Leslie E. Krupp

Solvating additives drive solution-mediated electrochemistry and enhance toroid growth in non-aqueous Li–O2 batteries

1 IBM Almaden Research Center, San Jose, CA, 95120 2 Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA, 94720 3 Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720 4 Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213 5 SUNCAT, SLAC National Accelerator Laboratory, Menlo Park, CA 94025Given their high theoretical specific energy, lithium-oxygen batteries have received enormous attention as possible alternatives to current state-of-the-art rechargeable Li-ion batteries. However, the maximum discharge capacity in non-aqueous lithium-oxygen batteries is limited to a small fraction of its theoretical value due to the build-up of insulating lithium peroxide (Li₂O₂), the batterys primary discharge product. The discharge capacity can be increased if Li₂O₂ forms as large toroidal particles rather than as a thin conformal layer. Here, we show that trace amounts of electrolyte additives, such as H₂O, enhance the formation of Li₂O₂ toroids and result in significant improvements in capacity. Our experimental observations and a growth model show that the solvating properties of the additives prompt a solution-based mechanism that is responsible for the growth of Li₂O₂ toroids. We present a general formalism describing an additives tendency to trigger the solution process, providing a rational design route for electrolytes that afford larger lithium-oxygen battery capacities.

Combining Accurate O2 and Li2O2 Assays to Separate Discharge and Charge Stability Limitations in Nonaqueous Li-O2 Batteries.

Li-air batteries have generated enormous interest as potential high specific energy alternatives to existing energy storage devices. However, Li-air batteries suffer from poor rechargeability caused by the instability of organic electrolytes and carbon cathodes. To understand and address this poor rechargeability, it is essential to elucidate the efficiency in which O2 is converted to Li2O2 (the desired discharge product) during discharge and the efficiency in which Li2O2 is oxidized back to O2 during charge. In this Letter, we combine many quantitative techniques, including a newly developed peroxide titration, to assign and quantify decomposition pathways occurring in cells employing a variety of solvents and cathodes. We find that Li2O2-induced electrolyte solvent and salt instabilities account for nearly all efficiency losses upon discharge, whereas both cathode and electrolyte instabilities are observed upon charge at high potentials.

Ordered Nanopillar Structured Electrodes for Depleted Bulk Heterojunction Colloidal Quantum Dot Solar Cells

A bulk heterojunction of ordered titania nanopillars and PbS colloidal quantum dots is developed. By using a pre-patterned template, an ordered titania nanopillar matrix with nearest neighbours 275 nm apart and height of 300 nm is fabricated and subsequently filled in with PbS colloidal quantum dots to form an ordered depleted bulk heterojunction exhibiting power conversion efficiency of 5.6%.

Phase change nanodot arrays fabricated using a self-assembly diblock copolymer approach

Self-assembling diblock copolymer, polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP), was used as the template for fabricating phase change nanostructures. The high density GeSb nanodots were formed by etching into an amorphous GeSb thin film using silica hard mask which was patterned on top of polymer. The nanodot arrays are 15nm in diameter with 30nm spacing. This is smaller than most structures obtained by e-beam lithography. Time-resolved x-ray diffraction studies showed that the phase transition occurred at 235°C, which is 5°C lower than blanket GeSb film but higher than that of Ge2Sb2Te5 (150°C). GeSb showed good temperature stability for fabrication of small memory devices.

Integrated on-chip inductors with electroplated magnetic yokes (invited)

Thin-film ferromagnetic inductors show great potential as the energy storage element for integrated circuits containing on-chip power management. In order to achieve the high energy storage required for power management, on-chip inductors require relatively thick magnetic yoke materials (several microns or more), which can be readily deposited by electroplating through a photoresist mask as demonstrated in this paper, the yoke material of choice being Ni45Fe55, whose properties of relatively high moment and electrical resistivity make it an attractive model yoke material for inductors. Inductors were designed with a variety of yoke geometries, and included both single-turn and multi-turn coil designs, which were fabricated on 200 mm silicon wafers in a CMOS back-end-of-line (BEOL) facility. Each inductor consisted of electroplated copper coils enclosed by the electroplated Ni45Fe55 yokes; aspects of the fabrication of the inductors are discussed. Magnetic properties of the electroplated yoke materials are...

Patterning ∼20nm half-pitch lines on silicon using a self-assembled organosilicate etch mask

Lines of ∼20nm half-pitch were generated on silicon surface using a self-assembled organosilicate nanostructure. A mixture of a poly(styrene-b-ethylene oxide) (PS-b-PEO) with an organosilicate precursor that is selectively miscible with PEO was used to create lamellar phase whose orientation was controlled perpendicular to the surface by tuning the surface energy of substrates. Thermal cross-linking of the organosilicate precursor followed by thermal decomposition of the PS-b-PEO leaves a robust organosilicate line pattern of sublithographic length scales on the surface. Line patterns on silicon substrate were created by transferring this self-assembled pattern into the underlying silicon substrate using anisotropic plasma etching.

Pattern Placement Accuracy in Block Copolymer Directed Self-Assembly Based on Chemical Epitaxy

The realization of viable designs for circuit patterns using the dense features formed by block copolymer directed self-assembly (DSA) will require a precise and quantitative understanding of self-assembled feature registration to guiding templates or chemical prepatterns. Here we report measurements of DSA placement error for lamellar block copolymer domains indexed to specific lines in the surface chemical prepattern for spatial frequency tripling and quadrupling. These measurements are made possible by the use of an inorganic domain-selective prepattern material that may be imaged upon polymer removal after DSA and a prepattern design incorporating a single feature serving as an in situ registration mark that is identifiable by pattern symmetry in both the prepattern and resulting self-assembled pattern. The results indicate that DSA placement error is correlated with average prepattern line width as well as prepattern pitch uniformity. Finally, the magnitude of DSA placement error anticipated for a uniform, optimized prepattern is estimated.

Phase change nanodots patterning using a self-assembled polymer lithography and crystallization analysis

Crystallization behavior of scalable phase change materials can be studied on nanoscale structures. In this paper, high density ordered phase change nanodot arrays were fabricated using the lift-off technique on a self-assembled diblock copolymer template, polystyrene-poly(methyl-methacrylate). The size of the nanodots was less than 15 nm in diameter with 40 nm spacing. This method is quite flexible regarding the patterned materials and can be used on different substrates. The crystallization behavior of small scale phase change nanodot arrays was studied using time-resolved x-ray diffraction, which showed the phase transition for different materials such as Ge15Sb85, Ge2Sb2Te5, and Ag and In doped Sb2Te. The transition temperatures of these nanodot samples were also compared with their corresponding blanket thin films, and it was found that the nanodots had higher crystallization temperatures and crystallized over a broader temperature range.

Two-phase microwave-assisted synthesis of Cu2S nanocrystals

We demonstrated a new two-phase microwave-assisted method for the synthesis of high-quality copper sulphide (Cu2S) nanocrystals with well-defined size, chemical composition and crystal structure.

Measurement of placement error between self-assembled polymer patterns and guiding chemical prepatterns

Extensive pattern customization will be necessary to realize viable circuit patterns from line-space arrays generated by block copolymer directed self assembly (DSA). In pattern customization with regard to chemical epitaxy of lamellar block copolymers, quantitative and precise knowledge of DSA-feature registration to the chemical prepattern is critical. Here we measure DSA pattern placement error for spatial frequency tripling and quadrupling indexed to specific lines in the chemical prepattern. A range of prepattern line widths where minimal DSA placement error can be expected is identified, and a positive correlation between DSA placement accuracy and prepattern uniformity is shown. Considering the experimental non-idealities present in the chemical prepatterns used in this work that arise from using electron-beam lithography, we anticipate that 3σ DSA placement errors will be at a minimal level if highly uniform chemical prepatterns produced by optical lithography are used.