Search

Developing high energy storage lithium ion batteries (LIBs) using manganese oxides as anodes is an attractive challenge due to their high theoretical capacity and abundant resources. However, the manganese oxides anodes still suffer from the low initial Coulombic efficiency and poor rate performance. Herein, we demonstrate that nano-sized morphological engineering is a facile and effective strategy to improve the electrochemical performance of the manganese dioxide (MnO 2 ) for LIBs. The tailored MnO 2 nanoparticles (NPs) exhibit high reversible capacity (1095 mAh g −1 at 100 mA g −1 ), high initial Coulombic efficiency (94.5%) and good rate capability (464 mAh g −1 at 2000 mA g −1 ). The enhanced electrochemical performance of MnO 2 NPs can be attributed to the presences of numerous electrochemically active sites and interspaces among the NPs. [ABSTRACT FROM AUTHOR]

Abstract The 4-D imaging and quantification of the desaturation of an initially flooded gas diffusion layer (GDL) with a serpentine gas flow channel by synchrotron radiography is presented. An imaging area with a diameter of 10 mm allows for the study of how the natural anisotropy of a GDL affects the desaturation profile. The GDL is progressively spatially segmented from the overall domain down to sections of the individual channels and ribs. Temporal saturation profiles and desaturation rates are presented for each step of this progressive segmentation. Although the desaturation of the overall domain initially appears to be a constant and steady process with a desaturation rate of 0.0030 μL cm−2 s−1, segmented results display heterogeneous behavior with over two-fold differences between areas of the flow field. Segmented saturation surface plots are presented that spatially show how this heterogeneity occurs within the entire domain. Results indicate that initial conditions, anisotropic material properties, and flow field geometry all play a key role in determining local desaturation behavior. The larger domain considered here provides valuable data for future modeling studies that combine continuum studies of flow in the gas flow channels with GDL pore network models that consider two-phase flow behavior. Highlights • Spatial and temporal GDL saturation is analyzed from Synchrotron X-ray CT data. • As the GDL is segmented spatially, variations in the desaturation rate are noted. • Overall desaturation rate of 0.0030 ± 0.0013 μL cm−2 s−1 is spatially investigated. • Spatially and temporally resolved desaturation rates are key to model validation. [ABSTRACT FROM AUTHOR]

Abstract Transition metal oxides can introduce high pseudocapacitance to an electric double layer capacitor for storing more electrical charges. Their role can be more than that since they possess high dielectric constant. Here, we propose a self-sustainable bi-functional configuration by eliminating traditional separator of a metal oxide film supercapacitor that is capable of providing good energy storage performance. We take advantage of super-aligned electrospun carbon nanofibers (SA-ECNFs) as an interconnected scaffold, coupling with electrochemical deposition of α-MnO 2 layers at different currents to introduce pseudocapacitance while providing dielectric layer functioning as a separator to assemble a state-of-the-art supercapacitor. The good electrochemical performance of galvanic charge-discharge specific capacitance at 141 F g−1 and energy density at 12.5 Wh kg−1 offers the promising applications in the energy storage field. Graphical abstract Image 1 Highlights • Manganese dioxide films play bifunctions for separation and pseudocapacitance. • The dielectric property of MnO 2 is critical for the membrane-free configuration. • A mechanistic model is proposed for understanding the bi-functions. [ABSTRACT FROM AUTHOR]

Hybrid Li-ion capacitors (LICs) are a new kind of electrochemical energy storage device with high energy and power densities. In this work, phosphorus-doped TiO 2 /phosphorus-doped carbon nanofibers (PTO/PC NFs) are fabricated through a simple electrospinning method with disodium hydrogen phosphate as a phosphorus source. Differing from the PTO prepared by hydrothermal method, sol-gel method or calcining treatment at phosphorous atmosphere. The P-doping evenly distributed in PTO/PC NFs and PTO nanoparticles are embedded in PC, which improves the conductivity, structure stability and Li+ ions diffusion of TiO 2. As a result, the PTO/PC NFs anode shows high capacities of 329 and 150 mA h g−1 (0.1 and 2 A g−1), long cycle life (201 mA h g−1 after 1000 cycles at 1 A g−1, 69 mA h g−1 after 1000 cycles at 5 A g−1), and superior pseudocapacitance (87%, 2 mV s−1). Furthermore, the LICs assembled with PTO/PC NFs anode and AC cathode show outstanding capacity of 35 F g−1 at a current density of 0.1 A g−1, high energy density of 72 Wh kg−1 at the power density of 250 W kg−1, and cycle stability (54%, 10 000 cycles, 1 A g−1). This suggests that PTO/PC NFs is a potential anode material for high-performance LICs. Image 1 • P-doped TiO 2 /P-doped C nanofibers (PTO/PC NFs) are fabricated by electrospinning. • The PTO/PC NFs exhibited good conductivity, stability and Li+ ions diffusion. • The PTO/PC anode showed high capacity, long cycle life and high pseudocapacitance. • LIC assembled with PTO/PC NFs anode showed a high energy density and power density. [ABSTRACT FROM AUTHOR]