The electrochemistry of lithium−sulfur (Li−S) batteries is heavily reliant on the structure and dynamics of lithium polysulfides, which dissolve into the liquid electrolyte and mediate the electrochemical conversion process during operation. This behavior is considerably distinct from the widely used lithium-ion batteries, necessitating new mechanistic insights to fully understand the electrochemical phenomena. Testing at low-temperature conditions presents a unique opportunity to glean new insights into the chemistry in kinetically constrained environments. Under such conditions, despite the low freezing point and favorable ionic conductivity of the glyme-based electrolyte, Li−S batteries exhibit counterintuitively poor performance. Here, we show that beyond just existing in singlemolecule conformations, lithium polysulfides tend to cluster and aggregate in solution, particularly at low-temperature conditions, which subsequently constrains the kinetics of electrochemical conversion. Energetics and coordination implications of this behavior are extended toward a new framework for understanding the solution coordination dynamics of dissolved lithium species. Based on this framework, a favorable strongly bound lithium salt is introduced in the Li−S electrolyte to disrupt polysulfide clustered networks, enabling substantially enhanced low-temperature electrochemical performance. More broadly, this mechanistic insight heightens our understanding of polysulfide chemistry irrespective of temperature, confirming the link between the solution conformation of active material and electrochemical behavior.

A Li-ion cell does not contain metallic lithium under normal conditions of operation. Under strenuous charge conditions, however, metallic lithium may deposit on the carbon anode in preference to lithium intercalation and may cause problems in terms of performance, reliability and safety of the cell. Factors that affect the anode polarization and also Li intercalation kinetics play a crucial role in determining the propensity for such lithium deposition. Such factors include the nature of electrolyte, anode/cathode capacity ration, which have been studied with specific examples here. Further, various prototype cells from different manufacturers have been examined for their susceptibility towards lithium plating from a set of systematic charge/discharge tests at different charge rates and temperatures.

We have demonstrated a route to reversibly intercalate fluoride-anion receptor complexes in graphite via a nonaqueous electrochemical process. This approach may find application for a rechargeable lithium-fluoride dual-ion intercalating battery with high specific energy. The cell chemistry presented here uses graphite cathodes with LiF dissolved in a nonaqueous solvent through the aid of anion receptors. Cells have been demonstrated with reversible cathode specific capacity of approximately 80 mAh/g at discharge plateaus of upward of 4.8 V, with graphite staging of the intercalant observed via in situ synchrotron X-ray diffraction during charging. Electrochemical impedance spectroscopy and 11 B nuclear magnetic resonance studies suggest that cointercalation of the anion receptor with the fluoride occurs during charging, which likely limits the cathode specific capacity. The anion receptor type dictates the extent of graphite fluorination, and must be further optimized to realize high theoretical fluorination levels. To find these optimal anion receptors, we have designed an ab initio calculations-based scheme aimed at identifying receptors with favorable fluoride binding and release properties. As cathodes in lithium batteries, carbon-fluoride ͑C-F͒ compounds offer very high theoretical specific capacity, on the scale of 1785 mAh/g for C 1.25 F, though to date, all C-F compounds regardless of preparation conditions are strictly non-rechargeable. A rechargeable C-F cathode would be very desirable in terms of specific energy relative to conventional lithium-ion transition metal oxide cathodes, though there are numerous difficulties associated with reversible fluorination of carbon which relate to a large extent to the nature of the C-F bond.The reaction of carbon and fluorine is well known to yield a wide range of useful compounds with varying properties, depending on preparation conditions and synthesis route. Many of these compounds, despite their relatively poor electronic conductivity, are useful as cathodes for primary Li batteries. Direct reaction of fluorine gas with graphite at temperatures greater than 350°C results in covalent bonding of C x -F with the transition of the planar sp 2 graphene sheets to buckled sp 3 carbon, and concomitant drop in electrical conductivity with decreasing x. Room temperature chemical fluorination of graphite in the presence of various fluorides such as HF, WF 6 , SbF 5 , and IF 5 has been demonstrated by others up to C 1.0 F 0.89 ͑I 0.02 H 0.06 ͒. 1 Under these preparation conditions, the sp 2 carbon hybridization is maintained, and the C-F bonding is ionic. Electrochemical fluorination of graphite in aqueous or anhydrous HF media is also possible, resulting in ionic or semi-covalent C x -F depending on the degree of fluorination, though this process is not significantly reversible and has poor Coulombic efficiency. 2-4 A candidate rechargeable C-F cathode must retain good electronic conductivity and thus the practical lower bound on C x F is likely near the C-F delocalizati...

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Lithium-sulfur cells exhibit poor cycle life, due to the well-known 'polysulfide shuttle' enabled by the dissolution of the sulfur reduction products in organic electrolyte. Different strategies have been implemented to reduce the shuttle effects, with limited success, especially through use of low sulfur loadings (1-2 mg/cm 2 ). Dense electrodes with high sulfur loadings are essential for high energy cells, however, such electrodes experience more serious polysulfide effects. In this paper, we describe the benefits of blending sulfur with a transition metal sulfide (here, TiS 2 and MoS 2 ) to form dense composite cathodes with enhanced conductivity. There is an improvement in both the initial capacity from sulfur utilization (∼800 mAh/g based on sulfur content), the coulombic efficiency (>96%) and also in cycle life upon blending with the metal sulfide. High sulfur loadings (>12 mg/cm 2 or ∼6 mAh/cm 2 per side) were demonstrated to display high sulfur utilization in Li-S cells containing the metal sulfide blends either with or without coatings over the sulfur cathode. XRD studies were carried out to understand the redox behavior of the metal sulfide additive during charge/discharge cycling of the sulfur cathodes. DC polarization and Potentiometric Intermittent Titration Technique (PITT) measurements were made on sulfur cathodes with and without metal sulfide blends to determine the charge transfer and diffusional kinetics. Since their inception in 1991, Li-ion batteries 1 have progressed at a rapid pace, with a three-fold enhancement in their performance achieved through many advances in both electrode materials and electrolytes.2-9 Current Li-ion cells from commercial vendors (e.g., Panasonic, LG and Samsung) provide an impressive specific energy of >250 Wh/kg and energy density of >600 Wh/l which are benefiting a wide range of applications including portable electronic devices, electric vehicles and aerospace needs. Yet, many of the emerging markets such as electric vehicles and renewable energy technologies place even higher demands on the battery technologies, both in terms of performance and cost. It is believed that the performance of lithium-ion technologies has reached a plateau, and any future improvements will only be marginal. Replacement of graphite anodes with Si, and conventional 4 V cathodes with the high voltage Li-rich layered-layered composite cathodes, 10,11 has not yet successfully been applied to commercial batteries. Accordingly, any gains in specific energy and energy density have been modest so far after a decade of development. 12,13 There is, thus, a pursuit for more energetic battery technologies beyond Li-ion batteries. This has led to a renewed interest in the lithiumsulfur system, which has the highest theoretical specific energy of all the known rechargeable systems (due to the high capacity of sulfur, 1672 mAh/g, ∼ 6-10x of Li-ion cathodes), with the notable exception of Li-O 2 which itself has several serious fundamental hurdles that are not close to being overcome.14-16 The spe...

The effects of lithium-ion electrolyte additives in ester-rich low temperature electrolyte blends, including vinylene carbonate (VC), lithiuma bis(oxalato) borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), propane sultone (PS) and lithium bis(fluorosulfonyl)imide (LiFSI), upon the likelihood of lithium plating are investigated in graphite-LiNiCoAlO2 three-electrode cells. Although metallic lithium is generally absent in lithium-ion cells, certain conditions, particularly charging at low temperature and/or at high rate, can lead to lithium metal plating on the surface rather than intercalating into the carbon anode. Metallic lithium reacts with the electrolyte and forms dendrites upon continuous plating, which can lead to cell shorting and capacity loss. The type of carbon anode, electrolyte, and solid-electrolyte-interphase (SEI) all influence this behavior. SEI stabilizing additives are generally detrimental to low temperature charging performance, however, 0.1 M LiFSI was found to be advantageous to low temperature charging. When charged at a C/5 rate to 4.10 V, lithium plating was evident at ∼20 °C higher temperature with VC and LiBOB additives compared to the baseline electrolyte without any additives (plating appears at −10 °C rather than −30 °C with the baseline electrolyte). In contrast, the cell containing 0.10 M LiFSI as an additive did not display lithium plating until −40 °C, or 10 °C lower than the baseline cell.

Europa is a premier target for advancing both planetary science and astrobiology, as well as for opening a new window into the burgeoning field of comparative oceanography. The potentially habitable subsurface ocean of Europa may harbor life, and the globally young and comparatively thin ice shell of Europa may contain biosignatures that are readily accessible to a surface lander. Europa’s icy shell also offers the opportunity to study tectonics and geologic cycles across a range of mechanisms and compositions. Here we detail the goals and mission architecture of the Europa Lander mission concept, as developed from 2015 through 2020. The science was developed by the 2016 Europa Lander Science Definition Team (SDT), and the mission architecture was developed by the preproject engineering team, in close collaboration with the SDT. In 2017 and 2018, the mission concept passed its mission concept review and delta-mission concept review, respectively. Since that time, the preproject has been advancing the technologies, and developing the hardware and software, needed to retire risks associated with technology, science, cost, and schedule.

Exploration missions to the moons of the outer planets (such as Europa) pose unique challenges regarding the design of the spacecraft power source. Current aerospace qualified primary battery technologies cannot adequately meet the mass and volume requirements of proposed missions. Although they have not been used in prior deep space landed missions, lithium carbon-fluoride (Li/CF x ) technologies were identified as a potentially viable option, both with and without blends of manganese dioxide (MnO 2 ). To meet the performance requirements over the intended operating conditions of future NASA missions requires further development of this technology, in particular in the delivery of a high specific energy at moderate to low temperatures, and low discharge rates. A cell development effort was therefore pursued with an industrial battery cell manufacturer. Low (50 mA) and medium (250 mA) discharge rates were used to assess the performance of D-size cells under mission relevant conditions, between 0 • C and −40 • C. Select AA-size and C-size cells were also evaluated using similar rates scaled to the lower cell capacities. Developmental Li/CF x -MnO 2 D-size cells designed for higher specific energy over these conditions were fabricated and tested, targeting operation between 0 and −40 • C and a 50 mA constant discharge current, as the baseline operating condition.