Lithium Storage Mechanism Research Articles

Fully sp2 Carbon-Conjugated Covalent Organic Frameworks with Multiple Active Sites for Advanced Lithium-Ion Battery Cathodes.

Covalent organic frameworks (COFs) hold great promise for rechargeable batteries. However, the synthesis of COFs with abundant active sites, excellent stability, and increased conductivity remains a challenge. Here, chemically stable fully sp2 carbon-conjugated COFs (sp2c-COFs) with multiple active sites are designed by the polymerization of benzo[1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarbaldehyde) (BTT) and s-indacene-1,3,5,7(2H,6H)-tetrone (ICTO) (denoted as BTT-ICTO). The morphology and structure of the COF are precisely regulated from "butterfly-shaped" to "cable-like" through an in situ controllable growth strategy, significantly promoting the exposure and utilization of active sites. When the unique "cable-like" BTT-ICTO@CNT is employed as lithium-ion batteries (LIBs) cathode, it exhibits exceptional capacity (396 mAh g-1 at 0.1 A g-1 with 97.9 % active sites utilization rate), superb rate capacity (227 mAh g-1 at 5.0 A g-1), and excellent cycling performance (184 mAh g-1 over 8000 cycles at 2.0 A g-1 with 0.00365 % decay rate per cycle). The lithium storage mechanism of BTT-ICTO is exhaustively revealed by in situ Fourier transform infrared, in situ Raman, and density functional theory calculations. This work provides in-depth insights into fully sp2c-COFs with multiple active sites for high-performance LIBs.

Fully sp2 Carbon‐Conjugated Covalent Organic Frameworks with Multiple Active Sites for Advanced Lithium‐Ion Battery Cathodes

AbstractCovalent organic frameworks (COFs) hold great promise for rechargeable batteries. However, the synthesis of COFs with abundant active sites, excellent stability, and increased conductivity remains a challenge. Here, chemically stable fully sp2 carbon‐conjugated COFs (sp2c‐COFs) with multiple active sites are designed by the polymerization of benzo[1,2‐b:3,4‐b′:5,6‐b′′]trithiophene‐2,5,8‐tricarbaldehyde) (BTT) and s‐indacene‐1,3,5,7(2H,6H)‐tetrone (ICTO) (denoted as BTT‐ICTO). The morphology and structure of the COF are precisely regulated from “butterfly‐shaped” to “cable‐like” through an in situ controllable growth strategy, significantly promoting the exposure and utilization of active sites. When the unique “cable‐like” BTT‐ICTO@CNT is employed as lithium‐ion batteries (LIBs) cathode, it exhibits exceptional capacity (396 mAh g−1 at 0.1 A g−1 with 97.9 % active sites utilization rate), superb rate capacity (227 mAh g−1 at 5.0 A g−1), and excellent cycling performance (184 mAh g−1 over 8000 cycles at 2.0 A g−1 with 0.00365 % decay rate per cycle). The lithium storage mechanism of BTT‐ICTO is exhaustively revealed by in situ Fourier transform infrared, in situ Raman, and density functional theory calculations. This work provides in‐depth insights into fully sp2c‐COFs with multiple active sites for high‐performance LIBs.

A cubic perovskite fluoride anode with the surface conversion reactions dominated mechanism for advanced lithium-ion batteries.

Perovskite fluorides are attractive anode materials for lithium-ion batteries (LIBs) because of their three-dimensional diffusion channels and robust structures, which is advantageous for the rapid transmission of lithium ions. Unfortunately, the wide band gap results in poor electronic conductivity, which limits their further development and application. Herein, the cubic perovskite iron fluoride (KFeF3, KFF) nanocrystals (~100 nm) are synthesized by a one-step solvothermal strategy. Thanks to the good electrical conductivity of carbon nanotubes (CNTs), the overall electrochemical performance of composite anode material (KFF-CNTs) has been significantly improved. In particular, the KFF-CNTs delives a high specific capacity (363.8 mAh g-1), good rate performance (131.6 mAh g-1 at 3.2 A g-1), and superior cycle stability (500 cycles). Noted that the surface conversion reactions play a dominant role in the electrochemical process of KFF-CNTs, together with the stable octahedral perovskite structure and nanoscale particle sizes achieving high ion diffusion coefficients. Furthermore, the specific lithium storage mechanism of KFF has explored by the distribution of relaxation times (DRT) technology. This work opens up a new way for developing cubic perovskite fluorides as high-capacity and robust anode materials for LIBs.

Anchored Bi with cobalt polyphthalocyanine enhances the reversibility of Bi2Te3 anode for endurable lithium-ion storage

As an intermetallic material, Bi2Te3 possesses great potential in lithium-ion batteries due to its attractive layered structure, intrinsic excellent conductivity and impressive theoretical specific capacity. However, the phase decomposition and the huge volume variation leading to rapid capacity fading hinder the further application of Bi2Te3 in lithium-ion batteries. In this study, two dimensional Bi2Te3 encapsulated in cobalt polyphthalocyanine (CoPPc) is synthesized by a facile recrystallization method, and its electrochemical properties and lithium storage mechanism are comprehensively studied. The Bi2Te3@CoPPc electrodes exhibit outstanding cycling stability with a specific capacity of 551.9 mAh g−1 at 100 mA g−1 and 628.5 mAh g−1 at 500 mA g−1 after 500 cycles, benefiting from the configured composite layered structure and the amiable interaction of Bi2Te3 and CoPPc. Our experimental and theoretic results demonstrate that the electron redistribution induced by the incorporation of CoPPc with charge accumulation around Bi2Te3 and low potential region around Co efficiently facilitates the fast lithium-ion transportation resulting in outstanding rate performance. Our explorative strategy of electron redistribution proposes a new avenue to enhance the catalysis activity and durability of alloy anodes in metal-ion batteries.

“Fast-charging” mechanism of Li3VO4 from the perspective of material science for lithium-ion battery

“Fast-charging” lithium-ion batteries enjoy extensive attention as energy storage devices for portable electronic devices and new energy vehicles. Regrettably, high safety could not be effectively ensured while the batteries undergo fast-charging process. Li3VO4 could be recognized as a high-safety “fast-charging” anode material considering its appropriate Li-insertion voltage and fast kinetic characteristics. Currently, notwithstanding the fact that Li3VO4 has been extensively investigated as an anode material for lithium-ion batteries and the encouraging research results have been accomplished, the distinction between ion diffusion mechanisms during fast-charging and slow-charging has not been well elucidated. Unlike previous reports, Li+ fast/slow diffusion mechanisms in Li3VO4 are investigated in detail in this work. Specifically, Li+ tends to diffuse along path a due to rather fast Li-insertion/deinsertion processes. Correspondingly, Li+ undergoes diffusion along path a and path b during slow-charging. Unlike the conventional view that Li+ prefers to diffuse along path a under all conditions. Additionally, the lattice changes of Li+ insertion into different sites are predicted. The findings could facilitate to comprehend the mechanism of doping, nanosizing, and other modification methods, and the fast-charging issue could be addressed in a targeted way. For instance, the optimal fast diffusion paths are modified at both atomic and lattice scales, inducing that Li+ could be inserted into the lattice of material faster during fast-charging and the power densities could be increased. Accordingly, understanding the fast diffusion mechanism of Li+ in Li3VO4 is crucial to addressing the “fast-charging” of these materials. Unfortunately, the inferior electronic conductivity restricts its Li-storage capacity in “fast-charging” devices. Herein, a Li3VO4 based anode material is prepared thorough a one-step hydrothermal method and liquid-phase dispersion technique in the existence of polyvinyl pyrrolidone, which demonstrates exceptional discharging and charging specific capacities, maintaining 273 mAh g−1 at 0.1 A g−1. It also presents considerably higher “fast-charging” performance even at 1.0–4.0 A g−1. Electrochemical kinetic studies indicate that the thin coating could improve the conductivity of Li3VO4. The Li-insertion sites and diffusion paths during fast-charging and slow-charging processes are predicted computationally. And the in-situ XRD is adopted to insight into the structural changes of composites during Li-insertion/deinsertion processes. The data furnishes a theoretical basis for comprehending the fast lithium storage mechanism of Li3VO4 and offers a new method for searching for “fast-charging” anode materials.

An innovative double-Shell layer nitrogen and sulfur co-doped carbon-Encapsulated FeS composite for enhanced lithium-Ion battery performance

FeS, with its high theoretical capacity and natural abundance, holds significant promise as an anode material for lithium-ion batteries (LIBs). However, its practical application is constrained by poor electrical conductivity and substantial volume expansion during cycling, which impair charge–discharge efficiency and cycling stability. To overcome these challenges, we developed a nitrogen and sulfur co-doped carbon-encapsulated FeS composite with a hollow double-layer structure (HDL-FeS@NSC). Utilizing sulfur spheres as a sacrificial template, our inside-out synthesis strategy produces a unique material design. The HDL-FeS@NSC composite exhibits significant improvements in electrochemical performance compared to pure FeS. These enhancements are due to its increased specific surface area, which facilitates lithium-ion diffusion; a shortened Li+ diffusion pathway; structural stability that mitigates volume expansion; and an optimized carbon layer that boosts conductivity. The HDL-FeS@NSC-70 anode demonstrates a specific capacity of 879.6 mAh/g after 600 cycles at 1.0 A/g and retains 558.0 mAh/g at 5.0 A/g. Additionally, the lithium storage mechanism has been thoroughly investigated using in-situ techniques. These results suggest that the HDL-FeS@NSC composite anode has the potential to significantly enhance lithium-ion battery performance, offering a promising solution for next-generation energy storage systems.

Introducing surface adsorption lithium storage mechanism to enhance safety of graphite

The thermal stability of lithiated graphite plays an important role in the thermal safety of lithium-ion batteries (LIBs). However, a safer graphite anode usually leads to a lower energy density. This article starts from multiple hazardous factors of lithiated graphite when thermal runaway occurs, considering the impact of defects on the electrochemical performance and thermal safety of graphite electrodes. In this study, turbostratic graphite was prepared as the anode for LIBs. The stacking of graphite was altered to form narrow pores and spherical aggregates, and introducing defects. By varying the ball-milling time, the structural changes of different ball-milled graphites were analyzed. The impact mechanism of defect structure on electrode electrochemical performance and safety performance was investigated. The results show that the spherical structure and large specific surface area are beneficial to increase the active sites and delay the self-heating of the battery. The formation of defects and pores increases the adsorption sites, which makes the surface adsorption of Li+ dominant and improves the ion diffusion. In addition, the dominance of surface adsorption and desorption effectively suppresses the problem of graphite flake peeling and intensified thermal runaway caused by graphite phase transition and lithium evolution heat release at high temperature. The thermal safety test was carried out by accelerated calorimeter (ARC), and its thermodynamics and reaction kinetics were quantitatively analyzed. It was proved that the introduction of surface adsorption lithium storage method successfully delayed the thermal runaway of the battery, realizing the balance between high electrochemical performance and high safety.

Synergetic effects of S, N co-doping and surface concave-pores rich in lotus-leaf-like carbon nanosheets enabled threefold lithium storage mechanisms

Carbon-based materials based on structural and dimensional optimization are appealing as anode materials in lithium-ion batteries (LIBs). However rational design of high-efficiency low-dimensional carbon-based electrodes is still challenging. Therefore, a synthesis strategy based on Schiff base reaction has been devised for S, N co-doped and surface-enriched concave pores coupled with two-dimensional lotus-leaf-like carbon nanosheets (S, N-SCP/LCN). Experimental and theoretical results disclose that the synergetic effect of S, N co-doping and surface concave pores synergistically contribute to the improved lithium storage efficiency. The numerous concave pores within the defective carbon substrates significantly enhance the specific surface area and boost the quantity of active sites. Furthermore, S, N co-doping induces additional surface and structural defects and widens the crystallographic spacing. Herein, the formed threefold lithium storage mechanisms work synergistically to increase the active lithium storage sites and ion diffusion channels, promoting ion diffusion and charge transfer during lithium storage. As expected, the S, N-SCP/LCN exhibits remarkably high lithium storage capacity (1250 mAh/g at 0.1 A/g) and exceptional rate performance (445.65 mAh/g at a high rate of 10 A/g).

A Review of Design Strategies in SiO/C Composite Anodes for Rechargeable Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) are widely used in electric vehicles, portable electronic devices, clean energy storage, and other fields due to their long service life, high energy density, and low self-discharge rate, which also puts forward higher requirements for the performance of lithium-ion batteries. As an anode for lithium-ion batteries, SiO materials have garnered significant attention from researchers due to its high specific capacity (2400 mAh g-1), abundance of raw materials, and simple preparation. However, its large volume change (~200 %) and poor electrical conductivity hinder its large-scale commercial application. Researchers employ various methods to reduce the volume change of SiO during lithium intercalation and improve its structural stability during cycling. This work mainly reviews the chemical structure and lithium storage mechanism of SiO, as well as the latest research progress on the preparation methods of SiO/C anode materials, focusing on summarizing the following preparation strategies: chemical vapor deposition, mechanical ball milling, spray drying, and in-situ reduction/oxidation methods. The obtained SiO-based anode materials' structural characteristics and electrochemical properties are compared and summarized. Finally, this review discusses the advantages and disadvantages of the current preparation methods, the future research directions, and the development prospects of SiO-based anode materials.

Phase Transitions and Ion Transport in Lithium Iron Phosphate by Atomic‐Scale Analysis to Elucidate Insertion and Extraction Processes in Li‐Ion Batteries

AbstractLithium iron phosphate (LiFePO4, LFP) serves as a crucial active material in Li‐ion batteries due to its excellent cycle life, safety, eco‐friendliness, and high‐rate performance. Nonetheless, debates persist regarding the atomic‐level mechanisms underlying the electrochemical lithium insertion/extraction process and associated phase transitions. A profound clarity on the fundamental lithium storage mechanisms within LFP is achieved through meticulous scanning transmission electron microscopy (STEM) and selected area electron diffraction (SAED) imaging. This study shows systematical tracking of lithium ions within their respective channels and unveils the phase distribution within individual LFP crystallites not only quantitatively but also at unprecedented atomic‐level resolution. Incontrovertible evidence of the co‐existence of segregated yet only partially lithiated LixFePO4 regions in electrochemically delithiated LFP crystals are provided using correlative electron microscopic methods and data analysis. Remarkably, by directly tracing ion transport within lithium channels a diffusion coefficient range (10−13–10−15 cm2s−1) for correlated lithium ion motion in LFP is estimated and Funke's ion transport jump relaxation model is validated experimentally for the first time. These findings significantly advance the understanding of olivine‐type materials, offering invaluable insights for designing superior battery materials.

Tailoring and understanding the lithium storage performance of triple-doped cobalt phosphide composites

Cobalt phosphide (CoP) with high theoretical capacity as well as ceramic-like and metal-like properties is considered as a promising anode for lithium-ion batteries (LIBs). However, the large volume change and sluggish kinetic response limit its practical application. The optimization of composition, structural control and performance regulation of CoP electrodes can be achieved by the bottom-up assembly technique of metal–organic frameworks (MOFs). Due to the effective electronic regulation and lithiophilicity brought by the multiple heteroatoms doping and the synergistic effect of the unique structure derived from MOFs, the N, O, P triple-doped carbon and CoP composites (ZCP@NOP) exhibited excellent rate capability (554.61 mAh g−1 at 2 A g−1) and cycling stability (806.7 mAh g−1 after 500 cycles at 0.5 A g−1). The essence and evolution of lithium storage mechanism in CoP electrodes are also confirmed by the ex-situ techniques. The synergistic benefits of heteroatom co-doping carbon and cobalt phosphide, such as the decrease of the diffusion energy barrier of Li-ions and the optimization of electronic structures, are highlighted in theoretical calculations. In conclusion, new thoughts and ideas for the creation of future battery anode are provided by the combination of the N, O, P co-doping and the adaptable structural adjustment technique.

The Lithium Storage Mechanism of Zero-Strain Anode Materials with Ultralong Cycle Lives.

At present, graphite is a widely used anode material in commercial lithium-ion batteries for its low cost, but the large volume expansion (about 10%) after fully lithiated makes the material prone to cracking and even surface stripping in the cycle. Therefore, the development of zero-strain anode materials (volume change <1%) is of great significance. LiAl5O8 is a zero-strain insertion anode material with a high theoretical specific capacity. However, the Li+ storage mechanism remains unclear, and the cycle life as well as fast-charging capability need to be greatly improved to meet the practical requirements. In this study, LiAl5O8 nanorods are prepared by utilizing aluminum ethoxide nanowires as a soft template and doped with the Zr element to further improve the Li+ diffusion coefficient and electronic conductivity, which in turn improves cycle and rate performances. The Zr-doped LiAl5O8 presents a high reversible capacity of 227.2 mAh g-1 after 20,000 cycles under 5 A g-1, which significantly outperforms the state-of-the-art anode materials. In addition, the Li+ storage mechanisms of LiAl5O8 and Zr-doped LiAl5O8 are clearly clarified with a variety of characterization techniques including nuclear magnetic resonance. This work greatly promotes the practical process of zero-strain insertion anode materials.

Outstanding Lithium Storage Performance of a Copper‐Coordinated Metal‐Covalent Organic Framework as Anode Material for Lithium‐Ion Batteries

Metal‐covalent organic frameworks (MCOF) as a bridge between covalent organic framework (COF) and metal organic framework (MOF) possess the characteristics of open metal sites, structure stability, crystallinity, tunability as well as porosity, but still in its infancy. In this work, a covalent organic framework DT‐COF with a keto‐enamine structure synthesized from the condensation of 3,3′‐dihydroxybiphenyl diamine (DHBD) and triformylphloroglucinol (TFP) was coordinated with Cu2+ by a simple post‐modification method to a obtain a copper‐coordinated metal‐covalent organic framework of Cu‐DT COF. The isomerization from a keto‐enamine structure of DT‐COF to a enol‐imine structure of Cu‐DT COF is induced due to the coordination interaction of Cu2+. The structure change of Cu‐DT COF induces the change of the electron distribution in the Cu‐DT COF, which greatly promotes the activation and deep Li‐storage behavior of the COF skeleton. As anode material for lithium‐ion batteries (LIBs), Cu‐DT COF exhibits greatly improved electrochemical performance, retaining the specific capacities of 760 mAh g−1 after 200 cycles and 505 mAh g−1 after 500 cycles at a current density of 0.5 A g−1. The preliminary lithium storage mechanism studies indicate that Cu2+ is also involved in the lithium storage process. A possible mechanism for Cu‐DT COF was proposed on the basis of FT‐IR, XPS, EPR characterization and electrochemical analysis. This work enlightens a novel strategy to improve the energy storage performance of COF and promotes the application of COF and MCOF in LIBs.

Phase Evolution of Multi-Metal Dichalcogenides With Conversion-Alloying Hybrid Mechanism for Superior Lithium Storage.

Traditional lithium-ion battery (LIB) anodes, whether intercalation-type like graphite or alloying-type like silicon, employing a single lithium storage mechanism, are often limited by modest capacity or substantial volume changes. Here, the kesterite multi-metal dichalcogenide (CZTSSe) is introduced as an anode material that harnesses a conversion-alloying hybrid lithium storage mechanism. Results unveil that during the charge-discharge processes, the CZTSSe undergoes a comprehensive phase evolution, transitioning from kesterite structure to multiple dominant phases of sulfides, selenides, metals, and alloys. The involvement of multi-components facilitates electron transport and mitigates swelling stress; meanwhile, it results in formation of abundant defects and heterojunctions, allowing for increased lithium storage active sites and reduced lithium diffusion barrier. The CZTSSe delivers a high specific capacity of up to 2266mA h g-1 at 0.1 A g-1; while, maintaining a stable output of 116mA h g-1 after 10000 cycles at 20 A g-1. It also demonstrates remarkable low-temperature performance, retaining 987mA h g-1 even after 600 cycles at -40°C. When employed in full cells, a high specific energy of 562Wh kg-1 is achieved, rivalling many state-of-the-art LIBs. This research offers valuable insights into the design of LIB electrodes leveraging multiple lithium storage mechanisms.

High-Energy Symmetric Li-Ion Battery Enabled by Binder-Free FeOF-MXene Heterostructure with Doubly Matched Capacity and Kinetics.

Fluorides are viewed as promising conversion-type Li-ion battery cathodes to meet the desired high energy density. FeOF is a typical member of conversion-type fluorides, but its major drawback is sluggish kinetics upon deep discharge. Herein, a heterostructured FeOF-MXene composite (FeOF-MX) is demonstrated to overcome this limitation. The rationally designed FeOF-MX electrode features a microsphere morphology consisting of closely packed FeOF nanoparticles, providing fast transport pathways for lithium ions while a continuous wrapping network of MXene nanosheets ensures unobstructed electron transport, thus enabling high-rate lithium storage with enhanced pseudocapacitive contribution. In/ex situ characterization techniques and theoretical calculations, both reveal that the lithium storage mechanism in FeOF arises from a hybrid intercalation-conversion process, and strong interfacial interactions between FeOF and MXene promote Li-ion adsorption and migration. Remarkably, through demarcating the conversion-type reaction with a controlled potential window, a symmetric full battery with prelithiated FeOF-MX as both cathode and anode is fabricated, achieving a high energy density of 185.5Whkg-1 and impressive capacity retention of 88.9% after 3000 cycles at 1Ag-1. This work showcases an effective route toward high-performance MXene engineered fluoride-based electrodes and provides new insights into constructing symmetric batteries yet with high-energy/power densities.

Insight of the evolution of structure and energy storage mechanism of (FeCoNiCrMn)3O4 spinel high entropy oxide in life-cycle span as lithium-ion battery anode

Recently, spinel high-entropy oxide (HEO) anode materials have garnered extensive attention for high-energy lithium-ion batteries due to their high specific capacity. Many studies have explored its energy storage mechanism, but few have paid attention to its characteristics in long cycle life. In this work, the whole life cycling performance of (FeCoNiCrMn)-HEO is presented and investigated for the first time. Distinct capacity trends are studied to divide the cycling life into three stages: activation, upgradation, and degradation. Ex situ morphological characterizations are conducted to reveal that the driving force of stage change is continuous particle fragmentation. As a result, refined particles promote conversion reaction reversibility and induce extra interfacial capacity, achieving 2831 mAh g−1 at 825 cycles. Density functional theory (DFT) calculations provide a deeper insight into the high entropy effect on the ultra-high extra interfacial capacity. However, continuous refinement brings about huge electrolyte interface-derived layers, which are also responsible for pre-decay and post-collapse. The view of the evolution of the lithium storage mechanism is explicitly presented and experimentally verified by high-energy ball milling and fluorinated vinyl carbonate (FEC). These above results can give practical solutions to design high specific capacity and long-life cycle stability HEO anode in the future.

Porous High-Entropy Oxide Anode Materials for Li-Ion Batteries: Preparation, Characterization, and Applications.

High-entropy oxides (HEOs), as a new type of single-phase solid solution with a multi-component design, have shown great potential when they are used as anodes in lithium-ion batteries due to four kinds of effects (thermodynamic high-entropy effect, the structural lattice distortion effect, the kinetic slow diffusion effect, and the electrochemical "cocktail effect"), leading to excellent cycling stability. Although the number of articles on the study of HEO materials has increased significantly, the latest research progress in porous HEO materials in the lithium-ion battery field has not been systematically summarized. This review outlines the progress made in recent years in the design, synthesis, and characterization of porous HEOs and focuses on phase transitions during the cycling process, the role of individual elements, and the lithium storage mechanisms disclosed through some advanced characterization techniques. Finally, the future outlook of HEOs in the energy storage field is presented, providing some guidance for researchers to further improve the design of porous HEOs.

Solvent-free synthesis of polytriazine-bithiophene for excellent lithium/sodium-ion storage

A conjugated microporous polymer (CMP) combining triazine and bithiophene units in the same framework is synthesized by a facile solvent-free one-pot method and employed as an anode material for lithium/sodium-ion batteries (LIBs/SIBs). It exhibits a large rate capability with a high reversible capacity for LIBs after activation, e.g., 1014 mAh g−1 at 0.1 A g−1 and 486 mAh g−1 at a current density of 5 A g−1 with outstanding cycling stability. Meanwhile, it delivers perfect electrochemical properties for SIBs, featuring high reversible specific capacities of 425/260/156 mAh g−1 at 0.1/1/5 A g−1. Especially, the CMP even outstrips most crystalline covalent organic frameworks (COFs) as SIB anodes at high current density. The lithium and sodium storage mechanisms of the CMP structural unit involve 11-electron redox reactions with four and three-step structure evolutions respectively, as follows from density functional theory calculations. The reported study demonstrates the CMP with redox-active electron donating units via triazine bonding as a promising electrode material for next-generation green sustainable energy storage devices.

Steering lithium and potassium storage mechanism in covalent organic frameworks by incorporating transition metal single atoms

Organic electrodes mainly consisting of C, O, H, and N are promising candidates for advanced batteries. However, the sluggish ionic and electronic conductivity limit the full play of their high theoretical capacities. Here, we integrate the idea of metal-support interaction in single-atom catalysts with π-d hybridization into the design of organic electrode materials for the applications of lithium (LIBs) and potassium-ion batteries (PIBs). Several types of transition metal single atoms (e.g., Co, Ni, Fe) with π-d hybridization are incorporated into the semiconducting covalent organic framework (COF) composite. Single atoms favorably modify the energy band structure and improve the electronic conductivity of COF. More importantly, the electronic interaction between single atoms and COF adjusts the binding affinity and modifies ion traffic between Li/K ions and the active organic units of COFs as evidenced by extensive in situ and ex situ characterizations and theoretical calculations. The corresponding LIB achieves a high reversible capacity of 1,023.0 mA h g-1 after 100 cycles at 100 mA g-1 and 501.1 mA h g-1 after 500 cycles at 1,000 mA g-1. The corresponding PIB delivers a high reversible capacity of 449.0 mA h g-1 at 100 mA g-1 after 150 cycles and stably cycled over 500 cycles at 1,000 mA g-1. This work provides a promising route to engineering organic electrodes.

Mesocrystallinely stabilized lithium storage in high-entropy oxides

High-entropy oxides (HEOs) have received growing recognition as an anode candidate for lithium-ion batteries, primarily attributed to their decent lithium storage capabilities and high cycling durability. However, the underlying lithium storage mechanism of HEOs remains ambiguous, particularly the origins for their high structural stability, necessitating more comprehensive investigations. In this research, the working mechanisms of one representative HEO anode, the rock salt-structured Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, are explored via state-of-the-art in-situ characterizations. Findings point to an interesting mesocrystal-stabilized lithium-ion storage mechanism responsible for maintaining the structural stability of HEOs during cycling, where, upon lithiation, Mg2+ remains electrochemically inactive within the oxygen lattice to stabilize the overall oxide framework. Co and Zn can be reversibly reduced/oxidized upon (de)lithiation, contributing to the electrochemical capacity; while for Cu and Ni, once reduced to metallic state under a relatively high current density, could not be re-oxidized but interconnect to form an electron-conductive network through the HEO body, contributing for the decent lithium-storage performance. Such feature depends on the applied current density, i.e. when decreasing the current, Ni regains its redox capability upon cycling with only Cu0 sustaining the conductive metallic network. This work is expected to serve as a benchmark for structurally and compositionally designing the next-generation high-entropy electrode materials for lithium storage.