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Developing high-performance, affordable, and durable batteries is one of the decisive technological tasks of our generation. Here, we review recent progress in understanding how to optimally arrange the various necessary phases to form the nanoscale structure of a battery electrode. The discussion begins with design principles for optimizing electrode kinetics based on the transport parameters and dimensionality of the phases involved. These principles are then used to review and classify various nanostructured architectures that have been synthesized. Connections are drawn to the necessary fabrication methods, and results from in operando experiments are highlighted that give insight into how electrodes evolve during battery cycling.

Lithium oxide (Li 2 O) is a highly relevant material for battery applications, and as a binary antifluorite compound of first-row elements, it is equally interesting for basic science. This work investigates the behavior of ionic and electronic charge carriers in Li 2 O. The predominantly ionic conductivity is shown to be well-explained by a defect chemical model based on Frenkel disorder, vacancy migration, and vacancy-dopant association. The enthalpies and entropies of these three processes are derived, and good agreement is seen to isostructural Li 2 S, SrF 2 , and BaF 2 . An upper bound is determined for the electronic conductivity of Li 2 O, which is very low. These results provide more reliable thermodynamic and kinetic parameters for future rigorous treatments of Li 2 O in batteries. For example, even under favorable doping conditions, the ionic conductivity of bulk crystalline Li 2 O (with no higher-dimensional defects or interfacial effects) is multiple orders of magnitude too slow to account for the resistance of typical solid-electrolyte interface (SEI) layers.

Lithium sulfide is a functional material of great importance for battery research, since it is the discharge product in Li–S cathodes and a frequent component of anode passivation layers. In both cases, transport of charge carriers in Li2S is critical for performance. The exploration of charge carrier chemistry in such a simple binary compound is also of fundamental scientific interest. For that purpose, impedance spectroscopy and electromotive force measurements are performed over a broad range of temperatures and doping conditions. The results indicate predominant ion conduction and can be quantitatively explained by a defect chemical model based on Frenkel disorder and vacancy‐dopant association. Mobilities and migration barriers for both vacancy and interstitial defects are deduced. The thermodynamic and kinetic parameters derived for Li+ transport in antifluorite Li2S show remarkable agreement with the analogous parameters for F− transport in fluorite compounds such as BaF2, thereby improving the structural understanding of charge carrier chemistry in such compounds. An application of these results to passivation layers in solid state batteries is also discussed.

Modern batteries are composite systems that contain a high density of interfaces. Device performance is often determined by effects that emerge at interfaces. A survey of these phemonena is presented here. At essentially all interfaces, space charge layers are present that can modify the charge transport, transfer, and storage properties. Practical interfaces show additional complex phenomena, including passivation layer formation, current constriction, partial blocking of mobile species, and a variety of other effects. Some characteristic interfacial issues associated with the four mass storage modes are described and a few specific points that arise in solid state batteries are discussed.

The perovskite SrCo 0.9 Nb 0.1 O 3−δ (SCN) has excellent electrochemical activity toward oxygen reduction, and it is also valuable as a possible model material for other state-of-the-art perovskite catalysts based on strontium and cobalt, such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF). Here we report thermogravimetric, conductivity, and diffraction measurements from SCN. We find that the thermodynamic stability limits of SCN are slightly more favorable than those reported for BSCF, although both materials exhibit a slow oxidative partial decomposition under likely operating conditions. In SCN, this decomposition is thermodynamically preferred when the average formal oxidation state of cobalt is greater than ∼3.0+, but due to sluggish kinetics, metastable SCN with higher cobalt valence can be observed. The oxygen stoichiometry 3−δ varies from 2.45 to 2.70 under the conditions studied, 500−1000 °C and 10 −4 −1 bar O 2 , which encompass both stable and metastable behavior. The electronic conductivity is p-type and thermally activated, with a value at 600 °C in air of 250 S cm −1 , comparable to that of La 0.8 Sr 0.2 MnO 3−δ . The polaron migration enthalpy decreases linearly from 0.30 to 0.05 eV as 3−δ increases from 2.52 to 2.64. Thermal and chemical expansivities are also reported.

Oxygen electro-reduction occurs preferentially at the exposed grain boundaries of (La,Sr)MnO3, as determined by automated impedance measurements of hundreds of microdot electrodes with varied geometrical and microstructural features.

The kinetics of storing mass in a battery electrode are typically limited by slow diffusion in storage particles. The diffusion timescale can be made faster by decreasing the size of the particles, but then it becomes more difficult to efficiently contact each particle with ionic and electronic current collectors, e.g., electrolyte and carbon. To achieve an optimal balance, the dimensions of the various phases in the electrode architecture should be tuned to the transport properties of the storage phase. Here we quantify this strategy by modeling the kinetics of galvanostatic charging for several particle geometries using the Nernst-Planck formalism and assuming mass storage via a solid solution. We show that when ions and electrons are inserted at separate contact surfaces, in general the storage kinetics depend on two length scales - the ionic and electronic wiring lengths - that characterize the transport distances within the storage material to the respective current collectors. Quantitative guidelines for the optimal wiring lengths are derived for two model geometries, and the dependence on transport parameters, particle shape, and contact geometry is discussed. These results can guide the optimization of various aspects of the architecture of a battery electrode, including the size and shape of individual particles and the configuration of the electrolyte and current collector networks.