A new method was developed to synthesize nanosheet-assembled TiO 2 -B microflowers for Li-ion batteries. Significantly higher electrochemical performance of these microflowers compared to other TiO 2 -B nanostructures was attributed to their hierarchical microstructure and exposed (1 1 0) facets of the individual nanosheets.One of the key challenges in modern electrochemistry is developing rechargeable batteries that meet environmental constraints and yet possess high energy density, long cycle life, and excellent rate capability. 1-5 Rechargeable Li-ion batteries have attracted signicant interest due to their wide range of applications including portable electronic devices, implantable medical devices, and electric vehicles. 6,7 Graphite was selected as the substitute for Li-metal anodes in rechargeable Li-ion batteries due to its low cost and rapid lithium-ion insertion/ extraction kinetics. 8 However, the electrochemical potential for Li-ion insertion is 0.2 V vs. Li +/0 , resulting in lithium metal plating and dendrite formation. 2,9,10 In addition, graphite also suffers from exfoliation into individual graphene layers due to solvent co-intercalation. 2 Moreover, complete lithiation of graphite is accompanied by an $10% volume increase. 11-13 These drawbacks of graphite anodes pose a serious challenge for adopting Li-ion batteries in larger scale applications. Recently, the various polymorphs of titanium dioxide (anatase, rutile, brookite, and bronze) and titanates such as O 13 have received attention as anode materials. 5,14-19 The advantages are low cost, smaller volume change (<3%), and increased lower potential limit of 1.0-1.5 V, which eliminates the lithium plating shortcoming of graphite. In contrast to other titanates, bronze-phase titanium dioxide (TiO 2 -B) has moved to the forefront due to its higher theoretical charge-storage capacity (335 mA h g À1 ), larger channels for Li + insertion, characteristic pseudocapacitive behavior, and faster charge-discharge capability. 20-22 In addition, TiO 2 -B has a relatively lower density (3.64 g cm À3 ), which provides adequate space for Li + compared to the other polymorphs. However, the low intrinsic electrical conductivity and poor Li + diffusion limit the application of TiO 2 -B in anodes. 23 One proven method to improve performance is to fabricate nanostructures, which result in better Li + solubility, improved interfacial kinetics, shorter length for e À and Li + transport, and better electrode-electrolyte contact. Superior specic capacities, rate capabilities, and capacity retention of TiO 2 -B nanotubes, nanowires and nanoparticles over bulk TiO 2 -B were reported previously. 16,22,24 Moreover, nanostructured electrodes possessing hierarchical microstructures can show superior performance compared to bulk and nanostructured electrodes since they combine the benets of nanostructures with high packing density. 4,25,26 Porosity of electrode materials is another critical factor governing performance. For instance, superior electrochemical performance o...

A novel dye-sensitized solar cell (DSSC) architecture based on vertically aligned carbon nanofibers coated with a thin nanoneedle-textured anatase TiO2 film is demonstrated. An encouraging overall conversion efficiency of approximately 1.09% and a rather high open-circuit voltage of approximately 0.64 V have been achieved. The efficient charge separation at the TiO2-CNF junction and the large outer TiO2 surface of this core-shell architecture provide new methods to tune the materials and interfaces in solar cells.

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Summary Multi‐walled carbon nanotube (MWCNT) protection layers have previously been used to trap polysulfides and suppress the shuttle effect in lithium sulfur (Li‐S) batteries, leading to significant performance improvement. While the MWCNT is inherently highly conductive and mechanically strong, the cost can be significant and in turn hampered wider application of MWCNT protection layers. Here, we employed lignin, a byproduct during high‐quality bleached paper manufacturing, to replace a portion of MWCNT in the protection layer to reduce cost and enhance surface properties of pristine MWCNT protection layers. We found that the protection layer with 25 wt% lignin leads to the best overall electrochemical performance of Li‐S batteries during charging/discharging at 0.5°C and 1C rate (1C = 1,675 mA g−1) among various weight‐ratios of lignin/MWCNT, and a low decay rate (0.20% per cycle) and high initial capacity (1342 mA g−1 and 1437 mA g−1 for 1C and 0.5C, respectively) are demonstrated. Besides, Li‐S cells with 25 wt% lignin/MWCNT composite protection layer also exhibited great rate capability, of which the specific capacities at 0.1C, 0.5C, 1C, and 2C were 1150, 913, 824, and 637 mAh g−1, respectively. The enhanced electrochemical stability and performance of Li‐S batteries can be attributed to strengthened polysulfide trapping and improved lithium ion transport with lignin reinforced MWCNT protection layers. We showcased an economic approach to extend cycle life and improve rate capability of Li‐S batteries.

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