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The previous decade has witnessed the emergence of 3D architectures in battery electrodes, in fully functioning batteries and in the computational modeling supporting these activities. In this paper, the most important strides made in achieving these accomplishments are identified: developing design concepts for wiring 3D electrodes, understanding the inherently non‐uniform current and voltage distributions in non‐planar geometries, and demonstrating the fabrication of spatially complex 3D structures in miniaturized systems. 3D batteries represent one of the most promising approaches for creating miniaturized power sources for Internet of Things‐based applications and future efforts towards integrating modeling, 3D electrode design, and enhanced fabrication are expected to lead to rapid advancement in the development of this technology. [ABSTRACT FROM AUTHOR]

Rechargeable zinc–air batteries may become safe, sustainable, low‐cost, and energy‐dense alternatives to Li‐ion batteries for many applications, but problems associated with today's air‐breathing electrodes limit zinc–air performance. To overcome this challenge, researchers have investigated hundreds of air‐breathing electrode variations over the last decade. Unfortunately, the efficacy of these variations remains ambiguous due to nonstandardized cycling protocols that map to areal‐energy values spanning five orders of magnitude. To compete with Li‐ion batteries, researchers should cycle zinc–air cells at 35 mWh cmgeo−2, but only 8, of the 100 publications reviewed here, breach this threshold. Once the community cycles zinc–air cells at the proposed areal energy and better understands failure mechanisms, lab‐scale results will translate to practical advancements. [ABSTRACT FROM AUTHOR]

By applying differential pair distribution function (DPDF) analyses to the energy-storage relevant MnOx/carbon system―but in a 3D architectural rather than powder-composite configuration―we can remove contributions of the carbon nanofoam paper scaffold and quantify the multiphasic oxide speciation as the nanoscale, disordered MnOx grafted to the carbon walls (MnOx@CNF) structurally rearranges in situ from disordered birnessite AMnOx (A = Na+; Li+) to tetragonal Mn3O4 to spinel LiMn2O4. The first reaction step involves topotactic exchange of interlayer Na+ by Li+ in solution followed by thermal treatments to crystal engineer the ∼10 nm-thick 2D layered oxide throughout the macroscale nanofoam paper into a cubic phase. The oxide remains affixed to the walls of the nanofoam throughout the phase transformations. The DPDF fits are improved by retention of one plane of birnessite-like oxide after conversion to spinel. We support the DPDF-derived assignments by X-ray photoelectron spectroscopy and Raman spectroscopy, the latter of which tracks how crystal engineering the oxide affects the disorder of the carbon substrate. We further benchmark MnOx@CNF with nonaqueous electrochemical measurements versus lithium as the oxide converts from X-ray-amorphous birnessite to interlayer-registered LiMnOx to spinel. The lamellar AMnOx displays pseudocapacitive electrochemical behavior, with a doubling of specific capacitance for the interlayer-registered LiMnOx, while the spinel LiMn2O4@CNF displays a faradaic electrochemical response characteristic of Li-ion insertion. Our results highlight the need for holistic understanding when crystal engineering an (atomistic) charge-storing phase within the (architectural) structure of practical electrodes. [ABSTRACT FROM AUTHOR]

The performance of electrochemical energy storage devices (e.g., batteries and electrochemical capacitors) is largely determined by the physicochemical properties of the active electrode materials, such as the thermodynamic potential associated with the charge-storage reaction, ion-storage capacity, and long-term electrochemical stability. In the case of mixed ion/electron-conducting metal oxides that undergo cation-insertion reactions, the presence of cation vacancies in the lattice structure can enhance one or more of these technical parameters without resorting to a drastic change in material composition. Examples of this enhancement include the charge-storage properties of certain cation-deficient oxides such as γ-MnO2and γ-Fe2O3relative to their defect-free analogues. The optimal cation-vacancy fraction is both material- and application-dependent because cation vacancies enhance some materials properties at the expense of others, potentially affecting electronic conductivity or thermal stability. Although the advantages of structural cation vacancies have been known since at least the mid-1980s, only a handful of research groups have purposefully integrated cation vacancies into active electrode materials to enhance device performance. [ABSTRACT FROM AUTHOR]

The article reports that the Lithium (Li) ion batteries use insertion processes for both the positive and negative electrodes, leading to the term "rocking chair" battery. The resulting transport of Li ions between the electrodes, usually arranged in a parallel-plate configuration, is 1-D in nature. To minimize power losses resulting from slow transport of ions, the thickness of the insertion electrodes, as well as the separation distance between them, is kept as small as possible. This approach may appear counterintuitive in the effort to produce a useful battery, because reducing the thickness of the electrode results in lower energy capacity and shorter operating time. Thus, battery design always trades off between available energy and the ability to release this energy without internal power losses.

Direct quantitative electroanalysis of submilligram quantities of nanoscale, high-surface-area electroactive powders is achieved by hand-pressing the solids onto the surface of a carbon–wax composite electrode. Since this ‘sticky carbon’ method does not require solvents or polymer binders to create electrode structures, such as cast films, one may now examine the innate electrochemical character of nanoscale materials. Electrode preparation with sticky carbon is rapid and simple and offers a convenient means to screen high-surface-area electrode materials whose inherently high RC time constants can compromise the resolution of the faradaic information. The effects on the electrochemical character of electrocatalysts, active materials in batteries, electrochromic materials, etc., of the common constituents (e.g. solvents, polymer binders, ionomers) and processes/forces (temperatures, pressures) necessary to create practical electrode structures may now be methodically explored. [Copyright &y& Elsevier]

Abstract: We have redesigned the air cathode for metal–air batteries by adapting fiber-paper-supported carbon nanofoams as the base electrode architecture. Electrocatalytic functionality for the oxygen reduction reaction (ORR) is added into the conductive, ultraporous nanofoam paper by electroless deposition at the carbon walls of conformal nanoscopic coatings of birnessite-like manganese oxide (10–20-nm thick MnO x ) via redox reaction with aqueous permanganate (MnO4 −). We report the ORR activity measured using an air-breathing electroanalytical cell for a series of native and MnO x -functionalized carbon nanofoams in which the size of the pore network is varied from tens to hundreds of nanometers, the thickness of the air cathode is varied, and the degree of hydrophilicity/hydrophobicity of the electrode structure is altered. Technologically relevant ORR activity is obtained at 0.9V vs. Zn for MnOx-functionalized carbon nanofoams that are ≥180-μm thick, have pores on the order of 100–200nm, and are modified with hydrophobic poly(vinylidene difluoride). [Copyright &y& Elsevier]