Ion Transport In Solid Electrolytes Research Articles

Recent Trends in Application of Memristor in Neuromorphic Computing: A Review

Abstract: Recently memristors have emerged as a form of nonvolatile memory that is based on the principle of ion transport in solid electrolytes under the impact of an external electric field. It is perceived as one of the key elements to building next-generation computing systems owing to its peculiar resistive switching characteristics. The switching mechanism in a memristor is mainly governed by filamentary conduction. Further, it can be employed as a memory as well as a logic element, which makes it an ideal candidate for building innovative computer architecture. Moreover, it is capable of mimicking the characteristics of biological synapses, which makes it an ideal candidate for developing a Neuromorphic system. In this review to begin with the switching mechanism of the memristor, primarily focusing on filamentary conduction, is discussed. Few SPICE models of memristor are reviewed, and their critical comparison is performed, which are widely used to build computing systems. An in-depth study on the various crossbar memory architecture augmented with memristors is reviewed. Finally, the application of memristors in neuromorphic computing and hardware implementation of Artificial Neural Networks (ANN) employing memristors is discussed.

Molecular-scale interaction between sub-1 nm cluster chains and polymer for high-performance solid electrolyte

Organic-inorganic interface in composite solid electrolyte could lead to increased ion transport for solid-state lithium batteries; however, most inorganic fillers have much larger size than polymer chains, which results in severe aggregation of inorganic fillers and poor ionic conductivity. Herein, functional sub-1 nm inorganic cluster chains were integrated with polymer chains to fabricate composite solid electrolyte with enhanced ionic conductivity. Different from all other inorganic fillers, the sub-1 nm inorganic cluster chains with diameter <1 nm have similar size and geometry compared with polymer chains, exhibiting polymer-like solution properties. A transparent sub-1 nm inorganic filler/polymer mixed solution was generated to realize monodispersion of cluster chains as functional fillers in polymer matrix. Meanwhile, abundant oxygen vacancies on cluster chains interact with polymer chains and lithium salts at molecular-scale, which decreases the complexation of polymer segments with Li+ and promote the dissociation of lithium salts, thereby improving Li+ transport. As a result, the composite solid electrolyte exhibits high ionic conductivity (0.4 mS cm−1) and large mobile Li+ distribution (50.8 %). This work pushes the size of nanofillers down to <1 nm, which is a unique approach to the molecular-scale interaction between nanofillers and polymers to boost ion transport in solid electrolytes.

Solid electrolytes redefine ion conduction.

A mechanism of ion transport in solid electrolytes can guide the design of lithium batteries.

Tradeoff between the Ion Exchange-Induced Residual Stress and Ion Transport in Solid Electrolytes

Rapid filament growth of lithium is limiting the commercialization of solid-state lithium metal anode batteries. Recent work demonstrated that lithium filaments grow into pre-existing or nascent cracks in the solid electrolyte, suggesting that increasing the fracture toughness of the solid electrolytes will inhibit filament penetration. It has been suggested that introducing residual compressive stresses at the surface of the solid electrolyte can provide this additional fracture toughness. One of the ways to induce these residual compressive stresses is by exchanging lithium ions (Li+) with larger isovalent ions such as potassium (K+). On the other hand, incorporation of too much potassium can alter the lithium-ion diffusion pathway and lower the diffusivity, thus limiting the performance of the solid-state electrolyte. Using multiscale modeling methods, we optimize this tradeoff and predict that exchanging 3.4% potassium ions up to a depth twice the grain sizes in Li7La3Zr2O12 solid electrolyte can induce a maximum residual compressive stress of around 1.1 GPa, corresponding to an increase in fracture strength by ∼8 times, while lowering the diffusivity in the ion-exchanged region by a factor of 5 at room temperature. The reduction of lithium diffusivity is due to K+-induced stress and (mainly) blockage of lithium ion pathways in the shallow ion-exchanged layer.

Synergy of non-lithium cation doping and the lithium concentration affecting lithium ion transport in solid electrolytes

Large-radius non-lithium cation doping can increase lithium-ion conductivity at low lithium-ion concentrations while the doping of non-lithium cations with a small radius can improve the lithium-ion conductivity at high lithium-ion concentrations.

(Invited) Entropy-Enhanced Ion Transport in Solid Electrolytes

Long-range ion transport is composed of microscopic steps of ion migration, which is governed by local structures and interactions of the charge carriers with their surroundings. Therefore, understanding the local environments of conducting ions and their impact on ion dynamics and transport pathways are critical to design of high-performance solid electrolytes. We have synthesized and studied a variety of Li superionic conductors. Systematic solid-state nuclear magnetic resonance (NMR) investigations, complemented by pair distribution analysis (PDF) and DFT/MD simulations, have revealed that entropies in structures, compositions, and Li-coordination play a key role in determining ion hoping frequencies, jumping distance, transport pathways, and activation barriers. Via maximizing these entropies, “liquid-like” Li-sublattice is produced with a flattened energy landscape yielding extremely low activation barrier for ion transport. A few such examples will be discussed, including glass, ceramic, and glass-ceramic composites.

Coupled Cation-Anion Dynamics Enhances Cation Mobility in Room-Temperature Superionic Solid-State Electrolytes.

Single-ion conducting solid electrolytes are gaining tremendous attention as essential materials for solid-state batteries, but a comprehensive understanding of the factors that dictate high ion mobility remains elusive. Here, for the first time, we use a combination of the Maximum Entropy Method analysis of room-temperature neutron powder diffraction data, ab initio molecular dynamics, and joint-time correlation analysis to demonstrate that the dynamic response of the anion framework plays a significant role in the new class of fast ion conductors, Na11Sn2PnX12 (Pn = P, Sb; X = S, Se). Facile [PX4]3- anion rotation exists in superionic Na11Sn2PS12 and Na11Sn2PSe12, but greatly hindered [SbS4]3- rotational dynamics are observed in their less conductive analogue, Na11Sn2SbS12. Along with introducing dynamic frustration in the energy landscape, the fluctuation caused by [PX4]3- anion rotation is firmly proved to couple to and facilitate long-range cation mobility, by transiently widening the bottlenecks for Na+-ion diffusion. The combined analysis described here resolves the role of the long-debated paddle-wheel mechanism, and is the first direct evidence that anion rotation significantly enhances cation migration in rotor phases. The joint-time correlation analysis developed in our work can be broadly applied to analyze coupled cation-anion interplay where traditional transition state theory does not apply. These findings deliver important insights into the fundamentals of ion transport in solid electrolytes. Invoking anion rotational dynamics provides a vital strategy to enhance cation conductivity and serves as an additional and universal design principle for fast ion conductors.

A finite strain electro-chemo-mechanical theory for ion transport with application to binary solid electrolytes

An electro-chemo-mechanical formulation of ion transport in solid electrolytes, in particular for binary systems, is presented. Starting with conservation laws and the second law of thermodynamic, we state a consistent Helmholtz-energy-based framework taking electrostatics, component transport and nonlinear elastic mechanical interaction into account. With the help of finite strain continuum mechanics, we include the effect of geometry changes on ion transport. Changes of local concentration cause swelling and shrinkage and hence stress assisted diffusion. Further coupling originates via an osmotic pressure. Since binary systems are of special interest in battery applications, we formulate both, a fully resolved and an electroneutral model for ion transport. The latter turns out to be an extended version of Newman’s concentrated solution theory taking mechanical effects into account. We demonstrate the importance of these mechanical effects by means of double layers adjacent to blocking electrodes and concentration profiles during galvanostatic charging. Further, we investigate the effect of external deformation as, e.g. found in dendrite growth.

Modeling the Effect of Mechanics on Ion Transport and Reaction Kinetics in Solid Electrolytes

Solid state batteries are gaining increasing attention due to their potential for high energy densities and their enhanced safety properties when using a solid electrolyte separator with a metal anode such as Lithium or Sodium. The solid electrolyte can be designed as a single ion conductor or as a solid solvent with both mobile anions and cations. Especially for the description of the latter case, the influence of mechanics on ion transport and reaction kinetics cannot be neglected or treated in a simplified manner as is usually done for liquid electrolytes, see e.g. [1]. In this contribution we present a coupled electro-chemo-mechanical modeling framework for ion transport in solid electrolytes and investigate the influence of mechanics on both ion transport and reaction kinetics. Drawing on ideas from Bucci et al. [2], we formulate a fully coupled large strain theory for ionic transport in terms of electric field, mechanical deformation and anion and cation concentrations. We derive suitable constitutive relations based on the Helmholtz energy and thermodynamic restrictions for the species fluxes of the different ionic constituents as done in the context of liquid electrolytes e.g. by Dreyer et al. [3]. We propose a constitutive formulation that allows the calculation of the electrochemical transport in the deformed state and consistently predicts the coupling between species transport and gradients of stress and material properties based on the choice of the Helmholtz energy, similar to e.g. lithium diffusion in active particles [4] or the swelling of polymeric gels [5]. Using the framework of the newly derived transport theory, we investigate the effect of mechanics on the interfacial kinetics at the metal anode/solid electrolyte interface. Based on energetic considerations as presented in [6] or [7], we propose a modified Butler-Volmer relation that not only establishes a relation between the exchange current density and potential/concentration differences across the interface but also takes into account the mechanical state of both solid electrolyte and metal anode. To illustrate the features of the model and to highlight cases where the electro-chemo-mechanical coupling plays an important role for ion transport and kinetics, we show numerical examples for a Lithium symmetric solid state cell with binary solid electrolyte. [1] NEWMAN, J. S.; THOMAS-ALYEA, K. E. [2004]: Electrochemical systems. J.Wiley, Hoboken, N.J., 3rd ed Edition. [2] BUCCI, G.; CHIANG, Y.-M.; CARTER, W. C. [2016]: Formulation of the coupled electrochemical mechanical boundary value problem, with applications to transport of multiple charged species. Acta Materialia, 104:33–51. [3] DREYER, W.; GUHLKE, C.; MÜLLER, R. [2013]: Overcoming the shortcomings of the Nernst–Planck model. Physical Chemistry Chemical Physics, 15(19):7075. [4] BOHN, E.; ECKL, T.; KAMLAH, M.; MCMEEKING, R. [2013]: A model for lithium diffusion and stress generation in an intercalation storage particle with phase change. Journal of the Electrochemical Society, 160(10):A1638–A1652. [5] HONG, W.; ZHAO, X.; ZHOU, J.; SUO, Z. [2008]: A theory of coupled diffusion and large deformation in polymeric gels. Journal of the Mechanics and Physics of Solids, 56(5):1779–1793. [6] BOCKRIS, J. O.; REDDY, A. K. N.; GAMBOA-ALDECO, M. [2000]: Modern Electrochemistry 2A: Fundamentals of Electrodics. [7] MONROE, C.; NEWMAN, J. [2004]: The effect of interfacial deformation on electrodeposition kinetics. Journal of The Electrochemical Society, 151(6):A880.

Effects of Mesoscopic Microstructural Features on the Effective Ionic Diffusivity of Solid Electrolytes for Li Batteries

The kinetics of ion transport in solid electrolytes is known to be highly sensitive to the topological characteristics of ion conduction pathways. The conduction mechanisms usually involve concurrent ionic diffusion along a variety of mesoscopic features of internal microstructures such as bulk grain, structural domains, and associated boundaries as well as their network. Due to the complexity of these structural features of the solid electrolytes during operation, it is significantly challenging to characterize the microstructure-ionic diffusion property relationship. For better mechanistic understanding of relevant conduction mechanisms, it is necessary to thoroughly explore the impacts of individual microstructural factors on the overall kinetic properties and performances. In this presentation, we will present our development of an efficient mesoscopic computational method for extracting the effective diffusivity of the solid electrolyte containing arbitrarily distributed microstructural inhomogeneities such as differently oriented multiple grains, several structural variants of phase domains, and grain/domain boundaries. Using two- and three-dimensional digital microstructures generated by phase-field simulations as well as the fundamental diffusivity tensors of reference phases and boundaries derived from atomistic calculations as inputs, the method enable us to efficiently compute the effective diffusivity tensor of the entire system. We will then discuss the applications of this framework to investigating the relationship between relevant individual microstructural features and effective diffusivity of highly conductive solid electrolytes (e.g., LLTO and LLZO) focusing on the impacts of topological features of grains, internal mesoscopic structures of high- and low-temperature phase domains, and grain/phase boundary networks. *This work of was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Interface Structure in Solid-State Lithium Batteries

Although solid-state batteries had been suffering from low rate capability due to low ionic conductivities of solid electrolytes, conductivities comparable to non-aqueous liquid electrolytes used in current lithium-ion batteries have been achieved in some recently-developed solid electrolytes. Especially among sulfide systems, the highest conductivity has reached 10−2 S cm−1 [1], which is even higher that of liquid electrolytes when taking the transport number of unity into account. Consequently, ion transport in solid electrolytes can cease from rate-determining; however, it has been replaced by that across interfaces. Ionic conductors often exhibit anomalous ionic conduction at their surface or interface, which is categorized as “nanoionics” taking place in space-charge layers formed with thickness around 10 nm at the interface or surface. It appears in solid-state batteries with sulfide electrolytes as high interfacial resistances to high voltage cathodes, which result in the unimproved power densities of the solid-state batteries in spite of the high ionic conductivities of the employed solid electrolytes. Classical Nernst equation infers that the high potential of cathode makes the space-charge layers lithium-depleted and thus highly-resistive due to the depletion of charge carriers. The high interfacial resistance has been successfully reduced by an interfacial design based on the space-charge model, where an ion-conducting and electron-insulating oxide is interposed at the interface in order to shield the sulfide electrolyte from the high cathode potential and thus act as a buffer against the lithium depletion [2]. The changes in the electrode properties upon the interposition are well explainable by the space-charge layer model [3]. However, because the space-charge layer that lies between solids with only several nanometers in thickness is difficult to access, it has not revealed its presence even before advanced analyses; whereas it has emerged in computations. Electronic structure of LiFePO4 and Li3PS4, which are cathode and solid electrolyte materials, respectively, obtained by the first principles calculation suggests preferential formation of lithium vacancies on the electrolyte side of the LiFePO4/Li3PS4 interface. In addition, when FePO4/Li3PS4 interface is relaxed in order to simulate the interface structure during the battery operation, lithium ions move from the electrolyte to electrode side to bring about lithium depletion on the electrolyte side.

A “Hidden” Mesoscopic Feature Revealed By Electron Microscopy Could Facilitate Ion Transport In Solid Electrolytes

A “Hidden” Mesoscopic Feature Revealed By Electron Microscopy Could Facilitate Ion Transport In Solid Electrolytes

Experimental and Computational Approaches to Interfacial Resistance in Solid-State Batteries

Solid-state batteries with inorganic solid electrolytes are expected to be an efficient solution to the issues of current lithium-ion batteries that are originated from their organic-solvent electrolytes. Although solid-state batteries had been suffering from low rate capability due to low ionic conductivities of solid electrolytes, some sulfide solid electrolytes exhibiting high ionic conductivity of the order of 10−2 S cm−1 have been recently developed. Since the conductivity is comparable to or even higher than that of liquid electrolytes, when taking the transport number of unity into account, ion transport in solid electrolytes has ceased from rate-determining; however, it has been replaced by that across interfaces. The sulfide electrolytes show high interfacial resistance to the high-voltage cathodes. Our previous studies have demonstrated that oxide solid electrolytes interposed at the interface reduces the resistance, and they also suggest that the high resistance is attributable to a lithium-depleted layer formed at the interface. This study employs the first-principles calculation in order to gain insight into the interface. The interface structure between an oxide cathode/sulfide electrolyte simulated by the first-principles molecular dynamics has disclosed the presence of lithium-depleted layer at the interface, and the electronic structure calculated on the basis of density functional theory strongly suggests that the charge current preferentially removes lithium ions from the sulfide electrolyte side of the interface to deplete the lithium ion there. These calculation results are consistent with the transport mechanism proposed from the experimental results.

Modelling of Ion Transport in Solids with a General Bond Valence Based Force-Field

Empirical bond length - bond valence relations provide insight into the link between structure of and ion transport in solid electrolytes. Building on our earlier systematic adjustment of bond valence (BV) parameters to the bond softness, here we discuss how the squared BV mismatch can be linked to the absolute energy scale and used as a general Morse-type interaction potential for analyzing low-energy pathways in ion conducting solid or mixed conductors either by an energy landscape approach or by molecular dynamics (MD) simulations. For a wide range of Lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. Our novel BV-based force-field has also been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB) applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV-based force-field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials (LiFePO 4 , LiVPO 4 F, LiFeSO 4 F, etc.). Received: 11 October 2010; Revised: 26 October 2010; Accepted: 28 October 2010

High power lithium ion battery materials by computational design

AbstractEmpirical bond length–bond valence (BV) relations provide insight into the link between structure of and ion transport in solid electrolytes and mixed conductors. Building on our earlier systematic adjustment of BV parameters to the bond softness, here we discuss how the squared BV mismatch is linked to the absolute energy scale and used as a general Morse‐type interaction potential for analyzing low‐energy ion migration paths in ion conducting solids or mixed conductors by either an energy landscape approach or molecular dynamics (MD) simulations. For a wide range of lithium oxides we could thus model ion transport revealing significant differences to an earlier geometric approach. This novel BV‐based force‐field has then been applied to investigate a range of mixed conductors, focusing on cathode materials for lithium ion battery (LIB) applications to promote a systematic design of LIB cathodes that combine high energy density with high power density. To demonstrate the versatility of the new BV‐based force field it is applied in exploring various strategies to enhance the power performance of safe low cost LIB materials including LiFePO4, LiVPO4F, LiFeSO4F, etc.

Application of nonlinear conductivity spectroscopy to ion transport in solid electrolytes

The field-dependent ion transport in thin samples of different glasses is characterized by means of nonlinear conductivity spectroscopy. Ac electric fields with strengths up to 77 kV/cm are applied to the samples, and the Fourier components of the current spectra are analyzed. In the dc conductivity regime and in the transition region to the dispersive conductivity, higher harmonics in the current spectra are detected, which provide information about higher-order conductivity coefficients. Our method ensures that these higher-order conductivity coefficients are exclusively governed by field-dependent ion transport and are not influenced by Joule heating effects. We use the low-field dc conductivity σ 1,dc and the higher-order dc conductivity coefficient σ 3,dc to calculate apparent jump distances for the mobile ions, a app. Over a temperature range from 283 K to 353 K, we obtain values for a app between 39 Å and 55 Å. For all glasses, we find a weak decrease of a app with increasing temperature. Remarkably, the apparent jump distances calculated from our data are considerably larger than typical values published in the literature for various ion conducting glasses. These values were obtained by applying dc electric fields. Our results provide clear evidence that the equation used in the literature to calculate the apparent jump distances does not provide an adequate physical description of field-dependent ion transport.

A Novel Electrochemical Method for Measuring Salt Diffusion Coefficients and Ion Transference Numbers

We have found it possible to determine salt diffusion coefficients and ion transference numbers by obtaining, respectively, the steady‐state ion‐transport‐limited current at a microdisk electrode in spherical diffusion geometry and the transient ion‐transport‐limited current at a macrodisk electrode in planar diffusion geometry in ionic solutions containing no supporting electrolyte. The method is demonstrated in aqueous solutions of and in propylene carbonate solutions of . The ion transport parameters obtained agree well with those reported previously. It would appear that the method also could be used in the study of ion transport in solid electrolytes.