Tunable Mechanochemistry of Lithium Battery Electrodes.

The interplay between mechanical strains and battery electrochemistry, or the tunable mechanochemistry of batteries, remains an emerging research area with limited experimental progress. In this report, we demonstrate how elastic strains applied to vanadium pentoxide (VO), a widely studied cathode material for Li-ion batteries, can modulate the kinetics and energetics of lithium-ion intercalation. We utilize atomic layer deposition to coat VO materials onto the surface of a shapememory superelastic NiTi alloy, which allows electrochemical assessment at a fixed and measurable level of elastic strain imposed on the VO, with strain state assessed through Raman spectroscopy and X-ray diffraction.

Sulfur Vapor-Infiltrated 3D Carbon Nanotube Foam for Binder-Free High Areal Capacity Lithium-Sulfur Battery Composite Cathodes.

Here, we demonstrate a strategy to produce high areal loading and areal capacity sulfur cathodes by using vapor-phase infiltration of low-density carbon nanotube (CNT) foams preformed by solution processing and freeze-drying. Vapor-phase capillary infiltration of sulfur into preformed and binder-free low-density CNT foams leads to a mass loading of ∼79 wt % arising from interior filling and coating of CNTs with sulfur while preserving conductive CNT-CNT junctions that sustain electrical accessibility through the thick foam. Sulfur cathodes are then produced by mechanically compressing these foams into dense composites (ρ > 0.

A Sugar-Derived Room-Temperature Sodium Sulfur Battery with Long Term Cycling Stability.

We demonstrate a room-temperature sodium sulfur battery based on a confining microporous carbon template derived from sucrose that delivers a reversible capacity over 700 mAh/g at 0.1C rates, maintaining 370 mAh/g at 10 times higher rates of 1C. Cycling at 1C rates reveals retention of over 300 mAh/g capacity across 1500 cycles with Coulombic efficiency >98% due to microporous sulfur confinement and stability of the sodium metal anode in a glyme-based electrolyte.

Nanoscale defect engineering of lithium-sulfur battery composite cathodes for improved performance.

For lithium-sulfur batteries to surpass the energy density of lithium-ion batteries, sulfur-containing cathodes require high sulfur loading (>70 wt%) relative to all inactive components, anchoring sites to prevent polysulfide shuttling, high capacity (>1000 mA h g), and stable cycling performance. Here we demonstrate a nanomanufacturing route to produce low-density hybrid nanomaterial electrodes that synergize the mechanical and electrical integrity of carbon nanotubes (CNTs) with the chemical defect properties of carbon nanohorns (CNHs) to produce carefully optimized properties for binder-free lithium-sulfur battery cathodes. High sulfur loadings (>75%) are achieved through a brief (<20 minute) vapor phase treatment at 155 °C, with sulfur infiltration kinetics that increase with defect content of the hybrid composite.

Electrically Conductive Hierarchical Carbon Nanotube Networks with Tunable Mechanical Response.

Small diameter carbon nanotube (CNTs) are synthesized directly from a parent CNT forest using a floating catalyst chemical vapor deposition (CVD) method. To support a new CNT generation from an existing forest, an alumina coating was applied to the CNT forest using atomic layer deposition (ALD). The new generation of small diameter CNTs (8 nm average) surround the first generation, filling the interstitial regions.

Noncovalent Pi-Pi Stacking at the Carbon-Electrolyte Interface: Controlling the Voltage Window of Electrochemical Supercapacitors.

A key parameter in the operation of an electrochemical double-layer capacitor is the voltage window, which dictates the device energy density and power density. Here we demonstrate experimental evidence that π-π stacking at a carbon-ionic liquid interface can modify the operation voltage of a supercapacitor device by up to 30%, and this can be recovered by steric hindrance at the electrode-electrolyte interface introduced by poly(ethylene oxide) polymer electrolyte additives. This observation is supported by Raman spectroscopy, electrochemical impedance spectroscopy, and differential scanning calorimetry that each independently elucidates the signature of π-π stacking between imidazole groups in the ionic liquid and the carbon surface and the role this plays to lower the energy barrier for charge transfer at the electrode-electrolyte interface.

Strain Engineering to Modify the Electrochemistry of Energy Storage Electrodes.

Strain engineering has been a critical aspect of device design in semiconductor manufacturing for the past decade, but remains relatively unexplored for other applications, such as energy storage. Using mechanical strain as an input parameter to modulate electrochemical potentials of metal oxides opens new opportunities intersecting fields of electrochemistry and mechanics. Here we demonstrate that less than 0.

Interface strain in vertically stacked two-dimensional heterostructured carbon-MoS2 nanosheets controls electrochemical reactivity.

Two-dimensional (2D) materials offer numerous advantages for electrochemical energy storage and conversion due to fast charge transfer kinetics, highly accessible surface area, and tunable electronic and optical properties. Stacking of 2D materials generates heterogeneous interfaces that can modify native chemical and physical material properties. Here, we demonstrate that local strain at a carbon-MoS2 interface in a vertically stacked 2D material directs the pathway for chemical storage in MoS2 on lithium metal insertion.

Particulate-free porous silicon networks for efficient capacitive deionization water desalination.

Energy efficient water desalination processes employing low-cost and earth-abundant materials is a critical step to sustainably manage future human needs for clean water resources. Here we demonstrate that porous silicon - a material harnessing earth abundance, cost, and environmental/biological compatibility is a candidate material for water desalination. With appropriate surface passivation of the porous silicon material to prevent surface corrosion in aqueous environments, we show that porous silicon templates can enable salt removal in capacitive deionization (CDI) ranging from 0.

Ultrafast Solvent-Assisted Sodium Ion Intercalation into Highly Crystalline Few-Layered Graphene.

A maximum sodium capacity of ∼35 mAh/g has hampered the use of crystalline carbon nanostructures for sodium ion battery anodes. We demonstrate that a diglyme solvent shell encapsulating a sodium ion acts as a "nonstick" coating to facilitate rapid ion insertion into crystalline few-layer graphene and bypass slow desolvation kinetics. This yields storage capacities above 150 mAh/g, cycling performance with negligible capacity fade over 8000 cycles, and ∼100 mAh/g capacities maintained at currents of 30 A/g (∼12 s charge).

Ultrafine Iron Pyrite (FeS₂) Nanocrystals Improve Sodium-Sulfur and Lithium-Sulfur Conversion Reactions for Efficient Batteries.

Nanocrystals with quantum-confined length scales are often considered impractical for metal-ion battery electrodes due to the dominance of solid-electrolyte interphase (SEI) layer effects on the measured storage properties. Here we demonstrate that ultrafine sizes (∼4.5 nm, average) of iron pyrite, or FeS2, nanoparticles are advantageous to sustain reversible conversion reactions in sodium ion and lithium ion batteries.

Roll-to-Roll Nanomanufacturing of Hybrid Nanostructures for Energy Storage Device Design.

A key limitation to the practical incorporation of nanostructured materials into emerging applications is the challenge of achieving low-cost, high throughput, and highly replicable scalable nanomanufacturing techniques to produce functional materials. Here, we report a benchtop roll-to-roll technique that builds upon the use of binary solutions of nanomaterials and liquid electrophoretic assembly to rapidly construct hybrid materials for battery design applications. We demonstrate surfactant-free hybrid mixtures of carbon nanotubes, silicon nanoparticles, MoS2 nanosheets, carbon nanohorns, and graphene nanoplatelets.

All silicon electrode photocapacitor for integrated energy storage and conversion.

We demonstrate a simple wafer-scale process by which an individual silicon wafer can be processed into a multifunctional platform where one side is adapted to replace platinum and enable triiodide reduction in a dye-sensitized solar cell and the other side provides on-board charge storage as an electrochemical supercapacitor. This builds upon electrochemical fabrication of dual-sided porous silicon and subsequent carbon surface passivation for silicon electrochemical stability. The utilization of this silicon multifunctional platform as a combined energy storage and conversion system yields a total device efficiency of 2.

On-chip high power porous silicon lithium ion batteries with stable capacity over 10,000 cycles.

We demonstrate the operation of a graphene-passivated on-chip porous silicon material as a high rate lithium battery anode with over 50 X power density, and 100 X energy density improvement compared to identically prepared on-chip supercapacitors. We demonstrate this Faradaic storage behavior to occur at fast charging rates (1-10 mA cm(-2)) where lithium locally intercalates into the nanoporous silicon, preventing the degradation and poor cycling performance attributed to deep storage in the bulk silicon. This device exhibits cycling performance that exceeds 10,000 cycles with capacity above 0.

Engineered porous silicon counter electrodes for high efficiency dye-sensitized solar cells.

In this work, we demonstrate for the first time, the use of porous silicon (P-Si) as counter electrodes in dye-sensitized solar cells (DSSCs) with efficiencies (5.38%) comparable to that achieved with platinum counter electrodes (5.80%).

A multifunctional load-bearing solid-state supercapacitor.

A load-bearing, multifunctional material with the simultaneous capability to store energy and withstand static and dynamic mechanical stresses is demonstrated. This is produced using ion-conducting polymers infiltrated into nanoporous silicon that is etched directly into bulk conductive silicon. This device platform maintains energy densities near 10 W h/kg with Coulombic efficiency of 98% under exposure to over 300 kPa tensile stresses and 80 g vibratory accelerations, along with excellent performance in other shear, compression, and impact tests.

Assessing the improved performance of freestanding, flexible graphene and carbon nanotube hybrid foams for lithium ion battery anodes.

We demonstrate the fabrication of three-dimensional freestanding foams of hybrid graphene-single-walled carbon nanotube nanomanufactured materials with reversible capacities of 2640 mA h g(-1) at 0.186 A g(-1) and 236 mA h g(-1) at 27.9 A g(-1).

Uniform, homogenous coatings of carbon nanohorns on arbitrary substrates from common solvents.

We demonstrate a facile technique to electrophoretically deposit homogenous assemblies of single-walled carbon nanohorns (CNHs) from common solvents such as acetone and water onto nearly any substrate including insulators, dielectrics, and three-dimensional metal foams, in many cases without the aid of surfactants. This enables the generation of pristine film-coatings formed on time scales as short as a few seconds and on three-dimensional templates that enable the formation of freestanding polymer-CNH supported materials. As electrophoretic deposition is usually only practical on conductive electrodes, we emphasize our observation of efficient deposition on nearly any material, including nonconductive substrates.

Surface engineered porous silicon for stable, high performance electrochemical supercapacitors.

Silicon materials remain unused for supercapacitors due to extreme reactivity of silicon with electrolytes. However, doped silicon materials boast a low mass density, excellent conductivity, a controllably etched nanoporous structure, and combined earth abundance and technological presence appealing to diverse energy storage frameworks. Here, we demonstrate a universal route to transform porous silicon (P-Si) into stable electrodes for electrochemical devices through growth of an ultra-thin, conformal graphene coating on the P-Si surface.

Thermal and optical activation mechanisms of nanospring-based chemiresistors.

Chemiresistors (conductometric sensor) were fabricated on the basis of novel nanomaterials--silica nanosprings ALD coated with ZnO. The effects of high temperature and UV illumination on the electronic and gas sensing properties of chemiresistors are reported. For the thermally activated chemiresistors, a discrimination mechanism was developed and an integrated sensor-array for simultaneous real-time resistance scans was built.