December 4, 2021

CoE Site Index  |  

Research Projects

Diametric Extremes in the Ionic Conductivity of Mixed Glass Former Solid Electrolytes

A rare coincidence of high ionic conductivity with improved physical and electrochemical properties of glassy solid electrolytes can be achieved by mixing two glass former cations, Boron (B) and Phosphate (P) for example, or by mixing two glass former anions, Oxygen (O) and Sulfur (S) for example, at a constant fraction of the mobile cation, such as Na+. Such optimized mixed glass former (MGF) glassy solid electrolytes based upon more earth-abundant Sodium (Na) may be candidates from which next-generation cheaper, safer, more energy dense, and longer lasting large grid-scale batteries can be developed. While the Na B P O MGF system exhibits a positive Mixed Glass Former Effect (MGFE). Our new research has also discovered MGF systems that show never before seen negative MGFEs. Hence, at the same fraction of mobile alkali cations, mixing an alkali borate glass with an alkali phosphate glass produces a strong positive MGFE, while mixing with an alkali silicate glass produces a negative MGFE. Brand new, but so far completely unexplored research by the PI shows that this dual behavior of the MGFE is also seen in sulfide glasses. Here, B additions to a Na P S glass exponentially increase the ionic conductivity, whereas Germanium (Ge) additions to the same glass decrease its ionic conductivity.

While progress has been made in understanding ionic conduction in solid electrolytes, significant knowledge gaps still exist and the diametrically extreme behavior of positive and negative MGFE systems is chief among these. Indeed, to the PI’s knowledge, there are no reports in the open literature of the study of a negative MGFE system. This research program is therefore grounded in the study of an entirely new phenomenon in entirely new systems that so far have never been studied before. Moreover, by studying the negative MGFE in two different systems, modestly conducting oxide glasses and more highly conducting sulfide glasses, it will be possible for the first time to use these negative and positive MGFEs to probe deeper into the atomic level details of ion conduction in solid electrolytes. Not only will this result in an enhanced understanding of ionic conduction in glassy solid electrolytes, but this transformative understanding will advance our understanding of all classes of solid electrolytes. This will enable us to develop an understanding of why these two systems, oxides and sulfides, have ternary systems that can exhibit both positive and negative MGFEs. Therefore, the goal of this research program is the entirely new comparative study of the simultaneous occurrence of both positive and negative MGFEs in oxide and sulfide MGF systems that will enable greater understanding of the fundamental materials chemistry and physics at root of the MGFE in these systems.

 

Next Generation Lithium-Sulfur Batteries for Mission-Enabling Energy Storage Systems

In this research capacity and competitiveness building project, a new type of high rate, high capacity, and high cycle life lithium-sulfur battery (LSB) will be developed that will advance the state-of-the-art in lithium cell energy, power densities, and cycle lifetime; while at the same time improving the safety of such cells over current designs. NASA has identified advanced batteries as critically important for the next generation of human space exploration and a recent report by the National Research Council has concurred that battery advances are needed to further expand our understanding of the Earth and universe. Lithium-ion batteries were employed in the 2011 Mars Science Laboratory Rover and have been selected for use on the International Space Center. NASA’s technical objective for battery technology development is to improve the performance of rechargeable cells to meet the energy storage requirements of human missions. NASA’s approach is to develop advanced lithium battery components to safely provide substantially higher specific energy and energy density than is currently available. Battery cells will be designed to address the needs of EVA suits and are expected to have broad benefit across the fleet of future exploration vehicles. New classes of high energy density batteries based upon the Lithium-Sulfur system are especially attractive and hold great promise in advancing the mission capabilities of NASA’s space exploration programs. The method of approach will be to develop a new double half-cell (DHC) LSB design where a high lithium ion conductivity solid electrolyte is placed between the anode and cathode and in doing so two different and independently optimized liquid electrolytes can be used for each electrode. This design will solve three major problems present in LSBs: first, it will completely stop polysulfide cross-over; second, it will limit dendritic lithium growth; and third, it will greatly limit self-discharge. Out of this research, there will be two major objectives of the project: to develop sustainable experimental and theoretical research capability, capacity, and competitiveness in high-rate high-capacity LSBs by collaborating with NASA researchers, industry partners, and 4- and 2- year college collaborators. And to develop sustainable battery research funding and programs in the broad area of electrochemical energy storage for load leveling, for plug-in and hybrid electric vehicles, and for portable electronics by using these research capacity and competitiveness building efforts. To achieve the first objective, there are three goals: to develop and characterize new high Li+ ion conductivity solid electrolytes for new DHC LSBs, to develop and characterize new high Li+ and e- conductivity, high surface area, high porosity nano- and mesoscale composite sulfur cathodes, and to evaluate liquid electrolytes that are optimized for the anode and cathode compartments to optimize the battery performance of DHC LSBs. To achieve the second objective, there are three goals: to develop computationally and laboratory procedures at ISU necessary to optimally select and then prepare materials for and assemble LSBs and then electrochemically test them, to use this EPSCoR project to enable ISU to compete in new research proposal competitions directed at new battery systems for use in large load leveling energy storage, for use in plug-in and electric vehicle applications, and for use in portable electronic applications, and to use this technology enabling research that is focused on NASA space applications to develop new research capacity and competitiveness in the state of Iowa and to develop new battery technologies of high commercial value for terrestrial applications. In doing so, we will develop a sustainable research program that will enable scientists to continue collaborations with NASA, other US federal agencies, industry, and educational partners in the state of Iowa.

 

Preparation and Assembly of Solid State Lithium Batteries

All solid-state lithium batteries offer the advantage of higher operating temperatures over traditional liquid electrolyte lithium batteries. In the latter, maximum operating temperatures are limited to at most 30 – 50 ℃ due to the high volatility of the liquid electrolyte used in these batteries. In newer all solid state batteries, operating temperatures as high as 160 ℃ can be used when metallic lithium is used as the anode and even higher temperatures when non-lithium anodes such as graphite or silicon are used. This is because the solid electrolyte separating the anode and cathode is a ceramic solid that does not typically melt until temperatures as high as 300 ℃ are reached.
The PI has long researched and studied high Li+ ion conducting solid electrolytes and has extensive experience in the synthesis, processing, and characterizing of these materials which can have Liion conductivities as high as 10-2 S/cm at room temperature.
In this project, the PI and his students will use this extensive experience to assemble a limited number of all solid state anode/solid electrolyte/cathode lithium battery stacks and deliver these to the Jet Propulsion Laboratory (JPL) for their testing and characterization. If time and resources permit, the PI and his students will receive back from the JPL results from some of their battery tests and use this performance data to make improvements in the cell stacks. In a similar way, if time and resources permit, ISU will also test some of the battery stacks being prepared for the JPL to further improve the quality of the battery stacks sent to the JPL.

 

Investigation of High-Performance Components of Novel Structure for Ambient Temperature High Energy Density Battery Systems.

There is currently an urgent need for rapid response, high capacity, electrochemical energy storage systems for load leveling functions as an increasing fraction of our energy becomes derived from renewable sources. Two of the most attractive systems from the point of view of energy density and economy of materials are the Na/S and Na/NiCl2 systems; each system employs liquid anodes and the former has both electrodes in the liquid state. So far, such Na/S cells have required a high-temperature operation to maintain both electrodes in the liquid state. The passage of sodium ions through a rigid, but fragile, ceramic separator is common to each. This has been the Achilles heel in past attempts to utilize them for automobile propulsion systems. In such use, the inherent fragility of the thin ceramic separator has proven to be an intractable problem, though it is apparently being overcome in recent high energy storage versions of the same technology (e.g. the GE technology). These systems are all operated at elevated temperature (about 300ºC). The present proposal is aimed at the possibility of reducing the temperature of operation of the above two chemical approaches, hopefully to ambient. More specifically it is aimed at developing new solutions to the electrolyte problem since this is where the PI’s both find their greatest expertise.
We will achieve room temperature liquids states of the Na and S electrodes by forming carefully considered multicomponent phases and use high liquid state non-ideality to maintain a high chemical activity for the primary, Na, and S, phases. For the former, we will use near eutectic compositions of Na and K, TE ~ -12 ºC, and take advantage of nearly identical Na+ and K+ conductivities in ”-alumina. For S, we will likewise form non-ideal (positive deviation) solutions with S2Cl2 that are liquid at 25 ºC for compositions as high as 80 mole% S. To create rigidly flexible high conductivity solid electrolytes, we will work along three parallel, but highly complementary, tracks. In one, we will carefully use flex inducing fast ion conducting glass and polymer films to produce more strain-resistant glass-ceramics that utilize their flow-rectifying character. In our second strategy, we will utilize the nascent observation that rigid, but porous structures can be assembled from chemical building blocks. In our new approach here, our resulting materials will be overall amorphous with a tunable porosity to control (and improve) the Na+ conductivity, but to control (and limit) polysulfide cross-diffusion.

 

Lithium Ion Thin Film Battery

Lithium thiogermanate thin amorphous films are prepared as electrolytes for lithium rechargeable batteries by RF magnetron sputtering deposition in Ar and N2 gases. The targets for RF sputtering are prepared by milling the appropriate amounts of the starting materials in the xLi2S+GeS2(x=2, 3), Li4GeS4 and Li6GeS5, binary system. The ~1 μm thin film electrolytes are grown onto a variety of substrates using 30 to 40 Watt power and 30 mtorr gas pressure. Films are sputtered in both inactive (Ar) and active (N2) gas atmospheres to examine the differences created between undoped and doped (N) films. XPS and Auger spectroscopies are used to characterize the composition of the films. IR and Raman spectroscopy are used to further characterize the chemical bonding in the films. Ionic conductivity measurements of the electrolyte film using impedance spectroscopy are used to examine the Li2S and N dependence of the conductivity.

 

Secondary Glass Transition Temperatures

The secondary glass transition project dealt with using low temperature DSC techniques to confirm Oguni’s observations of a β-glass transition, which he found using adiabatic calorimetry.  The thermal properties of the Li2O X + P2O5 (1-X) system were explored and the low temperature β-glass transition was not found.  Even though this secondary transition wasn’t discovered, the heat capacities of the mixed alkali system [(Na2O + Li2O) X + P2O5 (1-X)] can be reported.

 

Mechanochemical milling of sodium ion glasses

For large energy storage systems, Li is expensive and Na is a more attractive alternative. Na/S cells are actively being considered for large energy storage systems such as solar farms and wind turbines.  In the MGFE project, sodium ion conductors are being prepared by melt-quenching. This study aims to complement the MGFE project’s melt-quenching approach with a mechanochemically milled system.

 


Previous Projects

 

Materials World Network – Mixed Glass Former Effect (MGFE)

The Iowa State University GOM group is part of a Materials World Network research project to study the Mixed Glass Former Effect. In collaboration with five other universities; Central Michigan University, Cornell University, Ilmenau (Germany), Munster (Germany), and Chalmers (Sweden). Between the six universities they will investigate the MGFE through IR and Raman Spectroscopy, NMR Spectroscopy, neutron diffraction, x-ray diffraction, modeling (simulation molecular dynamics and reverse Monte Carlo), and finally dielectric spectrometry. The purpose of this research collaboration is to develop a composition-property-structure-dynamics understanding of the MGFE which may lead to the development of new glassy electroltyes to solve the problems of polymer electrolytes.