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.

Corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses after annealing and cryogenic treatments

The microstructural evolution and corrosion behavior of Ni_(62)Nb_(33)Zr_(5)bulk metallic glasses(BMGs)after annealing treatment(AT)at different crystallization temperatures and cryogenic treatment(CT)at−100℃are experimen-tally investigated.Appropriate AT and CT can both improve the thermal stability and comprehensive corrosion resistance of as-cast BMG in 3.5 wt.%NaCl solution.The annealed and cryo-treated BMGs exhibit one more finite diffusion layer loop in the electrical equivalent circuit than the as-cast BMG,indicating the complexity of the corrosion behavior.Superior corrosion resistance is obtained in the cryo-treated BMG because the high degree of amorphization caused by CT reduces the structural inhomogeneity.Lower C_(d)and higher R_(d)values are obtained for the cryo-treated BMG,revealing the formation of a more stable passive film.Among the annealed BMGs,the fully crystallized sample exhibits a higher anti-corrosion performance owing to the existence of Nb-rich oxides in the crystallization products.The passive film is found to be composed mainly of Nb_(2)O_(5)and ZrO_(2),demonstrating that Nb and Zr are conducive to reacting with oxygen to form a passive film.Based on the goal of maintaining a fully amorphous phase,appropriate CT causing structural homogeneity of the BMG is a simple and effective means to improve the comprehensive corrosion resistance.

Predicting torsional capacity of reinforced concrete members by data-driven machine learning models

Due to the complicated three-dimensional behaviors and testing limitations of reinforced concrete(RC)members in torsion,torsional mechanism exploration and torsional performance prediction have always been difficult.In the present paper,several machine learning models were applied to predict the torsional capacity of RC members.Experimental results of a total of 287 torsional specimens were collected through an overall literature review.Algorithms of extreme gradient boosting machine(XGBM),random forest regression,back propagation artificial neural network and support vector machine,were trained and tested by 10-fold cross-validation method.Predictive performances of proposed machine learning models were evaluated and compared,both with each other and with the calculated results of existing design codes,i.e.,GB 50010,ACI 318-19,and Eurocode 2.The results demonstrated that better predictive performance was achieved by machine learning models,whereas GB 50010 slightly overestimated the torsional capacity,and ACI 318-19 and Eurocode 2 underestimated it,especially in the case of ACI 318-19.The XGBM model gave the most favorable predictions with R^(2)=0.999,RMSE=1.386,MAE=0.86,andλ=0.976.Moreover,strength of concrete was the most sensitive input parameters affecting the reliability of the predictive model,followed by transverse-to-longitudinal reinforcement ratio and total reinforcement ratio.

Phase Selection and Microhardness of Directionally Solidified AlCoCrFeNi_(2.1) Eutectic High-Entropy Alloy

In the present work,the solidification behaviors and microhardness of directionally solidified AlCoCrFeNi_(2.1) eutectic highentropy alloy(EHEA)obtained at different growth velocities are investigated.The microstructure of the as-cast AlCoCrFeNi_(2.1) EHEA is composed of bulky dendrites(NiAl phase)and lamellar eutectic structures,indicating that the actual composition of the alloy slightly deviates from the eutectic point.However,it is interesting to observe that the full lamellar structure of this alloy is obtained through directional solidification.In order to explain this phenomenon,the maximum interface temperature criterion and the interface response function(IRF)theory are applied to calculate the velocity range of the transition from the primary phase to the eutectic,which is 1.2–2×10^(4)μm/s.Furthermore,microhardness is one of the important parameters to measure the mechanical properties of materials.Therefore,the microhardness test is performed,and the test result indicates that the microhardness(HV)increased with increasing growth velocity(V)or decreased with increasing lamellar spacing(λ).The dependences ofλand HV on V are determined by using a linear regression analysis.The relationships between theλ,V and HV are given as:λ=11.62V^(-0.48),HV=305.5V 0.02 and HV=328.1λ^(0.04),respectively.The microhardness of the AlCoCrFeNi_(2.1) EHEA increases from 312.38 HV to 329.54 HV with the increase in growth velocity(5–200μm/s).Thus,directional solidification is an effective method to improve the mechanical properties of alloys.

Investigation on peritectic solidification in Sn-Ni peritectic alloys through in-situ observation

The solidification of Sn-Ni peritectic alloys in which both the primary Ni_(3)Sn_(2)and peritectic Ni_(3)Sn_(4)phases were intermetallic compound phases(IMCs)with narrow solubility ranges was investigated through confocal laser scanning microscope.Analysis on the interface migration at different cooling rates shows that the rate of peritectic reaction is much smaller than previous reports,and the growth of peritectic phase is mainly attributed to direct precipitation from the melt in Sn-Ni alloy after peritectic reaction.In addition,different from other peritectic alloys where the solidified phases are solid solution phases,the"step"growth of both Ni_(3)Sn_(2)and Ni_(3)Sn_(4)phases was observed.The dependences of the step thickness on both the cooling rate and solidification time were measured,which shows that the step thicknesses of both phases gradually decrease as solidification proceeds.This was confirmed to be attributed to the difference between the actual and equilibrium melt concentrations during solidification.In addition,the increase of the normal growth velocity of Ni_(3)Sn_(4)phase with increasing cooling rate was also proved through both the experimental observation and quantitative prediction.