Computational Investigation of Carbon Based Anode Materials for Li- and Post-Li- Ion Batteries

Due to its negligible capacity with respect to sodium intercalation, graphite is not suited as anode material for sodium ion batteries. Hard carbon materials, on the other hand, provide reasonably high capacities at low insertion potential, making them a promising anode materials for sodium (and potassium) ion batteries. The particular nanostructure of these functionalized carbon-based materials has been found to be crucially linked to the material performance. However, there is still a lack of understanding with respect to the functional role of structural units, such as defects, for intercalation and storage. To overcome these problems, the intercalation of Li, Na, and K in graphitic model structures with distinct defect configurations has been investigated by density functional theory. The calculations confirm that defects are able to stabilize intercalation of larger alkali metal contents. At the same time, it is shown that a combination of phonon and band structure calculations are able to explain characteristic Raman features typically observed for alkali metal intercalation in hard carbon, furthermore allowing for the quantification of the alkali metal intercalation inbetween the layers of hard carbon anodes.

A High-Energy Density Li-Ion Hybrid Capacitor Fabricated from Bio-Waste Derived Carbon Nanosheets Cathode and Graphite Anode

The Li-ion hybrid capacitor (LIHC) system explores the possibility of achieving both high energy and power density in a single energy storage system with an intercalation anode and capacitive cathode. However, to achieve a high power and energy-based system, the properties of the cathode electrode material are vital. Here, bio-waste plant stem-derived activated porous carbon is explored as a cathode for LIHC application. A specific surface area of 1826 m² g^-1, enhanced degree of crystallinity, and graphitization results for porous carbon from activation by potassium hydroxide. When employed as supercapacitor material, the device exhibits good rate capability, energy, and power attributes with a specific capacitance of 116 F g^-1 (1 A g^-1). Simultaneously when tested for LIHC application the formulated device shows good capacity retention for 2500 cycles with a high energy density of 125 Wh kg^-1 at a power density of 69 W kg^-1. The work demonstrates unique, cost-effective strategy to develop a crystalline high surface area carbon from any such bio-waste sources to be employed as potential electrodes for energy storage applications.

Aberration-corrected transmission electron microscopy of a non-graphitizing carbon

Non-graphitizing carbons (NGCs) are an important class of solid carbons which cannot be converted into graphite by high-temperature heat treatment. They include commercially valuable materials such as activated carbon and glassy carbon. These carbons have been intensively studied for decades, but there is still no agreement about their detailed atomic structure, or the reasons for their resistance to graphitization. The first models for graphitizing and NGCs were proposed by Rosalind Franklin in the early 1950s, and while these are broadly correct, they are incomplete. Many alternative models of NGCs have been put forward since Franklin's time, but none has received universal acceptance. Diffraction and spectroscopic techniques can provide important insights into the nature of these carbons, but only direct microscopic imaging can reveal their true atomic structure. Here, we apply aberration-corrected transmission electron microscopy to an activated carbon prepared from waste biomass and present evidence for the presence of pentagonal and heptagonal carbon rings. This provides support for a model of the structure of NGC made up of curved fragments in which non-hexagonal rings are dispersed randomly throughout hexagonal networks.

Defects in Hard Carbon: Where Are They Located and How Does the Location Affect Alkaline Metal Storage?

Hard carbon anodes have shown significant promise for next-generation battery technologies. These nanoporous carbon materials are highly complex and vary in structure depending on synthesis method, precursors, and pyrolysis temperature. Structurally, hard carbons are shown to consist of disordered planar and curved motifs, which have a dramatic impact on anode performance. Here, the impact of position on defect formation energy is explored through density functional theory simulations, employing a mixed planar bulk and curved surface model. At defect sites close to the surface, a dramatic decrease ( ≥ 50%) in defect formation energy is observed for all defects except the nitrogen substitutional defect. These results confirm the experimentally observed enhanced defect concentration at surfaces. Previous studies have shown that defects have a marked impact on metal storage. This work explores the interplay between position and defect type for lithium, sodium, and potassium adsorption. Regardless of defect location, it is found that the energetic contributions to the metal adsorption energies are principally dictated by the defect type and carbon interlayer distance.

Tin Oxide Encapsulated into Pyrolyzed Chitosan as a Negative Electrode for Lithium Ion Batteries

Tin oxide is one of the most promising electrode materials as a negative electrode for lithium-ion batteries due to its higher theoretical specific capacity than graphite. However, it suffers lack of stability due to volume changes and low electrical conductivity while cycling. To overcome these issues, a new composite consisting of SnO2 and carbonaceous matrix was fabricated. Naturally abundant and renewable chitosan was chosen as a carbon source. The electrode material exhibiting 467 mAh g−1 at the current density of 18 mA g−1 and a capacity fade of only 2% after 70 cycles is a potential candidate for graphite replacement. Such good electrochemical performance is due to strong interaction between amine groups from chitosan and surface hydroxyl groups of SnO2 at the preparation stage. However, the charge storage is mainly contributed by a diffusion-controlled process showing that the best results might be obtained for low current rates.

Adsorption and migration of alkali metals (Li, Na, and K) on pristine and defective graphene surfaces

In this paper, a computational study of Li, Na, and K adsorption and migration on pristine and defective graphene surfaces is conducted to gain insight into the metal storage and mobility in carbon-based anodes for alkali metal batteries. Atomic level studies of the metal adsorption and migration on the graphene surface can help address the challenges faced in the development of novel alkali metal battery technologies, as these systems act as convenient proxies of the crystalline carbon surface in carbon-based materials including graphite, hard carbons and graphene. The adsorption of Li and K ions on the pristine graphene surface is shown to be more energetically favourable than Na adsorption. A collection of defects expected to be found in carbonaceous materials are investigated in terms of metal storage and mobility, with N- and O-containing defects found to be the dominant defects on these carbon surfaces. Metal adsorption and migration at the defect sites show that defect sites tend to act as metal trapping sites, and metal diffusion around the defects is hindered when compared to the pristine surface. We identify a defect where two C sites are substituted with O and one C site with N as the dominant surface defect, and find that this defect is detrimental to metal migration and hence the battery cycling performance.

Enhanced electron transfer mediator based on biochar from microalgal sludge for application to bioelectrochemical systems

This study is focused on the utilization of waste microalgal sludge (MS) from microalgal extraction and its potential as an electrode material. The MS was activated under N₂ at high temperature for conversion to biochar (MSB). In addition, cobalt (Co; metal hydroxide) and chitosan were used as a mediator for electron transfer by immobilization on MSB (MSB/Co/chitosan). Through analysis of the surface and components of the MSB/Co/chitosan, it was shown that Co and chitosan were properly synthesized with MSB. The enzymatic fuel cell (EFC) system successfully obtained a power density of 3.1 mW cm^-2 and a current density of 9.7 mA cm^-2. In addition, the glucose biosensors applied with the developed electron transfer mediator showed a sensitivity of 0.488 mA mM^-1 cm^-2.

Neutron vibrational spectroscopic studies of novel tire-derived carbon materials

Sulfonated tire-derived carbons have been demonstrated to be high value-added carbon products of tire recycling in several energy storage system applications including lithium, sodium, potassium ion batteries and supercapacitors. In this communication, we compared different temperature pyrolyzed sulfonated tire-derived carbons with commercial graphite and unmodified/non-functionalized tire-derived carbon by studying the surface chemistry and properties, vibrational spectroscopy of the molecular structure, chemical bonding such as C-H bonding, and intermolecular interactions of the carbon materials. The nitrogen adsorption-desorption studies revealed the tailored micro and meso pore size distribution of the carbon during the sulfonation process. XPS and neutron vibrational spectra showed that the sulfonation of the initial raw tire powders could remove the aliphatic hydrogen containing groups ([double bond splayed left]CH₂ and -CH₃ groups) and reduce the number of heteroatoms that connect to carbon. The absence of these functional groups could effectively improve the first cycle efficiency of the material in rechargeable batteries. Meanwhile, the introduced -SO₃H functional group helped in producing terminal H at the edge of the sp² bonded graphite-like layers. This study reveals the influence of the sulfonation process on the recovered hard carbon from used tires and provides a pathway to develop and improve advanced energy storage materials.

Low-Polarization Lithium-Oxygen Battery Using [DEME][TFSI] Ionic Liquid Electrolyte

The room-temperature molten salt mixture of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl) imide ([DEME][TFSI]) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is herein reported as electrolyte for application in Li-O₂ batteries. The [DEME][TFSI]-LiTFSI solution is studied in terms of ionic conductivity, viscosity, electrochemical stability, and compatibility with lithium metal at 30 °C, 40 °C, and 60 °C. The electrolyte shows suitable properties for application in Li-O₂ battery, allowing a reversible, low-polarization discharge-charge performance with a capacity of about 13 Ah g-1carbon in the positive electrode and coulombic efficiency approaching 100 %. The reversibility of the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is demonstrated by ex situ XRD and SEM studies. Furthermore, the study of the cycling behavior of the Li-O₂ cell using the [DEME][TFSI]-LiTFSI electrolyte at increasing temperatures (from 30 to 60 °C) evidences enhanced energy efficiency together with morphology changes of the deposited species at the working electrode. In addition, the use of carbon-coated Zn_0.9 Fe_0.1 O (TMO-C) lithium-conversion anode in an ionic-liquid-based Li-ion/oxygen configuration is preliminarily demonstrated.

Rethinking Coal: Thin Films of Solution Processed Natural Carbon Nanoparticles for Electronic Devices

Disordered carbon materials, both amorphous and with long-range order, have been used in a variety of applications, from conductive additives and contact materials to transistors and photovoltaics. Here we show a flexible solution-based method of preparing thin films with tunable electrical properties from suspensions of ball-milled coals following centrifugation. The as-prepared films retain the rich carbon chemistry of the starting coals with conductivities ranging over orders of magnitude, and thermal treatment of the resulting films further tunes the electrical conductivity in excess of 7 orders of magnitude. Optical absorption measurements demonstrate tunable optical gaps from 0 to 1.8 eV. Through low-temperature conductivity measurements and Raman spectroscopy, we demonstrate that variable range hopping controls the electrical properties in as-prepared and thermally treated films and that annealing increases the sp(2) content, localization length, and disorder. The measured hopping energies demonstrate electronic properties similar to amorphous carbon materials and reduced graphene oxide. Finally, Joule heating devices were fabricated from coal-based films, and temperatures as high as 285 °C with excellent stability were achieved.

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Trash to Treasure: From Harmful Algal Blooms to High-Performance Electrodes for Sodium-Ion Batteries

Harmful algal blooms (HABs) are frequently reported around the globe. HABs are typically caused by the so-called blue-green algae in eutrophic waters. These fast-growing HABs could be a good source for biomass. Unlike terrestrial plants, they need no land or soil. If HABs could be harvested on a large scale, it could not only possible to mitigate the issue of HABs but also provide a source of biomass. Herein, we demonstrate a facile procedure for converting the HABs into a promising high-performance negative-electrode material for sodium-ion batteries (SIBs). The carbon material derived from blue-green algae demonstrated promising electrochemical performance in reversible sodium storage. The algae used in this work was collected directly from Lake Erie during the algal blooms that affected 500 000 residents in Toledo in 2014. The carbon, derived from the freshly collected HABs by calcination in argon without any additional purification process, delivered a highly stable reversible specific capacity (∼230 mAh/g at a testing current of 20 mA/g) with nearly 100% Columbic efficiency in sodium storage. Impressive rate performance was achieved with a capacity of ∼135 mAh/g even after the testing current was increased fivefold. This proof of concept provides a promising route for mitigating the issue of HABs as "trash" and for generating high-capacity, low-cost electrodes for SIBs as "treasure".

Facile fabrication of a three-dimensional cross-linking TiO2 nanowire network and its long-term cycling life for lithium storage

We describe a simple preparation of amorphous TiO2 nanomaterial through a simple dealloying method with high throughput at room temperature. The as-made TiO2 sample has a unique three-dimensional network structure built by cross-linking nanowires with the diameter of ∼5 nm. As an anode material for Li-ion batteries, the TiO2 product exhibits high capacities and a long cycling life at high rates of 500 and 1000 mA g(-1). In addition, it has a good rate capability. The as-made TiO2 nanowire network shows great application potential as an anode material with the advantages of unique performance and easy preparation.

Mn0.5Co0.5Fe2O4 nanoparticles highly dispersed in porous carbon microspheres as high performance anode materials in Li-ion batteries

We report the preparation of Mn(0.5)Co(0.5)Fe2O4 (MCFO) nanoparticles highly dispersed within porous carbon microspheres as anodes for Li-ion batteries. In situ growth of MCFO nanoparticles (5-20 nm) on the surface of carbon black (CB) and graphitized carbon black (GCB) nanoparticles was conducted via a hydrothermal method to form MCFO-CB and MCFO-GCB composites, respectively, which were employed as building blocks to assemble MCFO-CB and MCFO-GCB porous microspheres (PM) with a size of 5-30 μm by the spray drying technique using sucrose as a binder, and followed by carbonization in N2 (labeled as MCFO-CB-PM and MCFO-GCB-PM, respectively). Compared with the pure MCFO, MCFO-CB, and MCFO-GCB, both MCFO-CB-PM and MCFO-GCB-PM showed a significantly improved electrochemical performance. This is attributed to their unique porous structure, in which, the abundant pores promote the diffusion of Li-ion and electrolyte solution, the microspherical morphology enhances the electrode-electrolyte contact, and the carbon substrates from CB (and GCB) and sucrose substantially prevent the aggregation of MCFO nanoparticles and buffer the volume change. Particularly, MCFO-GCB-PM exhibits the best rate performance and excellent cycling stability because of the high graphitization degree of GCB. This work opens up an effective route for large scale fabrication of metal oxide/carbon porous microspheres as anode materials for potential applications in the new generation of Li-ion batteries.