Pressure-Induced Defects and Reduced Size Endow TiO2 with High Capacity over 20 000 Cycles and Excellent Fast-Charging Performance in Sodium Ion Batteries.

Anatase TiO2 as sodium-ion-battery anode has attracted increased attention because of its low volume change and good safety. However, low capacity and poor rate performance caused by low electrical conductivity and slow ion diffusion greatly impede its practical applications. Here, a bi-solvent enhanced pressure strategy that induces defects (oxygen vacancies) into TiO2 via N doping and reduces its size by using mutual-solvent ethanol and dopant dimethylformamide as pressure-increased reagent of tetrabutyl orthotitanate tetramer is proposed to fabricate N-doped TiO2 /C nanocomposites. The induced defects can increase ion storage sites, improve electrical conductivity, and decrease bandgap and ion diffuse energy barrier of TiO2 . The size reduction increases contact interfaces between TiO2 and C and shortens ion diffuse distance, thus increasing extra ion storage sites and boosting ion diffusion rate of TiO2 . The N-doped TiO2 possesses highly stable crystal structure with a slightly increase of 0.86% in crystal lattice spacing and 3.2% in particle size after fully sodiation. Consequently, as a sodium-ion battery anode, the nanocomposite delivers high capacity and superior rate capability along with ultralong cycling life. This work proposes a novel pressure-induced synthesis strategy that provides unique guidance for designing TiO2 -based anode materials with high capacity and excellent fast-charging capability.

Multi-component surface engineering of Na3V2(PO4)2O2F for low-temperature (-40 °C) sodium-ion batteries.

A functional Na3V2(PO4)2O2F (NVPOF) cathode with a multi-component (Na3V(PO4)2, V2O3, and reduced graphene oxide) surface coating is developed via a facile hydrothermal reaction followed by calcination, and exhibits high reversible capability, and long-term cycling stability even at a low temperature of -40 °C. It is demonstrated that the multi-component-coating layer can significantly accelerate the e-/Na+ transport and reduce the interfacial resistance at low temperature. This work provides a novel strategy to boost the kinetics and stability of electrode materials for low-temperature sodium ion batteries.

Chemically Binding Vanadium Sulfide in Carbon Carriers to Boost Reaction Kinetics for Potassium Storage.

Potassium-ion batteries (PIBs) have received widespread interest on account of low redox potential, low price, and high abundance of potassium. However, attributing to the large radius of K+ ions, the structure of electrode material is easily damaged during the potassiation/depotassiation process. Herein, the unique chemical bonding of encapsulating V5.45S8 nanoparticles in N,S codoped multichannel carbon nanofibers (CB-VS@NSCNFs) is designed through electrospinning and in situ vulcanization techniques. The anchoring effect (V-C chemical bonding) of the V5.45S8 nanoparticles with carbon carriers assists in shortening the K+/e- transport path and alleviating the structural changes, which is highlighted to acquire a stable cycle lifespan. Also, codoped multichannel carbon nanofibers provide abundant active sites for pseudocapacitive behavior to achieve fast kinetics. As a synergistic result, when CB-VS@NSCNFs are evaluated as anode material for PIBs, they exhibit a high reversible capacity of 411 mA h g-1 at 0.1 A g-1, decent rate property with a capacity of up to 123 mA h g-1 at 6 A g-1, and good cycling stability of 500 cycles at 1 A g-1.