Ultralow-Temperature Li/CFx Batteries Enabled by Fast-Transport and Anion-Pairing Liquefied Gas Electrolytes.

Lithium fluorinated-carbon (Li/CFx ) is one of the most promising chemistries for high-energy-density primary energy-storage systems in applications where rechargeability is not required. Though Li/CFx demonstrates high energy density (>2100 Wh kg-1 ) under ambient conditions, achieving such a high energy density when exposed to subzero temperatures remains a challenge, particularly under high current density. Here, a liquefied gas electrolyte with an anion-pair solvation structure based on dimethyl ether with a low melting point (-141 °C) and low viscosity (0.12 mPa s, 20 °C), leading to high ionic conductivity (>3.5 mS cm-1 ) between -70 and 60 °C is reported. Besides that, through systematic X-ray photoelectron spectroscopy integrated with transmission electron microscopy characterizations, the interface of CFx is evaluated for low-temperature performance. The fast transport and anion-pairing solvation structure of the electrolyte are concluded to bring about reduced charge-transfer resistance at low temperatures, which results in significantly enhanced performance of Li/CFx cells (1690 Wh kg-1 , -60 °C based on active materials). Utilizing 50 mg cm-2 loading electrodes, the Li/CFx still displays 1530 Wh kg-1 at -60 °C. This work provides insights into the electrolyte design that may overcome the operational limits of batteries in extreme environments.

Designing better electrolytes.

Electrolytes and the associated interphases constitute the critical components to support the emerging battery chemistries that promise tantalizing energy but involve drastic phase and structure complications. Designing better electrolytes and interphases holds the key to the success of these batteries. As the only component that interfaces with every other component in the device, an electrolyte must satisfy multiple criteria simultaneously. These include transporting ions while insulating electrons between the electrodes and maintaining stability against electrodes of extreme chemical natures: the strongly oxidative cathode and the strongly reductive anode. In most advanced batteries, the two electrodes operate at potentials far beyond the thermodynamic stability limits of electrolytes, so the stability therein has to be realized kinetically through an interphase formed from the sacrificial reactions between electrolyte and electrodes.

Local Structure of Glassy Lithium Phosphorus Oxynitride Thin Films: A Combined Experimental and Ab†Initio Approach.

Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion conductor displaying exemplary cyclability against lithium metal anodes. There is no definitive explanation for this stability due to the limited understanding of the structure of LiPON. Herein, we provide a structural model of RF-sputtered LiPON. Information about the short-range structure results from 1D and 2D solid-state NMR experiments. These results are compared with first principles chemical shielding calculations of Li-P-O/N crystals and ab initio molecular dynamics-generated amorphous LiPON models to unequivocally identify the glassy structure as primarily isolated phosphate monomers with N incorporated in both apical and as bridging sites in phosphate dimers. Structural results suggest LiPON's stability is a result of its glassy character. Free-standing LiPON films are produced that exhibit a high degree of flexibility, highlighting the unique mechanical properties of glassy materials.

Virtual Texture Generated using Elastomeric Conductive Block Copolymer in Wireless Multimodal Haptic Glove.

Haptic devices are in general more adept at mimicking the bulk properties of materials than they are at mimicking the surface properties. This paper describes a haptic glove capable of producing sensations reminiscent of three types of near-surface properties: hardness, temperature, and roughness. To accomplish this mixed mode of stimulation, three types of haptic actuators were combined: vibrotactile motors, thermoelectric devices, and electrotactile electrodes made from a stretchable conductive polymer synthesized in our laboratory. This polymer consisted of a stretchable polyanion which served as a scaffold for the polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The scaffold was synthesized using controlled radical polymerization to afford material of low dispersity, relatively high conductivity (0.1 S cm-1), and low impedance relative to metals. The glove was equipped with flex sensors to make it possible to control a robotic hand and a hand in virtual reality (VR). In psychophysical experiments, human participants were able to discern combinations of electrotactile, vibrotactile, and thermal stimulation in VR. Participants trained to associate these sensations with roughness, hardness, and temperature had an overall accuracy of 98%, while untrained participants had an accuracy of 85%. Sensations could similarly be conveyed using a robotic hand equipped with sensors for pressure and temperature.

Materials science, energy transition, and the pandemic.

During the current pandemic shutdown, everyone has had to make decisions-many of which haven't been easy. For the first time in my life, I experienced what were previously unthinkable-airplanes being grounded, cars being off the roads, all classes and meetings being held virtually. The surreal experience has propelled me to think more deeply about what I do and why it is so important to push forward with doing better materials science to enable breakthroughs in energy technologies and to ensure a robust supply chain of relevant materials for the world.

COVID-19 disrupts battery materials and manufacture supply chains, but outlook remains strong.

The effects of the coronavirus global pandemic have rippled through many lives and have upended aspects of health care, transportation, and the economy in virtually every country. The energy materials and renewable generation and conversion market, which includes battery-powered electric vehicles, grid storage, and personal electronic devices, is no exception.

Wearable thermoelectrics for personalized thermoregulation.

Thermoregulation has substantial implications for energy consumption and human comfort and health. However, cooling technology has remained largely unchanged for more than a century and still relies on cooling the entire space regardless of the number of occupants. Personalized thermoregulation by thermoelectric devices (TEDs) can markedly reduce the cooling volume and meet individual cooling needs but has yet to be realized because of the lack of flexible TEDs with sustainable high cooling performance. Here, we demonstrate a wearable TED that can deliver more than 10°C cooling effect with a high coefficient of performance (COP > 1.5). Our TED is the first to achieve long-term active cooling with high flexibility, due to a novel design of double elastomer layers and high-ZT rigid TE pillars. Thermoregulation based on these devices may enable a shift from centralized cooling toward personalized cooling with the benefits of substantially lower energy consumption and improved human comfort.

Role of Crystal Symmetry in the Reversibility of Stacking-Sequence Changes in Layered Intercalation Electrodes.

The performance of many technologies, such as Li- and Na-ion batteries as well as some two-dimensional (2D) electronics, is dependent upon the reversibility of stacking-sequence-change phase transformations. However, the mechanisms by which such transformations lead to degradation are not well understood. This study explores lattice-invariant shear as a source of irreversibility in stacking-sequence changes, and through an analysis of crystal symmetry shows that common electrode materials (graphitic carbon, layered oxides, and layered sulfides) are generally susceptible to lattice-invariant shear. The resulting irreversible changes to microstructure upon cycling ("electrochemical creep") could contribute to the degradation of the electrode and capacity fade.

Three-Dimensional Nanoscale Mapping of State-of-the-Art Field-Effect Transistors (FinFETs).

The semiconductor industry has seen tremendous progress over the last few decades with continuous reduction in transistor size to improve device performance. Miniaturization of devices has led to changes in the dopants and dielectric layers incorporated. As the gradual shift from two-dimensional metal-oxide semiconductor field-effect transistor to three-dimensional (3D) field-effect transistors (finFETs) occurred, it has become imperative to understand compositional variability with nanoscale spatial resolution. Compositional changes can affect device performance primarily through fluctuations in threshold voltage and channel current density. Traditional techniques such as scanning electron microscope and focused ion beam no longer provide the required resolution to probe the physical structure and chemical composition of individual fins. Hence advanced multimodal characterization approaches are required to better understand electronic devices. Herein, we report the study of 14 nm commercial finFETs using atom probe tomography (APT) and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDS). Complimentary compositional maps were obtained using both techniques with analysis of the gate dielectrics and silicon fin. APT additionally provided 3D information and allowed analysis of the distribution of low atomic number dopant elements (e.g., boron), which are elusive when using STEM-EDS.

Liquefied gas electrolytes for electrochemical energy storage devices.

Electrochemical capacitors and lithium-ion batteries have seen little change in their electrolyte chemistry since their commercialization, which has limited improvements in device performance. Combining superior physical and chemical properties and a high dielectric-fluidity factor, the use of electrolytes based on solvent systems that exclusively use components that are typically gaseous under standard conditions show a wide potential window of stability and excellent performance over an extended temperature range. Electrochemical capacitors using difluoromethane show outstanding performance from -78° to +65°C, with an increased operation voltage. The use of fluoromethane shows a high coulombic efficiency of ~97% for cycling lithium metal anodes, together with good cyclability of a 4-volt lithium cobalt oxide cathode and operation as low as -60°C, with excellent capacity retention.

Effect of morphology and manganese valence on the voltage fade and capacity retention of Li[Li2/12Ni3/12Mn7/12]O2.

We have determined the electrochemical characteristics of the high voltage, high capacity Li-ion battery cathode material Li[Li2/12Ni3/12Mn7/12]O2 prepared using three different synthesis routes: sol-gel, hydroxide coprecipitation, and carbonate coprecipitation. Each route leads to distinct morphologies and surface areas while maintaining the same crystal structures. X-ray photoelectron spectroscopy (XPS) measurements reveal differences in their surface chemistries upon cycling, which correlate with voltage fading. Indeed, we observe the valence state of Mn on the surface to decrease upon lithiation, and this reduction is specifically correlated to discharging below 3.6 V. Furthermore, the data shows a correlation of the formation of Li2CO3 with the Mn oxidation state from the decomposition of electrolyte. These phenomena are related to each material's electrochemistry in order to expand upon the reaction mechanisms taking place-specifically in terms of the particle morphology produced by each synthetic approach.