Wet Spinning of Graphene Oxide Fibers with Different MnO2 Additives.

We present the fabrication of graphene oxide (GO) and manganese dioxide (MnO2) composite fibers via wet spinning processes, which entails the effects of MnO2 micromorphology and mass loading on the extrudability of GO/MnO2 spinning dope and on the properties of resulted composite fibers. Various sizes of rod and sea-urchin shaped MnO2 microparticles have been synthesized via hydrothermal reactions with different oxidants and hydrothermal conditions. Both the microparticle morphology and mass loading significantly affect the extrudability of the GO/MnO2 mixture. In addition, the orientation of MnO2 microparticles within the fibers is largely affected by their microscopic surface areas. The composite fibers have been made electrically conductive via chemical or thermal treatments and then applied as fiber cathodes in Zn-ion battery prototypes. Thermal annealing under an argon atmosphere turns out to be an appropriate method to avoid MnO2 dissolution and leaching, which have been observed in the chemical treatments. These rGO/MnO2 fiber cathodes have been assembled into prototype Zn-ion batteries with Zn wire as the anode and xanthan-gum gel containing ZnSO4 and MnSO4 salts as the electrolyte. The resulted electrochemical output depends on the annealing temperature and MnO2 distribution within the fiber cathodes, while the best performer shows stable cycling stability at a maximum capacity of ca. 80 mA h/g.

Impacts of Mg doping on the structural properties and degradation mechanisms of a Li and Mn rich layered oxide cathode for lithium-ion batteries.

The Li- and Mn-rich layered oxide cathode material class is a promising cathode material type for high energy density lithium-ion batteries. However, this cathode material type suffers from layer to spinel structural transition during electrochemical cycling, resulting in energy density losses during repeated cycling. Thus, improving structural stability is an essential key for developing this cathode material family. Elemental doping is a useful strategy to improve the structural properties of cathode materials. This work examines the influences of Mg doping on the structural characteristics and degradation mechanisms of a Li1.2Mn0.4Co0.4O2 cathode material. The results reveal that the prepared cathode materials are a composite, exhibiting phase separation of the Li2MnO3 and LiCoO2 components. Li2MnO3 and LiCoO2 domain sizes decreased as Mg content increased, altering the electrochemical mechanisms of the cathode materials. Moreover, Mg doping can retard phase transition, resulting in reduced structural degradation. Li1.2Mn0.36Mg0.04Co0.4O2 with optimal Mg doping demonstrated improved electrochemical performance. The current work provides deeper understanding about the roles of Mg doping on the structural characteristics and degradation mechanisms of Li-and Mn-rich layered oxide cathode materials, which is an insightful guideline for the future development of high energy density cathode materials for lithium-ion batteries.

Biomechanical Comparison Between Posterior Long-Segment Fixation, Short-Segment Fixation, and Short-Segment Fixation With Intermediate Screws for the Treatment of Thoracolumbar Burst Fracture: A Finite Element Analysis.

BACKGROUND: Posterior long-segment (LS) fixation, short-segment (SS) fixation, and short segment fixation with intermediate screws (SI) have shown good outcomes for the treatment of thoracolumbar burst fractures. However, limited data compared the biomechanical properties between LS fixation and SI. The purpose of this study was to compare the von Mises stresses on the pedicular screw system and bone between posterior LS fixation, SS fixation, and SI for the treatment of thoracolumbar burst fracture. MATERIALS AND METHODS: The finite element model of thoracolumbar spines from T11 to L3 was created based on the computed tomography image of a patient with a burst fracture of the L1 vertebral body. The models of pedicular screws, rods, and locking nuts were constructed based on information from the manufacturer. Three models with different fixation configurations-that is, LS, SS, and SI-were established. The axial load was applied to the superior surface of the model. The inferior surface was fixed. The stress on each screw, rod, and vertebral body was analyzed. RESULTS: The motion of the spine in SS (0.5 mm) and SI (0.9 mm) was higher than in LS (0.2 mm). In all models, the lowest pedicle screws are the most stressed. The stress along the connecting rods was comparable between SI and LS (50 MPa). At the fracture level, stress was found at the pedicles and vertebral bodies in SI. There was relatively little stress around the fractured vertebral body in LS and SS. CONCLUSIONS: Posterior SI preserves more spinal motion than the LS. In addition, it provides favorable biomechanical properties than the SS. The stress that occurred around the pedicle screws in SI was the least among the 3 constructs, which might reduce complications such as implant failure. SI produces more stress in the fractured vertebral body than LS and SS, which could potentially aid in bone healing according to the Wolff law. CLINICAL RELEVANCE: SI has proved to be a biomechanically favorable construct and helps preserve the spinal motion segment. It could be an alternative surgical option for treating patients who present with thoracolumbar burst fractures.

A multiscale investigation elucidating the structural complexities and electrochemical properties of layered-layered composite cathode materials synthesized at low temperatures.

Layered-layered composite (xLi2MnO3·(1 -x) LiMO2, M = Mn, Ni, Co, and Fe) cathode materials have attracted much attention as cathodes for high energy density lithium ion batteries. However, these materials are structurally unstable resulting from complicated phase transformation mechanisms during cycling. Additionally, the complex structural characteristics and structural stability of these materials largely depend on their preparation methods. Studying the correlation between multiscale structural properties and preparation methods is important in the development of layered-layered composite cathode materials. In this work, 0.5Li2MnO3·0.5LiCoO2 composite materials were prepared with different heating and cooling rates with a maximum temperature of 600 °C. The structural properties of the 0.5Li2MnO3·0.5LiMO2 composite materials were investigated using combined in situ X-ray absorption spectroscopy (XAS), in situ X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high resolution transmission electron microscopy (HRTEM) techniques. Heating and cooling rates have no significant effect on either the crystal or local atomic structures of the prepared samples. However, the microstructure was critically important for its impact on electrochemical properties.

Rate dependent structural transition and cycling stability of a lithium-rich layered oxide material.

Lithium-rich layered oxide materials, xLi2MnO3·(1 - x)LiMO2 (M = Mn, Fe, Co, Ni, etc.), are a promising candidate for use as cathode materials in the batteries of electric vehicles (EVs). This is due to their high energy density (∼900 W h kg-1), which is larger than those of the currently used commercial cathode materials. Moreover, EV technologies require lithium ion batteries with a high rate performance to achieve short charging times. The high rate property largely depends on the electrochemical properties of the electrodes in these batteries. However, the correlation between the cycling rate, structural stability and electrochemical properties of cathode materials is not clearly understood. In this work, the influence of cycling rate on structural transition behaviors and cycling stability of a 0.5Li2MnO3·0.5LiCoO2 composite-based material was investigated. The experimental results reveal that cycling rates significantly affect the activation of the Li2MnO3 component. A high cycling rate retards Li2MnO3 activation, leading to a smaller spinel phase transition and a higher cycling stability.

Structural and Electrochemical Kinetic Properties of 0.5Li2MnO3∙0.5LiCoO2 Cathode Materials with Different Li2MnO3 Domain Sizes.

Lithium rich layered oxide xLi2MnO3∙(1-x)LiMO2 (M = Mn, Co, Ni, etc.) materials are promising cathode materials for next generation lithium ion batteries. However, the understanding of their electrochemical kinetic behaviors is limited. In this work, the phase separation behaviors and electrochemical kinetics of 0.5Li2MnO3∙0.5LiCoO2 materials with various Li2MnO3 domain sizes were studied. Despite having similar morphological, crystal and local atomic structures, materials with various Li2MnO3 domain sizes exhibited different phase separation behavior resulting in disparate lithium ion transport kinetics. For the first few cycles, the 0.5Li2MnO3∙0.5LiCoO2 material with a small Li2MnO3 domain size had higher lithium ion diffusion coefficients due to shorter diffusion path lengths. However, after extended cycles, the 0.5Li2MnO3∙0.5LiCoO2 material with larger Li2MnO3 domain size showed higher lithium ion diffusion coefficients, since the larger Li2MnO3 domain size could retard structural transitions. This leads to fewer structural rearrangements, reduced structural disorders and defects, which allows better lithium ion mobility in the material.

Cellulose ultrafine fibers embedded with titania particles as a high performance and eco-friendly separator for lithium-ion batteries.

Mixtures of cellulose acetate (M.W. ∼3 × 104 g/mol) dissolved in 75% v/v acetic acid in water (17% w/w) and ground anatase titania particles with diameters of 197 ±â€¯75 nm (0%, 5% and 10% w/w) were electrospun at 17 kV with a fiber collection distance and a feed rate of 10 cm and 0.6 mL/h. Then, the fiber was treated with 0.5 M potassium hydroxide in ethanol. Rough regenerated cellulose (RC)-titania separators with diameters of ∼310 nm and uniformly dispersed titania particles showed ∼78% porosities. They decomposed at 300 °C, higher than the decomposition temperature of polyethylene separators (220 °C). Added titania particles increased the electrolyte wettability and lithium transference number (from 0.22 to 0.62). RC - 10% titania separator retained the capacity with 79 mA h/g after 30 cycles and had excellent discharge capacity. These fascinating properties make RC-titania separator promising for lithium ion battery.

Li2MnO3 domain size and current rate dependence on the electrochemical properties of 0.5Li2MnO3·0.5LiCoO2 cathode material.

Layered-layered composite oxides of the form xLi2MnO3·(1-x) LiMO2 (M = Mn, Co, Ni) have received much attention as candidate cathode materials for lithium ion batteries due to their high specific capacity (>250mAh/g) and wide operating voltage range of 2.0-4.8 V. However, the cathode materials of this class generally exhibit large capacity fade upon cycling and poor rate performance caused by structural transformations. Since electrochemical properties of the cathode materials are strongly dependent on their structural characteristics, the roles of these components in 0.5Li2MnO3·0.5LiCoO2 cathode material was the focus of this work. In this work, the influences of Li2MnO3 domain size and current rate on electrochemical properties of 0.5Li2MnO3·0.5LiCoO2 cathodes were studied. Experimental results obtained showed that a large domain size provided higher cycling stability. Furthermore, fast cycling rate was also found to help reduce possible structural changes from layered structure to spinel structure that takes place in continuous cycling.

Aqueous semi-solid flow cell: demonstration and analysis.

An aqueous Li-ion flow cell using suspension-based flow electrodes based on the LiTi2(PO4)3-LiFePO4 couple is demonstrated. Unlike conventional flow batteries, the semi-solid approach utilizes fluid electrodes that are electronically conductive. A model of simultaneous advection and electrochemical transport is developed and used to separate flow-induced losses from those due to underlying side reactions. The importance of plug flow to achieving high energy efficiency in flow batteries utilizing highly non-Newtonian flow electrodes is emphasized.