Boosting Zinc Storage Performance of Li3 VO4 Cathode Material for Aqueous Zinc Ion Batteries via Carbon-Incorporation: A Study Combining Theory and Experiment.

In the search for sustainable cathode materials for aqueous zinc ion batteries (AZIBs), vanadium (V)-based materials have garnered interest, primarily due to their abundance and multiple oxidation states. Among the contenders, Li3 VO4 (LiVO) stands out for its affordability, high specific capacity, and elevated ionic conductivity. However, its limited electrical conductivity results in significant resistance polarization, limiting its rate capability, especially under high currents. Through density functional theory (DFT) calculations, this study evaluates the electrochemical implications of carbon (C) incorporation within the LiVO matrix. The findings indicate that C integration significantly ameliorates the conductivity of LiVO. Moreover, C serves as a barrier, mitigating direct interactions between Zn2+ and LiVO, which in turn expedites Zn2+ diffusion. When considering various C materials for this role, glucose is emerged as the optimal candidate. The LiVO/C-glucose composite (LiVO/C-G) is observed to undergo dual phase transitions during charge-discharge cycles, resulting in an amorphous vanadium-oxygen (VO) derivative, paving the way for subsequent electrochemical reactions. Collectively, the insights pave a promising avenue for refining AZIB cathode design and performance.

Comprehensive Investigation of the Crystal Structure of Cation-Disordered Li3VO4 as a High-Rate Anode Material: Unveiling the Dichotomy between Order and Disorder.

This study investigates mechanochemical synthesis and cation-disordering mechanism of wurtzite-type Li3VO4 (LVO), highlighting its promise as a high-performance anode material for lithium-ion batteries and hybrid supercapacitors. Mechanochemical treatment of pristine LVO using a high-energy ball mill results in a "pure cation-disordered" LVO phase, allowing for meticulous analysis of cation arrangement. The X-ray and neutron diffraction study demonstrates progressive loss of order in LVO crystal with increasing milling duration. High-resolution transmission electron microscopy reveals disrupted lattice fringes, indicating cationic misalignment. Pair-distribution function analysis confirms loss of cation arrangements and the presence of short-range order. Combination of these multiple analytical techniques achieves a comprehensive understanding of cation regularity and clearly demonstrates order/disorder dichotomy in cation-disordered materials, ranging from short (<8 Å) to middle-long range (8-30 Å), using an integrated superstructure model of the cation-disordered LVO crystals. Electrochemical testing reveals that mechanochemically treated LVO exhibits superior rate capability, with a 70% capacity retention at a high current density of 50C-rate. Lithium diffusion coefficient measurements demonstrate enhanced lithium-ion mobility in the mechanochemically treated LVO, attributed to cation-disordering effect. These findings provide valuable insights into mechanochemical cation-disordering in LVO, presenting its potential as an efficient anode material for lithium-ion-based electrochemical energy storage.

Enhanced Electrochemical Properties of Li3 VO4 with Controlled Oxygen Vacancies as Li-Ion Battery Anode.

Li3 VO4 , as a promising intercalation-type anode material for lithium-ion batteries, features a desired discharge potential (ca. 0.5-1.0 V vs. Li/Li+ ) and a good theoretical storage capacity (590 mAh g-1 with three Li+ inserted). However, the poor electrical conductivity of Li3 VO4 hinders its practical application. In the present work, various amounts of oxygen vacancies were introduced in Li3 VO4 through annealing in hydrogen to improve its conductivity. To elucidate the influence of oxygen vacancies on the electrochemical performances of Li3 VO4 , the surface energy of the resulting material was measured with an inverse gas chromatography method. It was found that Li3 VO4 annealed in pure hydrogen at 400 °C for 15 min exhibited a much higher surface energy (60.7 mJ m-2 ) than pristine Li3 VO4 (50.6 mJ m-2 ). The increased surface energy would lower the activation energy of phase transformation during the charge-discharge process, leading to improved electrochemical properties. As a result, the oxygen-deficient Li3 VO4 achieved a significantly improved specific capacity of 495 mAh g-1 at 0.1 Ag-1 (381 mAh g-1 for pristine Li3 VO4 ) and retains 165 mAh g-1 when the current density increases to 8 Ag-1 .

Surface Modification of Li3VO4 with PEDOT:PSS Conductive Polymer as an Anode Material for Li-Ion Capacitors.

Li3VO4 (LVO) is a highly promising anode material for lithium-ion batteries, owing to its high capacity and stable discharge plateau. However, LVO faces a significant challenge due to its poor rate capability, which is mainly attributed to its low electronic conductivity. To enhance the kinetics of lithium ion insertion and extraction in LVO anode materials, a conductive polymer called poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is applied to coat the surface of LVO. This uniform coating of PEDOT:PSS improves the electronic conductivity of LVO, thereby enhancing the corresponding electrochemical properties of the resulting PEDOT:PSS-decorated LVO (P-LVO) half-cell. The charge/discharge curves between 0.2 and 3.0 V (vs. Li+/Li) indicate that the P-LVO electrode displays a capacity of 191.9 mAh/g at 8 C, while the LVO only delivers a capacity of 111.3 mAh/g at the same current density. To evaluate the practical application of P-LVO, lithium-ion capacitors (LICs) are constructed with P-LVO composite as the negative electrode and active carbon (AC) as the positive electrode. The P-LVO//AC LIC demonstrates an energy density of 107.0 Wh/kg at a power density of 125 W/kg, along with superior cycling stability and 97.4% retention after 2000 cycles. These results highlight the great potential of P-LVO for energy storage applications.

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 LiNi1/3Co1/3Mn1/3O2 (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.

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.

Boosting the Deep Discharging/Charging Lithium Storage Performances of Li3VO4 through Double-Carbon Decoration.

With high theoretical capacity, good ionic conductivity, and suitable working plateaus, Li3VO4 has emerged as an eye-catching intercalation anode material for lithium storage. However, Li3VO4 suffers from poor electrical conductivity and 20% volume variation under deep discharging/charging conditions. Herein, we present a "double-carbon decoration" strategy to tackle both issues. Deflated balloon-like Li3VO4/C/reduced graphene oxide (LVO/C/rGO) microspheres with continuous electron transport pathways and sufficient free space for volume change accommodation are fabricated through a facile spray-drying method. Under deep discharging/charging conditions (0.02-3.0 V), LVO/C/rGO achieves a high intercalation capacity of 591 mA h g-1. With high capacity and outstanding stability, LVO/C/rGO outperforms other intercalation anode materials (such as graphite, Li4Ti5O12, and TiO2). In situ X-ray diffraction measurement reveals that the lithium storage is realized through both solid-solution reaction and two-phase reaction mechanisms. A LVO/C/rGO//LiNi0.8Co0.15Al0.05O2 lithium-ion full cell is also assembled. In such full cell, LVO/C/rGO also demonstrates high specific capacity and excellent cycling stability. The above results manifest that the LVO/C/rGO anode has the potential to be applied in the next-generation high-performance lithium-ion batteries.

Mo6+ Doping in Li3VO4 Anode for Li-Ion Batteries: Significantly Improve the Reversible Capacity and Rate Performance.

Consider the almost insulator for pure Li3VO4 with a band gap of 3.77 eV, to significantly improve the electrical conductivity, the novel Li3V1-xMoxO4 (x = 0.00, 0.01, 0.02, 0.05, and 0.10) anode materials were prepared successfully by simple sol-gel method. Our calculations show that, by substitute Mo6+ for V5+, the extra electron occupied the V 3p empty orbital and caused the Fermi level shift up into the conduction band, where the Mo-doped Li3VO4 presents electrical conductor. The V/I curve measurements show that, by Mo doping in V site, the electronic conductivity of the Li3VO4 was increased by 5 orders of magnitude. And thence the polarization was obviously reduced. EIS measurement results indicated that by Mo-doping a higher lithium diffusion coefficient can be obtained. The significantly increased electronic conductivity combined the higher lithium diffusion coefficient leads to an obvious improvement in reversible capacity and rate performance for the Mo-doped Li3VO4. The resulting Li3V1-xMoxO4 (x = 0.01) material exhibited the excellent rate capability. At a high rate 5 C, a big discharge capacity of the initial discharge capacity 439 mAh/g can be obtained, which is higher than that of pure Li3VO4 (only 166 mAh/g), and after 100 cycles the mean capacity fade is only 0.06% per cycle.

Investigation of the Reversible Intercalation/Deintercalation of Al into the Novel Li3VO4@C Microsphere Composite Cathode Material for Aluminum-Ion Batteries.

The Li3VO4@C microsphere composite was first reported as a novel cathode material for rechargeable aluminum-ion batteries (AIBs), which manifests the initial discharge capacity of 137 mAh g-1 and and remains at 48 mAh g-1 after 100 cycles with almost 100% Coulombic efficiency. The detailed intercalation mechanism of Al into the orthorhombic Li3VO4 is investigated by ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) of Li3VO4@C electrodes and the nuclear magnetic resonance aluminum spectroscopy (27Al NMR) of ionic liquid electrolytes in different discharge/charge states. First-principle calculations are also carried out to investigate the structural change as Al inserts into the framework of Li3VO4. It is revealed that the Al/Li3VO4@C battery goes through electrochemical dissolution and deposition of metallic aluminum in the anode, as well as the insertion and deinsertion of Al3+ cations in the cathode in the meantime. The rechargeable AIBs fabricated in this work are of low cost and high safety, which may make a step forward in the development of novel cathode materials based on the acidic ionic liquid electrolyte system.

Carbon-Coated Li3 VO4 Spheres as Constituents of an Advanced Anode Material for High-Rate Long-Life Lithium-Ion Batteries.

Lithium-ion batteries are receiving considerable attention for large-scale energy-storage systems. However, to date the current cathode/anode system cannot satisfy safety, cost, and performance requirements for such applications. Here, a lithium-ion full battery based on the combination of a Li3 VO4 anode with a LiNi0.5 Mn1.5 O4 cathode is reported, which displays a better performance than existing systems. Carbon-coated Li3 VO4 spheres comprising nanoscale carbon-coating primary particles are synthesized by a morphology-inheritance route. The observed high capacity combined with excellent sample stability and high rate capability of carbon-coated Li3 VO4 spheres is superior to other insertion anode materials. A high-performance full lithium-ion battery is fabricated by using the carbon-coated Li3 VO4 spheres as the anode and LiNi0.5 Mn1.5 O4 spheres as the cathode; such a cell shows an estimated practical energy density of 205 W h kg-1 with greatly improved properties such as pronounced long-term cyclability, and rapid charge and discharge.

New Insights into the Structure Changes and Interface Properties of Li3VO4 Anode for Lithium-Ion Batteries during the Initial Cycle by in-Situ Techniques.

Li3VO4 has been regarded as a new-type anode of lithium-ion batteries in recent years, which has a high theoretical specific capacity of 394 mAh g(-1), a proper potential for Li(+) insertion/deinsertion (∼1 V), and a good rate capacity. However, its low initial Coulombic efficiency, poor conductivity, and poor cycle performance restricts its development. In order to figure out the cause of the low initial Coulombic efficiency of Li3VO4 material, the nanosized Li3VO4 material was synthesized by citric acid-assisted sol-gel method. The lithium storage behaviors of the prepared Li3VO4 material were studied by in-situ XRD and in-situ EIS techniques. In-situ XRD results indicated that there was irreversible phase transformation of Li3VO4 during the initial charging/discharging process. In-situ EIS experiment was performed during the potentiostatic intermittent titration technique (PITT) process to discuss the formation of the solid electrolyte interface (SEI) on the Li3VO4 and the kinetics of lithium-ion diffusion. It is worth pointing out that this is the first time to prove the existence of SEI on Li3VO4 during the initial charging/discharging process by in-situ EIS experiment. It turned out that the irreversible phase transformation and the formation of SEI on Li3VO4 were the two important reasons causing the low initial Coulombic efficiency of Li3VO4 material.

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.

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

Surface-amorphous and oxygen-deficient Li3VO4-δsynthesized by simple annealing of Li3VO4 powders in a vacuum shows great enhancements in both reversible capacity and coulombic efficiency for the first discharge/charge without delicate size control and carbon coating. The results are associated with the improved charge-transfer kinetics caused by the amorphous surface of Li3VO4-δ .

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.

Mesoporous Li3VO4/C Submicron-Ellipsoids Supported on Reduced Graphene Oxide as Practical Anode for High-Power Lithium-Ion Batteries.

Despite the enormous efforts devoted to high-performance lithium-ion batteries (LIBs), the present state-of-the-art LIBs cannot meet the ever-increasing demands. With high theoretical capacity, fast ionic conductivity, and suitable charge/discharge plateaus, Li3VO4 shows great potential as the anode material for LIBs. However, it suffers from poor electronic conductivity. In this work, we present a novel composite material with mesoporous Li3VO4/C submicron-ellipsoids supported on rGO (LVO/C/rGO). The synthesized LVO/C/rGO exhibits a high reversible capacity (410 mAh g-1 at 0.25 C), excellent rate capability (230 mAh g-1 at 125 C), and outstanding long-cycle performance (82.5% capacity retention for 5000 cycles at 10 C). The impressive electrochemical performance reveals the great potential of the mesoporous LVO/C/rGO as a practical anode for high-power LIBs.