Cobalt-Free Layered LiNi0.8Mn0.15Al0.05O2/Graphene Aerogel Composite Electrode for Next-Generation Li-Ion Batteries.

In this work, we introduce LiNi0.8Mn0.15Al0.05O2 (NMA), which is cobalt-free and has a high nickel content, and a conductive composite material to NMA by supporting it with a three-dimensional (3D) graphene aerogel (GA). With an easy freeze-drying approach, NMA nanoparticles are properly dispersed on graphene sheets, and GA creates a strong and conductive framework, significantly improving the structure and conductivity. The structure of the pure NMA and NMA/graphene aerogel (NMA/GA) composite was investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). XRD and FE-SEM analyses clearly indicated that ultrapure NMA structures are homogeneously dispersed among the GAs. In addition, the composite structure was examined using transmission electron microscopy (TEM) to determine the dispersion mechanisms. The electrochemical cycling performance of the pure NMA and NMA/GA composite was evaluated by rate capacitance, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The synthesized NMA/GA was able to provide 89.81% specific capacity retention after the 500th cycle at C/2. The average charge/discharge rates of the obtained cathode show good electrochemical results and exhibit capacities of 190.2,186.3, 185.2, 176.2, 161.2,142.6, and 188.5 mAh g-1 at C/20, C/10, C/5, C, 3C, 5C, and C/20, respectively. EIS data showed an improvement in the impedance of the composite containing GA. According to the results of the electrochemical tests, NMA nanoparticles formed a conductive network with its porous structure thanks to GA, formed a protective layer on the surface, prevented the side reactions between the cathode and the electrolyte, decreased the impedance of the cathode, and increased the redox kinetics. In addition, the changes in the structure were investigated in the NMA/GA composite cathode by XRD, FE-SEM, and Raman analyses at the end of the 50th, 250th, and 500th cycles. In summary, the NMA/GA cathode is expected to play an important role in lithium-ion batteries (LIBs) by taking advantage of its easy synthesis and excellent cycle stability.

Sulfur doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolytes with enhanced ionic conductivity and a reduced activation energy barrier.

Recently, tailored synthesis of solid electrolytes satisfy multiple challenges, i.e. high ionic conductivity and wide (electro)chemical stability window is of great interest. Although both oxide- and sulfide-based solid electrolytes have distinguished merits for meeting such concerns separately, a new solid electrolyte having the excellent aspects of both materials is pursued. Herein, we report the synthesis of a sulfur-doped Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte with a NASICON crystal structure that combines elevated ionic conductivity with intrinsic stability against an ambient atmosphere. Sulfur doping was carried out using sulfur-amine chemistry and the system was characterized by XRD, Raman, XPS, ICP-OES, and EDS analyses. Bader charge analysis was carried out with the aid of density functional theory calculations to characterize charge accumulation in the local environment of the bare and sulfur doped LATP structures. Our results indicate that the partial replacement of oxygen with sulfur yields higher ionic conductivity due to the lower electronegativity of sulfur compared to oxygen, which reduces the attraction of lithium ions. The enhanced ionic conductivity of LATP is attributed to a decreased lithium ion diffusion activation energy barrier upon sulfur doping. Compared to bare LATP, the as-prepared sulfur doped LATP powders were shown to decrease the activation energy barrier by 10.1%. Moreover, an ionic conductivity of 5.21 × 10-4 S cm-1 was obtained for the sulfur doped LATP powders, whereas bare LATP had an ionic conductivity of 1.02 × 10-4 S cm-1 at 40 °C.

Stress Bearing Mechanism of Reduced Graphene Oxide in Silicon-Based Composite Anodes for Lithium Ion Batteries.

Despite the significant research that has been carried out to improve cycling performance of lithium ion batteries (LIB) with silicon (Si) based composite electrodes, limited studies have been performed on these materials to evaluate the effects of internal microstructural changes and stress evolution on the electrochemical performance. Here, combined ex situ and in situ investigations on the accommodation of volume expansion in Si-based nanocomposite electrodes are reported. This work emphasizes the importance of conductive agents in light of the poor electronic conductivity of Si. A detailed comparison between commonly used carbon black (CB) and reduced graphene oxide (rGO) shows that these materials have substantial effects on microstructural evolution and internal stress in Si based composite electrodes that are employed in lithium ion cells. This study provides the first monitoring of stress evolution in Si-rGO based composite electrode during electrochemical cycling using in situ wafer curvature measurements. The prepared Si-rGO based electrode exhibits almost 10 times lower stress generation and consequently higher cycling performance in electrochemical cells. The resulting 3D networked structure not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber which hinders the formation of the solid electrolyte interphase (SEI) and limits the pulverization of active material and the evolution of severe stress during cycling. Moreover, investigations of the microstructural changes and internal charge transfer resistance in the electrodes after cycling provide further evidence that rGO produces superior structures for energy storage.

Assembling All-Solid-State Lithium-Sulfur Batteries with Li3 N-Protected Anodes.

The construction of all-solid-state batteries is now easier after the successful synthesis of sulfur-based solid electrolytes with extremely high ionic conductivities. Utilizing lithium metal as the anode in these batteries requires a protective solid electrolyte layer to prevent corrosion due to the highly reactive nature of lithium. Li3 N coating on lithium metal is a promising way of preventing the degradation of the electrolyte during charge and discharge. In this study, utilization of a Li3 N-coated lithium anode and Li7 P3 S11 solid electrolyte are reported, where a quaternary reduced graphene oxide (rGO)/S/carbon black/Li7 P3 S11 composite is used as cathode in the assembled cell. Our results indicate that protecting the Li metal with a Li3 N coating does not affect the electrochemical characteristics of the cell and extends the cycle life of the battery. A cell assembled with a protective layer was shown to having 306 mAh g-1 capacity after 120 cycles at 160 mAh g-1 current density, whereas a cell without protective layer had a capacity of 260 mAh g-1 .

Effect of Milling and Annealing on Carbon-Silver System.

Mechanical treatment of graphite silver mixture followed by heat treatment showed morphology and structure changes of both components. Silver is being distributed over graphite flakes randomly with higher concentration on the edges and nanometric size, which was observed using scanning and transmission electron microscopy. The annealing temperature 1300 °C is higher than melting temperature of silver (961.8 °C) and base on phase diagram C-Ag (C. L. Chen, et al., Appl. Phys. Lett. 96, 253104 (2010).) silver is being transferred from liquid phase to solid phase at rapid cooling, which is giving various crystallinity.

Silver/Chitosan Antimicrobial Nanocomposites Coating for Medical Devices: Comparison of Nanofiller Effect Prepared via Chemical Reduction and Biosynthesis.

Medical devices have an essential part in healthcare system in recent years, such as usage of heart valves, several types of stents and implants devices in patients. However, bacterial infection of medical devices causes critical issues for patients due to attachment of bacteria and formation of biofilm onto the medical devices. Therefore, finding an effective antibacterial coating to prevent biofilm formation and infection is our goal. In this study, we developed silver/chitosan nanocomposites for antimicrobial coating system by chemical and green methods using sodium borohydride and linden extract, respectively. Silver is known as a strong inorganic antimicrobial agent to kill bacteria by inactivating enzymes and dysfunction bacterial cell membranes. By immobilizing silver nanoparticles on chitosan biopolymer can prevent agglomeration of nanoparticles, besides it can improve the biocompatibility. We characterized properties of our silver chitosan nanocomposites samples using particle size distribution, ultraviolet-visible spectroscopy, X-ray diffraction analysis and scanning electron microscopy. Effective antimicrobial film preventing biofilm formation on medical devices was designed. Antimicrobial testing confirmed antimicrobial properties however variable for each type of nanosilver.

Freestanding graphene/MnO2 cathodes for Li-ion batteries.

Different polymorphs of MnO2 (α-, ß-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers' method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge-discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm-2 using CR2016 coin cells. The initial specific capacity of graphene/α-, ß-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg-1, 198 mAhg-1, and 251 mAhg-1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg-1 after 200 cycles with 72% capacity retention.

High Rate Capability Core-Shell SnO2/Multiwall Carbon Nanotube Nano Composite Electrodes for Li-Ion Batteries.

In this study, core-shell SnO2/MWCNT nanocomposites were produced as a high rate anode material for Li-ion batteries via two steps. Firstly, MWCNT based buckypapers were produced via vacuum filtration techniques. Then, a uniform layer of tin oxide nanocrystals which consist of highly homogenous SnO2 having average mean grain sizes of 7-14 nm was deposited onto the surfaces of buckypapers. The as-prepared nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), galvanostatic charging and discharging and electrochemical impedance spectroscopy (EIS) tests. As anode materials for Li-ion batteries, the nanocomposites showed excellent cyclic retention, with the high specific capacity of 314 mAh g(-1) up to 100 cycles. The special hybrid core-shell structure of the as produced nanocomposites are served as electron conductors and volume buffers in the anode electrodes.

ITO/MWCNT Nanocomposites as New Novel Anode Electrodes for Li-Ion Batteries.

In this study, we present a new anode electrode consisting of Indium Tin Oxide and multiwall carbon nanotube based buckypapers for high efficient lithium ion batteries. Core/shell Indium Tin Oxide/Buckypapers were produced by vacuum filtration techniques followed by an rf magnetron sputtering. The nanosized indium tin oxide particles were uniformly anchored onto the surfaces of buckypapers with a mean grain sizes of 2-7 nm confirmed by the FESEM, TEM and XRD results. The as-prepared nanocomposite anode electrodes exhibited outstanding reversible capacity (859, 875 and 895 mA h g(-1) after 50 cycles) and no significant capacity fading is observed after 50 cycles. The unique nanocomposite architecture which integrates both electronic conductivity and buffering matrix design strategies, contributing to enhanced lithium storage performance.

Porous ZnO thin films as anode electrodes for lithium ion batteries.

Zinc oxide (ZnO) nano structured thin films were prepared on Cr coated stainless substrates via a simple thermal chemical reactions vapor transport deposition method in air with a mixture of Zinc acetate anhydrate as reactants. The growth process was carried out at 200 degrees C, 300 degrees C and 400 degrees C in a stainless steel reactor with one side opened to the air. High purity oxygen gas was used as the carrier gas and kept at 1 L/min flow rate during the deposition process. There is no other metal catalyst and carrier gas in the process. The materials are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM). Their electrochemical properties as anodes of lithium ion batteries are examined by galvanostatic discharge-charge tests. The results show that porous ZnO nano structured thin films exhibit higher reversible capacities and better cyclabilities than those of commercial ZnO powders. When cycled at 0.958 mA (1 C = 1 hour charge + 1 hour discharge) for the films deposited at 200 degrees C, these nano structured pyramid-like structures deliver initial discharge and charge capacities of 954, in addition, good rate capabilities have also obtained after 20 cycles. It is believed that the porous sheet nano structure plays an important role in the electrochemical performance.

Synthesis of ZnO, SnO2 nanoparticles and preparation of ZnO-SnO2 nanocomposites.

This article reports the preparation of ZnO-SnO2 nanocomposites from ZnO and SnO2 nanoparticles produced by homogenous precipitation route. Zinc acetate dihydrate (Zn(CH3COO)2 x 2H2O) and tin(II) chloride dehydrates (SnCl2. 2H2O) have been used as precursors. Distilled water was used as a solvent, monoethanolamine (MEA) is used as sol stabilizer. Precursors individually dissolved and stirred at 60 degrees C for 1 h. Certain amount of MEA were added to solution and stirred for 2 h. Then solution was cooled to room temperature and gets precipitated. The collected nanosized precipitates were mixed together and deposited on glass substrates by drain coating and post-heated at different temperatures. X-ray diffractometer was used to determine preferred crystal orientation and particle size of the thin films. Morphologies of nanopowders were examined by scanning electron microscope (SEM).

Zinc oxide based nanocomposite thin film electrodes and the effect of D.C. plasma oxidation power on discharge capacity for lithium ion batteries.

Zinc oxide based thin films have been grown on glass and stainless steel substrates in two steps; thermal evaporation from high purity metallic zinc and D.C. plasma oxidation. X-ray diffraction has shown that the films were polycrystalline nature and small predominant orientation at some specific planes. Analysis showed that plasma oxidation starts from the thermally evaporated leaf-like surfaces and produces a core-shell structure of ZnO on the metallic Zn. Increasing plasma oxidation power causes increased amount of ZnO volume and resistivity. Coin-type (CR2016) test cells were assembled in an argon-filled glove box and cyclically tested. The electrochemical performance of the films has been studied by cyclic voltammetry. The dependence of converted Li-ions on voltage profile of the films has been determined. It was found that the Zn/ZnO films exhibited highest the number of converted Li-ions at 175 W plasma oxidation conditions. Discharge capacity measurements revealed the double phase structures of Zn/ZnO exhibited significantly high reversible capacities. The high capacity and low capacity fade values were attributed to the high electrical conductivity and buffering ability of metallic Zn in the anodes.

Nano crystalline TiO2 thin films as negative electrodes for lithium ion batteries.

In this study, rutile (tetragonal, P42/mnm), anatase (tetragonal, I41/amd) polymorphs of titanium dioxide films were synthesized successfully magnetron sputtering of titanium films on stainless steel substrates followed by in situ direct current plasma oxidation. The as-prepared titanium dioxide thin films were oxidized at 75 W, 100 W and 125 W plasma powers in order to optimize the system with best electrochemical performance. The mean grain sizes of the deposited films were found to be in the range of 14.2-12.9 nm as revealed by the scanning electron microscopy and X-ray diffractometer studies. The electrochemical studies were performed with pure metallic lithium foil cathode with the best performing nano structured titanium dioxide as anode. The specific capacity of the nanocrystalline titanium dioxide films oxidized at 125 W direct current was 207 mA h g(-1) even after 20 cycles in the 0.02-2 V region, indicating excellent cycling stability and reversibility.