High Reversible Capacity Research Articles

Internal Electron Donor Accelerated Sulfur Redox for Aqueous Zn─S Batteries

AbstractImproving the electrical conductivity of sulfur cathode while ensuring its high affinity to catalyst holds the key to facilitate the reaction kinetics of aqueous zinc–sulfur batteries. Herein, the sulfur redox in aqueous electrolyte is accelerated by introducing selenium–sulfur bonds into the sulfur structure to build an internal electron transport path. The Se with less electronegativity can act as an electron donor to accelerate the binding between S and Zn2+. Meanwhile, the bonded Se in the electron‐poor state endows the modified sulfur cathode with a strong affinity to the I3− catalyst, which further facilitates the conversion efficiency. Thus, the internal electron donor assisted sulfur cathode delivers excellent electrochemical performance in terms of high reversible capacity (1490 mAh g−1 at 0.5 A g−1), competitive rate performance (1010 mAh g−1 at 4 A g−1), as well as outstanding cycle stability (735 mAh g−1 at 4 A g−1 after 500 cycles).

Ice template-induced assembly coupled with carbonization strategy for preparation of sulfur-doped porous carbon nanosheets from lignite as high-capacity anode for lithium-ion batteries

Two-dimensional (2D) porous carbon nanosheets with heteroatom doping are promising anode materials for lithium-ion batteries (LIBs) due to their distinctive sheet-like structure and excellent electrical conductivity. Limited by high preparation costs and cumbersome preparation processes, the large-scale production of carbon nanosheets remains a major challenge. Herein, a series of sulfur-doped porous carbon nanosheets (SCNSs) are successfully synthesized through ice template-induced assembly coupled with a carbonization approach using aromatic ring fragments exfoliating from lignite as the precursor and K2SO4 as the sulfur source. The prepared SCNSs exhibit well-defined sheet-like structures, abundant hierarchical nanopores, large specific surface areas (∼1761 m2·g−1), and high sulfur doping contents (∼7.72 at%). Such unique microstructure characteristics of SCNSs not only provide favorable and efficient channels for the lithium-ions/electrons transportation but also offer sufficient available space or active sites for lithium-ions storage. When used as anode materials for LIBs, the SCNS-3 shows high reversible capacity (1620 mAh·g−1 at 0.05 A·g−1), excellent rate performance (315 mAh·g−1 at 2 A·g−1), and superior cycling stability (901 mAh·g−1 at 1 A·g−1 after 500 cycles). Lithium storage behavior analysis indicated that the capacitance enhancement in SCNSs anodes is primarily due to improved capacitive behavior. This study provides a novel and effective route for the large-scale production of sulfur-doped carbon nanosheets using aromatic ring fragments exfoliated from lignite, which demonstrates promising industrial application potential in LIBs anode materials.

Intercalation-Induced Localized Conversion Reaction in h-CuSe for Ultrafast-Rechargeable and Long-Cycling Sodium Metal Battery.

Cathode materials of sodium-based batteries with high specific capacity and fast charge-discharge mode, as well as ultralong reversible cycles at wide applied temperatures, are essential for future development of advanced energy storage system. Developing transition metal selenides with intercalation features provides a new strategy for realizing the above cathode materials. Herein, this work reports a storage mechanism of sodium ion in hexagonal CuSe (h-CuSe) based on the density functional theory (DFT) guidance. This work reveals that the two-dimensional ion intercalation triggers localized redox reaction in the h-CuSe bulk phase, termed intercalation-induced localized conversion (ILC) mechanism, to stabilize the sodium storage structure by forming localized Cu7Se4 transition phase and adjusting the near-edge coordination state of the Cu sites to achieve high reversible capacity and ultra-long cycling life, while allowing rapid charge-discharge cycling over a wide temperature range.

Constructing ZnSe/CoSe2/N-doped carbon composite with multiple heterointerfaces using a solvent-assisted strategy to enhance lithium storage

Interface engineering, as an effective strategy for preparing high power density and long-life battery anodes, can promote the electrochemical performance of materials. Herein, metal organic frameworks (MOFs) derived N-doped carbon nanosheets loaded nanoscale ZnSe/CoSe2 particle composite with multiple heterointerfaces is fabricated by solvent assisted strategy. Wherein the content of water in the solvent is a key factor in establishing a homogeneous heterojunction containing cubic phase CoSe2 (c-CoSe2) and orthorhombic phase CoSe2 (o-CoSe2). The built-in electric field generated by the energy band gap difference between ZnSe and CoSe2 or c-CoSe2 and o-CoSe2, and a strong interaction between ZnSe/CoSe2 particles and N-doped carbon nanosheets, can reduce the migration barrier of Li+ at the interface, accelerate charge transfer, and promote the lithium storage kinetic process. In addition, nanoscale ZnSe/CoSe2 particles coupled with N-doped carbon nanosheets can also generate more active sites, reduce volume expansion, and maintain the structural integrity of the anode material. Based on the above structural advantages, the prepared ZnSe/CoSe2-3# exhibits a high reversible capacity (1188 mAh g−1 after 280 cycles at 0.5 A g−1), and excellent long-term cycling stability (788 mAh g−1 at 1 A g−1 over 600 cycles).

Fully carbonate‐electrolyte‐based high‐energy‐density Li–S batteries with solid‐phase conversion

AbstractCarbonate‐electrolyte‐based lithium–sulfur (Li–S) batteries with solid‐phase conversion offer promising safety and scalability, but their reversible capacities are limited. In addition, large‐format pouch cells are paving the way for large‐scale production. This study demonstrates the in situ formation of a solid‐electrolyte interphase (SEI) as a protective layer using vinylene carbonate (VC), highlighting its industrial adaptability. A high reversible capacity is achieved by the lithiated poly‐VC SEI formed inside the cathode particles as a nanoscale ionic conduction path, along with the traditional surface protective layer. Furthermore, the severe dissolution of poly‐VC is mitigated by LiF derived from fluorine ethylene carbonate as a co‐solvent, enabling high rate performance and a long cycle life. A large 8 Ah pouch cell is successfully developed, which shows a high energy density of 400 Wh kg−1 based on the cell weight. This work demonstrates the high performance of large‐scale Li–S batteries with the in situ formation of a protective layer as a scalable technique for future applications.

To DISP or Not? The Far‐Reaching Reaction Mechanisms Underpinning Lithium‐Air Batteries

AbstractThe short history of research on Li−O2 batteries has seen a remarkable number of mechanistic U‐turns over the years. From the initial use of carbonate electrolytes, that were then found to be entirely unsuitable, to the belief that (su)peroxide was solely responsible for degradation, before the more reactive singlet oxygen was found to form, to the hypothesis that capacity depends on a competing surface/solution mechanism before a practically exclusive solution mechanism was identified. Herein, we argue for an ever‐fresh look at the reported data without bias towards supposedly established explanations. We explain how the latest findings on rate and capacity limits, as well as the origin of side reactions, are connected via the disproportionation (DISP) step in the (dis)charge mechanism. Therefrom, directions emerge for the design of electrolytes and mediators on how to suppress side reactions and to enable high rate and high reversible capacity.

DISP oder nicht? Die weitreichenden Reaktionsmechanismen, die den Lithium‐Luft‐Batterien zugrunde liegen

AbstractIn der kurzen Geschichte der Forschung an Li−O2‐Batterien gab es im Laufe der Jahre eine bemerkenswerte Anzahl mechanistischer Kehrtwendungen. Von der anfänglichen Verwendung von Karbonat‐Elektrolyten, die sich dann als völlig ungeeignet erwiesen, über die Annahme, dass (Su)Peroxid allein für die Degradation verantwortlich sei, bevor man feststellte, dass sich der reaktivere Singulett‐Sauerstoff bildet, bis hin zu der Hypothese, dass die Kapazität von einem konkurrierenden Oberflächen‐/Lösungsmechanismus abhängt, bevor ein praktisch ausschließlicher Lösungsmechanismus identifiziert wurde. Wir plädieren hier für einen immer neuen Blick auf die vorliegenden Daten ohne Voreingenommenheit gegenüber vermeintlich etablierten Erklärungen. Wir erläutern, wie die neuesten Erkenntnisse über Raten‐ und Kapazitätsgrenzen sowie die Entstehung von Nebenreaktionen über den Disproportionierungsschritt (DISP) im (Ent‐)Ladungsmechanismus miteinander verbunden sind. Daraus ergeben sich Hinweise für das Design von Elektrolyten und Mediatoren, wie Nebenreaktionen unterdrückt und hohe Raten und hohe reversible Kapazitäten ermöglicht werden können.

Nanoconfined Strategy Optimizing Hard Carbon for Robust Sodium Storage

AbstractDeveloping non‐graphitic carbons with unique microstructure is a popular strategy to enhance the significant potential in practical applications of sodium‐ion batteries (SIB), while the electrochemical performance imbalances arising from their intricate active surface and porous structure pose significant challenges to its commercialization. Inspired by the structure of biological cell membranes, N/P co‐doped hard carbon nanospheres (NPCS) anodes with abundant ultramicropores (≈0.6 nm) are proposed and synthesized as robust sodium anodes. Based on density functional theory calculations, optimizing ultramicropores can enable small Na+ to be well confined within the pores and hinder large solvent molecules from invading and reacting, introducing N/P species contributes to the rapid adsorption/diffusion of Na+. In situ XRD and Raman analysis suggest that the nanoconfinement strategy induced by abundant ultramicropores and N/P co‐doping enables highly reversible electrochemical reactions. Electrochemical test confirms that the nanoconfinement strategy endows the NPCS anode with high reversible capacity (376.3 mAh g−1 at 0.1 A g−1), superior initial coulombic efficiency (87.3% at 1.0 A g−1), remarkable rate capability (155.6 mAh g−1 at 50.0 A g−1) and excellent cycling stability (with capacity retention of ≈94.6% after 10 000 cycles), lightening a promising avenue for developing SIB with robust durability.

Boosting anions storage via union of in-situ N doping and mesoporous hollow hard carbon nanospheres for advanced dual-ion capacitors

High structural strength in-situ N-doped mesoporous hollow hard carbon nanospheres (NMHS) is prepared to overcome the low anions storage capacity (93 mAh g−1) of easy exfoliated graphite for dual-ion capacitors (DICs). The rich mesoporous structure facilitates the anions diffusion, and the hollow cavity provides expansion space in storage and weakens the high diffusion resistance in the nuclear bulge. With the synergistic effect, The NMHS delivers a high reversible capacity of 100 mAh g−1 with a low decay of 8 % over 5000 cycles at 2 A g−1. In-situ Raman reveals the storage mechanism on hard carbon is “adsorption (major)-intercalation (minor)”. DFT calculations decode the effective storage action of graphitic N and pyridinic N. Consequently, the assembled NMHS-DICs exhibit good long-cycle performance and heterotherm stability, providing a high energy/power density of 200 Wh kg−1 and 11858 W kg−1. This work verifies a feasible cathode design strategy with future application potential on DICs.

Polyaniline layered N-doped carbon-coated iron oxide nanocapsules for extremely active Li-ion battery anode and oxygen evolution reaction

We report the effective synthesis of polyaniline (PANi)-layered nitrogen-doped carbon-coated Fe3O4 (FNC@PANi) nanocapsules (NCs) for electrocatalysis of oxygen evolution reaction (OER) as well as anode material for lithium (Li)-ion batteries (LIBs) via a simple hydrothermal method and oxidative polymerization technique. The prepared FNC@PANi NCs revealed a dual core-shell structure, in which an intermediate carbon layer allowed excellent electrical conduction between the Fe3O4 NCs and PANi. The dual core-shell structure also allowed the Fe3O4 NCs to expand freely during the Li-ion insertion/extraction and OER processes without breaking the outer layer, thus providing a high surface area (147.85 m2 g−1) and enhanced electrical conductivity. These properties facilitate the application of the dual core-shell FNC@PANi NCs as an advanced electrode material for LIBs, delivering a high reversible specific capacity of 1556.48 mAh g−1 at 0.1 A g−1, excellent rate performance (896.96 mAh g−1 at 1 A g−1), and durable cycling life (680.12 mAh g−1 at 5 A g−1 for 3000 cycles). The dual core-shell FNC@PANi NCs exhibited high electrocatalytic activity in the OER, with a small Tafel slope of 108.7 mV dec−1 owing to synergistic effects between the copious active sites of the Fe3O4 NCs and the carbon core-shell structure and a modest overpotential of 219 mV at 10 mA cm−2. The electrodes showed excellent stability over 10 h, as determined by chronopotentiometry at 10 mA cm−1. The resultant dual-core-shell FNC@PANi NCs are efficient iron-oxide-based electrode materials for LIBs and OER electrocatalysts.

Coupling effect of defects and enriched adsorption sites in bimetal-MOF derived porous carbonaceous anode for high-performance lithium-ion capacitor

Lithium-ion capacitors (LICs) have attracted considerable attention for their ability to combine the high energy characteristics of lithium-ion batteries and the high power densities of supercapacitors. However, the development of LICs still faces critical challenges. Herein, a robust bimetal-MOF derived fluorine and nitrogen co-doped hierarchical porous carbon embedding with Co nanoparticles anode materials (Co@NFC-800) for LICs are developed, which combined with the advantages of amplified interlayer, enriched active sites and improved electrical conductivity. Both theoretically and experimentally results demonstrate that such advantaged structure via fluorine doping to introduce defects and regulate doped nitrogen atom configuration to enrich Li+ adsorption sites and enhance diffusion kinetics synergistically is attempted. Co@NFC-800 deliveres a high reversible capacity and excellent long cycling stability as anode in LIBs, By coupling the Co@NFC-800 anode with commercial activated carbon (AC) cathode, the assembled LICs deliver a high specific energy of 164 Wh kg−1 at 162.9 W kg−1 and maintained to 68.3 Wh kg−1 even at high specific power of 9.1 kW kg−1 as well as long cycling stability (80.2 % over 2000 cycles).The fluorine doping induced both enriched defects and regulable nitrogen atom configuration strategy opens up a new way of carboneous materials for lithium storage.

Controllable Synthesis of Sub‐10 nm ZnS Nanograins Confined in Micro‐Size Carbon Skeleton for Aqueous Zn–S Batteries

AbstractAqueous zinc–sulfur battery (AZSB) is a promising technology for energy storage, but its practical application is severely limited by the sluggish redox kinetics and large volume expansion of the sulfur cathode. Herein, the controllable synthesis of sub‐10 nm ZnS nanograins confined in micro‐size carbon skeleton (MN‐ZnS/C─H) and its application as the cathode for AZSB is reported. It is revealed that the carbon source, polyvinylpyrrolidone (PVP), can weakly coordinate with Zn2+ and provide a physical confinement for inhibiting the agglomeration of ZnS nanograins during the calcination process. Moreover, the particle size of ZnS (from sub‐10 to 350 nm) and the shape of ZnS/carbon composite (from bulk to sphere) can be well controlled by tuning the chain length of PVP. In the unique hierarchical structure, the ZnS nanograins can provide an optimized ion transmission path, and the micro‐size carbon network not only ensures high electronic conductivity but also maintains structure integrity upon volume variation, endowing the MN‐ZnS/C─H electrode with a high reversible capacity of 370 mA h g−1 at 0.2 A g−1, high rate capability of 209 mA h g−1 at 4 A g−1, and a long lifespan of 210 cycles with 93.2% capacity retention at 2 A g−1.

Exploring the Effect of TiO2 Coating on Na0.85Li0.12Ni0.22Mn0.66O2 Cathode Materials for Na-Ion Batteries

Layered transition metal oxides have great potential as cathode materials for sodium ion batteries, but some limitations like structural instability and poor rate performance restricts its further application. To overcome the above issues, a simultaneously modified P2-type cathode of Na0.85Li0.12Ni0.22Mn0.66O2 with 1% weight TiO2 coating (NLNMO-1%wt TiO2) based on doping and coating approaches was prepared by high-temperature solid-state reaction and liquid phase coating. This new strategy reduces the relative content of Mn3+, which suppresses the Jahn-Teller effect and enhanes the structural stability. The as-prepared cathode shows improved rate capability, with a high reversible capacity of 111.4 mAh g−1 at 1 C and a capacity retention of 94.5% after 100 cycles. At 5 C, it maintains a capacity of 87.1 mAh g−1 at 5 C with capacity retention of 81.8% after 400 cycles. Additionally, it provides a stable CEI film, reducing side reactions and electrode pulverization. which could be confirmed by scanning electron microscopy and high-resolution transmission electron microscopy. Overall, this synergistic modification strategy provides a pathway for improving the electrochemical performance of layered oxide cathode materials for sodium-ion batteries.

Constructing stable electrode–electrolyte interfaces by sulfone-based additive to improve the high-voltage performance of LiCoO2

LiCoO2 battery can provide high reversible capacity at a high voltage of 4.6 V, however, maintaining its stability at high voltages remains a major challenge. To address this issue, ethyl methyl sulfone (EMS) is employed as an electrolyte additive to construct stable interfaces between the electrode and electrolyte under high-voltage condition. The characterization results indicate that the addition of EMS can inhibit the decomposition of the standard electrolyte (STD) and the dissolution of Co2+ from cathode, as well as the formation of lithium dendrites on the Li anode, thereby enhancing the stability of both cathode/electrolyte and anode/electrolyte interfaces. Consequently, the cycling performance of LiCoO2 battery using STD+3 %EMS is augmented by 16.9 % at 1 C under a cut-off voltage of 4.6 V over 100 cycles, delivering a specific capacity of 137 mA h g−1. This research provides novel insights into the design of electrolyte additives for high-voltage LiCoO2 batteries and contributes to the further development of high-voltage lithium-ion batteries.

Designing carboxymethyl cellulose based hydrogel electrolyte membranes enhanced by inorganic nanoparticle toward stable zinc anode

Aqueous zinc metal batteries have garnered substantial attention ascribing to affordability, intrinsic safety, and environmental benignity. Nevertheless, zinc metal batteries yet are challenged with potential service life issues resulted from dendrites and side reaction. In this paper, a strategy of nanoparticles doped hydrogel is proposed for constructing carboxymethyl cellulose/graphite oxide hybrid hydrogel electrolyte membranes with exceptional ionic conductivity, anti-swelling property, and simultaneously addressing the dendrites and parasitic reaction. The pivotal functions of the carboxymethyl cellulose/graphite oxide hydrogel electrolyte in mitigating hydrogen evolution and fostering accelerated Zn deposition have been elucidated based on principles of thermodynamic and reaction kinetic. The carboxymethyl cellulose/graphite oxide hydrogel electrolyte endows exceptional cycling longevity (800 h at 1 mA cm−2/1 mAh·cm−2) for Zn||Zn battery, as well as high Coulombic efficiency for Zn||Cu battery (averagely 99.14% within 439 cycles at 1 mA cm−2/1 mAh·cm−2). The assembled Zn||NH4V4O10 battery delivers a high reversible specific capacity of 328.5 mAh·g−1 at 0.1 A g−1. Moreover, the device of Zn||NH4V4O10 pouch battery remains operational under severe conditions like bending and cutting. This work provides valuable reference in developing inorganic nanoparticle hybrid hydrogel electrolyte for realizing high-performance zinc metal batteries.

Conjugated polyaniline as “conveyor” in tungstate boosting cation storage for high-performance aqueous batteries

Aqueous ion storage systems have motivated great interest by virtue of low reduction, high eco-sustainability and safety. Among various cathode candidates, transition metal compounds are featured with easy dissolution in aqueous solutions and inferior conductivity, which severely hinder their application. Herein, advantages are taken of the “conveyor effect” of conjugated polyaniline to prepare an oxygen defective tungstate-linked polyaniline (Od-WOP) material with chrysanthemum-like microstructure. By virtue of the high electronic conductivity derived from conductive conjugated polyaniline skeleton, unbalanced charge distribution triggered by the defective structure, and reversibly rapid ion (de)intercalation benefited from the open framework with porous chrysanthemum-like microstructure, it delivers outstanding rate capability with a maximum specific capacity of 162.2 mAh g−1 and great cycle stability for storing NH4+. Additionally, it also adopts a high reversible capacity of 140.4 mAh g−1 and outstanding cycling performance to store Ca2+. Consequently, the assembled Od-WOP//PTCDI flexible aqueous ammonium ion batteries and calcium ion batteries exhibit superior capacities, energy densities and flexibilities. Od-WOP achieves the NH4+ and Ca2+ storage capability by interacting with them through hydrogen and ionic bonds, respectively. The deep insight from this work sheds light upon a novel strategy to excavate greater potential of transition metal compounds for aqueous ion batteries.

Heterostructured MnSe/FeSe nanorods encapsulated by carbon with enhanced Na+ diffusion as anode materials for sodium-ion batteries

The natural abundance of sodium has fostered the development of sodium-ion batteries for large-scale energy storage. However, the low capacity of the anodes hinders their future application. Herein, carbon-encapsulated MnSe-FeSe nanorods (MnSe-FeSe@C) have been fabricated by the in-situ transformation from polydopamine-coated MnO(OH)-Fe2O3. The heterostructure constructed by MnSe and FeSe nanocrystals induces the formation of built-in electric fields, accelerating electron transfer and ion diffusion, thereby improving reaction kinetics. In addition, carbon enclosure can buffer the volumetric stress and enhance the electrical conductivity. These aspects cooperatively endow the anode with superior cycling stability and distinguished rate performance. Specifically, the discharge capacity of MnSe-FeSe@C reaches 414.3 mA h g−1 at 0.1 A g−1 and 388.8 mA h g−1 even at a high current density of 5.0 A g−1. In addition, it still retains a high reversible capacity of 449.2 mA h g−1 after 700 long cycles at 1.0 A g−1. Further, the ab initio calculation has been employed to authenticate the existence of the built-in electric field by Bader charge, indicating that 0.24 electrons in MnSe were transferred to FeSe. The in-situ XRD has been used to evaluate the phase transition during the charging/discharging process, revealing the sodium ion storage mechanism. The construction of heterostructure material paves a new way to design performance-enhanced anode materials for sodium-ion batteries.

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.

Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications.

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g-1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al2O3 flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g-1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al2O3 layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al2O3 materials maintain a high capacity of 525 mAh g-1 at a current density of 50 mA g-1. Remarkably, at a higher current density of 2000 mA g-1, these materials still achieve a capacity of 220 mAh g-1. Moreover, after 200 cycles at a current density of 200 mA g-1, a high charge capacity of 319 mAh g-1 is sustained. In addition, a full cell consisting of a CuO@Al2O3 anode and a NaNi1/3Fe1/3Mn1/3O2 cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.

Carbon coated and oxygen vacancies incorporated Wadsley-Roth phase molybdenum niobium oxide for high-performance lithium-ion storage

Nb-based oxides with Wadsley-Roth shear structure have been aroused extensive research interest as promising anode for Li-ion batteries, due to the multi-electron redox, safe working voltage and open structural framework. However, the low intrinsic electronic conductivity limits their further practical applications. Herein, the lithium storage performances of MoNb6O18 with Wadsley-Roth shear structure are optimized by carbon coating and oxygen vacancies (VO-MNO@C), which synthesized with freeze-drying and subsequently heat treatment. As expected, the VO-MNO@C electrode demonstrates a high initial reversible capacity of 259.6 mAh/g at 0.2C and the capacity retention rate of 85.7 % after 200 cycles at 1C. Moreover, the reversible of Mo6+/Mo5+ and Mo5+/Mo4+ redox reaction can be effectively improved. In situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) characterization indicate that VO-MNO@C undergoes a solid-solution structural evolution disclosing the stepwise reaction of Mo5+/Mo6+, Mo4+/Mo5+, Nb4+/Nb5+ and Nb3+/Nb4+ redox couples with a small volume variation of 5.7 %. Also, the full cell based on commercial LiMn2O4 cathode and VO-MNO@C anode displays an operating voltage about 2.4 V with the high energy density of 681.4 Wh/kg (calculated with the mass of anode). This work will offer more insights for the development of Wadsley-Roth shear structure anode materials with excellent Li-ion storage properties.