Effect of homojunction structure in boosting sodium-ion storage: The case of MoO_(2)

High-efficiency sodium-ion batteries(SIBs) are in great demand for energy storage applications,which are dominated by the Na+storage performance of electrode materials.Here,a one-pot solvothermal method is developed to construct amorphous/crystalline MoO_(2)(a/c-MoO_(2)) homojunction for boosting Na+storage.Theoretical simulations signify that electrons redistribute at the homogenous interface of a/c-MoO_(2),resulting in an inbuilt driving force to easily adsorb charge carriers and promote the electron/ion transfer ability.Relying on its crystallographic superiorities,the a/c-MoO_(2)homojunction with high Na adsorbability(-1.61 eV) and low Na diffusion energy barrier(0.519 eV) achieves higher capacity(307 mA h g^(-1)at 0.1 A/g),better rate capability and cycling stability than either a-MoO_(2)or c-MoO_(2)counterpart.Combining in-situ X-ray diffraction(XRD) and ex-situ X-ray photoelectron spectroscopy(XPS)techniques,the ’adsorption-insertion-conversion’ mechanism is well established for Na+storage of MoO_(2).Our work opens new opportunities to optimize electrode materials via crystallographic engineering for efficient Na+storage,and helps to better understand the effects of homojunction structure in enhanced electrochemical performance.

In situ XRD and electrochemical investigation on a new intercalation-type anode for high-rate lithium ion capacitor

A new intercalation-type anode material is reported herein to improve the lithium storage kinetics for high-rate lithium ion capacitors.The crystal structure of orthorhombic NaNbO3 indicates two possible tunnels for lithium ions insertion into NaNbO3 host along the<101>and<141>directions.Moreover,in situ XRD is conducted to investigate the lithium storage mechanism and structural evolution of the NaNb O_(3) anode,demonstrating its intercalation behavior through(101)and(141)planes.Furthermore,the rGO nanosheets are introduced to facilitate the charge transfer,which also effectively prevent the aggregation of NaNbO3 nanocubes.As expected,the NaNbO_(3)/rGO nanocomposites possess remarkable reversible capacity(465 mA h g^(-1) at 0.1 A g^(-1)),superior rate capability(325 mA h g^(-1) at 1.0 A g^(-1))and cycling stability,attributed to their synergistic effect and high Li+diffusion coefficient DLi[D(NaNbO_(3)/rGO)/D(NaNbO_(3))≈31.54].Remarkably,the NaNbO3/rGO-based LIC delivers a high energy density of 166.7 W h kg^(-1) at 112.4 W kg^(-1) and remains 24.1 W h kg^(-1) at an ultrahigh power density of26621.2 W kg^(-1),with an outstanding cycling durability(90%retention over 3000 cycles at 1.0 A g^(-1)).This study provides new insights on novel intercalation-type anode material to enrich the materials system of LICs.