Conformal Carbon Layer Research Articles

Achieving High Rate and Long Cycle Performance of Na2FePO4F Cathode Through Co-Modification of Ti Doping and Carbon Coating.

Layered Na2FePO4F (NFPF) cathode material has received widespread attention due to its green nontoxicity, abundant raw materials, and low cost. However, its poor inherent electronic conductivity and sluggish sodium ion transportation seriously impede its capacity delivery and cycling stability. In this work, NFPF by Ti doping and conformal carbon layer coating via solid-state reaction is modified. The results of experimental study and density functional theory calculations reveal that Ti doping enhances intrinsic conductivity, accelerates Na-ion transport, and generates more Na-ion storage sites, and pyrolytic carbon from polyvinylpyrrolidone (PVP) uniformly coated on the NFPF surface improves the surface/interface conductivity and suppresses the side reactions. Under the combined effect of Ti doping and carbon coating, the optimized NFPF (marked as 5T-NF@C) exhibits excellent electrochemical performance, with a high capacity of 108.4mAhg-1 at 0.2C, a considerable capacity of 80.0mAhg-1 even at high current density of 10C, and a high capacity retention rate of 81.8% after 2000 cycles at 10C. When assembled into a full cell with a hard carbon anode, 5T-NF@C also show good applicability. This work indicates that co-modification of Ti doping and carbon coating makes NFPF achieve high rate and long cycle performance for sodium-ion batteries.

Laser-Induced Graphene Capacitive Killing of Bacteria.

Laser-induced graphene (LIG) is a method of generating a foam-like conformal carbon layer of porous graphene on many types of carbon-based surfaces. This electrically conductive material has been shown to be useful in many applications including environmental technology and includes low fouling and antimicrobial surfaces and can address persistent environmental challenges spawned by bacterial and viral contaminates. Here, we show that a single film of LIG stores charge when an electrical current is applied and dissipates charge when the current is stopped, which results in electricidal surface antibacterial potency. The amount of accumulated and dissipated charge on a single strip of LIG was quantified with an electrometer by generating LIG on both sides of a nonconducting polyimide film, which showed up to 65 pC of charge when the distance between the surfaces was 94 μm corresponding to an areal capacitance of 1.63 pF/cm2. We further corroborate the stored charge decay of a single LIG strip with bacteria death via direct electrical contact. Antimicrobial rates decreased with the same monotonic pattern as the loss of charge from the LIG film (i.e., AR ∼ 97% 0 s after voltage source disconnection vs AR ∼ 21% 90 s after disconnection) showing bacterial death as a function of delayed LIG exposure time after applied voltage disconnection. In terms of energy efficiency, this translates to an increased bacteria potency of ∼170% for the equivalent energy costs as that previously estimated. Finally, we present a mechanistic explanation for the capacitive behavior and the electricidal effects for a single plate of LIG.

The preparation and performances of lithium sulfide (Li2S)-oriented cathode composite via carbothermic reduction

Abstract The high theoretical energy density, high environmental adaptability and safety of lithium sulfide (Li2S)-oriented cathodes attract enough attention among lithium-sulfur batteries (LSBs). In this work, the lithium sulfide (Li2S)-oriented composite is fabricated via an in-situ carbothermic reduction method, in which lithium sulfate is reduced by CMK3 at an optimized temperature and subsequently the as-prepared Li2S is protected via the conformal carbon layer by carbonization of phenol-formaldehyde resin (PF). With the aid of the porous carbon structure of CMK3 and protection of PF-derived conformal carbon layer, the dispersity of Li2S and conductivity of cathode are availably enhanced. It has been found that the Li2S@CMK3-C prepared at optimum carbothermic reduction temperature of 835 °C has excellent electrochemical performance. The lithium-sulfur battery using Li2S@CMK3-C as cathode and metal Li as anode can deliver a high initial discharge capacity of 979 mAh g−1 at 0.1 C, the capacity retention after running at various current density is 94%, and the discharge specific capacity is still 530 mAh g−1 at 2 C after 450 cycles. Therefore, the preparation of CMK3-supported Li2S-based cathode material provides a new approach for the development and industrialization of new high-performance Li–S battery.

Rational structure design to realize high-performance SiOx@C anode material for lithium ion batteries

Silicon suboxide (SiOx) is considered to be one of the most promising materials for next-generation anode due to its high energy density. For its preparation, the wet-chemistry method is a cost-effective and readily scalable route, while the so-derived SiOx usually shows lower capacity compared with that prepared by high temperature-vacuum evaporation route. Herein, we present an elaborate particle structure design to realize the wet-chemistry preparation of a high-performance SiOx/C nanocomposite. Dandelionlike highly porous SiOx particle coated with conformal carbon layer is designed and prepared. The highly-porous SiOx skeleton provides plenty specific surface for intimate contact with carbon layer to allow a deep reduction of SiOx to a low O/Si ratio at relatively low temperature (700 °C), enabling a high specific capacity. The abundant mesoscale voids effectively accommodate the volume variation of SiOx skeleton, ensuring the high structural stability of SiOx@C during lithiation/delithiation process. Meanwhile, the three-dimensional (3D) conformal carbon layer provides a fast electron/ion transportation, allowing an enhanced electrode reaction kinetics. Owing to the optimized O/Si ratio and well-engineered structure, the prepared SiOx@C electrode delivers an ultra-high capacity (1,115.8 mAh·g−1 at 0.1 A·g−1 after 200 cycles) and ultra-long lifespan (635 mAh·g−1 at 2 A·g−1 after 1,000 cycles). To the best of our knowledge, the achieved combination of ultra-high specific capacity and ultra-long cycling life is unprecedented.

V4P7@C nanocomposite as a high performance anode material for lithium-ion batteries

The V4P7 phase is synthesized by a facile high energy mechanical milling (HEMM) using vanadium (V) and red phosphorus (P), and its electrochemical properties and reaction mechanism as an anode for lithium ion batteries (LIBs) are investigated. As-synthesized 100 nm-sized V4P7 nanopowder electrode shows the insertion reaction during lithiation/delithiation by forming the amorphous Li-V-P ternary phase and delivers the high discharge and charge capacities of 1035 and 882 mA h g-1, respectively, with a high Coulombic efficiency of 85% at the current density of 100 mA g−1. In addition, V4P7 nanopowder is encapsulated with the conformal carbon layer, which is achieved through polymerization of dopamine and subsequent carbonization. As-fabricated core-shell V4P7@C nanocomposite electrode exhibits the much improved high rate capability and long cycle stability, delivering a high capacity of 388 mA h g-1 after 200 cycles at a high current density of 1 A g−1, which is attributed to high electrical conductivity, high Li+ ion mobility, and structural stability to restrict the aggregation and pulverization of active materials.

Conformal carbon layer coating on well-dispersed Si nanoparticles on graphene oxide and the enhanced electrochemical performance

Abstract Silicon nanoparticles (SiNPs)–graphene oxide (GO) composites are synthesized using a simple, fast, and mild ball-milling route. Uniform and conformal carbon layer is coated on the surface of SiNPs and the carbon-coated SiNPs are well-dispersed on the GO matrix by forming Si O C linkages. A high reversible capacity of 1265 mA g −1 at 50 mA g −1 after 80 cycles, good rate capability of 238 mAh g −1 at 2.5 A g −1 , and long-term cyclability of 230 mAh g −1 at 1 A g −1 after 800 cycles are resulted. The mild ball-milling can be highly promising and scalable approach for producing high-performance Si anode material.

Porous Zn2GeO4 nanowires with uniform carbon-buffer layer for lithium-ion battery anodes with long cycle life

Germanium-based multimetallic-oxide materials have attracted significant attention as high-capacity anodes for next generation lithium-ion batteries (LIBs). However, they suffer from poor cyclic stability due to extreme volume expansion and reduced electrical conductivity after repeated cycles. To circumvent these issues, we propose that Ge-based multimetallic-oxide nanowires can be synthesized with electrically conductive carbon to significantly enhance the cyclic stability of the Ge-based anodes. We prepare conformal-carbon-coated Zn2GeO4 nanowires (NWs) using a microwave-induced hydrothermal method with subsequent thermal decomposition. The obtained carbon-coated Zn2GeO4-NW anode exhibits a discharge capacity of 485 mAh/g and a Coulombic efficiency (CE) of 98.4% after 900 cycles at 0.6C. Furthermore, these anodes exhibit outstanding rate-capability characteristics, even with an increased C-rate of 17.7C. This excellent electrochemical performance can be ascribed to the improved electron and ion transport provided and the structurally reinforced conductive layer comprising a conformal carbon layer. Therefore, it is expected that our approach can also be applied to other multimetallic-oxide materials, resulting in large, reversible capacities; excellent cyclic stabilities; and good rate capabilities for high-performance LIBs.

Liquid carbon dioxide-based coating of a uniform carbon layer on hierarchical porous MoO2 microspheres and assessment of their electrochemical performance

Hierarchical mesoporous MoO2 microspheres coated with a uniform and ultrathin carbon layer were synthesized via a supercritical methanol (scMeOH) route followed by high-pressure free-meniscus coating (hFMC) using liquid carbon dioxide (l-CO2) as a coating solution. The MoO2 particles synthesized in scMeOH without surfactants or structure-directing chemicals exhibited nanosized primary particles of 30–80nm diameter, whose loose aggregation produced microsized secondary particles of 0.5–4.8μm diameter. The MoO2 particles had a highly porous structure with an average pore diameter of 10.5nm and a porosity of 52.7%. An ultrathin, uniform, and conformal carbon layer with thickness in the range of 1.5–2.0nm was coated on the primary MoO2 particles using l-CO2 as low-viscosity and low-surface tension solvent. When tested as anode in lithium ion batteries, the carbon-coated, hierarchical porous MoO2 (C-MoO2) particles exhibited excellent electrochemical performance. C-MoO2 with a carbon content of 6.6wt% delivered a reversible discharge capacity of 451.5mAhg−1 at 83.8mAg−1 after 100 cycles. C-MoO2 with a carbon content of 14.1wt% exhibited 120.9mAhg−1 of discharge capacity at the fast charge–discharge current of 3352mAg−1. The enhanced electrochemical performance of C-MoO2 was attributed to enhanced charge transfer kinetics to the electrode surface and increased Li ion diffusivity to the MoO2 phase during the charge/discharge process, as confirmed by electrochemical impedance spectroscopy.

Reduced graphene oxide/carbon double-coated 3-D porous ZnO aggregates as high-performance Li-ion anode materials

The reduced graphene oxide (RGO)/carbon double-coated 3-D porous ZnO aggregates (RGO/C/ZnO) have been successfully synthesized as anode materials for Li-ion batteries with excellent cyclability and rate capability. The mesoporous ZnO aggregates prepared by a simple solvothermal method are sequentially modified through distinct carbon-based double coating. These novel architectures take unique advantages of mesopores acting as space to accommodate volume expansion during cycling, while the conformal carbon layer on each nanoparticle buffering volume changes, and conductive RGO sheets connect the aggregates to each other. Consequently, the RGO/C/ZnO exhibits superior electrochemical performance, including remarkably prolonged cycle life and excellent rate capability. Such improved performance of RGO/C/ZnO may be attributed to synergistic effects of both the 3-D porous nanostructures and RGO/C double coating.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0902-7) contains supplementary material, which is available to authorized users.

Lithium Sulfide (Li2S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg(-1), which is much higher than that of Li ion cells (400-600 W·h kg(-1)). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li2Sn, n = 4-8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core-shell nanostructure comprising Li2S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell. The conformal carbon coating is easily obtained by a unique CVD coating process using a lab-designed rotating furnace without any repetitive steps. The Li2S/GO@C cathode exhibits a high initial discharge capacity of 650 mA·h g(-1) of Li2S (corresponding to the 942 mA·h g(-1) of S) and very low capacity decay rate of only 0.046% per cycle with a high Coulombic efficiency of up to 99.7% for 1500 cycles when cycled at the 2 C discharge rate.

Carbon coating for Si nanomaterials as high-capacity lithium battery electrodes

We report a new method to generate a thin carbon layer on active materials for electrochemical energy storage. A solid precursor can be simply placed on the target material in a tailored vertical quartz tube and sublimated at a slightly high temperature. The carbon source gas remains around the target material during the heat treatment because of the vapor density difference and subsequent decomposition of the gas phase leads to a uniform carbon coating. For demonstration of the concept, carbon coating on Si nanoparticles, which are a high-capacity anode material for lithium-ion batteries, was realized by sublimation and decomposition of naphthalene. A conformal carbon layer was confirmed by various analyses and improved electrochemical performance of the Si nanoparticle electrode was clearly exhibited.

Enhanced rate capability of LiMn0.9Mg0.1PO4 nanoplates by reduced graphene oxide/carbon double coating for Li-ion batteries

The reduced graphene oxide (RGO)/carbon double-coated LiMn0.9Mg0.1PO4 (LMP) nanoplates are introduced as a cathode material for Li-ion batteries with excellent rate capability. The double coating of RGO and carbon simultaneously brings the unique advantages of conformal carbon layer on each particle surface, and soft RGO sheets connecting the nanoplates to each other, thereby provides easy conduction pathways for the whole LMP aggregates. In particular, the simple self-assembly process driven by the electrostatic interactions enables conducting RGO sheets effectively to wrap the carbon-coated LMP, establishing three-dimensional RGO network. The RGO/C/LMP nanocomposites exhibit remarkably enhanced rate capability compared to the only C- or RGO-coated LMP, which is well explained by the reduced charge-transfer resistance achieved from electrochemical impedance spectroscopy.