Ion Transfer Kinetics Research Articles

Quantifying Interfacial Ion Transfer at Operating Potassium-Insertion Battery Electrodes within Highly Concentrated Aqueous Solutions.

Electrode/electrolyte interfacial ion transfer is a fundamental process occurring during insertion-type redox reactions at battery electrodes. The rate at which ions move into and out of the electrode, as well as at interphase structures, directly impacts the power performance of the battery. However, measuring and quantifying these ion transfer phenomena can be difficult, especially at high electrolyte concentrations as found in batteries. Herein, we report a scanning electrochemical microscope method using a common ferri/ferrocyanide (FeCN) redox mediator dissolved in an aqueous electrolyte to track changes in alkali ions at high electrolyte concentrations (up to 3 mol dm-3). Using voltammetry at a platinum microelectrode, we observed a reversible E1/2 shift of ∼60 mV per decade change in K+ concentrations. The response showed high stability in sequential measurements and similar behavior in other aqueous electrolytes. From there, we used the same FeCN mediator to position the microelectrode at the surface of a potassium-insertion electrode. We demonstrate tracking of local changes in the K+ concentration during insertion and deinsertion processes. Using a 2D axisymmetric, finite element model, we further estimate the effective insertion rates. These developments enable characterization of a key parameter for improving batteries, the interfacial ion transfer kinetics, and future work may show mediators appropriate for molar concentrations in nonaqueous electrolytes and beyond.

The chemo-mechanics of initiation of crack advance in Niobium Tungsten Oxide single crystals due to delithiation

Niobium tungsten oxide (NWO) micron-sized single crystals show promise as the active particles in the anodes of lithium ion batteries due to their fast charge/discharge and high storage capabilities. Within the “block” phases such as Nb16W5O55, Nb14W3O44 and the HNb2O5 polymorph, Li ion diffusion occurs in a unidirectional manner along a single axis of the crystal and lithiation/delithiation results in significant length changes in this direction. A chemo-mechanics analysis is developed for delithiation of an NWO “block” phase single crystal that contains a pre-existing flaw in the form of a through-thickness edge crack. Galvanostatic delithiation occurs by the flux of Li ions through the free ends of the crystal and also through the faces of the crack, with concomitant shrinkage of the surface layer over a depth equal to that of the crack. The induced tensile stress in the surface layer can be of sufficient magnitude to advance the crack in the NWO crystal, consistent with recent experimental observations for Nb14W3O44. A 2D full-field finite element version of the chemo-mechanics model is used to explore the sensitivity of cracking to crack length, delithiation rate of the anode, diffusivity of Li ions within the NWO single crystal storage particle and to the kinetics of Li ion transfer across the particle surface-electrolyte interface. Additionally, a simplified, lumped parameter model is developed by assuming that the Li ion occupancy is spatially uniform in a surface layer that extends to a depth of the pre-existing crack, and has a spatially uniform but different value than that of the underlying core of the particle. This simplified model can be expressed as a set of first order differential equations in time and gives the main features of delithiation and the associated transient stress state in the single crystal. Both the full model and the lumped parameter version predict that crack advance from a pre-existing defect is triggered by a high delithiation rate, consistent with the experimental literature.

Engineering Sb/Zn4(OH)6SO4·5H2O interfacial layer by in situ chemically reacting for stable Zn anode

Rechargeable aqueous zinc ion batteries with abundant resources and high safety have gained extensive attention in energy storage technology. However, the cycle stability is largely limited by notorious Zn dendrite growth and water-induced interfacial side reactions. Here, a uniform and robust protection layer consisting of metal antimony (Sb) nanoparticles and micrometer-size sheets Zn4(OH)6SO4·5H2O (ZHS) is purposely designed to stabilize Zn anode via an in situ chemical reaction strategy. The two-phase protection layers (Sb/ZHS) induce a reinforcement effect on the Zn anode (Zn@Sb/ZHS). Specifically, Sb nanoparticles play the part of nucleation sites to facilitate uniform Zn plating and homogenize the electric field around the Zn surface. ZHS micrometer-size sheets possess sufficient electrolyte wettability, fast ion transfer kinetics, and anti-corrosion, thus guaranteeing uniform ion flux and inhibiting H2O decomposition. As expected, the symmetric Zn@Sb/ZHS//Zn@Sb/ZHS cells achieve a minimal voltage hysteresis and a reversible cycle of over 2000 h at 1 mA cm−2. By pairing with the MnO2 cathode, the full cell exhibits a significantly improved stability (∼94.17 % initial capacity after 1500 cycles). This study provides a new strategy to design artificial protection layers.

Enhanced sodium-storage performances of crumpled MXene nanosheets via alkali treatment–induced active ammonium ions

Ti3C2Tx MXene demonstrates excellent potential as an anode material for sodium-ion capacitors. However, the narrow interlayer spacing and self-stacking phenomenon limit its applicability. In this study, we demonstrate an easy two-step method involving freezing and crumpling of MXene nanosheets to improve their Na-ion storage via the addition of ammonium ions (referred to as FCM nanosheets). Flat MXene particles aggregate and undergo folding in an alkaline solution. Ammonium ions can penetrate the gaps between MXene nanosheets, expanding interlayer spaces and inducing the formation of folds. Compared to MXene nanosheets, FCM nanosheets exhibit improved ion transfer kinetics and additional high capacity owing to the intercalated ammonium ions. The manufactured FCM anode exhibits remarkable electrochemical properties, including a high specific capacity of 313 mAhg−1 and stability over 15,000 cycles.

Rational Design of Multinary Metal Chalcogenide Bi0.4 Sb1.6 Te3 Nanocrystals for Efficient Potassium Storage.

Multinary metal chalcogenides hold considerable promise for high-energy potassium storage due to their numerous redox reactions. However, challenges arise from issues such as volume expansion and sluggish kinetics. Here, a design featuring a layered ternary Bi0.4 Sb1.6 Te3 anchored on graphene layers as a composite anode, where Bi atoms act as a lattice softening agent on Sb, is presented. Benefiting from the lattice arrangement in Bi0.4 Sb1.6 Te3 and structure, Bi0.4 Sb1.6 Te3 /graphene exhibits a mitigated expansion of 28% during the potassiation/depotassiation process and demonstrates facile K+ ion transfer kinetics, enabling long-term durability of 500 cycles at various high rates. Operando synchrotron diffraction patterns and spectroscopies including in situ Raman, ex situ adsorption, and X-ray photoelectron reveal multiple conversion and alloying/dealloying reactions for potassium storage at the atomic level. In addition, both theoretical calculations and electrochemical examinations elucidate the K+ migration pathways and indicate a reduction in energy barriers within Bi0.4 Sb1.6 Te3 /graphene, thereby suggesting enhanced diffusion kinetics for K+ . These findings provide insight in the design of durable high-energy multinary tellurides for potassium storage.

Ultrafast Ion Transfer of Metal-Organic Framework Interface for Highly Efficient Energy Storage.

Flexible supercapacitors are favorable for wearable electronics. However, their high-rate capability and mechanical properties are limited because of unsatisfactory ion transfer kinetics and interfacial modulus mismatch inside devices. Here, we develop a metal-organic framework interface with superior electrical and mechanical properties for supercapacitors. The interfacial mechanism facilitates ultrafast ion transfer with an energy barrier reduction of 43% compared with that of conventional transmembrane transport. It delivers high specific capacity at a wide rate range and exhibits ultrastability beyond 30000 charge-discharge cycles. Furthermore, meliorative modulus mismatch benefited from ultrathin interface design that improves mechanical properties of flexible supercapacitors. It delivers a stable energy supply under various mechanical conditions like bending and twisting status and displays ultrastable mechanical properties with performance retention of 95.5% after 10 000 bending cycles. The research paves the way for interfacial engineering for ultrastable electrochemical devices.

Synergistically regulating Zn-ion flux and accelerating ion transport kinetics via zincophilic covalent organic framework interlayer for stable Zn metal anode

Zn metal is considered as an ideal anode for aqueous zinc-ion batteries (AZIBs) owing to the inherent merits of low cost, high theoretical capacity, and remarkable safety. However, the formation of Zn dendrites and water-induced parasitic reactions hamper the commercialization of AZIBs. Herein, a synergetic strategy to accelerate ion transfer kinetics and regulate Zn-ion flux has been proposed to achieve dendrite-free Zn anodes via a series of zincophilic covalent organic framework (COF) films. The nanoporous and mechanically stable COF films synthesized by the liquid–liquid interfacial polymerization can be straightforward transferred on the Zn foil surface through a dip-coating technique. Benefiting from the affinity between Zn2+ and electron-rich ketone, the zincophilic COF interlayers promote the de-solvation of hydrated Zn2+, simultaneously offer ample Zn2+ transport channels to facilitate rapid diffusion and regulating a homogenous Zn2+ flux, thereby inhibiting the dendritic growth and leading to the uniform Zn deposition. Additionally, the COF films with strong adherence and large surface area effectively separate Zn anodes from bulk aqueous electrolytes, inhibiting the water-induced corrosion reactions. As a result, the symmetric cell with COF-modified Zn anode exhibited a stable cycling lifetime more than 900 h at 1 mA∙cm−2 and 1 mAh∙cm−2, accompanied by a low voltage polarization of merely 74.3 mV. As a simple approach to synergistically restrict Zn-ion flux and enhance ion transport kinetics using zincophilic COF films via interfacial synthesis, this work would provide new insights into developing highly stable Zn anodes.

Small but mighty: Empowering sodium/potassium‐ion battery performance with S‐doped SnO2 quantum dots embedded in N, S codoped carbon fiber network

AbstractSnO2 has been extensively investigated as an anode material for sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) due to its high Na/K storage capacity, high abundance, and low toxicity. However, the sluggish reaction kinetics, low electronic conductivity, and large volume changes during charge and discharge hinder the practical applications of SnO2‐based electrodes for SIBs and PIBs. Engineering rational structures with fast charge/ion transfer and robust stability is important to overcoming these challenges. Herein, S‐doped SnO2 (S–SnO2) quantum dots (QDs) (≈3 nm) encapsulated in an N, S codoped carbon fiber networks (S–SnO2–CFN) are rationally fabricated using a sequential freeze‐drying, calcination, and S‐doping strategy. Experimental analysis and density functional theory calculations reveal that the integration of S–SnO2 QDs with N, S codoped carbon fiber network remarkably decreases the adsorption energies of Na/K atoms in the interlayer of SnO2–CFN, and the S doping can increase the conductivity of SnO2, thereby enhancing the ion transfer kinetics. The synergistic interaction between S–SnO2 QDs and N, S codoped carbon fiber network results in a composite with fast Na+/K+ storage and extraordinary long‐term cyclability. Specifically, the S–SnO2–CFN delivers high rate capacities of 141.0 mAh g−1 at 20 A g−1 in SIBs and 102.8 mAh g−1 at 10 A g−1 in PIBs. Impressively, it delivers ultra‐stable sodium storage up to 10,000 cycles at 5 A g−1 and potassium storage up to 5000 cycles at 2 A g−1. This study provides insights into constructing metal oxide‐based carbon fiber network structures for high‐performance electrochemical energy storage and conversion devices.

Industrial Waste Derived Separators for Zn-Ion Batteries Achieve Homogeneous Zn(002) Deposition Through Low Chemical Affinity Effects.

Designing a cost-effective and multifunctional separator that ensures dendrite-free and stable Zn metal anode remains a significant challenge. Herein, a multifunctional cellulose-based separator is presented consisting of industrial waste-fly ash particles and cellulose nanofiber using a facile solution-coating method. The resulting fly ash-cellulose (FACNF) separators enable a high ion conductivity (5.76 mS cm-1) and low desolvation energy barrier of hydrated Zn2+. These features facilitate fast ion transfer kinetics and inhibit water-induced side reactions. Furthermore, experimental results and theoretical simulations confirm that the presence of fly ash particles in FACNF separators effectively accommodate the preferential deposition of Zn(002) planes, due to the weak chemical affinity between Zn(002) plane and fly ash, to mitigate dendrite formation and growth. Consequently, the utilization of FACNF separators causes an impressive cycling performance in both Zn||Zn symmetric cells (1600h at 2mA cm-2/1 mAh cm-2) and Zn||(NH4)2V10O25 (NVO) full cells (4000 cycles with the capacity retention of 92.1% at 5 A g-1). Furthermore, the assembled pouch cells can steadily support digital thermometer over two months without generating gas and volume expansion. This work provides new insights for achieving crystallographic uniformity in Zn anodes and realizing cost-effective and long-lasting aqueous zinc-ion batteries (AZIBs).

Building Stable Anodes for High-Rate Na-Metal Batteries.

Due to low cost and high energy density, sodium metal batteries (SMBs) have attracted growing interest, with great potential to power future electric vehicles (EVs) and mobile electronics, which require rapid charge/discharge capability. However, the development of high-rate SMBs has been impeded by the sluggish Na+ ion kinetics, particularly at the sodium metal anode (SMA). The high-rate operation severely threatens the SMA stability, due to the unstable solid-electrolyte interface (SEI), the Na dendrite growth, and large volume changes during Na plating-stripping cycles, leading to rapid electrochemical performance degradations. This review surveys key challenges faced by high-rate SMAs, and highlights representative stabilization strategies, including the general modification of SMB components (including the host, Na metal surface, electrolyte, separator, and cathode), and emerging solutions with the development of solid-state SMBs and liquid metal anodes; the working principle, performance, and application of these strategies are elaborated, to reduce the Na nucleation energy barriers and promote Na+ ion transfer kinetics for stable high-rate Na metal anodes. This review will inspire further efforts to stabilize SMAs and other metal (e.g., Li, K, Mg, Zn) anodes, promoting high-rate applications of high-energy metal batteries towards a more sustainable society.

Carbonized polyacrylonitrile-coated three-dimensional porous TiP2O7 as a high-rate capability anode for lithium-ion batteries

TiP2O7 is a hopeful anode material for lithium-ion batteries (LIBs) due to its three-dimensional (3D) open skeletons, excellent ion transfer kinetics, and good structural stability. However, the inferior intrinsic electronic conductivity degrades seriously the electrochemical performance of LIBs. Herein, a strategy of carbonized polyacrylonitrile-coated TiP2O7 (TPO/cPAN) with 3D porous structures was proposed to enhance Li+-storage capability. The TPO/cPAN modified with 30 wt% polyacrylonitrile and calcined at 800 ℃ delivers superior long-term cycling stability at 0.5 A g−1 and excellent rate capacities of 558.7, 523.8, 477.5, 409.8, and 303.4 mAh g−1 at 0.1, 0.2, 0.4, 0.8, and 1.6 A g−1, respectively. Structural characterizations and electrochemical analysis reveal that the pyrolytic N-doped carbon layer markedly ameliorates the electron transferability and protects the electrode from organic electrolyte erosion. Meanwhile, the design of 3D porous structures and the generation of rich oxygen defects facilitate Li+ transport and pseudocapacitance energy storage. The work provides a novel pathway for optimizing the electron/ion migration of polyanionic electrode materials.

A nitrile solvent structure induced stable solid electrolyte interphase for wide-temperature lithium-ion batteries.

Lithium-ion batteries (LIBs) are extensively employed in various fields. Nonetheless, LIBs utilizing ethylene carbonate (EC)-based electrolytes incur capacity degradation in a wide-temperature range, which is attributable to the slow Li+ transfer kinetics at low temperatures and solvent decomposition during high-rate cycling at high temperatures. Here, we designed a novel electrolyte by substituting nitrile solvents for EC, characterized by low de-solvation energy and high ionic conductivity. The correlation between the carbon chain length of nitrile solvents with reduction stability and the Li+-solvated coordination was investigated. The results revealed that the valeronitrile (VN) solvent displayed an enhanced lowest unoccupied molecular orbital energy level and low de-solvation energy, which helped construct robust SEI interfacial layers and improved kinetics of interfacial ion transfer in wide-temperature LIBs. The VN-based electrolyte employed in graphite‖NCM523 pouch cells achieved a discharge capacity of 89.84% at a 20C rate at room temperature. Meanwhile, the cell exhibited 3C rate cycling stability even at a high temperature of 55 °C. Notably, the VN-based electrolyte exhibited a high ionic conductivity of 1.585 mS cm-1 at -50 °C. The discharge capacity of pouch cells retained 75.52% and 65.12% of their room temperature capacity at -40 °C and -50 °C, respectively. Wide-temperature-range batteries with VN-based electrolytes have the potential to be applied in various extreme environments.

A dendrite-free Zn anode enabled by PEDOT:PSS/MoS2 electrokinetic channels for aqueous Zn-ion batteries.

Notorious Zn dendrites and severe parasitic side reactions severely disrupt the anode-electrolyte interface during Zn plating/stripping, resulting in uncontrollable Zn deposition and limiting the application of aqueous zinc-ion batteries (AZIBs). Although the construction of an artificial interface is a highly desirable strategy, it is often limited by slow Zn2+ transport kinetics. To address these issues, we present a bifunctional polymer coating (PEPM) constructed from highly conductive PEDOT:PSS and monolayer MoS2, where the introduced PEDOT plays an important role in driving the fast Zn ion transfer kinetics as a zincophilic site and 2D MoS2 acts as a buffer layer to induce uniform Zn nucleation. With this corrosion inhibition and nucleation-oriented coating, the mobility of Zn2+ flux and the uniformity of Zn deposition were significantly improved, resulting in a stable plating/stripping performance at an ultra-low overpotential (<50 mV) of 2000 h and a high average coulombic efficiency (>99.4%) of 1000 cycles without significant dendrite formation. The proposed strategy provides a cost-efficient remedy and opens a new avenue for the development of dendrite-free zinc anodes.

Oxygen Vacancies on NH4 V4 O10 Accelerate Ion and Charge Transfer in Aqueous Zinc-Ion Batteries.

Vanadium-based compounds are identified as promising cathode materials for aqueous zinc ion batteries due to their high specific capacity. However, the low intrinsic conductivity and sluggish Zn2+ diffusion kinetics seriously impede their further practical application. Here, oxygen vacancies onNH4 V4 O10 is reported as a high-performing cathode material for aqueous zinc ion batteries via a facile hydrothermal strategy. The introduction of oxygen vacancy accelerates the ion and charge transfer kinetics, reduces the diffusion barrier of zinc ions, and establishes a stable crystal structure during zinc ion (de-intercalation). As a result, the oxygen vacancy enriched NH4 V4 O10 exhibits a high specific capacity of ≈499mAhg-1 at 0.2Ag-1 , an excellent rate capability of 296mAhg-1 at 10Ag-1 and the specific capacity cycling stability with 95.1% retention at 5Ag-1 for 4000 cycles, superior to the NVO sample (186.4mAhg-1 at 5Ag-1 , 66% capacity retention).

Tuning interlayer environment of V2C MXene by cobalt ion intercalation to boost zinc ion transfer kinetics in aqueous zinc-ion hybrid capacitors

Zn-ion hybrid capacitors (ZIHCs) combined the high energy density of battery-type electrodes with the high power density of capacitor-type electrodes have shown great potential for next-generation energy storage. However, the limited capacity of conventional carbon-based cathode materials does not meet the requirements of practical applications. In this study, a universal and effective electrostatic self-assembly strategy has been proposed and developed for synthesizing the Co2+ ions intercalated V2C cathodes to boost the kinetics of Zn2+ ion transport and achieve excellent electrochemical reversibility and chemical stability. By adjusting the amount of intercalated Co2+ ions, the optimal ratio of sample (2:1 V2C-Co) showed an excellent specific capacity of 333 mAh g−1 at a current density of 0.1 A g−1 and an admirable rate performance of 175 mAh g−1 at 5 A g−1. Furthermore, the specific capacity retains 67 % of the initial value after 3000 cycles at 5 A g−1. This work provides an effective method for developing high efficient V2C cathodes for advanced aqueous zinc-ion hybrid capacitors.

RGO-Induced Flower-like Ni-MOF In Situ Self-Assembled Electrodes for High-Performance Hybrid Supercapacitors.

Currently, the primary bottlenecks that hinder the widespread application of supercapacitors are low energy density and narrow potential windows. Herein, the hybrid supercapacitor with high energy density and wide potential window is constructed via an in situ self-assembly method employing RGO-induced flower-like MOF(Ni). Benefiting from the synergistic effect between RGO and MOF(Ni), the interfacial interactions are effectively improved, and the contact area with the electrolyte is enhanced, which increases the ion transfer kinetics and overall electrochemical performance. The MOF(Ni)@RGO electrode exhibits a specific capacitance of 1267.73 F g-1 at a current density of 1 A g-1. Crucially, the assembled MOF(Ni)@RGO//BC with a broad potential window and good stability employing a MOF(Ni)@RGO anode and biomass carbon cathode, combined with a 2 M PVA-KOH gel-electrolyte, achieves a maximum energy density of 70.16 Wh kg-1 at a power density of 2200.09 W kg-1, outperforming most reported supercapacitors. This hybrid supercapacitor exhibits excellent stability and high energy density, providing a novel strategy for further large-scale applications.

Mechanistic Insights into Anion-Induced Electrochromism of Ru(II)-Based Metallo-Supramolecular Polymer.

The metallo-supramolecular polymer (MSP) is considered one of the most promising electrodes for electrochromic devices due to its intrinsically stable redox properties. Nevertheless, despite extensive work focusing on improving the electrochromic and electrochemical properties of MSPs, little experimental evidence exists from in-depth investigations on the anion-induced electrochromism of MSPs. Herein, Ru-based metallo-supramolecular polymer (polyRu) films with excellent electrochromic performance were fabricated through a novel electrochemical deposition method, and the electrochromic mechanism was further understood. The polyRu films possess fast reaction kinetics with a short switching time of 4.0 s (colored) and 2.8 s (bleached) and highly reversible redox properties due to the resulting impacts on the capacitive behaviors (containing surface, near-surface and intercalation pseudo-capacitance) of the perchlorate ions in the electrochromic process. Moreover, the electrochromic degradation of the polyRu films is considered to stem from the numerous nanopores in the film induced by ClO4- transport and the exchange of counter anions from Cl- to ClO4-. In addition, a physical model, revealing the transport of conduction ions and the evolution of the structure and properties of the polyRu film during the electrochromic process, is presented. It is observed that the charge balance of Ru3+ and Ru2+, achieved through the adsorption/desorption of ClO4- on the film, provides electrochromic and electrochemical reversibility to the polyRu film under positive/negative bias. Correspondingly, a transformation from polyRu·(Cl-)2n to polyRu·(ClO4-)x(Cl-)2n-x in the polyRu film is induced by a counter anion exchange from Cl- to ClO4-. Revealing the detailed perchlorate ion transfer kinetics and electrochromic mechanism in this film can offer new insights into the application of metallo-supramolecular polymers in electrochromic devices.

Building oxygen-rich vacancy coating for fast Li-ion diffusion kinetics and stable cycling of lithium-rich layered oxide cathode at wide-temperature

As a cathode with a high energy density for Li-ion batteries, Li-rich layered oxide (LLO) cathodes suffer from short lifespans and poor rate performance, mainly due to their irreversible lattice oxygen evolution leading to severe structural degradation and oxygen release. Herein, we propose the use of Zn-doped SnO2 coated with LLO cathode to tackle these issues. Compared to the traditional method of coating oxides on the surface of lithium-rich cathodes, Zn doping of SnO2 coating can artificially create abundant oxygen vacancies for LLO cathode, which can provide a buffer boundary for active oxygen generated by lithium-rich cathode during circulation, effectively promoting the reversible reaction of oxygen redox couple and stabilizing lattice oxygen. The experimental results show that the surface of the LLO cathode's Zn-doped SnO2 is rich in oxygen vacancies could significantly boost the kinetics of lithium ion transfer, and effectively inhibit layer-to-spinel phase transition, and lattice oxygen release. By taking advantage of the Zn-doped SnO2 coating, the capacity stability of LLO cathode is raised from 58.1 % to 86.7 % at 1C after 500 cycles and also obtains outstanding rate performance and cycling durability at wide-temperature (−10 to 55 °C).

Nanopore rigidity as an atomic descriptor of ion-transfer kinetics in sieving membranes: Insights from two-dimensional g-C3N4

Kinetics of ions play a crucial role in the performance of materials for a wide range of applications, including solid electrolytes, fuel cells, and sieving membranes. However, establishing a quantitative correlation between microscopic characteristics of a material and kinetics of conducting species inside remains a major challenge. Combining first-principles and metadynamics methods, we investigate sieving behavior of two-dimensional graphitic carbon nitride (g-C3N4) for various species (H+, Na+, K+, and Cl−). We reveal that mechanism of proton conduction changes with a pore size of carbon-nitrogen ring in g-C3N4: varying from a pure H+ transportation when crossing narrow pores into a dual pathways (via both H+ and hydronium ions H3O+) when transmitting across wide pores. We introduce a novel local descriptor, nanopore rigidity (C), to quantify the rigidity of a material and relate the dynamics of sieving species to mechanics of the pore. The kinetic barrier of an arbitrary intercalating ion (ΔGion) can then be obtained via ΔGion=Cδρ2+B with B being a residual barrier of the pore and δρ being the local strain of the pore induced by the conducting ion. The descriptor as a microscopic metric can be extended to other porous materials, allowing a screening for electrochemical energy transition materials.

Pre‐intercalation of Ammonium Ions in Layered δ‐MnO2 Nanosheets for High‐Performance Aqueous Zinc‐Ion Batteries

AbstractLayered manganese dioxide is a promising cathode candidate for aqueous Zn‐ion batteries. However, the narrow interlayer spacing, inferior intrinsic electronic conductivity and poor structural stability still limit its practical application. Herein, we report a two‐step strategy to incorporate ammonium ions into manganese dioxide (named as AMO) nanosheets as a cathode for boosted Zn ion storage. K+‐intercalated δ‐MnO2 nanosheets (KMO) grown on carbon cloth are chosen as the self‐involved precursor. Of note, ammonium ions could replace K+ ions via a facile hydrothermal reaction to enlarge the lattice space and form hydrogen‐bond networks. Compared with KMO, the structural stability and the ion transfer kinetics of the layered AMO are enhanced. As expected, the obtained AMO cathode exhibits remarkable electrochemical properties in terms of high reversible capacity, decent rate performance and superior cycling stability over 10000 cycles.