Ion Diffusion Kinetics Research Articles

Enabling fast diffusion/conversion kinetics by thiourea-induced wrinkled N, S co-doped functional MXene for lithium-sulfur battery

The long lifespan of high-energy density lithium-sulfur batteries (LSBs) is still hindered by severe polysulfide (PS) shuttling and sluggish sulfur reduction/evolution kinetics process. Herein, we report a facile preparation of thiourea-induced wrinkled nitrogen and sulfur co-doped functionalized MXene (NSMX) to modify the separator to enhance the ion diffusion and conversion kinetics for high-energy LSBs. The combination of theoretical calculations and experimental conclusions demonstrates that the introduction of N, S heteroatoms induces the shift of the d-band center in transition metal Ti towards the Fermi level and results in the robust bonding effect between N/S atoms and Li atom in PS, hence exhibiting admirable adsorption capability to PS and fast catalytic PS reversible conversion rate, which quickly deplete soluble high-order PS and expedites the depletion of the Li2S6 in high potential. The 2D wrinkled polar surface with excellent conductivity assures fast electron transfer and ion migration. Profiting from the enhancement of S utilization and the reduction of unfavorable accumulated Li2S6, the LSBs equipped with NSMX modified separators exhibit a high specific capacity of 1249 mAh g−1 at 0.2 C. At a high rate of 5 C, the LSBs also delivered an impressive reversible capacity of 600 mAh g−1. Moreover, a high capacity and stable cycling can be achieved even under the condition of high S load and lean electrolyte consumption.

Molecular-Level Interfacial Chemistry Regulation of MXene Enables Energy Storage beyond Theoretical Limit.

Ti3C2Tx MXene often suffers from poor lithium storage behaviors due to its electrochemically unfavorable OH terminations. Herein, we propose molecular-level interfacial chemistry regulation of Ti3C2Tx MXene with phytic acid (PA) to directly activate its OH terminations. Through constructing hydrogen bonds (H-bonds) between oxygen atoms of PA and OH terminations on Ti3C2Tx surface, interfacial charge distribution of Ti3C2Tx has been effectively regulated, thereby enabling sufficient ion-storage sites and expediting ion transport kinetics for high-performance energy storage. The results show that Li ions preferably bind to H-bond acceptors (oxygen atoms from PA), and the flexibility of H-bonds therefore renders their interactions with adsorbed Li ions chemically "tunable", thus alleviating undesirable localized geometric changes of the OH terminations. Meanwhile the H-bond-induced microscopic dipoles can act as directional Li-ion pumps to expedite ion diffusion kinetics with lower energy barrier. As a result, the as-designed Ti3C2Tx/PA achieves a 2.4-fold capacity enhancement compared with pristine Ti3C2Tx (even beyond theoretical capacity), superior long-term cyclability (220.0 mAh g-1 after 2000 cycles at 2.0 A g-1), and broad temperature adaptability (-20 to 50 °C). This work offers a promising interface engineering strategy to regulate microenvironments of inherent terminations for breaking through the energy storage performance of MXenes.

Evolving non-aggregated ZIF-8 nanoparticles into hierarchically porous hollow carbon nanofibers for high-performance flexible zinc-ion hybrid supercapacitor

Zinc-ion hybrid supercapacitors are garnering widespread interest in wearable energy storage devices due to their high power density, intrinsic safety and cost-effectiveness. However, the primary obstacle to their progress lies in the scarcity of cathode materials that concurrently demonstrate excellent flexibility and high energy density. Herein, we deliberately design a coaxial electrospinning ZIF-8 derived hollow carbon nanofiber film electrode (C-PAN(ZIF-8)@PVP) to achieve high-performance flexible ZHSCs. The distinctive configuration of C-PAN(ZIF-8)@PVP electrode comprises a shell of homogeneously distributed ZIF-8 derived porous carbon nanoparticles, which are bound together by N-doped carbon fibers derived from polyacrylonitrile (PAN), and a channel through the fiber created by the decomposition of polyvinylpyrrolidone (PVP). This unique architecture coupled with N, O co-doping bestows ample electrolyte infiltration, complete exposure of active sites, and a rapid pathway for electron conduction, resulting in facilitated ion diffusion kinetics, abundant active sites and enhanced electronic conductivity of the C-PAN(ZIF-8)@PVP electrode. As a result, the assembled ZHSC delivers a high reversible capacity of 116 mAh g−1 at 0.1 A g−1 and remarkable capacity retention of 100% over 4000 cycles at 5 A g−1. Moreover, it exhibits exceptional mechanical flexibility, capable of delivering stable output under arbitrary deformation. The intricate structural design strategy offers valuable insights for the development of high-performance electrode materials.

Benefits of Femtosecond Laser 40 MHz Burst Mode for Li-Ion Battery Electrode Structuring.

In Li-ion batteries, ion diffusion kinetics represent a limitation to combine high capacity and a fast charging rate. To bypass this, textured electrodes have been demonstrated to increase the active surface, decrease the material tortuosity and accelerate the electrolyte wetting. Amongst the structuring technologies, ultrashort pulse laser processing may represent the key option enabling, at the same time, high precision, negligible material deterioration and high throughput. Here, we report a study on the structuring of electrodes with both holes and grooves reaching the metallic collector. Electrochemical models emphasize the importance of hole and line dimensions for the performances of the cell. We demonstrate that we can control the hole and line width by adjusting the applied fluence and the repetition rate. In addition, results show that it is possible to drill 65 µm-deep and ~15 µm-wide holes in nearly 100 µs resulting in up to 10,000 holes/s. To further reduce the takt time, bursts of 40 MHz pulses were also investigated. We show that bursts can reduce the takt time by a factor that increases with the average power and the burst length. Moreover, at comparable fluence, we show that bursts can shorten the process more than theoretically expected.

Synergistic structure and oxygen-vacancies engineering of lithium vanadate for kinetically accelerated and pseudocapacitance-dominated lithium storage

The high reversibility, capacity, and safety make lithium vanadate (LVO) an attractive anode to Li-ion batteries, yet they still suffer from the low intrinsic electrical conductivity and ion diffusion rate. Modulating the electronic and crystal structure of materials by vacancies engineering could significantly affect the lithium storage performance. Herein, high concentration of oxygen-vacancies incorporated Li3VO4 nanowires (HLVO) were prepared to make up conductivity and ion diffusion kinetics of LVO as a competitive fast-charging anode. The oxygen-vacancies were derived from the controllable oxidation of local V4+ ions via the thermal treatment, enabling the redistribution of electrons and optimized charge‐transport properties of LVO on the basis of the experimental results and theoretical calculations. The reduced reaction energy barriers, enhanced Li-ion diffusion, improved electrical conductivity, and additional active sites induced by oxygen-vacancies drastically accelerate the redox kinetics, enhancing the capacitive behavior. Thus, the HLVO anode delivers superior electrochemical performance with large specific capacities of 553.8 mA h g−1, exceptional rate capacity of 312.2 mA h g−1 even at 4.0 A g−1 and excellent cycling stability. This finding provides the credence to the prospect of vacancy engineering contributing to develop the matter-of-fact transition metal oxides as high-performance anodes for Li-ion batteries.

Tailoring Cu-rich surface spinel phase for high-performance O3-type layered cathode materials for sodium-ion batteries

O3-type layered oxide cathodes are primarily limited by complex phase transitions and sluggish kinetics resulting in rapid capacity drop and poor rate capability. Even worse, its inherent air sensitivity leads to spontaneous extraction of lattice Na-ions and the deactivation of the cathode. Simultaneous modification of both the bulk phase and the surface structure is promising to offset the above deficiencies. A spinel@O3 type layered composite structure Na0.9Mn0.5Ni0.5Cu0.1O2+x (NMNCO-SL) was constructed for the design of cathodes with higher cycling, rate and air stability. The atomic-level Cu-rich spinel structure on the surface was identified by scanning transmission electron microscopy, elemental linear scanning analysis and Raman spectra. In situ charge-discharge X-ray diffraction results show that the phase transition of NMNCO-SL is significantly suppressed. Finally, the material maintains good electrochemical properties after exposure to stringent humidity environments. The results indicate that the spinel structure at the surface plays a significant role in improving ion-diffusion dynamics, enhancing structural integrity, and increasing air stability. 1 Ah pouch cell based on NMNCO-SL showed 92% capacity retention after 500 cycles of charge/discharge cycling at 1 C, demonstrating the potential prospects of customizing the surface phase structure for materials engineering applications.

Multiscale modification of graphdiyne-based electrodes and diffusion kinetics analysis of lithium ions

The diffusion of lithium ions is highly related to the chemical structure, packing mode, and pore size distribution of the electrode materials. In this paper, a multiscale modification strategy is performed to investigate the correlation between the chemical structure and diffusion kinetics of lithium ions in graphdiyne (GDY) based electrodes. Various electrochemical tests show consistent results that hydrogen-substituted GDY has the fastest lithium-ion diffusion rate, and the doping of Cl and F atoms with large atomic radii leads to slower lithium-ion diffusion in the system. The functional groups (H, Cl, F) introduced in the GDY-based electrodes not only regulate the pore size of the materials but also modulate the binding energy with lithium ions. chlorine-substituted GDY shows a higher diffusion coefficient than that of fluorine-substituted GDY for proper affinity to lithium. In addition, the specific surface area and the pore size distribution also collectively contribute to the differences in lithium-ion diffusion. Finally, the lithium storage mechanism of substituted GDY electrodes is explored. Our strategy sheds some light on the design and fabrication of anode materials for lithium-ion batteries.

Unleashing the Power of Sn2S3 Quantum Dots: Advancing Ultrafast and Ultrastable Sodium/Potassium-Ion Batteries with N, S Co-Doped Carbon Fiber Network.

Tin sulfide (Sn2S3) has been recognized as a potential anode material for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to its high theoretical capacities. However, the sluggish ion diffusion kinetics, low conductivity, and severe volume changes during cycling have limited its practical application. In this study, Sn2S3 quantum dots (QDs) (≈1.6nm) homogeneously embedded in an N, S co-doped carbon fiber network (Sn2S3-CFN) are successfully fabricated by sequential freeze-drying, carbonization, and sulfidation strategies. As anode materials, the Sn2S3-CFN delivers high reversible capacities and excellent rate capability (300.0 mAh g-1 at 10 A g-1 and 250.0 mAh g-1 at 20 A g-1 for SIBs; 165.3 mAh g-1 at 5 A g-1 and 100.0 mAh g-1 at 10 A g-1 for PIBs) and superior long-life cycling capability (279.6 mAh g-1 after 10 000 cycles at 5 A g-1 for SIBs; 166.3 mAh g-1 after 5 000 cycles at 2 A g-1 for PIBs). According to experimental analysis and theoretical calculations, the exceptional performance of the Sn2S3-CFN composite can be attributed to the synergistic effect of the conductive carbon fiber network and the Sn2S3 quantum dots, which contribute to the structural stability, reversible electrochemical reactions, and superior electron transportation and ions diffusion.

Front Cover image

The cover image focuses on a new class of solid electrolytes termed frameworked electrolytes, where the “macroscopically solid” frameworks are purposely laden with 3D ionic channels in the sub‐nano scales, giving rise to both a high ionic conductivity and a desirable interface with the electrode solids. The authors demonstrate a zeolite framework structure based frameworked electrolyte with superior ion diffusion kinetics, which ensures the design of high‐performance all solid state battery running at room temperature. It is confident that the emergence of frameworked electrolyte serves as a powerful motivator for embarking on a new expedition to design the next‐generation battery for EVs or portable electronics in the future. image

Crystallinity engineering of carbon nitride protective coating for ultra‐stable Zn metal anodes

AbstractIneffective control of dendrite growth and side reactions on Zn anodes significantly retards commercialization of aqueous Zn‐ion batteries. Unlike conventional interfacial modification strategies that are primarily focused on component optimization or microstructural tuning, herein, we propose a crystallinity engineering strategy by developing highly crystalline carbon nitride protective layers for Zn anodes through molten salt treatment. Interestingly, the highly ordered structure along with sufficient functional polar groups and pre‐intercalated K+ endows the coating with high ionic conductivity, strong hydrophilicity, and accelerated ion diffusion kinetics. Theoretical calculations also confirm its enhanced Zn adsorption capability compared to commonly reported carbon nitride with amorphous or semi‐crystalline structure and bare Zn. Benefiting from the aforementioned features, the as‐synthesized protective layer enables a calendar lifespan of symmetric cells for 1100 h and outstanding stability of full cells with capacity retention of 91.5% after 1500 cycles. This work proposes a new conceptual strategy for Zn anode protection.

Polyanionic Cathode Materials: A Comparison Between Na‐Ion and K‐Ion Batteries

AbstractSodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs) are considered the next‐generation candidates for future energy storage systems to partially substitute commercial lithium‐ion batteries because of their abundant sodium/potassium reserves, cost‐effectiveness, and high safety. Polyanionic cathode materials are widely used in alkali ion batteries due to their stable structural framework, high thermal stability, excellent alkali ion diffusion kinetics, and adjustable working voltage. Generally, the polyanionic cathodes used for SIBs surpass PIBs in the aspect of energy density and cycle life in most cases, however, the PIBs also have their unique advantages that are seldom reported. To this end, the polyanionic materials are classified by the valence states of active metal sites, the storage mechanism of Na+ and K+ in different crystal structures is summarized, and the electrochemical performance between SIBs and PIBs is compared. Particularly, some unique advantages of polyanionic cathodes in PIBs, such as high working voltage, superior rate capability, and excellent capacity retention are revealed, and the possible reasons are discussed in detail. Finally, various viable solutions are proposed to improve the battery performance of polyanionic compounds for future development.

Liquid-like thermal conductivity in solid materials: Dynamic behavior of silver ions in argyrodites

Argyrodite-type compounds are renowned for their exceptional thermoelectric performance and ultralow thermal conductivity. While the latter is commonly attributed to the superionic behavior of cations, there has been limited research into how cations' static or dynamic behavior affects the thermal transport properties of argyrodites. To address and bridge this research gap, we employ a wide range of measurements and develop ab-initio based machine-learning interatomic potentials to perform large-scale molecular dynamics simulations on Ag8SiTe6 under different temperatures. We highlight the symmetry breaking and lattice-distortion scattering caused by chilled ions at low temperatures and the enhanced ionic diffusion behavior at elevated temperatures endowing argyrodites with superior superionicity and liquid-like thermal conductivity. Our findings also provide valuable insights into the ionic diffusion kinetics and the exotic lattice dynamics of liquid-like thermoelectrics.

Anisotropy of Anion Diffusion in All-Inorganic Perovskite Single Crystals.

Ion diffusion is a fundamentally important process in understanding and manipulating the optoelectronic properties of semiconductors. Most current studies on ionic diffusion have been focusing on perovskite polycrystalline thin films and nanocrystals. However, the random orientation and grain boundaries can heavily interfere with the kinetics of ion diffusion, where the experimental results only reveal the average ion exchange kinetics and the actual ion diffusion mechanisms perpendicular to the direction of individual crystal facets remain unclear. Here, the anion (Cl, I) diffusion anisotropy on (111) and (100) facets of CsPbBr3 single crystals is demonstrated. The as-grown single crystals with (111) and (100) facets exhibit anisotropic growth with different halide incorporation, which lead to different resulting optoelectronic properties. Combined experimental characterizations and theoretical calculations reveal that the (111) CsPbBr3 shows a faster anion diffusion behavior compared with that of the (100) CsPbBr3, with a lower diffusion energy barrier, a larger built-in electric field, and lower inverse defect formation energy. The work highlights the anion diffusion anisotropic mechanisms perpendicular to the direction of individual crystal facets for optimizing and designing perovskite optoelectronic devices.

Significant improvement in cycling and rate ability originating from regulation of bonding and transport channel via Ba2+ decoration in P2 layer oxide cathode

Nowadays, commercialization of layered transition metal oxides is hindered by irreversible phase transition during charging and discharging, low-capacity retention rate at high rate and slow Na+ diffusion kinetics. In this work, Ba2+ was introduced into the alkali metal layer to improve the electrochemical performance of layered transition metal oxides. XRD refinement and first principle calculations demonstrate that the introduced Ba2+ can effectively enlarge the distance between Na layers and reduce the potential barrier of sodium ion migration, thus leading to faster sodium ion diffusion kinetics. Simultaneously, charge distribution density calculation indicates that the introduced Ba2+ enhances overlap of electron clouds between transition metal (TM) and O, which result in more obvious covalence of TM-O bond, bigger electrostatic attraction between TM and O, and stronger bond energy of TM-O. These microstructures are beneficial to maintain structural stability and suppress the formation of OP4 phase during charging, which is demonstrated by XRD during charging and discharging process. The optimized Na0.6Ba0.012Mn0.62Ni0.22Fe0.16O2 provides reversible specific capacity of 133.8mAh g−1 at 0.5C (1C = 150mA g−1) and 122.1mAh g−1 at 2C. The strategy of regulating chemical bond environment by introducing Ba2+ achieves excellent the electrochemical performances and promotes the commercial development of sodium ion batteries.

Facile Route to Synthesize a Highly Sinterable Li1.3Al0.3Ti1.7(PO4)3 Solid Electrolyte.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a widely used solid electrolyte in solid-state lithium batteries, owing to its excellent chemical stability against moisture and high total ionic conductivity. However, traditionally, densification of LATP has been achieved through a high-temperature sintering process (approximately 1000 °C) owing to its poor sinterability. Herein, we report a facile synthesis route to obtain highly sinterable LATP solid electrolyte using tetrabutyl titanate (C16H36O4Ti) as the titanium source and incorporating the traditional solid-state reaction method. The synthetic LATP powder mixed with a low ratio of LiTiPO5 exhibited a hybrid crystalline-amorphous phase structure, which facilitated grain fusion, promoted structural homogeneity, and facilitated structural densification under low-temperature sintering. The sintered LATP pellet, which exhibited an interconnected structure and indistinct grain boundaries, achieved a relative density of >90% and an ionic conductivity of 0.667 mS/cm at a sintering temperature of only 750 °C. Additionally, we systematically studied and demonstrated the synthesis reaction mechanism, sintering behavior, and ionic diffusion kinetics of LATP electrolytes. Our study paves the way for synthesizing highly sinterable LATP solid electrolytes using a simple, additive-free, and cost-effective method.

Suppressing the P2–O2 phase transition of P2-type Ni/Mn-based layered oxide by synergistic effect of Zn/Ti co-doping for advanced sodium-ion batteries

P2-type Ni/Mn-based layered oxides are regarded to be promising cathode materials for advanced sodium-ion batteries (SIBs) owing to their rapid sodium ion diffusion kinetics, high working voltage, and high theoretical capacity. However, P2-type Ni/Mn-based layered oxides are prone to phase transition during charging and discharging processes, resulting in serious capacity fading. Here, introduction of Zn and Ti into transition-metal layers of P2-type layered Na0.66Ni0.33Mn0.67O2 can effectively inhibit P2–O2 phase transition at high voltage, leading to the improved cycling endurance. When being used as cathode materials for SIBs, Na0.66Ni0.27Zn0.06Mn0.61Ti0.06O2 (NNZMT) can deliver a discharge specific capacity of 106.6 mAh g−1, with 95.17% capacity retention after the 100th cycle at 100 mA g−1 within 2.1–4.3 V, which are much higher than those (58.4 mAh g−1 and 45.2%) of Zn/Ti-undoped Na0.66Ni0.33Mn0.67O2 (NNM). Besides, NNZMT displays a much better rate capability compared to the NNM sample. The full cell, based on P2-type layered NNZMT as cathode material and hard carbon as anode material, can provide an initial discharge specific capacity of 94.1 mAh g–1, with a capacity retention of 75.6% after 100 cycles at 100 mA g–1 within 1.0–4.2 V. This research work confirms that low-lost Zn/Ti co-doping strategy is an effective approach for designing and preparing cathode materials for advanced SIBs.

Understanding the electrochemical properties of Mg-doped Li2MnO3: first-principles calculations.

Non-transition metal doping, especially for Mg, has been gradually employed to optimize the electrochemical performance of Li-rich cathode material Li2MnO3. However, the effects of Mg doping on the electrochemical behavior of Li2MnO3 have not been studied extensively. In this work, we investigate the effect of Mg doping at both the 2b (in the Li/Mn mixed layer) and 4h (in the Li layer) Li sites on the electrochemical properties of Li2MnO3 through first-principles calculations and ab initio molecular dynamics simulations. The local lattice structure, electronic density of states, Bader charge, delithiation voltage, lattice oxygen stability and Li diffusion kinetics are examined. Electronic structure analysis shows that Mg can activate the electrochemical activity of surrounding Mn by charge transfer, making Mn participate in charge compensation at the initial delithiation stage. Mg doping can also cause an increase in the average oxygen vacancy formation energy and hence depress the oxygen release during the delithiation process. Molecular dynamics simulations show that the diffusion kinetics of Li ions in Mg2b-Li2MnO3 is enhanced with respect to the undoped one, whereas Mg doped at the 4h site cannot improve the diffusion kinetics of Li ions. Further studies found that Mg doped at the 2b site results in a decrease in the energy barrier for the intra-layer diffusion and an increase in the energy barrier for the inter-layer diffusion of the nearby Li vacancies.

SnO2/Sn with core-shell structure Schottky heterojunctions loaded in graphene to promote electrochemical reaction kinetics and enable efficient lithium-ion storage.

The stannic oxide (SnO2) anode expands in volume during cycling causing a decrease in reversible capacity. In this work, we generated a spherical SnO2/Sn heterojunction with core-shell structure composites encapsulated by graphene (SnO2/Sn/G) in situ using a simple one-step hydrothermal and subsequent annealing process. SnO2/Sn heterojunction nanospheres dispersed in a porous graphene framework accelerate the diffusion kinetics of electrons and ions. In addition, the structure plays a key role in mitigating large volume changes and nanostructure agglomeration. As a result, SnO2/Sn/G exhibits excellent performance as an anode material for lithium-ion batteries (LIBs), maintaining a reversible specific capacity of 720.6 mA h g-1 even after 600 cycles at a current density of 0.5 A g-1.

Exploring lithium ion interactions in graphite electrodes through non-equilibrium molecular dynamics and density functional theory.

In molecular dynamics (MD) simulations, selecting an appropriate potential function is a crucial element for accurately simulating the kinetic properties of lithium ion intercalation, storage, and diffusion in graphite systems. This work employed a combination of non-equilibrium molecular dynamics (NEMD) and density-functional theory (DFT) for simulation and analysis. The findings indicate that the AIREBO potential function precisely describes the motion of ordered lithium ions between graphite layers, consistent with the models proposed by Rüdorff and Hofmann (R-H) and Daumas and Hérold (D-H). Conversely, for the folded structure within the graphite layer, the Tersoff potential function provides a more suitable description, consistent with the localized-domains model. Further analysis reveals that with increasing Li-ion concentration, the voltage, Young's modulus, and ultimate tensile strength of the LixC6 system exhibit a decreasing trend. Notably, the diffusion coefficient of lithium ions within the graphite layer varies widely, ranging from 10-6 cm2 s-1 to 10-16 cm2 s-1. In summary, this work is anticipated to provide further insights into the mechanism of lithium ion intercalation and diffusion kinetics in graphite electrodes. It also serves as a valuable theoretical framework for guiding the design and optimization of high-performance lithium-ion batteries.

Long-cycle stable operation of fluoride-ion batteries at room temperature enabled by an advanced interface engineering and ion diffusion kinetics regulation strategy

An advanced interface engineering strategy for long-life stable operation of fluorine ion batteries at room temperature.