Biphase-to-monophase structure evolution of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) toward ultradurable Na-ion batteries

Layered composite oxide materials with O3/P2 biphasic crystallographic structure typically demonstrate a combination of high capacities of the O3 phase and high operation voltages of the P2 phase.However,their practical applications are seriously obstructed by difficulties in thermodynamic phase regulation,complicated electrochemical phase transition,and unsatisfactory cycling life.Herein,we propose an efficient structural evolution strategy from biphase to monophase of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) through Li+substitution.The role of Li+substitution not only simplifies the unfavorable phase transition by altering the local coordination of transition metal(TM)cations but also stabilizes the cathode–electrolyte interphase to prevent the degradation of TM cations during battery cycling.As a result,the thermodynamically robust O_(3)-Na_(0.826)Li_(0.06)Ni_(0.27)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) cathode delivers a high capacity of 139.4 mAh g^(-1) at 0.1 C and shows prolonged cycling life at high rates,with capacity retention of 81.6%at 5 C over 500 cycles.This work establishes a solid relationship between the thermodynamic structure evolution and electrochemistry of layered cathode materials,contributing to the development of long-life sodium-ion batteries.

Elucidation of the sodium kinetics in layered P-type oxide cathodes

Sodium-ion intercalation oxides generally possess high compositional diversity according to their different stacking sequences.The sodium diffusion pathway in layered P-type materials used in sodium-ion batteries is open,which can increase their rate capability by directly transmitting Na+between adjacent triangular prismatic channels,rather than passing through an intermediate tetrahedral site in O-type structure.However,how the structure chemistry of the P-type oxides determines their electrochemical properties has not been fully understood yet.Herein,by comparing the crystalline structures,electrochemical behaviors,ion/electron transport dynamics of a couple of P-type intercalation cathodes,P2-Na_(2/3)Ni1/3Mn_(2/3)O_(2)and P3-Na_(2/3)Ni_(1/3)Mn_(2/3)O_(2)with the same compositions,we demonstrate experimentally and computationally that the P2 phase delivers better cycling stability and rate capability than the P3 counterpart due to the predominant contribution of the faster intrinsic Na diffusion kinetics in the P2 bulk.We also point out that it is the electronic conductivity that captures the key electrochemistry of layered P3-type materials and makes them possible to enhance the sodium storage performance.The results reveal that the correlation between stacking structure and functional properties in two typical layered P-type cathodes,providing new guidelines for preparing and designing alkali-metal layered oxide materials with improved battery performance.

A study on noise reduction for dual-energy CT material decomposition with autoencoder

Purpose A major challenge for the material decomposition task of the dual-energy computed tomography(DECT)is the algorithm often suffers from heavy noise in the results.The purpose of this study is to propose a scheme to increase the noise performance of material decomposition.Methods The scheme we propose in this paper is to apply an autoencoder-based denoising procedure to the photon-counting DECT images before they are fed into the material decomposition algorithm.We implement the autoencoder(AE)by stacking a series of convolutional and deconvolutional layers.The decomposition technique adopted in our work is an iterative method using least squares estimation with the Huber loss function.The noises of the input and the output of material decomposition are analyzed with both simulated data and real data.Phantom and chicken wing experiments are conducted with a photoncounting-based spectral CT scanner to evaluate the proposed material decomposition scheme.Results The noise analysis of the input and the output of material decomposition demonstrates a positive correlation between them.Comparative experiment indicates a noise reduction in the output density maps for 26.07%to 35.65%after the autoencoder pre-processing is applied.The resultant contrast-to-noise ratio is largely increased,correspondingly.Conclusions By utilizing the additional autoencoder denoising step,the material decomposition algorithm achieves an improvement in the noise performance of the resultant density maps.

Improved projection-based energy weighting for spectral CT

Purpose Conventional X-ray CT scanners have limited ability to distinguish low-contrast substances.However,spectral CTs with photon counting detectors can identify photon energy and utilize spectral information,which is expected to achieve improved contrast.Energy weighting is a kind of reconstruction method for spectral CT.By assigning appropriate weight for each energy channel,the image contrast can be improved.Hence,how to determine the optimal weights is very important.Methods In this paper,we developed an improved projection-based energy weighting model for spectral CT.In this model,the object thickness of low-density materials is assumed as a constant,and the measured spectrum distribution is used to calculate the weight coefficients.Both phantom and tissue experiments were conducted in spectral CT scanner.Results The results showed that the thickness of low-density materials has little influence on the energy weight,so it can be regarded as a constant.For low-contrast phantom,the contrast-to-noise ratio was improved~32%by the proposed projectionbased weighting method.Conclusions The improved projection-based energy weighting model is effective in practice.It can increase the contrast of low-density materials.