Practical Li-ion Batteries Research Articles

Wet-chemical coordination synthesized Li3V2(PO4)3/C for Li-ion battery cathodes

Lithium vanadium phosphate (Li3V2(PO4)3) is one of the most promising cathode materials for developing practical Li-ion batteries due to its advantages of structural stability, low cost, relatively high energy density. For this purpose, a wet-chemical coordination approach has been applied to synthesis of the Li3V2(PO4)3/C (LVP/C) cathode materials for Li-ion batteries. The structure, morphology, and electrochemical and kinetic behaviors of LVP/C samples calcined at different temperatures are studied. The optimized Li3V2(PO4)3 sample calculated at 850 °C (denoted as LVP-850) exhibits excellent rate performance: at high rate of 0.5, 1, 5, 10 and 20 C, impressive specific capacity of 110.9, 106, 91.2, 83 and 43.6 mAh g−1 can still be attainted, respectively. Even through it recovers back to 0.1 C, the cell can still deliver a capacity of 114.4 mAh g−1 (about 97.9% of the initial capacity). Combined with cyclic voltammetry technique and ex-situ X-ray photoemission spectroscopy (XPS), the Li+ insertion/extraction reaction mechanisms are also confirmed. Such an efficient method plays a critical role in improving rate performance and cyclic reversibility of Li3V2(PO4)3 particles, and should also be appropriate for other functional electrode materials.

Micron-sized Secondary Silicon Spherical Composite for Practical Li-ion Batteries

The ever-growing demand for smaller batteries with higher energy density and longer life cycle has triggered research interest on metal alloy materials as an anode for Li-ion batteries (LIBs) in broad applications such as electric vehicle and portable electronics, because metal alloys usually possess much higher theoretical gravimetric and volumetric capacities than those of graphite. Si has been considered as potential candidate due to its highest capacity (4200 mAh/g, according to a state of Li4.4Si), low price and high abundancy. However, progressively large volume change during the charge and discharge reactions hinders Si from being commercially used. We have successfully developed a micron-szied secondary Si-based composite (MSC), with Si nanoparticles (diameter ~70 nm, commercial) embedded in a porous conductive network constructed with conductive carbon and binder materials. Si NPs were purchased in bulk and used as received. The MSC anode exhibited an initial CE of 81%, and >99.8% thereafter. The volume expansion of Si has been effectively limited inside the secondary particle, avoiding damage to the structure of electrode. As a result, the MSC electrode delivered excellent cycling stability with 8% loss over 500 cycles at a rate of 0.5C. Considering the advantages of micron-sized composite, this material could be of interest in the application of real-life LIBs.

Practical Li-Ion Battery Assembly with One-Dimensional Active Materials.

Research activities on the development of one-dimensional (1D) nanostructures and their successful implementation in the fabrication of high-performance practical Li-ion batteries (LIBs) are described. Although numerous 1D-structured materials have been explored for use in LIBs as anodes, cathodes, and separator-cum-electrolytes, only a very limited number of studies report the practical assembly of LIBs using these components. As a result, the salient features of using 1D materials in charge-storage devices have not been realized from an application perspective. Exceptional battery performance is reported when all-1D-based electro-active materials are used to fabricate LIBs. Using all-1D nanostructures not only provides high power capability, energy density, and durability, it also opens up new avenues for developing high-performance next-generation Li-ion power packs.

A practical Li ion battery anode material with high gravimetric/volumetric capacities based on T-Nb2O5/graphite composite

Much progress has been made in developing high capacity, high rate capability and long life lithium ion batteries with nanomaterials, however, nanomaterials have two major issues to be addressed, including low tap density and severe side reactions due to active surface. Herein, we present a solution by forming layered micrometer-sized secondary architecture with a nanostructured building block. A composite of orthorhombic Nb2O5 (T-Nb2O5) inserted mesocarbon microbeads (MCMB) is prepared. Electron microscope images demonstrate the T-Nb2O5 nanoparticles distributing in gaps of graphitic layers homogenously. The layered structure endows the composite good electron conductivity and facilitated ion transport channels when using it as Li ion battery anode material, which possesses capacities of more than 1000 and 100mAhg−1 at 0.06 and 90Ag−1 (discharge in 4.0s), respectively, much better than raw MCMB. Furthermore, stable surface leads the composite a small initial irreversible capacity (8.7%) and good durability (2500 cycles) at high rate currents. More attractively, a reasonable tap density (0.58gcm−3) of the composite results in large volumetric capacity densities (e.g. 120AhL−1 at a rate current of 30Ag−1), making it more practical than traditional nanostructured materials.

High Performance Arsenic: Multiwall Carbon Nanotube Composite Anodes for Li-Ion Batteries

Li-alloying materials for Li-ion anodes have garnered much attention because of their abilities to react with large amounts of Li. As is another Li alloying element with a specific capacity of 1073 mAh g−1. Despite having a high specific capacity to alloy Li (1073 mAh g−1), As has been largely ignored and little is known of its electrochemical behavior. The synthesis of nanoparticulate As is described herein and its excellent performance as the active material in Li-ion battery anodes demonstrated. Comparison of micron and nanoscale As mixed with multiwall carbon nanotubes (MWCNT) shows the later to have dramatically better performance, particularly when cycled in FEC:DEC rather than EC:DMC electrolyte. Further improvement is shown by synthesizing the nanoscale As directly on the MWCNT, with excellent performance with mass loadings up to 80% As, achieving a maximum capacity of 746 mAh g−1 and fading only 17% over 200 cycles. The reversible capacity demonstrated here is more than twice that of the best previously reported, showing that As could be an inexpensive, high performance alternative active material for practical Li-ion battery anodes.

Scalable synthesis of Si/SiO2@C composite from micro-silica particles for high performance lithium battery anodes

Silicon/silica (Si/SiO2) composite is prepared directly from irregular micro-silica via mechanical milling followed by modified magnesiothermic reduction process. After that, phenolic resin is introduced as carbon source to fabricate the silicon/silica@carbon (Si/SiO2@C) composite. The structure of the composite is revealed by x-ray diffraction (XRD). SEM and TEM observations reveal that the micro-silica particles are broken into submicron scale and part of the silica particles are reduced to silicon by Mg reduction. When evaluated as an anode material for Li-ion batteries, the electrochemical performance of the composite is good. At 50mAg−1, the Si/SiO2@C (50wt.% C) sample exhibits a high initial charge capacity of 685.8mAhg−1. After 100cycles, it retains reversible capacity of 482mAhg−1. The composite also shows superior rate performance. At 500mAg−1, it can deliver high reversible capacity of 462.3mAhg−1. Considering the facile preparation and low-cost of raw material, the prepared Si/SiO2@C composite holds promise in practical Li-ion batteries.

Molybdenum oxide-iron oxide/graphene composite as anode materials for lithium ion batteries

Molybdenum oxide-iron oxide/graphene (MoO2-Fe3O4/G) ternary nanocomposite is firstly prepared as for an anode material for lithium ion batteries. The MoO2-Fe3O4/G hybrid electrode exhibits a high specific capacity, long cycle life, and good rate capability. The initial charge specific capacity is 922.0 mAh g−1 of MoO2-Fe3O4/G nanocomposite and it increases to 1154.9 mAh g−1 gradually after 100 cycles, which is 125 % comparing to the initial charge capacity. The conductive graphene and Fe3O4 nanoparticles facilitate the conductivity of electrons and the diffusion of lithium-ions by shortening the transport distance. Additionally, the graphene and Fe3O4 not only work as a mechanical support to buffer the volume changes but also protect the MoO2 crystals from agglomeration during lithium ion intercalation/de-intercalation. The results demonstrate that the MoO2-Fe3O4/G nanocomposite is a promising alternative anode material for practical Li-ion batteries.

Revisit of metallothermic reduction for macroporous Si: compromise between capacity and volume expansion for practical Li-ion battery

We revisit the metallothermic reduction process to synthesize shape-preserving macro-/nanoporous Si particles via aluminothermic and subsequent magnesiotheric reaction of porous silica particles. This process enables us to control the specific capacity and volume expansion of shape-preserving porous Si-based anodes. Two step metallothermic reactions have several advantages including a successful synthesis of shape-preserving Si particles, tunable specific capacity of as-synthesized Si anode, accommodation of a large volume change of Si by porous nature and alumina layers, and a scalable synthesis (hundreds of gram per batch). An optimized macroporous Si/Al2O3 composite anode exhibits a reversible capacity of ~1500mAhg−1 after 100 cycles at C/5 and a volume expansion of ~34% even after 100 cycles.

Preparation and characterization of imidazolium-PEO-based Ionene/PVDF(HFP)/LiTFSI as a novel Gel polymer electrolyte

The synthesis and properties of a solvent-free gel polymer electrolyte based on an imidazolium-poly(ethylene oxide) (PEO)-based ionene electrolyte, a poly(vinylidene fluoride-hexafluoropropylene) (PVDF(HFP)) support, and the lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt are reported. A ternary gel polymer electrolyte film, produced from mixtures of the imidazolium-PEO-based ionene ([IPI][Br]), PVDF(HFP), and LiTFSI, displayed good thermal and mechanical stability. A very high room temperature conductivity of 2.6×10-3 S/cm and a broad electrochemical stability window were obtained, demonstrating the utility of the electrolyte for practical Li-ion battery applications. Open image in new window

Tin oxide-titanium oxide/graphene composited as anode materials for lithium-ion batteries

A tin oxide-titanium oxide/graphene (SnO2-TiO2/G) ternary nanocomposite as high-performance anode for Li-ion batteries was prepared via a simple reflux method. The graphite oxide (GO) was reduced to graphene nanosheet, and the SnO2-TiO2 nanocomposites were evenly distributed on the graphene matrix in the SnO2-TiO2/G nanocomposite. The as-prepared SnO2-TiO2/G nanocomposites were employed as anode materials for lithium-ion batteries, showing an outstanding performance with high reversible capacity and long cycle life. The composite delivered a superior initial discharge capacity of 1,594.6 mAh g−1 and a reversible specific capacity of 1,500.3 mAh g−1 at a current density of 100 mA g−1. After 100 cycles, the reversible discharge capacity was still maintained at 1,177.4 mAh g−1 at a current density of 100 mA g−1 with a high retained rate of reversible capacity of 73.8 %. The addition of small amount of TiO2 nanoparticles improved the cycling stability and specific capacity of SnO2-TiO2/G nanocomposite, obviously. The results demonstrate that the SnO2-TiO2/G nanocomposite is a promising alternative anode material for practical Li-ion batteries.

Investigation of Graphite Foil as Current Collector for Positive Electrodes of Li-Ion Batteries

We present herein results from a study on replacing the materials for two Li-ion battery (LIB) components: (1) LiPF6 by LiN(SO2CF3)2 (a.k.a. LiTFSI) as electrolyte in alkyl carbonate based solutions and (2) aluminum foil by graphite foil (a.k.a. Grafoil) as current collector for positive electrodes. LiTFSI may be a better electrolyte than LiPF6 since it does not decompose in water, has increased thermally stability, and its solutions in organic solvents do not contain acidic species detrimental to battery performance. However, since LiTFSI solutions do not passivate aluminum, they must be used with alternative current collectors like Grafoil. We used LiMn0.33Ni0.33Co0.33O2 as active positive electrode material and compared its electrochemical performance and thermal behavior in LiTFSI/EC:DMC when supported by Grafoil with that obtained in LiPF6/EC:DMC when supported by aluminum. We show that LiTFSI solutions can be used together with Grafoil current collectors for positive electrodes with operating potentials below 4.3 V. While significant development efforts to successfully replace aluminum foil by Grafoil in practical Li-ion batteries are still needed, our results indicate that such work may lead to improved battery performance and is therefore worth pursuing.

Enhanced nanoscale conduction capability of a MoO2/Graphene composite for high performance anodes in lithium ion batteries

A MoO2/Graphene composite as a high performance anode for Li ion batteries is synthesized by a one pot in-situ low temperature solution phase reduction method. Electron microscopy and Raman spectroscopy results confirm that 2D graphene layers entrap MoO2 nanoparticles homogeneously in the composite. X-ray photoelectron spectroscopy shows the presence of oxygen functionalities on graphene, which allows intimate contact between MoO2 nanoparticles and the graphene. Conductive atomic force microscopy reveals an extraordinarily high nanoscale electronic conductivity for MoO2/Graphene, greater by 8 orders of magnitude in comparison to bulk MoO2. The layered nanostructure and the conductive matrix provide uninhibited conducting pathways for fast charge transfer and transport between the oxide nanoparticles and graphene which are responsible for the high rate capability, a large lithium ion capacity of 770 mAh g−1, and an excellent cycling stability (550 mAh g−1 reversible capacity retained even after 1000 cycles!) at a current density of 540 mA g−1, thereby rendering it to be superior to previously reported values for neat MoO2 or MoO2/Graphene composite. Impedance analyses demonstrate a lowered interfacial resistance for the composite in comparison to neat MoO2. Our results demonstrate the enormous promise that MoO2/Graphene holds for practical Li-ion batteries.

Mesoporous Co3O4Nanowire Arrays for Lithium Ion Batteries with High Capacity and Rate Capability

We report the high capacity and rate capability of mesoporous Co3O4 nanowire (NW) arrays as anodes in Li ion batteries. At a current of 1C, the NW arrays maintain a capacity of 700 mAh/g after 20 discharge/charge cycles. When the current is increased to 50C, 50% of the capacity can be retained. With their ease of large area synthesis and superior electrochemical properties, these Co3O4 NW arrays will be interesting for practical Li ion batteries.

Thermal behavior analysis of lithium-ion batteries for electric and hybrid vehicles

Abstract Thermodynamics experiment and study were carried out for the lithium-ion (Li-ion) batteries that are expected as the power sources for electric and hybrid vehicles. It is confirmed that the heat coming in and going out depend on charging and discharging, respectively. And the thermal generation factors will be decomposed to three elements: reaction heat value Qr, polarization heat value Qp, and Joule heat value QJ. Furthermore, the contribution degree of each factor was able to be expressed quantitatively by dividing these thermal generation factors for charging and discharging. The accuracy of thermodynamics logic was verified since the thermodynamics calculation coincided with the experimental data of thermal generation for the practical Li-ion batteries for electric vehicles (EV). It is possible to utilize the calculation and simulation for the development of Li-ion battery and the establishment of thermal control technology not only for EV but also for hybrid electric vehicles (HEV).

Thermal behavior analysis of lithium-ion batteries for electric and hybrid vehicles

Thermodynamics experiment and study were carried out for the lithium-ion (Li-ion) batteries that are expected as the power sources for electric and hybrid vehicles. It is confirmed that the heat coming in and going out depend on charging and discharging, respectively. And the thermal generation factors will be decomposed to three elements: reaction heat value Q r, polarization heat value Q p, and Joule heat value Q J. Furthermore, the contribution degree of each factor was able to be expressed quantitatively by dividing these thermal generation factors for charging and discharging. The accuracy of thermodynamics logic was verified since the thermodynamics calculation coincided with the experimental data of thermal generation for the practical Li-ion batteries for electric vehicles (EV). It is possible to utilize the calculation and simulation for the development of Li-ion battery and the establishment of thermal control technology not only for EV but also for hybrid electric vehicles (HEV).

The Study of Surface Film Formation on Noble-Metal Electrodes in Alkyl Carbonates/Li Salt Solutions, Using Simultaneous in Situ AFM, EQCM, FTIR, and EIS

In this study, surface film formation on nonactive-metal electrodes was analyzed using several in situ spectroelectrochemical techniques. These techniques included in situ Fourier transform infrared spectroscopy in both internal and external reflectance modes, impedance spectroscopy, electrochemical quartz crystal microbalance, and atomic force microscopy. The solutions studied included ethylene carbonate−dimethyl carbonate (EC−DMC) and EC−tetrahydrofurane (EC−THF) mixtures with Li salts, such as LiAsF6, LiPF6, LiClO4, and LiBr, part of which are essential for practical Li ion batteries. This work aimed to determine the onset of surface film formation, the impact of the solvent and salt used, and to compare the stability of the surface films formed in the various systems. The onset of surface film formation in these systems usually approximated 1.5 V (Li/Li+). EC reduction products, probably (CH2OCO2Li)2, are dominant constituents in the surface films. However, in LiPF6 solutions, Li salt reduction products become dominant in the surface films. The surface film formation is accompanied by an injection of charge which does not form stable surface species and by dissolution processes of surface species (until the solution becomes saturated with them). The coherence of the data obtained from the four techniques mentioned above and the relative stability of the surface films formed in the various solutions are discussed.