Architectural integration of the components necessary for electrical energy storage on the nanoscale and in 3D

Toward Solid-State 3D-Microbatteries Using Functionalized Polycarbonate-Based Polymer Electrolytes

3D microbatteries (3D-MBs) impose new demands for the selection, fabrication, and compatibility of the different battery components. Herein, solid polymer electrolytes (SPEs) based on poly(trimethylene carbonate) (PTMC) have been implemented in 3D-MB systems. 3D electrodes of two different architectures, LiFePO₄-coated carbon foams and Cu₂O-coated Cu nanopillars, have been coated with SPEs and used in Li cells. Functionalized PTMC with hydroxyl end groups was found to enable uniform and well-covering coatings on LiFePO₄-coated carbon foams, which was difficult to achieve for nonfunctionalized polymers, but the cell cycling performance was limited. By employing a SPE prepared from a copolymer of TMC and caprolactone (CL), with higher ionic conductivity, Li cells composed of Cu₂O-coated Cu nanopillars were constructed and tested both at ambient temperature and 60 °C. The footprint areal capacity of the cells was ca. 0.02 mAh cm^-2 for an area gain factor (AF) of 2.5, and 0.2 mAh cm^-2 for a relatively dense nanopillar-array (AF = 25) at a current density of 0.008 mA cm^-2 under ambient temperature (22 ± 1 °C). These results provide new routes toward the realization of all-solid-state 3D-MBs.

Advances on Microsized On-Chip Lithium-Ion Batteries

Development of microsized on-chip batteries plays an important role in the design of modern micro-electromechanical systems, miniaturized biomedical sensors, and many other small-scale electronic devices. This emerging field intimately correlates with the topics of rechargeable batteries, nanomaterials, on-chip microfabrication, etc. In recent years, a number of novel designs are proposed to increase the energy and power densities per footprint area, as well as other electrochemical performances of microsized lithium-ion batteries. These advances may guide the pathway for the future development of microbatteries.

Rewriting Electron-Transfer Kinetics at Pyrolytic Carbon Electrodes Decorated with Nanometric Ruthenium Oxide

Platinum is state-of-the-art for fast electron transfer whereas carbon electrodes, which have semimetal electronic character, typically exhibit slow electron-transfer kinetics. But when we turn to practical electrochemical devices, we turn to carbon. To move energy devices and electro(bio)analytical measurements to a new performance curve requires improved electron-transfer rates at carbon. We approach this challenge with electroless deposition of disordered, nanoscopic anhydrous ruthenium oxide at pyrolytic carbon prepared by thermal decomposition of benzene (RuOx@CVD-C). We assessed traditionally fast, chloride-assisted ([Fe(CN)₆]^3-/4-) and notoriously slow ([Fe(H₂O)₆]^3+/2+) electron-transfer redox probes at CVD-C and RuOx@CVD-C electrodes and calculated standard heterogeneous rate constants as a function of heat treatment to crystallize the disordered RuOx domains to their rutile form. For the fast electron-transfer probe, [Fe(CN)₆]^3-/4-, the rate increases by 34× over CVD-C once the RuOx is calcined to form crystalline rutile RuO₂. For the classically outer-sphere [Fe(H₂O)₆]^3+/2+, electron-transfer rates increase by an even greater degree over CVD-C (55×). The standard heterogeneous rate constant for each probe approaches that observed at Pt but does so using only minimal loadings of RuOx.

Competitive Oxygen Evolution in Acid Electrolyte Catalyzed at Technologically Relevant Electrodes Painted with Nanoscale RuO2

Using a solution-based, non-line-of sight synthesis, we electrolessly deposit ultrathin films of RuO₂ ("nanoskins") on planar and 3D substrates and benchmark their activity and stability for oxygen-evolution reaction (OER) in acid electrolyte under device-relevant conditions. When an electrically contiguous ∼9 nm thick RuO₂ nanoskin is expressed on commercially available, insulating SiO₂ fiber paper, the RuO₂@SiO₂ electrode exhibits high current density at low overpotential (10 mA cm^-2 @ η = 280 mV), courtesy of a catalyst amplified in 3D; however, the mass-normalized activity falls short of that achieved for films deposited on planar, metallic substrates (Ti foil). By wrapping the fibers with a <100 nm thick graphitic carbon layer prior to RuO₂ deposition (RuO₂@C@SiO₂), we retain the high mass activity of the RuO₂ (40-60 mA mg^-1 @ η = 330 mV) and preserve the desirable macroscale properties of the 3D scaffold: porous, lightweight, flexible, and inexpensive. The RuO₂@C@SiO₂ anodes not only achieve the 10 mA cm^-2 figure of merit at a low overpotential (η = ∼270 mV), but more importantly they do so while (1) minimizing the mass of catalyst needed to achieve this metric, (2) incorporating the catalyst into a practical electrode design, and (3) improving the long-term stability of the catalyst. Our best-performing anodes achieve state-of-the-art or better performance on the basis of area and mass, and do so with a catalyst density 300-580× less than that of bulk RuO₂. By limiting the oxidizing potential required to evolve O₂ at the electrode, even at 10 mA cm^-2, we achieve stable activity for 100+ h.

Self-assembled three-dimensional and compressible interdigitated thin-film supercapacitors and batteries

Traditional thin-film energy-storage devices consist of stacked layers of active films on two-dimensional substrates and do not exploit the third dimension. Fully three-dimensional thin-film devices would allow energy storage in bulk materials with arbitrary form factors and with mechanical properties unique to bulk materials such as compressibility. Here we show three-dimensional energy-storage devices based on layer-by-layer self-assembly of interdigitated thin films on the surface of an open-cell aerogel substrate. We demonstrate a reversibly compressible three-dimensional supercapacitor with carbon nanotube electrodes and a three-dimensional hybrid battery with a copper hexacyanoferrate ion intercalating cathode and a carbon nanotube anode. The three-dimensional supercapacitor shows stable operation over 400 cycles with a capacitance of 25 F g⁻¹ and is fully functional even at compressions up to 75%. Our results demonstrate that layer-by-layer self-assembly inside aerogels is a rapid, precise and scalable route for building high-surface-area 3D thin-film devices.

It is challenging to construct three-dimensional thin-film energy-storage devices. Here the authors present supercapacitors and batteries based on layer-by-layer self-assembly of interdigitated thin films inside aerogels, demonstrating energy storage as well as compressibility in three-dimensional devices.

Hydroxyl-functionalized poly(trimethylene carbonate) electrolytes for 3D-electrode configurations

Hydrogen-bonding hydroxyl side groups in a polycarbonate solid polymer electrolyte lead to improved surface adhesion and enable the application of thin, conformal electrolyte films onto complex 3D-structured electrode substrates.

An all-in-one nanopore battery array

A single nanopore structure that embeds all components of an electrochemical storage device could bring about the ultimate miniaturization in energy storage. Self-alignment of electrodes within each nanopore may enable closer and more controlled spacing between electrodes than in state-of-art batteries. Such an 'all-in-one' nanopore battery array would also present an alternative to interdigitated electrode structures that employ complex three-dimensional geometries with greater spatial heterogeneity. Here, we report a battery composed of an array of nanobatteries connected in parallel, each composed of an anode, a cathode and a liquid electrolyte confined within the nanopores of anodic aluminium oxide, as an all-in-one nanosize device. Each nanoelectrode includes an outer Ru nanotube current collector and an inner nanotube of V₂O₅ storage material, forming a symmetric full nanopore storage cell with anode and cathode separated by an electrolyte region. The V₂O₅ is prelithiated at one end to serve as the anode, with pristine V₂O₅ at the other end serving as the cathode, forming a battery that is asymmetrically cycled between 0.2 V and 1.8 V. The capacity retention of this full cell (relative to 1 C values) is 95% at 5 C and 46% at 150 C, with a 1,000-cycle life. From a fundamental point of view, our all-in-one nanopore battery array unveils an electrochemical regime in which ion insertion and surface charge mechanisms for energy storage become indistinguishable, and offers a testbed for studying ion transport limits in dense nanostructured electrode arrays.

A 3.5 V lithium-iodine hybrid redox battery with vertically aligned carbon nanotube current collector

A lithium-iodine (Li-I2) cell using the triiodide/iodide (I3(-)/I(-)) redox couple in an aqueous cathode has superior gravimetric and volumetric energy densities (∼ 330 W h kg(-1) and ∼ 650 W h L(-1), respectively, from saturated I2 in an aqueous cathode) to the reported aqueous Li-ion batteries and aqueous cathode-type batteries, which provides an opportunity to construct cost-effective and high-performance energy storage. To apply this I3(-)/I(-) aqueous cathode for a portable and compact 3.5 V battery, unlike for grid-scale storage as general target of redox flow batteries, we use a three-dimensional and millimeter thick carbon nanotube current collector for the I3(-)/I(-) redox reaction, which can shorten the diffusion length of the redox couple and provide rapid electron transport. These endeavors allow the Li-I2 battery to enlarge its specific capacity, cycling retention, and maintain a stable potential, thereby demonstrating a promising candidate for an environmentally benign and reusable portable battery.

Hyperbranched polydendrons: a new controlled macromolecular architecture with self-assembly in water and organic solvents

A new macromolecular architecture comprising multiple linear-dendritic hybrid copolymer sub-units is presented – hyperbranched polydendrons. The materials are very high molecular weight and disperse but undergo extremely uniform self-assembly behaviour.

Hybrid nanostructures for energy storage applications

Materials engineering plays a key role in the field of energy storage. In particular, engineering materials at the nanoscale offers unique properties resulting in high performance electrodes and electrolytes in various energy storage devices. Consequently, considerable efforts have been made in recent years to fulfill the future requirements of electrochemical energy storage using these advanced materials. Various multi-functional hybrid nanostructured materials are currently being studied to improve energy and power densities of next generation storage devices. This review describes some of the recent progress in the synthesis of different types of hybrid nanostructures using template assisted and non-template based methods. The potential applications and recent research efforts to utilize these hybrid nanostructures to enhance the electrochemical energy storage properties of Li-ion battery and supercapacitor are discussed. This review also briefly outlines some of the recent progress and new approaches being explored in the techniques of fabrication of 3D battery structures using hybrid nanoarchitectures.

On the configuration of supercapacitors for maximizing electrochemical performance

Supercapacitors, which are attracting rapidly growing interest from both academia and industry, are important energy-storage devices for acquiring sustainable energy. Recent years have seen a number of significant breakthroughs in the research and development of supercapacitors. The emergence of innovative electrode materials (e.g., graphene) has clearly provided great opportunities for advancing the science in the field of electrochemical energy storage. Conversely, smart configurations of electrode materials and new designs of supercapacitor devices have, in many cases, boosted the electrochemical performance of the materials. We attempt to summarize recent research progress towards the design and configuration of electrode materials to maximize supercapacitor performance in terms of energy density, power density, and cycle stability. With a brief description of the structure, energy-storage mechanism, and electrode configuration of supercapacitor devices, the design and configuration of symmetric supercapacitors are discussed, followed by that of asymmetric and hybrid supercapacitors. Emphasis is placed on the rational design and configuration of supercapacitor electrodes to maximize the electrochemical performance of the device.

3D nanoporous nanowire current collectors for thin film microbatteries

Conventional thin film batteries are fabricated based on planar current collector designs where the high contact resistance between the current collector and electrodes impedes overall battery performance. Hence, current collectors based on 3D architectures and nanoscale roughness has been proposed to dramatically increase the electrode-current collector surface contact areas and hence significantly reduce interfacial resistance. The nanorod-based current collector configuration is one of several 3D designs which has shown high potential for the development of high energy and high power microbatteries in this regard. Herein we fabricate a nanoporous nanorod based current collector, which provides increased surface area for electrode deposition arising from the porosity of each nanorods, yet keeping an ordered spacing between nanorods for the deposition of subsequent electrolyte and electrode layers. The new nanostructured 3D current collector is demonstrated with a polyaniline (PANI)-based electrode system and is shown to deliver improved rate capability characteristics compared to planar configurations. We have been able to achieve stable capacities of ~32 μAh/cm(2) up to 75 cycles of charge/discharge even at a current rate of ~0.04 mA/cm(2) and have observed good rate capability even at high current rates of ~0.8 mA/cm(2).