The design and fabrication of three-dimensional multifunctional architectures from the appropriate nanoscale building blocks, including the strategic use of void space and deliberate disorder as design components, permits a re-examination of devices that produce or store energy as discussed in this critical review. The appropriate electronic, ionic, and electrochemical requirements for such devices may now be assembled into nanoarchitectures on the bench-top through the synthesis of low density, ultraporous nanoarchitectures that meld high surface area for heterogeneous reactions with a continuous, porous network for rapid molecular flux. Such nanoarchitectures amplify the nature of electrified interfaces and challenge the standard ways in which electrochemically active materials are both understood and used for energy storage. An architectural viewpoint provides a powerful metaphor to guide chemists and materials scientists in the design of energy-storing nanoarchitectures that depart from the hegemony of periodicity and order with the promise--and demonstration--of even higher performance (265 references).

Three‐dimensionally ordered macroporous (3DOM) materials are composed of well‐interconnected pore and wall structures with wall thicknesses of a few tens of nanometers. These characteristics can be applied to enhance the rate performance of lithium‐ion secondary batteries. 3DOM monoliths of hard carbon have been synthesized via a resorcinol‐formaldehyde sol–gel process using poly(methyl methacrylate) colloidal‐crystal templates, and the rate performance of 3DOM carbon electrodes for lithium‐ion secondary batteries has been evaluated. The advantages of monolithic 3DOM carbon electrodes are: 1) solid‐state diffusion lengths for lithium ions of the order of a few tens of nanometers, 2) a large number of active sites for charge‐transfer reactions because of the material's high surface area, 3) reasonable electrical conductivity of 3DOM carbon due to a well‐interconnected wall structure, 4) high ionic conductivity of the electrolyte within the 3DOM carbon matrix, and 5) no need for a binder and/or a conducting agent. These factors lead to significantly improved rate performance compared to a similar but non‐templated carbon electrode and compared to an electrode prepared from spherical carbon with binder. To increase the energy density of 3DOM carbon, tin oxide nanoparticles have been coated on the surface of 3DOM carbon by thermal decomposition of tin sulfate, because the specific capacity of tin oxide is larger than that of carbon. The initial specific capacity of SnO2‐coated 3DOM carbon increases compared to that of 3DOM carbon, resulting in a higher energy density of the modified 3DOM carbon. However, the specific capacity decreases as cycling proceeds, apparently because lithium–tin alloy nanoparticles were detached from the carbon support by volume changes during charge–discharge processes. The rate performance of SnO2‐coated 3DOM carbon is improved compared to 3DOM carbon.

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Templating with colloidal crystals, arrays of close-packed polymer or silica spheres, [1] is a general method of forming three-dimensionally ordered macroporous (3DOM) materials or inverse opals composed of metals, oxides, polymers, and other compositions. [2] The resulting structures consist of nanometer thick walls that surround interconnected close-packed spherical voids with sub-micrometer diameters. Because of their periodic features with unit-cell dimensions of the order of the wavelengths of UV-visible-IR light, inverse opals have generated significant interest as photonic crystals.[3] Other applications, such as those involving reactivity of the skeleton (e.g., catalysis, biomaterials) [2] can also benefit from the 3DOM structure. To enhance functionality of an inverse opal, pore surfaces can be modified, not merely with small organic groups, but also with polymer films and nanoparticles.[4] Here, we employ a strategy involving multiple surface-modification steps to create a threefold interpenetrating functional structure based on a conducting, monolithic inverse opal, an ultrathin polymer coating, and a second conducting phase that permeates the remaining pore space. In the example provided here the resulting composite material forms an electrochemical cell in which the interpenetrating electrode materials are electronically isolated. We demonstrate the ability to shuttle an intercalant between electrodes in this nano-/microstructured cell, whose design may be adaptable to battery, capacitor, or sensor applications. [5][6][7][8][9][10][11][12][13][14] It was recently demonstrated that the 3DOM architecture can lead to improved rate performance of individual electrodes. [15][16][17][18] For example, monolithic 3DOM carbon anodes have several advantages that facilitate rapid intercalation and deintercalation of Li ions: 1) nanometer-scale solid-state diffusion lengths, 2) high ionic conductivity of a suitable electrolyte in the porous matrix, 3) reasonable electrical conductivity and 4) no need for a binder and/or a conducting agent. Furthermore, the bicontinuous pore and wall structure of the inverse-opal architecture permits facile access and sufficient void space to accommodate a second electrode throughout the monolithic macropore system. Challenges in synthesizing such an interpenetrating electrode structure on a sub-micrometer length scale include the need to isolate electrodes from each other to prevent shorts, the ability to make electrical contact to each individual electrode, [19] and the assembly of such a functional composite under reaction conditions that maintain the integrity of the underlying structure. We developed a strategy that can achieve these requirements by combining colloidal crystal templating with electrochemical thin-film growth and soft sol-gel chemistry. Monolithic 3DOM carbon was coated with a conformal layer of poly(phenylene oxide) (PPO) or sulfonated PPO (SPPO) by electro-oxidative deposition of phenolic monomers. The remaining void space was infiltrated with a vanadium al...

This paper presents a general method of preparing three-dimensionally ordered macroporous ͑3DOM͒ electrode materials, including both cathode materials (V 2 O 5 and LiNiO 2 ) and an anode material (SnO 2 ). The method is based on templated precipitation of inorganic precursors within a colloidal crystal of poly͑methyl methacrylate͒ spheres and subsequent chemical conversion. 3DOM electrodes possess several features of interest in the design of novel battery materials, such as high accessible surface areas, continuous networks, and structural features on the nanometer scale. Optimal synthesis conditions and structural features of 3DOM electrode materials are described on the basis of X-ray diffraction, scanning electron microscopy, nitrogen adsorption, and chemical analysis.Conventional lithium secondary batteries experience large capacity losses when they are charged/discharged at high rates. This behavior is attributed to the rate-limiting step during the electrochemical processes, i.e., slow diffusion of lithium ions through the electrode materials. 1 At high charge/discharge rates, large Li ϩ insertion or extraction fluxes at the surface, and slow Li ϩ transport in the bulk result in concentration polarization of Li ϩ within the electrode material. This causes a rise/drop in battery voltage, which leads to termination of the charge/discharge before the maximum capacity of the electrode material is utilized. 2,3 Therefore, optimization of the electrode material parameters that influence ion kinetics is an important subject in battery research.Recently, numerous investigations have focused on processing of electrode materials with submicrometer grain sizes. 4-20 By several low-temperature preparation techniques ͑sol-gel methods, 4-13 wet chemical Pechini techniques 14-16 ͒ or fast microwave synthesis, 17-20 various ultrafine electrode materials have been prepared. Since the grain sizes ͑Ͻ1 m͒ of these electrode materials are much smaller than those produced from solid-state techniques ͑Ͼ10 m͒, the Li ϩ diffusion distances are correspondingly shorter; hence, less time is needed to achieve full charge or discharge at the same current density. In addition, the larger surface areas of these electrode materials lower the current density, resulting in a decrease of concentration polarization. Although the utilization of submicrometer-grained materials has the significant advantage of increasing rate capacity, it also leads to several drawbacks for practical applications. First, reducing average grain size, while keeping the mass constant, increases the grain boundary resistances of the electrode ͑internal resistance͒. To maintain the internal resistance at the same level, conductive additives ͑such as carbon black͒ are used, which decrease the energy density of the electrode. In addition, it is possible for very small grains to penetrate the porous membrane separating the electrodes, thereby short-circuiting the system and resulting in severe safety problems. Therefore, it is necessary to assemble the ultrafine electro...

This paper presents general methods of preparing three-dimensionally ordered macroporous (3DOM) metals or alloys via templated precipitation and subsequent chemical conversion of metal salts (acetates, oxalates) within colloidal crystals of poly(methyl methacrylate) (PMMA) or polystyrene (PS) spheres. Three approaches are given to prepare 3DOM metallic Ni, Co, and Fe and the alloy Ni 1-x Co x : (1) calcination of the metal oxalate/template composite in a nitrogen atmosphere, (2) formation of a 3DOM metal oxide followed by reduction in hydrogen, and (3) direct reduction of the metal oxalate/template composite in hydrogen. The 3DOM products obtained by these routes differ in size of the grains that compose the wall skeletons, in surface areas, and in compositions. Method 1 leads to very small grains and high surface areas but incomplete removal of carbon with graphitic layers surrounding metal grains. Method 2, as a two-step process, leads to relatively large metal grains, smaller surface areas, and carbon-free products. Method 3 strikes a compromise in these properties, with intermediate surface areas and small (<2%) amounts of remaining carbon. This paper presents synthetic details, discusses effects of the template choice (PMMA vs PS), and compares structural features of the macroporous metals and alloys, using the results of XRD, TGA, SEM, TEM, nitrogen adsorption data, and chemical analysis.