Surface-Amorphous and Oxygen-Deficient Li3VO4-δ as a Promising Anode Material for Lithium-Ion Batteries

Constructing surface protective film of V-Se-O to promote zinc ion storage by surface oxygen implantation strategy

Interfacial chemical modification is an effective strategy to adjust the strong Coulombic ion-lattice interactions with high valence cations experienced by electrode materials, facilitating the reaction kinetic. In this paper, a simple and fast surface oxygen implantation strategy was designed to adjust the electronic structure of stainless steel (SS) supported vanadium diselenide (VSe2) nanosheets and form a surface protective film, which effectively accelerates the reaction kinetics of Zn2+ and extends the cycle life of the battery. It is demonstrated that the conductivity, pseudocapacitance and specific capacity can be tuned by selectively introducing oxygen species to the surface, which provides an important reference for the design of electrodes with controlled surface chemistry. Density functional theory (DFT) calculations also confirm that the electronic structure can be adjusted by surface oxygen injection strategy, which not only improves the conductivity, but also adjusts the adsorption energy, thus providing favorable conditions for zinc ion storage. Benefiting from the selenium vacancies and pores generated by the removal of part of selenium, and the oxide film formed on the surfaces, the VSe2-xOx-SS-30 electrode showed higher specific capacity (188.4 mAh/g at 0.5 A g-1 after 50 cycles), better rate performance (107.1 mAh/g at 4 A g-1) and more satisfactory cycling stability (83.1 mAh/g at 5 A g-1 after 1800 cycles) than VSe2-SS electrode. Importantly, the flexible quasi-solid-state VSe2-xOx-SS-30//Zn battery also exhibits high specific capacity and excellent environmental adaptability. Furthermore, the zinc (de)intercalation and transformation reactions mechanism was revealed by some ex-situ/in-situ techniques.

The synthesis and application of crystalline-amorphous hybrid materials

Crystalline-amorphous hybrid materials (CA-HMs) possess the merits of both pure crystalline and amorphous phases. Abundant dangling bonds, unsaturated coordination atoms, and isotropic structural features in the amorphous phase, as well as relatively high electronic conductivity and thermodynamic structural stability of the crystalline phase simultaneously take effect in CA-HMs. Furthermore, the atomic and bandgap mismatch at the CA-HM interface can introduce more defects as extra active sites, reservoirs for promoted catalytic and electrochemical performance, and induce built-in electric field for facile charge carrier transport. Motivated by these intriguing features, herein, we provide a comprehensive overview of CA-HMs on various aspects-from synthetic methods to multiple applications. Typical characteristics of CA-HMs are discussed at the beginning, followed by representative synthetic strategies of CA-HMs, including hydrothermal/solvothermal methods, deposition techniques, thermal adjustment, and templating methods. Diverse applications of CA-HMs, such as electrocatalysis, batteries, supercapacitors, mechanics, optoelectronics, and thermoelectrics along with underlying structure-property mechanisms are carefully elucidated. Finally, challenges and perspectives of CA-HMs are proposed with an aim to provide insights into the future development of CA-HMs.

Research Advances in Amorphous-Crystalline Heterostructures Toward Efficient Electrochemical Applications

Interface engineering of heterostructures has proven a promising strategy to effectively modulate their physicochemical properties and further improve the electrochemical performance for various applications. In this context related research of the newly proposed amorphous-crystalline heterostructures have lately surged since they combine the superior advantages of amorphous- and crystalline-phase structures, showing unusual atomic arrangements in heterointerfaces. Nonetheless, there has been much less efforts in systematic analysis and summary of the amorphous-crystalline heterostructures to examine their complicated interfacial interactions and elusory active sites. The critical structure-activity correlation and electrocatalytic mechanism remain rather elusive. In this review, the recent advances of amorphous-crystalline heterostructures in electrochemical energy conversion and storage fields are amply discussed and presented, along with remarks on the challenges and perspectives. Initially, the fundamental characteristics of amorphous-crystalline heterostructures are introduced to provide scientific viewpoints for structural understanding. Subsequently, the superiorities and current achievements of amorphous-crystalline heterostructures as highly efficient electrocatalysts/electrodes for hydrogen evolution reaction, oxygen evolution reaction, supercapacitor, lithium-ion battery, and lithium-sulfur battery applications are elaborated. At the end of this review, future outlooks and opportunities on amorphous-crystalline heterostructures are also put forward to promote their further development and application in the field of clean energy.

In/Ce Co-doped Li3VO4 and Nitrogen-modified Carbon Nanofiber Composites as Advanced Anode Materials for Lithium-ion Batteries

Li₃VO₄ (LVO) is considered as a novel alternative anode material for lithium-ion batteries (LIBs) due to its high capacity and good safety. However, the inferior electronic conductivity impedes its further application. Here, nanofibers (nLICVO/NC) with In/Ce co-doped Li₃VO₄ strengthened by nitrogen-modified carbon are prepared. Density functional theory calculations demonstrate that In/Ce co-doping can substantially reduce the LVO band gap and achieve orders of magnitude increase (from 2.79 × 10^-4 to 1.38 × 10^-2 S cm^-1) in the electronic conductivity of LVO. Moreover, the carbon-based nanofibers incorporated with 5LICVO nanoparticles can not only buffer the structural strain but also form a good framework for electron transport. This 5LICVO/NC material delivers high reversible capacities of 386.3 and 277.9 mA h g^-1 at 0.1 and 5 A g^-1, respectively. Furthermore, high discharge capacities of 335 and 259.5 mA h g^-1 can be retained after 1200 and 4000 cycles at 0.5 and 1.6 A g^-1, respectively (with the corresponding capacity retention of 98.4 and 78.7%, respectively). When the 5LICVO/NC anode assembles with commercial LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111) into a full cell, a high discharge capacity of 191.9 mA h g^-1 can be retained after 600 cycles at 1 A g^-1, implying an inspiring potential for practical application in high-efficiency LIBs.

Hierarchical Self-Assembly Strategy for Scalable Synthesis of Li3VO4/N Doped C Nanosheets for High-Rate Li-Ion Storage

While the comprehensive merits of high safety and high capacity make Li₃VO₄ (LVO) a potential anode material for lithium-ion batteries, the practical application of LVO was severely impeded by the unfavorable high-rate capability and unscalable preparation. Here, LVO/N doped C nanosheets (LVO@NC NSs) assembled from primary LVO@NC nanoparticles are prepared via a scalable and concise spray drying approach. The 2D morphology and the interconnected LVO@NC constituents endow the LVO@NC NSs with continuously excellent reaction activity, leading to prominent rate performance. When cycling at 0.2 A g^-1, the obtained LVO@NC NSs exhibit a high charge capacity of 628.4 mAh g^-1 after 300 cycles, showing little improvement compared with the initial charge capacity. After 9 periods of rate testing ranging from 0.1 to 6.0 A g^-1 for 460 cycles, a high charge capacity of 610.3 mAh g^-1 remains. It also exhibits an outstanding long lifespan at the charge/discharge currents of 3.0/6.0 A g^-1, delivering a high charge capacity of 277.0 mAh g^-1 in the 5000th cycle. The scalable and concise preparation as well as the enhanced high-rate capability of the LVO@NC NSs make them hold great promise as an anode candidate for high-power lithium-ion storage devices.

Polyvinylpyrrolidone-regulated synthesis of hollow manganese vanadium oxide microspheres as a high-performance anode for lithium-ion batteries

We report the fabrication of well-defined phase-pure Mn₂V₂O₇ hollow microspheres (h-MVO), assembled from the porous plate-like building blocks, via a facile solvothermal method followed by annealing, with the assistance of polyvinylpyrrolidone (PVP) as the structure-regulating agent. The microstructure dependent electrochemical properties of h-MVO as anode materials for lithium ion batteries (LIBs) are investigated, and excellent lithium storage performance is obtained with a reversible capacity of 1707 mAh g^-1 after 700 cycles at 0.5 A g^-1, revealing that the unique hierarchical framework of the h-MVO microspheres with hollow interiors and porous building blocks could not only accelerate the transport of Li⁺ ions and electrolyte, but also efficiently suppress the electrode pulverization upon cycling. More importantly, we demonstrate that PVP can be an effective agent to tune the microstructures, which would be promising for the development of high-performance energy storage devices.

Ga2O3–Li3VO4/NC nanofibers toward superb high-capacity and high-rate Li-ion storage

Porous Ga2O3–Li3VO4/N-doped C nanofibers consisting of ultrafine nanoparticles embedded in nanoflakes were designed and firstly prepared via electrospinning, showing superb high-rate Li-ion storage.

Novel Li3 VO4 Nanostructures Grown in Highly Efficient Microwave Irradiation Strategy and Their In-Situ Lithium Storage Mechanism

The investigation of novel growth mechanisms for electrodes and the understanding of their in situ energy storage mechanisms remains major challenges in rechargeable lithium-ion batteries. Herein, a novel mechanism for the growth of high-purity diversified Li3 VO4 nanostructures (including hollow nanospheres, uniform nanoflowers, dispersed hollow nanocubes, and ultrafine nanowires) has been developed via a microwave irradiation strategy. In situ synchrotron X-ray diffraction and in situ transmission electron microscope observations are applied to gain deep insight into the intermediate Li3+ x VO4 and Li3+ y VO4 phases during the lithiation/delithiation mechanism. The first-principle calculations show that lithium ions migrate into the nanosphere wall rapidly along the (100) plane. Furthermore, the Li3 VO4 hollow nanospheres deliver an outstanding reversible capacity (299.6 mAh g-1 after 100 cycles) and excellent cycling stability (a capacity retention of 99.0% after 500 cycles) at 200 mA g-1 . The unique nanostructure offers a high specific surface area and short diffusion path, leading to fast thermal/kinetic reaction behavior, and preventing undesirable volume expansion during long-term cycling.

In situ interfacial architecture of lithium vanadate-based cathode for printable lithium batteries

Most Li₃VO₄ anodes are obtained by pre-architecture methods in which Li₃VO₄ anode materials are prepared with more than six key processes including high-temperature annealing and long preparation time. Herein, we propose an in situ post-architecture strategy including Li₃VO₄-precursor solution (ink) preparation and then annealing at 250°C. The integrated Li₃VO₄ based electrode not only possesses good electrical conductivity and porous microstructure but also has superior stability because of Cu anchoring and inclusion by in situ catalysis. The integrated electrode demonstrates a high reversible capacity (865 mA h g^-1 at 0.2 A g^-1) and good cyclability (100% capacity retention after 200 cycles at 1 A g^-1). More importantly, the post-architecture electrode has a high energy density of 773.8 Wh kg^-1, much higher than reported Li₃VO₄-based materials, as well as most cathodes. Therefore, the electrode could be used to the printable cathode of low-voltage high-energy-density lithium batteries.

Sub-micro droplet reactors for green synthesis of Li3VO4 anode materials in lithium ion batteries

The conventional solid-state reaction suffers from low diffusivity, high energy consumption, and uncontrolled morphology. These limitations are competed by the presence of water in solution route reaction. Herein, based on concept of combining above methods, we report a facile solid-state reaction conducted in water vapor at low temperature along with calcium doping for modifying lithium vanadate as anode material for lithium-ion batteries. The optimized material, delivers a superior specific capacity of 543.1, 477.1, and 337.2 mAh g-1 after 200 and 1000 cycles at current densities of 100, 1000 and 4000 mA g-1, respectively, which is attributed to the contribution of pseudocapacitance. In this work, we also use experimental and theoretical calculation to demonstrate that the enhancement of doped lithium vanadate is attributed to particles confinement of droplets in water vapor along with the surface and structure variation of calcium doping effect.

The oxygen vacancy in Li-ion battery cathode materials

The substantial capacity gap between available anode and cathode materials for commercial Li-ion batteries (LiBs) remains, as of today, an unsolved problem. Oxygen vacancies (OVs) can promote Li-ion diffusion, reduce the charge transfer resistance, and improve the capacity and rate performance of LiBs. However, OVs can also lead to accelerated degradation of the cathode material structure, and from there, of the battery performance. Understanding the role of OVs for the performance of layered lithium transition metal oxides holds great promise and potential for the development of next generation cathode materials. This review summarises some of the most recent and exciting progress made on the understanding and control of OVs in cathode materials for Li-ion battery, focusing primarily on Li-rich layered oxides. Recent successes and residual unsolved challenges are presented and discussed to stimulate further interest and research in harnessing OVs towards next generation oxide-based cathode materials.

Towards fast-charging technologies in Li+/Na+ storage: from the perspectives of pseudocapacitive materials and non-aqueous hybrid capacitors

Since the discovery of the pseudocapacitive behavior in RuO₂ by Sergio Trasatti and Giovanni Buzzanca in 1971, materials with pseudocapacitance have been regarded as promising candidates for high-power energy storage. Pseudocapacitance-involving energy storage is predominantly based on faradaic redox reactions, but at the same time the charge storage is not limited by solid-state ion diffusion. Besides the search for pseudocapacitive materials, their implementation into non-aqueous hybrid capacitors stands for the strategy to increase power density by a rational design of the battery structure. Composed of a battery-type anode and a capacitor-type cathode, such devices show great promise to integrate the merits of both batteries and capacitors. Today, the availability of fast-charging technologies is of fundamental importance for establishing electric vehicles on a mass scale. Therefore, from the perspective of materials and battery design, understanding the basics and the recent developments of pseudocapacitive materials and non-aqueous hybrid capacitors is of great importance. With this goal in mind, we introduce here the fundamentals of pseudocapacitance and non-aqueous hybrid capacitors. In addition, we provide an overview of the latest developments in this fast growing research field.

Oxygen Vacancy Engineering in Tin(IV) Oxide Based Anode Materials toward Advanced Sodium-Ion Batteries

A high theoretical capacity of approximately 1400 mA h g^-1 makes SnO₂ a promising anode material for sodium-ion batteries (SIBs). However, large volume expansion, poor intrinsic conductivity, and sluggish reaction kinetics have greatly hindered its practical application. The controlled creation of oxygen vacancy (OV) defects allows the intrinsic properties of SnO₂ to be effectively modulated, but related work concerning SIBs is still lacking. In this Minireview, the mechanism of failure of SnO₂ electrodes is discussed and an overview of recent progress in the general synthesis of OV-containing SnO₂ materials and the feasible detection of OVs in SnO₂ is presented. The use of OV-containing SnO₂ -based anode materials in SIBs is also reviewed. Finally, challenges and future opportunities to engineer OVs for semiconductor oxides are examined.

Electrochemical Performance of Nanosized Disordered LiVOPO4

ε-LiVOPO₄ is a promising multielectron cathode material for Li-ion batteries that can accommodate two electrons per vanadium, leading to higher energy densities. However, poor electronic conductivity and low lithium ion diffusivity currently result in low rate capability and poor cycle life. To enhance the electrochemical performance of ε-LiVOPO₄, in this work, we optimized its solid-state synthesis route using in situ synchrotron X-ray diffraction and applied a combination of high-energy ball-milling with electronically and ionically conductive coatings aiming to improve bulk and surface Li diffusion. We show that high-energy ball-milling, while reducing the particle size also introduces structural disorder, as evidenced by ⁷Li and ³¹P NMR and X-ray absorption spectroscopy. We also show that a combination of electronically and ionically conductive coatings helps to utilize close to theoretical capacity for ε-LiVOPO₄ at C/50 (1 C = 153 mA h g^-1) and to enhance rate performance and capacity retention. The optimized ε-LiVOPO₄/Li₃VO₄/acetylene black composite yields the high cycling capacity of 250 mA h g^-1 at C/5 for over 70 cycles.

Ultrathin Mesoporous Co3O4 Nanosheet Arrays for High-Performance Lithium-Ion Batteries

Transition metal oxides, such as Co₃O₄, have attracted great attention for lithium-ion batteries (LIBs) due to their high theoretical capacity and satisfactory chemical stability. However, the slow kinetics of Li-ion and electron transport as well as poor cycling stability still largely restrains their applications. Here, we report the rational design of well-defined mesoporous ultrathin Co₃O₄ nanosheet arrays (NSAs) by topological transformation of layered double hydroxides nanosheet arrays (NSAs), which demonstrate significantly enhanced performance as anode for LIBs. The as-obtained Co₃O₄ NSAs with suitable thickness and abundant mesopores show excellent electrochemistry performance for LIBs, giving a high specific charge capacity of 2019.6 mAh g^-1 at 0.1 A g^-1, a good rate capability, and a remarkable cycling stability (1576.9 mAh g^-1 after the 80th cycle), which is much superior to that of Co₃O₄ with thicker or thinner nanosheets as well as to that of the reported results. This facile strategy may be extended to the synthesis of other transition metal oxide NSAs, which can be potentially used in energy storage and conversion devices.

Enhancement of Electrochemical Performance by the Oxygen Vacancies in Hematite as Anode Material for Lithium-Ion Batteries

The application of hematite in lithium-ion batteries (LIBs) has been severely limited because of its poor cycling stability and rate performance. To solve this problem, hematite nanoparticles with oxygen vacancies have been rationally designed by a facile sol-gel method and a sequential carbon-thermic reduction process. Thanks to the existence of oxygen vacancies, the electrochemical performance of the as-obtained hematite nanoparticles is greatly enhancing. When used as the anode material in LIBs, it can deliver a reversible capacity of 1252 mAh g^-1 at 2 C after 400 cycles. Meanwhile, the as-obtained hematite nanoparticles also exhibit excellent rate performance as compared to its counterparts. This method not only provides a new approach for the development of hematite with enhanced electrochemical performance but also sheds new light on the synthesis of other kinds of metal oxides with oxygen vacancies.

BiVO4 Fern Architectures: A Competitive Anode for Lithium-Ion Batteries

The development of high-performance anode materials for lithium-ion batteries (LIBs) is currently subject to much interest. In this study, BiVO₄ fern architectures are introduced as a new anode material for LIBs. The BiVO₄ fern shows an excellent reversible capacity of 769 mAh g^-1 (ultrahigh volumetric capacity of 3984 mAh cm^-3 ) at 0.12 A g^-1 with large capacity retention. A LIB full cell is then assembled with a BiVO₄ fern anode and LiFePO₄ (LFP, commercial) as cathode material. The device can achieve a capacity of 140 mAh g^-1 at 1C rate, that is, 81 % of the capacity of the cathode and maintained to 104 mAh g^-1 at a high rate of 8C, which makes BiVO₄ a promising candidate as a high-energy anode material for LIBs.

One-pot synthesis of Li3VO4@C nanofibers by electrospinning with enhanced electrochemical performance for lithium-ion batteries

Electrospinning is firstly used to one-pot synthesis of Li₃VO₄@C nanofibers in a large scale. Although with the presence of organic sources in synthesis process, the pure phase Li₃VO₄ with superior nanofibrous morphology is still successfully obtained through adjusting different heat treatment processes and different vanadium sources. The prepared Li₃VO₄@C nanofibers exhibit a unique structure in which nanosized Li₃VO₄ particles are uniformly embedded in amorphous carbon matrix. Compared with Li₃VO₄/C powder, Li₃VO₄@C nanofibers display enhanced reversible capacity of 451mAhg^-1 at 40mAg^-1 with an increased initial coulombic efficiency of 82.3%, and the capacity can remain at 394mAhg^-1 after 100 cycles. This superior electrochemical performance can be attributed to its unique structure which ensures a high reactivity by nanosized Li₃VO₄, more stable electrode/electrolyte interface by carbon encapsulation, improved electronic conductivity and buffered volume changes by flexible carbon matrix. The electrospinning technology provides an effective method to obtain high performance Li₃VO₄ as a promising anode material for lithium-ion batteries.

Peapod-like Li3 VO4 /N-Doped Carbon Nanowires with Pseudocapacitive Properties as Advanced Materials for High-Energy Lithium-Ion Capacitors

Lithium ion capacitors are new energy storage devices combining the complementary features of both electric double-layer capacitors and lithium ion batteries. A key limitation to this technology is the kinetic imbalance between the Faradaic insertion electrode and capacitive electrode. Here, we demonstrate that the Li₃ VO₄ with low Li-ion insertion voltage and fast kinetics can be favorably used for lithium ion capacitors. N-doped carbon-encapsulated Li₃ VO₄ nanowires are synthesized through a morphology-inheritance route, displaying a low insertion voltage between 0.2 and 1.0 V, a high reversible capacity of ≈400 mAh g^-1 at 0.1 A g^-1 , excellent rate capability, and long-term cycling stability. Benefiting from the small nanoparticles, low energy diffusion barrier and highly localized charge-transfer, the Li₃ VO₄ /N-doped carbon nanowires exhibit a high-rate pseudocapacitive behavior. A lithium ion capacitor device based on these Li₃ VO₄ /N-doped carbon nanowires delivers a high energy density of 136.4 Wh kg^-1 at a power density of 532 W kg^-1 , revealing the potential for application in high-performance and long life energy storage devices.

Enhanced Electrochemical Performance of Ultracentrifugation-Derived nc-Li3VO4/MWCNT Composites for Hybrid Supercapacitors

Nanocrystalline Li3VO4 dispersed within multiwalled carbon nanotubes (MWCNTs) was prepared using an ultracentrifugation (uc) process and electrochemically characterized in Li-containing electrolyte. When charged and discharged down to 0.1 V vs Li, the material reached 330 mAh g(-1) (per composite) at an average voltage of about 1.0 V vs Li, with more than 50% capacity retention at a high current density of 20 A g(-1). This current corresponds to a nearly 500C rate (7.2 s) for a porous carbon electrode normally used in electric double-layer capacitor devices (1C = 40 mA g(-1) per activated carbon). The irreversible structure transformation during the first lithiation, assimilated as an activation process, was elucidated by careful investigation of in operando X-ray diffraction and X-ray absorption fine structure measurements. The activation process switches the reaction mechanism from a slow "two-phase" to a fast "solid-solution" in a limited voltage range (2.5-0.76 V vs Li), still keeping the capacity as high as 115 mAh g(-1) (per composite). The uc-Li3VO4 composite operated in this potential range after the activation process allows fast Li(+) intercalation/deintercalation with a small voltage hysteresis, leading to higher energy efficiency. It offers a promising alternative to replace high-rate Li4Ti5O12 electrodes in hybrid supercapacitor applications.

Hollow-Cuboid Li3VO4/C as High-Performance Anodes for Lithium-Ion Batteries

Li3VO4 has been demonstrated to be a promising anode material for lithium-ion batteries with a low, safe voltage and large capacity. However, its poor electronic conductivity hinders its practical application particularly at a high rate. This work reports that Li3VO4 coated with carbon was synthesized by a one-pot, two-step method with F127 ((PEO)100-(PPO)65-(PEO)100) as both template and carbon source, yielding a microcuboid structure. The resulting Li3VO4/C cuboid shows a stable capacity of 415 mAh g(-1) at 0.5 C and excellent capacity stability at high rates (e.g., 92% capacity retention after 1000 cycles at 10 C = 4 A g(-1)). The lithiation/delithiation process of Li3VO4/C was studied by ex situ X-ray diffraction and Raman spectroscopy, which confirmed that Li3VO4/C underwent a reversible intercalation reaction during discharge/charge processes. The excellent electrochemical performance is attributed largely to the unique microhollow structure. The voids inside hollow structure can not only provide more space to accommodate volume change during discharge/charge processes but also allow the lithium ions insertion and extraction from both outside and inside the hollow structure with a much larger surface area or more reaction sites and shorten the lithium ions diffusion distance, which leads to smaller overpotential and faster reaction kinetics. Carbon derived from F127 through pyrolysis coats Li3VO4 conformably and thus offers good electrical conduction. The results in this work provide convincing evidence that the significant potential of hollow-cuboid Li3VO4/C for high-power batteries.

Constructing Highly Graphitized Carbon-Wrapped Li3VO4 Nanoparticles with Hierarchically Porous Structure as a Long Life and High Capacity Anode for Lithium-Ion Batteries

Li3VO4 nanoparticles (NPs) embedded in a continuous, highly graphitized carbon network with an interconnected hierarchically porous structure (HP-Li3VO4/C) were prepared using a facile, green freeze-drying method followed by in situ carbonizing. Because of its unique microstructure, the resultant HP-Li3VO4/C exhibits excellent lithium storage performance in terms of specific capacity, cycling stability, and rate capability when used as an anode material in lithium-ion batteries (LIBs). Specifically, it delivers an extremely high capacity of 381 mAh g(-1) for up to 300 cycles at 0.2 A g(-1), and even at a rate as high as 4 A g(-1), a high reversible capacity of 275 mAh g(-1) can be retained after testing for 500 cycles. This excellent electrochemical performance can be attributed to Li3VO4 NPs wrapped with highly graphitized carbon conductive framework and hierarchically porous structure. This work may offer a new methodology for the preparation of other electrode materials for LIBs.