Doping sites modulation of T-Nb_(2)O_(5) to achieve ultrafast lithium storage

Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few reports focus on enhancing the lithium storage performances of Nb_(2)O_(5) via heteroatoms doping,yet the effect of different doping sites remains unclear.Herein,nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))via a urea-assisted annealing process.Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb_(2)O_(5) can be tuned by the heating rate,in which substitutional N can increase the spacing of the Li^(+)transport layer as well as reduce the band gap,while interstitial N can provide an electron-rich environment for Li^(+)transport layer and then reduce the Li^(+)diffusion barrier.Arising from the synergistic effect of N doping at different sites,the N-doped T-Nb_(2)O_(5) without carbon coating delivers impressive rate performance(104.6 mA h g^(-1) at 25 C)as well as enhanced cycle stability with a retention of 70.5%over1000 cycles at 5 C.In addition,the assembled lithium ion capacitor exhibits a high energy density of46.6 Wh kg^(-1) even at high power density of 8.4 kW kg^(-1).

Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

Niobium pentoxide(Nb_(2)O_(5))anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety.However,Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications.Herein,the over-reduction of Nb5+has been demonstrated to be the critical reason for the capacity loss for the first time.Besides,an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb_(2)O_(5),which can be achieved by the incorporation of vanadium to form a new rutile VNbO_(4)anode.The highly reversible V^(3+)/V^(2+)redox couple in VNbO_(4)can effectively inhibit the over-reduction of Nb^(5+).Besides,the electron migration from V^(3+)to Nb5+can greatly increase the intrinsic electronic conductivity for VNbO4.As a result,VNbO4 anode delivers a high capacity of 206.1 mAh g^(−1)at 0.1 A g^(−1),as well as remarkable cycle performance with a retention of 93.4%after 2000 cycles at 1.0 A g^(−1).In addition,the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg^(−1)at 5.8 kW kg^(−1).In summary,our work provides a new insight into the design of ultra-fast and durable anodes.

Self-assembled MoS_(2)/C nanoflowers with expanded interlayer spacing as a high-performance anode for sodium ion batteries

Two-dimensional(2D)MoS_(2) nanomaterials have been extensively studied due to their special structure and high theoretical capacity,but it is still a huge challenge to improve its cycle stability and achieve superior fast charge and discharge performance.Herein,a facile one-step hydrothermal method is proposed to synthetize an ordered and self-assembled MoS_(2) nanoflower(MoS_(2)/C NF)with expanded interlayer spacing via embedding a carbon layer into the interlayer.The carbon layer in the MoS_(2) interlayer can speed the transfer of electrons,while the nanoflower structure promotes the ions transport and improves the structural stability during the charging/discharging process.Therefore,MoS_(2)/C NF electrode exhibits exceptional rate performance(318.2 and 302.3 mA·h·g^(-1) at 5.0 and 10.0 A·g^(-1),respectively)and extraordinary cycle durability(98.8%retention after 300 cycles at a current density of 1.0 A·g^(-1)).This work provides a simple and feasible method for constructing high-performance anode composites for sodium ion batteries with excellent cycle durability and fast charge/discharge ability.