Compact solid discharge products enable energy storage devices with high gravimetric and volumetric energy densities, but solid deposits on active surfaces can disturb charge transport and induce mechanical stress. In this Letter we develop a nanoscale continuum model for the growth of Li 2 O 2 crystals in lithium-oxygen batteries with organic electrolytes, based on a theory of electrochemical non-equilibrium thermodynamics originally applied to Li-ion batteries. As in the case of lithium insertion in phase-separating LiFePO 4 nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li 2 O 2 with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li 2 O 2 that limits cell performance. We predict that the transition between these surface growth modes occurs at current densities close to the exchange current density of the cathode reaction, consistent with experimental observations.

Perspective on recent improvements in experiment and theory towards realizing lithium metal electrodes with liquid electrolytes.

No abstract

In this Letter we propose to simulate acoustic black holes with ions in rings. If the ions are rotating with a stationary and inhomogeneous velocity profile, regions can appear where the ion velocity exceeds the group velocity of the phonons. In these regions phonons are trapped like light in black holes, even though we have a discrete field theory and a nonlinear dispersion relation. We study the appearance of Hawking radiation in this setup and propose a scheme to detect it.PACS numbers: 04.70. Dy, 04.62.+v, 37.10.Ty In 1974 Hawking showed that the theory of quantum fields in curved spacetime predicts that, surprisingly, black holes emit thermal radiation [1]. Unfortunately, the temperature of this radiation is too small to be detected for typical astrophysical black holes. Furthermore, the original theoretical derivation suffers from the problem that the wave equation is assumed to be valid on all scales, whereas the theory of quantum fields in curved space is assumed to break down at the Planck energy. Unruh showed that the Hawking effect is also manifested in analogous hydrodynamical systems which have a region of supersonic flow and hence a sonic horizon [2]. Such analogous systems offer great advantages, since the effect can potentially be accessible to experiments. Moreover, its robustness can be examined based on the well known microphysics of the hydrodynamical systems. This will contribute to deepen our understanding of the Hawking effect also in gravitational black holes.The hydrodynamic analogy of gravitational spacetimes has inspired many proposals for experimental tests of Hawking radiation in continuous fields in recent years [3], e.g., phonons in Bose-Einstein condensates [4-6], Fermi gases [7], superfluid Helium [8], slow light [9,10], and nonlinear electromagnetic waveguides [11]. So far, no proposal has been physically implemented.In the present work we show how to build an analog model of a black hole in an experimentally realizable system of ions. This is the first experimental proposal in which a discrete system is completely analyzed in the discrete limit (see also [11]). A sublinear dispersion relation at high wave numbers naturally results from the discreteness of the physical system. This affects the trajectories of blue-shifted waves close to the event horizon [12]. The dispersion relation is, additionally, nontrivial at low wave numbers because of the long range Coulomb force. We study how much this affects the appearing Hawking radiation. Explicit numerical calculations show that the Hawking effect is robust against such short scale modifications, e.g., for a continuous field with a sublinear dispersion relation [13] and a discretized field on a falling lattice [14]. Our proposal uses a parameter regime which is accessible in experiments at temperatures currently achieved. Thus, it could lead to the first experimental observation of Hawking radiation.The main idea of our proposal can be summarized as follows. We are constructing a discrete analog of a hydrodynamical system with s...

Continued growth of the solid-electrolyte interphase (SEI) is the major reason for capacity fade in modern lithium-ion batteries. This growth is made possible by a yet unidentified transport mechanism that limits the passivating ability of the SEI towards electrolyte reduction. We, for the first time, differentiate the proposed mechanisms by analyzing their dependence on the electrode potential. Our calculations are compared to recent experimental capacity-fade data. We show that the potential dependence of SEI growth facilitated by solvent diffusion, electron conduction, or electron tunneling qualitatively disagrees with the experimental observations. Only diffusion of Li interstitials results in a potential dependence matching the experiments. Therefore, we identify the diffusion of neutral radicals, such as Li interstitials, as the cause of long-term SEI growth.

Metal-air batteries are among the most promising next-generation energy storage devices. Relying on abundant materials and offering high energy densities, potential applications lie in the fields of electro-mobility, portable electronics, and stationary grid applications. Now, research on secondary zinc-air batteries is revived, which are commercialized as primary hearing aid batteries. One of the main obstacles for making zinc-air batteries rechargeable is their poor lifetime due to the degradation of alkaline electrolyte in contact with atmospheric carbon dioxide. In this article, we present a continuum theory of a commercial Varta PowerOne button cell. Our model contains dissolution of zinc and nucleation and growth of zinc oxide in the anode, thermodynamically consistent electrolyte transport in porous media, and multi-phase coexistance in the gas diffusion electrode. We perform electrochemical measurements and validate our model. Excellent agreement between theory and experiment is found and novel insights into the role of zinc oxide nucleation and growth and carbon dioxide dissolution for discharge and lifetime is presented. We demonstrate the implications of our work for the development of rechargeable zinc-air batteries. Highlights• Modeling and simulating of VARTA button cell • Validation of galvanostatic discharge and lifetime analysis• Nucleation and growth of ZnO and its impact on discharge curve• Degradation due to carbonation of alkaline electrolyte (Birger Horstmann) promising candidates to fulfill this demand, because of their high specific energy density and the use of cheap and abundant materials. These batteries are open at the cathode and use atmospheric oxygen.Several metals, e.g., lithium, sodium, and zinc, are potential active anode materials in metal-air cells [1]. The high theoretical energy density of lithium-air batteries has stimulated a lot of research [2]. For aprotic electrolytes, the challenge is to influence growth mechanisms in order to maximize capacity, while maintaining sufficient reversibility [3,4,5,6,7,8,9]. Aqueous lithium-air batteries require a stable lithium conducting anode protection [10,11,12,13]. Non-aqueous sodium-air cells rely

We study abrupt changes in the dynamics and/or steady state of fermionic dissipative systems produced by small changes of the system parameters. Specifically, we consider fermionic systems whose dynamics is described by master equations that are quadratic (and, under certain conditions, quartic) in creation and annihilation operators. We analyze phase transitions in the steady state as well as "dynamical transitions". The latter are characterized by abrupt changes in the rate at which the system asymptotically approaches the steady state. We illustrate our general findings with relevant examples of fermionic (and, equivalently, spin) systems, and show that they can be realized in ion chains.

In this article, we present a novel theory for the long term evolution of the solid electrolyte interphase (SEI) in lithium-ion batteries and propose novel validation measurements. Both SEI thickness and morphology are predicted by our model as we take into account two transport mechanisms, i.e., solvent diffusion in the SEI pores and charge transport in the solid SEI phase. We show that a porous SEI is created due to the interplay of these transport mechanisms. Different dual layer SEIs emerge from different electrolyte decomposition reactions. We reveal the behavior of such dual layer structures and discuss its dependence on system parameters. Model analysis enables us to interpret SEI thickness fluctuations and link them to the rate-limiting transport mechanism. Our results are general and independent of specific modeling choices, e.g., for charge transport and reduction reactions. In the near future, automotive and mobile applications demand power storage with large energy and power density. Currently, lithiumion batteries (LIBs) are the technology of choice for devices with these demands. They operate at high cell potentials and offer high specific capacities while providing long lifetimes. The latter is a consequence of the stable chemistry of modern LIB systems. A significant part of this stability can be attributed to the passivation ability of the solid electrolyte interphase (SEI). This thin layer forms between the negative electrode and the electrolyte. Hence contact between these phases is prevented and the continuous reduction of electrolyte molecules is suppressed. These reduction processes occur because the operating potential of the negative electrode lies well below the stability window of the electrolyte.1 They are suppressed because reduction products quickly form the SEI during the first charge of a pristine electrode. The self passivating ability is one of the most important distinctions between a well and a badly performing lithium-ion battery chemistry. It is of such importance because the reduction reactions consume lithium-ions, directly reducing battery capacity. However, a real SEI is not perfectly passivating and electrolyte reduction is never completely suppressed. Consequently, the lifetime of a battery is directly related to the long-term passivating ability of the SEI.Numerous studies on SEI have been conducted since Peled reported on this correlation in 1979.2 Most of these studies are experimental, investigating cycling stability as well as SEI impedance and composition. Theoretical studies are scarce in comparison, despite established methods such as DFT and DFT/MD derivatives. This can be partially explained with the chemical diversity of SEI, which has been investigated by Aurbach et al. for decades. Results are summarized in Refs. 3, 4 and include the study of SEI formation on graphite electrodes in organic solvent mixtures. The most significant finding of this time is that ethylene carbonate (EC) forms a stable SEI on graphite as opposed to propylene carbonate (PC). Another...