Associating and Tuning Sodium and Oxygen Mixed‐Ion Conduction in Niobium‐Based Perovskites

Pure ionic conductors as solid‐state electrolytes are of high interest in electrochemical energy storage and conversion devices. They systematically involve only one ion as the charge carrier. The association of two mobile ionic species, one positively and the other negatively charged, in a specific network should strongly influence the total ion conduction. Nb⁵⁺‐ (4d⁰) and Ti⁴⁺‐based (3d⁰) derived‐perovskite frameworks containing Na⁺ and O^2? as mobile species are investigated as mixed ion conductors by electrochemical impedance spectroscopy. The design of Na⁺ blocking layers via sandwiched pellet sintered by spark plasma sintering at high temperatures leads to quantified transport number of both ionic charge carriers t_Na+ and t_O2?. In the 350–700 °C temperature range, ionic conductivity can be tuned from major Na⁺ contribution (t_Na+ = 88%) for NaNbO₃ to pure O^2? transport in NaNb_0.9Ti_0.1O_2.95 phase. Such a Ti‐substitution is accompanied with a ≈100‐fold increase in the oxygen conductivity, approaching the best values for pure oxygen conductors in this temperature range. Besides the demonstration of tunable mixed ion conduction with quantifiable cationic and anionic contributions in a single solid‐state structure, a strategy is established from structural analysis to develop other architectures with improved mixed ionic conductivity.     

Enhanced Interfacial Stability of Hybrid‐Electrolyte Lithium‐Sulfur Batteries with a Layer of Multifunctional Polymer with Intrinsic Nanoporosity

The use of lithium‐ion conductive solid electrolytes offers a promising approach to address the polysulfide shuttle and the lithium‐dendrite problems in lithium‐sulfur (Li‐S) batteries. One critical issue with the development of solid‐electrolyte Li‐S batteries is the electrode–electrolyte interfaces. Herein, a strategic approach is presented by employing a thin layer of a polymer with intrinsic nanoporosity (PIN) on a Li⁺‐ion conductive solid electrolyte, which significantly enhances the ionic interfaces between the electrodes and the solid electrolyte. Among the various types of Li⁺‐ion solid electrolytes, NASICON‐type Li_1+xAl_xTi_2‐x(PO₄)₃ (LATP) offers advantages in terms of Li⁺‐ion conductivity, stability in ambient environment, and practical viability. However, LATP is susceptible to reaction with both the Li‐metal anode and polysulfides in Li‐S batteries due to the presence of easily reducible Ti⁴⁺ ions in it. The coating with a thin layer of PIN presented in this study overcomes the above issues. At the negative‐electrode side, the PIN layer prevents the direct contact of Li‐metal with the LATP solid electrolyte, circumventing the reduction of LATP by Li metal. At the positive electrode side, the PIN layer prevents the migration of polysulfides to the surface of LATP, preventing the reduction of LATP by polysulfides.     

Highly‐Cyclable Room‐Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

Despite significant interest toward solid‐state electrolytes owing to their superior safety in comparison to liquid‐based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high‐power density batteries. Here, a novel quasi‐solid Li⁺ ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm^?2 at room temperature. The cycling overpotential is dropped by 75% in comparison to BP‐free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li⁺ ions around (trifluoromethanesulfonyl)imide (TFSI^?) pairs and ethylene‐oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li⁺ transport through the polymer host. Density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li⁺ ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid‐state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long‐life cycling.     

Identifying Migration Channels and Bottlenecks in Monoclinic NASICON-Type Solid Electrolytes with Hierarchical Ion-Transport Algorithms

Monoclinic natrium superionic conductors (NASICON; Na₃Zr₂Si₂PO₁₂) are well-known Na-ion solid electrolytes which have been studied for 40 years. However, due to the low symmetry of the crystal structure, identifying the migration channels of monoclinic NASICON accurately still remains unsolved. Here, a cross-verified study of Na⁺ diffusion pathways in monoclinic NASICON by integrating geometric analysis of channels and bottlenecks, bond-valence energy landscapes analysis, and ab initio molecular dynamics simulations is presented. The diffusion limiting bottlenecks, the anisotropy of conductivity, and the time and temperature dependence of Na⁺ distribution over the channels are characterized and strategies for improving both bulk and total conductivity of monoclinic NASICON-type solid electrolytes are proposed. This set of hierarchical ion-transport algorithms not only shows the efficiency and practicality in revealing the ion transport behavior in monoclinic NASICON-type materials but also provides guidelines for optimizing their conductive properties that can be readily extended to other solid electrolytes.     

Thermo‐Switchable Charge Transport and Electrocatalysis Using Metal‐Ion‐Modified pNIPAM‐Functionalized Electrodes

Metal ions (Ag⁺, Cu²⁺, Hg²⁺) are incorporated into an electropolymerized, poly(N‐isopropyl acrylamide), pNIPAM, thermosensitive polymer associated with an electrode using the “breathing‐in” method. The ion‐functionalized pNIPAM matrices reveal ion‐dependent gel‐to‐solid phase‐transition temperatures (28 ± 1 °C, 25 ± 1 °C, 40 ± 1 °C for the Ag⁺, Cu²⁺, and Hg²⁺‐modified pNIPAM, respectively). Furthermore, the ion‐functionalized polymers exhibit quasi‐reversible redox properties, and the ions are reduced to the respective Ag⁰, Cu⁰, and Hg⁰ nanocluster‐modified polymers. The metal‐nanocluster‐functionalized pNIPAM matrices enhance the electron transfer (they exhibit lower electron‐transfer resistances) in the compacted states. The electron‐transfer resistances of the metal‐nanocluster‐modified pNIPAM can be cycled between low and high values by temperature‐induced switching of the polymer between its contracted solid and expanded gel states, respectively. The enhanced electron‐transfer properties of the metal nanocluster‐functionalized polymer are attributed to the contacting of the metal nanoclusters in the contracted state of the polymers. This temperature‐switchable electron transfer across a Ag⁰‐modified pNIPAM was implemented to design a thermo‐switchable electrocatalytic process (the temperature‐switchable electrocatalyzed reduction of H₂O₂ by Ag⁰‐pNIPAM).     

Highly Selective Ionic Transport through Subnanometer Pores in Polymer Films

Novel transport phenomena through nanopores are expected to emerge as their diameters approach subnanometer scales. However, it has been challenging to explore such a regime experimentally. Here, this study reports on polymer subnanometer pores exhibiting unique selective ionic transport. 12 μm long, parallel oriented polymer nanopores are fabricated in polyethylene terephthalate (PET) films by irradiation with GeV heavy ions and subsequent 3 h exposure to UV radiation. These nanopores show ionic transport selectivity spanning more than 6 orders of magnitude: the order of the transport rate is Li⁺>Na⁺>K⁺>Cs⁺>>Mg²⁺>Ca²⁺>Ba²⁺, and heavy metal ions such as Cd²⁺ and anions are blocked. The transport can be switched off with a sharp transition by decreasing the pH value of the electrolyte. Structural measurements and molecular dynamics simulations suggest that the ionic transport is attributed to negatively charged nanopores with pore radii of ≈0.3 nm, and the selectivity is associated with the dehydration effect.     

Transport and Charge Carrier Chemistry in Lithium Sulfide

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.     

Ionic Nanosystems: Large Space‐Charge Effects in a Nanostructured Proton Conductor (Adv. Funct. Mater. 23/2010)

Decreasing the dimensions of heterogeneous mixtures of ionic conductors towards the nanoscale results in ionic conduction enhancements, caused by the increased influence of the interfacial space‐charge regions. For a composite of TiO₂ anatase and solid acid CsHSO₄, the strong enhancement of the ionic conductivity at the nanoscale also can be assigned to this space‐charge effect. Surprisingly high hydrogen concentrations in the order of 10²¹ cm^?3 in TiO₂ are measured, which means that about 10% of the available sites for H⁺ ions are filled on average. Such high concentrations require a specific elaboration of the space‐charge model that is explicitly performed here, by taking account of the large occupation numbers on the exhaustible sites. It is shown that ionic defects with negative formation enthalpy reach extremely high concentrations near the interfaces and throughout the material. By performing first‐principles density functional theory calculations, it is found that proton insertion from CsHSO₄ into the TiO₂ particles is preferred compared to neutral hydrogen atom insertion and indeed that the formation enthalpy is negative. Moreover, the average proton fractions in TiO₂, estimated by the theoretical ionic density profiles, are in good agreement with the experimental observations.     

Large Space‐Charge Effects in a Nanostructured Proton Conductor

Decreasing the dimensions of heterogeneous mixtures of ionic conductors towards the nanoscale results in ionic conduction enhancements, caused by the increased influence of the interfacial space‐charge regions. For a composite of TiO₂ anatase and solid acid CsHSO₄, the strong enhancement of the ionic conductivity at the nanoscale also can be assigned to this space‐charge effect. Surprisingly high hydrogen concentrations in the order of 10²¹ cm^?3 in TiO₂ are measured, which means that about 10% of the available sites for H⁺ ions are filled on average. Such high concentrations require a specific elaboration of the space‐charge model that is explicitly performed here, by taking account of the large occupation numbers on the exhaustible sites. It is shown that ionic defects with negative formation enthalpy reach extremely high concentrations near the interfaces and throughout the material. By performing first‐principles density functional theory calculations, it is found that proton insertion from CsHSO₄ into the TiO₂ particles is preferred compared to neutral hydrogen atom insertion and indeed that the formation enthalpy is negative. Moreover, the average proton fractions in TiO₂, estimated by the theoretical ionic density profiles, are in good agreement with the experimental observations.     

Scalable Oxygen‐Ion Transport Kinetics in Metal‐Oxide Films: Impact of Thermally Induced Lattice Compaction in Acceptor Doped Ceria Films

In this paper, we focus on the effect of processing‐dependent lattice strain on oxygen ion conductivity in ceria based solid electrolyte thin films. This is of importance for technological applications, such as micro‐SOFCs, microbatteries, and resistive RAM memories. The oxygen ion conductivity can be significantly modified by control of lattice strain, to an extent comparable to the effect of doping bulk ceria with cations of different diameters. The interplay of dopant radii, lattice strain, microstrain, anion‐cation near order and oxygen ion transport is analyzed experimentally and interpreted with computational results. Key findings include that films annealed at 600 °C exhibit lattice parameters close to those of their bulk counterparts. With increasing anneal temperature, however, the films exhibited substantial compaction with lattice parameters decreasing by as much as nearly 2% (viz, Δd_{600–1100 °C}: –1.7% (Sc⁺³) > –1.5% (Gd⁺³) > –1.2% (La⁺³)) for the annealing temperature range of 600–1100 °C. Remarkably 2/3^rd of the lattice parameter change obtained in bulk ceria upon changing the acceptor diameter from the smaller Sc to larger La, can be reproduced by post annealing a film with fixed dopant diameter. While the impact of lattice compaction on defect association/ordering cannot be entirely excluded, DFT computation revealed that the main effect appears to result in an increase in migration energy and consequent drop in ionic conductivity. As a consequence, it is clear that annealing procedures should be held to a minimum to maintain the optimum level of oxygen ion conductivity for energy‐related applications. Results reveal also the importance to understand the role of electro‐chemo‐mechanical coupling that is active in thin film materials.     

A New Lithium‐Ion Conductor LiTaSiO5: Theoretical Prediction,Materials Synthesis,and Ionic Conductivity

Owing to the nonleakage and incombustibility, solid electrolytes are crucial for solving the safety issues of rechargeable lithium batteries. In this work, a new class of solid electrolyte, acceptor‐doped LiTaSiO₅, is designed and synthesized based on the concerted migration mechanism. When Zr⁴⁺ is doped to the Ta⁵⁺ sites in LiTaSiO₅, the high‐energy lattice sites are partly occupied by the introduced lithium ions, and the lithium ions at those sites interact with the lithium ions placed in the low‐energy sites, thereby favoring the concerted motion of lithium ions and lowering the energy barrier for ion transport. Therefore, the concerted migration of lithium ions occurs in Zr‐doped LiTaSiO₅, and a 3D lithium‐ion diffusion network is established with quasi‐1D chains connected through interchain channels. The lithium‐ion occupation, as revealed by ab initio calculations, is validated by neutron powder diffraction. Zr‐doped LiTaSiO₅ electrolytes are successfully synthesized; Li_1.1Ta_0.9Zr_0.1SiO₅ shows a conductivity of 2.97 × 10^?5 S cm^?1 at 25 °C, about two orders of magnitude higher than that of LiTaSiO₅, and it increases to 3.11 × 10^?4 S cm^?1 at 100 °C. This work demonstrates the power of theory in designing new materials.     

Direct Observation of Photoinduced Ion Migration in Lead Halide Perovskites

Unique optoelectronic, electronic, and sensing properties of hybrid organic–inorganic perovskites (HOIPs) are underpinned by the complex interactions between electronic and ionic states. Here, the photoinduced field ion migration in HOIPs is directly observed. Using newly developed local probe time-resolved techniques, more significant CH₃NH₃⁺ migration than I⁻/Br⁻ migration in HOIPs is unveiled. It is found that light illumination only induces CH₃NH₃⁺ migration but not I⁻/Br⁻ migration. By directly observing temporal changes in bias-induced and photoinduced ion migration in device conditions, it is revealed that light illumination suppresses the bias-induced ion redistribution in the lateral device. These findings, being a necessary compensation of previous understandings of ion migration in HOIPs based on simulations and static and/or indirect measurements, offer advanced insights into the distinct light effects on the migration of organic cation and halides in HOIPs, which are expected to be helpful for improving the performance and the long-term stability of HOIPs optoelectronics.     

Optical Sensor Based on Nanomaterial for the Selective Detection of Toxic Metal Ions

A heterogeneous “naked‐eye” colorimetric and spectrophotometric cation sensor, SNT‐ 1 , was prepared by immobilization of the azo‐coupled macrocyclic receptor 1 on a silica nanotube (SNT) via sol–gel reaction. The optical sensing ability of SNT‐ 1 was studied by addition of metal ions such as Ag⁺, Co²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Fe³⁺, Cu²⁺, and Hg²⁺ (all as nitrates) in water. Upon the addition of Hg²⁺ in suspension SNT‐ 1 resulted in a color change from yellow to violet. This is novel rare example for chromogenic sensing of a specific metal ion by inorganic nanotubes. On the other hand, no significant changes in color were observed in the parallel experiments with Co²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Fe³⁺, Cu²⁺, and Ag⁺. These findings confirm that SNT‐ 1 can be useful as chemosensors for selective detection of Hg²⁺ over a range of metal ions. More interestingly, after addition of NO₃^– and ClO₄^– SNT‐ 1 was observed to change color from yellow to violet and pink, respectively. However, no color changes were observed upon addition of Cl^–, Br^–, I^–, SCN^–, or SO₄^2–. Furthermore, the extraction ability of SNT‐ 1 was also estimated by measuring the amount of Hg²⁺ adsorbed by ion chromatography, showing that 95 % of the Hg²⁺ ion is extracted by SNT‐ 1 . This suggests that SNT‐ 1 is potentially useful as a stationary phase for the separation of Hg²⁺ in liquid chromatography. In order to extend the above performance to a portable chemosensor kit, SNT‐ 1 was coated as a thin film of 50 μm thickness onto a glass substrate. The supported SNT‐ 1 also changed from yellow to violet when dipped into Hg²⁺ solution. On the other hand, no significant change in color was observed in other metal‐ion solutions. The results imply that the supported SNT‐ 1 is applicable as a portable colorimetric sensor for detection of Hg²⁺ in the field.     

Nanoconfined LiBH4 as a Fast Lithium Ion Conductor

Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid‐state batteries. LiBH₄ is a promising solid electrolyte for Li‐ion batteries. It displays high lithium mobility, although only above 110 °C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH₄ in the pores of ordered mesoporous silica scaffolds leads to high Li⁺ conductivity (0.1 mS cm^?1) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO₂. Solid state ⁷Li NMR confirmed that the high conductivity can be attributed to a very high Li⁺ mobility in the solid phase at room temperature. Confinement of LiBH₄ in the pores leads also to a lower solid‐solid phase transition temperature than for bulk LiBH₄. However, the high ionic mobility is associated with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO₂ pore walls. These results point to a new strategy to design low‐temperature ion conducting solids for application in all solid‐state lithium ion batteries, which could enable safe use of Li‐metal anodes.     

Li6ALa2Ta2O12 (A = Sr, Ba): Novel Garnet‐Like Oxides for Fast Lithium Ion Conduction

Oxides with the nominal chemical formula Li₆ALa₂Ta₂O₁₂ (A = Sr, Ba) have been prepared via a solid‐state reaction in air using high purity La₂O₃, LiOH·H₂O, Sr(NO₃)₂, Ba(NO₃)₂, and Ta₂O₅ and are characterized by powder X‐ray diffraction (XRD) in order to identify the phase formation and AC impedance to determine the lithium ion conductivity. The powder XRD data of Li₆ALa₂Ta₂O₁₂ show that they are isostructural with the parent garnet‐like compound Li₅La₃Ta₂O₁₂. The cubic lattice parameter was found to increase with increasing ionic size of the alkaline earth ions (Li₆SrLa₂Ta₂O₁₂: 12.808(2) Å; Li₆BaLa₂Ta₂O₁₂: 12.946(3) Å). AC impedance results show that both the strontium and barium members exhibit mainly a bulk contribution with a rather small grain‐boundary contribution. The ionic conductivity increases with increasing ionic radius of the alkaline earth elements. The barium compound, Li₆BaLa₂Ta₂O₁₂, shows the highest ionic conductivity, 4.0×10^–5 S cm^–1 at 22 °C with an activation energy of 0.40 eV, which is comparable to other lithium ion conductors, especially with the presently employed solid electrolyte lithium phosphorus oxynitride (Lipon) for all‐solid‐state lithium ion batteries. DC electrical measurements using lithium‐ion‐blocking and reversible electrodes revealed that the electronic conductivity is very small, and a high electrochemical stability (> 6 V/Li) was exhibited at room temperature. Interestingly, Li₆ALa₂Ta₂O₁₂ was found to be chemically stable with molten metallic lithium.     

Stabilizing Polymer–Lithium Interface in a Rechargeable Solid Battery

Solid polymer electrolytes (SPEs) are promising candidates for developing high‐energy‐density Li metal batteries due to their flexible processability. However, the low mechanical strength as well as the inferior interfacial regulation of ions between SPEs and Li metal anode limit the suppress ion of Li dendrites and destabilize the Li anode. To meet these challenges, interfacial engineering aiming to homogenize the distribution of Li⁺/electron accompanied with enhanced mechanical strength by Mg₃N₂ layer decorating polyethylene oxide is demonstrated. The intermediary Mg₃N₂ in situ transforms to a mixed ion/electron conducting interlayer consisting of a fast ionic conductor Li₃N and a benign electronic conductor Mg metal, which can buffer the Li⁺ concentration gradient and level the nonuniform electric current distribution during cycling, as demonstrated by a COMSOL Multiphysics simulation. These characteristics endow the solid full cell with a dendrite‐free Li anode and enhanced cycling stability and kinetics. The innovative interface design will accelerate the commercial application of high‐energy‐density solid batteries.     

Magnesium Ion Doping and Micro-Structural Engineering Assist NH4V4O10 as a High-Performance Aqueous Zinc Ion Battery Cathode

Layered ammonium vanadate materials exhibit significant mass-specific capacity and ion transport rate due to their small molecular weight and large ionic radius. However, the strong electrostatic interactions of Zn²⁺ and V–O bonds and the fragile ionic bonding of N-H^…O bonds hinder their development. Therefore, this work reports Mg²⁺ doping NH₄V₄O₁₀ materials accompanied by flower-like morphology to lower the migration energy barrier and inhibit amine dissolution. Owing to the 3D-flower-like morphology and the combined impact of Mg²⁺ and structural water, the binding of Zn^2+…V-O is significantly enhanced and additional ion channels were constructed. Pre-intercalated Mg²⁺ enhances the structural integrity and prevents irreversible deammoniation from obtaining excellent cyclic stability. Density functional theory (DFT) calculations show that MNVO provides a smoother Zn²⁺ diffusion path with a lower migration barrier. Benefited from these advantages, the MNVO cathode exhibits a high specific capacity of 410 mAh g⁻¹ at 0.1 A g⁻¹, satisfactory cyclic stability (90.2 % capacity retention at 10 A g⁻¹ after 5000 cycles), and capable rate ability (118 mAh g⁻¹ at 25 A g⁻¹) within 0.4-1.5 V. Furthermore, the zinc ion storage mechanism in the MNVO cathode is investigated through multiple analyses.     

Interface Engineering for Solid‐State Dye‐Sensitized Nanocrystalline Solar Cells: The Use of Ion‐Solvating Hole‐Transporting Polymers

The control of interfacial charge transfer is central to the design of photovoltaic devices. This charge transfer is strongly dependent upon the local chemical environment at each interface. In this paper we report a methodology for the fabrication of a novel nanostructured multicomponent film, employing a dual‐function supramolecular organic semiconductor to allow molecular‐level control of the local chemical composition at a nanostructured inorganic/organic semiconductor heterojunction. The multicomponent film comprises a lithium ion doped dual‐functional hole‐transporting material (Li⁺–DFHTM), sandwiched between a dye‐sensitized nanocrystalline TiO₂ film and a mono‐functional organic hole‐transporting material (MFHTM). The DFHTM consists of a conjugated organic semiconductor with ion supporting side chains, designed to allow both electronic and ionic charge transport properties. The Li⁺–DFHTM layers provide a new and versatile way to control the interface electrostatics, and consequently the charge transfer, at a nanostructured dye‐sensitized inorganic/organic semiconductor heterojunction.     

A Mixed Lithium‐Ion Conductive Li2S/Li2Se Protection Layer for Stable Lithium Metal Anode

Constructing artificial solid‐electrolyte interphase (SEI) on the surface of Li metal is an effective approach to improve ionic conductivity of surface SEI and buffer Li dendrite growth of Li metal anode. However, constructing of homogenous ideal artificial SEI is still a great challenge. Here, a mixed lithium‐ion conductive Li₂S/Li₂Se (denoted as LSSe) protection layer, fabricated by a facile and inexpensive gas–solid reaction, is employed to construct stable surface SEI with high ionic conductivity. The Li₂S/Li₂Se‐protected Li metal (denoted as LSSe@Li) exhibits a stable dendrite‐free cycling behavior over 900 h with a high lithium stripping/plating capacity of 3 mAh cm^?2 at 1.5 mA cm^?2 in the symmetrical cell. Compared to bare Li anode, full batteries paired with LiFePO₄, sulfur/carbon, and LiNi_0.6Co_0.2Mn_0.2O₂ cathodes all present better battery cycling and rate performance when LSSe@Li anode is used. Moreover, Li₂Se exhibits a lower lithium‐ion migration energy barrier in comparison with Li₂S which is proved by density functional theory calculation.     

Ions Matter: Description of the Anomalous Electronic Behavior in Methylammonium Lead Halide Perovskite Devices

Carrier transport in methylammonium lead iodide (MAPbI₃)‐based hybrid organic–inorganic perovskites (HOIPs) is obscured by vacancy‐mediated ion migration. Thus, the nature of migrating species (cation/anion) and their effect on electronic transport in MAPbI₃ has remained controversial. Temperature‐dependent pulsed voltage–current measurements of MAPbI₃ thin films are performed under dark conditions, designed to decouple ion‐migration/accumulation and electronic transport. Measurement conditions (electric‐field history and scan rate) are shown to affect the electronic transport in MAPbI₃ thin films, through a mechanism involving ion migration and accumulation at the electrode interfaces. The presence of thermally activated processes with distinct activation energies (E_a) of 0.1 ± 0.001 and 0.41 ± 0.02 eV is established, and are assigned to electromigration of iodine vacancies and methylammonium vacancies, respectively. Analysis of activation energies obtained from electronic conduction versus capacitive discharge shows that the electromigration of these ionic species is responsible for the modification of interfacial electronic properties of MAPbI₃, and elaborates previously unaddressed issues of “fast” and “slow” ion migration. The results demonstrate that the intrinsic behavior of MAPbI₃ material is responsible for the hysteresis of the solar cells, but also have implications for other HOIP‐based devices, such as memristors, detectors, and energy storage devices.