caused by rearrangement of electrode structure, instability of the electrode/electrolyte interface or some combinations of these. While application of nano-structured Si (nanoparticles, nanowires) as anode largely resolved the pulverization issue, the use of nano-silicon inevitably increases the reactive surface between active materials and the electrolyte. Additionally, the continuous growth of solid-electrolyte-interphase (SEI) on the particle surface remains a significant cause for performance deterioration. Therefore, an increasing number of research has focused on the correlation between surface functionality of Si NPs and their electrochemical performance. Previous studies in this area mainly focused on the study of the inherent SiOx layers on Si NPs or the effect of electrolyte additives on the surface properties of Si NPs. We take a different strategy to address the Si anode issue. We propose to chemically modify the surface of Si NPs and study how the chemical modification would affect the electrochemical performance of the Si-based anode. Commercially available Si NPs usually bear a native layer of silicon oxide on the surface of the particle. The first step in the surface modification of Si NPs is to enrich the surface silanol (Si-OH) groups as the new working platform. The silanol enriched surfaces will be converted to a variety of functional groups on the Si NPs. (Scheme 1). In this paper, we will present some preliminary results on the surface-modified Si NPs with methacrylate group and amine group and discuss the effects of the functional groups on the electrochemical performance of the Si anode. Scheme 1. Chemical surface modification of Si NPs via silane chemistry. Figure 1

The exploration for the next generation of anode materials in the lithium-ion batteries is a vital subject in the past few years due to the huge demand of high capacity batteries. Silicon (Si) stands out as a promising anode material due to its high theoretical specific capacity (4200 mAh/g), enviroment friendliness and low costs. However, Si nanoparticles (NPs) experience severe volume changes up to 300 % during the lithiation/delithiation process, which leads to dramatic particle degradation and thus capacity loss. Novel polymeric binders with enhanced mechanical properties have been identified as one effective approach to alleviate this issue, and some examples include carboxymethyl cellulose (CMC), alginate, and poly(acrylic acid) (PAA), etc. By using those binders, cell performance has been greatly improved as compared to the conventional polyvinylidene fluoride (PVDF) binder. Among those candidates, PAA outperforms others possibly due to its superior mechanical properties. In this report we have attempted to investigate the lithiation effect of the PAA binders. Lithiating PAA binders could benefit the electrode laminate processing as well as cycling performance. A commercially available PAA sample with a characterized Mn of 147 kDa was used in this study. By titrating with LiOH solution, we controlled the pH of 10 wt% PAA solutions as well as the lithiation ratio (Table 1). Those binder solutions were used to fabricate silicon/ graphite composite electrodes that composed of 10 % PAA, 73 % Hitachi MagE, 15 % Si NPs (NanoAmour, 70-130 nm), and 2 % Timcal C45. Half-cell cycling results (Figure 1) indicated that different lithiation of PAA binders has dramatic impact on their corresponding cycling performance. Lower lithiation tends to afford higher initial specific capacities and better capacity retentions. Actually, the best performer is PAA binder with no lithiation at all. This result is a little contradicting to previous study but we reason that our lithiation agent, LiOH, may have side reasons with silicon particles, as evidenced by the dramatic decrease of the silicon capacity. Full cell cycling as well as further characterization of electrode surface is ongoing. Table 1. The calculated mol% of LiOH (to AA monomer) and the resulting pH values of the final PAA solutions. LiOH % 0 25 50 75 85 90 91 92.5 95 100 pH 2.08 4.22 4.84 5.49 5.97 6.97 10.03 11.96 12.28 12.59 Figure 1. Specific discharge capacity and Coulombic efficiency of PAA binders with different pH values. Figure 1

Lithium-sulfur batteries are considered as one of the most promising battery chemistries for the next generation electrochemical energy storage. Due to remaining challenges with respect to lithium polysulfide dissolution and subsequent redox shuttling/active material loss, current lithium-sulfur batteries remain unviable for wide applications in both electric vehicle and stationary electrical grid. In the recent years, several electrolytes and electrolyte additives have been reported using a fluorinated ether based compound to address the issues associated with polysulfide dissolution/shuttling and fast capacity fading, however the exact function and the structure-property correlation of these fluorinated ethers remain largely unknown. Current efforts from our group in this area have expanded to new fluorinated ethers with different degrees and patterns of fluorination and various skeletal structures of substitutions. One area is the fluorinated aliphatic ether based solvents with inspiration drawn from previously reported 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE). A quick overview of the research into a newly designed fluorinated benzyl ether based solvents will also be presented which have been investigated by our group to further mitigate the polysulfide dissolution due to the strong interaction between the fluorinated benzyl group and the polysulfide anions. Figure 1

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

The ( n − k + 1 ) -out-of- n system is an important structure of the reliability of technical systems. In this paper, we consider the residual lifetime and the inactivity time of the system consisting of independent and identically distributed components, under the condition that the total number of failures of the components at time t 1 is r ( r k ), and at time t 2 ( t 2 > t 1 ) the system is still working or it has failed. Under these conditions, some ordered properties of one system or between two systems with two sets of independent components are obtained both for the hazard rate order and the likelihood ratio order. The results obtained here are stronger than the results included in Poursaeed (in press) .

This paper investigates some ordering properties of the residual lives and the inactivity times of coherent systems with dependent exchangeable absolutely continuous components, based on the stochastically ordered signatures between systems, extending the results of Li and Zhang [2008. Some stochastic comparisons of conditional coherent systems. Applied Stochastic Models in Business and Industry 24, 541–549] for the case of independent and identically distributed components.

New comb polysiloxanes with mixed substituents were synthesized by hydrosilylation of PMHS with 4-allyloxymethyl-[1,3]dioxolan-2-one and tri(ethylene glycol) allyl methyl ether (AMPEO3). The effect of the incorporation of carbonate groups on ionic transport, viscosity and thermal properties has been investigated. When doped with lithium bis(trifluorosulfonyl) imide, LiTFSI, the mixed substituted polysiloxane polymers with varying carbonate content all exhibited conductivity higher than those for the polysiloxanes with pure carbonate or pure oligoethyleneoxy substituents. The maximum ambient conductivity in this series was 1.62× 10−4 S/cm, occurring for the polymer containing 8.5% polar carbonate groups at a doping level of EO/LiTFSI = 15. The impedance measurement results showed that polymers containing larger amounts of carbonate groups exhibited lower conductivity, probably because of their increased viscosity and higher glass transition temperature. The conduction mechanism for these new comb polymers obeys free volume theory, as indicated by conductivity data fit to the VTF equation.

A novel Lewis acid-free and phenolate-based magnesium electrolyte has been established. The excellent reversibility and stability of this electrolyte in battery cycling render this novel Lewis acid-free synthetic approach as a highly promising alternative for the development of highly anodically stable magnesium electrolytes for rechargeable magnesium batteries.

Direct evidence of Mg2+ intercalation into a spinel-type Mn2O4 is provided. By com­bining tools with different sensitivities, from atomic-resolution X-ray spectro­scopy to bulk X-ray diffraction, it is demonstrated that Mg2+ reversibly occupies the tetrahedral sites of the spinel structure through the reduction of Mn when the electrochemical reaction is performed.

In this chapter, new trends in the formulation of non-aqueous liquid electrolytes will be discussed. Novel solvents and salts used in Li-ion battery electrolytes are categorized and illustrated, and the progress in understanding the formation mechanism behind the solid-electrolyte interphase (SEI) is discussed.

Rechargeable batteries are a most energy- and cost-effective device for electrical energy storage in a wide range of energy levels from portable electronics through transportation vehicles to load-leveling stationary storage. This chapter outlines the current status and challenges that remain for the key materials of rechargeable batteries, especially lithium-ion batteries, including the cathode, anode, electrolyte, and separator. In addition, the prospectus and challenges of battery systems beyond Li-ion, such as sodium–ion, magnesium, lithium–air, and lithium–sulfur batteries, are also discussed for the future research and development of rechargeable batteries.

Separator is an indispensable component for the liquid electrolyte battery, which absorbs liquid electrolyte for necessary ionic conductivity and isolates two electrodes from coming into contact. In a battery, the separator does not participate in any electrochemical reaction; however, it greatly affects the battery’s performance, particularly the rate capability and safety. The separator currently used in state-of-the-art Li-ion batteries is typically a microporous polyolefin membrane whose pores are formed either by a dry process or by a wet process. For improved cyclability and safety of the batteries, surface modification has been further used to enhance the uptake and uphold of liquid electrolyte as well as the mechanical strength of the membrane, especially at elevated temperatures. In this chapter, the manufacturing properties and surface modifications of polyolefin-based battery separators are reviewed, and the membrane property differences by the pore-forming process are discussed.

The electrolyte is an indispensable element of Li-ion batteries. In normal operation, the electrolyte does not participate in electrochemical reactions but rather conducts ions to enable the electrode reactions on the cathode and anode. The electrolyte is typically composed of a lithium salt as the solute for lithium ions and a solvent or mixed solvent as the medium for ionic conduction.

Safe lithium ion batteries with long life and high energy density have long been a promising energy storage technology for emerging applications in automobiles and smart grids. Development of functionalized electrolytes is an effective approach to dramatically improve the performance of these batteries. In this chapter, several classes of fluorinated electrolyte components will be introduced and their mechanism to improve the battery performance discussed. The fluorinated compounds include (1) electrolyte additives that form a stable artificial solid-electrolyte interphase, (2) fluorinated redox shuttles for overcharge protection and automatic capacity balance of lithium ion batteries, and (3) fluorinated solvents to enable high voltage cathode materials.

Non-aqueous electrolyte Li-air batteries are unique in that the oxygen reduction reaction (ORR) products (Li2O2 and Li2O) are insoluble in liquid electrolyte and the ultimate ORR product (Li2O) is electrochemically irreversible. In order to make the Li-air batteries rechargeable with high specific capacity, it is required that the ORR must be strictly selective towards the two-electron reduction so as to form the reversible Li2O2, and that both the catalyst and air electrode are very porous to maximally accommodate the ORR products for high specific capacity. The knowledge learnt from aqueous electrolyte metal-air batteries and fuel cells can be shared to develop the ORR catalyst of the non-aqueous electrolyte Li-air batteries. In this chapter, the ORR in non-aqueous Li-ionic electrolyte is discussed in comparison with those occurring in the aqueous electrolytes. Recent advances and status in study of the electrocatalysts for non-aqueous electrolyte Li-air batteries are reviewed and discussed.

Novel silane compounds such as {2-[2-(2-methoxyethoxy)ethoxy]ethoxy} trimethylsilane (1), bis{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}dimethylsilane (2), {3-[2-(2-(2-methoxyethoxy)ethoxy)ethoxy]-propyl}trimethylsilane (3) and {[2-(2-(2-methoxyethoxy)ethoxy)ethoxy]-methyl} trimethylsilane (4) have been synthesized and used as non-aqueous electrolyte solvents in lithium-ion batteries. These silane molecules can easily dissolve most lithium salts including lithium bis(oxalato)borate (LiBOB), LiPF6, LiBF4, and lithium trifluoromethylsulfonimide. The LiBOB salt was found to be very appropriate for these silane molecules because, unlike LiPF6, LiBOB can provide a good passivation film on a graphite anode. Cyclic voltammetry analyses show that silane-based electrolytes with a 0.8 M LiBOB salt concentration are stable to 4.4 V; they also exhibit very high lithium-ion conductivities up to 1.29 × 10−3 S/cm at room temperature. Full cell performance tests with LiNi0.08Co0.15Al0.05O2 as the positive electrode and MCMB graphite as the negative electrode have shown excellent cyclability both at room temperature and at 40 °C. Cells with these new silane electrolytes exhibit long calendar life; they show no impedance rise after aging at 80% state of charge and 55 °C for one year. The results suggest that silane-based electrolytes have great potential for use in lithium-ion batteries. Keywords: Silane, Electrolyte solvent, Lithium ion battery, Calendar and cycle life

Pentamethylcyclopentasiloxanes (D5H) with oligo(ethylene glycol) substituents, D5N3 and D5S3, and a short-chain siloxane derivative MD6N3M were synthesized by B(C6F5)3-catalyzed dehydrogenative coupling and by platinum-catalyzed hydrosilylation reactions. Conductivities were studied when doped with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The oxygen-linked cyclic siloxane D5N3 exhibits higher conductivity than trimethylene-linked siloxane D5S3. The substituted linear oligmeric siloxane MD6N3M has a lower Tg than the D5 siloxanes, and showed much higher conductivity at the same Li+ concentration. The curvature of the plot of conductivity vs temperature dependence indicates a free volume mechanism of ion transport.

Network-type solid polymer electrolytes (NSPEs) were synthesized containing oligoethylene oxide chains, CH3(OCH2CH2)3(CH2)3−, within the network structures. Hydrosilylation reactions of precursors 1 and 2 (oligoethyleneoxy partially substituted pentamethylccyclopentasiloxanes (D5H)) with an α,ω-diallyloligo(ethylene glycol) were employed for the formation of the cross-linked networks. The conductivities of the network polymer/LiX complexes with variable EO/Li ratios were measured by impedance experiments. NSPE-2, with 36.0% cross-linking density, exhibited higher conductivity than NSPE-1, with 43.8%. The optimum conductivity (σ = 9.24 × 10-5 S/cm at 25 °C, 2.11 × 10-4 S/cm at 37 °C) was found for NSPE-2 with lithium bis(oxalato)borate (LiBOB). LiBOB-doped polymers exhibited higher conductivity than those doped with LiTFSI at the same salt concentration.

Polysiloxanes with pendant poly(ethylene oxide) side chains (4 were prepared by the dehydrocoupling reaction of poly(methylhydrosiloxane) (PMHS, 3 with 2-(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethoxy)ethanol (1 and poly(ethylene glycol) methyl ether (2 using a metal catalyst. Catalysts investigated were tin(II) 2-ethylhexanoate, Rh(Ph3P)3Cl, and Pd2(dba)3. The reaction of a cyclic siloxane, D4 H, with 1 catalyzed by Pd2(dba)3 was also carried out to synthesize siloxane 6. The polysiloxanes were characterized by 1H NMR, 29Si NMR, FT-IR, and GPC. 29Si NMR study of these comb-like polysiloxanes revealed that there is a significant difference in the structure of the siloxane polymers prepared depending upon the catalyst. M, D, and T units were observed when tin(II) was used as a catalyst, but only M and D units were detected when Rh(Ph3P)3Cl or Pd2(dba)3 was employed. Furthermore, M and T units are negligible for the cyclic siloxane 3 using Pd2(dba)3. A mechanism is proposed to account for these observations.

A novel cross-linked siloxane-based solid polymer network has been synthesized by the hydrosilylation of polymethylhydrosiloxane (PMHS) partly substituted with oligo(ethylene glycol) methyl ether side groups and a α,ω-diallyl poly(ethylene glycol) cross-linking reagent. The ionic conductivities of the networks doped with LiTFSI are high at ambient temperature (σ = 1.33 × 10-4 S cm-1 at the optimum LiTFSI concentration EO/Li+ = 20:1). The temperature dependence of the conductivity followed the VTF form, indicating that polymer segmental motion assists the ion transport in the solid networks.

Poly(ethyleneoxide) (PEO) based gel network polymer electrolytes prepared from crosslinking reaction were applied in fabricating quasi-solid-state dye-sensitized TiO 2 photoelectrochemical cells. Incident photon-to-current conversion efficiencies up to 48% and 40%, overall energy conversion efficiencies up to 3.6% and 2.9% have been achieved respectively for the resulting cells containing PEO 2000 and PEO 1500 segments.

Redox flow batteries have special advantages for grid energy storage applications because of the unique cell architecture that can decouple the stored energy and power. This has offered excellent scalability and design flexibility to meet different grid requirements. Traditional inorganics-based flow batteries such as all-vanadium are at near-commercialization stage. However, the high chemical cost has led to considerable capital cost that great limits their broad market penetration. On the other hand, some redox-active aqueous soluble organic (ASO) materials can offer significant cost and performance merits and enable competitive flow battery systems.1,2Facile molecular diversity and structural tailorability also gain benefits in achieving high solubilities and cell voltages for flow batteries. Here we report our materials developmental accomplishments in pursuing high-performance ASO flow batteries.3A variety of promising ASO candidates have been identified with desirable redox potentials and kinetics. Our strategies to improve the solubilities, chemical stabilities, and system performance of these ASO materials will be discussed. We also have gained fundamental understandings of the key performance-limiting factors in determining chemical stability of these redox species and capacity degradation of flow systems. These insights can effectively guide future ASO materials development and improvement. References 1. Winsberg, J.; Hagemann, T.; Janoschka, T.; Hager, M. D.; Schubert, U. S. Angew. Chem. Int. Ed. 2017, 56, 686 –711. 2. Park, M.; Ryu, J.; Wang, W.; Cho, J. Nat. Rev. Mater. 2016, 2, 16080. 3. Liu, T.; Wei, X.; Nie, Z.; Sprenkle, V.; Wang, W. Adv. Energy Mater. 2016, 6, 1501449. Figure 1. The stable cycling efficiencies and capacities of an ASO flow battery. Figure 1

The practical application of non-aqueous redox flow batteries (NRFBs) sets stringent requirements on the electrochemical stability of the redox active materials. In the redox pair for NRFBs, the high-potential species is referred to as the catholyte, which is oxidized into the radical cation state in the charging process. Hydroquinone ethers are a key class of catholyte materials, but the intermolecular reaction between the radical cations is a dominating decomposition pathway of the catholyte during functioning. In order to increase the electrochemical stability of the catholyte materials, the introduction of bulky alkyl spacers at 2,5- positions of the arene ring is commonly used as a strategy in the molecular design to suppress this type of undesirable side reaction. However, the unsubstituted 3,6- positions that are favored for the electrochemical reversibility are responsible for the radical cation reaction in the long-time cycling. Tetrasubstitution of the arene core with either primary or secondary alkyl groups often leads to a compromised redox reversibility. This talk will describe a tetrasubstituted hydroquinone ether-based catholyte molecule that retains excellent redox reversibility and illustrates exceptional stability. Unique bicyclic alkyl groups are incorporated to the molecular scaffold, eliminating the bimolecular reaction between the radical cations. A hybrid NRFB using such catholyte has been operated for over 150 charge-discharge cycles with minimal loss of capacity.

Silicon (Si) has been regarded as the next generation anode material for the lithium-ion batteries due to its high theoretical specific capacity about 4200 mAh/g and low costs. However, the Si nanoparticle (NP) experiences repeated volume changes in size up to 300 % during the lithiation/delithiation processes, which leads to a series of problems like particle pulverization, electrode delamination, and destabilization of solid-electrolyte interface (SEI) layer. The conventional polyvinylidene fluoride (PVDF) binder does not work on the Si anode and by far quite a few polymer binders have been studied and some have shown promising results, such as carboxymethyl cellulose (CMC), alginate, and poly(acrylic acid) (PAA), and some synthesized conductive polymers. While some impressive improvements have been obtained, none of those binders could afford comparable cycling performance to that of carbonaceous anode cells, and the deep understanding of the degradation mechanism of Si NPs is not fully established. Therefore, it is of paramount importance and practical interest to conduct a more systematic study to carefully investigate the relationship between the polymer structures and cycling performance and seek opportunities for next generation binder development. Here linear polysiloxanes (PSs) polymers were chosen as the polymer backbone that can allow us to precisely engineer different properties into the binder polymers. PSs can afford some desirable properties as silicon anode compatible binders, such as elasticity and durability, which were evidenced by previous studies in graphite anodes.[1] On the other hand, PSs do possess several weak spots as a binder material, such as low molecular weight, lack of adhesion to the Si particles, and non-conductivity. Fortunately, it is convenient to utilize hydrosilylation reaction to introduce desirable properties into the PS polymer backbones. For instance, the molecular weight and mechanical stiffness could be easily improved by incorporation crosslinking ability into PSs. The adhesion and conductivity can also be tuned via introductions of groups with high affinity to silicon particles and large conjugation groups that can prompt electron hopping via Pi-Pi stacking (Scheme 1).[2] Those choices of properties could be unlimited as long as we know what properties we are looking for. Moreover, the added properties can be precisely tuned by controlling the ratio of different functional groups, which, combined with the cell testing data, provides an excellent system to investigate the relationship of the binder properties and cell performance. References Xue, Z.; Zhang, Z.; Hu, L.; Amine, K. J. Electrochem. Soc. 2013, 160, A1819-A1823. Zhao, H.; Wei, Y.; Qiao, R.; Zhu, C.; Zheng, Z.; Ling, M.; Jia, Z.; Bai, Y.; Fu, Y.; Lei, J.; Song, X.; Battaglia, V. S.; Yang, W.; Messersmith, P. B.; Liu, G. Nano Lett. 2015, 15, 7927-7932. Scheme 1. Illustration of synthesis of comb-like polysiloxanes with different functional groups to increase the flexibility, adhesion, conductivity as well as crosslinking ability. Figure 1

1,4-Dimethoxybenzene derivatives are materials of choice for use as catholytes in non-aqueous redox flow batteries, as they exhibit high open-circuit potentials and excellent electrochemical reversibility. However, chemical stability of these materials in their oxidized form needs to be improved. Disubstitution in the arene ring is used to suppress parasitic reactions of their radical cations, but this does not fully prevent ring-addition reactions. By incorporating bicyclic substitutions and ether chains into the dialkoxybenzenes, a novel catholyte molecule, 9,10-bis(2-methoxyethoxy)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanenoanthracene (BODMA), is obtained and exhibits greater solubility and superior chemical stability in the charged state. A hybrid flow cell containing BODMA is operated for 150 charge–discharge cycles with a minimal loss of capacity.

A high voltage LiNi0.5Mn0.3Co0.2O2/graphite cell with a fluorinated electrolyte formulation 1.0 m LiPF6 fluoroethylene carbonate/bis(2,2,2-trifluoroethyl) carbonate is reported and its electrochemical performance is evaluated at cell voltage of 4.6 V. Comparing with its nonfluorinated electrolyte counterpart, the reported fluorinated one shows much improved Coulombic efficiency and capacity retention when a higher cut-off voltage (4.6 V) is applied. Scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy data clearly demonstrate the superior oxidative stability of the new electrolyte. The structural stability of the bulk cathode materials cycled with different electrolytes is extensively studied by X-ray absorption near edge structure and X-ray diffraction.

In order to extend the lifetime and performance of lithium ion battery systems, the use of electrolyte additives continues to be one of the most effective and economical approaches currently under investigation. Common metrics used to measure the relative performance enhancement of these electrolyte additives include capacity retention and impedance rise. This study details efforts to 1) perform a combinatorial analysis of electrolyte additives for use in high voltage lithium ion battery systems, and 2) evaluate the performance of the tested electrolyte systems using two figures of merit (FOM) which address both capacity (energy) and impedance (power). Eight known additives were used throughout the course of the test: three additives known to work on the positive (cathode) electrode (TMSPi, TEPi, LiDFOB) and five additives known to work on the negative (anode) electrode (LiBOB, VC, tVCBO, PBE, PES). Electrochemical testing was performed on LiNi0.5Mn0.3Co0.2O2 /graphite full cells operating between 3.0-4.4 V. The cycling protocol combines several C rates (C/1, C/3, C/10) for capacity and rate information and intermittent hybrid pulse power characterization (HPPC) tests from which area specific impedance (ASI) values are calculated. Results from extensive testing reveal interesting trends in the electrolyte systems. In general, TMSPi performed well as an additive while a structurally analogous molecule, TEPi, performed poorly. Other trends, such as the effects of LiBOB on energy fade and VC on power fade, were found. Capacity, impedance and other electrochemical data will be presented to give a comprehensive overview of performance effects of the tested electrolyte additives. This work underscores the importance of developing evaluation methodologies in order to objectively view the performance of electrolyte systems and identify trends in electrolyte additive behavior.

Sulfur (S) has been identified as one of the most promising cathode material due to its high theoretical specific capacity (1675 mAh/g), good environment compatibility, and low cost. These features make lithium-sulfur battery a potential candidate for the next-generation battery, especially in electric vehicles and portable devices. However, the application of lithium-sulfur (Li-S) battery is still impeded by some limitations, including the low electrical and ionic conductivity of the elemental sulfur and the discharge product (Li2S), and the shuttle effect due to the presence the dissolved polysulfide (PS) species in electrolyte. 1,1,2,2-Tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) has been identified as an effective secondary solvent in electrolyte for lithium sulfur batteries. In this study, fluorinated ethers (FEs) other than TTE were attempted in 1,3-dioxolane (DOL) based electrolyte, and comparison was made over cell performance, viscosity/conductivity of electrolyte, and aggregation states of lithium PS species. 1,1,2,2-Tetrafluoroethyl 2,2,2-trifluoroethyl Ether (HFE), ethyl 1,1,2,2-tetrafluoroethyl ether (ETE), and 1,1,2,3,3,3-hexafluoropropyl ethyl ether (HEE) were identified as promising alternatives to TTE to accommodate wider range of applications of Li-S batteries. However, amphiphilic FEs, like 1,1,1,2,2,3,3,4,4-Nonafluoro-6-(pentyloxy)hexane (NHPE) and 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluoro-8-(pentyloxy)octane (TDPE) were not effective at all. Depending on formula weight, viscosity and conductivity, cell performance of Li-S batteries containing electrolytes with different FEs also varied. And FEs with coulombic efficiency higher than that of TTE were discovered. In DOL/FE based electrolyte, the aggregation states of lithium PS species were investigated via small-angle X-ray scattering (SAXS), and revealed a variation in dimension of assemblies of lithium PS species in the presence of different FEs. The difference of cell performance can therefore be concluded as the variation in transport behavior of lithium PS species in electrolyte. In addition, this would offer some insights into the failure mechanisms of Li-S batteries, and promote further development of electrolyte for Li-S batteries. Figure 1

Nickel-rich layered oxide cathode materials have seen widespread deployment due to their high gravimetric capacity and high average discharge voltage. However, achieving this high capacity requires charging voltages above the potential at which the electrolytes decompose at the cathode surface (>4.5 V vs. Li/Li+). This interfacial instability leads to impedance rise and capacity loss. One strategy to stabilize this interface is by the addition of additives to the electrolyte, in which small amounts of a new component change the interactions of the interface. Potentiostatic holds with LiNi0.5Mn0.3 Co0.2O2 (NMC) as the working electrode and Li4Ti5O12 (LTO) as the counter/reference allow a quantitative measurement of the oxidation reactions occurring at cathode. A 60 hour hold allows for concentration polarizations to relax and oxidative side reactions to dominate the current. A more stable electrolyte at the cathode/electrolyte interface would lead to a lower current during the potentiostatic hold. In this work, the performance of five phosphorus-based additive electrolyte formulations (1% wt. ratio) is evaluated against a baseline organic carbonate electrolyte in NMC (LiNi0.5Mn0.3 Co0.2O2 ) / LTO (Li4Ti5O12) full cells. These additives include triethylphosphite (TEPi), tris(2,2,2-trifluoroethyl)phosphite (TTFPi), tris(trimethylsilyl) phosphite (TMSPi), and tris(trimethyl silyl) phosphate (TMSPa). The electrochemical protocol used to evaluate these additives comprises multiple cycles up to 4.4 V vs. Li+/Li, a potentiostatic hold at 4.6 V vs. Li+/Li, followed by AC impedance spectroscopy and extended cycling. Of the formulations surveyed, only electrolytes containing TMSPa and TMSPi (aged for one week) increased the coulombic efficiency during the initial cycling. For the potentiostatic hold, only the aged TMSPi electrolyte lowered the terminal oxidation current compared to the baseline electrolyte, indicating increased stability of the cathode/electrolyte interface. AC impedance spectra indicated the aged TMSPi electrolyte had a slightly elevated high-frequency semicircle (traditionally associated with phenomena at the solid-electrolyte interphase) and a vastly decreased mid-frequency semicircle (traditionally associated with charge-transfer phenomena), compared with all other electrolytes tested. Characterization of cycled electrodes was performed with XPS and SEM will be presented. 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.

Hydroquinone ethers are a key class of catholyte materials for non-aqueous redox flow batteries, showing high open-circuit potential, electrochemical reversibility and chemical tunability. However, the instability of many hydroquinone ethers, particular to electrochemical oxidation, limits their applicability. 2,5-dialkylation of the benzene core has been by far the only effective chemical approach to suppress the side reactions of the corresponding radical cations, restricting the chemical space of structures from which to choose. This talk will describe a bicyclo-alkyl substitution strategy that yields a hydroquinone ether with unprecedentedly high electrochemical stability. The influences of different substituents on the electrochemical properties are investigated. The electrochemical stability is determined via a full flow cell using a benzothiadiazole-based anolyte. In addition, the low impedance shown in the single electrolyte flow cell indicates its great promises as catholyte for high-performance non-aqueous redox flow batteries.