Crystal structural design of exposed planes: express channels, high-rate capability cathodes for lithium-ion batteries

Optimized In Situ Doping Strategy Stabling Single-Crystal Ultrahigh-Nickel Layered Cathode Materials

Single-crystal Ni-rich cathodes offer promising prospects in mitigating intergranular microcracks and side reaction issues commonly encountered in conventional polycrystalline cathodes. However, the utilization of micrometer-sized single-crystal particles has raised concerns about sluggish Li+ diffusion kinetics and unfavorable structural degradation, particularly in high Ni content cathodes. Herein, we present an innovative in situ doping strategy to regulate the dominant growth of characteristic planes in the single-crystal precursor, leading to enhanced mechanical properties and effectively tackling the challenges posed by ultrahigh-nickel layered cathodes. Compared with the traditional dry-doping method, our in situ doping approach possesses a more homogeneous and consistent modifying effect from the inside out, ensuring the uniform distribution of doping ions with large radius (Nb, Zr, W, etc). This mitigates the generally unsatisfactory substitution effect, thereby minimizing undesirable coating layers induced by different solubilities during the calcination process. Additionally, the uniformly dispersed ions from this in situ doping are beneficial for alleviating the two-phase coexistence of H2/H3 and optimizing the Li+ concentration gradient during cycling, thus inhibiting the formation of intragranular cracks and interfacial deterioration. Consequently, the in situ doped cathodes demonstrate exceptional cycle retention and rate performance under various harsh testing conditions. Our optimized in situ doping strategy not only expands the application prospects of elemental doping but also offers a promising research direction for developing high-energy-density single-crystal cathodes with extended lifetime.

Ultrahigh Lithium Selective Transport in Two-Dimensional Confined Ice

Inspired by selective ion transport in biological membrane proteins, researchers developed artificial ion channels that sieve monovalent cations, catering to the increasing lithium demand. In this work, we engineered an ion transport channel based on the confined ice within two-dimensional (2D) capillaries and found that the permselectivity of monovalent cations depends on the anisotropy of the confined ice. Particularly, the 2D confined ice showed an anomalous lithium selective transport along the (002) direction in the vermiculite capillary, with the Li+/Na+ and Li+/K+ permselectivity reaching up to 556 ± 86 and 901 ± 172, respectively, superior to most ion-selective channels. However, the 2D confined ice along the (100) direction showed less Li+ permselectivity. Additionally, the anisotropy of 2D confined ice can be tuned by adjusting the interlayer spacing. By providing insights into the ion transport in the 2D confined ice, our work may inspire more design of monovalent ion-selective channels for efficient lithium separation.

Critical Review on Crystal Orientation Engineering of Antimony Chalcogenide Thin Film for Solar Cell Applications

The emerging antimony chalcogenide (Sb2 (Sx Se1-x )3 , 0 ≤ x ≤ 1) semiconductors are featured as quasi-1D structures comprising (Sb4 S(e)6 )n ribbons, this structural characteristic generates facet-dependent properties such as directional charge transfer and trap states. In terms of carrier transport, proper control over the crystal nucleation and growth conditions can promote preferentially oriented growth of favorable crystal planes, thus enabling efficient electron transport along (Sb4 S(e)6 )n ribbons. Furthermore, an in-depth understanding of the origin and impact of the crystal orientation of Sb2 (Sx Se1-x )3 films on the performance of corresponding photovoltaic devices is expected to lead to a breakthrough in power conversion efficiency. In fact, there are many studies on the orientation control of Sb2 (Sx Se1-x )3 colloidal nanomaterials. However, the synthesis of Sb2 (Sx Se1-x )3 thin films with controlled facets has recently been a focus in optoelectronic device applications. This work summarizes methodologies that are applied in the fabrication of preferentially oriented Sb2 (Sx Se1-x )3 films, including treatment strategies developed for crystal orientation engineering in each process. The mechanisms in the orientation control are thoroughly analyzed. An outlook on perspectives for the future development of Sb2 (Sx Se1-x )3 solar cells based on recent research and issues on orientation control is finally provided.

General Synthesis of Single-Crystal Spinel Cathodes with the Tailored Orientation of Exposed Crystal Planes for Advanced Lithium-Ion Batteries

The spinel Mn-based cathodes with 3D Li+ diffusion channels, high voltage, and low-cost show promise for developing high-power lithium-ion batteries (LIBs). But the disproportionation and Jahn-Teller distortion lead to structural degeneration and capacity decay, especially at high working temperatures. Herein, considering the merits of single crystals and orientation of exposed crystal planes, single-crystal truncated octahedral LiMn2 O4 (TO-LMO) with exposed {111}, {100} and {110} facets is rationally designed, in which the mainly exposed {111} facets are truncated by a small portion of {100} and {110} facets. The Li-deficient intermediate phase is innovatively proposed to prepare the single-crystal TO-LMO. The synergistic effects of single crystals and the orientation of exposed crystal planes significantly reduce the disproportionation of Mn3+ ions and thereby improve their structural stability. Consequently, the cycling stability of the single-crystal TO-LMO is remarkably enhanced, obtaining outstanding capacity retention of 84.3% after 2000 cycles, much better than that of 61.2% for octahedral LiMn2 O4 . The feasibility of preparing single-crystal truncated octahedral LiNi0.5 Mn1.5 O4 with exposed {111}, {100}, and {110} facets via the Li-deficient intermediate phase is further demonstrated. These findings offer new insight into regulating the orientation of exposed crystal planes and improving the reversibility of Mn-based redox couples in LIBs.

2D Layered Materials for Fast-Charging Lithium-Ion Battery Anodes

The development of electric vehicles has received worldwide attention in the background of reducing carbon emissions, wherein lithium-ion batteries (LIBs) become the primary energy supply systems. However, commercial graphite-based anodes in LIBs currently confront significant difficulty in enduring ultrahigh power input due to the slow Li+ transport rate and the low intercalation potential. This will, in turn, cause dramatic capacity decay and lithium plating. The 2D layered materials (2DLMs) recently emerge as new fast-charging anodes and hold huge promise for resolving the problems owing to the synergistic effect of a lower Li+ diffusion barrier, a proper Li+ intercalation potential, and a higher theoretical specific capacity with using them. In this review, the background and fundamentals of fast-charging for LIBs are first introduced. Then the research progress recently made for 2DLMs used for fast-charging anodes are elaborated and discussed. Some emerging research directions in this field with a short outlook on future studies are further discussed.

Achieving structural stability and enhanced electrochemical performance through Nb-doping into Li- and Mn-rich layered cathode for lithium-ion batteries

Although Li- and Mn-rich layered oxides are attractive cathode materials possessing high energy densities, they have not been commercialized owing to voltage decay, low rate capability, poor capacity retention, and high irreversible capacity in the first cycle. To circumvent these issues, we propose a Li_1.2Ni_0.13Co_0.13Mn_0.53Nb_0.01O₂ (Nb-LNCM) cathode material, wherein Nb doping strengthens the transition metal oxide (TM-O) bond and alleviates the anisotropic lattice distortion while stabilizing the layered structure. During long-term cycling, maintaining a wider LiO₆ interslab thickness in Nb-LNCM creates a favorable Li⁺ diffusion path, which improves the rate capability. Moreover, Nb doping can decrease oxygen loss, suppress the phase transition from layered to spinel and rock-salt structures, and relieve structural degradation. Nb doping results in less capacity contributions of Mn and Co and more reversible Ni and O redox reactions compared to pristine Li_1.2Ni_0.133Co_0.133Mn_0.533O₂ (LNCM), which significantly mitigates the voltage decay (Δ0.289 and Δ0.516 V for Nb-LNCM and LNCM, respectively) and ensures stable capacity retention (82.7 and 70.3% for Nb-LNCM and LNCM, respectively) during the initial 100 cycles. Our study demonstrates that Nb doping is an effective and practical strategy to enhance the structural and electrochemical integrity of Li- and Mn-rich layered oxides. This promotes the development of stable cathode materials for high-energy-density lithium-ion batteries.

Recent achievements toward the development of Ni-based layered oxide cathodes for fast-charging Li-ion batteries

The driving mileage of electric vehicles (EVs) has been substantially improved in recent years with the adoption of Ni-based layered oxide materials as the battery cathode. The average charging period of EVs is still time-consuming, compared with the short refueling time of an internal combustion engine vehicle. With the guidance from the United States Department of Energy, the charging time of refilling 60% of the battery capacity should be less than 6 min for EVs, indicating that the corresponding charging rate for the cathode materials is to be greater than 6C. However, the sluggish kinetic conditions and insufficient thermal stability of the Ni-based layered oxide materials hinder further application in fast-charging operations. Most of the recent review articles regarding Ni-based layered oxide materials as cathodes for lithium-ion batteries (LIBs) only touch degradation mechanisms under slow charging conditions. Of note, the fading mechanisms of the cathode materials for fast-charging, of which the importance abruptly increases due to the development of electric vehicles, may be significantly different from those of slow charging conditions. There are a few review articles regarding fast-charging; however, their perspectives are limited mostly to battery thermal management simulations, lacking experimental validations such as microscale structure degradations of Ni-based layered oxide cathode materials. In this review, a general and fundamental definition of fast-charging is discussed at first, and then we summarize the rate capability required in EVs and the electrochemical and kinetic properties of Ni-based layered oxide cathode materials. Next, the degradation mechanisms of LIBs leveraging Ni-based cathodes under fast-charging operation are systematically discussed from the electrode scale to the particle scale and finally the atom scale (lattice oxygen-level investigation). Then, various strategies to achieve higher rate capability, such as optimizing the synthesis process of cathode particles, fabricating single-crystalline particles, employing electrolyte additives, doping foreign ions, coating protective layers, and engineering the cathode architecture, are detailed. All these strategies need to be considered to enhance the electrochemical performance of Ni-based oxide cathode materials under fast-charging conditions.

Addressing voltage hysteresis in Li-rich cathode materials via gas-solid interface modification

Li-rich layered materials have attracted much attention for their large capacity (>250 mA h g^-1) stemming from anion redox at high voltage. However, inherent problems, such as capacity decay and voltage decay/hysteresis during cycling, hinder their commercial progress. In this work, an oxygen vacancy-accompanied spinel interface layer is constructed by gas-solid reaction via NiCO₃ treatment at 650 °C, which reduces the asymmetry of anion redox and improves structural stability. Therefore, a 1 mol% NiCO₃-modified sample powerfully reduces the voltage hysteresis (∼0.23 V) in the first cycle, simultaneously exhibiting an excellent discharge capacity of 275 mA h g^-1 at 0.1 C with a capacity retention of 90% for 200 cycles at 1 C.

Engineering Crystal Orientation of Cathode for Advanced Lithium-ion Batteries: A Minireview

Engineering crystal orientation has attracted widespread attention since it is related to the cyclability and rate performance of cathode materials for lithium-ion batteries (LIBs). Regulating the crystal directional growth with optimal exposed crystal facets is an effective strategy to improve the performance of cathode materials, but still lacks sufficient attention in research field. Herein, we briefly introduce the characterization techniques and identification methods for crystal facets, then summarize and illuminate the major methods for regulating crystal orientation and their internal mechanism. Furthermore, the optimization strategies for layered-, spinel-, and olivine-structure cathodes are discussed based on the characteristic of crystal structure, and the relationship between exposure of special crystal facets and lithium storage performance is deeply analyzed, which could guide the rational design of cathodes for LIBs.

Anisotropic Crystal Growth of Layered Nickel Hydroxide along the Stacking Direction Using Amine Ligands

Edge surfaces of two-dimensional crystals play crucial roles in their properties, such as intercalation behavior and catalytic activities; however, reports on the preparation of crystals with a high aspect ratio of thickness to lateral size, typically a prism-like crystal morphology composed of stacked layers, are scarce. We report the anisotropic crystal growth of β-Ni(OH)₂ along the stacking direction using bidentate amine ligands, which act as both the base and the reservoir of Ni²⁺ through the formation of Ni-diamine complexes. Various characterization results of the crystal structure, composition, and crystal orientation indicate the formation of hexagonal prisms of β-Ni(OH)₂ with an unusually high aspect ratio of the thickness to the lateral size higher than 1. A systematic investigation focusing on the molar ratio of amine ligands to Ni²⁺, the concentration of Ni-diamine complexes, and stability constants of the complexes revealed that anisotropic growth was promoted when the supersaturation was relatively high and was maintained constant for a long time. We clarified the role of amine ligands in controlling supersaturation through the controlled release of metal ions from stable complexes. β-Co(OH)₂ with a hexagonal prism shape was prepared using this protocol. This study provides valuable indications for developing synthetic chemistry for various layered compounds to achieve a controlled aspect ratio.

Layered Cathode Materials: Precursors, Synthesis, Microstructure, Electrochemical Properties, and Battery Performance

The exploitation of clean energy promotes the exploration of next-generation lithium-ion batteries (LIBs) with high energy-density, long life, high safety, and low cost. Ni-rich layered cathode materials are one of the most promising candidates for next-generation LIBs. Numerous studies focusing on the synthesis and modifications of the layered cathode materials are published every year. Many physical features of precursors, such as density, morphology, size distribution, and microstructure of primary particles pass to the resulting cathode materials, thus significantly affecting their electrochemical properties and battery performance. This review focuses on the recent advances in the controlled synthesis of hydroxide precursors and the growth of particles. The essential parameters in controlled coprecipitation are discussed in detail. Some innovative technologies for precursor modifications and for the synthesis of novel precursors are highlighted. In addition, future perspectives of the development of hydroxide precursors are presented.

Screening LiMn2O4 Surface Modification Schemes under Theoretical Guidance

Mn dissolution is one of the most important factors for the failure of LiMn₂O₄ batteries. Doping has been widely adopted in the modification of LiMn₂O₄ cathodes; however, there is still a lack of theoretical guidance on screening the dopants. Here, through first-principles calculations, we systematically investigated the effects of all 3, 4d transition metals as well as Mg, Ca, Sr, Al, Ga, and In on the surface oxygen stability of LiMn₂O₄ cathodes, which has been proved to be correlated with the stability of the surface Mn atoms. Six competitive dopants, namely Nb, Ru, Mo, V, Tc, and Ti, were screened out. Besides, for three dopants in low valence states (Mg, Cu, and Zn), their Li-site doping can more effectively stabilize the surface oxygen atoms compared with Mn-site doping. Finally, we synthesized LiMn₂O₄ samples with Mg, Mo, and Nb surface doping to validate the rationality of the computational results. We found that particle morphology should also be considered in addition to surface oxygen stability for controlling Mn dissolution. Moreover, the electrochemical performance of LiMn₂O₄ batteries is a more complex issue and cannot be solely regulated by Mn dissolution. During the experiments, we have explored novel efficient binary chromogenic reagents for ultraviolet-visible spectroscopy analysis that can be used for rapid and low-cost Mn dissolution detection. This work provides a paradigm for the systematic design of the surface modification of the LiMn₂O₄ cathode under theoretical guidance.

A nano-truncated Ni/La doped manganese spinel material for high rate performance and long cycle life lithium-ion batteries

A nano-truncated octahedral LiNi0.08La0.01Mn1.91O4 cathode material with {111} and {100} crystal planes achieves capacity retention of 89.0% after 1000 cycles at 10C.

Challenges and Recent Advances in High Capacity Li-Rich Cathode Materials for High Energy Density Lithium-Ion Batteries

Li-rich cathode materials have attracted increasing attention because of their high reversible discharge capacity (>250 mA h g^-1 ), which originates from transition metal (TM) ion redox reactions and unconventional oxygen anion redox reactions. However, many issues need to be addressed before their practical applications, such as their low kinetic properties and inefficient voltage fading. The development of cutting-edge technologies has led to cognitive advances in theory and offer potential solutions to these problems. Herein, a recent in-depth understanding of the mechanisms and the frontier electrochemical research progress of Li-rich cathodes are reviewed. In addition, recent advances associated with various strategies to promote the performance and the development of modification methods are discussed. In particular, excluding Li-rich Mn-based (LRM) cathodes, other branches of the Li-rich cathode materials are also summarized. The consistent pursuit is to obtain energy storage devices with high capacity, reliable practicability, and absolute safety. The recent literature and ongoing efforts in this area are also described, which will create more opportunities and new ideas for the future development of Li-rich cathode materials.

Boosting the Electrochemical Performance of a Spinel Cathode with the In Situ Transformed Allogenic Li-Rich Layered Phase

High-voltage spinel materials have attracted widespread attention because of their advantages such as good rate performance, low cost, abundant source, and easy preparation. However, the Mn dissolution and Jahn-Teller effect of spinel materials during cycling limit their practical application. In this paper, the allogenic composites (1 - x)Li(Ni_0.2Co_0.1Mn_0.7)₂ O₄·xLi_1.2(Ni_0.2Co_0.1Mn_0.7)_0.8O₂ (x = 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) are developed by the carbonate co-precipitation method combined with the high-temperature sintering method, which are certified by the X-ray diffraction (XRD) spectrum and transmission electron microscopy (TEM) image. The results show that the lithium-rich phase of the allogenic composites can effectively improve the initial discharge capacity, alleviate the side reaction between the spinel material and the electrolyte, and improve the cycle stability. This work reveals the relationship between the structure and electrochemical performance of the in situ transformed spinel@Li-rich allogenic composites and provide a new clue to design a high-performance spinel cathode for advanced Li-ion batteries.

Twin boundary defect engineering improves lithium-ion diffusion for fast-charging spinel cathode materials

Defect engineering on electrode materials is considered an effective approach to improve the electrochemical performance of batteries since the presence of a variety of defects with different dimensions may promote ion diffusion and provide extra storage sites. However, manipulating defects and obtaining an in-depth understanding of their role in electrode materials remain challenging. Here, we deliberately introduce a considerable number of twin boundaries into spinel cathodes by adjusting the synthesis conditions. Through high-resolution scanning transmission electron microscopy and neutron diffraction, the detailed structures of the twin boundary defects are clarified, and the formation of twin boundary defects is attributed to agminated lithium atoms occupying the Mn sites around the twin boundary. In combination with electrochemical experiments and first-principles calculations, we demonstrate that the presence of twin boundaries in the spinel cathode enables fast lithium-ion diffusion, leading to excellent fast charging performance, namely, 75% and 58% capacity retention at 5 C and 10 C, respectively. These findings demonstrate a simple and effective approach for fabricating fast-charging cathodes through the use of defect engineering.

Facile combustion synthesis of amorphous Al2O3-coated LiMn2O4 cathode materials for high-performance Li-ion batteries

The unique Al₂O₃-coating layer can suppress the Mn dissolution and resist HF corrosion, hence stabilizing the crystal structure of spinel LiMn₂O₄ cathode materials.

Effects of crystal structure and plane orientation on lithium and nickel co-doped spinel lithium manganese oxide for long cycle life lithium-ion batteries

Various Li-rich spinel Li_1+xNi_0.05Mn_1.95-xO₄ (0 ≤ x ≤ 0.10) cathode materials with a truncated octahedron were synthesized by a solution combustion method. The relationship of crystalline structure, particles morphology and electrochemical properties of the as-prepared samples was investigated via a series of physicochemical characterizations. The Li-Ni co-doping changes the lattice parameters and atomic configuration, whilst resulting in a contraction of unit cell dimension and giving rise to a variation of bond length. In this regard, the shrinkage of octahedral MnO₆ provides a robust structure and the expansion of tetrahedral LiO₄ facilitates a fast electrochemical process. Additionally, the resulted polyhedral Li_1+xNi_0.05Mn_1.95-xO₄ samples present the exposed (110), (100), and (111) crystal planes, which provide the favorable Li⁺ ions diffusion/transmission channel and alleviate Mn dissolution. Owing to these merits of polyhedral structure and Li-Ni co-doping, the optimized Li_1.02Ni_0.05Mn_1.93O₄ exhibits good electrochemical performance with high initial discharge capacity of 119.8, 107.1 and 97.9 mAh·g^-1 at 1, 5 and 10 C, respectively. Even at a high current rate of 15 C, an excellent capacity retention of 91.7% is obtained after 1000 cycles, whilst the high temperature performance was also improved.

Recent Developments of Nanomaterials and Nanostructures for High-Rate Lithium Ion Batteries

Lithium ion batteries have been considered as a promising energy-storage solution, the performance of which depends on the electrochemical properties of each component, including cathode, anode, electrolyte and separator. Currently, fast charging is becoming an attractive research field due to the widespread application of batteries in electric vehicles, which are designated to replace conventional diesel automobiles in the future. In these batteries, rate capability, which is closely linked to the topology and morphology of electrode materials, is one of the determining parameters of interest. It has been revealed that nanotechnology is an exceptional tool in designing and preparing cathodes and anodes with outstanding electrochemical kinetics due to the well-known nanosizing effect. Nevertheless, the negative effects of applying nanomaterials in electrodes sometimes outweigh the benefits. To better understand the exact function of nanostructures in solid-state electrodes, herein, a comprehensive review is provided beginning with the fundamental theory of lithium ion transport in solids, which is then followed by a detailed analysis of several major factors affecting the migration of lithium ions in solid-state electrodes. The latest developments in characterisation techniques, based on either electrochemical or radiology methodologies, are covered as well. In addition, state-of-the-art research findings are provided to illustrate the effect of nanomaterials and nanostructures in promoting the rate performance of lithium ion batteries. Finally, several challenges and shortcomings of applying nanotechnology in fabricating high-rate lithium ion batteries are summarised.

Synthesis and Manipulation of Single-Crystalline Lithium Nickel Manganese Cobalt Oxide Cathodes: A Review of Growth Mechanism

Lithium nickel manganese cobalt oxide (NMC) cathodes are of great importance for the development of lithium ion batteries with high energy density. Currently, most commercially available NMC products are polycrystalline secondary particles, which are aggregated by anisotropic primary particles. Although the polycrystalline NMC particles have demonstrated large gravimetric capacity and good rate capabilities, the volumetric energy density, cycling stability as well as production adaptability are not satisfactory. Well-dispersed single-crystalline NMC is therefore proposed to be an alternative solution for further development of high-energy-density batteries. Various techniques have been explored to synthesize the single-crystalline NMC product, but the fundamental mechanisms behind these techniques are still fragmented and incoherent. In this manuscript, we start a journey from the fundamental crystal growth theory, compare the crystal growth of NMC among different techniques, and disclose the key factors governing the growth of single-crystalline NMC. We expect that the more generalized growth mechanism drawn from invaluable previous works could enhance the rational design and the synthesis of cathode materials with superior energy density.

Kinetic and Thermodynamic Studies on Synthesis of Mg-Doped LiMn2O4 Nanoparticles

In this work, a first study on kinetics and thermodynamics of thermal decomposition for synthesis of doped LiMn₂O₄ nanoparticles is presented. The effect of Mg doping concentration on thermal decomposition of synthesis precursors, prepared by ultrasound-assisted Pechini-type sol–gel process, and its significance on nucleation and growth of Mg-doped LiMn₂O₄ nanoparticles was studied through a method based on separation of multistage processes in single-stage reactions by deconvolution and transition state theory. Four zones of thermal decomposition were identified: Dehydration, polymeric matrix decomposition, carbonate decomposition and spinel formation, and spinel decomposition. Kinetic and thermodynamic analysis focused on the second zone. First-order Avrami-Erofeev equation was selected as reaction model representing the polymer matrix thermal decomposition. Kinetic and thermodynamic parameters revealed that Mg doping causes an increase in thermal inertia on conversion rate, and CO₂ desorption was the limiting step for formation of thermodynamically stable spinel phases. Based on thermogravimetry experiments and the effect of Mg on thermal decomposition, an optimal two-stage heat treatment was determined for preparation of LiMg_xMn_2−xO₄ (x = 0.00, 0.02, 0.05, 0.10) nanocrystalline powders as promising cathode materials for lithium-ion batteries. Crystalline structure, morphology, and stoichiometry of synthesized powders were characterized by XRD, FE-SEM, and AAS, respectively.

In situ synthesis of a nickel concentration gradient structure of Ni-rich LiNi0.8Co0.15Al0.05O2 with promising superior electrochemical properties at high cut-off voltage

Nickel-rich layered cathode materials have aroused widespread interest due to their high discharge capacity, which is a basic requirement for next-generation high energy density lithium batteries. However, with the increase of nickel content, cathode materials face the serious challenge of capacity degradation, which is attributed to the formation of rock salt-type oxides such as NiO on the surface of cathode particles. To overcome this shortcoming, a novel Ni concentration gradient LiNi0.8Co0.15Al0.05O2 (NCG-NCA) cathode material was successfully synthesized using the characteristic reaction of Ni2+ and dimethylglyoxime. The final synthesized nickel concentration gradient material combines the advantages of high discharge capacity and excellent stability, which are attributed to the high nickel content in the core and high cobalt content on the surface of the material particles. The cycling stability of the NCG material is remarkably improved, exhibiting an excellent capacity retention of 75% after 200 cycles at a current density of 10C (1C = 160 mA g-1) under a high cut-off voltage of 4.5 V, much higher than that of a pristine NCA (P-NCA) cathode without NCG (50%). The excellent cycling stability of NCG-NCA is due to formation of a stable surface, which is not prone to serious atomic rearrangement on the surface. More importantly, with the structural analysis of NCA materials by neutron diffraction, we find that the proportion of Li/Ni mixing of NCA is reduced by utilizing the NCG structure; in turn, the rate performance of NCG-NCA cathode materials is improved greatly.

Hierarchical Fusiform Microrods Constructed by Parallelly Arranged Nanoplatelets of LiCoO2 Material with Ultrahigh Rate Performance

The past few decades have witnessed the unprecedented success of the commercialized LiCoO₂ layered cathode in consumer electronics, but it still faces the poor rate capability and cycling performance because of its hexagonal layered α-NaFeO₂ structure and the high energy of electrochemically active crystal planes. In a bid to address these problems, we report the delicate design and synthesis of hierarchical fusiform LiCoO₂ microrods constructed by directionally assembled nanoplatelets along the [001] direction via a self-template route (PAHF-LCO). Remarkably, it is the first time that almost all the exposed surfaces of layered cathodes are dominated by the consistent {010} facets, which enable the express channels of Li⁺ diffusion to penetrate throughout the entire fusiform microrods. The as-obtained PAHF-LCO cathode material delivers specific capacities of 113 and 106 mA h g^-1 at 10 and 20 C after 200 cycles, respectively. Even under the high rate of 50 C, the discharge capacity initializes around 105 mA h g^-1 and ends around 80 mA h g^-1 after 200 cycles. The improvement mechanisms to the high-rate performance through crystal habit tuning have also been unraveled. The enhanced electrochemical performance can be attributed to the hierarchical fusiform structure as well as the coordinated crystal orientation of {010} facets.

Crystal engineering for electrochemical applications

Welcome to this themed issue of CrystEngComm entitled: ‘Crystal engineering for electrochemical applications’.

In situ synthesis and electrochemical performance of MoO3-x nanobelts as anode materials for lithium-ion batteries

MoO_3-x nanobelts with different concentrations of oxygen vacancies were synthesized by a one-step hydrothermal process. XPS test results show that oxygen vacancies are distributed from the exterior to the interior of the MoO_3-x nanobelts. As an anode material for lithium-ion batteries, MoO_3-x-10 releases excellent rate capacitance. It can maintain a high specific capacitance of about 500 mA h·g^-1 at a high current density of 1000 mA·g^-1. In the aspect of cycling stability, MoO_3-x-10 can retain a high specific capacity of 641 mA h·g^-1 after cycling for 50 times at 100 mA·g^-1 and 420 mA h·g^-1 after cycling for 100 times at 500 mA·g^-1. The coexistence of oxygen vacancies and low-valence Mo ions is conducive to the intercalation/de-intercalation of Li ions and to promoting redox reactions. It has been proved to be a significantly effective way in which oxygen vacancies can improve the integrated performance of MoO_3-x nanobelts as anode materials.

Coordination-Induced Interlinked Covalent- and Metal-Organic-Framework Hybrids for Enhanced Lithium Storage

Covalent organic frameworks (COF) or metal-organic frameworks have attracted significant attention for various applications due to their intriguing tunable micro/mesopores and composition/functionality control. Herein, a coordination-induced interlinked hybrid of imine-based covalent organic frameworks and Mn-based metal-organic frameworks (COF/Mn-MOF) based on the MnN bond is reported. The effective molecular-level coordination-induced compositing of COF and MOF endows the hybrid with unique flower-like microsphere morphology and superior lithium-storage performances that originate from activated Mn centers and the aromatic benzene ring. In addition, hollow or core-shell MnS trapped in N and S codoped carbon (MnS@NS-C-g and MnS@NS-C-l) are also derived from the COF/Mn-MOF hybrid and they exhibit good lithium-storage properties. The design strategy of COF-MOF hybrid can shed light on the promising hybridization on porous organic framework composites with molecular-level structural adjustment, nano/microsized morphology design, and property optimization.

Hierarchical nanostructures derived from cellulose for lithium-ion batteries

Recent advances in natural cellulose substance derived hierarchical nanomaterials applied as anodic materials for lithium-ion batteries are summarized.