Coating lithium titanate with nitrogen-doped carbon by simple refluxing for high-power lithium-ion batteries

Porous layered ZnV2O4@C synthesized based on a bimetallic MOF as a stable cathode material for aqueous zinc ion batteries

Vanadium-based oxides are considered potential cathode materials for aqueous zinc ion batteries (AZIBs) due to their distinctive layered (or tunnel) structure suitable for zinc ion storage. However, the structural instability and sluggish kinetics of vanadium-based oxides have limited their capacity and cycling stability for large-scale applications. To overcome these shortcomings, here a porous vanadium-based oxide doped with zinc ions and carbon with the molecular formula ZnV2O4@C (ZVO@C) as the cathode material is synthesized by the pyrolysis of a bimetallic MOF precursor containing Zn/V. This electrode demonstrates a remarkable specific capacity of 425 mA h g-1 at 0.5 A g-1 and excellent cycling stability with about 97% capacity retention after 1000 cycles at 10 A g-1. The excellent electrochemical performance of ZVO@C can be attributed to more reaction active sites and the faster reaction kinetics for zinc ion diffusion and storage brought about by the porous layered spinel-type tunnel structure with high surface area and massive mesoporosity, as well as the enhanced electron transport efficiency and more stable channel structure achieved from the doped conductive carbon. The reaction mechanism and structural evolution of the ZVO@C electrode are analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, revealing the formation of a new phase of ZnxV2O5·nH2O during the first charge, which participates in reversible cycling together with ZVO@C during the charging and discharging processes. Moreover, the energy storage mechanism is revealed, in which zinc ions and hydrogen ions jointly participate in intercalation and extraction. The present study demonstrates that constructing composite vanadium-based oxides based on bimetallic organic frameworks as precursor templates is an effective strategy for the development of high-performance cathode materials for AZIBs.

Review of the Scalable Core-Shell Synthesis Methods: The Improvements of Li-Ion Battery Electrochemistry and Cycling Stability

The demand for lithium-ion batteries has significantly increased due to the increasing adoption of electric vehicles (EVs). However, these batteries have a limited lifespan, which needs to be improved for the long-term use needs of EVs expected to be in service for 20 years or more. In addition, the capacity of lithium-ion batteries is often insufficient for long-range travel, posing challenges for EV drivers. One approach that has gained attention is using core-shell structured cathode and anode materials. That approach can provide several benefits, such as extending the battery lifespan and improving capacity performance. This paper reviews various challenges and solutions by the core-shell strategy adopted for both cathodes and anodes. The highlight is scalable synthesis techniques, including solid phase reactions like the mechanofusion process, ball-milling, and spray-drying process, which are essential for pilot plant production. Due to continuous operation with a high production rate, compatibility with inexpensive precursors, energy and cost savings, and an environmentally friendly approach that can be carried out at atmospheric pressure and ambient temperatures. Future developments in this field may focus on optimizing core-shell materials and synthesis techniques for improved Li-ion battery performance and stability.

Effect of Calcination Temperature on the Physicochemical Properties and Electrochemical Performance of FeVO4 as an Anode for Lithium-Ion Batteries

Several electrode materials have been developed to provide high energy density and a long calendar life at a low cost for lithium-ion batteries (LIBs). Iron (III) vanadate (FeVO₄), a semiconductor material that follows insertion/extraction chemistry with a redox reaction and provides high theoretical capacity, is an auspicious choice of anode material for LIBs. The correlation is investigated between calcination temperatures, morphology, particle size, physicochemical properties, and their effect on the electrochemical performance of FeVO₄ under different binders. The crystallite size, particle size, and tap density increase while the specific surface area (S_BET) decreases upon increasing the calcination temperature (500 °C, 600 °C, and 700 °C). The specific capacities are reduced by increasing the calcination temperature and particle size. Furthermore, FeVO₄ fabricated with different binders (35 wt.% PAA and 5 wt.% PVDF) and their electrochemical performance for LIBs was explored regarding the effectiveness of the PAA binder. FV500 (PAA and PVDF) initially delivered higher discharge/charge capacities of 1046.23/771.692 mAhg^-1 and 1051.21/661.849 mAhg^-1 compared to FV600 and FV700 at the current densities of 100 mAg^-1, respectively. The intrinsic defects and presence of oxygen vacancy along with high surface area and smaller particle sizes efficiently enhanced the ionic and electronic conductivities and delivered high discharge/charge capacities for FeVO₄ as an anode for LIBs.

Core-shell structure of LiMn2O4 cathode material reduces phase transition and Mn dissolution in Li-ion batteries

Although the LiMn₂O₄ cathode can provide high nominal cell voltage, high thermal stability, low toxicity, and good safety in Li-ion batteries, it still suffers from capacity fading caused by the combination of structural transformation and transition metal dissolution. Herein, a carbon-coated LiMn₂O₄ cathode with core@shell structure (LMO@C) was therefore produced using a mechanofusion method. The LMO@C exhibits higher cycling stability as compared to the pristine LiMn₂O₄ (P-LMO) due to its high conductivity reducing impedance growth and phase transition. The carbon shell can reduce direct contact between the electrolyte and the cathode reducing side reactions and Mn dissolution. Thus, the cylindrical cell of LMO@C//graphite provides higher capacity retention after 900 cycles at 1 C. The amount of dissoluted Mn for the LMO@C is almost 2 times lower than that of the P-LMO after 200 cycles. Moreover, the LMO@C shows smaller change in lattice parameter or phase transition than P-LMO, indicating to the suppression of λ-MnO₂ phase from the mixed phase of Li_1-δMn₂O₄ + λ-MnO₂ when Li-delithiation at highly charged state leading to an improved cycling reversibility. This work provides both fundamental understanding and manufacturing scale demonstration for practical 18650 Li-ion batteries.

Bio-Phenolic Resin Derived Porous Carbon Materials for High-Performance Lithium-Ion Capacitor

In this article, hierarchical porous carbon (HPC) with high surface area of 1604.9 m2/g is prepared by the pyrolysis of rubberwood sawdust using CaCO3 as a hard template. The bio-oil pyrolyzed from the rubber sawdust, followed by the polymerization reaction to form resole phenolic resin, can be used as a carbon source to prepare HPC. The biomass-derived HPC shows a three-dimensionally interconnected morphology which can offer a continuous pathway for ionic transport. The symmetrical supercapacitors based on the as-prepared HPC were tested in 1.0 M tetraethylammonium tetrafluoroborate/propylene carbonate electrolyte. The results of electrochemical analysis show that the HPC-based supercapacitor exhibits a high specific capacitance of 113.3 F/g at 0.5 A/g with superior rate capability and cycling stability up to 5000 cycles. Hybrid lithium-ion capacitors (LICs) based on the HPC and Li4Ti5O12 (LTO) were also fabricated. The LICs have a maximum energy density of 113.3 Wh/kg at a power density of 281 W/kg. Moreover, the LIC also displays a remarkable cycling performance with a retention of 92.8% after 3000 cycles at a large current density of 0.75 A/g, suggesting great potential application in the energy storage of the LIC.

Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries

Carbon-coated Li₄Ti₅O₁₂ (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Boosting Ultra-Fast Charge Battery Performance: Filling Porous nanoLi4Ti5O12 Particles with 3D Network of N-doped Carbons

Lithium titanium oxide (Li₄Ti₅O₁₂)-based cells are a promising technology for ultra-fast charge-discharge and long life-cycle batteries. However, the surface reactivity of Li₄Ti₅O₁₂ and lack of electronic conductivity still remains problematic. One of the approaches toward mitigating these problems is the use of carbon-coated particles. In this study, we report the development of an economical, eco-friendly, and scalable method of making a homogenous 3D network coating of N-doped carbons. Our method makes it possible, for the first time, to fill the pores of secondary particles with carbons; we reveal that it is possible to cover each primary nanoparticle. This unique approach permits the creation of lithium-ion batteries with outstanding performances during ultra-fast charging (4C and 10C), and demonstrates an excellent ability to inhibit the degradation of cells over time at 1C and 45 °C. Furthermore, using this method, we can eliminate the addition of conductive carbons during electrode preparation, and significantly increase the energy density (by weight) of the anode.

One-Step Synthesis of a Nanosized Cubic Li2TiO3-Coated Br, C, and N Co-Doped Li4Ti5O12 Anode Material for Stable High-Rate Lithium-Ion Batteries

Nanosized Li₄Ti₅O₁₂ with both a Li₂TiO₃ coating and C-N-Br co-doping (CLLTO) was successfully synthesized via a facile reverse microemulsion method in one step using hexadecyl trimethyl ammonium bromide as a surface control agent and as a carbon, nitrogen, and bromine source. A uniform Li₂TiO₃ layer was formed on the surface and strongly adhered to the host material Li₄Ti₅O₁₂ (LTO), which played an important role in improving the cyclic stability of CLLTO. The thin and stable Li₂TiO₃ layer has the same cubic structure as LTO, which provides many three-dimensional channels for ion transport. C, N, and Br co-doping in CLLTO promoted the transition of Ti⁴⁺ to Ti³⁺ in Li₄Ti₅O₁₂, which could improve the capacity and facilitate the Li⁺ ion and electron transfer at the interface. The conductive behavior induced by co-doping was estimated by UV-vis diffuse reflectance spectra and further supported by theoretical calculations. The electrical conductivity of both p-type and n-type LTO can be well improved by co-doping C, N, and Br. This improvement may be due to the band gap reduction and the increased n-type electronic modification of the entire LTO. Owing to the synergistic effect of coating, co-doping, and nanosizing at one time, the CLLTO exhibits a high discharge capacity of 177.3-153.9 mA h g^-1 at the working rate of 0.1C-20C, with a capacity retention of 86%. The stable cycling of CLLTO is also obtained after 500 cycles at 20C, with a capacity retention of 95.5% (approximately 8 times higher than that of pure LTO) and almost 100% Coulombic efficiency. With high capacity, excellent rate performance, and good cycling stability, CLLTO can be applied in high-power lithium-ion batteries.

Fabrication of Li4Ti5O12@CN Composite With Enhanced Rate Properties

Folic acid is first time applied as a carbon-nitrogen precursor to fabricate Li4Ti5O12@CN composites via ball milling Nano-TiO2, Li2CO3 and folic acid with ethanol as solvent, and then followed by heating treatment in argon. XRD, SEM, TEM, XPS, charge-discharge test and EIS are used to evaluate the influence of N-doped carbon coating on its structure, morphologies and electrochemical property. It is demonstrated that the N-doped carbon coated Li4Ti5O12 composite exhibits superior high-rate performance compared with pure Li4Ti5O12. It possesses a high discharge capacity of 174, 165 mAh g-1 at 0.5 and 10 C, respectively. Additionally, an initial specific capacity of 96.2% is obtained after 200 cycles at 10 C. The remarkable performance might be put down to the N-doped carbon layer providing efficiently electron conductive network and nanosized decreasing lithium ion diffusion path.

Preparation of Lithium Titanate/Reduced Graphene Oxide Composites with Three-Dimensional "Fishnet-Like" Conductive Structure via a Gas-Foaming Method for High-Rate Lithium-Ion Batteries

With use of ammonium chloride (NH₄Cl) as the pore-forming agent, three-dimensional (3D) "fishnet-like" lithium titanate/reduced graphene oxide (LTO/G) composites with hierarchical porous structure are prepared via a gas-foaming method. Scanning electron microscopy and transmission electron microscopy images show that, in the composite prepared with the NH₄Cl concentration of 1 mg mL^-1 (1-LTO/G), LTO particles with sizes of 50-100 nm disperse homogeneously on the 3D "fishnet-like" graphene. The nitrogen-sorption analyses reveal the existence of micro-/mesopores, which is attributed to the introduction of NH₄Cl into the gap between the graphene sheets that further decomposes into gases and produces hierarchical pores during the thermal treatment process. The loose and porous structure of 1-LTO/G composites enables the better penetration of electrolytes, providing more rapid diffusion channels for lithium ion. As a result, the 1-LTO/G electrode delivers an ultrahigh specific capacity of 176.6 mA h g^-1 at a rate of 1 C. Even at 3 and 10 C, the specific capacity can reach 167.5 and 142.9 mA h g^-1, respectively. Moreover, the 1-LTO/G electrode shows excellent cycle performance with 95.4% capacity retention at 10 C after 100 cycles. The results demonstrate that the LTO/G composite with these properties is one of the most promising anode materials for lithium-ion batteries.

Synthesis of Spherical Silver-coated Li4Ti5O12 Anode Material by a Sol-Gel-assisted Hydrothermal Method

ᅟ: Ag-coated spherical Li₄Ti₅O₁₂ composite was successfully synthesized via a sol-gel-assisted hydrothermal method using an ethylene glycol and silver nitrate mixture as the precursor, and the influence of the Ag coating contents on the electrochemical properties of its was extensively investigated. X-ray diffraction (XRD) analysis indicated that the Ag coating does not change the spinel structure of Li₄Ti₅O₁₂. The electrochemical impedance spectroscopy (EIS) analyses demonstrated that the excellent electrical conductivity of the Li₄Ti₅O₁₂/Ag resulted from the presence of the highly conducting silver coating layer. Additionally, the nano-thick silver layer, which was uniformly coated on the particles, significantly improved this material's rate capability. As a consequence, the silver-coated micron-sized spherial Li₄Ti₅O₁₂ exhibited excellent electrochemical performance. Thus, with an appropriate silver content of 5 wt.%, the Li₄Ti₅O₁₂/Ag delivered the highest capacity of 186.34 mAh g^-1 at 0.5C, which is higher than that of other samples, and maintained 92.69% of its initial capacity at 5C after 100 cycles. Even at 10C after 100 cycles, it still had a capacity retention of 89.17%, demonstrating remarkable cycling stability.

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ISRCTN NARL-D-17-00568.

Enhanced Rate Capability and Low-Temperature Performance of Li4Ti5O12 Anode Material by Facile Surface Fluorination

A commercial Li₄Ti₅O₁₂ material was modified by NH₄F using a facile and dry method at a low temperature in air. X-ray diffraction reveals that the fluorination did not change the bulk structure of Li₄Ti₅O₁₂. X-ray photoelectron spectroscopy demonstrates that LiF was formed at the surface and Ti⁴⁺ was partially changed into Ti³⁺. Microscopic images show that some nanoislands were formed on the surface, which enlarged the surface area. Consequently, the NH₄F-modified Li₄Ti₅O₁₂ material exhibited significantly enhanced capacities and rate capabilities, even at low temperatures. The discharge capacity was increased from 149 to 167 mA h g^-1 at 1 C, and the capacity retention was increased from 17.8 to 52.0% at 15 C. The capacity retention of NH₄F-modified Li₄Ti₅O₁₂ was greater than that of Li₄Ti₅O₁₂ at each low-temperature point. Additionally, the introduction of F can protect the Li₄Ti₅O₁₂ material from side reactions with the electrolyte and the atmosphere, enhancing the surface stability and reducing the release of gaseous products. It is believed that the NH₄F-modified Li₄Ti₅O₁₂ with enhanced electrochemical performance is a promising anode material for lithium ion batteries. Furthermore, this facile surface fluorination strategy is amenable to large-scale production.

A Novel Ultrafast Rechargeable Multi-Ions Battery

An ultrafast rechargeable multi-ions battery is presented, in which multi-ions can electrochemically intercalate into graphite layers, exhibiting a high reversible discharge capacity of ≈100 mAh g^-1 and a Coulombic efficiency of ≈99% over hundreds of cycles at a high current density. The results may open up a new paradigm for multi-ions-based electrochemical battery technologies and applications.

Chromium-Modified Li4Ti5O12 with a Synergistic Effect of Bulk Doping, Surface Coating, and Size Reducing

Bulk doping, surface coating, and size reducing are three strategies for improving the electrochemical properties of Li4Ti5O12 (LTO). In this work, chromium (Cr)-modified LTO with a synergistic effect of bulk doping, surface coating, and size reducing is synthesized by a facile sol-gel method. X-ray diffraction (XRD) and Raman analysis prove that Cr dopes into the LTO bulk lattice, which effectively inhibits the generation of TiO2 impurities. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) verifies the surface coating of Li2CrO4 on the LTO surface, which decreases impedance of the LTO electrode. More importantly, the size of LTO particles can be significantly reduced from submicroscale to nanoscale as a result of the protection of the Li2CrO4 surface layer and the suppression from Cr atoms on the long-range order in the LTO lattice. As anode material, Li4-xCr3xTi5-2xO12 (x = 0.1) delivers a reversible capacity of 141 mAh g(-1) at 10 °C, and over 155 mAh g(-1) at 1 °C after 1000 cycles. Therefore, the Cr-modified Li4Ti5O12 prepared via a sol-gel method has potential for applications in high-power, long-life lithium-ion batteries.

Eco-friendly nitrogen-containing carbon encapsulated LiMn2O4 cathodes to enhance the electrochemical properties in rechargeable Li-ion batteries

This study describes the synthesis of nitrogen-containing carbon (N-C) and an approach to apply the N-C material as a surface encapsulant of LiMn₂O₄ (LMO) cathode material. The N heteroatoms in the N-C material improve the electrochemical performance of LMO. A low-cost wet coating method was used to prepare N-C@LMO particles. The N-C@LMO was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), high-resolution Raman spectroscopy (HR-Raman), field emission scanning electron microscopy (FE-SEM), and field emission scanning transmission electron microscopy (FE-TEM) with elemental mapping. Furthermore, the prepared samples were electrochemically studied using the AC electrochemical impedance spectroscopy (EIS) and the electrochemical cycler. XPS suggested that the N-C coating greatly reduced the dissolution of Mn and EIS showed that the coating greatly suppressed the charge transfer resistance, even after long-term cycling. The control of Mn dissolution and inner resistance allowed faster Li-ion transport between the two electrodes resulting in improved discharge capacity and cycling stability.

Preparation of a graphitic N-doped multi-walled carbon nanotube composite for lithium–sulfur batteries with long-life and high specific capacity

One of the challenges for lithium–sulfur batteries is a rapid capacity fading owing to the insulating of sulfur and Li₂S₂/Li₂S compounds, the dissolving and consequent shuttling of polysulfide.

Sb doped Li4Ti5O12 hollow spheres with enhanced lithium storage capability

The Sb doped Li₄Ti₅O₁₂ hollow spheres with an average diameter of around 3.5 μm were synthesized successfully via through a two-step process. Sb⁵⁺ doping can improve the capacity and maintain the cycling stability.